question

dixonge avatar image
dixonge asked

Lost all confidence in my settings

Here are my basics:

4 100W panels in series/parallel

4 Duracell EGC2 (Deka GC-15) in series/parallel

BMV-712

SmartSolar MPPT 100/30

This is in an RV - no grid. We live in it.

After I rearranged where things were mounted my SOC on the BMV-712 was reset to --

I've been waiting to sync the SOC back to 100% but I am unable to disconnect everything for 12 hours to verify the actual battery voltage. In the meantime, my system has never left the bulk state of charging, in spite of multiple mostly sunny days.

Current BMV-712 settings are as follows:

Capacity: 460Ah

Charged voltage: 14.3V

Discharge floor: 50%

Tail current: 4%

Peukert: 1.27

Charge efficiency: 85%

Current threshold: 0.10A


Current MPPT 100/30 settings are as follows:

Absorption: 14.6v

Float: 13.9v

Temp compensation: -18mV/C


Do any of these settings look off?

MPPT SmartSolarBMV Battery Monitor
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4 Answers
seb71 avatar image
seb71 answered ·

That is a big battery (460Ah/12V). From your post it appears that you also have some loads drawing energy. So your 400W PV array might not be big enough for your energy needs.

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dixonge avatar image dixonge commented ·
My only constant loads are:
  • DC control board on propane fridge
  • CO detector
  • Water pump
  • lights (all LED)
  • routers/modems
  • the inverter

Typically I see 4-6 amps. Right now, before sunrise, with one LED light on and my networking electronics I'm showing -5.87A on my BMV-712.

Before I switched to the MPPT controller the SOC rarely dropped below 90%.


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pwfarnell avatar image
pwfarnell answered ·

The settings look OK. The question I believe is more about what charge you are getting in fro m the solar compared to your usage if you are permanently in bulk. What charge condition were the batteries in when you installed the system. What voltage, current and power are you getting from the panels into the MPPT, and what voltage and current out of the MPPT and what current into the batteries. Do you have a bad connection on one of the parallel solar panel strings. How much power are you using.

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pwfarnell avatar image pwfarnell commented ·
The only setting that I would question is the 4% tail current, the SOC will automatically reset to 100% when the current falls below 4% x 460 = 18.4A if above 14.3V. The batteries are not fully charged till the tail current is perhaps 1%. This is not the cause of your issues and can be tweaked in the future.


The other thought is do you have another way of charging the batteries just to get them full, the engine alternator even if you use jump leads from the starter battery, or a one off hook up.

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dixonge avatar image dixonge pwfarnell commented ·
After switching from PWM to MPPT controller I rewired the panels from parallel to series/parallel. Using yesterday as an example I was showing 33-35 V most of the day coming in to the controller. Batteries got up to 13.65v. Current was net positive, 15-20amps. Last time I ran an ammeter on the panel lines they were each 4.5amps, 9 amps in series.

All batteries were installed by me, new. Last test everything showed in the green range on the hydrometer.

Our typical default load overnight is 3-6amps, depending on if I leave my electronics on (two modems, one router, one RaspberryPi).

This system, all added by me, is completely separate from the RV electrical and I run it by plugging the shore power cable in to the inverter. This saved me a huge wiring cost and/or headache but it also means I have no other way of charging the batteries.

Given that none of the settings seem incorrect, I'm tempted to change the panels back to full parallel. I was trying to give higher voltage to the MPPT controller as this was supposed to be a much more efficient configuration, but it seems to charge much more slowly/inefficiently (so far).

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rickp avatar image
rickp answered ·

I have 4 panels running, and tried various schemes to see which worked best. A full series arrangement worked best for me. I purchased a large solar charge controller, the SmartSolar 250 | 100, so voltage or amperage wouldn’t be a concern in any configuration, and to allow for expansion.

If your panels will not overload your SCC, experiment to see what wiring arrangement gives you the best performance.

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dixonge avatar image
dixonge answered ·

follow-up:

1 - underpaneling (or at least under-configuration) is probably a major culprit here - most charge rates I have seen indicate 10% is a good target, so 46amps in my case. I typically see no more than 20-25. All good in the summer, not so much when the sun starts to drift south.

2 - maintenance - I let the water get low. A few cells may have had the top edge of the plates get exposed. Not much, but close enough that the SG is *bad* on all cells. I've been trying to equalize but the panels struggle to get to full charge, much less an EQ cycle on top of that. This is true even when I split the bank up into two pairs and charged them separately.

3 - settings - best I can tell, my charge controller settings are fine

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