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DC motor driving problem

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h9876

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Hi,

I want to drive a windscreen wiper motor. It is 12vdc and consumes about 5-6 A of current when used in full load. Since I am not doing any fast switching and the speed of the motor is not important for me I decided to drive it using a bridge made out of 4 relays. The only problem I have now is that I don't know what source to use for it's power. I was thinking of using a 16V or 12v transformer, a full bridge rectifier and a large capacitor to create a dc voltage. But ofcourse the output of such a circuit will not be fully DC. The question I have is that will this unstable DC source damage the motor or not? Can these kind of motors tolerate higher voltages than the 12 volt rated? The motor will be on in forward or revers direction for at most twenty seconds everytime.

Thanks
 

h9876 said:
Hi,

I want to drive a windscreen wiper motor. It is 12vdc and consumes about 5-6 A of current when used in full load. Since I am not doing any fast switching and the speed of the motor is not important for me I decided to drive it using a bridge made out of 4 relays. The only problem I have now is that I don't know what source to use for it's power. I was thinking of using a 16V or 12v transformer, a full bridge rectifier and a large capacitor to create a dc voltage. But ofcourse the output of such a circuit will not be fully DC. The question I have is that will this unstable DC source damage the motor or not? Can these kind of motors tolerate higher voltages than the 12 volt rated? The motor will be on in forward or revers direction for at most twenty seconds everytime.

Thanks
Click to expand...

No, noise in the DC supply will not cause damage to the motor. I mean - remember that it's designed for an automotive environment. That is an incredibly noisy environment.

As for if they can handle higher voltages - yes and no. If it's rated for 12V and you're operating it at 16V, it'll generate more heat than its designers expected. So it could overheat. But it has a large thermal mass and thus operating for 20 seconds (with a small duty cycle, I'm assuming) should pose little to no danger to it, unless you're already operating in a very high temperature environment.

Hope this helps.
 
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    h9876

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Just keep in mind that the actual peak voltage of a transformer is higher than the RMS - peak V is theoretically ~1.414 times the RMS voltage ..
By adding a filter capacitor that "fills the valleys" between each of the wave peaks the output voltage will approach the "peak" voltage ..

So, I would use a rectifier bridge without a smoothing capacitor and I’m pretty sure those 12V-wiper-motors will happily operate of voltages mentioned above ..

IanP
:wink:
 
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    h9876

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Thanks both of you! that was great help.
 
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    sxbg

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Ok. Well the relay circuit worked, but now I want to drive the same motor (See the first post) this time using 4 transistors/mosfets/etc instead of 4 relays.

What components and circuit do you recommend for this? Preferably mention components which can be easily found like 2n3055 transistor etc.

thanks
 

Hi,

For Driving the motor you can use source power with a bridge rectifier circuit,

But the power supply and the driver circuit should not be on the same board,

use a battery, it is a noise free solution,

the noise in the power suplly may cause jerks in the motor,

instead of using relays you can use driver ic's like IR3220,

with out mosfet circuit there is one more driver BTS 7960.

see the attached image for the circuit,

with controller pwm or with a 555 timer pwm we can drive easily



regards
Sreekanth
 

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