electrical problem

[dave p]

hi guys

i wonder if someone on here could shed some light on a electrical problem .

i have a twin engine aquabell and when i start the port engine it fires up straight away but when i go to start the starbooard engine the amp meter shows a 50 amps discharge and the engine will not start unless i turn the key a few times . the problem is still there if i start the starboard engine first then the port amp meter shows a 50 amp discharge and the engine wont start.

i dont think its abig problem as i am still using the boat ,its just a annoying problem that i need to fix

 

[kashurst]

when the first engine starts does it spin easily or is it a bit slow to get going?
do you have separate batteries for each engine?

if so have you tried linking them together(usually a switch to do this)

sounds like either a dying battery, or a poor connection in the starter circuits. check out the negative connections as you problem appears to be happening when one engine has been started.

If you have a multi meter can you measure the voltage at the starter motors as you try and start them, and do the same for the battery banks. This will show you where your problem lies.

 

[Jim@sea]

Try swapping ignition switches round and see if the problem changes engine. You have the advantage of having 2 identical engines. then try swapping starter motors, by doing this sort of diagnostic by elimination if you cant sort it, at least you can tell a professional what you have tried if you have to call one in.

 

[tinkicker0]

You have not made it clear whether the engine spins without starting or not.

If it does not spin, I would be looking at your starter solenoid first. It may be that the copper bridge is worn or dirty and not making a good connection.

A starter motor on a diesel will nominally draw about 2% of the base engines rated power as a rule of thumb.

 

[pampas]

Are the engines fitted with glow plugs/heater? If so check that voltage appears in the start posion on the solenoid, might be the ignition switch, 50 amps could be the heaters although it seems a bit high.

 

[PCUK]

He said the problem is on both engines depending on which he starts first so none of the normal checks will be relevant.

 

[Seahope]

Try swapping ignition switches round and see if the problem changes engine. You have the advantage of having 2 identical engines. then try swapping starter motors, by doing this sort of diagnostic by elimination if you cant sort it, at least you can tell a professional what you have tried if you have to call one in.

I love the theory, for my boat this would be totally impractical. I was unable to work out how to get to my starter motor and needed to call in a professional to look at mine when I had a problem years ago.

 

[Alpha22]

I would guess a single starter battery for both engines. Or at least a single bank.

The problem is not enough current being delivered. This could be due to old, duff, undercapacity, undercharged battery, and/or high resistance connection somewhere in the battery cabling/switching.

First engine to start gets the fully charged hit on the starter motor and starts fine. The second engine now has a partially discharged battery to attempt a start. The starter motor gear is thrown into the flywheel but is unable to turn as there is not enough 'omph' left in the battery. This shows as a 50A drain as the stater motor is effectivley stalled.

All works well a few minutes later as some charge has now been put back in the battery by the running engine and/or the battery has recovered from the previous start.

 

[dave p]

First engine to start gets the fully charged hit on the starter motor and starts fine. The second engine now has a partially discharged battery to attempt a start. The starter motor gear is thrown into the flywheel but is unable to turn as there is not enough 'omph' left in the battery. This shows as a 50A drain as the stater motor is effectivley stalled.


that is exactly whats happening , but when the boat was out in april 2011 i put four new batterys on the boat ,i have two batterys per engine on battery selection switchs ,new alternators ,all new 12mm bore battery cables ,new ignitions on both dash panals ,and about 2 weeks ago i put two new starter motors on,

 

[kashurst]

I think you have a dodgy connection in the negative leads. As both engines have their own batteries and own starters, if they had totally independent wiring a starting problem would be specific to one engine and could not switch sides as you describe (or arguably both but separate). However usually on boats the negative or ground return is connected up so that the negative terminal of your battery banks are connected together. Usually this is a parallel connection so that the engine batteries can be charged from either alternator through a diode block etc. i.e. a negative cable goes from each engine to each battery bank, with a separate cable that connects the engines together. You may have a series connection where by all the starter current goes through one connection at some point. i.e. the engines are connected together, one engine is connected to the battery bank negative and another connection links the two battery bank negatives together. this is getting hot and loose on the first engine start up and is too resistive then to permit the second engine start up after. (does that make any sense???)

Anyway, To try and help you out to separate a battery issue from an engine issue from an wiring issue, get a long pair of jump leads and link the relevant battery bank to the correct engine and if engine is OK and battery OK, it will start willingly. try and start/stop it a few times. (if necessary just move the batteries near to the engine) connect the positive battery to the big positive starter motor connection, negative battery to a good contact point on the engine (lifting eye, big bolt head etc but get the paint of it first)

Then swap the jump leads to your other engine and other battery bank and repeat the test. I suspect both engines will start fine (check you batteries are charged up first!). If that works then use the negative jump lead to connect one battery bank negative to the same engine negative, and the other jump lead again from the relevant battery negative to the relevant engine negative. Both engines should start independently and repeatedly.
Again if that works you have got a poor negative engine/battery connection somewhere.

Assume nothing is connected properly unless you have taken it to bits and examined and cleaned it ( even a thin film of grease will be an issue, clean with meths not petrol), because the start up current on engines is really big and any slight resistance is a problem. I had a similar problem a few years ago with a generator. In the end it was the brass threaded rod used as a battery connection. Overtime it had been overtightened and it had stretched. Inside the brass rod had become hollow and the smaller cross sectional area created a high resistance when trying to start the genny. I only found it by taking it apart and reconnecting it when it snapped in half and all was revealed.

 

[dave p]

cheers guys for the advice ,i am just going out to the boat so will have a look ,think i will start with the earths then go from there .

 

[dave p]

well i have sorted my starting problem out ,i had to get a marine engineer out to have a look in the end we found i wasn't getting enougth amps to the starter from the ignition so i re-wired everything from the the ignition to the the starter moter with 2.0 wire and i put 12v 70 amp relays in which have solved the proplem

dave