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Author Topic: Question on transistor to use for DC motor  (Read 1165 times)
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Waite Park, MN
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I am looking for some help on a circuit design for turning on and off some motor pumps from an arduino. My background is a programmer and I'm a bit weak on the mechanical side. I've been able to do this on a small scale, but the motors I will be using require more power than the little 1.5-3v ones I used for a concept. My main question is if a TIP120 would be able to handle the task or what should I use if I need to go with something else.

Here is the spec of the motor that I will be using. (2885 model)
http://www.mabuchi-motor.co.jp/cgi-bin/catalog/j_catalog.cgi?CAT_ID=rs_360sh
I'm not sure if I'm reading this right, but they would be pulling 3-6amps?

I am looking to run them at 5v. There will be 6 motors total, but it would be rare to run at the same time, 2-3 at one time would be common. They would periodically run for short bursts anywhere from 1/8 second up to 3 seconds and strictly an on/off operation.
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The Stall current, which your current sees when the motor first starts up, or when it gets jammed, is 8.6A - your supply needs to provide that and your transistor must be able to switch that amount on/off.
TIP120 is only rated to 5A
http://www.digikey.com/product-search/en?lang=en&site=us&KeyWords=tip120
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Thank you. Crazy how much these little things pull. I just didn't think it would be that much. I have a couple large motors that pull half of these. I just may buckle and go with relays.
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Actually found some mosfets at a acceptable price that I think should work.
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_669871_-1
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Actually found some mosfets at a acceptable price that I think should work.
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_669871_-1

Not a good choice as that mosfet is not a 'logic level' mosfet and requires +10vdc gate/source voltage to reach full current capacity (lowest Ron value). Also be careful in selecting mosfets on their published max current rating, as this can only be reached with very effective heatsinking. If you need 8 amps get a 20amp rated device at least with as low an Ron value as you can find, and be sure it's a logic level device if you plan on operating it with an arduino output pin.

This is more like you should be looking for:

https://www.sparkfun.com/products/10213
Lefty
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I found some TIP3055's from Radio Shack on my way home last night and got them to work on an initial test. I realize that I may have to heat sink these, but any other issues that I should be aware of? And where can I identify that a component is logic level or not? I appreciate the help. Thanks.
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NPN transistors
http://www.digikey.com/product-search/en?lang=en&site=us&KeyWords=TIP3055
are not Logic Level, that only refers to MOSFETs, such as
http://www.digikey.com/product-detail/en/NTD5867NL-1G/NTD5867NL-1GOS-ND/2401422
http://www.digikey.com/product-detail/en/AOI516/785-1568-5-ND/3152480
http://www.digikey.com/product-detail/en/AOI518/785-1569-5-ND/3152481
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The TIP3055 has too little current gain to drive safely from an Arduino pin (which can only source 40mA safely), if it needs to pass 8.6A.
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