Bosch Router fault, lots of sparks, faulty armature?

[tinnews]

I posted recently about both my routers (a Bosch GOF1300 ACE and a Ferm cheapie from Screwfix) failing with apparently worn/crumbled brushes.

Well new brushes for the Ferm (it is the same as the Trend T3) fixed that but new brushes for the Bosch didn't help at all.

So, what has gone wrong with the Bosch and is it worth fixing? The symptoms are lack of power/speed and lots of sparking from the brushes. Does this indicate an armature insulation failure between windings? Is it possible to test for this? If it's of any significance the failure was quite sudden, the router ran quite happily for several minutes when I started using it last week and then suddenly lost power, ran slowly and there were lots of sparks around the commutator/brush contact.

Any ideas or suggestions would be welcome, I'd want to be very sure that it's a failed armature before replacing it. ... in fact if it is the armature that has failed a replacement costs significantly more than a complete new router, I just looked it up.

[Weatherlawyer]

What voltage was the router?

If it was intended for 110 volt use and you just changed the plug, you blew it.

If there was some fault with the armature then you should get it replaced.

[John Rumm]

Sounds that way.

What sort of Bosch is it? Usually with the pro tools the spares can be quite cost effective compared to the whole tool. For the green ones its more pot luck.

You could try:

[tinnews]

No, I'm not quite that stupid, or at least not normally! :-) It's a 240V router and I hadn't changed anything on it, just dug it out of its drawer and started using it.

It's well over 5 years old so no warranty/guarantee.

[tinnews]

It's a blue Bosch GOF1300ACE, a replacement armature from

is £162.15 which is a whole lot more than quite a few 1/2" routers available nowadays. I think the GOF1300ACE is a model that Bosch no longer make.

[meow2222]

Why not test it and see. A multimeter wont pick up all faults, but it will some. Clean carbon despots from between the commutator segments first.

Damaged armatures can be bodged to make them run, and its an option tha can work happily enough, so worth considering..

NT

[Pete C]

Hi,

Might be worth a call to Bosch, explain it's a blue pro model with light use and see what they say.

Failing that look for a local motor rewinding co, I'd expect they can at least diagnose it for a small fee.

cheers, Pete.

[John Rumm]

Yup at that price it is not worth it since you could have a Freud FT2000E or similar for that.

(Quite often armatures work out at £30-£40 which is far more reasonable repair price).

[meow2222]

Rewind may be cheaper too.

NT

[Bob Martin]

I had something similar - turned out to be a piece of metal had got inside via the ventilation slots.

[tinnews]

Er, yes, but what do I test? That was part of my original question, using a multimeter what sort of resistance values should I expect? Does the armature comprise a load of separate windings each of which goes from one commutator 'bar' to another? If so I would expect all commutator 'bars' to be unconnected except for the one at the other end of the particular winding, is this correct? I'm quite happy to spend a little time and effort on this and have two multimeters, can solder, etc.

I'm considering it! :-)

[meow2222]

OK, the commutator has several segments, and there are several armature windings, each one connected between 2 commutator segments.

A multimeter can pick up:

- a difference in R of one winding from the others

- any conduction from armature to the rotor.

The simplest way to test it is to put the meter across the mains plug pins (NOT plugged in), and turn the tool round very slowly so you see the R of each section of the motor armature. Analogue meters are much easier to use for this.

Comparing Rs wil pick up some faults, though not all. If this doesnt work you'll need to compare L values rather than R, as L nosedives with a shorted turn or 2, whereas R can stay almost the same. Its easiest to do this by connecting the tool in series with a lightbulb, and putting the pair across a low voltage ac supply, eg 12v. Measuring the voltage across the tool will show up a bad winding section as the motor is turned. The lightbulb's non-linearity accentuates the fault. Your psu v needs to be low enough that the tool doesnt spin.

Despite the bodginess, motors run very close to full speed with one (faulty) winding section disconnected. If the section is identified, the section's 2 wires can simply be snipped to disconnect it. Its not ideal, but where a tool will retain almost all its utility, and would cost almost as much as a new one to fix, such a trick can become a sensible option.

A much bodgier option, which I really dont recommend, but used to do years ago, is to put a partially shorted motor in series with a ballast of some kind (eg a 3kW heater). This enables shorted motors to run. The motor will never reach full speed like that, and they do run hot. So not a great option, but one anyone can do easily if stuck, and it can easily resurrect kit thats not worth a proper repair, hence its effectively a way to get free tools.

NT

[tinnews]

OK, that's what I thought (and my poor description above was trying to say).

OK, I have an analogue meter as well as a digital one, I'll try this and see what I get.

Very clever! :-)

If it is a failed winding then this would seem to be a sensible approach.

Thanks for the very complete and helpful explanation, I'll report the results of my examination/repair in due course.