wire ampacity and temperature derating

Status
Not open for further replies.
Some thoughts .......

If these are being used in an automotive environment, are they pushed up against the radiator ?
How much clearance is there between the blades and radiator ? Is there any play in the shafts that allows an aparrently large clearance to reduce when under load ?
Do the fans draw much more current when an air obstruction (i.e. the radiator fins) are close to the fan ?
Are the fans being used the right way round ? If a car is travelling at 60+mph and they are trying to blow against the wind hitting the front of the car, this will massively increase the current draw.
 
There is about 2 inches space from the radiator face, although they are used on various setups. We have mounted some fans straight onto radiators on some projects, the radiator should not prove a significant obstruction.

the vehicles are rock crushers so I guess mostly work at a standstill. The fans don't seem to draw more power when obstruct or even stalled completely we can't understand this. I am seeing normal current draw when about 60% of the fan area is blocked off for testing (screwed down to a small pallet to stoop it taking off)
 
Copper melts at 1083 C, so there is another 1000C to go before you see your problem. Look for a short either to the inductor core (If it is conductive and grounded) or from the brush holders to ground. If the core is grounded, then you are looking at the insulation breakdown temperature and you are on the right track.
 
The inductor cores are not grounded, as it is the inductors that are the point of failure due to sheer melting, I can only conclude that for some reason the inductor temperature is reaching 1083.62C The motors in fact cease to function when the coil melts
 
Last edited:
Do they run again if you jumper the melted inductor?
 
Maybe you could measure the resistance from brush to brush and brush to ground while turning the fan by hand?
 
Sure, but if you turn it slowly you can see if there is a short when it is stopped.
I think you are looking for a short, not a temperature problem.
You mentioned brush wear. Maybe they are down to where they become cocked or even the brush wire shorting?
 
yes it could be a shorted coil in the armature, although those windings look fine and there are a number of them so no single winding sees power for ling where as the inductors do.
 
the vehicles are rock crushers
Click to expand...
Rock crushers? As in big yellow conconstruction truck.
I was thinking this was in a car.
OK is it still a 12 volt system?
Is there a lot of dust?
How hot do the hydraulics on that thing get?
New theory;
Dust something else stalls the motor, the Hydralics heat up, the ambent temp goes up, insulation on the wire in the coil melts, coils short out and the hole thing heats up to the melting point.
it may be posible for the coils to be made of cheep Chinese copper that has a higher resistance and lower melting point.
Just some thoughts, Andy
 
It looks like the coil is smaller wire than the inductor so I doubt it's a shorted coil, but why don't you measure them while your measuring for the shorts.
 
If you look at your second picture it looks like the brush holder is in contact (and bridging) the commutator.
 

the used ones are a bit dusty but not that bad
 
Status
Not open for further replies.

Similar threads

L
spot weld wire to wire?
Replies
15
Views
2K
ChrisP58
A ferrite core & 6' of 24AWG enameled wire
Replies
7
Views
2K
ThomsCircuit
A
  • Question
enamelled wire
2 3
Replies
57
Views
6K
ZipZapOuch
  • Question
What is the maximum temperature of a lithium battery when overloaded?
Replies
5
Views
2K
aliarifat794
A
  • Question
How can a clamp meter be used to measure the amperage of a wire or cable from the phase and neutral of two strands?
Replies
6
Views
2K
Nigel Goodwin
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…