Jump start engine battery

[Brentwales]

I stupidly left some switches on for a few weeks which have drained my batteries. I left the switch on that joins the house and engine battery so both drained. I've bought a 1500amp Noco Jump start power bank.

My engine is a Yanmar 2YM15.

Both batteries when leaving the boat over the weekend were reading about 11.31V.

To jump start the engine, should I isolate to just the engine battery by removing the wires that link the batteries or would it be safe to jump start as is?

Thanks

 

[pvb]

If there's a switch which joins the batteries, just turn that off. Can't see any need to remove battery cables. Then try jump-starting it.

It's not a good idea to leave the boat with flat batteries; it'll greatly reduce their life.

 

[Brentwales]

Thanks, it's a good lesson for me to double check everything is off when I leave the boat.

 

[MarkCX]

Might be worthwhile fitting a ‘battery saver’ device if there’s any chance of it happening again.

 

[RichardS]

Have you tried starting the engine with the batteries at 11.3V? It might start and then you can recharge them from the alternator.

Can you charge them with a mains battery charger?

Richard

 

[AntarcticPilot]

Have you tried starting the engine with the batteries at 11.3V? It might start and then you can recharge them from the alternator.

Can you charge them with a mains battery charger?

Richard

Yes - there's a trick that might work. Decompress the engine, get it turning as fast as possible with the decompressor on (even flat batteries can manage to turn the engine when there's no compression), then drop the decompressor. It worked for me when the batteries were too low to start the engine and we were being launched with a VERY narrow tidal window.

 

[Brentwales]

Have you tried starting the engine with the batteries at 11.3V? It might start and then you can recharge them from the alternator.

Can you charge them with a mains battery charger?

Richard

Yeah I tried turning it over a few times, but no luck.

 

[Brentwales]

Yes - there's a trick that might work. Decompress the engine, get it turning as fast as possible with the decompressor on (even flat batteries can manage to turn the engine when there's no compression), then drop the decompressor. It worked for me when the batteries were too low to start the engine and we were being launched with a VERY narrow tidal window.

Thanks, I've flicked through the engine manual but can't find any reference to a decompressor.

 

[pvb]

Thanks, I've flicked through the engine manual but can't find any reference to a decompressor.

Depends on the engine - older engines often had a decompression lever, newer engines don't.

 

[VicS]

Depends on the engine - older engines often had a decompression lever, newer engines don't.

2YM15 ... post #1

 

[pvb]

2YM15 ... post #1

OK, so a newer engine, no decompression lever.

 

[William_H]

OP is asking about jump start. Yes to parallel a jump start battery to the flat engine battery will tend to try to charge the engine battery from the jump start. So in cases where engine battery is very low or damaged you would be better off with that battery disconnected. However I would say with the engine battery at 11.3 it would be Ok to parallel to it. Providing you don't tarry too long before attempting the start. The voltage of the jump battery will drop dramatically with starter load current and one would think the flat battery will be able to contribute. That case where you left batteries paralleled is a reason to go VSR. ol'will

 

[Stemar]

OP is asking about jump start. Yes to parallel a jump start battery to the flat engine battery will tend to try to charge the engine battery from the jump start. So in cases where engine battery is very low or damaged you would be better off with that battery disconnected. However I would say with the engine battery at 11.3 it would be Ok to parallel to it. Providing you don't tarry too long before attempting the start. The voltage of the jump battery will drop dramatically with starter load current and one would think the flat battery will be able to contribute. That case where you left batteries paralleled is a reason to go VSR. ol'will

Good advice, especially about the VSR. Chances are you've got away with it this time, but a VSR's a LOT cheaper than a new set of batteries. Of course, if you're a total tightwad, you could use a cheapy headlamp relay that's change from a fiver. It's what I have, but VSRs were a lot dearer when I installed it.

 

[Spirit (of Glenans)]

Not to sound censorious, but if I found that my battery was flat on leaving the boat I would seriously consider bringing it home to charge up.

 

[James_Calvert]

If the batteries are not too bulky or inaccessible, why not simply buy a fully charged replacement and take it with you to swap over when you are next on board.

 

[HissyFit]

If the battery is not enough to crank the engine on it's own, is there an accessible pulley off the crankshaft with an accessible nut/bolt and do you have a beefy cordless drill/driver with a socket that will fit that nut/bolt? That's how crank handles used to work, except for the added benefit of not having to risk the kickback.

 

[affinite]

If the battery is not enough to crank the engine on it's own, is there an accessible pulley off the crankshaft with an accessible nut/bolt and do you have a beefy cordless drill/driver with a socket that will fit that nut/bolt? That's how crank handles used to work, except for the added benefit of not having to risk the kickback.

That sounds like a sure way to break your arm !

 

[RichardS]

That sounds like a sure way to break your arm !

Or, hopefully, just the cordless drill.

Richard

 

[Biggles Wader]

If the batteries are not too bulky or inaccessible, why not simply buy a fully charged replacement and take it with you to swap over when you are next on board.

If they have been left discharged for "a few weeks" you will quite likely have destroyed the batteries anyway so a new set might be the best option.

 

[AntarcticPilot]

If the battery is not enough to crank the engine on it's own, is there an accessible pulley off the crankshaft with an accessible nut/bolt and do you have a beefy cordless drill/driver with a socket that will fit that nut/bolt? That's how crank handles used to work, except for the added benefit of not having to risk the kickback.

Crank handles are designed to disengage from the crank shaft when the engine starts. Sockets aren't, so when the engine starts you could find yourself faced with a drill rotating with the engine, either that or a kick back. In either case, a broken wrist is about the best you could hope for.

In any case, I'd be surprised if a drill had enough torque to rotate a diesel over the compression. The starter motor uses a very large mechanical advantage to turn the engine; I don't know the numbers, but consideration of the relative size of the starter motor pinion and the flywheel suggest something like 20:1. A high revving (in engine terms) electric drill probably lacks the torque.

There's always the Moitessier approach - wrap the main sheet round the fly-wheel and then gybe!