60A fuse blowing

[WinterDeere]

Do you have this meter? Curious because one review says: "The amp meter part has never worked and didn’t even know it until I needed it for the first time. Everything else is great but I got it for the amp clamp".
Maybe he got a defective one.

Yes, I have that exact meter, and it works well enough for the home user. The low-end drop out is higher than listed, it won't measure 340 mA Christmas light strings without making a few turns around the clamp, but Michael Faraday figured out the solution to that way back in the 1830's.

I had two vintage Amprobe meters, but my father's (AC / DC 1970's? vintage) was stolen by a contractor working in our house, and my grandfather's (AC only 1940's? vintage) reads about 20% low. I should take the time to figure out how to adjust or repair grandpa's, but there isn't a lot of information to be found for these on the web.

I use both analog and digital. I have this ammeter and it works, I'd rather see the analog movement than flashing numbers for this application.

Agreed. Analog is definitely better for seeing anything quick... unless you have an o'scope.

That fused 60 amp circuit goes many places and my curiosity is what the current draw is with glow plugs disconnected. It's possible having a load then adding plugs blows fuse.

I like zzvyb6's ungrounded starter theory. Seems a reasonable possibility.

 

[hayden]

Yes, I have that exact meter, and it works well enough for the home user. The low-end drop out is higher than listed, it won't measure 340 mA Christmas light strings without making a few turns around the clamp, but Michael Faraday figured out the solution to that way back in the 1830's.

I had two vintage Amprobe meters, but my father's (AC / DC 1970's? vintage) was stolen by a contractor working in our house, and my grandfather's (AC only 1940's? vintage) reads about 20% low. I should take the time to figure out how to adjust or repair grandpa's, but there isn't a lot of information to be found for these on the web.


Agreed. Analog is definitely better for seeing anything quick... unless you have an o'scope.


I like zzvyb6's ungrounded starter theory. Seems a reasonable possibility.

The fuse blows before the starter is activated, so it can’t be starter current. I’d guess one of the glow plugs shorts when there is current flow, so an intermittent problem in the plug.

If the plugs are out, you could try applying 12v to each individually to see how much current each draws. My guess is you will find one that shorts.

 

[garry1p]

When you connect the glow plugs one at a time watch the tractor volt meter if one is not drawing enough current to blow the fuse but a partial short when that one is connected there will be a significant voltage drop.

 

[Fuddyduddy1952]

I'm curious with glow plugs disconnected how much current does that 60A line draw? It could be not enough to blow fuse but glow plugs added in circuit blows fuse.
I have a large container of 12V incandescent bulbs. One is 450 watts so about 35 amps. Instead of blowing fuses I would clip that in place of fuse. If it is a bad glow plug bulb would glow bright when bad one is connected.

 

[ldurmon]

I'm curious with glow plugs disconnected how much current does that 60A line draw? It could be not enough to blow fuse but glow plugs added in circuit blows fuse.
I have a large container of 12V incandescent bulbs. One is 450 watts so about 35 amps. Instead of blowing fuses I would clip that in place of fuse. If it is a bad glow plug bulb would glow bright when bad one is connected.

I have not had time to investigate yet but I like your idea. I may get to it tomorrow. Thanks.

 

[ning]

I'm curious with glow plugs disconnected how much current does that 60A line draw? It could be not enough to blow fuse but glow plugs added in circuit blows fuse.
I have a large container of 12V incandescent bulbs. One is 450 watts so about 35 amps. Instead of blowing fuses I would clip that in place of fuse. If it is a bad glow plug bulb would glow bright when bad one is connected.

Wouldn't it always be lit up?
The fuse has current running through it all the time, just doesn't blow unless it's too much current. Swap the headlight in there and you'll have current running through the light instead, not sure how this helps.

 

[WinterDeere]

Wouldn't it always be lit up?
The fuse has current running through it all the time, just doesn't blow unless it's too much current. Swap the headlight in there and you'll have current running through the light instead, not sure how this helps.

The intensity will vary according to the resistance of the glow plug. So if a glow plug is a typical 2 ohms, no matter what bulb you put in the loop, you'll never have more than 6A flowing off a 12V battery, through the series bulb/plug circuit.

But if a glow plug drops to 0.1 ohms due to an intermittent internal short, then up to 120 amps could flow in the circuit, depending on DC resistance of the bulb. Result: Bulb will glow much brighter.

In these numbers, I'm ignoring the resistance of the bulb itself, which is probably relatively low on a 12VDC circuit. I'm no lightbulb expert, but I suspect they have a very high PTC factor, resistance only goes up when they get hot. Measured with your ohmmeter, it might have a much lower resistance than it's rated wattage would have you expecting.

But those numbers don't matter here. Fuddy's idea works, as long as resistance of the bulb is not too much greater than that of the plugs, which is probably why he suggested a big honkin' 450-watter. The bigger the better, since a high bulb resistance (low wattage bulb) will make differences between two plugs much harder to detect.

 

[Fuddyduddy1952]

All I did for 43 years, and actually still do after 11 years retirement is troubleshoot electronic problems. I had to be creative. I never liked blowing fuses ($). A light inserted does two things: now it's a current limited circuit and a dead short lights the bulb. Of course the available current depends on the bulb itself...or parallel it with a shunt.
Of course a 60 amp circuit gets "tough" because now we're at 700-800 Watts depending on available battery voltage.
I prefer a circuit breaker, at least temporarily instead of fuse like this (Amazon of course) $10 one.
Try different things until it trips.

 

[WinterDeere]

Yeah, I know you know your stuff, Fuddy! The guy I replaced at my prior job actually started life as a TV repairman in the 1950's, and his trouble-shooting skills as a result of that history were way better than mine.

But I just thought of one possible trouble with the lightbulb method, here. If the plug is only shorting out when it gets hot, you'll need to be sure your bulb allows enough current flow to get the plug to that state. A bulb rated 450 watts at 12VDC is going to limit the circuit to 37 amps or less, and when figured in series with a 1 ohm plug, you're looking at knocking plug current down something like 25%. That's probably fine when testing just one plug at a time, but you'd want a much larger bulb for testing them in groups.

 

[MinnesotaEric]

I'm on the glowplug bus. Components can test okay with an ohm meter but once current is flowing through them, they can short out.

Think of this like a spark plug coil that allows the engine to start and idle, but it internally shorts out on acceleration of the engine because of increased power draw.