PDA

View Full Version : what size generator?

envelopes2007
December 17th, 2007, 1:09 PST
I'm having trouble calculating.... what size generator I need?
.......to operate a xantrex DR3624 inverter/charger?
Q: Would the DR3624 charger be powerful enough to maintain a
1) 24V@ 580a/h or
2) 24V@ 640a/h or
3) 24V@ 800 a/h ? battery bank?
I am thinking of a purchasing a yamaha YG2800i generator? from ebay?

crewzer
December 17th, 2007, 4:58 PST
Envelopes,

Starting at the top and assuming a target charge current of 10% to 13% of battery capacity (per Trojan recommendation), your charger will need to be able to supply 80 A to 104 A to the 800 Ah battery bank. The 3624’s charger is rated at 70 ADC max. That’s a bit on the low side, but may be OK if there are no significant loads on the batteries while they’re being recharged. It’ll just take a while for them to recharge.

Maximum sustained power from the charger to the battery bank will be 70 A x ~28.8 V = 2.016 kW. Assuming full power charger efficiency of 85%, the generator will need to be able to supply ~2.37 kW, or 20 A at 120 VAC. Assuming a power factor of 95%, the generator will need to be able to supply 21 A.

The Yamaha EF2800i is rated at 2,800 W max (120 V x 23.3 A) max and 2,500 W (120 VAC x 20.8 A) continuous. If you are located above sea level, the power specs will need to be derated at ~3%-4% per 1,000 feet in elevation. See: http://mayberrys.com/yamaha/generators/model-specific/ef2800.htm

Personally, I think that the combination of the “2800 W” generator, the 3624 inverter/charger, and the 24 V x 800 Ah battery bank would be running too close to the ragged edge. You might try similar calculations for the smaller battery banks. Without crunching the numbers, my gut feel is that the 24 V x 640 Ah bank would be the practical limit.

HTH,
Jim / crewzer

envelopes2007
December 17th, 2007, 8:43 PST
Hi Jim,
Thanks for the info.
I was thinking of constructing (2) battery banks namely "A" and "B" and making a 100amp charger "switch" back and forth.
I might charge "A" whilst I was using "B" and vice versa?
Is this practical thinking?
If, I went this way?
I could purchase just one charger and one separate inverter (is this correct?).
I could use a 100amp charger that "switches" back and forth between "A" and "B" and a one (1) separate inverter ....ie: Not use a DR3624!
I am just running power tools in the summer months (at sea level).
So, what would be the effect of operating such a system?
I know that power tools I can run from the generator! I am maintaining the banks for no other reason other than they are there (at the present time)
Wiring conditions?
Wire size?
Complexity?
Kevin

mike95490
December 17th, 2007, 9:08 PST
Hi Jim,
Thanks for the info.
I was thinking of constructing (2) battery banks namely "A" and "B" and making a 100amp charger "switch" back and forth.
I might charge "A" whilst I was using "B" and vice versa?
Is this practical thinking?

Sounds like double your trouble, with high current DC switching.. If you need 2 large banks, consider going to a higher voltage, or larger individual batteries. 2 strings in parallel are OK, more gets complex with current shareing.

envelopes2007
December 17th, 2007, 9:37 PST
Posters
My generator needs to be "quiet" so, therefore that means Honda/Yamaha?
So, if I start with a generator 2500W-2600W continuous then that limits the charger size? is that correct? which limits the battery bank size? Is that also correct?
Therefore I am thinking using (1) inverter charger for side "A" and (1) for side "B" and move the generator back and forth
....is this making any make sense?
practical issues?
what voltage for "A" and "B' is simpler
I have two battery stands and two sides to the battery shack...
and more than two minds!!

BB.
December 17th, 2007, 9:37 PST
I would also question charging one bank (generator) while using power from the other bank...

Efficiency wise, you would be better just running the generator (assuming fuel powered generator, not solar/wind RE power) to run the tools and charge the bank at the same time. Then shut down the generator and run off the battery bank/inverter once the batteries are full and the power needs become less/more sporadic...

This saves you the losses of generating 120 VAC, converting to DC (85%) , storing in battery (80%), then inverting back to AC (85%) (=58% overall efficiency or 42% losses from running tools from battery bank when generator power is available).

Running the Generator to power large continuous loads (tools+charging when generator is most efficient) and use the batteries to power intermittent / smaller loads (evening, night, morning) when the generator is less efficient (and noisy). It also may allow you to size the battery bank smaller and saves battery charging cycles--extending the bank's life (and saving you money).

And even if you are running solar panels (for example), you would still be better running one bank of batteries as the power from the panels to the inverter would still "bypass" the 20% losses incurred when charging batteries (A:B bank switch idea).

-Bill

BB.
December 17th, 2007, 9:40 PST
Regarding battery bank voltage--Generally, run the highest voltage that you can buy cost effective chargers/inverters for... It reduces your current and therefore wiring size/costs. 48 VDC is the typical maximum for an off-the shelf home system. Larger/special purpose systems have higher voltages (such as computer room UPS type units) are sometimes also available used.

-Bill

envelopes2007
December 17th, 2007, 10:03 PST
Here is my generator size See: http://mayberrys.com/yamaha/generato...fic/ef2800.htm

I would also question charging one bank (generator) while using power from the other bank...

Efficiency wise, you would be better just running the generator to run the tools and charge the bank at the same time. Then shut down the generator and run off the battery bank/inverter once the batteries are full and the power needs become less/more sporadic...-Bill

OK this is great idea Thank you

IRunning the Generator to power large continuous loads (tools+charging when generator is most efficient) and use the batteries to power intermittent / smaller loads (evening, night, morning) when the generator is less efficient (and noisy). -Bill

OK great idea also. Thank you.
Q: what will happen if I start my 1HP motor with the Yamaha while it is charging my deep cycle batteries? Small fire? stalling engine? what?

...also may allow you to size the battery bank smaller and saves battery charging cycles--extending the bank's life -Bill

size smaller like what? I have (20) 6V 180a/h batteries (20) of them. ten on one side of the shop.... and ten on the other

Any ideas for smaller ? The generator and batteries are NOW fixed. ie; I cannot change them..... the only variables we can change are the voltage(s), the charger/inverter size and me?

can you help me please? no solar - just gas (diesel later) .....solar after that!

kevin

mike95490
December 17th, 2007, 13:21 PST
Any ideas for smaller ? The generator and batteries are NOW fixed. ie; I cannot change them..... the only variables we can change are the voltage(s), the charger/inverter size and me?

Watts are watts, you have what you have.

If you fire up the generator, the first 10 minutes, the battery bank is going to take all the juice it can get from the charger. Shortly, it will start to taper off. When it tapers off, you are safe to start up a saw (the generator will handle the start up surge better than the inverter will.) If you are using the tools intermittently, the overall load won't likely fry the generator.

When charge cycle finishes (that last 20% is going to be a real bear, the generator will be lightly loaded then, that's the BEST time to use power tools) be SURE you disconnect the loads off the generator, and let it run a couple more minutes, to get the generator head cool down, before switching off the fuel. You can overheat the head, if it's loaded pretty good, and shut the engine down, without a cooling cycle. (ever notice a car boils over when you fill the tank after a long highway drive. it lost the cooling air, and the parts are still hot.)

Don't make the mistake of chronic undercharging the batteries - maybe get 2 generators, run the big one for the bulk charging, and then shut down, and run the smaller one (honda inverter series ??) to do the finishing charge. Most fuel efficient way I can think of. Batteries need at least 3 full charges a week. Or consider sealed AGM cells, they are supposed to tolerate undercharge better than flooded.

BB.
December 17th, 2007, 14:59 PST
The Yamaha here is an inverter type--so I don't think you can overload and sag through starting a large motor as well as the pure copper and iron type alternator systems...

There is always a big problem starting heavy loads. However, once the motor is rotating, the steady state current is usually much lower... So, dropping all the loads, starting the motor, and ramping up the other loads (like the charger) can frequently be done.

So, in the end, it depends on the type of loads and the total loads. You will have to decide if you, for example; 1. start generator and charge battery bank for 12-30 minutes first thing in the morning. Then 2. drop the battery charger and start up the 1 hp motor (say pump, fan, or something with a clutch that allows the motor to keep running during the day). And 3., now that the 1HP starting load is gone and the batteries are starting to taper off their charging current, you can reconnect the charger + motor to continue charging your battery banks...

Part of what you need to determine is how hard you need to charge your banks... If you run the banks done 2 kWHours per night, you might charge at 1 kW for the first two hours and drop down to less than 500 watts for the next 6 hours + 2 kW of tool usage (assuming 8 hours of generator requirement per day)...

There is probably no right answer--the best is to make sure that your batteries are properly charged and keeping your fuel usage low... So, that means enough generator runtime to recharge your batteries every day or two and keeping your low power generator usage (say at 40% to 0% watt loads) as low as possible (i.e., generator off, battery/inverter on when occasionally using a skill saw. Generator on, battery charger on, when multiple saws, large motors (table saw, well pump) are operating.

The worst (efficiency wise) time for your generator / fuel use is near the end of the charge cycle (last 5-10% of battery charge and/or equalization). If you can time your tool use for this period, it would be good.

Also, you may wish to get a few solar panels just for that last portion of the charge cycle. Maybe 500-700+ watts of solar PV which can finish charging your battery bank... Would be especially nice if this was when the generator is not required, and no battery power is required either (say noon and bit after, weekends, etc.)...

-Bill

crewzer
December 17th, 2007, 15:59 PST
Another consideration is that some inverter/chargers can be set to limit total AC current from the source. If the downstream AC loads powered via the "pass-thru" mode draw too much current, the inverter/charger will back off the output from the charger to the batteries.

For example, if you set the inverter/charger's maximum total input current to 20 A, and the charger input current to 15 A, then the inverter/charger will only allow up to 5 A AC to pass through to downstream loads before it starts self-limiting the current from the charger. This way, total current load on the generator won't exceed 20 A.

The OutBack inverters operate this way, but they need a Mate to be programmed. I don't know about the DR. You'll have to check the owner's manual, which can be viewed on (and/or downloaded from) the Xanrtrex website.

HTH,
Jim / crewzer

envelopes2007
December 17th, 2007, 16:01 PST
[QUOTE=envelopes2007;11047]Here is my generator size See: http://mayberrys.com/yamaha/generato...fic/ef2800.htm

Bill,
Thanks for explaining how a (3) stage battery charger will affect the function of my generator. I know that Yamaha3000i/Honda 3000eu are both undersized for an 800a/h battery bank but its a NOISE ISSUE.... and right now and we will have to accept that 2500Watts or 2800Watts is all I can generate.

My storage batteries will simply be spectating while I build my cabin with generator and my power tools.

Now, the \$6,000,000 question is this?

My electrician friend says that I can run my power tools from a 129Vdc battery bank because the motors on them say AC/DC. Is this correct? If the appliance says AC/DC why can't I hook up batteries into a breaker box and then out to a GCFI duplex receptacle?

He says they re-charge their configuration with a 129 Volt battery charger and use breaaker box and power tools out the other end!

Is he misguided? What about 129V array? Thats how the batteries were configured before they were given to me? ie; in a 129Volt array?

Can anyone explain this? to me?

crewzer
December 17th, 2007, 16:10 PST
Can you be more specific about the tools you're using? Brand? Model number?

Regards,
Jim / crewzer

BB.
December 17th, 2007, 17:18 PST
Short answer--probably yes for brushed motors...

In the old days, Brushed motors were called "universal motors" because they can run on AC or DC.

With modern tools, many of these have variable speed controllers (electric drills are one). I believe, IIRC, those tools will generally just turn on at full power (because they need the AC power to turn off the triac twice per cycle).

However, if your table saw is an induction motor--no, it will not run on DC.

The last issue you have to worry about is protection against short circuits. typical AC breakers will not work for this application. You would need DC breakers (and probably up stream DC fuses too) to protect against shorts.

You will also not have ground fault protection either (needs AC to reliably operate the current sense transformer).

-Bill

envelopes2007
December 17th, 2007, 17:33 PST
OK Jim,

I can pretty much build my entire cabin with,

1) Dewalt DW131 7Amp @ 120V ac/dc 50/60 HZ.....1/2" drill
2) Sears Craftsman radial arm saw motor# C48BXFD 250
3) Makita recipro saw model JR 300V 5amp
4) Samona Table saw model # TSC 10L (Taiwan)

But essentially he says if I use tools that say AC/DC that would eliminate? the need for 12V or 48V configuration of my battery bank? and the losses associated with AC to DC to AC conversion and bacK?

These batteries were probably on grid so they may have had a special charger attached. He told me it was a company out of Calgary Alberta called ....Oh, I forget? now!

Would anything help me understand? how they maintained these batteries on grid without a multi stage charger?

envelopes2007
December 17th, 2007, 17:40 PST
Hi Bill,
My electrician friend gave me the DC beakers c/w the batteries and the bus bars and stands, hygrometer, et al.
I added th GFCI outlet thinking I was being smart.....but what do you think about setting them up in a 129Vdc array?
Could I recharge them efficiently? What would I need?
Would I need a DC charge controller and what generator?
What do you think? I am 2 years away from solar or wind powered back-up system.
Thanks

Kevin

westbranch
December 17th, 2007, 18:19 PST
Kevin, have to assume he also supplied the distribution boxes...? type, size(capacity/rating) of breakers?

Eric

BB.
December 17th, 2007, 20:29 PST
In of itself--given that the inverter is probably 85-90% efficient, it is probably not worth going "native" DC unless you have a heavy load that is a large percentage of your total daily power usage that you can use the DC for...

Your bigger issue may be the DR3624 which is a modified square wave inverter... It would be much better if it were a true sine wave inverter. Probably won't hurt the universal motors--but the other types of non-brushed motors will run a bit hotter (and less efficient) because of it... And the old question of 90% of your stuff will run OK on MSW--but what of the 10% that may die young will not....

Building a 129 VDC battery system (charging, distribution, etc.) may be OK if you can find the stuff surplus (and cheap)... But with the price of recycled copper and such--it may be difficult snag the equipment before it gets sold off for scrap. And finding something that will work solar to battery charging (efficiently) may require you to cobble together your own system.

In a way, get a good true sine inverter that would integrate with the solar charger (Outback or Xantrex as examples)--you would have a working battery based system that you can pretty easily add solar panels and a electric start generator too without having to "scrap/modify" your existing system. So, you are already close to 50% on the way to solar/wind right now.

-Bill

envelopes2007
December 17th, 2007, 22:09 PST
The Yamaha here is an inverter type--so I don't think you can overload and sag through starting a large motor as well as the pure copper and iron type alternator systems...-Bill

Hi Bill,

I understood a little bit of this quote

Q: Honda 3000eu and yamaha2800 are superior generators? If so, is it because of the sine wave that they produce? inverter type? explain?

Does the Honda act differently (under load) than other generators?

How?

Thanks

BB.
December 17th, 2007, 22:30 PST
A regular generator is a rotating mass (at 1,800 or 3,600 rpm typically) and when subjected to heavy, temporary loads will overload the engine and slow down, but still supply current as the rotating masses act like an energy storage flywheel (and usually more instantaneous current than the rated nameplate). Of course, the frequency (and voltage) will drop too at this point--sometimes an issue for critical loads that require precise line frequency control.

The Yamaha and Honda are inverter type generators... Really a three phase alternator (kind of like your car alternator without the diodes) that is connected to a "black box" that takes the power from the motor/alternator and converts it to 120 VAC at 60 Hz. Since the inverter is electronic, it has very specific circuits and parameters it maintains under normal operations... And large currents are usually prevented electronically (much faster than fuses/breakers to prevent damage to its one switching devices). So, I would expect an Inverter Generator to be less able to exceed its nameplate rating by as much as pure mechanical generator system can.

Also, from comments here, there are several other issues... One is the Honda and Yamaha have very small rotating masses... In the Honda's case (from reading the manual) the alternator is also the flywheel for the motor. In a regular generator, you still have a flywheel and the rotating mass of the alternator--so a better ability to "rotate" through heavy loads until the generator's gas motor can open the throttle and get back up to speed again. (sounds like the Honda motors can quickly stop turning because of the lower rotating mass).

Also, the Honda (and your Yamaha model I believe) have a throttle switch. With Eco(nomy) throttle switch on--the motor speed is dropped down when little power is needed. And if more power is needed, the engine speed ramps back up. However, if there is a sudden load, the engine may not be able to ramp back up quickly enough to start the load.

So, there is the other position--engine running at 100% rpm (Eco off). Here the engine and alternator are capable of better supplying instantaneous heavy loads (like starting an AC unit) without stalling or hunting speeds up and down as the load cycles.

-Bill

PS: I should add that the Honda and Yamaha generators are superior in some aspects. Control of Frequency, reduced fuel consumption at low loads (such as 1/4 load with eco-throttle on), and for the Honda eu line--the ability to run two generators in parallel to double their output current. And their inverters (at least the Honda) are sine wave output--not modified square wave like many less expensive inverters. Also Honda engines generally have a pretty good reputation.

"Regular Generators" can be more rugged and cheaper to build. However, when the generators are built "cheaper"--frequently that means the use of bushings rather than bearings and other cost reductions (no low oil sensor and such).

Larger/better generators are going to include pressurized oil system and oil filter. Hardly any small generator will have an oil filter--so they will not last near as long because of that (and require more frequent oil changes too).

So--in many ways, you get what you pay for...

PPS: I should add that these are probably near the best generators for their size (small)... I looked at the smallest "standby" generator sold for homes--and that was something like 10kW and cost about \$1 per hour to run with zero load.

My home needs about 300-400 watts (on 24 hour average) to run--or about \$0.22 per hour (at the current cost of gasoline). Just a whole lot cheaper and I can take the Honda with me on an emergency or for other uses.

The closest I have found as a good home emergency generator is one of those Onan (and other brand) units intended for RV's. They are compact, not too large, have an oil filter, can run on propane (and probably natural gas), and are very quiet. In fact, we have a friend that did just that for his family's home (was around the time that California was threatening rotating electrical blackouts through the state).

nigtomdaw
December 18th, 2007, 6:22 PST
If you already own a Xantrex DR inverter charger then unlike the SW unit and the OB units it does not have the generator charger back off facility that Crewzer mentioned ealier. So you will have to manually de-rate your charger output when using large loads as well as charging your batteries

When I first started out similar to you renovating my finca (barn) I had a very similar setup a DR2424E inverter charger small 330 ah battery bank, no solar and my main consumer of electricity was a fridge freezer. I also had a Kipor 1600 watt suitcase inverter generator . Very similar because I had half the batt bank capacity and half the gen power that you have. My main problem was the fridge freezer which is not in your senario, yet!

So on a day to day basis I got through in this fashion.

Up in the morning run the genny with the DR charger set to about 35 amps this allowed the fridge freezer to kick in with out the genny tripping out. During this morning charge up Id charge up all my Dewalt Batteries as the genny power was pure sine unlike the DR frying modwave. Took between 1.5.-2 hours to get those batteries back up to fully charged. If the DR charger had gone from bulk to absorbtion charge then I would maybe use some smaller power tools and allow absorption charge of a hour. When we got to float I would disconnect the generator.

I would then take the genny with me around my site and use it directly for water pumping cement mixer power tools ect.
At the end of the days work in the summer with the fridge on all day the batteries were ready for a boost, if the missus wanted to do a clothes wash with the automatic washing machine (heater switched off) again Id let the Kipor max charge at 35-40 amps then when on absorbtion charge kicked in then we ran the washing machine. Our biggest problem was our water booster pump which would kick in and trip the genny if the DR charger was set too high.So if we needed the batteries to get charged quickly after a bit of bad battery management we shut everything down and turned the DR charger up to 60 amps to get the batteries back.

600 watts of solar the following season greatly simplified things as the solar took care of the batteries and fridge loads. But a digital DC Amp Clamp Meter was an essential tool in this manual power aintainance system. I am now as my signature and my SW3024E does it automatically. if you havent bought a DR unit yet dont save up for a SW or OB. If you have put it on your upgrade list.

I enjoyed my second hand DR2424E and it got me through 2 years of working visits to my barn, fried a couple of PIR security lights 2 mobile phone chargers and a dewalt charger, but it kept my beer cold,my laptop connected and the lights on , I upgraded and sold it on at a profit to a friend down the lane, hes had it nearly 2 years he hasnt fried anything as hes aware of its limitations and only charges stuff up when his gennys running. Practical eg of living off grid no solar, married to a DR and just not enough genny power to make it work.as it should If I had a 3.0kw genny it would have been alot less fuss.

Life married to a DR has fond memories , however the divorce was pleasant and profitable,;) the new Sw bride is a lot smarter making my life a lot easier.

HTH.

envelopes2007
December 18th, 2007, 9:49 PST
GREAT POSTS!!!
THATS JUST FANTASTIC ...THANKS.

When I started this forum I was told "You will be investing heavily in expensive equipment, so invest heavily in some knowledge.....read, post and learn"
And fortunately...... I did NOT purchase a DR3624 today!

I have 6-9 mos to learn some more before I buy expensive solar/wind equipment and set up my system!

In a few days I will purchase a Honda3000eu or Yamaha2800i to get some juice into my deep cycle storage batteries.

In this emergency situation I will be borrowing a decent car charger to get some juice into my batteries because this is a dire and critical situation.

I am off grid, on an island, no roads. But I do have 24v alternator on my Komatsu D21A Dozer?

Any suggestions?
How to do it?
What charge rate?
Automatic charger?
I need a (band aid) solution while batts are still alive and speaking?
Amps?
Volts?
Prayers?
need help for (20) 6.45Volt storage batteries.

Kevin

Bill- I do have my eyes firmly set on an ONAN 6KW diesel generator (1800rpm) for installation this summer but I need survival techniques right now!

envelopes2007
December 26th, 2007, 14:16 PST
Hi Jim,
I took into consideration all your comments and have purchased a 5.0KW Onan generator. It has 120Vac or 240Vac option.
I also bought a 12V battery charger.
It is (3) stage ie: 20amp, 10amp, 2amp ....with a 60 amp engine start (whatever that means!!)
So, I have now (10) 12v @ 160a/h batteries to charge.
Q:Would it be wise to purchase a 2nd charger so the generator was not wasting fuel and energy all the time!! How about a third charger if I can find one on the island?
Generator is 1800rpm. Onan. CCK. 2Cyl gas, 5.0KW ....air cooled etc.
Any suggestions?
Kevin

BB.
December 27th, 2007, 0:36 PST
Kevin,

Your charger sounds like the standard automotive charger with 60amps to quickly charge/jump start your car with a dead battery (usually for something like 5 minutes).

While this type of charger may or may not work for your particular application (even in the short term), you really need a charger designed for use with storage battery banks (2-3 stage charger). Your car type charger is just not up to the job for long term use.

Iota makes good chargers (from what I have read)... You might look through them here (http://store.solar-electric.com/bach1.html)and search for a manual (and read about their IQ4 smart charger adapter--pretty much required for good battery life).

You can also look at the Outback (http://store.solar-electric.com/outback.html) (and other brands) of pure sine wave inverter/chargers... The are basically a big UPS device. They connect to your generator and pass AC through to the load while the generator is running and at the same time charge your batteries. Once the batteries are full, it can automatically shut down your generator and supply AC power (120 and/or 240 VAC). And once the batteries are drained, it will automatically start the generator again... And they integrate with a solar charge controller too...

The down side is this stuff is highly programmable, has lots of options, and is not cheap. But if installed correctly, it very reliable. Also, look a getting a battery monitor (http://store.solar-electric.com/metersmonitors.html) too--much better way to manage your battery charge levels (once you are ready to go "off grid" solar/battery).

It is overwhelming to try and figure this stuff out--but it is worth taking the time to study and setup a good system right the first time.

-Bill

envelopes2007
December 28th, 2007, 10:25 PST
Hi Bill,
I know I need a decent batt charger for permanent solution.
I have been looking at a XANTREX FREEDOM COMBI 12v 2500w INVERTER CHARGER with a LINK 1000.
or ......... an IOTA DLS 55amp (that has recently come available).
What would you suggest?
My expected loads are just power tools, lights and music.
I have (noisy) generator for now.
limitations?
benefits?

Kevin

BB.
December 28th, 2007, 10:47 PST
Kevin,

I probably don't have enough experience in this area to really guide you other than suggesting a good Outback, Xantrex, etc. pure sine inverter that is designed for generator/RE use.

The unit you are looking at is not pure sine and probably does not have some of the nicer features that an inverter/charger designed for off-grid/RE use would have (see other threads)...

Also, you might want to keep your posts more in one thread--it is getting kind of confusing with multiple posts will similar/overlapping questions.

-Bill

envelopes2007
December 28th, 2007, 18:00 PST
OK......so I now have two (2) pieces to my puzzle and (1) more to solve.
I have,
1) a large battery bank. 1600a/h @ 12V.
2) a medium size generator.
I went to the Xantrex site and there was a warning! or a section about matching generator size to batt charger size.
I don't understand it completely but apparently a medium sized generator like mine needs a "resistive load" wired to it permanently, in conjunction with the "inductive" load supplied by the presence of the batt charger?
Is this correct?
Apparently, this is to increase the generators capacity to produce more-usable decent quality AC?
Is this true?
Is it as simple as plugging in a 500Watt lightbulb? while the generator is running and attempting to supply power to the battery charger?
Did I understood this correctly?
thx

BB.
December 28th, 2007, 23:03 PST
From the document you pointed at basically talks about, what sounds like, a simple diode bridge rectifier (probably with an inductor to limit current a bit--I am not a power expert).

Basically, the Freedom series has an "old fashion" front end that takes only the "peak voltage" of the AC wave form to charge up a DC capacitor--which is converted downstream to your 12 VDC (or whatever) battery charging voltage.

So, what happens is the charger draws a lot of current for only a small part of the AC wave form... The regulator circuit on the generator sees the "average voltage" and so the peak voltage drops where there is heavy current and the average voltage (where there is no current) stays "in regulation". This type of power supply would probably require that the peak AC voltage be above some minimum level to keep the input capacitor charged. If the capacitor voltage falls too much, then the power supply will not be able to supply the full amount of DC charging voltage/current.

These type of "electronic loads" are very ugly for generators or even utilities. In some cases (like a credit card processing center with 100s of PC used for data entry), these poor PF systems can overheat building wiring (happened several decades ago in California--took them a while to figure out why the "average or RMS current" was normal--but wires and connections were melting because of the very high peak currents).

By adding an additional load (like a 1,000 watt heat), the generator sees the average current from the resistive load and bumps up the field current and now the peak voltages are back higher again. Brings the PF of the combined load back closer to a PF of 1.0 (ideal)--but does waste fuel if the heater load is not needed.

Years ago, we had to change our computer power supplies that had these simple diode rectifier front ends to what is commonly called a power factor corrected front end. These supplies, basically, electronically mimic the apparent load curve of a purely resistive load. This makes the Power Factor rating be very close to 1.0--and for a generator (and any home/utility/etc. wiring in general) this allows it to output maximum power.

I looked a bit through the Outback and Xantrex websites and did not find anything listing the Power Factor ratings of their battery charger sections for either vendor...

I am sure that one of the BoBs, Solar Guppy, or somebody else (like sales/tech support) can identify if there are any power factor corrected inverter/chargers out there that would meet your needs (PF Correction is actually a very nice feature and I would think it would be heavily advertised if any of the units had this feature).

-Bill

niel
December 29th, 2007, 5:07 PST
xantrex does have some chargers with a power factor correction.
http://www.xantrex.com/web/id/180/p/1/pt/7/product.asp
in a search i ran into much info that you can sort through so here is the search page:

crewzer
December 29th, 2007, 5:10 PST
I looked a bit through the Outback and Xantrex websites and did not find anything listing the Power Factor ratings of their battery charger sections for either vendor...
This can be tough information to come by. Xantrex says their new XW inverter’s “power factor corrected charging” spec is 0.98. See: http://www.xantrex.com/xw/pdf/DS20070618_XW-Hybrid.pdf

I conducted some PF tests on my OutBack inverter/charger some months ago. The results are posted here: http://www.outbackpower.com/forum/viewtopic.php?t=2134

HTH,
Jim / crewzer

niel
December 29th, 2007, 5:17 PST
good info jim. i only looked at the straight chargers and didn't go to the inverter chargers.
adding here that the xw inverter chargers are also pf corrected.

BB.
December 29th, 2007, 9:45 PST
Good Find Jim and Niel!

From the Xantrex Products link by Niel:

Auto-ranging universal input voltage (100-260 VAC, 47-63Hz) is also compatible with generator or other low quality power sources...
Power Factor Corrected for efficient chargingThe "Wide Range" or "Universal Input" AC input (not Auto-ranging as Xantrex sales states) of 100-260 volts with no "dead zone" (rated not to run between~140-180 VAC, or a spec that reads something like voltage range: 100-135, 187-264 VAC 50/60 Hz), is another indication of a power factor corrected supply.

"Auto Ranging" and power supplies with a 120/240 VAC switch are typically diode bridge front ends with a voltage doubler at 120 VAC, and non-voltage doubling at 240 VAC setting. Auto Ranging just makes the voltage switch detection automatic (switching between voltage doubler or non-doubler).

Also statements like these (again from the product specs pages):

In addition to meeting global safety and emission standards...
CE marked, meeting LVD and EMC directivesAlso are indication that the unit in question may have power factor correction.

Kevin, that was a great question you originally asked. It had been so many years since I had to worry about PFC, that I had forgotten to even look for it in battery chargers--I just assumed that all presently shipping product would have this feature--except for the very cheap stuff (i.e., the \$29.95 special auto battery charger).

Obviously, there is still a lot of this non-PFC product out there... The PFC requirement was first a European requirement for larger devices (more than a few 10's of or hundred watts). Actually, I don't remember at this point if the US/NRTL's made PFC a US requirement or not (been years since I did regulator work)...

And yes, having a PF corrected battery charger is a very worthwhile investment--especially if you are running off of a generator or using larger battery chargers.

You can have a 120 VAC only rated PFC power supply--but it is usually a 100-264 VAC 50/60 Hz rated power supply because it was originally a European requirement and the universal input was one of the basic requirements that allowed you to pretty much ship anywhere in the world with one product.

-Bill

envelopes2007
December 30th, 2007, 21:13 PST
Hi Bill,
I've been told that my generator does not even have a voltage regulator?
So how does that effect my choice of battery charger (power rectified or not?)
Also someone was stunned at my decision to operate a 2.5KW inverter from 12volts. They say 2.5KW load at 12Volts may warp the battery plates.?
Can you help me?
I have a Xantrex Prosine2000 in mind or a Xantrex Freedom 428 Combi 2.5KW unit but they are both 12V units. Prosine 2000 is powerfactored.
My only loads are a 1HP table saw and/or a circular saw whilst I am running the charger at the same time. (daytime)
Lights and stereo from the batts in the evening!
Kevin

BB.
December 30th, 2007, 21:45 PST
Kevin,

Your generator may or may not have what you would recognize as a voltage regulator... It is possible to wind generators and/or add a few passive components to create a reasonably accurate output voltages and not have a "regulator box"...

The problem is that a "old style" battery charger (or even computer power supply) draws very short, high current spikes--and any limited sized power source (generator or inverter) has problems supplying the spikes--and instead will typically chop off the voltage crest of the sine wave.

If you want to use more than 25%-50% of your generator's capacity to charge the batteries, then you would want to get the power factor corrected charger (or inverter/charger).

I don't have a battery/generator system--so I cannot give you the exact numbers--perhaps somebody else can give you more exact recommendations for charging capacity vs generator capacity...

Regarding 12 volts for a 2.5kW inverter... Current wise, you will need to account for peak amps of:

2,500 watts / (0.8 eff * 10.5 VDCmin) = 298 amps at "12 volts"...

Problem is to supply that load you will need large diameter copper cables from the inverter to the bus bar/central distribution area..

Connection your batteries in series/parallel, that would, ideally divide the load by 1/10 or about 30 amps per battery pair.

I don't remember the ratings of your batteries--but that is a pretty hefty load. Hopefully, the saw will only draw a 1,000 watts or so under load, so that will cut the continuous current 1/2 (or a bit more).

A higher voltage inverter will cut the current in your wiring (24 VDC cuts it in half, 48 VDC cuts it by 1/4--vs a 12 VDC inverter)... Wiring up a multiple hundred amp circuit is not something that people would like to do--if it can be avoided.

But, if you are going to be doing a lot of cutting at one time--it is probably worth firing up your generator to power the saw--more efficient and friendlier for your batteries.

-Bill

envelopes2007
January 1st, 2008, 8:31 PST
Hi Bill,
Thanks for indulging me with this discussion.
Yep, you are right the generator operates the table saw.
.....and the batt charger at the same time!!.

These batts are only 'on site' because they were given to me.
The batts are 10 years old and were originally connected to the grid and installed in a 120Vdc array and were used to operate and run 120vdc equipment.

So the bus bars and 00 welding cables are all supplied for a 120Vdc@ 160a/h array (there is no 120Vdc charger however).

I have been told 120Vdc is nasty......is it?
and a 12Vdc system a little too small.?
Do you agree? Where is 206amp load? for how long?

kevin

BB.
January 1st, 2008, 9:31 PST
Kevin,

My system is a 3kW Xantrex 3.0 Grid Tied inverter a little over two years old.

My other experiences are as a design engineer that included one project designing a large voice mail system to run off of 48-60 VDC battery banks at the phone company...

The problem I have with predicting your system performance is that we don't have the average power required by the saw or know the details about the batteries.

In theory, you should find a chart from your batteries that show Amp*Hour rating vs load curves...

A load on a lead acid storage battery that is 1/10 or 1/20 of capacity is pretty normal and that is why you see 20 hour ratings (1/20 * C). If you batteries are around 100 AH, and run them at 30 amps, you are around a 1/3 rating--For the typical Lead Acid storage battery, that is quite a load--it will tend to heat them up and also have issues with the rate at which the chemical transformation can occur--all leading to an apparent loss in battery capacity.

In theory, you could run your saw about 2-3 hours to 100% dead battery--but you don't want that, so--just as a guess if all was running well, you could run it for about 1 hour of heavy use.

Of course, if you know you are going to run your saw for an hour straight--you should probably using your generator at this point--both for fuel economy and avoiding strain on your batteries.

But, if you are typically using your saw for a 1/2 minute at a time every 5-10 minutes like most people just working around the site--I am sure that you could probably go all day without needing to recharge--the blessings of a battery backed hybrid generating system...

However, if you end up running the generator for 5-10 hours to recharge the bank (0.1C charging a 50% discharged battery string)--you might as well as just run the generator for your work loads anyway.

Once you have solar (probably a couple kW array--depending on your loads), that will allow you to cut way back on your generator/noise machine usage.

The 200 amp load is from the input of your inverter to the battery bus/combiner bar/connection... If the battery wiring and batteries are all balanced that each battery will supply 1/n portion of the parallel load (10 parallel connections then 200/10=20 amps). The problem is that it is difficult to achieve good balanced current flow in multiple parallel connections and there will be some batteries supplying more current and some less.

Some final thoughts... You should look up the model number for your batteries on the web. If these were for battery back systems--may are specialized storage batteries that were for emergency use and not designed for daily deep cycle usage. Some only achieved long life by limiting discharge to only 20% or so--not the 50%-80% normally spec'ed for a solar deep cycle battery.

And yes, 120 VDC from a storage battery can provide "more excitement" in terms of arcs, short circuit current, and melting of wires vs a typical home wiring circuit. Batteries supply huge amounts of surge current vs the pole transformer and DC sustains Arcs much better than AC. However, DC is slightly safer than AC in terms of electrocution (AC causes your muscles to contract and you can't let go of an electrified wire).

I am sorry that I am more or less dancing around your questions...

-Bill

PS: I should also add that storage battery systems actually have quite a wide range of operational voltages... For your "120 VDC" system this would range from ~105 to ~155 volts DC (dead to equalization voltages). Most 120 VAC items would start to have "issues" with voltages over about 132 Volts. Trying to run your tools and such from a DC battery bank would probably require you to carefully monitor/control your charging voltage while using your 120 VDC...

envelopes2007
January 1st, 2008, 12:10 PST
Hi Bill,

Exide storage batteries info.

Exide CA-9's 6V@160 a/h each.

Discharge rating. TO (reach) 1.75VPC is:
8hr @ 25.0 amps, 5hr @ 35.2 amps, 4hr @ 41.4 amps.

The table saw is not an issue because I just won't run it or other large loads from batts. I will run generator.

My hand tools ie; typical circular saws is 120V@12amps and some LED's or flourescent lights and stereo at night time.

These batts are deep and weigh 150lbs each.

Bill, there is a prosine 2000 on Ebay right now and I am quite interested because I believe it might actually solve my charging needs at least - and operate some cabin needs. I believe it will plug into my 5.0KW generator which is fine with me!