LiPo starter battery?

[earthbm]

On the mad quest to save weight in a race boat, if I change the starter battery to a 20AH LiFePO one, do I need to run it through a charge regulator or can it be plugged directly like a lead starter battery?

The system:

Yanmar 3jh40 with 120A alternator
Balmar MC-614 regulator kit
100AH house battery

[ThereAndBack]

See: https://balmar.net/wp-content/upload...ember-2017.pdf

Note that Balmar strongly recommends you use a temp sensor because the lithiums will put a huge load on your alternator if it is deeply discharged.

[CaptainRivet]

Originally Posted by earthbm

On the mad quest to save weight in a race boat, if I change the starter battery to a 20AH LiFePO one, do I need to run it through a charge regulator or can it be plugged directly like a lead starter battery?

The system:

Yanmar 3jh40 with 120A alternator
Balmar MC-614 regulator kit
100AH house battery

Due to you have a Balmar regulator kit you can connect it directly like a lead starter battery. I would also highly recommend to add the temp sensor as it’s needed so the alternator can be regulated according to its working temp and protect the alternator.

[smac999]

The max draw of a 20ah lithuim bank is probably too small to start an engine. It’ll just trip the bms. Even a bigger 100ah is only like 100a max draw.

[T1 Terry]

Originally Posted by smac999

The max draw of a 20ah lithuim bank is probably too small to start an engine. It’ll just trip the bms. Even a bigger 100ah is only like 100a max draw.

If you build your own lithium battery from 4 x 20Ah cells in series, you can pull a peak of 100 amps from the 20Ah battery, just not for very long because the 20Ah capacity will drop below 60% usable capacity because of the very high current load, 5CA, so about 12Ah usable before the voltage drops off, roughly 7 mins until completely flat, so in reality, less than 5 mins total cranking with a recharge, you wouldn't want to be relying on a cold cranky engine that didn't start first time every time .....
I use 40Ah cells for the lithium batteries in all my vehicles ... mostly because I have them on hand, second hand used DIY electric vehicle cells ....

T1 Terry

[CaptainRivet]

It will do, i started a 7l V8 and a 5.2lV10 with a 20AH Lifepo4 daily 5 years long without any issue, you just need to use a starter LifePo4, not a service type one.
https://cs-batteries.de/Lithium-LiFe...2V-20Ah-750AEN

I would simply go with 30Ah LTO, 6 cells and no BMS needed . They deliver 10C constant and 20 peak, so 600A for starting.
https://www.amazon.de/-/en/YINLONG-b.../dp/B07WRHH9KQ

[Pete7]

If the aim is to save weight, ditch the 100AH house battery and replace it with a small red flash or Oddesey battery to do everything.

Red Flash High Rate | DMS technologies

https://eu.odysseybattery.com/

It will be cheaper and simpler.

How big is the boat? that's a 40hp engine.

[CaptainRivet]

Originally Posted by Pete7

If the aim is to save weight, ditch the 100AH house battery and replace it with a small red flash or Oddesey battery to do everything.

Red Flash High Rate | DMS technologies
Agree ditch the house and starter and use one
https://eu.odysseybattery.com/

It will be cheaper and simpler.

How big is the boat? that's a 40hp engine.

Agree ditching house and starter too, didn't realize he has a house too.
Suggest to use the LTO 40AH cells and make one battery of 6 cells so you have a 40AH 12V LTo battery. For your setup the ultimate weight saver.
Try it out, it should be really enough, if not add 6 cells more so you have a 80AH LTO but I highly toubt you need more then a 40Ah LTO. Your alternator will recharge it very quick if needed and you can completely discharge it too. The abuse this LTO can take is from another world.

[Adelie]

Originally Posted by smac999

The max draw of a 20ah lithuim bank is probably too small to start an engine. It’ll just trip the bms. Even a bigger 100ah is only like 100a max draw.

I believe the bigger ones have a 200A surge capacity.

The little jump packs you can get for your car are probably 10-20Ahr.

[earthbm]

So I ended up getting 100ah house and 50ah starter, both LiFePO. LTO is a bit new (meaning BMS and charging systems are probably not optimized for it), heavier for AH capacity. The aim is to run instruments, computers and lights in an 8-hour coastal race without running the engine.

My new question is: do I need a DC-DC charger, or a simple battery isolator is enough because there is already the Balmar controller?

[CaptainRivet]

Originally Posted by earthbm

So I ended up getting 100ah house and 50ah starter, both LiFePO. LTO is a bit new (meaning BMS and charging systems are probably not optimized for it), heavier for AH capacity. The aim is to run instruments, computers and lights in an 8-hour coastal race without running the engine.

My new question is: do I need a DC-DC charger, or a simple battery isolator is enough because there is already the Balmar controller?

Why do you need a house and starter on a race boat? Makes things complicated and heavier.
Make one big battery so you have most reserve for everything, you don‘t need a complicated and also again weight isolation system and a dedicated starter or house.
Yes you need an isolater and a big one in your setup now as both lifepo can deliver serious amps plus or a dc to dc charger, suggest the Victron smart Orion. 50AH is a total waste and weight, 20AH starts every Diesel or a 7l V8 without any problem.
But all unnecessary and too complicated
As I wrote LTO doesn‘t need BMS or any complicated charging solution. One 80AH starter and house, no BMS, dump it in instead all your batteries and connect to the Balmar and job done. Lighter, safer, operational stable as you can discharge it to 0 and super simple. Nothing additional needed. And the LTO even starts your Diesel if down to 7V, do that with the lifepo and it is toast
Perfect for a race boat.

And not new, since 20 years available and using it since 15 years in my race cars, Mini doesn‘t have even an alternator and a 40AH LTO is good for a 5h race stint where all electronics and ignition go off the 40AH LTO without any recharging, even thrown that out to squeeze last hp out of the engine.

[earthbm]

Thanks. Got the 30a smart Orion (wish they had 50a).

The reason for the separate starter battery is that it would suck if the batteries died during Transpac, and 12people looked at me badly.