Simple van system: MPPT limiting charge even though battery is low

DIY
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EDIT: ISSUE FOUND

Not sure why this fuse failed so spectacularly though.

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I have a Victron 100/30 MPPT, Renogy 200ah lifepo4 battery, and 400w foldable solar panels, in a DIY van build.

Current settings and history in screenshot. History may not be super useful because my solar panels are moved around a lot, sometimes not out all day, etc.

System has been working fine for a couple of years, with one brief hiccup easily fixed with a setting.

About a week ago, the MPPT began moving rapidly into float even though the battery was <70% full.

After googling and in some desperation, I changed the absorption time from fixed at 2 hours to 7 hours.

This worked for a couple of days but today the controller moved almost immediately from bulk to absorption (battery was only at ~50%) and dropped the incoming watts very low (solar panels could have provided 70+ watts but were only providing 10w)

I unplugged the panels, disabled and re-enabled the MPPT controller, and bumped the battery voltage up for a couple of minutes (and then back down to 14.4) and it at least started charging at 70-100 watts. But it should be providing more with the current sun.

Would love any help and please make it as simple as possible because I am ok with very basic wiring and settings but don’t really understand how all of this works.

Thanks!

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This is probably not the best to do, but if I temporarily (like for 60 seconds) change the battery voltage setting to 16, it will pull upwards of 230w. So the panels are getting enough sun to charge more. While it’s doing that, it shows the battery v as actually at 14.4-14.8, so it’s not like it’s actually charging it to 16v while providing the additional watts)

It won’t let me add another pic but it would show:

239w

Solar

V 37.32

Current 6.4A

Battery

V 14.79

Current 15.8A

State: absorption

2

The MPPT measures 14.4V on its output but the battery only 13.4V, you are loosing 1V somewhere. Most likely a high contact resistance, at a fuse/MCB, a crimp or screw connection.

Your float voltage should not be set to the same level as absorption, but thats independent of the voltage drop

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Hmm. Lets see if we can sort through some things here. Like @chrigu a very common and easy to check issue is bad or loose connections. If, indeed you have 13.4 at the battery but the MPPT is charging at 14.4 that’s a problem. Other thought is possibly the internal shunt in the BMS being inaccurate. They can drift over time. A smartshunt would be more reliable. In fact, I don’t know if I would trust the info you are seeing on the battery app only. I would do actual readings with a reliable volt meter.

You can turn this back down. 7 hours is too long for 200AH.

4

The absorption/float settings are confusing to me because the user manual for my battery says to set them the same (14.4v) but I keep seeing people say that it should be different

Is there a difference of opinion on this between knowledgeable users and the companies?

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I have turned it back down to 2 hours. It dropped back into float but seems to still be charging at 115 amps.

I noticed the difference in voltage between the battery and charge controller not long after posting this.

Since it was about 1 v different, I decided to experiment with what would happen if set the charge controller to 15.4 (1 v higher than recommended), with the plan to ask here if that was a bad idea for the short term (just to get the battery charged so I could continue troubleshooting).

It bumped the incoming watts up to where I thought it should be (mid-upper 200s), and didn’t seem to affect the voltage readings much on the battery side or the charge controller side.

However, the charge controller did start to smell. I immediately turned it back down to 14.4v and the amps dropped back to ~115. And I am recalling that a friend of mine recently said that something smelled like burning plastic in the back of the van. So now I am concerned that my problem may be inside the charge controller itself.all of my connections have seemed secure but I am going to double-check and also check the fuses

Edit to add: FOUND THE ISSUE!! :scream:

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Yep. That’s bad.:grin:

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You can ask a 100 people about their charge voltage preferences and you will get 100 different answers.

Personally i would say, as a setting in an MPPT, it may be ok. The sun isnt out 24/7 so the battery is not held at that high voltage level all the time, it does get some “rest” at least daily. However the general consensus is, that float voltage should be lower than absorption. If it isnt, then theres no point in distinguishing between the two. Two different voltage levels is what defines the two charge stages. Also holding the cells constantly at a high level will very likely lead to faster degradation.

I would definitely not run 14.4V as both absorption and float in an inverter-charger, or a charger fed by mains voltage, since that can keep the voltage at this level indefinitely. Even 14.4V as solely absorption is a bit high, i would go for 14.0V absorption and 13.4V float (but again, personal opinion, also check if the BMS properly balances at only 3.5V per cell)

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It’s that a fuse on the negative wire?

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YES

I don’t recall why or whether this was my doing or the guy who put my system together.

Do you think that could have caused the problem? I had no idea it was weird but my friends who came to help me out also thought it was odd.

The same friend also told me I used the wrong kind of wire to connect the charge controller to the battery and that the MPPT controller would be better off closer to the battery. He’s going to rewire with proper wires, lower gauge (4-6awg) and add some other stuff (a cut-off switch I can get to without crawling into the back of my van, for example).

So crisis averted and future crises hopefully also averted.

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Thanks for this thorough reply. I am going to check what my inverter-charger and my DC-to-DC charger are set to and will also set my MPPT float lower, since it seems like it would be all benefit and no downside to have it be different.