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Cooked wiring from Alternator


Christophe lamby pie
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Here we go again, one problem fixed now another!!!

 

Can anyone help with this alternator query.

 

I had a new Beta 38 fitted in March 2013 which has 2 alternators, one for the starter and the other or the domestic batteries.

 

Until yesterday I've had no problems with it (although when it was fitted I was told my wiring is a bit odd). I went to start the engine and the warning buzzer continued to beep even after the engine was running. Also the domestic battery charge lamp was out. Then I noticed the smell of burning plastic and on opening the boards was greeted with a cloud of acrid smoke.

After turning the engine and batteries off and letting the smoke clear I found the green/yellow (earth?) wire from the alternator had melted off most of the insulation and the wire was exposed and snapped in places.

I tried to replace the earth cable and turned the batteries on only to hear more cracking and smoke issuing from the repaired wire.

 

I've now disconnected the Domestic Charge Sub Loom (95 Amp) and fortunately because of my odd wiring the smaller alternator is charging both my starter and domestic batteries although it seems at a slower rate and not as deep.

 

I fear the worse that the alternator has died but as a minimum the Domestic Charge Sub Loom (95 Amp) will need replacing - am I missing anything obvious do you think?

 

I'm very much an electrical novice, so please use idiot proof terms for me

 

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Here we go again, one problem fixed now another!!!

 

Can anyone help with this alternator query.

 

I had a new Beta 38 fitted in March 2013 which has 2 alternators, one for the starter and the other or the domestic batteries.

 

Until yesterday I've had no problems with it (although when it was fitted I was told my wiring is a bit odd). I went to start the engine and the warning buzzer continued to beep even after the engine was running. Also the domestic battery charge lamp was out. Then I noticed the smell of burning plastic and on opening the boards was greeted with a cloud of acrid smoke.

After turning the engine and batteries off and letting the smoke clear I found the green/yellow (earth?) wire from the alternator had melted off most of the insulation and the wire was exposed and snapped in places.

I tried to replace the earth cable and turned the batteries on only to hear more cracking and smoke issuing from the repaired wire.

 

I've now disconnected the Domestic Charge Sub Loom (95 Amp) and fortunately because of my odd wiring the smaller alternator is charging both my starter and domestic batteries although it seems at a slower rate and not as deep.

 

I fear the worse that the alternator has died but as a minimum the Domestic Charge Sub Loom (95 Amp) will need replacing - am I missing anything obvious do you think?

 

I'm very much an electrical novice, so please use idiot proof terms for me

 

That is not just overloaded wires, that is a dead short. Try following the cables from the alternator to make sure there are no + and - bare ends or bare cables touching each other anywhere.

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I trust that you have a very large (25 sq mm CSA min.) negative bond between the battery negatives and the engine block or starter negative stud.

Also how thick was that earth wire. i do not like the sound of "green and yellow earth wire. It makes me think it may be domestic type cable with thick conductors in it and that could be subject to fatigue fracturing by vibration.

 

As long as the cable was thick enough and correctly wired I agree that it sounds like a dead short so do what Bizzard says and check for short circuits.

 

If the alternator is a true insulated return unit and one or more main diodes failed short circuit that could produce the symptoms BUT would have expected the short current to blow the diode open circuit very quickly.

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Apart from what all the others say this bit is a little worrying.

 

 

I had a new Beta 38 fitted in March 2013 which has 2 alternators, one for the starter and the other or the domestic batteries.

 

Until yesterday I've had no problems with it (although when it was fitted I was told my wiring is a bit odd).

 

So who ever fitted it noticed you had odd wiring but obviously diid not investigate and put it right if it needed putting right.

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The green/yellow small wire on the domestic alt B+ terminal should only connect to the indicator light on the control panel via a small relay operated by the ignition switch. It does sound like this is shorted to -ve or earth/hull somewhere. There is no fuse protection on this wire. You could safely disconnect it at the alternator as a 'get you home' measure.

 

NB it also may connect to the purple wire in the harness via the relay, which can be used for an external alternator controller, so this wire could be shorted to earth.

 

Richard

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Thanks all.

The alternator came with the engine from Beta and was fitted at the same time - I would hope Beta would supply equipment fit for purpose and not dodgy earth wiring?!?!?

 

Do you think the alternator is US or how do I check?

 

Many thanks


Sorry - assumed it was earth because of the colouring

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Sounds like the OP could do with the DC clamp ammeter recommended in the other thread, would likely make it a 5 minute job:

 

http://www.canalworld.net/forums/index.php?showtopic=60551&p=1181563

 

Just switch off everything, connect a car headlight bulb across the isolator, then trace where the current is going to and coming back from, should lead you right to the fault. smile.png

 

cheers, Pete.

~smpt~

Edited by smileypete
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When the engine is off this wire is fed via the warning lamp bulb only when the ignition is on. As the bulb will limit the current a short on this wire will have no effect with the engine off. However when the alternator is charging the B+ terminal will be fed from the field or axillary diodes in the alternator so any short on that wire or the purple one Ryland mentions would allow excess current to flow UNLESS that current overloaded the field diodes and they burned out.

 

Personally I would see if I could find a short as described and if so deal with it, insulate the burnt section of wire and try the alternator. If the charging voltage across the relevant battery set is within the 14.2 to 14.6 after a fair period of running I would say the alternator was fine. If it is higher check what Beta say the charging voltage should be and if it is lower than you measure you may will have one or more faulty field diodes. (have heard some Betas are supposed to charge at 214.7 to 8).

 

I agree that you should not start dismantling anything until you have talked to Beta and/or the builder/fitter.

Edited by Tony Brooks
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  • 2 weeks later...

Eventually managed to get the boat back to the chap who installed the engine (after 1 snapped gearbox cable and empty canal between Banbury & Cropredy).

After checking the wiring, alternator, etc he couldn't find what caused the problem but replaced the damaged wiring and checked everything was working which it still is (fingers crossed).

I'm guessing somehow it was a direct or dead short as suggested by Bizzard and others but we were unable to find where.

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