# Wiper Motor Power



## scream1973 (Dec 23, 2007)

Heres a question that i am sure will be relatively easy to answer.. How many wiper motors can you run off say a 300 watt PC power supply ?

Or what would be a good power source if say i wanted to run 5-6 wiper motors ..


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## Abunai (Oct 28, 2007)

scream1973 said:


> Heres a question that i am sure will be relatively easy to answer.. How many wiper motors can you run off say a 300 watt PC power supply ?
> 
> Or what would be a good power source if say i wanted to run 5-6 wiper motors ..


I could have sworn I replied to this message last night. I guess not.

Anyway, Scary Terry has a good page addressing this here:

http://www.scary-terry.com/wipmtr/wipmtr.htm

The bottom line seems to be, you should figure on about 5 amps for each motor. Since Watts equals Volts multiplied by Amps (W=VxR), a 12 volt wiper motor drawing 5 Amps, requires 60 Watts.

A 300 Watt, 12 Volt power supply should drive 5 wiper motors, but with no room to spare.

A couple of things to consider:

Some power supplies say they are rated at a certain wattage, but that is divided between a few different voltage outputs. Make certain that you know how much power is allocated to the 12 Volt output. Most power supplies that I've seen specify the Amperage capacity for each voltage output.

The harder it is for the motor to move the prop, the more power it will draw. Scary Terry's page said that he measured 14 amps being drawn by a motor that got bound up. Leave yourself some extra capacity (i.e. use more power supply capacity than your motors will draw under normal circumstances.)


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## CraigInPA (Sep 28, 2007)

Most PC power supplies I've seen provide only 10-12A of 12v. Even with a 12A supply, simultaneously turning on 2 5A motor loads usually creates an overload condition on the supply. Why? Because a motor has two current requirements: start and run. It takes a lot more current to start the motor than to keep it running. Some motors require 3x the current to start than to run. 

Scary Terry mentions this in a "Note" about switching power supplies, where the motor start-stop is more apparent. With a linear supply, the inrush (start) current is usually so short that the power supply will operate, start the motor, and then, as the current load is lessened, continue to run the motor. Unfortunately, after some number of cycles, you'll burn up the output filtering capacitors or the diode bridge, and the power supply will cease to function. So, it's best to properly size your power supply to the needs of the start current of your motors.


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## scream1973 (Dec 23, 2007)

Perfect this is the type of information that i was looking for .. 

I am planning ahead so i can figure out the best ways to power props with wiper motors etc.


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