35 AMPs of Solar to a 100 AMP AGM Deep Cycle battery

[mschulz]

Sunking, I hope you can chime in here. I was given (yeah free) two brand new Kyocera panels and I want to hook them up to my 100 AMP Trojan AGM (31- AGM) battery that is 4 months old. I plan to run a 40 AMP MPPT charge controller. Is 420 Watts to high of a C/ rate for that battery. I calculate out around C/2.85 . Is this too much? I wanted to run them in series to reduce voltage loss. Or would I be better to run only one panel (C/5.88) and wait until I upgrade to 200 AMP hours or convert to 24volt system. This project is my small cabin with my daily watt-hours of 395 on the weekends 2 to 3 weekends per month running at 12 volts. Daily Sun Isolation in the winter 3 hrs. Honda EU2000 with a 25 AMP charger is my current charging system.


Panel Specs.
Maximum Power (Pmax) 210W (+5%/-5%)
Maximum Power Voltage (Vmpp) 26.6V
Maximum Power Current (Impp) 7.90A
Open Circuit Voltage (Voc) 33.2V
Short Circuit Current (Isc) 8.58A
Max System Voltage 600V
Temperature Coefficient of Voc -.12V/°C
Temperature Coefficient of Isc 5.02x10-3A/°C

[Mike90250]

While you are waiting for Sunking's esteemed opinion, mine is that it would "Likely be OK" maybe set your charge controller absorb/bulk voltage to the low end, just to be safer to not BBQ the battery.

[Sunking]

Page 20 answers your question.

Trojan Battery User Manual

C/5 or .2C

You have me confused. Do you have 1 or 2 of the Trojan 31-AGM batteries? If you have 2 of them, then you can either charge them in series for a 24 volt 100 AH, or in parallel for 12 volt 200 AH. Either way with 2 batteries 420 watts is perfect . If you only have one battery just use one panel of 210 watts.

[jony101]

AGM's can handle tremendous charge current, 35 amps is well within the limits of what a 100ah agm can handle. Trojan is a high end agm, it can handle the 35 amps.

Many car audio enthusiasts use agm's as there start batteries with high output alternators(over 60 amps). Its a proven technology.

High charge Voltage is what will kill you battery, high current wont damage it, the battery will only accept the amps it needs. To force the battery to take more amps then it needs you need to increase the voltage beyond the battery specs and that will cause it to vent.

I hooked my 240 watt panel with mppt controller to my fully charge 17 ah agm jump pack to see if the controller would try and overcharge it, but it was uneventful. Controller recognize the battery as charged and started to float charge at less than an amp.

Your charge controller will keep your battery safe.

[mschulz]

While you are waiting for Sunking's esteemed opinion,

Classic Mike. You made me laugh and I also appreciate everyones opinion, It just seems that Sunking's battery knowledge is pretty strong.

Thanks Sunking, but I do not understand what they are telling me on Page 20. What does 10-13%C20 mean, etc? Sorry for being a dunce on that one. I get the volts thing and can set my charge controller for that, but I am worried about the AMPS that will hit the battery.

I am only running 1- T-31AGM for a total of 100 AMP hours. The plan is when I kill this battery, I am going to upgrade to 2- T-31's and make my system 24 volts.

[Sunking]

Thanks Sunking, but I do not understand what they are telling me on Page 20. What does 10-13%C20 mean, etc?

C means the battery rated Amp Hour specification at the 20 hours discharge rate. Trojan 31-AGM 20 hour rates is 100 AH.

For Trojan AGM recommended charge rate is 20% of C or 20 amps or C/5. The 10 to 13 % you quoted are for Flooded batteries, not AGM.

OK with that said the 31-AGM is a cranking battery, and Trojans user manual is generic tailored on the conservative side to Deep Cycle batteries. You can get away with 35 amp if you use Temperature compensation as Trojan recommends for all AGM batteries. The TC will lower the voltage if the battery starts heating up. Otherwise stick with C/5 or 20 amp max.