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Can a 120VAC/12VDC LED driver also power a small DC motor?

I have a project in mind using 120VAC with some 12VDC LED tape and a small 12VDC motor (about 100mA).  Can I run the motor off an LED driver in parallel with the LEDs, or do I need a separate transformer for it?

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gmoon2 years ago

If the driver is constant current, probably not...

The cheap LED drivers I have here (for LED strips) are not constant current.

They only adjust from zero to full with a PWM signal.

Drivers for single Cree LED's for example are constant current.

Maybe the thread starter can specify what type he is using...

walter.warren1 (author)  Downunder35m2 years ago
The LED's I planned to use are the 3258 tape kind that you can cut to length. I only need a little over a foot. The only other LED project I've done used a CV driver. However, I'm inexperienced enough with them to not know why to use one vs the other.

OK, I guess that could work. Du35m's warning about an inductive load is worthy of attention. Maybe a clamping diode would help...

How "replaceable" are the LED strip and the driver?

walter.warren1 (author)  gmoon2 years ago

The driver wouldn't be so bad to replace in the future, but the LED strip would be a pain to replace. If you don't mind, what does a clamping diode do and how might it help?

See flyback diode. The diode offers a current path for any voltage spikes induced by motor coils (or relays, etc). They are common additions to solid state motor drivers, etc.

Try it with some spare individual LEDs with the same specs?

walter.warren1 (author)  gmoon2 years ago

Looking at other instructables using motors seems to say you're dead on about the diode. I can only buy the tape style LEDs in rolls of 5 meters and I only need a foot, so I have plenty of extra to experiment with. It's been a couple of decades since my one and only electrical engineering class, but I have a EE buddy from back then who can probably offer some advice. Thanks.

The diode when using a motor is only really good if the motor is able to keep spinning with the load once the power is off.

A ceramic capacitor parallel to the motor is what filters out the unwanted voltage spikes when working.

Some motors (mostly the bigger ones) also use a small inductor in series with the motor, in rare cases two capacitors and two inductors.

Use an addition doide for sure if your controller changes voltage fast and the motor can keep spinning when the voltage goes down e.g. motor moves a heavy fan blade.

You should not need it if the motor is driving something that does not allow for a free spin after the voltage is reduced / cut off.

This is for the normal use with DC only, since you might have a PWM signal from your LED controller the diode might be a good idea to protect the controller:

The PWM signal is basically a quite fast on-of- signal, the frequencies can be in the kHz region.

This means the controller can produce the change from high to low while one coil of the motor is still connected through the bushes to the controller.

In this case the motor acts like any other inductor or relay: it produces a voltage of oppsite polarity to what went in.

Be aware that for PWM signals standard diodes like the 1N4007 are too slow, you should opt for a fast diode like a shottky diode.

The diode should be rated for at least 4 times the voltage of the motor and be able to withstand at least the amp rating of the motor to prevent overheating.

walter.warren1 (author)  Downunder35m2 years ago

With a low mass motor and nothing of any appreciable mass in the system to act as a flywheel, I suspect it will stop almost immediately when power is removed. When the parts arrive, I'm going to try it without and see what happens.

I don't know if your driver would be able to handle an inductive load.

In general I would say it is no problem as long as the driver is rated for a bit more amps than LED's and motor together.

Most drivers work with PWM signals to adjust the brightness, a DC motor can handle this.

You can try it but there is always the risk of failure.