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?

BMV Battery MonitorMPPT SmartSolar
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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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pwfarnell avatar image pwfarnell dixonge commented ·
You should be able to read the amps from the panels from Victron Connect on your phone reading from the Smart MPPT. Rough numbers, 9A at 34V in on the panels is 300W, 20A at 13.65V is 270W so that seems consistent.


A continuous draw on the batteries of 6A over 24 hours is 140Ah, which at nett 15-20Amp is going to take 7 to 10 hours and you are not going to get full sun and full output for the period. Something has changed. Are all of your panels facing exactly the same direction and do any of them see partial shade when the others do not. The series - parallel arrangement is only OK if all the panels receive the same sunlight, i.e. direction and none of them get partially shaded. If you can not meet these requirements then with the series parallel arrangement one string can get hampered by poor sunlight and the good string gets pulled down by the MPPT hunting for the maximum power point. 2 strings at partial power can be better than one string doing nothing and the other giving full output. If your panels are in different directions / see partial shade over one or two panels then you may be better putting them all in parallel because the controller may then work off 3 panels only. If the controller and panel wiring is the only change then the panel series parallel should be reversed to see what happens and all joints checked in case you have introduced a poor connection / high resistance at some point, are any of the connectors warm.

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dixonge avatar image dixonge pwfarnell commented ·
Panels are all on a flat roof, two different directions. No shade at all, ever. Right now at 10:45am the controller is sending 19.8A to the batteries. BMV is showing a net input current of 14.7A - which matches standard usage (with all lights off).
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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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