Poey50
Well-known member
At least you are doing no harm now. But why it has risen in current is odd. Do keep a close eye on things.
270ah DIY LiFePO4 build
- Thread starter Poey50
- Start date
At least you are doing no harm now. But why it has risen in current is odd. Do keep a close eye on things.
Alan S
Well-known member
Don't do what Wiil Prowse does in the title screen of that video. He is using long thin leads with crocodile clips with neg and pos on same end of the bank. There's going to be excess voltage drop (possibly intermittent) between power supply and last cell.
GHA
Well-known member
How much current will there be going into a cell to keep it at 3.6V? Enough mA to result in measurable voltage drop with connecting bars that size?
Poey50
Well-known member
If the voltage output for the PSU is measured at the ends of the leads with an accurate meter (rather than rely on the PSU meter) there isn't a problem. He deals with the issue of possible imbalance (through charging at one end of the bank) in the comments as many people make the same point. With such slow charging he doesn't believe it matters. But it was the downloadable document I was recommending.
Kelpie
Well-known member
So by way of update, I've rearranged the cells in a 4S configuration. PSU set to 14v (measured, before being attracted to cells).
When I first tried this, after maybe ten minutes the cell at the negative end of the pack was rising much faster than the rest- and when it hit 3.6v whilst the rest were reading 3.4v, I turned everything off. I was worried I had a bad cell.
I marked the offending cell, then rebuilt the pack placing it in the middle. This time I'm getting identical voltages on each cell whilst charging, and the pack is taking about 7.5A. So maybe it was just a bad connection in my temporary setup?
When I first tried this, after maybe ten minutes the cell at the negative end of the pack was rising much faster than the rest- and when it hit 3.6v whilst the rest were reading 3.4v, I turned everything off. I was worried I had a bad cell.
I marked the offending cell, then rebuilt the pack placing it in the middle. This time I'm getting identical voltages on each cell whilst charging, and the pack is taking about 7.5A. So maybe it was just a bad connection in my temporary setup?
vas
Well-known member
Kelpie, some of these PSUs have a Voltage or Amp priority so to speak.
If you try to dial some amps, it will try to get you there no matter what the V will be (useful for testing LED lights)
so check the manual and that you're operating it correctly!
If you try to dial some amps, it will try to get you there no matter what the V will be (useful for testing LED lights)
so check the manual and that you're operating it correctly!
Alan S
Well-known member
You rebuilt the pack - in series or parallel? If one cell was 3.6 and the others 3.4 it most likely means they are unnalanced. That's why you connect them in parallel to baance them. By the way makes no difference if a certain cell is at one end or the middle, series or parralel. I'm sure you knew that ☺
Poey50
Well-known member
A pre-charge in 4S configuration is a great idea for speeding things up before top-balancing in parallel, but if you don't have a BMS to disconnect when the first cell reaches 3.65 volts then I assume you are watching like a hawk as it moves from a glacial pace to an avalanche. I had exactly the same problem of a poor connection making me assume that one cell was dud. This happened twice but the second time I was ready. It's a good reminder how carefully the final connections should be made. I burnished all contacting surfaces, cleaned any dust throughly and smeared with Ox-gard which itself is a conductor as well as keeping out damp. Sounds like you may be on track. Good luck!
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Poey50
Well-known member
As said above, that degree of imbalance is very unlikely. Poor connection is almost certainly the cause.
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Kelpie
Well-known member
Yes I think it was a bad connection. When making a parallel bank, there is an argument that the position of the cell might matter, although charging 'diagonally' should counter that.
Glacial is certainly the word! I'm only charging at 14v just now, which is pulling around 7.5A from my 10A PSU. It's a few hours now and the cells have risen from 3.31 to 3.35... but until my BMS turns up this will have to do... and I won't be leaving it unattended until then either.
Glacial is certainly the word! I'm only charging at 14v just now, which is pulling around 7.5A from my 10A PSU. It's a few hours now and the cells have risen from 3.31 to 3.35... but until my BMS turns up this will have to do... and I won't be leaving it unattended until then either.
sailaboutvic
Well-known member
Kelpie please don't charge them any more then you have (14v) any more and you could easily top a cell out without a bms .
Although mine where all balance to 3.65v , I still fine if I tried to charge over 14.2V one cell will start to take off above the others.
Upto 14.2v every cell is within 0.01.
after using mind for some months and now we have longer days charging to 13.8v then float at 13.5v , they working very well.
Before anyone tells me you should float lithium , mppt as to be set at something .
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Kelpie
Well-known member
Don't worry Vic I won't go above 14v... it's going to take a while even to get that high at this rate! But I appreciate the comment.
I'm checking each cell individually every ten minutes or so, so far all staying identical...
I'm checking each cell individually every ten minutes or so, so far all staying identical...
sailaboutvic
Well-known member
Sorry don't mean to tell you how to charge i sure your very capable, but so many post about charging to 14.4v , and it just be ashame to top a cell .
Good luck with them , we very happy with ours so far.
Dukester52
Active member
Great thread and very informative! It hadn't occurred to me that, in certain situations, the batteries could cut out, leaving you without instruments and lights... and also the problem with alternators. Thanks so much for pointing that out.
I don't have the skills to build my own bank , so I'd be looking for a prebuilt pack... and I also wouldn't want to rewire the boat. So it would have to be a hybrid system.
Does something like this look worthy (at least hypothetically)? Specifically It has a built-in BMS and separate connections for charging and load.
OANCO 12V 100Ah Deep Cycle Lifepo4 Lithium Iron Phosphate Battery,bms Built-in,for Golf Cart Ev Rv Solar Energy Storage Battery (Color : 12V 100Ah): Amazon.co.uk: Kitchen & Home
So I'd plan to keep a 12v lead-acid connected to the alternator, with all of the critical systems running from that, and then use something like a victron b2b to the LifePO4 pack to charge it, and then have the non-critical systems and luxuries running from that. Does that sound like it might work, or have I misunderstood?
I don't have the skills to build my own bank , so I'd be looking for a prebuilt pack... and I also wouldn't want to rewire the boat. So it would have to be a hybrid system.
Does something like this look worthy (at least hypothetically)? Specifically It has a built-in BMS and separate connections for charging and load.
OANCO 12V 100Ah Deep Cycle Lifepo4 Lithium Iron Phosphate Battery,bms Built-in,for Golf Cart Ev Rv Solar Energy Storage Battery (Color : 12V 100Ah): Amazon.co.uk: Kitchen & Home
So I'd plan to keep a 12v lead-acid connected to the alternator, with all of the critical systems running from that, and then use something like a victron b2b to the LifePO4 pack to charge it, and then have the non-critical systems and luxuries running from that. Does that sound like it might work, or have I misunderstood?
sailaboutvic
Well-known member
I start off by say , although I build my own no expert .
My view is the problem with drop in is you don't know what cell service are being use or the BMS used , coinciding my BMS was a third of the battery you posted , just wonder what's in side .
Although there a couple of misleading wording as in deep cycle and store 90% But that can just be selling talk .
Regarding batteries disconnecting that depend of the BMS and power used ,
I dayly use 180to 220A at any one time and so far never had a problem ,
After saying all that if your a weekend boater and only using the battery to power normal equipment a disconnection should happen as long as the use of a windlass is kepted on the starter battery .
On normally use I would connect every thing on to the lithium and windlass to the LA starter battery if you also got a BT then connect that too the LA ,
Charge the LA as you said through the alternator and the lithium from the starter LA through the B2B .
Dukester52
Active member
thanks vic, that's very helpful - and affirming I haven't completely misunderstood - and more food for thought!
sailaboutvic
Well-known member
I would imagine the most crap BMS would allow 50A so using would I would call normal boat equipment you not going to be drawing 50A .
We had the micro way , electric Hob , hot water boiler on at the same time as all the boat stuff and not had a disconnection.
We had the micro way , electric Hob , hot water boiler on at the same time as all the boat stuff and not had a disconnection.
Poey50
Well-known member
The question always to ask with any LFP system is "what will be the outcome of a sudden BMS disconnect?" Your lead acid should absorb the voltage spike and your essential systems run from the lead acid are maintained. However you won't know when your LFP will reconnect nor will you always know why it disconnected since there is no means of communication. Anyone who has lived with a sulking non-communicative teenager will know the problem. The pack is a set of inexpensive prismatic cells, as shown, put in a box with an inexpensive BMS .. probably a Daly. How well that has been done is impossible to tell. What is clear is that you could do the same for about a third of the cost. I'm not saying you should but if you check the Will Prowse videos you can see how little has been done to charge that much. You will also need to consider how to manage solar and shore charging.
Dukester52
Active member
Thanks Poey, my thinking was to charge the LA with the solar and mains battery charger in the usual way, and let the B2B charge the LFP? I'll check out those videos...
Poey50
Well-known member
You would lose charging efficency but it would be perfectly safe.
