Cooked engine loom question, Looking for cause.

[Barking Mat]

Also bear in mind how starter motor solenoids work, there are actually two sets of windings - pull-in & hold-in. Pull-in takes the most current and has a larger coil, physically & electrically. It is wired from term. 50 to the output stud (so that it has zero current draw once the contacts are closed). the hold-in coil is wired from term. 50 to ground, and will obviously be drawing a lesser current whilst the starter is engaged.

It's not beyond the bounds of possibility that loose or corroded terminals on the solenoid cap battery & motor contacts (or indeed inside the solenoid cap) can cause volt drop and cause the pull-in coil to still be active albeit at 1-2VDC whilst cranking, but passing a much higher current than intended. Typically, this will show itself as a warm/hot starter solenoid after a few cranking attempts.

So, yes, once again good point, but this winter just gone, I rewired all three similar boats, to cure stupid starting issues, due to had contacts, and undersized cabling.

 

[Barking Mat]

Also bear in mind how starter motor solenoids work, there are actually two sets of windings - pull-in & hold-in. Pull-in takes the most current and has a larger coil, physically & electrically. It is wired from term. 50 to the output stud (so that it has zero current draw once the contacts are closed). the hold-in coil is wired from term. 50 to ground, and will obviously be drawing a lesser current whilst the starter is engaged.

It's not beyond the bounds of possibility that loose or corroded terminals on the solenoid cap battery & motor contacts (or indeed inside the solenoid cap) can cause volt drop and cause the pull-in coil to still be active albeit at 1-2VDC whilst cranking, but passing a much higher current than intended. Typically, this will show itself as a warm/hot starter solenoid after a few cranking attempts.

Are you talking about in side the starter motor ?

Brand new starter 8 months ago.

Not ruling out anything though.

 

[Ubique]

Yes, internally in the starter motor solenoid.
To test, put a voltmeter across the two large terminals (battery +ve & motor +ve) volt drop should be less than 0.2VDC with the engine cranking. It's easier to test if you pull the wire off the fuel solenoid to prevent the engine starting.

 

[RichardM]

What does the starter solenoid look like? On the bike (600cc single) I have had it before that when the battery voltage drops and it doesn't fire up first or second turn over, the solenoid connectors can weld together so that even though the engine has started the solenoid contact keeps draining the battery.

 

[Barking Mat]

Yes, internally in the starter motor solenoid.
To test, put a voltmeter across the two large terminals (battery +ve & motor +ve) volt drop should be less than 0.2VDC with the engine cranking. It's easier to test if you pull the wire off the fuel solenoid to prevent the engine starting.

No fuel solenoid, it's a lift pump.

It's not the engine cranking, which is the issue, it's the lack of, caused by excitation circuit playing up.

 

[Barking Mat]

What does the starter solenoid look like? On the bike (600cc single) I have had it before that when the battery voltage drops and it doesn't fire up first or second turn over, the solenoid connectors can weld together so that even though the engine has started the solenoid contact keeps draining the battery.

Not a flat battery situation, battery was well happy, excitation wire had cooked ++.

 

[Ubique]

Yep, I understand that, but volt drop across the 'heavy' contacts on the solenoid will cause excessive current to be drawn through the 'pull-in' coil in the solenoid.

 

[Ubique]

Here's the first circuit diagram I could find - circuit 'B'

If there is any volt drop (resistance) across the heavy contacts between battery +ve and the motor +ve, the pull-in coil will be used to draw the proportion of the current required to fulfil the starter current requirement - which will overheat the circuit.

 

[ajlelectronics]

My vote is for starter solenoid too.

 

[arther dailey]

Yes - yes - yes...

Fuse is there to protect the wire - wire size is there to take the current.

But at 12/24v - nobody ever gets the wire cross section right for marine applications - don't know why - but they just don't...

few people realize or know about cross section of wire and power capability of from my experiance .

 

[Seadog]

it wouldn't be the first time low voltage has caused a high current to flow

 

[ajlelectronics]

The early K1200LT had that issue. Low Voltage cranking caused a welded solenoid and many fireworks! Later models had a low Voltage inhibit relay.

 

[8ob]

You can get a situation on diesels where the starters will carry on cranking, if its not going to start and the battery is less than ideal the torque loading on the starter pinion is too much for the solenoid return spring to overcome.

Bob

 

[Seadog]

You’ve heard of Ohm’s Law, too.

What's that?

 

[Barking Mat]

Well, three odd hours later, one of the culprits was the loom wire to excite the starter was mainly 6mm2, but the last 70cms was 1 or 1.5mm2, this last bit was cooked, as was the starter motor, there is no starter relay, it's the key barrel which does that, which was changed to by precaution.

Suspect starter motor got stuck on, but not 100% sure.

 

[Ubique]

You’ve heard of Ohm’s Law, too.

Its nothing to do with Ohm's law, its P=IV, so if for example a kettle draws 3kw, that's 12.05A at good old British 240V, but 13.04A at that foreign 230V, electricity meters monitor current flow, so you'll get charged more to boil a kettle with harmonised EU voltages.

Back to the starter, if there is sufficiently high resistance across the solenoid contacts to cause volt drop, then the motor will try and draw the remainder of its running current through the pull-in coil and associated wiring, thereby causing an overload. Looking at the photo, I'd say that was the cause as the link from the solenoid to the motor generally gets fried like that when the solenoid contacts overheat.

 

[500e]

Check the rest of the fleet Mat

 

[arther dailey]

What's that?

who ever s ohme first starts cooking the meal

 

[PhillipM]

Its nothing to do with Ohm's law, its P=IV, so if for example a kettle draws 3kw, that's 12.05A at good old British 240V, but 13.04A at that foreign 230V, electricity meters monitor current flow, so you'll get charged more to boil a kettle with harmonised EU voltages.

Back to the starter, if there is sufficiently high resistance across the solenoid contacts to cause volt drop, then the motor will try and draw the remainder of its running current through the pull-in coil and associated wiring, thereby causing an overload. Looking at the photo, I'd say that was the cause as the link from the solenoid to the motor generally gets fried like that when the solenoid contacts overheat.

Well no, because the kettle is a resistive load, therefore what will actually happen is it just won't give you 3kw on the 'foreign 230v' - it'll give you 2.75kw instead.
Much the same as adding resistance to a 12v/24v DC circuit will reduce the current. If you have a pull in coil with the output hooked to the starter input, it's plausible to burn that out that way - but more resistance leads to less current.

It's not a fixed power value, it's a fixed resistance.
It's no good using the right equation if you can't use it the right way around.

 

[Barking Mat]

Check the rest of the fleet Mat

Yes, good comment that man.