Jump Starting from domestics...

[helrow]

Hello all,

 

Just after a very quick bit of advice. I managed to knock my headlight on while dragging my fold-up bike from the engine room on my way out for a few days and now have a lovely, flat starter battery.

 

I'm gathering from other posts on here that it's possible to jump start my starter battery from my domestic bank... Is this safe or will I run the risk of blowing myself up? Does anyone have any tips as to how to do this safely if it is possible (I've jump started a few cars in my time but never a boat.) Wondering if I should just wait for a friend to cruise in this direction and get a jump from him...

 

Any advice, as always, hugely appreciated.

 

Helena

 

 

[kevinl]

As the negative terminals (black wires) of the batteries will already be connected together you only need a lead across the positive terminals (red wires).

I usually connect both jump leads across the positive side specially if the starter battery is completely flat (my jump leads are pretty cheap).

Just check you connect red to red and double check the + sign on the battery.

K

[helrow]

Excellent, Kevin. Thanks loads.

[Scholar Gypsy]

.. and then perhaps adjust the wiring so that the headlight and horn etc do not run off the engine battery ?

[helrow]

Yeah, this thing is pretty eccentrically (if not dangerously) wired. I'll add that to the to do list! Thanks.

[MtB]

The bit that puzzles me is how come the domestic batteries are not flat too?

 

Assuming you have solar, shoreline or some way of charging them other than with the engine, then just leaving the jump lead in place for a few hours will charge the starter battery anyway, from whatever is charging the domestic bank.

(Which means you don't need to go and buy a set of heavy duty jump leads suitable for starting a diesel, the cheapest thinnest ones on ebay will do the trick!)

[helrow]

I've got a big solar panel for my domestics and 4 110v batteries that only charge a few LEDs (overkill.)

 

I'll get myself some cheapy leads and do as you said then, Mike. Thanks ever so much for your prompt reply.

[MtB]

Yer welcome!

 

Even a bit of spare wire of almost any size will do, to link the domestic positive to the starter positive for charging it. No need to actually buy jump leads at all if you have some spare wire.

[Chewbacka]

all this assumes your starter and domestics are all 12v. If you have 24v domestic battery do NOT just connect it to your 12v starter.

[ditchcrawler]

.. and then perhaps adjust the wiring so that the headlight and horn etc do not run off the engine battery ?

Mine do but only live while the engine is running. In Thames locks I just stop the engine but leave the "ignition" switch on.

[Alan Saunders]

It is all too easy to leave the tunnel light on or have it turned on by a 'malevolent spirit' - it must be the most common cause of flat batteries (start or house). I now isolate mine by removing a fuse/tripping a CB but it is a bit embarrassing when I enter a tunnel and find it is not working.

 

If you have a '1, both, 2, off' switch, set it to 'both' and start the engine - make sure you set it to 'house' (could be 1 or 2) after stopping the engine.

 

Another strategy is, having switched off the cause of the current drain, leave the battery to recover for half an hour or so and try to start the engine again. In desperation, if the engine turns over slowly, you could resort to 'Easy Start', an aerosol that you spray into the inlet manifold. Many will say that this damages engines but, mostly, it is only used on an already badly worn engines. A quick 'puff' (< a second), may get you out of trouble - loud knocking noises may indicate that you have used too much!

 

Last year a neighbouring boater was asking to borrow long jump leads, to jump from an adjacent boat as you would with a road vehicle. It transpired that his batteries were buried under decking but the two isolators were easily accessible and only a couple of inches apart. My cheap (aluminium) jump lead was sufficient to bridge between them and start the engine. If that was my boat I would have made a link from copper pipe flattened and drilled at the ends for a more robust solution. Maybe even, an additional, rarely used, red-key isolator to connect the starter to the house batteries.

 

Chances are that your start battery (like mine) is in need of replacement and/or may not be fully recharged by any 'split-charge relay'. A typical tunnel lamp is ~55W (<5A) so you would only need to leave it on for 20 hours to flatten a 90Ah (original capacity) start battery. OTOH, a good engine will start after a few seconds of cranking and the battery will be recharged within 20 minutes of running above idle.

 

Helping other boaters may be hazardous, what if one of the above isolators had been connected in the +'ve and the other in the -'ve? I had not thought to take my DVM but I quickly 'splashed' the jump lead and saw no 'sparks'.

 

Alan

[arcsyst]

Yer welcome!

 

Even a bit of spare wire of almost any size will do, to link the domestic positive to the starter positive for charging it. No need to actually buy jump leads at all if you have some spare wire.

Do NOT use 'a spare bit of wire of any old size' you risk causing a fire as it is almost impossible to charge one battery by connecting it to another and the starter will pull 200A ish through your bit of wet string.

[Ricco1]

As the negative terminals (black wires) of the batteries will already be connected together you only need a lead across the positive terminals (red wires).

I usually connect both jump leads across the positive side specially if the starter battery is completely flat (my jump leads are pretty cheap).

Just check you connect red to red and double check the + sign on the battery.

K

 

Just picking up on this: The negatives on my batteries (2 x domestic 1 x starter) are not wired together. Could this be a problem? Sorry should clarify that: the negatives on the domestics are wired together, but not to the starter battery.

Edited May 22, 2015 by Ricco1

[arcsyst]

Just picking up on this: The negatives on my batteries (2 x domestic 1 x starter) are not wired together. Could this be a problem?

They'd better be, somewhere!

[jonathanA]

Do NOT use 'a spare bit of wire of any old size' you risk causing a fire as it is almost impossible to charge one battery by connecting it to another and the starter will pull 200A ish through your bit of wet string.

Err no firstly MTB was suggesting only using the wet string for charging not starting and secondly some of the chsrge will transfer between not flat and flat battery. How much is a moot point

 

Yes trying to start using s bit of crappy flex will probably result in lot of smoke and red glowing wires. But a bit of patience will mean you get some chsrge into the start battery and can get away with cheapo jump leads

 

I always connect the jump leads wait a few minutes then try to start when jump starting a car for that reason

[DHutch]

I always connect the jump leads wait a few minutes then try to start when jump starting a car for that reason

In this case however, often the thing your jumping from is a car with its engine running an hence alternator charging, which is not the same as jumping from a battery.

 

In this instance I have found even really fairly nasty £12 leads will jump straight away.

 

 

Daniel

[kevinl]

 

Just picking up on this: The negatives on my batteries (2 x domestic 1 x starter) are not wired together. Could this be a problem? Sorry should clarify that: the negatives on the domestics are wired together, but not to the starter battery.

Normal, in so far as it exists on boats is all the negatives connect then go to the isolator switch so one switch isolates everything, however, some boats have more then one isolator so there may be one for the starter and a second one for the domestic or even one for each battery in which case they shouldn't be interconnected.

All the electric need an isolator switch and connecting all the negs together through one master switch is (I believe) the most common way of doing it.

I've got 3 domestic and one starter and they all run through the one isolator switch but I have seen boats with 4 isolator switches which (in my view) makes a nonsense of the whole idea of a single point of emergency electrical disconnection, less so it they're all in the same place.

K

[MtB]

 

Just picking up on this: The negatives on my batteries (2 x domestic 1 x starter) are not wired together. Could this be a problem? Sorry should clarify that: the negatives on the domestics are wired together, but not to the starter battery.

 

 

They must be connected or one battery would not charge.

 

Try using your multimeter to test for continuity between all the negatives. I bet you'll find they are all connected to each other, you just haven't spotted the cable.

 

 

 

Do NOT use 'a spare bit of wire of any old size' you risk causing a fire as it is almost impossible to charge one battery by connecting it to another and the starter will pull 200A ish through your bit of wet string.

 

Obviously not true when the other battery is connected to a charger, as is the case here.

 

Nor was I advocating using the thin bit of wire for jump starting. Of course it would melt. Credit the OP with some intelligence please.

[Tony Brooks]

Normal, in so far as it exists on boats is all the negatives connect then go to the isolator switch so one switch isolates everything, however, some boats have more then one isolator so there may be one for the starter and a second one for the domestic or even one for each battery in which case they shouldn't be interconnected.

All the electric need an isolator switch and connecting all the negs together through one master switch is (I believe) the most common way of doing it.

I've got 3 domestic and one starter and they all run through the one isolator switch but I have seen boats with 4 isolator switches which (in my view) makes a nonsense of the whole idea of a single point of emergency electrical disconnection, less so it they're all in the same place.

K

 

This is not best practice. Gibbo has explained on here why switching the negatives can cause major damage.

 

Once again do not assume that just because a single boat has things done one way that all boats will be the same.

[Arthur Brown]

Switching the negatives is very bad form, but it can be found. Separated negatives are highly unlikely but may possibly exist, -even if the wiring local to the battery looks separate the negative wires may well be commoned on the engine block. Different voltages for the start system and domestic system are possible but unlikely, you are usually aware of your own boat's system -or should be.

 

Ultimately remove a domestic battery and join it with jump leads to the starter battery.

[Ricco1]

Just been out to check: There is no wire connecting the negative of the 2 domestic batteries with the negative of the starter. There is however a connection somewhere, my multimeter confirms this. There is one isolator for the starter, another for the domestics. Everything works fine, batteries charge etc. Should I be looking to change this set up at all?

[DHutch]

Switching the negatives is very bad form, but it can be found.

 

Cant speak for boats, where it does appear common to isolate the positive, as is commonly done on cars also. However all of the JCB Loadall range have the battery isolator on the negative side.

 

 

Daniel

[Murflynn]

Just been out to check: There is no wire connecting the negative of the 2 domestic batteries with the negative of the starter.

no, I wouldn't expect there to be.

but if it is a steel boat then both battery negatives are connected to the hull shell. Ideally this should be to separate earth studs located close together near to the batteries.

 

 

 

 

MtB suggested linking the batteries with a bit of cable to allow the start batteries to recharge to an extent. Problem is that you often don't expect the start battery to be flat, so you won't link them unless you have the luxury of being able to plan ahead. A cheap jumper lead should suffice to start the engine from the domestic bank.

[Dave Clinton]

there isn't half some rubbish spouted about electrics on this forum since Gibbo and Sir Nibble left and Smiley Pete doesn't post so much.

just for clarity; it is standard practice to link the negatives of all batteries with exactly one connection to hull. if you can't find an obvious link you need to track down the continuity because it could cause a dangerous fault.

[Timleech]

 

Cant speak for boats, where it does appear common to isolate the positive, as is commonly done on cars also. However all of the JCB Loadall range have the battery isolator on the negative side.

 

 

Daniel

 

It used to be common practice to have isolators in the Negative on boats, and two banks could be isolated with one switch if this were done.

It's rather frowned upon now, but I'll bet there are plenty of boats around which still have negative isolators.

 

Tim