Power tool armature and field coil query

Thread Starter

abjay

Joined Mar 14, 2014
10
Hi

I have just got hold of a drill with a strange problem. The drill is rated at 110v when switched on it turns slowly and starts to smell and heat up.
I have telted the field coil and the armature for resistance and continuity and they both read good. The armature actually looks brand new. I live in the UK and am now wondering if someone has replaced the armature with a 240v one by mistake. Does anyone know if there is a way to check the armature for the correct voltage rating?
 

MaxHeadRoom

Joined Jul 18, 2013
19,485
I guess you mean replace with a 110v in place of 240v?
If the drill says 110v and you are using it on UK 230v then that may be the answer, if this is the usual Universal motor then it will run on low voltage AC or DC for testing, unless it has a Triac type speed controller.
If it runs slow and smells the damage may already have been done.
Max.
 

Thread Starter

abjay

Joined Mar 14, 2014
10
I guess you mean replace with a 110v in place of 240v?
If the drill says 110v and you are using it on UK 230v then that may be the answer, if this is the usual Universal motor then it will run on low voltage AC or DC for testing, unless it has a Triac type speed controller.
If it runs slow and smells the damage may already have been done.
Max.
It looks like someone has replaced the armature,it looks brand new, the drill says 110v I am running it through a 110v transformer, no triac controller, is it possible to determine if the armature is a 240v component?
 

Tonyr1084

Joined Sep 24, 2015
3,955
I have telted the field coil and the armature for resistance and continuity and they both read good.
How do you know what the readings should be? Just because you get some sort of resistance doesn't necessarily mean it's good. There could be a shorted winding causing the effective inductance to be somewhere in-between what it should be.

If it's getting hot and smelling then my first assumption would be that one of the coils (or more) may be shorted somehow. You said you "got a hold of" a drill. How? Did you buy it at a yard sale? A thrift store? E-bay? If you bought it new then take it back for a warranty replacement. If you bought it used then you may have bought a paperweight. If it was something you got for free - since it's acting up, and potentially a fire hazard, I'd suggest you don't use it. Scrap it for its metal content and copper content.
 

MrAl

Joined Jun 17, 2014
6,835
Hi,

A 240v armature in a universal motor should run OK on 120v, just slower, but not get hot. It's the other way around that wont work very well though it should just run very fast for a short time but could burn out the windings.

I've had a similar motor with an 'open' winding that ran somewhat ok but got hot if it was run for any length of time. I could use it for maybe 10 minutes before it got too hot to hold anymore.

Windings are not easy to fix unfortunately.
 

MaxHeadRoom

Joined Jul 18, 2013
19,485
If it is a common Universal motor (brushed motor) then you can even test it on low voltage DC, automotive battery for e.g.
Particularly if you can separate the motor from all load when testing, e.g. gear box etc.

The rpm on 120v would indicate whether the armature has been changed etc.
Max.
 

Dodgydave

Joined Jun 22, 2012
8,609
You can try it using an ordinary light dimmer or step down transformer, is there a current or wattage rating on the information plate?
 
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