BMS cutoff happening?

[edfardos]

Can anyone confirm from this video that the BMS of the lifepo is triggering?

The seller insists it's normal for the battery to disconnect itself from the circuit when the voltage reaches 13.9V, they don't understand why it needs to reach 14.6V for a period of time, then float back down to 13.somthing volts. You can see the charge controller flash a red "high voltage" warning when the battery BMS assumably disconnects itself from the circuit, and we momentarily see the full voltage of the panel over the battery terminals (19V). No loads were destroyed yet.

Yellow fluke meter is battery voltage across posts.
Blue watt meter is amps from the panel.

This charge/disconnect cycle goes on forever.

Same behavior is observed on three different charge controlers, all of which indicate a "battery error" at this stage.

Is this battery defective?

genasun controler
weize 100Ah lifepo
100watt 18V panel (6A at my latitude)

thanks in advance,
-edfardos

 

[John Frum]

Sure looks like a high cell disconnect.
How have an average voltage of ~3.485 per cell at disconnect and presumably one or more cells shot through 3.65 volts.
If your solar charge controller is configurable I would set my bulk/absorb to 3.45 volts per cell and see if you can get to charge termination without the BMS disconnecting on you.
3.45 volts per cell will get a battery full it just takes a bit longer.
This will give the BMS a chance to converge the cells.
After a few dozen cycles at 3.45 you could try higher bulk/absorption voltages is you want.

 

[John Frum]

Are you running that solar charge controller un-fused?
If yes that is not a good idea.

 

[edfardos]

Thanks for the reply! The charge controller is fixed at 14.2V peak. I drew it down 5Ah or so, then retried, same result.

 

[edfardos]

I have fuses for all legs, this is a bench-test. thanks for the good advice.

 

[John Frum]

Thanks for the reply! The charge controller is fixed at 14.2V peak. I drew it down 5Ah or so, then retried, same result.

I'm guessing the charge current is also fixed, confirm?
What is the scc output in amps?
I'm trying to determine if you are hitting absorption or not.

 

[edfardos]

Current from panel is displayed on the blue meter, we see 4.3amps before the error. I don't have a way to measure current form SCC.

 

[mikefitz]

Since you are charging at a low current the battery will be fully charged at a much lower voltage than 14.6 volts, its most likely charged by the time it reaches 14.0 volts.
The battery is not defective as such, just has cells that are not ideally balanced, very common in low cost batteries.
Your solar charger, Genasun, seems to have a fixed output charge voltage of 14.2 volts, an alternative controller set to a lower voltage would avoid BMS cut off and may give more time for the cells to balance.
Many 'casual' users of batteries having these issues just accept it's the way things are, and happily report on Amazon how Weize batteries have transformer their lives!
Mike

 

[edfardos]

Okay, so if I buy a replacement "Weize" lifepo it's likely to do the same thing? The Genasun SCC wasn't cheap, and has a lower fixed output voltage than most SCC's (14.2 vs 14.6). I have much smaller lifepo batteries that don't exhibit this behavior.

My primary concern is that when the BMS disconnects the battery, my loads see nearly 19V for a moment until the charge controller notices the BMS fault and cuts the current. This is normal for cheaper batteries?

So, is this battery defective, and should I buy the same model? something else? I'd like to have 1kWh of storage.

thanks again for the help!

-edfardos

 

[John Frum]

Okay, so if I buy a replacement "Weize" lifepo it's likely to do the same thing? The Genasun SCC wasn't cheap, and has a lower fixed output voltage than most SCC's (14.2 vs 14.6). I have much smaller lifepo batteries that don't exhibit this behavior.

My primary concern is that when the BMS disconnects the battery, my loads see nearly 19V for a moment until the charge controller notices the BMS fault and cuts the current. This is normal for cheaper batteries?

The battery is doing the "right thing"TM.
Its protecting itself.
On the other hand the solar charge controller is very slow in regulating its voltage.

 

[mikefitz]

The 19 volts is from the solar controller not the battery. The voltage falls quickly ( stored energy within the controller circuits) and with some load on the battery may not be noticeable.
There is a good chance the battery will be almost fully charged and will be at specified capacity at the cut off voltage you are seeing.
You don't need to charge to 14.6 volts , where you have a low charge current compared to battery capacity,, a lower voltage is good.
It's not uncommon to use voltages in the range 13.8 to 14.2 volts.
The battery is not defective, just has slightly unbalanced cells. A replacement in the same price range may be better or may be worse.

You battery is now charged, I suggest you carry out a load test to confirm firm its capacity.

The Genasun solar controller is way overpriced with no user settings. For a similar cost a Victron Smart solar controller offers considerable advantages with full user setting and status of charge. It also stores 30 days of charge state.

Mike

 

[edfardos]

Other cheap SCC's do the same thing... 13.9V, BMS cutoff, loads see 19V, SCC stops, battery voltage floats down to 13.8V, SCC resumes charge. So all my loads see 19V every eight seconds. Any significant loads will blackout during the BMS cutoff every 8 seconds?

I need the Genasun SCC because of FCC/RF radio noise requirements.

I don't think this is going to work, if a 100Ah battery can't achieve the peak voltages standard SCC's use . cheap 16Ah lifepos seem to work just fine in this regard, at least in my experience.

All SCC's slow-charge things at dusk and dawn, and mine peaks at 6amps at noon.

so.. try another $400-range 100Ah lifepo and hope it works with my charger and my loads aren't destroyed by the 19V every 8 seconds? I'm trying to figure out a next step here.

thanks!
-edfardos

 

[mikefitz]

The BMS is switching off the charge path fets, the discharge path is still operational and the battery will deliver power to load.
It seems the trip was at 13.9x, charge at 13.8 volts would be OK.

Could you use a power supply set to 13.8 volts for the battery and give it time to balance?
Mike

 

[edfardos]

Okay, cool, so I can still put a load on the battery, i guess the fets have diodes depending on the direction with a problem?

Let me find a supply. I have a couple 30amp supplies at 13.8V. Just hook them up, since the battery is already there?

I'm currently loading it down as far as i can (using a 10amp ham radio).

 

[edfardos]

Ran box fan for 13 hours to depletion (estimated 75Watts)

BMS low-voltage-cutoff, woke up bms with jump start, 11.61V. Charging at 5A.

I expect the BMS to readily reach 14.4V (charge controller's absorbtion voltage) on the first complete charge.

If batteries rebalance, I should be able to keep it at 14.4V? even after running it down a few percent?

If batteries don't rebalance, I can expect the system to flip between 13.8V and 19V every 8 seconds per the video?

I've used little lifepos for about a year with solar chargers, but have no experience with full size 100Ah lifepos.


Please let me know if I'm making bad assumptions here - thanks!

 

[mikefitz]

If the cells get more in balance you may be able to use a higher charge voltage. However provided the charge voltage is over 13.6 ( the usual voltage where cell balancing becomes active) there is no need to go much higher than 14.0 volts, where thee charge currect is low.

When you say 'estimate 110 watts ' do you mean 110 Ah' ? ( you made an edit to 75 watts)

It will take some time with the voltage at just below trip level for the cell balance to improve.

The battery under charge will have a voltage of around 13.5 volts over the majority of the bulk charge duration. As it reaches near full charge the voltage will rise very quickly. The lower the charge current compared to battery capacity, the more pronounced the voltage rise at high SOC. Thus at the point where the voltage for your battery and charge conditions rises through the 13.8 region the battery is a very high state of charge.

As discussed earlier the voltage surge is stored energy in the controller having nowhere to go, my guess is a small load on the battery would disipate this energy with minimal rise in volts.

As Implied earlier, most lithium battery users of 'drop in' batteries don't identify BMS cutoff as an issue, the battery charges and powers loads, so no problem is deemed to exist. OK, it's not ideal from a 'nerd' viewpoint, but if folk want low cost batteries, so the cells are not well balanced as delivered.

What is so special about the Genasun controller?
What are these 'little lifepos'?

Mike

 

[edfardos]

Yah, that all makes good sense. I'll put a load on it when hvco triggers, and see if that keeps the voltage spike down when the BMS trips.

AFAIK, Genasun has capacitor/inductor pi circuit to inhibit RF noise. All the radio nerds use them. The cheap mppt SCC's are a radio wipeout from 1 to 144Mhz, by nerd standards.

"little lifepo" is the cheap Maidy 16Ah found on amazon. Evidently I received a balanced one.

So the battery can/will/should balance itself to the point it'll hold 14.2 across the posts and make the SCC happy? Just need patience? a few partial cycles? hold at 13.8V with my big power-supply until there is no current?

Would a 13.8V voltage regulator work in my situation? I only need ~15A of DC current. I'm sure it'd be a radio noise festival too.

thanks again,
-craig

 

[740GLE]

Cycling doesn’t help the battery bank balance, if there is an active/passive balancer in the BMS, holding at 13.6v 13.8v for a long time will.

People only use higher voltage to charge quicker knowing the hours of sun is limited (that’s assuming they have a nice balanced system and can run their system up to 14.4v)

If you’re a radio guy, you should have a stand alone adjustable power supply, let the battery bake a a nice low current at 13.6-13.8v for a day or so.

 

[edfardos]

Confirmed, and thanks for the info, a deep cycle did nothing. BMS kicked in again during recharge at 13.8V. I returned the battery.

Could you guys be brutally honest with me and share a convenient way to get a working 100Ah lifepo? I had no idea these were inherently flawed with balance sensitivity. Try another lifepo from amazon, or get a pallet of Pb batteries?

thanks again for all the help, I know I learned a lot

-edfardos

 

[mikefitz]

As suggested the cycle would no nothing to help.
Having the battery on charge for many hours, perhaps days, at a voltage just lower than the BMS cutoff , say 13.75, would/may have produced a better balance.

Mike