Change to LifePO4 - Emergency engine starting ?

Ian_Edwards said:
I'd change the electrical system.
My view is that the starter battery should only be used for starting. Normally this will only take a few joules of energy ( a fraction of a kWh or a few amp hours .... which isn't really a unit of energy unless you know the voltage)
I connect all the charging circuits to the LiFePO4 battery bank, through appropriate charge controller and fuses). Because LiFePO4 batteries are far more effective at storing energy that lead acid.
The starter battery is charged by a B to B with the correct charging profile. That way the starter battery is always fully charged. The single point of failure is the B to B.
This can always bypassed with a mechanical switch, which brings you back to Paul's original question. The answer to which is it depends on the specific electrical system he has installed. There's no general answer to the question.
It's a how long is a piece of string question.
However, by using a B to B to charge a dedicated starter battery, you are much less likely to have a "dead" starter battery.
For the record, I have 4 @ 105 amp hr at 12v LiFePO4 batteries, connected in parallel. Each battery has an internal BMS which limits the maximum discharge current to 200 amps, so 800 amps total.
Click to expand...
If a cell shorts in your lead starter battery then you can only produce 10V if you are lucky. You won't be starting your engine. The DC/DC charger will be working flat out to raise the voltage.
With DIY batteries, you can bypass the BMS fairly easily in an emergency to start the engine. I suspect leaving the bms in the system but bridging from the battery -ve and the NH fuse live side with jump leads to the starter wires would work fine.
Whether your system will start the engine through the BMS will depend on the inrush current of your starter motor. I have heard predictions of up to 10 times the run current but the only way to know is to try it.
 
I've recently done this, though with a small, easily started, Yanmar 2GM.
To avoid alternator damage due to a lifepo disconnect, I've kept the LA starter battery and use it to feed a Renogy B2B.
The 1-2-Both is now used as '1' for engine. 'Both' emergency combine, '2' not used.
The lifepo has a seperate main switch and runs everything else, electonics, house, bow thruster.
The lifepo is capable of starting on its own but I wouldn't leave it connected thus.
No 'white smoke of death' yet.
 
Sorry, haven't read all the replies but with a twin engine boat do you not have 2 lead acid starting batteries?
If one engine fails to start because it's battery is dead, parallel both together with the other engine running.
 
Alan S said:
Sorry, haven't read all the replies but with a twin engine boat do you not have 2 lead acid starting batteries?
If one engine fails to start because it's battery is dead, parallel both together with the other engine running.
Click to expand...
Blimey Alan, if it was that simple do you not think i'd have thought of that ;)
 
thinwater said:
Jump packs have been suggested. No personal expereince with boats, but they work a treat on cars.
Click to expand...

I have a LiCo pack that has started mt 4.4 FDV8 Range Rover ... my Opel Movano truck and my Volvo XC70 .....

But when I put it to my Perkins 4-107 on the boat - it was not so happy .... the problem is that a reasonable sized engine like that - 4 cyl 43HP ... if not used often - gets hard to turn over and the Li packs are not designed to sustain more than a few seconds demand.
But if the engine is often in use - then it should be fine .. just don't expect long bursts of starter !!
 
NickRobinson said:
I've recently done this, though with a small, easily started, Yanmar 2GM.
To avoid alternator damage due to a lifepo disconnect, I've kept the LA starter battery and use it to feed a Renogy B2B.
The 1-2-Both is now used as '1' for engine. 'Both' emergency combine, '2' not used.
The lifepo has a seperate main switch and runs everything else, electonics, house, bow thruster.
The lifepo is capable of starting on its own but I wouldn't leave it connected thus.
No 'white smoke of death' yet.
Click to expand...
Pretty much identical to my setup. And it did start that once
 
john_q said:
That is the solution I have gone for with a Perkins 4236. Mine claims to start a 7 litre diesel or 9 litre petrol engine
Click to expand...

As you know - as long as the battery already on the car is not dead - just discharged too low ..

If the battery is dead - then the Jump Pack will give a kick .. maybe a few sec's - but will not sustain starting power ....

That's what I found anyway ...
 
Rappey said:
A quick Google says the starter is 2.1kw so that would be 175 amps.

Will Prowse tests many lithium batteries. Some often hit 500+ amps before cutting out. Possibly not a great thing to do but it would start an engine ?
Click to expand...

Surely the problem is not the continuous ampage - its the initial high amp 'kick' to get turning ?
 
Rappey said:
A quick Google says the starter is 2.1kw so that would be 175 amps.
Click to expand...
The maximum inrush current of the starter motor will be much higher than the nominal power rating suggests. 700-900A (or higher) is not atypical for a yacht diesel engine.

However, these very high currents are only required briefly, so a battery with a lower continuous current rating may be acceptable.
 
Just to add to the data set. I have a Rolls 150AH lithium and a Yanmar 2qm15. No problem starting from the lithium either parallel with a completely flat LA or with the LA disconnected.
 
PaulRainbow said:
Many people have an emergency parallel switch to start the engine in the event of a flat/faulty engine battery, but what happens if the domestic banks is changed to LifePO4 ?

Can you still use the emergency parallel switch or is it not possible to start an engine from LFP ?

In another recent thread it was claimed that a 200Ah LFP battery would not be able to start an engine.

I have 280Ah of LFP @24V, a 200Ah JK BMS and two 7 litre diesel engines, will they start ?
Click to expand...
I would say just carry a modern (small but powerful) 'emergency' battery starter thingy (same as for your car). They are not expensive and are easy to use and store.
 
You must log in or register to reply here.

Share this page

Top