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I have a Blendtec blender that just decided to break on me. The blender has an electric brushed motor that looks like this:

http://www.ifixit.com/Teardown/Blendtec-Total-Blender-Teardown/1128/2

When it broke I smell some "electric smell". The kind you usually smell when electronics break.

I opened up the blender and have taken the rotor out, as I suspect the problem might be in the rotor coils.

My question is I have no idea how electric rotor coils are supposed to be wired. How can I use my multimeter and test if the coils are shorted, connected, or otherwise in proper order or not?

For example if I measure the resistance between two adjecent copper "pads" (the pads that the brushes touch), the resistance is zero. Is that normal?

Half of the pads on one side of a the pad circle seem connected to each other. And half on the other side. Except one pad that doesn't seem to be connected anywhere. So something is clearly not right, but I'm not sure what. Should adjecent pads be connected to each other or not?

Blendtec Motor Rotor

UPDATE

After a couple of weeks waiting for the replacement rotor it finally arrived and I measured it for comparison.

The rotor contact points are all connected to each other. Each one is connected to each other with increasing resistance the farther you move from adjacent contacts.

Not sure if this is a special case with this rotor. But that is what I measured.

I put in the new rotor and assembled everything. Now works as good as new. So the original rotor was clearly the faulty component (as measured with the multimeter also - not all contacts were connected any more).

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  • \$\begingroup\$ This is difficult because the resistances are quite small. You can easily detect an open coil with the multimeter, but not the situation when some of the windings are shorted. \$\endgroup\$
    – Kaz
    Commented Aug 17, 2016 at 22:50

1 Answer 1

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Rotor brushes are on opposite sides so, look for something ~< 1 Ω on armature contacts in pairs from opposite sides , and continue all around.

Also check the stator windings from the main plug in the ON position or some other convenient method.

Then look under the switch panel for a triac and fixed resistors and look for evidence of burn marks.

Is this a design question?

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  • \$\begingroup\$ Thanks. That's what I suspected that it has to be on opposite sides. However I can find no opposite connected pairs, which is really weird. But I can find adjecent connected pairs, where I see 1 ohm resistance. Doesn't make any sense to me, so I must assume the motor has blown and shorted itself somehow. Thanks for the other tips, will check those too. Not specifically a design question..simply trying to determine which parts are broken so I can try and get replacements (and general curiosity on the rotor/motor wiring). \$\endgroup\$
    – Casper
    Commented Aug 9, 2012 at 0:11
  • \$\begingroup\$ The brush position will be the obvious clue to where to check rotor windings for continuity. But smells like a triac to me. The electronic smell is often the sweet skunk odor of carcinogenic epoxy fumes. \$\endgroup\$
    – user11355
    Commented Aug 9, 2012 at 0:51
  • \$\begingroup\$ I looked at the triacs with even a magnifying glass and can't find a single sign of burn marks. None of the resistors either. Although I agree "that smell" would indicate burnt epoxy. Here's why I still suspect the rotor wiring: I was able to get the motor to rotate kind of haphazardly by giving it a manual nudge to get it started. However there was a lot of sparking and it generally ran very unevenly. If a triac was burned I would assume it didn't run at all(?) But on the other hand perhaps burned electronics can still behave randomly. \$\endgroup\$
    – Casper
    Commented Aug 9, 2012 at 1:53
  • \$\begingroup\$ Anyway, going to try and find a replacement rotor for now and see what happens. Will post results here once I know more for the curious. Thanks a lot for your help. \$\endgroup\$
    – Casper
    Commented Aug 9, 2012 at 1:55
  • \$\begingroup\$ Hmm this is new info. OK you may be right, if a winding was shorted in magnet wire, it might appear ok but draw excess current and erratic. "insulation failure" and smell like burnt varnish. That might be harder to detect with an ohm meter. \$\endgroup\$
    – user11355
    Commented Aug 9, 2012 at 8:20

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