Disconnecting charge controller after bulk phase?

[solarabcd]

If I have 4 FM80 Charge Controllers used for rapid charge during the bulk phase but due to battery limitations I can only have the current from 1 of the 4 Controllers during the absorb phase (higher vpc rate).

Is it possible to have 3 of the 4 shut down via the charge controller settings, i.e, not have them enter the absorb phase, or would I have to have an external (AUX) switch to disconnect 3 of the 4 once the Absorb voltage set point is reached?

Or Can all 4 keep running but limit the output to the equivalent of 1 of the controllers once the absorb voltage set point is reached?

Reading the operating manual for voltage set points doesn't seem to answer this for me.

Thanks.

[Cariboocoot]

Please do not take offense, but this set-up doesn't make sense.

First of all, the output from an FM80 is up to 80 Amps at any system Voltage. Four of them could push out 320 Amps in parallel, if you have enough panel to drive them all. For any size system, this would be in the realm of a megabank of battery. Otherwise you're pushing the charge too fast.

Secondly, once Absorb Voltage is reached it stays there; current is reduced so that the Voltage level is maintained. It wouldn't matter how many FM80's were attached: if they're all programmed alike, they'll all respond alike.

Thirdly, if you've got four you either have to have four RTS units or else (and this is a really good idea with this many units) have all the charge controllers communicate through an Outback Hub and controlled by a MATE.

May I ask just what sort of system you've got in terms of battery capacity, array size, system Voltage, and inverter? I've never encountered anyone needing 320 Amps of charge current before. I'd suspect you have a massively over-sized bank on a 12V system when you should be going up in Voltage to supply the power requirements.

I don't mean to be mean, but the idea of having four FM80's just floored me!

[solarabcd]

Thanks for the reply.
Yes don't take the hypothetical scenario as gospel.

I think you answered my question when you said that they 'reduce their current' to stay at the absorb vpc point.

Lets say the max charging amps a certain 48 v battery bank is 47 A in the absorb phase. During the bulk phase they can be charged at 275A providing the vpc point is at 54v i.e. lower to avoid heating issues and damage to the batteries.

So I was thinking that if all '4' (or 2 or what ever produces more than 47A pending array size and config) where putting out 47 x 4 = 188A (under the 275A limit) then when the lower voltage setting for the beginning of the absorb phase it reached (54v), then they would all continue to put in more current than the 47A limit...... The 47A is per string, so I could increase the battery strings to allow more current but in this example that is not possible.

With what you are saying; the 4 controllers would reduce each of their outputs to keep at the lower set point for the rapid bulk charge below that 47A limit?? So this absorb phase would just continue until the battery is full then go into float?

[Cariboocoot]

Okay you may have got hold of some confused information about charging phases. Maybe you should review this part of he battery FAQ first:

http://www.windsun.com/Batteries/Bat...ery%20Charging

When you're setting up a system, the charge current rate is set as a function of the battery bank size. In other words you plan for 5%-13% of the Amp/hrs to be the peak current. The most current will flow during the BULK phase. In the ABSORB phase Voltage is held at a predetermined level, and current fluctuates. FLOAT functions the same way, only at a lower Voltage because you're not 'replacing Amp/hrs'.

If you try to charge batteries at too high of a rate they will fry. Or 'boil' might be more accurate, as the water in the electrolyte solution will be 'gassed off' as it turns into hydrogen and oxygen. This is something to avoid. The excess heat and (possibly) exposed plates can lead to a destroyed battery in one go.

That 320 Amps I mentioned the four FM80's can supply? That's enough for 3,200 Amp/hrs. On a twelve Voltage system that's roughly 19 kilowatt hours. On a 48 Volt system it would be 4 times that: 76 kilowatts.

[solarabcd]

47.6 amps is 20% of the 6hr rate for the battery bank. 275 is the max they can handle providing the vpc is at 54v i.e so it cuts off before it 'boil's the battery bank.

These figures are straight from the manufacture and also discussed directly over the phone and email to their engineer.

I just want to know how you can configure the settings (cutoff points,triggers) of the charge controllers to ensure that output from the charge controllers is at the MAX current limit (potentially 275A), ONLY during the bulk phase and then reduces to the 47.6amps for the Absorb phase...?

[Cariboocoot]

47.6 amps is 20% of the 6hr rate for the battery bank. 275 is the max they can handle providing the vpc is at 54v i.e so it cuts off before it 'boil's the battery bank.

These figures are straight from the manufacture and also discussed directly over the phone and email to their engineer.

I just want to know how you can configure the settings (cutoff points,triggers) of the charge controllers to ensure that output from the charge controllers is at the MAX current limit (potentially 275A), ONLY during the bulk phase and then reduces to the 47.6amps for the Absorb phase...?

When we talk about charge current in RE we are usually referring to the battery's 20 hour rate, not the 6 hour rate. What batteries are these?

There's no worries here; ABSORB is governed by Voltage, not current. There is also programming capability to limit time (min and max) and to have the cut-off be determined by current level (drops to float if current falls below a certain level).

You can read the whole FM80 manual here: http://www.outbackpower.com/pdf/manuals/flexmax_80.pdf
(Always a good idea before you spend the money! )

I have to say this sounds like a most unusual, and therefor interesting, system you're working on.

[solarabcd]

Yes I was surprised they used the 6hr rate rather than the 20 too but it is 20% of the discharge rate in amps at the 6hr rate, which is 238A x 20%=47.6A).

This works out at around 2-3% of the full 20hr rate (1808AH). The 275A for bulk charge works out at about 15% of 20hr capacity.

I guess that is why you ask the manufacture, they all seem to have different methods.

I have read the manual but I don't get how the bulk phase can be set at 54v and then the absorb phase at a higher voltage... I assume from what you are saying that the charge controllers will prevent to HIGH a rate during the ABSORB phase? So there is no need to have to shut down anything to reduce array power during the ABSORB phase in order to stay within these limits above?

[Cariboocoot]

Yes I was surprised they used the 6hr rate rather than the 20 too but it is 20% of the discharge rate in amps at the 6hr rate, which is 238A x 20%=47.6A).

This works out at around 2-3% of the full 20hr rate (1808AH). The 275A for bulk charge works out at about 15% of 20hr capacity.

I guess that is why you ask the manufacture, they all seem to have different methods.

I have read the manual but I don't get how the bulk phase can be set at 54v and then the absorb phase at a higher voltage... I assume from what you are saying that the charge controllers will prevent to HIGH a rate during the ABSORB phase? So there is no need to have to shut down anything to reduce array power during the ABSORB phase in order to stay within these limits above?

The BULK mode pushes the most current it can to the battery (with an upper limit) varying as the Voltage comes up until the Voltage reaches the ABSORB set point; there is no specific "BULK Voltage". In ABSORB mode the Voltage is held steady and the current is varied to maintain that Voltage. During BULK the ABSORB timer counts up; whatever time is "on the clock" at the moment ABSORB mode is achieved is the time period the controller will remain in ABSORB (with programmable limits) after which it drops into the lower Voltage FLOAT mode, which it will maintain until this level can't be held due to drop in PV output and/or loads.

Does that help clarify it? Frankly, the FM80 manual isn't as good as the MX60's (its predecessor) and that was a bit lax in key areas (just my opinion).

And yes, each battery manufacturer has their own specs for charge rate. I think they do it on purpose - to confuse people!

[solarabcd]

Thanks Marc.
What threw me off in all of this was that the battery guy I spoke with indicated that the absorb charge would have to be lower and using either a super-large array or a high output generator to provide the bulk charge, then have something to provide the absorb phase. I assumed the charge controller would take care of the limits if I set them correctly - not sure what he is thinking.

[Cariboocoot]

Thanks Marc.
What threw me off in all of this was that the battery guy I spoke with indicated that the absorb charge would have to be lower and using either a super-large array or a high output generator to provide the bulk charge, then have something to provide the absorb phase. I assumed the charge controller would take care of the limits if I set them correctly - not sure what he is thinking.

You're welcome.

One of the advantages, and consequently frustrations, of the OB charge controllers is the amazing amount of programmability in them. There are a lot of options! I found I get the best performance on mine with some changes to the defaults like expanding the maximum ABSORB time to "up to 4 hours" (normally it's 2).

BTW, one thing they don't tell you (and this is true of any component) is that running them close to their maximum limit (80 output Amps) isn't the most efficient range. The extra heat produced can cost efficiency. Several of us find that 75% capacity seems to be peak efficiency.

I'll guess what you've got are some industrial batteries, like forklift or telecom units.