newbie beggar asking for advice

[West]

howdy,

beggars can't be choosers so any advice is welcomed in advance.

I have six 15 watt solar panels that I wish to use to charge up my mobile 36 volt battery pack system which is six 6 volt golf cart batteries. I need a 36 volt solar charge controller, from what I understand in reading, so any advice or links would be much appreciated on that.

Would also like to be able to run a small appliance (120 volt, 6 amps) someday off the same battery bank, an hour or two a day. So any advice on that would also be appreciated.

Currently I'm doing my own due diligence and reading as much as I can, (especially on battery care and charging).

another question, are desulfinators (sp?) worth the money? thanks again.

[SolarJohn]

Here's what I would do:

Wire the solar panels in parallel, for a 12-volt system.
Wire the batteries in a series-parallel fashon to make it a 12-volt battery bank.
Use a 10- or 20-amp 12-volt PWM Charge Controller. (Much cheaper than one that can convert dc voltages).
Use a 12-volt dc to ac inverter, sized appropriatly for your intended load.

You'll end up with about 675ah of battery capacity, and 90-watts of PV. You could certainly use some additional PV if your budget will allow it. If you discharge your battery 50%, your 90-watt array probably won't be able to fully recharge the battery bank each day (depending on how much sun you get of course).

If your 120v 6a load is a motor, don't forget about the high starting current that might be involved. An Exeltech 1100-watt inverter might do the job. I love mine. It has no trouble running my refrigerator and freezer.

I have diagrams of my system wiring on my blog. You might want to take a look. http://solarjohn.blogspot.com

I haven't heard many good comments about desulfators. I wouldn't buy one. A PWM charge controller "pulses" the battery, probably doing about the same thing as a desulfator does IMHO.

If rewiring for 12-volts isn't an option, you might have to buy a (more expensive) MPPT Charge Controller, like the Outback, since the less expensive charge controllers can only handle 12, 24, or 48 volts. Likewise, inverters tend to be 12, 24, or 48 volts. I don't know if anyone makes a decent 36-volt dc to ac inverter, maybee someone else can answer that. You might need to purchase a dc to dc converter.

good luck!
John

[mike95490]

I'd wire the panels 3 in series (36V?) and 2 strings in parallel, then directly to the battery bank.
No charge controller.

The panels are barely above a trickle charge, and if you use the batteries even a tiny bit, you won't over charge them. If you use the batteries a lot, it may take several days to trickle charge them back up to full.

Unusual, but 90W of solar is not going to damage 6 golf cart batteries, unless it's from UNDERcharge.

[Solar Guppy]

What Mike said, just would suggest adding a blocking diode so the panels don't discharge the battery's at night.

[BB.]

As everyone above has said--you are just trickle charging your batteries and don't really need a charge controller... Just connecting to the battery bank with 3 in series, and then the two sets in parallel. And watch the water level (check once a month).

Regarding how much power you can draw from your battery bank... A good recommendation for an off-grid use is to size the bank for 3 days of no sun and don't drain below 50% capacity (for long life)... So, for day to day use, draining between 1/6th and 50% of your Amp*Hour rating per day... And, once below ~75% state of charge (1/4 used)--recharge the batteries as soon as you can (within hours or day--to extend battery life by preventing sulfate hardening).

Remember that batteries are typically rated at a 20 hour discharge rate--if you discharge faster (or charge faster), you will loose some "apparent" capacity as some of the energy goes into heating up the battery bank.

For charging by solar... Take a look at this link for your area (assuming US).

If you are looking to better predict your system--this website does a very good job. Note that the minimum panel size accepted is 1kW (1,000 watt)--for smaller panels, simply divide by 1kW and multiply by your panel size (100watt/1kW=output in Watt*Hours).

For derating factor--I would suggest you use 0.52 for flooded cell batteries and an AC inverter (vs 0.77 default) because of the extra losses in an "off-grid" system.

For a good 36 volt inverter--check with NAWS (our forum host)... They can special order other input rated inverters (other suppliers may also have the option).

-Bill

[West]

As everyone above has said--you are just trickle charging your batteries and don't really need a charge controller... Just connecting to the battery bank with 3 in series, and then the two sets in parallel. And watch the water level (check once a month).

Thank you! I'll give that a try. And will shop at NAWS.

What Mike said, just would suggest adding a blocking diode so the panels don't discharge the battery's at night.

Thank you, now to find a blocking diode....


Thanks mike90045, I'll will get more panels (compact with high watts) before this is done. Just want to learn the basics before I spend the money and break things. For $150 I got a 1990 EZ-GO 36 volt cart with charger and $300 for 6-6v one year old trojans 125s. The panels I got new from a friend $200. The old cart does pretty good!


SolarJohn, Thanks I'll check out your blog. Once I learn more I'll be rideing a solar powerd vehicle that will double as a power bank and a welder. I hope.


I'll post some pics and more questions as I move along.

Best,