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Big Battery 24V inconsistencies

rvsolarconnections

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Joined
Jul 22, 2021
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Hey all,

I've read some critical things about BigBattery here, and know there are mixed reviews all over the web. That said, we decided to give them a try.

In their literature, for the 24v Husky Elite battery, they claim that fully charged is 29.4V. I spoke with someone on the phone who recommended I set the charged voltage to 29.2V. I set float and absorption on my inverter/charger and MPPTs to 29.2V, but the battery will not go above 29v.

I then spoke to a representative who said that there is a bit of variation from battery to battery, and it was nothing to worry about.

What are your thoughts here? Is it concerning that the battery won't reach the voltage that is recommended on the spec sheet? Has anyone else experienced this with BigBattery or batteries from other manufacturers.

I appreciate your time and input. Thanks!
-Caza
 
I have bought the Hawk model from them and the info I read shows 29.2v for the settings. However I was unfortunate to receive a brand new defective battery from them so I have never gotten to cycle it even once yet. After charging it for the first time, it never made it to 29.2v and the display showed 28.2v was the highest it would get. At the same time I noticed the power button no longer would function and the battery and display stays on all the time.

I also noticed once the charger was turned off, the battery voltage would drop to 27.5 right away and then it seems to be losing approx 1 volt per day without any load on the battery. They confirmed with me the new battery is defective and they would replace it but it is extremely difficult to get them to send me the rma info they promised over a week ago and I am now reaching out to the dealer I bought it from to see if they can get BB to get my rma completed.

I'm not sure what the issue is and why after ordering this on 7-3-21, receiving the battery finally in September and it being defective, that is now taking weeks to receive my rma info to complete a return process for this battery. It is getting ridiculous now and I am hoping the dealer can either get my rma finished or return my money.

This battery has been the hardest piece of my system to obtain and when I finally got it, its defective.
 
I believe Big Battery uses used cells. They likely do some tests to batch them for a given battery array. A different battery of same model can be made of cells with different age and slightly different performance. Aging makes the cell terminal voltage slump more under load.

I assume from the voltages you listed they are LiFePO4 battery packs with eight series cells., You should follow LFP cell charging profiles.,

You did not state the AH capacity so cannot recommend max bulk current for charging. 3.65v per cell is max absorb voltage you should use so with 8 cells that would be 29.2v. 29.0 v would be 3.625v per cell if fully balanced and it is fine. There should be no reason for it to not go above 29.0v unless your charger is limiting you. Unless you are saying BMS shuts system down at 29v.

Balancers typically do not engage cell balancing until a cell gets above 3.4v so to accomplish some balancing time you have to be above about 28.0 v to ensure some balancing time. Should at least do this level of charging periodically to stay in balance. Once a week should be okay but may depend on how much leakage the cells have, how much current you typically draw, or how much AH range you run the battery pack over.

Most common problem when cells get out of balance is the BMS will have a cell overvoltage shutdown when trying to get near full charge voltage. You will also get less net capacity out of battery bank as weakest state of charge cell will trip cell undervoltage shutdown of BMS.
 
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I believe Big Battery uses used cells. They likely do some tests to batch them for a given battery array. A different battery of same model can be made of cells with different age and slightly different performance. Aging makes the cell terminal voltage slump more under load.

I assume from the voltages you listed they are LiFePO4 battery packs with eight series cells., You should follow LFP cell charging profiles.,

You did not state the AH capacity so cannot recommend max bulk current for charging. 3.65v per cell is max absorb voltage you should use so with 8 cells that would be 29.2v. 29.0 v would be 3.625v per cell if fully balanced and it is fine. There should be no reason for it to not go above 29.0v unless your charger is limiting you. Unless you are saying BMS shuts system down at 29v.

Balancers typically do not engage cell balancing until a cell gets above 3.4v so to accomplish some balancing time you have to be above about 28.0 v to ensure some balancing time. Should at least do this level of charging periodically to stay in balance. Once a week should be okay but may depend on how much leakage the cells have, how much current you typically draw, or how much AH range you run the battery pack over.

Most common problem when cells get out of balance is the BMS will have a cell overvoltage shutdown when trying to get near full charge voltage. You will also get less net capacity out of battery bank as weakest state of charge cell will trip cell undervoltage shutdown of BMS.
It is my understanding the are supposed to be using brand new cells. At least that is what they were claiming. If this is true and they are using used cells then that is unacceptable and a false claim. I truly hope this is not the case. Can anyone confirm they are really using used cells?
 
From the marketing I read on the Hawk it was supposed to be all new quality cells. I would never buy a battery purposely with used cells. I'm hoping it has new cells in the new replacement if I ever get them to complete the rma on this one
 
“New quality cells” doesn’t mean brand new, never used cells ?
 
Looks like some models claim 'brand new', some say 'new quality', some does not mention anything on new or used. Some say say 'new LiFePO4 chemistry' whatever that means.
 
“New quality cells” doesn’t mean brand new, never used cells ?
This is right from thier website

``Utilizing brand new cells paired with our advanced BMS, you can rest easy knowing that 24V HAWK will provide you with safe, energy efficient power that can be used safely within a wide temperature range``

I interpret that as brand new cells
 
This is right from thier website

``Utilizing brand new cells paired with our advanced BMS, you can rest easy knowing that 24V HAWK will provide you with safe, energy efficient power that can be used safely within a wide temperature range``

I interpret that as brand new cells
I would interpret the statement the same way.

It does make me a little uncomfortable buying batteries from a vendor that also puts together battery packs with used cells. If push comes to shove to get an order out there is temptation to use what you have in stock.
 
This is right from thier website

``Utilizing brand new cells paired with our advanced BMS, you can rest easy knowing that 24V HAWK will provide you with safe, energy efficient power that can be used safely within a wide temperature range``

I interpret that as brand new cells
Seeing as how the reputation is not the best. They probably use bulk commodity cells. Many of us use bulk cells building our own packs. Bulk cells are perfectly fine for most. The problem with buying a finished battery is let's say one of the cells is bad. There's a post on here a guy bought six or seven batteries from them and they were put together pretty shoddy. After him taking them apart fixing them up they were working but he had one bad cell. Big battery apparently refuses to send him a new cell. With how they treated Will I would personally never do business with them.
 
This is right from thier website

``Utilizing brand new cells paired with our advanced BMS, you can rest easy knowing that 24V HAWK will provide you with safe, energy efficient power that can be used safely within a wide temperature range``

I interpret that as brand new cells

I was just going off your original comment, thanks for the clarification.

Maybe the cells were never properly top balanced or one is slightly weaker?
 
I was just going off your original comment, thanks for the clarification.

Maybe the cells were never properly top balanced or one is slightly weaker?
No problem. This whole battery industry seems to me to be a confusing one to say the least. I have been as careful as I could in selecting a finished pack for my needs.

However, despite my research I did give them the benefit of the doubt even though there were some complaints being raised on them. I learned along time ago that there is always good and bad experiences with any company. I even once bought a brand new Toyota corolla that turned out to be the biggest lemon. I suppose I could have made a mistake in trusting them but until its over I won't know for sure. I'm hoping they are legit, take care of replacing my defective unit and the replacement is not only functional but new cells.

I will post back on the outcome once this is over. Its a shame what I went through so far but I'm hoping for a happy outcome in the end.
 
I believe Big Battery uses used cells. They likely do some tests to batch them for a given battery array. A different battery of same model can be made of cells with different age and slightly different performance. Aging makes the cell terminal voltage slump more under load.

I assume from the voltages you listed they are LiFePO4 battery packs with eight series cells., You should follow LFP cell charging profiles.,

You did not state the AH capacity so cannot recommend max bulk current for charging. 3.65v per cell is max absorb voltage you should use so with 8 cells that would be 29.2v. 29.0 v would be 3.625v per cell if fully balanced and it is fine. There should be no reason for it to not go above 29.0v unless your charger is limiting you. Unless you are saying BMS shuts system down at 29v.

Balancers typically do not engage cell balancing until a cell gets above 3.4v so to accomplish some balancing time you have to be above about 28.0 v to ensure some balancing time. Should at least do this level of charging periodically to stay in balance. Once a week should be okay but may depend on how much leakage the cells have, how much current you typically draw, or how much AH range you run the battery pack over.

Most common problem when cells get out of balance is the BMS will have a cell overvoltage shutdown when trying to get near full charge voltage. You will also get less net capacity out of battery bank as weakest state of charge cell will trip cell undervoltage shutdown of BMS.

These are 228 ah batteries, 2 in parallel. You're saying I should go above 28v once per week, put their recommended charged voltage (and float and absorption voltage) is 29.2v, so I'll be going over 28v every day.

All three of my chargers (MultiPlus and two MPPTs) are programmed to 29.2v, but the battery doesn't go above 29v. The BMS doesn't shut off, and everything works as it should, I'm just missing that last .2v.

Sounds like this isn't something to be too concerned over though?
 
I have 8 of the 24 volt hawks and I had to balance the cells and do other repairs before I could get the correct voltage from them.
I still have one with what looks like to have bad cell that I am currently repairing.
They refuse to send out or sell replacement parts so the only way to get them repaired under warranty is to ship them at your expense.
 
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