Jump starting from leisure batts.

[PeterDHS]

Kristian has a recent topic about 'running an engine without a starter battery'. I don't want to hijack his topic so am starting a new one.

Can anyone tell me step-by-step how you would safely jump start from my 4 leisure batteries if the starter battery was flat ?

I can guess the obvious bits but frinstance would it be adviseable to remove the leisure 'plug' whilst cranking the starter ? would it damage the leisure alternator ? would it boil/damage the leisure batteries ?

Is the safest (and least effective no doubt) route to connect and 'equalise' the two sets of batteries for an hour with both plugs out, then reconnect and try again on the stater battery only ?

 

TIA

Peter.

[Chalky]

In the case of my own boat I had to do this once. Since the negative sides (0V, gnd, -ve) of the domestic and starter battery banks are connected together it was simply a matter of adding a temporary connection between the positive (12V, V+, Vbatt) sides of the banks. This allowed the engine to crank and start. Once running the temporary lead was removed. I used a standard car jumper cable.

 

You're only running the whole lot for a minute or two - it's exactly the same process as jump starting a car, its just that the 0V leads are permanently connected and the the alternators are strapped to the same engine.

Edited June 11, 2014 by Chalky

[bottle]

As per Chalky's post

[ditchcrawler]

More fun with 24 volt domestic and 12 volt starter. I even recharged the 24 volt domestics from the 12 volt alternator when the 24 volt one died.

[Alan de Enfield]

I have made up a very short (about 18" long) jump lead using very heavy cable, added strong heavy duty croc clips and now have an emergency 'bridge' for the domestics to starter battery. Lives in the emergency spares kit on the boat.

[Robbo]

Many boats have a switch were you can combine the leisure and starter batteries together purely start the engine.

 

On my voltage sensitive relay there's a option to manually combine the battery banks for this reason.

[Flyboy]

More fun with 24 volt domestic and 12 volt starter. I even recharged the 24 volt domestics from the 12 volt alternator when the 24 volt one died.

Can you please explain how you managed to get a 12 volt alternator to charge a 24 volt battery ? Must be some miracle of science I've not come across yet.

[Paul C]

More fun with 24 volt domestic and 12 volt starter. I even recharged the 24 volt domestics from the 12 volt alternator when the 24 volt one died.

 

Why have 2 different voltages, why not a 24V starter motor etc?

[Scholar Gypsy]

Just going back to the OP's request for step-by-step instructions, unless you want a big spark it is of course very important to make sure the positive croc clips do not touch anything they are not meant to, in particular any part of the hull or other metalwork.

 

[You don't have the option of what you do with car jump leads, namely to connect the positives first and then the negatives.]

 

I made up my own short jump lead, it gets used about once every five years.

[ditchcrawler]

 

Why have 2 different voltages, why not a 24V starter motor etc?

Because the engine came with 12 volt ancillaries, starter, alternator, instruments all ready wired up, so why change it.

[Paganboat]

Kristian has a recent topic about 'running an engine without a starter battery'. I don't want to hijack his topic so am starting a new one.

Can anyone tell me step-by-step how you would safely jump start from my 4 leisure batteries if the starter battery was flat ?

I can guess the obvious bits but frinstance would it be adviseable to remove the leisure 'plug' whilst cranking the starter ? would it damage the leisure alternator ? would it boil/damage the leisure batteries ?

Is the safest (and least effective no doubt) route to connect and 'equalise' the two sets of batteries for an hour with both plugs out, then reconnect and try again on the stater battery only ?

 

TIA

Peter.

red to red, black to black, wont hurt, just dont touch the boat

[Alan Saunders]

Recently, a neighbour enquired if I had long jump leads to start his engine. As it turned out he had start and house battery isolators mounted within inches of each other so a connection between the two was easy.

 

My boat has a split-charge relay and a '1/2/both' isolator. Redundancy, if the starter battery is 'flat', chances are I could start the engine by switching to 'both'.

 

'Leisure' and deep cycle batteries have a Cold Cranking Amp (CCA) rating. One 50% charged 'house' battery should be able to start an engine. A bank of two or more have far more CCA capacity than a typical starter battery.

 

Alan

[Chalky]

Can you please explain how you managed to get a 12 volt alternator to charge a 24 volt battery ? Must be some miracle of science I've not come across yet.

 

You can charge them as 2 separate 12V batteries then re-combine then to get 24V.

 

It's more interesting the other way round. It's used to be common for cars shipped over seas to have flat batteries on arrival at a port after 6 weeks on a ship. The standard practice was to jump start them off a lorry or other vehicle with 24V applied to the 12V system. This is the reason why automotive electronics is designed to survive a 24V dock side start.

[PeterDHS]

Thanks for all the advice you peeps.

Seems that the concensus is that I need not worry about about stray currents or removing the leisure isolator, but simply connect jumpers black to black then red to red (carefully). Then crank to start, and remove jumpers asap and no damage should be done.

Correct ?

 

Peter.

[Keeping Up]

You don't normally need the black-to-black jumper as the battery negatives are normally connected together already, all you need is the single red-to-red jumper

Edited June 15, 2014 by Keeping Up

[Arthur Brown]

If you would use a 1Kw inverter from the house battery then you should be able to use the starter motor from it!

 

If you have one alternator then removing the jump lead is no problem. -but how will the starter battery recharge?

 

If you have two alternators then removing the jump lead to a missing starter battery could damage an alternator.

 

With so much negative referenced steel about it is good to use fully insulated croc clips to prevent and inadvertent shorts from +ve to hull.

[Sir Nibble]

Can you please explain how you managed to get a 12 volt alternator to charge a 24 volt battery ? Must be some miracle of science I've not come across yet.

You byepass the regulator. It's vicious but it's astonishing what you can get away with if you know what you're doing and when to wince.

[ditchcrawler]

I talked that one up, I have just brought the 24 alternator home with me.