Single bank LFP?

[Rusty123]

My 28' sailboat spends most of the time at the marina (mainly a daysailer), but I just retired so I hope to go on some multi-day trips in the future. I currently have a single battery bank (2xL16 FLA) that serves as both house and starting (Yanmar 2QM15). This arrangement works fine, but the batteries are probably near end of life.

Until recently, my use case didn't really seem to justify LiFePO4, but with the drastically dropping prices, LiFePO4 might actually be cheaper than lead, so I'm reconsidering. I already have a programmable (Victron BlueSmart) charger and an externally regulated (Balmar MC-614) alternator, so I'm in good shape on the charging side (no solar). I also have a Victron BMV-712 monitor.

But I really want to stay with a single bank (probably around 200 AH), and there's the rub. I'm doubtful that I can start my engine reliably with one of the budget batteries (LiTime, WattCycle, etc.), but the cranking rated batteries (Epoch, Dakota, etc.) seem to be way overkill (and expensive) for my tiny engine.

My preference would actually be to build my own bank (I've built a couple other LiFePO4 banks for emergency preparedness and camping, so I'm familiar with the procedure), but the generally available/reasonably priced FET BMS's seem marginal for starting purposes.

I suppose I could build a bank with 4S Eve cells and a BMS like this and see if it works OK, but I'd rather follow the footsteps of someone who has already gone down this road.

Suggestions?

[Adelie]

Poulsbo, loved cruising out there occasionally when I lived in Seattle.

There is a secondary issue to going LFP, the alternator. LFPs can accept so much current it can frag an alternator. Don’t know all the details, I suspect that the proper regulator would prevent this problem. Check the manual on your regulator, perhaps Val Balmar if that isn’t clear.

From periodically watching Will Prouse I’d be willing to plunk down money on 2 of those cheap LFPs. You probably only need 200amps to start that engine. Even if you need 300amp they should be able to handle that momentary surge no problem.

Check Prouse’s YT channel, one of his recent videos talked about this with a really cheap battery and he was impressed.

[Rusty123]

Originally Posted by Adelie

Poulsbo, loved cruising out there occasionally when I lived in Seattle.

There is a secondary issue to going LFP, the alternator. LFPs can accept so much current it can frag an alternator. Don’t know all the details, I suspect that the proper regulator would prevent this problem. Check the manual on your regulator, perhaps Val Balmar if that isn’t clear.

From periodically watching Will Prouse I’d be willing to plunk down money on 2 of those cheap LFPs. You probably only need 200amps to start that engine. Even if you need 300amp they should be able to handle that momentary surge no problem.

Check Prouse’s YT channel, one of his recent videos talked about this with a really cheap battery and he was impressed.

Thank you. Yes, the Balmar regulator has the ability to reduce alternator output ("belt manager"), as well as temperature cutback, so I should be set there.

I have watched many of Will Prouse's videos, but I hadn't seen the one where he did surge testing on a cheap battery, so thanks for the tip!

[barnakiel]

How to make a good new concept and wrap it in our old mindset ?


Well, try !


But sure a plain small lithium starts an engine. Just look at those emergency lithium banks now sold in mass for the car market.


One bank is enough. Just build it out of = x components - so that if one element bricks, you can still use the remaining capacity.


b.

[Adelie]

https://m.youtube.com/watch?v=UDkJ7Sq21Qw

[Adelie]

So he didn't say it was surge rated to 200A, he indicated that overcurrent protection kicked in above 200A. It looks like it kicks in after a minute or so and is related to heat build up. If you are cranking your engine for more than 10sec then the engine probably needs service of some kind.

BattleBorns are surge rated to 200A for 30s and 500A for 1/2s. These aren't the same as what Prouse reviewed but I think short term surges would probably not cause problems.

The pluses and minuses of DIY vs buying a cheap battery is that
A. DIY has a BMS that is easily replaced. And it will be exposed to marine air and not last as long. I suspect that the BMS will not last as long as the cells whether sealed or not.
B. Plug and play battery has a sealed container that will protect the electronic components from damage for a significant period. But also seals in heat which will be hard on the cells and the electronics.

On the whole it's probably a wash which is the better way to go.

I would suggest finding out how much your engine draws when cranking.

I have a clamp meter, if I can get my son to crank my car for me I'll tell you what that draws.

[Rusty123]

Originally Posted by Adelie

I would suggest finding out how much your engine draws when cranking.

I have a clamp meter, if I can get my son to crank my car for me I'll tell you what that draws.

I have a clamp ammeter, but (at least mine) doesn't accurately record short duration surges. But this photo from marinehowto indicates that starting surge for a 40 HP diesel is around 640 amps. So mine should be well short of that.

[newhaul]

Originally Posted by Rusty123

My 28' sailboat spends most of the time at the marina (mainly a daysailer), but I just retired so I hope to go on some multi-day trips in the future. I currently have a single battery bank (2xL16 FLA) that serves as both house and starting (Yanmar 2QM15). This arrangement works fine, but the batteries are probably near end of life.

Until recently, my use case didn't really seem to justify LiFePO4, but with the drastically dropping prices, LiFePO4 might actually be cheaper than lead, so I'm reconsidering. I already have a programmable (Victron BlueSmart) charger and an externally regulated (Balmar MC-614) alternator, so I'm in good shape on the charging side (no solar). I also have a Victron BMV-712 monitor.

But I really want to stay with a single bank (probably around 200 AH), and there's the rub. I'm doubtful that I can start my engine reliably with one of the budget batteries (LiTime, WattCycle, etc.), but the cranking rated batteries (Epoch, Dakota, etc.) seem to be way overkill (and expensive) for my tiny engine.

My preference would actually be to build my own bank (I've built a couple other LiFePO4 banks for emergency preparedness and camping, so I'm familiar with the procedure), but the generally available/reasonably priced FET BMS's seem marginal for starting purposes.

I suppose I could build a bank with 4S Eve cells and a BMS like this and see if it works OK, but I'd rather follow the footsteps of someone who has already gone down this road.

Suggestions?

Ok here's my opinion . Get a 100ah wattcycle with Bluetooth
https://www.amazon.com/Wattcycle-LiF...s%2C430&sr=8-3

Set your balmar to charge the house and a 5 amp dc2dc from the house to charge a maintance free lead starting battery to start the engine .

[Adelie]

Originally Posted by Rusty123

I have a clamp ammeter, but (at least mine) doesn't accurately record short duration surges. But this photo from marinehowto indicates that starting surge for a 40 HP diesel is around 640 amps. So mine should be well short of that.

My 4cyl petrol/gas engine peaked at 135A to start. Let's assume that it's really 200A because it was short duration and the meter couldn't keep up.

I expect your 2cyl diesel will be similar or lower. Let's say it's actually double my worst cast, so 400A, that's still within the short term capacity of 2-100Ahr LiFePo batteries.

[newhaul]

Originally Posted by Adelie

My 4cyl petrol/gas engine peaked at 135A to start. Let's assume that it's really 200A because it was short duration and the meter couldn't keep up.

I expect your 2cyl diesel will be similar or lower. Let's say it's actually double my worst cast, so 400A, that's still within the short term capacity of 2-100Ahr LiFePo batteries.

Don't know yanmar but my mitsubishi k2b.( westerbeke 10-two) Peaks at 128 amps according to my electric shop at point defiance.

[s/v Jedi]

What is the CCA requirement for the engine starter?

[Rusty123]

Originally Posted by newhaul

Ok here's my opinion . Get a 100ah wattcycle with Bluetooth
https://www.amazon.com/Wattcycle-LiF...s%2C430&sr=8-3

Set your balmar to charge the house and a 5 amp dc2dc from the house to charge a maintance free lead starting battery to start the engine .

I'm sure that approach would work well, but it would require making my system (somewhat) more complex (two banks, with B2B charger). I'm not 100% opposed to that approach, but my I'd really like to stick with the simplicity of a single bank for everything, if possible (and rational).

[Rusty123]

Originally Posted by newhaul

Don't know yanmar but my mitsubishi k2b.( westerbeke 10-two) Peaks at 128 amps according to my electric shop at point defiance.

That's actually much less than I would have thought. Many of the FET BMS's that I've considered are rated for 200A (or more) steady state, so would seem more than adequate for a peak like that (or even double that).

[Rusty123]

Originally Posted by Adelie

My 4cyl petrol/gas engine peaked at 135A to start. Let's assume that it's really 200A because it was short duration and the meter couldn't keep up.

I expect your 2cyl diesel will be similar or lower. Let's say it's actually double my worst cast, so 400A, that's still within the short term capacity of 2-100Ahr LiFePo batteries.

Thanks for checking on that -- very encouraging!

[Rusty123]

Originally Posted by s/v Jedi

What is the CCA requirement for the engine starter?

I'm not entirely sure -- Google AI says that "a battery with a CCA rating between 250 and 300 would be suitable", but I don't know where that's coming from. I have copies of the operation manual, service manual, and data sheet, but none of these list the CCA requirement, at least that I can see.