LiFePO4 woes in Caribbean

[Gary H]

Hi all,

I've been using a DIY setup of 4 x 700AmpHr Balqon LiFePO4 cells for about two years and am sailing my way south. Right now I'm anchored in St. Martin and was awakened to the sound of the BMS under voltage alarm. It looks like one of my four prismatic cells is bad. It was showing 2.77V when the other three cells were at a normal 3.33V. The battery monitor indicated less than 60 amp hours from full.

By way of history, I have always been suspect of this cell. It has often been out of step in terms of voltage with the other closely matched cells. I got a "deal" on some slightly used cells from the manufacturer two years ago and three were sequentially numbered and this one was not. Yeah, false economy.

My plan is to head to a marina *shudder* for some shore power and attempt to rebalance the cells. I have a 30 Amp Mastech power supply on board but no other AC battery charger. Other than the LiFePO4 bank, I have no 12 volt capacity on board and cannot operate. I am hopeful but not optimistic.

Does anyone have any advice for procuring a replacement cell in or near St. Martin? I was not planning on returning to the USA until summer.

Thanks much,
Gary

[offpist]

I would try to put all 4 cells in paralell and then charge until 3,6V. (Or even 3,8v if it is within the specs, it is for Winston cells).

Most 12V chargers will not work on 3V but some do.. make sure you watch the voltmeeter all the time so you dont overcharge.

[donradcliffe]

I would never put all 4 cells in parallel at this point. You would have some very serious current going from the good cells into the bad cell, and no control over it. Think flames.

[Gary H]

Hopefully will get to a marina today for some shore power. Plan is to charge the low cell individually to 3.5v using the bench power supply and hope for the best.

[Camp Director G]

What are you using to charge? The RC (remote control planes drones etc.) world had many AC/DC smart balancing chargers.

[MarkJ]

Does anyone have any advice for procuring a replacement cell in or near St. Martin?

Ship it in with Tropical Shipping.

[masonc]

Four star cargo , then you can dingy over to pink iguana and get it

[Maine Sail]

Gary,

Balqon is gone and Winston cells are now distributed in the US under the Voltronix brand. Last time I spoke with Brennan he had some 700Ah stock, otherwise it is about a 6-8+ week lead time..

That said the 700Ah cells have been the least reliable I know of in the marine environment. Also mixing and matching cells is likely to put you right back where you are.

Tip: A lead acid reserve battery is always a good idea and a Firefly or GEL works very, very well for an LPF back up...

[barnakiel]

I think that if the cell was out of synch for any longer period, it may as well be dead (bad). When you build a 12 kit out of 3.3 cells they should all be in nearly identical condition. Otherwise you kill the weaker one and pull down the good ones.

Unless lifepo has some magic technology (in the controller) that prevents this.

b.

[Gary H]

Thanks for the info and advice. I have arranged for a marina slip starting tomorrow morning. I will put the low cell on the bench power supply to charge to 3.5v (full) and see if I can make it play nice with the other three cells. This will take over 24 hours.

I understand that using this "bad" cell or any other unmatched cell in the bank is not ideal, but the truth is that I have been actually using probably less than 100 amp hours of this capacity. If I can make this cell work enough to get by for a while that's what I will do. If I have to replace them all, I will probably go with much smaller cells.

Thanks again. I will let you all know what happens when I fianlly get plugged in.

[Gary H]

Update:

After 27 hours of charging using the bench power supply, the low cell reached 3.5v. Based on my estimate of its state of charge prior to this, it looks like it accepted just under 600 amp/hours.

I have opted not to parallel the cells at this time or try and balance them further. They are within .01 volt of each other at a full state of charge. I will make every effort to stay away from the "knees" on the charging curve and get back to sailing! (although the feee use of the marina pool could become addictive...)

Based on the advice here, I would no longer consider replacing just one cell. If it becomes ncessary to replace the cells, I am going to downsize to 400 amp/hours and probably go with CALBs. Live and learn.

When I embarked upon he LiFePO4 project, I understood that they are not a drop in replacement for lead acid and I have learned quite a bit along the way. Even given this setback, I do not regret my decision to go lithium.

Many thanks to this forum and the members who give so freely of their time and expertise.

Gary

[donradcliffe]

I use the LiFe cells in my models. In most cases I do a balancing charge each time, but sometimes its not practical. In the models I don't balance each time, I have checked the individual cells and rarely see voltage differences more than 0.05 volts, even after months of use/recharge/storage cycles.

I am very curious why your one cell got so far from the others to start with. It sounds like it took a reasonable charge. I'm sure you will be monitoring things more closely, and it would be great if you could let us know what happens with time.

[poiu]

Originally Posted by Gary H

Update:

After 27 hours of charging using the bench power supply, the low cell reached 3.5v. Based on my estimate of its state of charge prior to this, it looks like it accepted just under 600 amp/hours.

I have opted not to parallel the cells at this time or try and balance them further. They are within .01 volt of each other at a full state of charge. I will make every effort to stay away from the "knees" on the charging curve and get back to sailing! (although the feee use of the marina pool could become addictive...)

Based on the advice here, I would no longer consider replacing just one cell. If it becomes ncessary to replace the cells, I am going to downsize to 400 amp/hours and probably go with CALBs. Live and learn.

When I embarked upon he LiFePO4 project, I understood that they are not a drop in replacement for lead acid and I have learned quite a bit along the way. Even given this setback, I do not regret my decision to go lithium.

Many thanks to this forum and the members who give so freely of their time and expertise.

Gary

I have 8 ex Balqon 700Ah cells, bought 3 years ago. I have had similar problems on 3 occasions, with 3 different cells, all happening after long idle periods. At first I thought it was a total failure, like you, but I charged up the bad cells to balance the voltage with the good ones at a near discharged state and they seem to stay in balance again. What I do is to run down the good cells, whilst charging the bad one with a bench charger off an inverter. The bad one eventually comes into line. Then I charge the pack. I only do this when the good ones are nearly discharged because I find that when the bad cells are part charged, their voltage is the same as the good cells and it is impossibly hard and long to balance, it is only at the bottom of the discharge curve that cell voltage changes quickly and in large magnitude.

I think a top balance might not work at all because I have lost a bit of capacity because of the bad cells and starting with a bottom balance and measuring capacity up from there does give me an accurate capacity count.

Fickle sods aren't they

[Gary H]

Another update:

After the top-up of the weak cell, I discharged the bank at relatively normal rates (40 Amps or less) until the bank was negative 400 Ah. The cells stayed reasonably balanced (usually about 25mV between the highest and lowest cells). I then charged to 90% SOC and the cells stayed in balance. 90% is my new "full" going forward. I have programmed the battery monitor to cut off charging at this point. When the bank drops to 80% SOC the monitor is programmed to resume charging. Since I only charge using solar and the occasional bit of alternator, it is not really practical for me to deeply discharge the bank before recharging - I have to take advantage of energy when its available.

Given my modest power draw, I will seldom need to discharge more than 100Ah from "full."

My best guess is that I have been keeping the bank at too high a state of charge and being at the top of the charge curve every day was the root of my problems. Another possibilty is that I did a half-assed job with the initial balancing when I installed them, not fully apprciating the importance of balanced cells.

I will leave the cell logger plugged in and keep a closer eye on the voltages of the individual cells than I had been doing. This way, if a cell starts to get out of balance, I can address it before it becomes critical.

One thing is for certain - I will never go back to lead.

[Typhoon]

I hope it works out.

Yes these cells like to be on the low side , people ruin them by thinking they have to keep them topped up. Still thinking the lead way .

"I will never put on a life jacket again."

Regards John