why is the fuse blowing??

My craftsman riding mower, Model# 917.275661 run fine for 20-30 minutes then shuts down when the 20 amp fuse blows, it doesn't appear to be hot and will restart and run right away for a short time when the fuse is replaced. So what is the problem?
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mart wrote:

Hmmm, Wild guess, something is shorting out due to heat, some electrical parts(electronics component) is heat sensitive on the verge of solid failure. Don't keep replacing fuse, it is trying to protect something.
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On Tue, 14 May 2013 00:45:02 +0000, mart

The fuse is blowing because YOU are not blowing <lol>
I'd look for a wire that has worn insulation and is rubbing against the frame. Vibration will cause a worn spot to short out randomly.
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On May 14, 1:45 am, mart

ng-7483...

You need to measure the current going through the fuse. Likely it is overloaded. The likely cause is there is undue load on the system or a short circuit. You will have to identify what it is. You need to do this urgently or something will get damaged.
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On 5/14/2013 1:04 AM, harry wrote:

...

Since he's blowing 20A fuses repeatedly, he already knows the current is >20A. That's good enough--it's not the magnitude of current that he needs to know; it's obvious it's too much. That it is apparently time-related, one presumes as another has already done it's temperature-related and somewhere in the ignition/charging system.

Ya' think???

Well, it would help if had diagram to know what is on this particular fuse if there is more than one or only a specific portion of the system is fused through the one if this is the only one used...
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On Tuesday, May 14, 2013 9:42:40 AM UTC-4, dpb wrote:

You might, but it might not occur to the OP. Most people fit into two major categories:
1. They *THINK* they know how electricity works but couldn't be more wrong. 2. They have absolutely no conceptual knowledge of electricity altogether. It may as well be magic.
People fitting into category 1 would replace the fuse with larger and larger fuses until the problem went away. Eventually the wiring harness would catch fire, ultimately solving the problem.
People fitting into category 2 repeatedly replace the fuse with the correct-sized one, hoping that the problem will somehow heal itself.
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{{
Testing smoke/failure mode has it's place. You can spend a lot of tech time playing guess what or test to failure then replace the intermittant now failed part.
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The OP never mentioned what the fuse is for. If it goes to the engine, the ignition coil may be bad, or a bad capacitor (just replace the cap for starters). But the fuse could be for a headlight, or anything else. I still say there is a frayed wire, second guess would be the cap, then the coil. If it's electronic ignition, it could be that too.
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On Thu, 16 May 2013 00:22:54 -0500, snipped-for-privacy@workshop.com wrote:

Most likely an electric PTO clutch shorting. - or something similar. EXTREMELY unlikely to be ignition related.
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On Mon, 13 May 2013 23:04:51 -0700 (PDT), harry

Just as coimmon on a yard tractor is a corroded fuse holder which overheats and blows the fuse at well within the rated current - but the only way to KNOW is to install an ammeter in place of the fuse to check the current (well there is another way - a clamp on ammeter - but it is less accurate unless you spend more money than necessary)
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On May 14, 7:24 pm, snipped-for-privacy@snyder.on.ca wrote: but

Clamp on ammeters are mostly for AC circuits and the lawn tractor is most likely completely DC, stabilized by the battery, with the charging alternator using a rectifier stack ...
Clamp on DC ammeters are possible, but use a different principle, and all the ones I have seen are much more expensive...
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On May 13, 5:45 pm, mart

ng-7483...

Runs for a short time after replacing fuse, but not as long as when it had been off for a long time.
Sounds like a possibility that the wiring in the motor 'swells' with heat, shifts and shorts out a small section of a turn - fuse blows. Starts cooling down while you look for a fuse, the wiring starts shrinking back until no more short, you replace fuse, and it runs for a while, but not as long as before.
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Too much current? :)
--
There is always an easy solution to every human problem -- neat,
plausible, and wrong." (H L Mencken)
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