Motor keeps blowing fuse after a period of time ??

[gray]

I have a pair of electrically operated gates (underground motors). One leaf has always worked perfectly OK, with no problems. The other is progressively blowing fuses more and more regularly.

The motor is a forward and reverse (ie 2 windings with a phase shift capacitor).

The motor winding resistances are the same as the good one.

Why would the fuse blow, with more and more regularity. Any ideas.

I have swopped the motors connections over to proof that its not the control box causing the problem.

One thought was maybe the capacitor is going faulty ?? But do they go faulty and then repair themsleves.

As when I open and close the gate, it works perfectly OK for say 7 days, then the fuse blows. I replace the fuse and I then get another 7 days out of it.

[The Natural Philosopher]

Because its under more load.

Motors draw current according to the load.

Not generally ;-)

Probably you are on the limit, and thermal cycling is the last straw that breaks the fuses back.

Strip, check everything for free running, and then grease/oil any bearings or sliding stuff. Also, if the gates swing, check that the pivot axis is truly vertical, otherwise the gate weight will be adding to the load.

[Usenet Nutter]

Strip ?

Does he really need to take his clothes off to do all that? and as for checking everything for free running ...

[The Natural Philosopher]

Go back in side your cave, Troll!

[NT]

a few likelyish possibles:

1. greater load - eg it only takes a few degrees of tilt on the gate to make it noticeably harder to turn
2. muck in motor or gearbox
3. partial short on one winding - you wont spot that with a resistance measurement, its hte inductance it affects mainly
4. there are different types of time delay fuses, they're not all equal, and replacing with the wrong type can cause this

NT

[Rick]

depends on capacitors ... many electrolytic were designed with self healing built in.

[Ian French]

The fact that the motor winding resistances are the same is not an acid test that the windings are OK. For example a short between 2 physically adjacent turns would not effect the resistance very much but would LOWER the Inductance of the winding considerably, causing a much HIGHER current to flow, thereby blowing the fuse. As to why the motor is OK sometimes but not others is less clear, possibly these overcurrent episodes weakens the fuse over time (this does happen) and eventually it can stand no more stress. I notice that the motors are underground, can they get wet ?, are they sealed, ? does this happen when it rains, are all things that you should consider. Somebody mentioned intermittently faulty capacitors, other types than electrolytics can self heal, see this article

luck. Ian.

[John]

Good luck.

Given that it is a gate mechanism I would first check for mechanical friction / lack of lubrication/ mis-alignment, etc

[gray]

As the gate post is a rustic softwood farm type, it does tend to warp and bow dependant on the time of year and weather conditions.

The problem is getting an average for it work all year, and as the gate motor/gbox is bolted to the bottom of the gate, it has no leaway.

Any ideas on how fix the bottom of the gate to the gbox, but loosely ??

Not possible (I think) as IP66 rated.

Any ideas on how to check, and why ??

The fuses are right for the job 'quick blow'.

[gray]

This particular motor/gbox is always in dampness, for some strange reason. The good motor/gbox box is perfectly dry. Even thou there are many holes in the housing to the outside world.

Weather conditions do not seem to have any effect, as the last time with the housing damp. I opened the gate 40 odd times perfectly OK, so much so that the housing cover over the motor was beinging to dry out, then the fuse blew. New fuse fitted and it worked perfectly OK (last Wednesday, 5 days ago).

The motor/gbox is IP66 rated.

May be I will have to take the motor/gbox out and dry it in the house. Then get a fan heater and dry the housing out. Put it all back together again, and then silicone seal all the holes up (bar the one where the shaft comes out to drive the gate).

Yeh I had read that pdf paper.

I was wondering if the phase shift capacitor was going UTS. But would the capacitor work fine for a bit, then blow, then heal itself and at the same time blow the fuse, and then work fine again for a bit ??

Next time the fuse blows (my prediction is next Wednesday, 3 days time) I will swop over the good gate capacitor with the bad gate capacitor, and see how it goes.

[NT]

With no pic? :)

measure rms current draw.

No wonder...stick some time delay fuses in, no-one runs motors on fast fuses

NT