DC motor looks like it's gonna start but doesn't (vacuum cleaner motor)

Thread Starter

rambomhtri

Joined Nov 9, 2015
481
Hi, they have given me a portable vacuum cleaner that got broken, it's a BISSELL 1987N, 14.4V 90W:

1632760408205.png

It won't start; when you press ON, and I charged it for a few hours, the LED turns on, but nothing, still won't move (the motor). First thing I noticed is that when you press down the ON button, it does a little low sound but nothing happens. It looks like it's gonna start but doesn't. The sound is like... a mechanical sound, like if you stop/break with rubber blocks the motor after 1ms (best I can explain), I would say that it's like the very beginning of the motor start, it's not a beep or a cable burning or a spark.

Anyways, I opened it, and the first thing I checked was the battery pack. It's a x12 AA battery pack (Ni-MH 14.4V 1500mAh). I read with the DMM 10.80 V DC. That's the first "error". I charged the battery for a few hours and measured the battery terminals and the voltage was the same. So it looks like the battery is topping 10.80V, or the charging circuit is broken (though the LED light turns red which means charging).

I checked the charger itself, and I see it's not the original, it's a 12V 1.5A no brand charger. Anyways, it works, read with DMM and gives 12.28V DC on the IC itself.

I don't know if 10.8V is enough to start the motor, I believe it is.

Anyways, I checked the motor and it says D3648d-f 14.4V 80W. The resistance between the 2 terminals (coiling) is between 7ohm and 3ohm, it varies a lot I don't know why. I moved the rotor manually and it runs freely. I checked the the IC output that goes to the motor, and this is interesting. When I click the ON button, the V for the DC terminals goes to 10V (I guess) but instantly goes to zero. It's like it peaks to suddenly turns off. Another error here I believe.

As many of you know, some devices don't work when they are charging. So I tested measuring the output for motor while charging, and surprisingly (or not), there was no peak, clicking ON OFF made no changes, always 0V at output.

Anyways, then I did this: unsoldered the battery cables from the IC, put the charging cables as input (replacing battery by charger cables). Then I checked the output for the motor, and this time I read 12.28V steady. One click 12.28V (on), another click 0V (off). Looked like it was the battery.

I then connected the output to the motor itself, click ON and the same sound, and still not working. I know 12.28V is not 14.4V (besides I'm having real trouble finding a 14.4V charger...), but that steady 12.28V should at least start the motor and run it... unless the end of the story is that the motor is broken, and the battery somehow is not getting beyond 10.8V.

What else can it be? What do you think is the problem?
 

MaxHeadRoom

Joined Jul 18, 2013
25,469
To eliminate the motor as a problem i would test it on a known 12v source such as an automotive battery, if the motor still does not revolve then remove the motor itself for diagnosis.
Test again after removal first.
 

Thread Starter

rambomhtri

Joined Nov 9, 2015
481
To eliminate the motor as a problem i would test it on a known 12v source such as an automotive battery, if the motor still does not revolve then remove the motor itself for diagnosis.
Test again after removal first.
Isn't it this:
Anyways, then I did this: unsoldered the battery cables from the IC, put the charging cables as input (replacing battery by charger cables). Then I checked the output for the motor, and this time I read 12.28V steady. One click 12.28V (on), another click 0V (off). Looked like it was the battery.

I then connected the output to the motor itself, click ON and the same sound, and still not working. I know 12.28V is not 14.4V (besides I'm having real trouble finding a 14.4V charger...), but that steady 12.28V should at least start the motor and run it... unless the end of the story is that the motor is broken, and the battery somehow is not getting beyond 10.8V.
 

MaxHeadRoom

Joined Jul 18, 2013
25,469
The motor should operate at 12vdc.
If you disconnect the motor completely and try it with a known/good 12vdc source, if it still does not operate, then remove the motor for further testing.
 

Thread Starter

rambomhtri

Joined Nov 9, 2015
481
The motor should operate at 12vdc.
If you disconnect the motor completely and try it with a known/good 12vdc source, if it still does not operate, then remove the motor for further testing.
Isn't enough "known/good" connecting the motor to the IC that I read with DMM and gives 12.26V output?

I can connect the motor directly to the charger (12V 1.5A)... is that what you mean?
The problem is it's 1.5A, and the motor says it's 80W.
 

MaxHeadRoom

Joined Jul 18, 2013
25,469
If you find that you have 12vdc at the motor and it does not turn, that indicates the motor is bad.
If the voltage collapses, then use a sufficient external supply e.g. automotive etc.
 

Thread Starter

rambomhtri

Joined Nov 9, 2015
481
By the way, the motor specifically says it's 14.4V, the battery package is 14.4V, so why would you say connect it to a 12V supply?

x12 NiMH rechargeable batteries, which are 1.2V each, equals 14.4V... btw, I was thinking, why I don't take a total of 10 1.5V batteries and power the motor?
Any quick and easy way to connect 10 batteries in series?
I just realized an AA battery can supply 5-10 A, so that means I got about 50-100W of power, enough to power the 80W motor I guess to check if it works.
 
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Thread Starter

rambomhtri

Joined Nov 9, 2015
481
Is the motor brushed or brushless? If the latter, my money is on the commutation electronics being faulty.
I believe it's brushless.

Commutation inside the motor case? Or outside in the IC?

Anyways, if the motor is faulty, why the charger won't charge beyond 10.8V?
It's really weird 2 things got broken at the same time.

EDIT: I tried to power the motor directly with the 12V 1.5A (18W) charger and same sound. I just don't have a charger that's 12V and allows anything near 80W.... How would a 80W 12V motor behave if you connect it to a 20W or so power supply?
 
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Thread Starter

rambomhtri

Joined Nov 9, 2015
481
One or more duff cells in the battery?

Any decent power supply would probably go into self-protect mode and shut down quickly, so the motor might jerk then stop.
About the battery, it's weird that some cells are failing and also now the motor is faulty. Two problems at once is weird.

Can somebody tell if the motor at least should spin a little?
It won't move a bit when connected to a 20W supply, just the sound every second or so but no movement at all.

Wait... could I use the power supply of a PC?
One of the rails is +12V (max 62A)... Can I just plug the PSU and connect the motor to the 12V pin and ground?
 
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MaxHeadRoom

Joined Jul 18, 2013
25,469
By the way, the motor specifically says it's 14.4V, the battery package is 14.4V, so why would you say connect it to a 12V supply?
.
I indicated a method that can be used to test the motor with a battery capable of operating the motor without the voltage collapse for e.g.
A 12v automotive or similar source should be quite capable of operating a 14v motor for test purposes, motor will revolve without requiring the Exact stated voltage.
With a capable alternative source, You should be able to determine wither the fault is due to battery source or motor in a matter of very brief time! :confused:
 

Alec_t

Joined Sep 17, 2013
12,906
It won't move a bit when connected to a 20W supply, just the sound every second or so but no movement at all.
That sound is probably due to the supply switching off due to overload, re-starting, switching off, re-starting ....
A 12V 80W motor has a normal running current of about 6.6A, but the start-up current will be several times that. Could be 30A or so (though the internal resistance of the original battery may have pulled that down). Any supply you use to test the motor should be rated for around 30A to prevent shut-off.
 
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