controller settings

[Hans Zurne]

Hi i would like some advice on what the best voltage setting is for my charge controllers.
I have 24 2 volt AGM batteries 1000 a/h in series
on the batteries is : cycle use 2.43 - 2.47
standby use 2.27 - 2.3
Up to now i have had the voltage on the charge controllers set at 56 volt , but that is probably not ideal
Does anybody know the ideal setting ?
There is always some draw on the batteries
Would it be safe and better to set the charge at say 59 volt ?
Looking fore ward to a reply
Thank you
Hans

[Rob Beckers]

Hi Hans,

I assume you're using the batteries in an off-grid system that sees frequent cycling? If so, I would look at the 'cycle' settings, or 58.3 - 59.3 Volt for bulk/absorb. The manufacturer would know more, but I would see the high end of that range as more of an "equalize" Voltage (even if AGM batteries are not equalized), to be used if you note that the Ah capacity of your battery bank starts to drop, that high a Voltage would help de-sulphate the plates a bit better. The low end is appropriate if you cycle shallowly and get a full charge back in right after.

Looking at Fullriver, another maker of deep-cycle AGM batteries that I'm more familiar with (https://www.solacity.com/product/fullriver-dc400-6/), they recommend 58.8V as the bulk/absorb Voltage for their batteries. Given the range your batteries recommend that is probably a good one for you as well, possibly with those fine-tune suggestions I've mentioned above.

Float would be 54.6V, which is pretty much universal for lead-acid based batteries.

The other setting that is at least as important as the absorb Voltage is the absorb time. Everyone underestimates what it takes to put that last 20% charge back into the batteries. The equation (from Rolls, which is based on flooded lead-acid, though the principle really doesn't change) is:

Time = 0.42 x Ah-Capacity / Current

You have a 48V @ 1000 Ah (20-hour rated) battery bank. Charge current shouldn't exceed 20% of that or 200A, though staying at/under 15% or 150A really is much better for the batteries. But let's say your charge controllers on a nice sunny day can push 120A around noon as a realistic current value.

That makes absorb time:

Time = 0.42 x 1000 / 120 = 3.5 hours

It really takes THAT long to do the last 20% of charge and to get the sulphate on the plates to reverse back to lead and lead-oxide! Of course, if your (realistic) current value is different the time will be different.

Hope this helps!

-RoB-

[Hans Zurne]

Thank you Rob
Yes this helps me a lot, and i start to understand things better now.
My system is working well , but i want of course get the most out of my batteries and with winter just around the corner here i soon can see if the system can deliver what i hope it can do
Thanks again
Hans