diy solar

diy solar

First solar system on RV. Need recommended charging voltages for Victron MPPT controller.

busterbrown

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Jun 29, 2020
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This is my first attempt ever at solar so I'm learning as I go.

I've recently installed two 100 watt polycrystalline panels on the roof of my RV. I have a relatively new bank of AGM deep cycle 12 Volt batteries from Weize (three 100 amp hour group 31's)

I purchased and use a Victron 712 battery monitor (which works great). I decided to buy a Victron Bluesolar 100/20 amp solar charge controller to harness the panel voltage. The problem I'm faced with is the recommended settings on that controller for my battery type and brand. I'm reading conflicting advice online. Weize has this stickered on each battery:

Cycle use: 14.5 - 14.9V
Stand-by use: 13.5 - 13.8V

I've read that AGMs should be limited to 14.4V during cycle use (I'm assuming this is another name for asorbsion??) and 13.2V for Stand-by use (another name for float charge??)

I've also read that undercharging weakens AGMs more than overcharging. Not sure if this a truly accepted statement.

I'm looking for ideal charging parameters for the longest life of these batteries. In addition, I did purchase the temperature sensor for the Victron SCC.

Any help with these controller settings is much appreciated.Screenshot_20200630-001348_Chrome.jpg20200628_183947.jpg
 
Most of the AGMs on the market are not designed for regular equalisation charging so they have to be bought up to full charge, ie all cells fully charged, during absorption charging. If you don't use a high enough absorption stage voltage this won't happen and you'll drop capacity as the cells wander away from each other's SOC. You should pick a voltage within the range recommended by your battery manufacturer.

There are long service life AGM batteries available and they do have lower than typical absorption and float voltages, they are designed for it. That's likely where a lot of the advise regarding low absorption voltages stems from.

The trade off using higher voltages, and why regular equalisation isn't a good idea for most, is that the higher you go the faster the water gets split and your battery can only recombine at a certain rate. Any excess gas is vented, ie water is lost and there's really not a lot to spare in an AGM in the first place. If you are trying to extend the life of your batteries go for a lower end absorption voltage and when the time comes that their capacity dips lower than you like, give them a manually triggered equalisation charge cycle.

Victron's default AGM profile assumes you are using an AGM that can handle regular equalisation charging so, IMO, you should go into the charging settings and turn that off.
 
Thank you for your input. Was helpful. So, would 14.5V absorption and 13.5V float be the ideal profile based on this manufacturer's recommendation?
 
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