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ivan&alice

Cheap LiFePO4 BMS?

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My system is probably more complicated than it needs to be as I use a external alternator controller to control charging. The problem with using relays, is the continuous current draw - particularly high power relays as would be needed for main boat services. 

 

As to useable capacity, we generally use between 30-90%, but that's just convenience. They're so reliable that we got caught out the other day.  We've got used to solar keeping up with our needs, together with an hours charge or so when filling with water. Couple nights ago we had an alarm going off during the evening as batteries had dropped to 20%! No worries though, silence alarm, and charge back up next morning when they'd dropped to 10%. We also occasionally charge to 100% which resets BMV, often when cruising or going for pumpout. Charging to 100% doesn't necessarily cause damage, provided cells are well balanced and voltages are kept within limits, it's storing them at 100% that they don't like. 

 

See comments above re cheap bms you mentioned. Most similar types have totally inappropriate voltage limits, which is the main problem using them. 

 

If I was to install another system, I'd probably use this together with a couple of bi-stable relays such as thiis (often available cheaper 2nd hand on Ebay - try searching for bds-a, Ford battery disconnect, v23130, or 6C1T10B728). For monitoring, I use Victron BMV to give SOC readings, and alarms. If paralleled with lead acid start battery during alternator charging, that would take care of alternator damage if disconnected, and other charge sources could then be set with appropriate voltages and you have a working system. Only extras you might want is balancing and cheap cell voltage monitor with alarms, but that's not strictly necessary. I did find cells tended to drift a bit (probably due to not being very conservative with using available capacity) so now have this installed which seems to keep cells very well balanced. 

 

I didn't bother with temperature protection - if batteries are less than 0c then I've other problems to worry about such as burst pipes, calorifier etc. Mine are installed just inside back doors in bedroom, opposite side to calorifier with central heating pipes running underneath, and skin tank at the back. I don't intend to let bedroom drop below freezing! If away for few days then they won't be charged anyway, but as above, bigger problems than batteries to think about if boat ever gets that cold!

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do we have an alternative Gibbo on this forum, who can design and assemble an appropriate BMS for all of us electrically-challenged muppets?

 

could be a nice moneyspinner.

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1 hour ago, Murflynn said:

do we have an alternative Gibbo on this forum, who can design and assemble an appropriate BMS for all of us electrically-challenged muppets?

 

could be a nice moneyspinner.

 

I've considered making my BMS into a product, but It's probably five times more work and ten times more money than I've put in so far, for very little guarantee of return.

 

If someone want to sponsor the program by providing me with three or four sets of different batteries and comprehensive test rig, please get in touch.

 

MP.

 

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1 hour ago, Murflynn said:

an appropriate BMS for all

 

 

 

23 minutes ago, MoominPapa said:

 

I've considered making my BMS into a product, but It's probably five times more work and ten times more money than I've put in so far, for very little guarantee of return.

 

If someone want to sponsor the program by providing me with three or four sets of different batteries and comprehensive test rig, please get in touch.

 

MP.

 

I think the problem is that it would be very difficult to get a universal BMS......every setup is different.

If I did mine again then it would be great to follow MP's system but no I deer how to link it in to my alternator or tune it to my system. The BMS would have to be bullet proof and that is a huge amount of work for MP.

Even if I got the Arduino board and programming from MP, it would be a lot of work for me to work out how to integrate.

It would be simpler to follow Tom's recommendations above and get an 'off the shelf' system which just abouts gets a system as good as MP's IF you are careful with your charging regimes.

1 minute ago, rusty69 said:

Maybe we could crowd fund it for MP.

Maybe we could make MP and MP?

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12 minutes ago, rusty69 said:

Maybe we could crowd fund it for MP.

Or maybe we could fit sealed lead acids. No rewiring, no alternator changes, no MBS, no safety cut outs, no temperature worries, have done and still do a stirling job on 99 percent of boats for hugely less money....................just sayin like 😎

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4 minutes ago, mrsmelly said:

Or maybe we could fit sealed lead acids. No rewiring, no alternator changes, no MBS, no safety cut outs, no temperature worries, have done and still do a stirling job on 99 percent of boats for hugely less money....................just sayin like 😎

 

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19 minutes ago, mrsmelly said:

Or maybe we could fit sealed lead acids. No rewiring, no alternator changes, no MBS, no safety cut outs, no temperature worries, have done and still do a stirling job on 99 percent of boats for hugely less money....................just sayin like 😎

 

The thing is, when you are running your engine 8 hours at the weekend and annoying the feck out of everyone witin 100 yards, us lithium users simply don't need to.

 

Our batts charge in less than half the time yours do, and never need fully charging anyway. Less noise, less annoying your neighbours, less fuel, less engine wear, less servicing.

 

That is the beginning and the end of why lithiums are good thing, really. 

 

:icecream:

 

 

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4 minutes ago, Mike the Boilerman said:

 

The thing is, when you are running your engine 8 hours at the weekend and annoying the feck out of everyone witin 100 yards, us lithium users simply don't need to.

 

Our batts charge in less than half the time yours do, and never need fully charging anyway. Less noise, less annoying your neighbours, less fuel, less engine wear, less servicing.

 

That is the beginning and the end of why lithiums are good thing, really. 

 

:icecream:

 

 

So you are only annoying the feck out of people for 4 hours at the weekend then!:giggles:

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7 minutes ago, rusty69 said:

So you are only annoying the feck out of people for 4 hours at the weekend then!:giggles:

 

No, because charging to 100% at the weekends is not necessary in the first place with lithiums! This is the bit that nice mrsmelly doesn't seem to get.

 

So I was just trying to keep it simple, and tripped you up.... :giggles:

 

 

 

Edited by Mike the Boilerman

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1 hour ago, Dr Bob said:

I think the problem is that it would be very difficult to get a universal BMS...

Not THAT difficult. Victron have done so. Not many boaters like the cost though. 

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Just now, WotEver said:

Not THAT difficult. Victron have done so. Not many boaters like the cost though. 

 

And from what I read, the Victron BMS still does not protect the alternator from high voltage cut-off. The chap at Springwood Haven sees a need to fit a LA batt in parallel for this.

 

I would imagine it would be technically possible to design a BMS to introduce a temporary load to the alternator at the instant of cell isolation, and progressively ramp down the alternator current to zero over say 30 seconds. Would this protect the alternator too? I've never seen this idea mentioned anywhere. 

 

 

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8 minutes ago, Mike the Boilerman said:

 

And from what I read, the Victron BMS still does not protect the alternator from high voltage cut-off. The chap at Springwood Haven sees a need to fit a LA batt in parallel for this.

 

I would imagine it would be technically possible to design a BMS to introduce a temporary load to the alternator at the instant of cell isolation, and progressively ramp down the alternator current to zero over say 30 seconds. Would this protect the alternator too? I've never seen this idea mentioned anywhere. 

 

 

Keep it simple Mike my mate still has the LA starter battery in place works for him

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13 minutes ago, peterboat said:

Keep it simple Mike my mate still has the LA starter battery in place works for him

It's Mike the Boilerman to you. Only I can call him simple Mike.

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13 minutes ago, rusty69 said:

It's Mike the Boilerman to you. Only I can call him simple Mike.

I didnt know Mike was simple!

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4 hours ago, Mike the Boilerman said:

I would imagine it would be technically possible to design a BMS to introduce a temporary load to the alternator at the instant of cell isolation, and progressively ramp down the alternator current to zero over say 30 seconds. Would this protect the alternator too? I've never seen this idea mentioned anywhere. 

You could ramp the load down over a second to achieve the same result, but as Peter says, why bother? A cheap LA makes a perfectly suitable dump load. 

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6 hours ago, WotEver said:

Not THAT difficult. Victron have done so. Not many boaters like the cost though. 

Victron's BMS only works with Victron's batteries.

 

MP.

 

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3 minutes ago, MoominPapa said:

Victron's BMS only works with Victron's batteries.

Yes indeed. But Bob was complaining that there wasn’t a simple ‘fit and forget’ system that would suit everyone. The Victron system does just that, but at extreme cost. 

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32 minutes ago, WotEver said:

Yes indeed. But Bob was complaining that there wasn’t a simple ‘fit and forget’ system that would suit everyone. The Victron system does just that, but at extreme cost. 


except for the need to add a LA batt, and do it right! 

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7 minutes ago, Mike the Boilerman said:

except for the need to add a LA batt

Presumably you’ll already have at least one of those, so you won’t even have to spend £50 on one. 

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30 minutes ago, WotEver said:

Presumably you’ll already have at least one of those, so you won’t even have to spend £50 on one. 

 

My point being if you have to add your own LA batt, it isn't a complete BMS.

 

 

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27 minutes ago, Mike the Boilerman said:

My point being if you have to add your own LA batt, it isn't a complete BMS.

Sure it is. It’ll protect and manage your LI-ions perfectly. 
 

How you wish you protect your charge source is your problem. 

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11 hours ago, Murflynn said:

do we have an alternative Gibbo on this forum, who can design and assemble an appropriate BMS for all of us electrically-challenged muppets?

 

could be a nice moneyspinner.

I di really like MP's setup. Bit too complicated for me to design and install myself though, although if my design and programming skills were better, it's certainly a system I'd seriously consider. 

 

One of the problems is that of liability. If the BMS you designed or spec'd was to wreck an alternator, or worse, a set of (new) lifepo4 batteries at a cost of several thousands who would bear the cost? And having seen the state of some boats electrics I wouldn't want any system I designed anywhere near them! Our boats electrics were bad enough, and that was an ex-hire with recent BSS.

1 hour ago, Mike the Boilerman said:


except for the need to add a LA batt, and do it right! 

Even assuming a new build so no previous LA batteries to use, I'm sure if you can afford a victron setup you can afford to add a small LA battery! You also need to add your own charging sources,  fuses, distribution system etc, where do you draw the line?

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2 hours ago, Tom and Bex said:

You also need to add your own charging sources,  fuses, distribution system etc, where do you draw the line?

Exactly. 

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