LiFe batteries (again...)

If charging from alternator you'll need a dc to dc charger suitable for lifepo4, I have one from Renogy which is working fine so far.
The discharge limit of the BMS is pretty low, mine is 100a (1C)
 
andyj301 said:
If charging from alternator you'll need a dc to dc charger suitable for lifepo4, I have one from Renogy which is working fine so far.
The discharge limit of the BMS is pretty low, mine is 100a (1C)
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Thanks, that's useful to know. Am I reading things correctly that the BMS limited to 40A?
 
Yes, it's an cheap Daly BMS rated at 40 amps. That's pretty low especially as the cells are capable of higher charge and discharge rates (according to the blurb in any event). The BMS has a common port - that means that you cannot separate the charging and load circuits. So a BMS that shuts the battery down because of high voltage does not allow discharge and conversely if the battery is closed down because it is dangerously close to empty it cannot immediately be recharged. It's exactly the same problem as with drop-in LFP batteries. The other problem with these cells is that they use only M4 machine screws. Given that the terminals are aluminium and easily stripped then I think there could be serious problems in a mobile application such as a boat. M6 is really a minimum in my view.

Better deals are available by direct import (which I think the seller is probably doing despite his "oops I over-ordered" schtick). As I've said repeatedly there is as yet no straightforward method with LFP on boats. Reading this thoroughly and repeatedly is a good start.

LiFePO4 Batteries On Boats - Marine How To
 
andyj301 said:
You'd also need a waterproof container for the cells. I've read somwhere that the aluminium cell cases have been known to rupture due to corrosion. So decided to go for drop in rather than diy build.

Also I got a Tracer waterproof solar controller 30A Waterproof 12v--24v MPPT charge Controller - Tracer 7810BP - works with Lithium LiFePO4 Batteries - 100VOC PV
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Be careful with that solar controller. The LFP setting for float is stated to be 14.4 volts. LFP doesn't like to be floated (it shortens the life of the battery). You can get away with floating up to 13.6 volts (even then I wouldn't do it) but anything above that will overcharge. Some of these older controllers had inappropriately high settings for LFP. You'd be better off with a Victron.
 
Thanks, I dialled down the settings having seen about trying to extend the life of the battery by not fully charging. The display (MT50) reads 13.2 - 13.4v whenever i get onboard. I'll be reading through your article as I need to improve my understanding of lifepo4
 
Just for interest, lunaa lina and andyj301, how do you manage the potential problem of sudden disconnect and non-communication of your LFP battery.
 
Poey50 said:
Yes, it's an cheap Daly BMS rated at 40 amps. That's pretty low especially as the cells are capable of higher charge and discharge rates (according to the blurb in any event). The BMS has a common port - that means that you cannot separate the charging and load circuits. So a BMS that shuts the battery down because of high voltage does not allow discharge and conversely if the battery is closed down because it is dangerously close to empty it cannot immediately be recharged. It's exactly the same problem as with drop-in LFP batteries. The other problem with these cells is that they use only M4 machine screws. Given that the terminals are aluminium and easily stripped then I think there could be serious problems in a mobile application such as a boat. M6 is really a minimum in my view.

Better deals are available by direct import (which I think the seller is probably doing despite his "oops I over-ordered" schtick). As I've said repeatedly there is as yet no straightforward method with LFP on boats. Reading this thoroughly and repeatedly is a good start.

LiFePO4 Batteries On Boats - Marine How To
Click to expand...

Thanks for that link, I've been reading and digesting that. I hadn't realised just how important the BMS was, and that they are very much not created equal.

Browsing for cheap LiFe packs makes it seem as though for only a little more money than good lead-acids, you can make the switch. But you'll end up with very low rate BMSs and be stuck with paltry discharge currents, charging currents, and potential risk of damage to any connected equipment if and when that BMS does kick in.

I'm still hopeful that a system can be put together that leverages some of the advantages of LiFe, without the full price tag. What I'm considering is a hybrid system where solar charges both banks, with the LiFe reaching 100% first, and then the LiFe is used to slowly charge the lead-acids via a B2B charger. I'm hoping to use a fairly small LiFe pack to extend the lifespan of the lead-acids. The big current draws would still come from the lead-acids, which would represent the vast majority of the total system capacity.
 
Kelpie said:
I'm still hopeful that a system can be put together that leverages some of the advantages of LiFe, without the full price tag. What I'm considering is a hybrid system where solar charges both banks, with the LiFe reaching 100% first, and then the LiFe is used to slowly charge the lead-acids via a B2B charger. I'm hoping to use a fairly small LiFe pack to extend the lifespan of the lead-acids. The big current draws would still come from the lead-acids, which would represent the vast majority of the total system capacity.
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I mentioned this very simple sounding hybrid model on another thread. I'm not advocating it, as I haven't tried to explore it in any depth, but they sound like they know what they are talking about.

Lithium-Hybrid

The promise of the system is that you don't need to upgrade any chargers / alternators, the LFP does literally drop in to a lead acid system. Whereas with a dual bus system like mine the BMS is used only as a last resort to prevent catastrophic damage, in this set-up the low voltage and high voltage disconnect are a routine part of the day to day operation. It sounds too good to be true - but it very possibly isn't. You might need to take some care in choosing a suitable drop-in battery however as some have high voltage disconnect above 3.65 volts per cell which would shorten its life.
 
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Yes I read that and it's a different approach to what I was thinking of- quite elegant and simple, though.
As far as I know it's still just a theory, and has not been built and tested.

My concern with the simple hybrid approach is that the naturally higher voltage of the lithium pack would want to keep topping up the lead-acids continuously, which might be bad for both, and certainly not a good use of power. But perhaps something stops this happening, e.g. the lead acid charge acceptance slows right down.
 
Kelpie said:
Yes I read that and it's a different approach to what I was thinking of- quite elegant and simple, though.
As far as I know it's still just a theory, and has not been built and tested.

My concern with the simple hybrid approach is that the naturally higher voltage of the lithium pack would want to keep topping up the lead-acids continuously, which might be bad for both, and certainly not a good use of power. But perhaps something stops this happening, e.g. the lead acid charge acceptance slows right down.
Click to expand...

It's a cleverer system than that making use of the different charging profiles. The lead acid barely gets used and will stay mostly at float. I've asked the Lithium Batteries on a Boat Facebook Group to critique the system and will post anything relevant here. They are a pretty knowledgable bunch.
 
A good battery charger to balance them
Poey50 said:
It's a cleverer system than that making use of the different charging profiles. The lead acid barely gets used and will stay mostly at float. I've asked the Lithium Batteries on a Boat Facebook Group to critique the system and will post anything relevant here. They are a pretty knowledgable bunch.
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Certainly be interested in a second opinion.
 
Poey50 said:
Not according to the model. Standard lead acid charger.

See the section Charging
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Sorry, I was aiming that at Kelpie, to enable him to top balance the LifePO4 cells when they first arrive, wiring them in parallel with a charge of 3.2v (or something) so all cells are all at the same capacity before dismantling and building them in series.

Pete
 
Here's the first reply from someone on the Lithium Batteries on a Boat Facebook Group (henceforth LBBFG} who is using this method ...

Björn Johansson

Yes, there will be a small charge current to the lead batteries (which is good). I am running like this with a lead battery close to the bow thruster, another in the stern for starting the heater and for stern windlass + one main. LifePO4 400 Ah main controlled with 123BMS. Works just like the article.
 
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Poey50 said:
Just for interest, lunaa lina and andyj301, how do you manage the potential problem of sudden disconnect and non-communication of your LFP battery.
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So far, short answer is I don't. I'm not travelling any distance or spending nights on the boat, the navigation is opencpn on laptop which would continue running for an hour or so, but is really not needed for my current range. No electric winch, bow thruster runs from lead acid engine battery.

As stated, I need to learn more. The article you link talks about using the right BMS, though I've not yet summoned the courage to tear open the case. So far I've tested the battery with trolling motor and electric bike (through boost converter) drawing up to 53amps, and have run the battery down to 12volts, no problems. The dc to dc charger has delivered up to 42.5amps.

My current strategy would be monitoring voltage and charging with engine if necessary. The solar controller is set low and so far all good. Perhaps the lifepo4 could be bypassed and nav lights etc connected to starter battery as a get you home measure.
 
andyj301 said:
So far, short answer is I don't. I'm not travelling any distance or spending nights on the boat, the navigation is opencpn on laptop which would continue running for an hour or so, but is really not needed for my current range. No electric winch, bow thruster runs from lead acid engine battery.

As stated, I need to learn more. The article you link talks about using the right BMS, though I've not yet summoned the courage to tear open the case. So far I've tested the battery with trolling motor and electric bike (through boost converter) drawing up to 53amps, and have run the battery down to 12volts, no problems. The dc to dc charger has delivered up to 42.5amps.

My current strategy would be monitoring voltage and charging with engine if necessary. The solar controller is set low and so far all good. Perhaps the lifepo4 could be bypassed and nav lights etc connected to starter battery as a get you home measure.
Click to expand...

Thanks. It sounds like you are well aware of the limitations and not pushing beyond.
 
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