2 chargers with different set points

stephendv

For traction batts the manufacturers recommend a charging profile which isn't supported by standard charge controllers - what they want to see is:
1. Bulk
2. Absorb at 2.4V ish for x hours
3. After absorbing, increase voltage to 2.65V and as soon as the batt hits this voltage stop charging and switch to float.

I think I can get this charging profile by using 2 chargers with different set points, but want to make sure I'm not missing something. The first charge controller (A) with the most solar PV connected (2.8kW) will be programmed the standard way, absorb at 2.4V for 2 hours. The second controller (B) with relatively little PV connected (500W) to it will be programmed to absorb at 2.65V for 1 minute. So with both controllers connected to the battery, would I see the charging profile I'm expecting?

What happens when the battery reaches absorb at 2.4V as programmed in A, but controller B wants to push this to 2.65V ?

vtmaps

Re: 2 chargers with different set points

I like your thinking (why didn't I think of that?). I don't know if it will work.

My first thought is that you may not get the full two hours of absorb at 2.4 volts. As soon as your charge current from the big array tapers down to about 7 amps (or whatever the 500 watt array can produce) the 500 watt array will take over. How many hours does it take for your large array to taper down to 7 amps?

Second thought: does your sunny Island have a relay that can trigger when it gets to float? If so, use that to turn on the 500 watt array.

--vtMaps

westbranch

Re: 2 chargers with different set points

what effect are you expecting from charging for 1 MINUTE at 2.65V?

stephendv

Re: 2 chargers with different set points

I'm expecting to create the charge curve published by most traction batt manufacturers, like the one from trojan attached. Remember the charge to 2.65 happens after absorb. They call it a "finish charge" whatever that means.

vtmaps, yeah the sunny island has 2 relays, but I won't be able to use them because I actually want to AC couple the small panel and use the sunny island as the second charger... just didn't want to complicate the subject with AC coupling.

Attachment not found.

niel

Re: 2 chargers with different set points

it almost sounds like eqing after absorb charging doesn't it?

westbranch

Re: 2 chargers with different set points

I was wondering if 1 Minute is long enough to even come close to creating an EQ effect, bubbling, in a 48 V bank, 500w / 48v = ~ 10A.