Charge controller overcharging lithium battery to 15.4v...how...why? Please help

[Tomthumb62]

Ok, perhaps someone can help me out here. I am not physically present with the system and am relying upon our GPS tracker to feed me the system voltage. 10 minutes ago, it said 14.13V (SCC is set for 14.2V on bulk/boost) but then a couple of minutes ago I checked again and it said 15.4V! Then a minute later it said 14.34V and now it must be in float at 13.44v (float is set I think to 13.4 or 13.6v). Can someone help me figure out what might have happened?

12v system
400W panels (4x100w wired in parallel)
Renogy Rover 30A solar charge controller
Powerurus 200Ah 12v LiFePO4 battery
Load is mostly a Victron 1000W inverter that usually only powers a apartment fridge drawing a max of 100W AC

Now if the 15.4v reading I saw momentarily was correct, why didn't the BMS cut-off? I mean maybe it did and since I can't be there to check (wife is not too thrilled about using apps to read all our solar system info). But when I've charged it up full before to 14.6V, the BMS most certainly did cut-off the charging circuit that I confirmed in the battery BMS app.

But nontheless, I'm trying to understand how the battery could have gotten overcharged. Either the SCC is failing or the GPS voltage sensor is wonky (it's been accurate in the past) or some other issue.

Thanks!

 

[Tomthumb62]

Ok update: now the GPS voltage is reading 13.71V. This doesn't make sense. Just literally a few minutes ago it was at 13.43v and I expected it to stay there or close to it for the next bit while it likely would stay in float. Maybe it's voltage drop or something, but it doesn't fit the pattern I've seen over the last 48 hours since the system was deployed.

 

[Lt.Dan]

If your reading the 15.4v at the Solar Charge Controller, that DOESNT mean the battery is actually at 15.4v

If the battery disconnects, then yeah the Voltage might spike on the SCC side, but the battery voltage will be safe on the BMS side.

 

[Tomthumb62]

If your reading the 15.4v at the Solar Charge Controller, that DOESNT mean the battery is actually at 15.4v

If the battery disconnects, then yeah the Voltage might spike on the SCC side, but the battery voltage will be safe on the BMS side.

Whew, thank you for explaining that. That makes sense. LoL here I am hundreds of miles away watching only the voltage go up and down. I must’ve caught it just at the moment the battery hit full and disconnected and there was a spike in the SCC voltage like you said.

 

[Tomthumb62]

If your reading the 15.4v at the Solar Charge Controller, that DOESNT mean the battery is actually at 15.4v

If the battery disconnects, then yeah the Voltage might spike on the SCC side, but the battery voltage will be safe on the BMS side.

Oh wait…No I’m not reading voltage at the SCC. I’m reading it from the GPS tracker which gets its power from the house 12v battery (the only battery and one in question). Isn’t that more concerning, assuming the voltage reading is accurate for the tracker?

 

[timselectric]

Oh wait…No I’m not reading voltage at the SCC. I’m reading it from the GPS tracker which gets its power from the house 12v battery (the only battery and one in question). Isn’t that more concerning, assuming the voltage reading is accurate for the tracker?

Still the same as explained by @Lt.Dan

 

[Tomthumb62]

Still the same as explained by @Lt.Dan

Ok, thanks for confirming that. Wife just confirmed that the BMS did cut off due to full charge. Which leads to another question. If a lipo battery BMS cuts off due to full charge, doesn't that electrically disconnect it from the charge controller? And isn't it supposedly bad for a SCC to be connected to panels but no battery? I know Will did a video where he debunked this myth but then there are people who claim to have fried their SCC by doing just that. And since this disconnect is going to likely happen about once a day, over the months isn't this a bad thing? Or do I completely misunderstand what is going on? Thanks again.

 

[Lt.Dan]

Well I'm not sure about damaging the SCC, but you definitely should NOT be using the BMS to cutoff every day. The BMS should be last resort, last line of defense. If the BMS is constantly having to disconnect, it will fail quicker. Also, if the BMS is constantly having to disconnect, then you need to lower your charge settings on the SCC to prevent that disconnect.

Preventing that disconnect will prevent the SCC from spiking. Its a win-win.

 

[Lt.Dan]

What GPS voltage thing are you using? Perhaps theres something else we can recommend?

 

[Tomthumb62]

Well I'm not sure about damaging the SCC, but you definitely should NOT be using the BMS to cutoff every day. The BMS should be last resort, last line of defense. If the BMS is constantly having to disconnect, it will fail quicker. Also, if the BMS is constantly having to disconnect, then you need to lower your charge settings on the SCC to prevent that disconnect.

Preventing that disconnect will prevent the SCC from spiking. Its a win-win.

Ok, thank you, again, that makes sense. I had set the Rover SCC bulk charge to 14.2V. Now I've read that these Rover charge controllers are often off by about 0.2v, so I'm assuming that it actually charged to 14.4v, which is within the max voltage of the battery (14.6v max). Maybe the SCC is failing or something is wrong with the battery (it's brand new but the SCC is a few years old).

What GPS voltage thing are you using? Perhaps theres something else we can recommend?

It's this one: https://optimustracker.com/products...-tracker-cars-trucks-motorcycles-boats-assets

We got it as a tracker but the voltage reading has turned out pretty handy. It's been accurate in the past.

Now this is the first LiFePO4 battery I've owned, so maybe I'm not understanding something here. I also have a Victron IP22 12v 30A charger. I've set the bulk charge to 14.0v, 14.2, 14.4 and 14.6v. I think it's currently set at 14.4v. Every time I've used it to charge this battery, regardless of the bulk voltage (float has been set from 13.5 to 13.8v), the BMS shows a fault of "full charge" and that the charging mosfet had been triggered off but it would soon resest and turn it back on. Is this not normal for a LiFePO4 BMS?

 

[timselectric]

Not normal for the BMS to shut off daily.
Charging voltage should be lowered.

 

[Tomthumb62]

Not normal for the BMS to shut off daily.
Charging voltage should be lowered.

Not sure if you saw my post just before yours here, but I've charged at 14.0v on up to 14.6v. It seems the BMS throws a "fault code" of "full charge" regardless of what voltage I charge it at. Maybe it's not a true fault, but i'm pretty sure I've seen the charging mosfet get turned off when it reaches full charge. I thought that was normal, but you're telling me it's not. Sucks that I'm not physically present with the system to confirm any of this and don't know if the battery/BMS is faulty or some other part of my system. Or maybe I am mis-remembering of the BMS actually cutting out and the "fault code" is a poor use of terms for simply saying the battery is fully charged.

 

[timselectric]

The BMS should only cutoff during charging for battery over voltage, cell over voltage, or over amperage. Some BMS's see the first two as a full charge state.

 

[Tomthumb62]

The BMS should only cutoff during charging for battery over voltage, cell over voltage, or over amperage. Some BMS's see the first two as a full charge state.

Well when I get a chance I will set bulk charge to lower like 13.8v and see if the BMS does the same thing. But nonetheless you are telling me this isn't how a BMS should act? Unfortunately, it will be 6 weeks before I will be able to be physically present with the system to really check any of this. Hope the battery/bms isn't getting damaged in the process. Wife isn't really interested in this sort of technical electrical stuff but maybe I will have to train her

 

[timselectric]

Well when I get a chance I will set bulk charge to lower like 13.8v and see if the BMS does the same thing. But nonetheless you are telling me this isn't how a BMS should act? Unfortunately, it will be 6 weeks before I will be able to be physically present with the system to really check any of this. Hope the battery/bms isn't getting damaged in the process. Wife isn't really interested in this sort of technical electrical stuff but maybe I will have to train her

If I had to guess. I would say that one of the cells is running higher than the others. 6 months might be long enough for the balancing to correct it.

 

[Tomthumb62]

If I had to guess. I would say that one of the cells is running higher than the others. 6 months might be long enough for the balancing to correct it.

Ah, you are correct on that. Yes, one of the cells does run a bit high. So is the remedy simply to wait for the battery to balance itself, 6 months like you said? Or would lowering the charge voltage help at all? I mean I've charged from 14.0 to 14.6v and this is the behavior I believe I've seen each time so not sure that would help. Would charging it at a lower rate help (how low if so)?

Now the battery is very new, maybe a month old now, cycled for testing about 10 times now. Would this be enough of a concern to try to warranty the battery for replacement?

 

[timselectric]

Ah, you are correct on that. Yes, one of the cells does run a bit high. So is the remedy simply to wait for the battery to balance itself, 6 months like you said? Or would lowering the charge voltage help at all? I mean I've charged from 14.0 to 14.6v and this is the behavior I believe I've seen each time so not sure that would help. Would charging it at a lower rate help (how low if so)?

Now the battery is very new, maybe a month old now, cycled for testing about 10 times now. Would this be enough of a concern to try to warranty the battery for replacement?

I wouldn't warranty claim it unless it's way off, and remains that way.
Lowering the bulk can keep it from running away.
As it gets more balanced, the voltage can be gradually increased.

 

[Tomthumb62]

I wouldn't warranty claim it unless it's way off, and remains that way.
Lowering the bulk can keep it from running away.
As it gets more balanced, the voltage can be gradually increased.

Ok thanks so much. I’ll try lowering to 13.8v and see what happens. I’ll also reach out to the battery maker and see what they say about the over volt protection kicking in every charge cycle.

 

[HarryN]

Try turning on a small load when charging - for instance a fan or refrigerator.

Sometimes this helps to tamp down spikes when you have a small battery pack like that.

 

[Tomthumb62]

Try turning on a small load when charging - for instance a fan or refrigerator.

Sometimes this helps to tamp down spikes when you have a small battery pack like that.

Thanks, yes there is/was a load at the time, a 7.2cf AC fridge that draws 60-90W. Seeing if I can convince my wife to adjust the charge voltage on the SCC today.