Blown engine fuse

windlipper

windlipper

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My Volvo Penta with saildrive blows the main engine fuse while the engine is running which means it cannot be restarted without a new fuse. It then blows that one. Checked all the wiring, no sign of any problem.
I've just had a rope cutter fitted and this meant the anode on the saildrive had to be modified.
Is there any possible connection between this and the blown fuses?
 
I dont think so, the high amperage needed for starting rules out a starter fault, I'd be thinking its charging side possibly the alternator, regulator / rectifier gone which if gone allows the volts to rise with the engine rev's then blows the fuse

another point is there are two ways a fuse blows the first is when the positive connects straight to earth and blows the fuse
the second when the circuit is over loaded and you'll see the fuse wire melt

but hey could be wrong its always difficult when some things not in front of you

Mick
 
Sounds like the fuse is doing what it's supposed to, I'd have a very careful check that your wiring isn't chafed. It won't be anything to do with the anodes.
 
Thanks, yes the fuse actually melts, all four have now gone and I have another fuse block ready for when I have found the fault. My first instinct is also that it is an alternator fault.
I just can't get it out of my mind that all was fine until the rope cutter was fitted.
Your opinion is much appreciated, cj=heers.
 
When I first hd my 2030, I had this and luckily there was a electrickery expert with me. In the little black box that contains the relays for the starter and glow plugs is a - 'something'. I can't remember what actually it was called as this was 10 years ago. On one ofthe red wires I think, it is a small cylinder about an inch and a half long and 3/8ths in diameter. That was rubbing against the side of the bracket and my chum found it had a break in its insulation or something. Anyway it was shorting against the metal bracket and blowing the fuses instantly. It was wound with insulating tape and left dangling which it has done sucessfully for 10 years or so. I recall, it was held in a small circular metal bracket and that was I think breaking the insulation of the cylinder. I never could see the bare metal that caused the short but the bandage of insultating tape solved the problem. Volspec's take on it was that it 'happens'
 
You dont say which engine or which of the Volvo panels is fitted, so cannot be sure I am looking at the right wiring diagram. With or without a key switch, with or without the extra gauges (volts, temp and pressure)
I deduce though that you have four fuses of which only 1 is in use.

Basically it supplies all the power to the panel but then of course power is fed back from the panel to energise the relays for the glow plugs (I assume we are talking diesel engine? ) the starter solenoid, the engine stop solenoid and if applicable the earthing relay.

At what point does it fail.
If just the main isolator is switched on is it OK?
Is it OK when the glow plugs are energised?
Does it fail when you attempt to operate the starter?
Does it only fail after the engine is started ? That'll involve a lot of head scratching I think!

I cannot believe it has anything to do with fitting the rope cutter or modifying the anode. That should not have required access to any of the wiring at all, not even to the inside of the boat. I take it that's the ring anode behind the prop.

I dont think it has anything to do with the alternator, its output goes directly to the battery although there are connections for the warning light, and the tacho.

Do you have a wiring diagram in your owners manual to help you? Older ones do newer ones dont.

EDIT

I have heard something along the lines of what Tiller girl is saying before (or it could be the same story of course) There is a wire in that black box that can chafe. I totally forget all the details as well but it is something well worth investigating.
 
another point is there are two ways a fuse blows the first is when the positive connects straight to earth and blows the fuse
__________________________________________________________________

And that is the most likely cause.
 
sounds like the engine vibration is causing the short otherwise the fuse would probably blow as soon as ign sw turned on and or starter engaged, looking for broken wire insulation is difficult but in my experience with motorbikes etc it is sometimes easier to spot the telltail burn marks on the engine/frame where the short takes place FWIW.
 
Thanks for the replies. Unforunately I am now 130 miles from the boat so cannot instantly check the suggestions. I will collate and take with me when i go in a few days.
The engine starts OK when there is an intact fuse and runs normally. The fuse then blows while the engine is running,this can be seen because the tacho stops working. Of course then it will not start unless a new fuse is put in.
It is a Volvo 2020 and only 3 years old
 
Best friend for this job would be a really bright white LED torch to help look for the short. That and a dentist style mirror to see behind things. Best of luck
 
Has there been any addition or modification to the original Volvo circuitry?
Theoretically, if you simply switched on the ignition(don't start engine) and then carefully inspect with gentle movement of the cables, you should blow the fuse and see the spark that caused it.
The running engine only puts current between the alternator and starter motor connection, so if no sterling/splitters etc., should not be in the equation.
If it blows without movement (or the engine running) how long does it take?
Any smell or heat detectable? ( will be purely electrical if engine off). Before you blow the last fuse, try replacing it with a 12v 10watt. bulb which will light up when the fault is "on". You should be able to flash it on and off by waggling the cables - if that's the source of the problem.
Good luck.
 
out of interest, how would you go about fitting the bulb into the fuse connection, it seems like a good idea just not sure how to implement it if I get into the same situation as OP
 
Now I know the engine type I can be sure to look at the correct wiring diagram and have a good think.

I reckon Tiller girl may have the answer esp as the short occurs once the engine is running.

Billjerat's suggestion with a bulb in place of the fuse sounds like a good one.

In that black box the red wire(s) are energised once the isolator is closed. So switch on and have a wiggle of the red wire.

The red/blue wires are energised once the panel switch or key switch is turned on. So next step is to switch that on and have another wiggle of the red/blue wire.

I think the cylindrical object may be the "excitation resistor" if so it has the red/blue wires connected to it.

Hopefully its one of those.
 
Yes "excitation resistor" rings a bell. But there's only one thing like it inside the Relay 'box'. Given the nature of the box, you wouldn't be able to see any spark if it shorted. Having the wiring diagram for the 2030 here, the Exitation resistor is on the Blue/Red wire
 
Probably completely irrelevant but who knows!! I had for months problems with my MD2030 electricity been cut off after turning off the engine and then on by itself, low readings of the alternator outcome on splitter etc, etc. All these crazy things were due to the alternator earthing wire that was wounded (almost cut actually). So, why not check that as well. It's a couple of seconds work and you have nothing to loose. And honestly I have no idea why it caused me all these strange symptoms.
Good luck.
 
-TabernacleMan.. It's a good idea to have a decent sized bulb soldered to a couple of wires. It can be jammed anywhere for testing or used as a worklamp to see in the bilge etc.
 
Mm.. got one of them for testing circuits etc, but wondered about the actual mechanics of jointing into the fuse holder on the engine block which I think the volvo has, cheers
 
[ QUOTE ]
Mm.. got one of them for testing circuits etc, but wondered about the actual mechanics of jointing into the fuse holder on the engine block which I think the volvo has, cheers

[/ QUOTE ]The fuse block has male spade terminals, the engine wiring has female spade terminals. So a test bulb would need male spade terminals on the end of its wires, to plug in to the engine wiring.
 
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