Replace speaker of alarm clock with dc motor

Joined Jun 14, 2013
26
hi.
I want to replace speaker of table alarm clock with dc motor for some reason.
It uses 1.5 volts AA battery.
I cut the speaker wires, multi-meter show the dc voltage that goes up to 0.8 while fluctuating.

when i connected two terminals to dc motor, it do not run.
What to do ?

crutschow

Joined Mar 14, 2008
28,215
First, you can post what is the voltage and current rating of the motor?

Joined Jun 14, 2013
26
First, you can post what is the voltage and current rating of the motor?
The resistance of motor is 1.2 ohm, Is that enough?
If not, then tell me how do i find the voltage and current rating ?
There is no label on the motor.

crutschow

Joined Mar 14, 2008
28,215
Well, 1.2 ohms requires a startup current of over an amp from a 1.5V source which likely can't be provided by the speaker output amp.

Does the motor run if connected directly to a 1.5v battery?
If not how much voltage does it take to run as you want?

Johann

Joined Nov 27, 2006
190
You cannot run a dc motor directly from the speaker wires since the signal resembles AC at some frequency. This needs to be integrated and used to activate, for example, a relay which in turn can connect a separate DC supply to the motor in question.

ISB123

Joined May 21, 2014
1,236
You're going to need mini DC motor found in cell phones which is used for producing vibrations.

Johann

Joined Nov 27, 2006
190
You still need dc to run a dc motor (permanent magnet type, I presume).

Joined Jun 14, 2013
26
Crutschow.
The motor runs when directly connected to 1.5 V battery.

But i can feel that it runs slow as compared to when it is in original device in which the battery voltage is higher.

But thats enought for me if it runs slow

Joined Jul 18, 2013
23,945
Use a small sensitive AC relay in place of the speaker and a latch contact that can be unlatched by P.B. , the typical cycle start circuit, this way you can switch any voltage you like and a suitable DC level for the motor in question.
Or a small DC relay fed with a small bridge off the spkr output.
Max.

Last edited:

Joined Jun 14, 2013
26
any way to amplify the signal using tranister ?
If no, then why?
If yes, the how?

Joined Jul 18, 2013
23,945
Did you want to run the motor continuously because the speaker signal varies in frequency and amplitude, what about dead air or pauses, there will be zero output, I would have thought that the latching relay or similar would be optimum otherwise the results will vary with signal?
You could amplify it, but the same situation will occur at zero modulation.
What does the motor do?
Max.

Joined Jun 14, 2013
26
No problem if the motor runs discontinously.

Joined Jul 18, 2013
23,945
The speaker output will not run a DC motor, even amplifying the signal without extra circuitry.
Max.

Joined Jun 14, 2013
26
If not dc then, Is there any AC motor that can run with or without amplification?

If not, then, other than amplifying with transistor, what are other options?

Joined Jul 18, 2013
23,945
We are back to post #9
Max.

ISB123

Joined May 21, 2014
1,236
I'm pretty sure that generated alarm wave never drop's below 0V so you basically have half wave AC which means motor will only make half of turn.

crutschow

Joined Mar 14, 2008
28,215
Can you use a separate battery to power the motor or do you want to use the clock battery?

Joined Jun 14, 2013
26
Can you use a separate battery to power the motor or do you want to use the clock battery?
yes, i can use separate battery

crutschow

Joined Mar 14, 2008
28,215
Can you measure the DC and AC voltage coming from the speaker wires? Does this go to zero when the alarm is off?
Is this alarm a tone or from a radio?
If you can use a separate battery then you can likely use a transistor amp to turn on the motor.

Johann

Joined Nov 27, 2006
190
Just use a sensitive relay and latch it on as was suggested, then use the external battery to power the dc motor via the n.o. contact of the relay. Also a N.C. push button to interrupt the current through the latching circuit. Finish!