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Odd behaviour from battery motor

I made my Curtain Controller 6 years ago based on a motor I stripped from an inexpensive battery-operated screwdriver drill (3V). In general it has worked fine. But for the last year or two it has developed a strange intermittent fault. Suddenly, instead of opening or closing the bedroom curtains in under

2 seconds, it will become glacially slow, taking maybe 10 seconds or so. Although it always gets there in the end (closing the appropriate microswitch), it's irritating.

I don't mean 'intermittent' in the usual sense. It continues in this slow mode for several *months*. Then, just as suddenly, it will revert to its normal fast mode. And stay that way for months.

A few days ago it once again reverted to slow mode, perhaps the 3rd or 4th time in 2 or 3 years. I made an even more concerted but fruitless effort than before to isolate the cause. It's definitely *not* the batteries, my primary suspect. I've tried several sets of 3 x NiCd/NiMh C-types, well-charged, all giving identical results. Voltage during operation remains more than adequate for the 3V motor. I'm also sure it's not the mechanics, friction, obstruction, etc.

Logically that seems to leave only the motor itself. Is it possible for such a motor to exhibit this sort of behaviour and if so what's the likely cause please? Is it fixable or am I going to have to find an identical motor?

-- Terry, East Grinstead, UK

Reply to
Terry Pinnell
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Bad contact with the rotor commutator, a bad connection in the field coils or the rotor coils, a bad on/off switch, loose screws on the (internal) motor wiring ....etc.... Most probable the commutator contact, or an intermittent break in one of the rotor coils. Unless that last one is just on the commutator connection, it wont be easy to repair.

Reply to
Sjouke Burry

an

worked

under

remains

such

cause

I would settle for "if it ain't actually broke, don't poke", live with it knowing that there is a break in the internal wiring and sometimes the motor will run like a washing machine motor in wash cycle rather than spin cycle, designed-in in that situation

Reply to
N_Cook

Have you looked at the brushes? Perhaps they're binding in the brush- holders, or getting to be too short.

Mike

Reply to
mike

When you were measuring voltages did you measure the voltage at the motor, or upstream? You could have a bad connection between your battery and your motor which would leave your battery as happy as a clam, yet leave your motor under fed.

Have you checked for mechanical resistance? Perhaps the mechanism is at fault, and the electronics are fine.

If the motor isn't seeing excess back-torque, and it's getting proper voltage, then the problem is the motor. If not -- not.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
Reply to
Tim Wescott

an

worked

under

remains

such

cause

Bad brushes and or dirty commutator is the most likely cause. Clean or replace the brushes. If possible chuck up the motor rotor in a lathe and lightly sand the commutator exposing fresh metal, blow clean. A three volt motor has almost no voltage "head room" to allow for loses in the brush-commutator junction. Dirt and bad contact can cause the loss of half of the drive which is what you apparently experience. A higher voltage motor is much less prone to such failures.

Reply to
Bob Eld

Thanks all, much appreciated.

-- Terry, East Grinstead, UK

Reply to
Terry Pinnell

How about the mechanics of the motor assembly?

Does the motor have gear pack reduction unit attached to it?

Reply to
tnom

Terry Pinnell Inscribed thus:

Grease solidifying with age in the gearbox.

--
Best Regards:
                     Baron.
Reply to
Baron

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