The 12.6 volt mystery

onebad

I'll make this as concise as I can. I bought a Renogy 400 watt system, at the time I could only afford 2 one hundred watt panels, the intent is to buy two more 100 watt panels. I also bought a 100 amp hour battery. I was not ready to install my system because I still needed to buy other things like a second battery and a fridge and a heating system, all of which I did buy. So it was almost a year from first purchase to installation. I put the batteries in and the panels on the roof. I apologize for the simplistic explanation but series and parallel always confuses me. The panels are connected with the negative of one panel connected to the positive of the other panel. The other lead of each panel is connected to the charge controller (yes Renogy provided an in line fuse for the positive side). The batteries are connected with jumpers between the positives of each battery and another between the negatives (parallel?), and the wires from the charge controller go to the appropriate terminal on each battery. Outside of Boston where I am we aren't getting that much sun but I see my batteries charge up to 12.7 volts then fall back to 12.6 with no load, even on a sunny day with several hours of sunlight left they will not charge above 12.6v. The techs at Renogy say it's due to lack of sun but I'm skeptical. I've taken one battery out and put it on a charger (the charger Renogy suggested a Noco Genius 3500) and after 22 hours it's charged somewhere between 75% and 100%. The other battery still in the van charged up to 12.7v then fell back to 12.6v again with no load. I don't have a meter that reads amperage so voltage is all I have to go by but If I connect my 12v fridge it drains the batteries overnight. Have I done something wrong? an electrician friend is telling me voltage means nothing only amperage matters but he doesn't have a amp meter so I can't diagnose further. Are these batteries toast? I am at a loss.  HELP! please.

Raj174

Hi, welcome to the forum. What kind of 100 amp hour battery is this? Lithium? Gel? AGM? How long did it go without a charge?
The charger you have provides only 3.5 amps for charging a 100 amp hour battery. If the battery was very low, it could take 2 to 3 days.

Marc Kurth

What voltage are you seeing while your batteries are charging? 

onebad

Hi Marc and Raj, thanks for responding. The batteries are Renogy lithium and while they are charging they are reading from 12.0 to 12.7v and then back to 12.6 as I described. One battery sat uninstalled for approximately 10 months the other for about 4. As I write this at 9:50am the battery that’s in the van is up to 12.8! and flickering to 12.9!! This is the highest voltage since I installed them at 13.0. The battery on the charger was reading 12.6 (installed with the other one) when I took it out and put it on the charger. The 25% light pulsed once or twice then stayed on, the 50% light did the same. The 75% light took overnight to stay light. The 100% light was pulsing as of 10:30 last night after approximately 28 hours on charge. I’ll report back after I check it this morning. 

onebad

The 100% light on the charger is still pulsing so the battery is not fully charged. I’ll give it till tomorrow. 

onebad

Monday morning and the 100% light is not lit. Instead the charger is flashing between the start light and the repair light. After three days on the charger I take this to mean it won’t charge fully and needs to be repaired. 

Raj174

Check the voltage, a full charge should read 13.4 for a lithium battery.

onebad

I did check the voltage and it read 13.43! Woohoo full charge. We had a few sunny days and the battery in the van was reading 13.1. I reinstalled the battery that was on the charger and the charge controller read 13.2. I purposely didn’t put any load of the system and with moderate sun it’s up to 13.3. It seems the 12.6 volt mystery has been solved. As soon as I am able I intend to buy the Renogy DC to DC charger, that puppy pushes 60 amps into your battery Bank. Thanks for your hellp Raj and Marc. 

BB.

Remember that the solar panels (number of panels, wiring to controller, etc.) and controller to battery wiring (long/small diameter wire, has higher voltage drop/can limit charging current to battery bank).

Using a DC Current Clamp meter to see what current you are actually getting into the battery bank (when bank should be under full charging current), and what the battery bus voltage is vs the charge controller Vbatt terminals, etc... There can be issues with wiring that is limiting your charging current.

A 400 Watt array with PWM controller (assuming 12 volt system) will nominally output a working maximum current to your battery bank of:

• 400 Watts * 1/17.5 volts Imp = 22.9 Amps under full noon time sun, clear day, and controller "bulk charging"

If you are getting less than ~11 amps on a typical noon time sunny day (no partial shading, good angle to sun, etc), there is a good chance that you have wiring or other issues.

-Bill