Fuse Blowing when trying to start inboard diesel

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Eastanglian87

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Hi im hoping anyone can help or guide me in right direction, i have searched the threads but cant find much.
When trying to start engine it turns over a few times and then the main fuse blows (150amp mega Fuse)

Any advice is appriciated
 
Fuse blowing

Have you tried turning the engine over by hand when cold, does it do it when it is warmed up?
Have you checked the fuse rating for the engine,

if you look at the fuses does it glow red hot and just Melt slowly or does it just go with explosive force?
 
Not being an expert, but just applying some basic fault finding principles...

The fuse blows because the act of starting the enginge draws >150A, so the problem is to discover what is causing that. Options for me would include a short in the starting circuit, or something vastly increasing the load on the starter to draw more current... I'll let others add their 2p....
 
Ive found some basic checks online to carry out
*dis connect wire from solenoid, try starting again and if the fuse blows its thee wire,
Alternativly check resistance from end to engine ground reading should be high, if its grounding instulation worn somewhere or salt water in bilge?

Would you say there good tests to check?

Havent tried starting off starter as had bit of fuel trouble last week so best not to, couldnt see how fuse was blowing glowing or sparking as was coverd will check with cover off next time.

Dont know if its anything to do with me taking batterys off yesterday to charge , i put them back on today and this happend.
 
The first question has to be what make and model of engine is it you have?

150 amp isn't much cranking current, 12 or 24 volt. Have you altered the wiring in any way?
 
This could be caused by a many things but first things first, check your battery voltage, it should be 12.5 or above, any less and the fuse could blow. Its all about amps and inductive load . . . . .

Yes you charged them but a day probably isn't long enough, check the voltage.

IF the voltage is OK we have to have another think.
 
That will have a starter motor rated at around 2.5kW- which will draw around
200 amps while cranking the engine, and more than likely double that to start moving a heavy flywheel.
 
Just read it is 150Amp, I suspect that you either have an internal short inside the starter motor or the big fat battery positive lead from the fuse has chaffed between the fuse and the starter after the starter solenoid and all it does is connect the battery positive to earth via the chaffing or the internal short.

As others have said above, you need to follow the lead from the fuse (which blows) and inspect it very carefully and if you find no fault between the fuse and the starter/solenoid, then you will need to disconnect it at the starter end, protect the free end of the lead very carefully with insulating tape and re try to start the engine. The fault either is still there or is gone.

If gone then it is internal to the starter/solenoid and you will need to remove the starter for further inspection. :(

If when the lead is disconnected (and insulated carefully) and you try to restart the engine and the fuse still blows, you have a short to earth between the fuse and some metal (earth) on the engine block?
 
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Is it normal to have a fuse in the starting cct? i thought it was normal just to have cabling direct to the starter motor and earth return via the engine block. As other say 150 amps cranking power is not much. That would blow with a starter motor rated at 2KW. So I would have thought for protection you would be looking at fuse rated at something around 300 amps and that is just not feasable. You would not want that going bang.
 
Spyro said:
Is it normal to have a fuse in the starting cct? i thought it was normal just to have cabling direct to the starter motor and earth return via the engine block. As other say 150 amps cranking power is not much. That would blow with a starter motor rated at 2KW. So I would have thought for protection you would be looking at fuse rated at something around 300 amps and that is just not feasable. You would not want that going bang.
Click to expand...

Some people like to have a main fuse

"mega fuses" available from 100 to 300 amps from Merlin Power store http://www.power-store.com/?id=387
 
The question is:- Did it start before with a 150A fuse?

Like others, I think 150A is WAY too low. I would say that 300A or even 400A would be more like it. The starter can easily draw more than 150A if the engine is cold, I would suspect.
 
I've actually measured the current on a Yanmar 2GM20 starter and it was about 250A peak. It will be more in some circumstances. Mega fuses are slow blow design so fault current has to be high and sustained. You need to know what your starter current should be and check if the Mega fuse will sustain the current for sufficient time. You may have some fault condition in the engine that is increasing the load if it worked previously.
 
When you charged the battery were they dead flat and is it possible that you put the charging leads on back the front (+ lead to - on battery and - lead to + on battery)

With a dead flat battery and a old style charger it is possible to charge it up back the front and this will cause the fusible link to blow

The other thing is when you fitted the batterys back in have you connected the correct lead to the correct terminal

Regards Don
 
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Spyro said:
Is it normal to have a fuse in the starting cct? i thought it was normal just to have cabling direct to the starter motor and earth return via the engine block.
Click to expand...

That is normal, but it's not unheard of to have a fuse. I do, because I don't have a switch on that circuit, so I wanted some protection against fire in the unlikely event of a short in the engine bay while the boat was unattended.

Spyro said:
I would have thought for protection you would be looking at fuse rated at something around 300 amps and that is just not feasable.
Click to expand...

Perfectly feasible. I have a fuse on top of both the domestic and engine batteries. The domestic one is 100 amps, the engine I can't remember if I picked 300 or 500 in the end.

Pete
 
Thanks for all your messages yes boat has worked fine previously with the 150amps fuse, only now i have the problem and have no idear why, Im getting down to the boat in the morning to do some checks, Hoping to try get done myself even though wires/electrics is not my strong point.
 
Spyro said:
Is it normal to have a fuse in the starting cct? i thought it was normal just to have cabling direct to the starter motor and earth return via the engine block.
Click to expand...

A fuse in the battery lead can be quite a good idea.

Let me tell you about a problem I have recently been dealing with on a yacht. This yacht had a major wiring loom failure when the grey water bilge pump failed, bearing seized and the wiring to the bilge pump started to get hot and melt. That in its self is not a problem BUT the wiring was tie-wrapped and taped as a bundle with a load of other wiring (nav lights, engine starting and charging circuits, forepeak lighting etc) right back to the fuse panel. As the wiring got hot, and before it tripped out its own fuse, it melted into and shorted together all the other wiring in the major loom, including the big fat battery lead to the starter solenoid which did not have a big fuse. Once that was shorted to earth, it went into avalanche mode and did enormous damage to the wiring as you can appreciate! :eek:


Spyro said:
As other say 150 amps cranking power is not much. That would blow with a starter motor rated at 2KW. So I would have thought for protection you would be looking at fuse rated at something around 300 amps and that is just not feasable. You would not want that going bang.
Click to expand...

Even though the fuse is rated at 150 Amps, I suspect you will find it is possibly capable of handling double that current for 10 seconds or so. I think it really is a 150 Amp fuse with a 300 Amp peak rating for no more than 10 seconds and even the 10 seconds would probably be up to 15 or 20 max before the fuse finally blew, plenty of time for normal start operations. :(
.
.
 
lenseman said:
This yacht had a major wiring loom failure when the grey water bilge pump failed, bearing seized and the wiring to the bilge pump started to get hot and melt.
Click to expand...

I feel sorry for the owner :( - didn't they have a fuse in the bilge pump supply?

Having no gas or inboard the wiring is the thing I worry about most. I made sure on my boat that there are no wires at all that leave the positive terminal on the battery that don't have an in-line fuse connected within a few inches. I really hope if I ever have a failure on some cable or other or the main fuse/switch panel then this will help protect me... but I have the advantage of no inboard engine starter to supply.
 
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