Nothing foretold trouble...

Last fall, I struggled with vegetation in the back of the garden. It took half a day to cut out the wild bushes and undergrowth that had been advancing on my yard for years in the part of it where I don't grow anything.

Finally, I decided to put things in order there and with the help of an electric saw I figured out all this “forest”.

The electric saw adequately withstood such a load. However, a few days later I decided to remove a few extra branches on the apple tree.

And then I look ... Between the brushes and the collector, it’s not like sparks ... the arc burns !!!

Of course, I immediately stopped working.

I will say right away - similar symptoms of a malfunction have already happened with this electric saw. 5 years ago.

Then the cause of the malfunction was the rotor.

I did not keep track that the brushes were completely worn out and when the graphite dried up, springs with a copper leash “walked” along the lamellas for several seconds. After a short-term fireworks, 3 lamellas burned out and two rotor windings burned out.

At that time, the repair cost me 1200 rubles (the cost of a new rotor). I did not hand it over for rewinding, because. this work cost a little less than a new rotor. It makes sense to rewind if you can buy a new one for the same money.

So…

The symptoms now were the same - an arc under the brushes. But this time, the arc power was much greater.

The first thing I did was check the brushes (I don’t know why, because the reason is not 100% in them).

In the photo below are the same brushes (left and right). In the center is a new brush for comparison.

The fact that they were on fire is an obvious fact.

Without hesitation, I dismantled the electric saw.

Remembering the circumstances of the last breakdown, I measured the resistance of all neighboring lamellas (“walked” along the entire collector).

Surprisingly, in all cases, the resistance was 1.1 ohms! That is ... the rotor has no obvious signs of winding breakage.

Last time, when the previous rotor "wound up", the malfunction was visible to the naked eye: burnt lamellas, the resistance between which was 15-16 ohms.

In the photo below - the same rotor.

And this time, everything is somehow suspiciously good. Maybe interturn? You can’t determine such a malfunction with my tester, but I don’t have a stand. I had to take it to the workshop, pay 100 rubles, to get the answer of the experts: "ROTOR IS OK!"

Of the possible contenders for the culprit of all this disgrace, only the stator remained. But the external examination did not give anything - no damage. And measuring the resistance of the winding will only show whether there is a break or not. By the way, the stator resistance was 2.5 ohms (And what does this give me? Nothing!!!)

However, I decided to apply a reduced voltage to the stator. To do this, I used a powerful homemade transformer, which has a tap every 6 volts. The maximum secondary voltage is 36 V. That's what I applied to the stator.

In just a couple of seconds, a light smoke began to go from the winding. And what is it??? Well, I just filed 36 V !!! The conclusion is obvious: interturn.

I gave it to rewind. The guy who was rewinding my stator took this picture (somehow the sharpness did not grow together).

The brake winding turned out to be the culprit of the interturn short circuit! Moreover, burning herself, she pulled the worker along with her (just at the junction of two windings). The emergency place was in the grooves of the "iron", so I did not notice it.

The master suggested that I abandon the further use of the brake winding:

Do you really need her? In almost all cases that I have encountered, it was she who was the cause of the burnout. And behind him, the working winding is burned. Well, you won’t have the chain to slow down by itself ... But the stator will last almost forever!

That's what they decided on! He wound me only a working winding:

As soon as I took the stator, I immediately assembled an electric saw.

Works like clockwork!!! Well, the fact that after releasing the start button, the chain moves by inertia for some time ... Well, I will adapt.