Brushless motors?

Hi Bob, The motor in your saw has two wires so that would make it a brushed motor with commutator…..The motor in the advertisement is also a two wire motor…. Yes, you should be able to see a few ohms thru the windings when you connect your meter… It also should run when you connect power straight to the terminals of the motor…In the saw it’s probably a high current application and the brushes have worn down and/or failed….

Brushless motors have three wires…. You could also use an ohm meter and should be able to read though the windings in any combination of the three wires …. You couldn’t however connect voltage directly to the motor and it run…. It would need a speed control which basically converts DC to variable AC….

Hi Robert, I don't know much about brushless motors.. but I don't think what you have there is brushless. All the brushless motors that I've seen; have more than two (2) wires controlling them.

Hi Robert,
You have the same meter as I have.

What you have is defiantly a "brushed" motor.
I've been flying electric planes since the late 1980's (brushed motors with nicad batteries)

Now 1st this is to check continuity?
Turn your meter to the one picture graph that looks like an arrow with a line thru it (above the "on" word)

Touch the motors leads ---- you should get some numbers higher than the "1" in the digital readout.
If you don't get any number higher than the "1", then you have a burnt-out motor (windings).

Now if you do, then the windings are not burnt out.
Next is to see "if" the switch has failed? It is just an on/off switch?
Put one lead on the red wire and the other on one of the motor leads.
Press the switch, if not thing happens on the meter switch to the other motor lead?
Do the same for the "black" wire from the battery / thru the switch, most of the time the black wire is the one that doesn't cut the circuit in the switch.

Looking at the age and maybe the usage. The motor brushes are probably worn down and needs to be replaced?
There are brushed motors out there that have replaceable brushes over the "cheap" brushed motor with fixed brushes.

Here is one of my "old" Brushed Trinity motors I used for my plane years ago


Thes motors could draw more amps without burning out the windings and after a while I could change out the worn-out brushes with new brushes.
Back in the day, these brushed motors were used more for R/C cars and Monster trucks.

Thanks Mike and all.

I did check the switch and it's good.  Now that I have it out where I can see it, it does look like there is a commutator in there and what would pass for brushes but not in a normal sense.  When I get the replacement I will cut into it and see what's going on.

 I'm not unfamilar with electric motors - check my RX-7 window wind up and down thread but I have no experience with "brushless" motors which both Saker and replacement suppliers advertize them as.  Replacement was $10.99 shipped, but I saw others for $5.99 with shipping added.  

Something peeking in there.






Edit. BTW there is a metal non-magnetic stud (to the left of the motor) that is placed in the blue motor housing, and another in the stack to the right of the motor. No reason for them to be there other than to affect the motor.

It's a typical brushed "can" motor. The brushes look like this. Chinaco advertising is what it is.

Looks pretty simple Greg, I will crack it open and post pictures.

Edit:

One more thing. This motor does not act like a typical brushed motor which turns smoothly by hand. This one has definate stops as if magnets align attracting as it turns. Turn, stop, turn stop, etc..

Hi Bob, yes brushed motors don't turn smoothly by hand as you described. Turn, stop is quite normal with brushed motors.
The outer ring around motor can adds torque. Motor has more RPM, less torque without it.

I took the 20V motor out of the short 4" bar chainsaw and it's much easier to see that there is a commutator and brushes in there despite advertizements otherwise.  Applying 20 volts from the battery I get no action here either.  Finding the 21 volt motor was easy, I can't seem to find a replacement 20 volt.  

The end cap is crimpted on, so it should be easy to open it up.  Maybe I will get lucky repairing it like I did with the RX-7 window windup motor.  



I have to say Levent that I have serviced A/C and D/C motors most of my life, part of my job in the Navy was maintaning the motors that drove the ball disc integrators in our command ship simulators.  Long before the computers of today.  And, these two motors are completely different in feel from the ordinary.

Model locomotives too, the defective can motors I just toss, but I have been able to keep these old smooth turning Pittmans alive and running.

A motor may or may not exhibit "cogging". This depends on the magnetic design and doesn't mean anything in and of itself.

I took one of them apart, had to grind the ears off as they were too small to bend.  

There are brushes in there, or at least one and a wiper that rides on the outer edges of the commutator, the brush runs on the center.  The brushes and the commutator look good.  There are three stators.  





I will meter around in there looking for an open just for fun.  Both motors are 21 volts DC, but the smaller Saker saw comes with a 20 volt battery.  Det Hong is 6" and 21 volts.  The chargers are different, makes you wonder.  

I cleaned up the 4" Saker's housing a bit, can't put a clean motor in a dirty housing.   Both the Saker and the Dei Hong are identical except for nameplate.

There should be two brushes riding the commutator…..I think you found the problem

rdw777 wrote:There should be two brushes riding the commutator…..I think you found the problem

Time to upgrade to a new motor ---- this one is worn out!
One brush there and the other one is gone!

rdw777 wrote:There should be two brushes riding the commutator…..I think you found the problem

I thought so too Robert, until I checked the second motor which has only one brush also and if it detatched, where is it?  There was no second brush in the housing or in the motor itself on either motor.   Mystery solved when I get the new motor but it is logical that there should be a second brush there somewhere.

Edit:

It looks like the spring broke right at the bend. But, still no broken part in the saw or the motor.





I love the things, easy on the arms and a time saver. No babying either, these have been 6 inches deep in the soil cutting off roots. I have one in the tractor and one in the ATV and backups. Gave some new ones to my neighbors.

I bet the loose brush found it’s way out of one of the vents at the back of the motor….. It probably failed from heat…. The brushes are a critical point for current to pass thru…. When the commutator and brushes get dirty it just causes heat to rise more…. I think your saws are a fairly high current gadget and the brushes take the most of it…. If there was a way to get some contact cleaner thru a spray straw without having to disassemble a working saw, Might be good to treat it from time to time….

rdw777 wrote:I bet the loose brush found it’s way out of one of the vents at the back of the motor….. It probably failed from heat…. The brushes are a critical  point for current to pass thru…. When the commutator and brushes get dirty it just causes heat to rise more…. I think your saws are a fairly high current gadget and the brushes take the most of it…. If there was a way to get some contact cleaner thru a spray straw without having to disassemble a working saw, Might be good to treat it from time to time….

Thanks Robert.  It's a pretty big chunk to get though the motors openings especially when attached to the copper spring.  No way it could escape through the vents in the housing either.  I looked for powder/graphite dust but couldn't find any.  If I had found some or parts, well it ate a brush but there wasn't any, so I thought that those clever Chinese had found a better motor.  But no-way would a copper base contacting the commutator last for long.  

I'm already thinking about making one good motor out of the two by removing a brush from one and adding it to the other.  

There absolutely should be two brushes.

It's probably just a pressed pin holding the brush in the plastic. I've opened motor like this using the end of serrated jaw pliers. If you end up grinding again, just solder it back together.

Brushes like this will outlast the rest of the device. They are extremely hard in general. Nothing like much softer RC car brushes, Mike showed above.

Appears the brush popped off (debonded from) the commutator brush spring, then operated for a short time with continuity provided by the spring, which wore out from electrical arcing a short time later, or defect in spring caused it to break off.

Old days, where you had US and Canadian companies making these, parts were available for about 10 years by law. Since these are manufactured overseas, no telling if parts are avaiable. Once shot they are a throw-away?

Brushless requires a special power timing circuit, perhaps for these battery operated tools, it is simpler to use brushed motors for torque and circuit simplicity.

Bought a replacement motor for my 38 year old bath exhauster fan, still available. (Note manufacturing date code of 0586 - May 1986.)


Also replaced the radiant heater fan motor maybe 7 years ago.


However, don't know if with the newer makes made offshore, that such sustainability will be with us 30 years later.

Man after my own heart George, use it until it breaks then repair it and use it again, and again..........

Just got the Chinese Drone, more brushless motors. This time they probably are.





I ordered two more 21V 14 toothed gear motors. Cheap when compaired with the complete saw package. $10.99 ea shipped. If I lost two with the identical proplem chances are others will fail.

rsv1cox wrote:I'm already thinking about making one good motor out of the two by removing a brush from one and adding it to the other.  Smile

Nothing wrong with that at all Bob, That’s exactly what I would try…. I have an electric foamy that uses a “180” size brushed motor….I had a few of these in a drawer leftover from some GWS equipment that I used in the past…. A few brushed type speed controls too….I swap end bells, armatures, and cans around to keep one good one running…. I’m down to the last good runner…. Will have to do something different when it goes out….

Nothing wrong with that at all Bob, That’s exactly what I would try….

Darn, darn, darn Robert, it's not going to happen. It gets worse when I opened the second motor. The one brush is still missing but the remaining "good" brush is split right down the middle negating any chance to use it.





I have never seen this before.

Hmmm, no comments on the split brush. I thought it strange but maybe common.

Mail ladies delivered the replacement motor today, 21 volts. They both have 21V motors but they do not share battery connections or chargers the 4" bar saw being 20 volts, the 6" bar being 21. Pictured with a new one that I no longer need. New motor works great just like the old one. I couldn't resist cleaning it up with a little Howards Feed-N-Wax. Handiest tool I have in the tool box.

I'm not pushing Temu, a business like Amazon. But sometimes their prices are better and if their suppiers do not ship in time for you to complete your project you get a $5.00 credit to your account. Got a couple of those already. One for some lawn edging that I cancelled.

They have a $15 minimum, but display items based on your interests that make up the difference. The motor was $10.99 so I added a set of slim shaft Torx wrenches that reach into deep holes. Came in handy with this thing. (First picture)

This is good to know, Bob. I skipped Temu because it seemed too good to be true, but glad to here you had success with them, that they are trustworthy, and when occasional slip happens, are willing to make good on them.

Great you got the replacement motors to keep your saws running….What a handy little tool, …..I can see where there would be many times it would be useful for one handed operation, Especially on an awkward reach….Are you able to re-sharpen the chains that are on them as part of their maintenance?