Can I bypass the speed controller on a metabo we 14-125 angle grinder?

Thread Starter

metiz

Joined Oct 27, 2014
62
I found a Metabo angle grinder and it's super dead. Turning it on does nothing. No crappy running, humming, sparks or smoke. The brushes are ok, so is the wiring to them. I tested the switch and that's fine too. It could of course be the motor or armature, but I've got one thing left to try. The grinder has a speed controller. What I want to know is: can I get rid of the speed controller and just hook up the switch to the brushes? I have had plenty if cheap crappy grinders without any speed control and they do exactly that. It's just a switch and a capacitor. IF I can get away with it, I should probably wire a new capacitor too right? I have a couple lying around from said crappy grinders. Those grinders are about 1000W, the Metabo is about 1400. Is that an issue?

I've posted a picture below of the insides. I think the red wires are feedback to the speed controller.
 

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MaxHeadRoom

Joined Jul 18, 2013
23,088
Grinder? , going to be a universal motor, mine is direct drive, you just need to find the two motor conductor leads and power direct from the switch.
Normally no capacitor needed for Universal motor.
Max.
 

Thread Starter

metiz

Joined Oct 27, 2014
62
Thanks for the replies guys. I just checked connectivity on a simpler style grinder, from the prongs of the power plug to the brushes. When the switch is off, there is no connectivity (obviously) and when the switch is on, there is connectivity from each prong to one brush, like you'd expect. I then tried the same with the Metabo. No connectivity with the switch in the off position, but with the switch in the on position, there is connectivity on ONE prong to BOTH brushes. I tried this with the speed controller hooked up to the switch and disconnected, no differences. That can't be right, right? (the speed controller is connected to the power plug with 4 prongs, as well as to the armature with 2 black wires. I only unplugged it from the switch)
 

MaxHeadRoom

Joined Jul 18, 2013
23,088
You say "one prong to both brushes", are you sure you are not reading from one side through the motor, out of the other side of the motor?
In a Universal grinder motor, the field and (brushed) armature are all in series, so you only normally have two leads to the motor.
Max.
 
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Thread Starter

metiz

Joined Oct 27, 2014
62
You say "one prong to both brushes", are you sure you are not reading from one side through the motor, out of the other side of the motor?

In a Universal grinder motor, the field and (brushed) armature are all in series, so you only normally have to leads to the motor.
Max.
Yes, I was in fact measuring the motor like you say I was. I tried that with the other angle grinder without result so that threw me off, until I realized there were no brushes in the 2nd grinder. I'm an idiot. Anyway, the switch on the metabo only switches one wire, contrary to the cheap grinder. So I can't just rip out the speed controller and hook it up directly to the switch, unless I keep 1 wire live all the time. Doesn't seem safe(?)
 

Thread Starter

metiz

Joined Oct 27, 2014
62
In is normal on 1ph 120 for the neutral to be non-switched, if it is 240 with no neutral, then both are switched.
Max.
I'm on 240...So what's happening here? I have the switch open and it really does only switch one wire. Does the speed controller switch something too when it sees a voltage on one wire or something?
 

MaxHeadRoom

Joined Jul 18, 2013
23,088
So are you N.A. 240v L1 & L2 (neutral separate) or somewhere where you have 240v L & N ?
If the former, it should be both lines switched.
Max.
 

Thread Starter

metiz

Joined Oct 27, 2014
62
Then if same as N.A. only live is switched.
Max.
Ok. Funny how the cheap angle grinders have a safer switch then. I will hook it up to the switch alone and see if I release the blue smoke. I still think I should wire a capacitor after the switch. It's to prevent arcing at the switch when you turn it off right?
 

Thread Starter

metiz

Joined Oct 27, 2014
62
Well I got it working. I managed to break the crappy switch (not my fault, made to fail pos) so I just butchered in a new one. Also wired in a snubber cap. It's....functional haha. Thanks for the help.
 

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