What happened to my system?

[PatBlack]

My system is (or was, I dismantled it):
2 100w HQST solar panels in series
50' solar cables
victron MPPT 100 | 30 SCC
2' 12 gauge solid conductor wires, positive fused with 40 amp automotive spade-type fuse
2 battleborn 12v 100 Ah batteries wired in parallel
6' 2 gauge 130 degrees C stranded wires
Harbor Freight Item #63432 Jupiter 1500 Watt Modified Sine Wave Inverter

I was using the system off grid to run 2 florescent shop lights (total combined load 115 watts), charge a laptop, run a 1000 watt pressure cooker, run a small fan. All was working fine for months. Then I started running the shop lights for more hours. I'd still make sure that the system got into float mode every day. Looking at the victron connect app I was making about 1kWh a day. Then one day the lights started flickering and the inverter gave a low voltage alarm. That puzzled me because I hadn't been using a lot of power. I turned off the inverter and looked at the victron connect app and it said the battery bank was at 10.3v.

The next day the SCC went into float mode after about 1.5 hours. That puzzled me because I believe that 200w of solar panels in the morning couldn't possibly take a 200 Ah lithium battery bank from 10.3v to 13.6v in that amount of time. Later that day I tried running the shop lights again. Once again I got a low voltage alarm from the inverter in a very short amount of time. I turned off the inverter.

I suspected there was something wrong with that Harbor Freight inverter. So I disconnected the positive wire to it, but left the negative attached. I don't know why just the one wire, but that's what I did. I guess I figured that would be enough to keep the inverter from drawing any power.

I left the inverter off for a month. Each day the SCC would be in float mode. I used no power from the system. I figured the batteries were fully charged. After that month I used a multimeter and the batteries read 9.8v. More puzzlement. I disconnected the solar panels, then disconnected the batteries, and charged them each separately using a marine battery charger on the grid. Now I have 2 batteries holding steady at 13.37v.

I hooked one of the batteries up to the SCC just to look at the history in the victron connect app. It shows a month of data. It went from
14.6 v max, 10.0 v min on the first day with the v min going gradually down ferther each day over the 30 days. On the last day it showed 14.6 max 3.53 v min. I should have been checking what was going on, but life got in the way for a month there.

So now I'm lost. I guess maybe I should have disconnected the negative wire from the batteries to the inverter? I am thinking about hooking everything back up except for the inverter, then run a 12v compressor cooler for a while to see if I at least have the 12v side working properly. I would have to use that inverter to run a full load test on the battery bank, but I am fearful that the inverter has a short or some other malfunction. Since there's no fuse between it and the battery, I'm afraid to use it, given what's been going on.

My overall question is what is going on with this system? More specifically, is there a way to test if the inverter has a short that is draining the batteries? Why would the victron app indicate 3.53v and the multimeter indicate 9.8v?

I would be grateful for any assistance on how I can diagnose this and suggestions on how I could improve the safety and capability of my system. Like buying a quality pure sine wave inverter and a circuit breaker! I am in an remote area and there's very little I can buy locally. I do have a victron battery monitor bmv-712 smart that I could add into the system to get more useful information.

Thanks for reading all this if you made it this far! I hope I gave enough information for someone to help. I tried to search the forums for a similar discussion, but didn't find a good match in the search.

 

[HRTKD]

Is it possible that one of the batteries is bad?
I would have asked if the inverter was drawing a large amount at idle, but you said it was disconnected and the problem persisted.

 

[PatBlack]

When I disconnected them and charged them each on their own, they both started at 9.8v and ended at 13.37v, so I think they are both behaving the same. I have them back on the solar charger today with no loads, but the 3" of snow on the panels this morning means they're not generating any current.

 

[Hedges]

I'm guessing high resistance between charge controller and battery, so with very little charge current the voltage it sees rises.
14.6V is when it is charging it a resistor. 10.0V or 3.56V is when sun has gone down and it is measuring battery voltage, with its own load applied, through a resistor.

Connect charge controller, disconnect solar panels. See what voltage charge controller reports and check battery voltage. If not same, check voltage drop across positive wire. Check voltage across negative wire.

With separate battery charger you were able to recharged batteries properly.
Inverter with only negative wire connected is as good as disconnected.

 

[HRTKD]

When I disconnected them and charged them each on their own, they both started at 9.8v and ended at 13.37v, so I think they are both behaving the same. I have them back on the solar charger today with no loads, but the 3" of snow on the panels this morning means they're not generating any current.

13.37v is not a full charge and may not have been high enough to engage the cell balancing routine. The default charge for LiFePO4 with the Victron 100/30 would be to 14.4v.

Channeling Captain Obvious: The Victron solar charge controller isn't going to know what's going on with each battery. It's perspective is limited to what the battery bank as a whole is showing. So one battery could be off and the other battery at the right voltage.

 

[Hedges]

I don't think there is any indication cells are imbalanced or battery (BMS) is "off".
It only looks like an SCC issue to me. Batteries, Marine charger, Inverter are all working properly.

System:
One, $135 inverter https://www.harborfreight.com/1500-...-modified-sine-wave-power-inverter-63432.html
One, $226 charge controller https://store.santansolar.com/product/victron-energy-smartsolar-mppt-100-30-solar-charge-controller/
Two, $85 PV panels https://hqsolarpower.com/100-watt-12-volt-monocrystalline-solar-panel-pre-order/
Two, $900 batteries https://battlebornbatteries.com/product/12v-lifepo4-deep-cycle-battery/

Me, I prefer to spend a fraction of my money on batteries, use most power as it is produced. But my usage model is different; grid tied 99% of the time, running PV direct with small battery during occasional grid outages.

I think if you doubled the amount of PV installed, it would almost always fit within SCC limits and you could fully recharge batteries on one summer day. Even more PV (if Victron can shrug off the excess on more sunny days) and you could have as much power in the winter.

 

[HRTKD]

I hooked one of the batteries up to the SCC just to look at the history in the victron connect app. It shows a month of data. It went from
14.6 v max, 10.0 v min on the first day with the v min going gradually down ferther each day over the 30 days. On the last day it showed 14.6 max 3.53 v min. I should have been checking what was going on, but life got in the way for a month there.

Hedges, at first glance I would think the problem is with the solar charge controller also. However, given the above quote, it seems the solar charge controller is getting the batteries to 14.6v. Perhaps there is another load on the system that is draining the voltage overnight.

 

[Hedges]

Perhaps. But if batteries were 14.6V during the day, loads would run a while.

I'm guessing the charge controller isn't getting batteries to 14.6V. Charge controller is getting charge controller to 14.6V, and charge current is abysmally low. Just like when someone top-balances with cheap wires and alligator clips. But even worse, because the power draw of the charge controller to operate it's display caused IR drop from 9.8V (DMM reading of battery) to 3.53V (shown on Victron app.) Practically open circuit, k-ohm or meg-ohm of resistance.

Simple enough to test - with PV and SCC connected, does Victron show 14.6V? Does battery show significantly lower?
If battery has just been recharged with separate battery charger, connect a load to inverter and draw some amps, so battery drops a bit. Does Victron continue to show much higher battery voltage?

Got fuses? Voltage across them is the first thing to test, if battery and SCC (or inverter) don't have same voltage.

"positive fused with 40 amp automotive spade-type fuse" You can probably probe on the exposed tops of the fuses.
Contacts can corrode, in whice case voltage will be between female spade terminal and fuse rather than across the fuse. My Saab had a fusebox with copper grommets that corroded, got hot, made fuse contacts bad, caused cooling fan to shut off, overheated engine, cracked head. I ended up wire-brushing the connections and soldering them with acid-core flux, which I then neutralized and rinsed.

I think a blown fuse can leave a conductive/resistive deposit, maybe just enough continuity to turn on a high-impedance load

 

[PatBlack]

Thank you @Hedges and @HRTKD , you've given me a path forward for tomorrow. I feel optimistic that you've guided me toward finding the culprit and an easy fix. I'll check the voltages versus the app, check for resistance everywhere, replace something if I find something out of whack. I'll report back tomorrow. And yes more PV is most certainly in order, and a pure sine wave inverter, too. I have been upgrading components as I am able, hence the current mix of high-end and low-end, on my way to a more integrated and quality system. Thanks again!

 

[Mac6792]

There was an issue with victron scc's getting hung up. There was either a firmware or software update. Make sure yours is current