Starting a big diesel with lifepo4

[Fuss]

To start my motor, I need paralleled 2x 12v 750 cca batteries.
Has anyone changed to lifepo4 to start a big diesel?

[goboatingnow]

Originally Posted by Fuss

To start my motor, I need paralleled 2x 12v 750 cca batteries.
Has anyone changed to lifepo4 to start a big diesel?

I’ve tried it as a test no issues, the BMS must be setup to allow the current, much better then AGM , the engine doesn’t know what hit it

I have a stand-alone LFp backup starter system , ie portable etc.

[Fuss]

Originally Posted by goboatingnow

I’ve tried it as a test no issues, the BMS must be setup to allow the current, much better then AGM , the engine doesn’t know what hit it

I have a stand-alone LFp backup starter system , ie portable etc.

Thanks for this feedback.
At the moment my motor does not start cleanly on 1 battery, it will start, but it sounds like the battery is flat. So as per the specs, it is always started on 2 batteries. However, in the interests of redundancy, I would like to keep 2 batteries but I would like it that it could start properly on 1. That's why I thought that Lifepo4 batteries with their superior power might now be the answer.

[davil]

Originally Posted by goboatingnow

I’ve tried it as a test no issues, the BMS must be setup to allow the current, much better then AGM , the engine doesn’t know what hit it

I have a stand-alone LFp backup starter system , ie portable etc.

===================================

what size is your stand alone battery?,planning to have same set up?

thanks

Westerbeke 25 hp

[tanglewood]

The bottleneck using LFP as a start battery is typically the BMS's current limits. Drops-ins tend to have FET-based BMS disconnects with current limits in the 100A range. A BMS with a large contactor will be able to support higher currents. Either way, check the power system's current specs to see.


I've never looked into what the CCA specs actually say & mean, but if we take it at face value, your engine spec wants batteries that can deliver a total of 1400A. Using that, you should be able to figure out how many LFP batteries you need based on the BMS rating.

[goboatingnow]

Originally Posted by tanglewood

The bottleneck using LFP as a start battery is typically the BMS's current limits. Drops-ins tend to have FET-based BMS disconnects with current limits in the 100A range. A BMS with a large contactor will be able to support higher currents. Either way, check the power system's current specs to see.


I've never looked into what the CCA specs actually say & mean, but if we take it at face value, your engine spec wants batteries that can deliver a total of 1400A. Using that, you should be able to figure out how many LFP batteries you need based on the BMS rating.

Indeed LFP has no problems acting as a starter the issue as you mention is the bms mAy not be setup to support it.

[SOLAR SUPPORT]

Originally Posted by Fuss

To start my motor, I need paralleled 2x 12v 750 cca batteries.
Has anyone changed to lifepo4 to start a big diesel?

https://www.lifepo4battery-factory.c...nking-battery/

Can the alternator deal with this battery? I think it will need to be modified.

[tanglewood]

Originally Posted by SOLAR SUPPORT

https://www.lifepo4battery-factory.c...nking-battery/

Can the alternator deal with this battery? I think it will need to be modified.

In what respect? It will need to follow the charge voltage requirements of the battery, be able to survive whatever sustained output the battery can absorb, and survive a BMS disconnect.


Also note that the spec says the higher CCA current is only for 1 second. Max sustained load current is 100A.

[Fuss]

Thanks for all the replies.
So far it looks like I can get a battery that has no BMS but closely matched cells and can handle 900cca for max 10 seconds in every minute. Its a WINSTON Lithium Battery 12V/90Ah (WB-LP12V90Ah) for this I would still need 2, so no real advantage for me.

Or I could get a Lifepo4 starter battery like the one earlier mentioned but this has a CCA rating just for 1 second so not really providing any security or a solution. I looked for others with high CCA ratings but they all look a little dubious to me.

So to sum up, sofar it looks like there is not a solution in 1 battery that might reliably provide around 1400 CCA.



Maybe a battery could bypass the BMS when cranking and use the BMS when charging, and also when installed, have the ability to switch off the charging...my FLA start batteries at the moment are not charged with an alternator so this change would not be difficult.

I will continue looking.

[Fuss]

A few more thoughts,
-Lifepo4 as a starter is very different to deep cycle. As a starter, it needs to deliver the CCA but can be kept for example at partial charge for long life. So my charging regime can be switched on and off as I think fit. (assuming that these start batteries only have the starting job)



-Also, its amount of use in a typical day/week is not that much so I could imagine that some huge current abuse for starting might reduce its life and cause some damage but possibly not enough to make its life alot less... it might reduce its life from 15 years to 10 years for example.


-So a question would be...what if I had a 12v 90ah Lifepo4 start battery with no BMS like the Winston WB-LP12V90Ah and I tried to start my motor, would it deliver enough cranking amps? I imagine that it would and these cranking amps would be over the spec of 900cca for max 10 seconds in every minute. Maybe with Lifepo4, the actual cranking amps required are alot less than FLA. My FLAs get drawn down to 11 volts turning the starter where as Lifepo4 will not, so the CCA with Lifepo4 will be less than with FLA for the same result.


- It might be that 1400 CCA in FLA batteries is equal to 900 in Lifepo4. Does anyone know this??

[SOLAR SUPPORT]

You may check this

https://m.alibaba.com/product/160010...D&from=Android

[goboatingnow]

Originally Posted by Fuss

A few more thoughts,
-Lifepo4 as a starter is very different to deep cycle. As a starter, it needs to deliver the CCA but can be kept for example at partial charge for long life. So my charging regime can be switched on and off as I think fit. (assuming that these start batteries only have the starting job)



-Also, its amount of use in a typical day/week is not that much so I could imagine that some huge current abuse for starting might reduce its life and cause some damage but possibly not enough to make its life alot less... it might reduce its life from 15 years to 10 years for example.


-So a question would be...what if I had a 12v 90ah Lifepo4 start battery with no BMS like the Winston WB-LP12V90Ah and I tried to start my motor, would it deliver enough cranking amps? I imagine that it would and these cranking amps would be over the spec of 900cca for max 10 seconds in every minute. Maybe with Lifepo4, the actual cranking amps required are alot less than FLA. My FLAs get drawn down to 11 volts turning the starter where as Lifepo4 will not, so the CCA with Lifepo4 will be less than with FLA for the same result.


- It might be that 1400 CCA in FLA batteries is equal to 900 in Lifepo4. Does anyone know this??

There’s no real issue other then the bms limits

[tanglewood]

Originally Posted by Fuss

Thanks for all the replies.
So far it looks like I can get a battery that has no BMS but closely matched cells and can handle 900cca for max 10 seconds in every minute. Its a WINSTON Lithium Battery 12V/90Ah (WB-LP12V90Ah) for this I would still need 2, so no real advantage for me.

Or I could get a Lifepo4 starter battery like the one earlier mentioned but this has a CCA rating just for 1 second so not really providing any security or a solution. I looked for others with high CCA ratings but they all look a little dubious to me.

So to sum up, sofar it looks like there is not a solution in 1 battery that might reliably provide around 1400 CCA.



Maybe a battery could bypass the BMS when cranking and use the BMS when charging, and also when installed, have the ability to switch off the charging...my FLA start batteries at the moment are not charged with an alternator so this change would not be difficult.

I will continue looking.

Cranking and current-wise it's no problem. In fact, LFP is much better than LA for delivering large wallops of current. But with no BMS you have created a non-compliant battery system in the eyes of both ABYC and ISO.


I think you have identified a market for an LFP start battery. Capacity doesn't need to be large, but it needs a BMS, and one that can delivery high amperage for some suitable period of time.

[wholybee]

Seldom brought up in these discussions, but important, is the effect of voltage drop/sag on the starting of an engine. You don't actually know the current required unless you measure it, nor do you know the voltage at the starter.

With the starting currents present, the lead batteries voltage will sag, and the voltage at the starter is probably only 8-9 volts or so. (not relevant on a diesel, but this is why there is a ballast wire or resistor on an older gas engine and coils are designed for 9V. So that when the resistor is removed when cranking the voltage at the coil is the same as when not cranking)

The engine might only draw few hundred amps, but might need a higher voltage, closer to 12.5V than to 9V. A large 1500CCA battery will have much less voltage drop and that is what the engine needs, not the higher CCA.

The point of this is that you might not need a very large LFP battery at all, because LFP will not sag so much as lead. You will get a higher voltage than even the 1500CCA lead, which will reduce the current even further. The only way to know is to measure the voltage and current at the starter, or try a smaller LFP and test. You know that a single lead battery will start the engine, only that it does so slowly because the voltage is too low.

I would not be surprised if a 100Ah(or even 50Ah) LFP battery with no BMS were enough to start the engine reliably. You could omit the BMS by adding an active balancer and ensuring that whatever charge sources never exceed 13.8V. This flies in the face of accepted guidelines/ABYC etc. and carries risk, but I see no reason it wouldn't start the engine just fine.

As a point of comparison, I can start a large Cummins diesel in a mid 1980's F350 truck with an 18Ah Li-Ion (not LFP) battery. Done many times.

[SOLAR SUPPORT]

The initial inertia of the moving parts of the engine, such as the flywheel, crank, pistons, connecting rods, and additionally the compression pressure that the piston must overcome, forces the starter motor very hard for a few seconds at the start of the first movement. If you cannot provide the high power required to start the starter motor in the first few seconds, the starter motor can not start.

If the required current can be measured during the first start, the CCA value of the battery required for this job becomes clear. These small-capacity Lifepo4 batteries, which are used as starter batteries, must have circuit elements that can accumulate energy and discharge instantly. A power-increasing circuit that allows the 50 Ah Lifepo4 battery to produce 1450 A, albeit for a short time.