Will new brushes fix it?

[JimG]

My 2 month old Bosch Ergoflex lawn mower got seriously abused when cutting grass that was too long and wet. The yooof using it said that it got slower and slower and then stopped.

Next day I checked it and the motor (DC) barely started then stopped almos t immediately. I took the cover off the motor and saw that one of the brush holders was partially melted. See photo.

ort=2&o=8

I prized away most of the melted plastic and saw that the brush was loose a nd at an angle.

ort=2&o=17

I don't have a megger to test the insulation on the windings so the questio n is what are the chances that a new pair of brushes will be enough to fix it.

The cheapest source of a new motor wants £126. Crazy considering you can buy a new mower complete for £130.

Any advice would be appreciated.

[Capitol]

It's under warranty, return to aupplier. Seems to be not fit for purpose. My tiny £50 Mcculloch will stall on long grass(10 inches) if you feed it too much. After 12 years, I have failed to destroy it, even when using it to shred shrub cuttings piled on the grass. It has an AC motor, so starting on load doesn't work but I'd buy it again.

[Brian-Gaff]

Normally an internal cut out trips before any damage is done. if its still in warranty, I'd have a word with the place you bought it and see if they think the cut out, um did not. Brian

[JimG]

Warranty is not a possibility as dont have paperwork. The question is...... if I fix the brushes, what are the chances that this will be enough as I have no way of finding out if the insulation on the windings hasn't melted.

[newshound]

Difficult to say TBH. At the very least you will need to replace the melted plastic to get the brush-holder square again. If it's polythene or polypropylene, the usual standby of epoxy won't stick to it.

Perhaps you can do a crude lashup to see if it runs with new brushes.

[Richard]

If you didn't pay cash, there must be some sort of paper trail. I have used a bank statement before to prove when the purchase was made by debit card.

[tabbypurr]

Simple way to test winding inductance: connect neon across winding touch 1.5v battery to them for a moment if its not part shorted the neon will pulse

NT

[Andrew Gabriel]

The windings usually discolour if they overheat. The small part visible in your photo looks fine. Check the rest, and the windings on the armature.

[JimG]

That's reassuring. I can source new carbon brushes but Bosch will not supply a new brush holder. So, I'm going to try and get a replacement holder by getting a 3D print based on the remaining good one.

I'm not sure what the existing one is made of but the choice off materials for 3D is plastic, nylon or resin.

Which do you suggest would be best?

[Andrew Gabriel]

Brushes get hot even when running normally. A thermo-softening plastic as used by most 3D printers would be unsuitable. A thermo-setting resin might work.

[newshound]

Doesn't look like an application for 3D printing to me. If I were tackling it I think I would either be using epoxy, or cutting out a bit of the end plate and inserting a bit of tufnol, having fixed the brush carrier securely to that first.

I don't doubt that a serious prototyping firm could do it by 3D printing, but only for multiples of the price of the machine.