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using solid state relays with servos

mikgol

Jul 6, 2013
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Jul 6, 2013
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Hi there,

I'm using an MG995 servo, which is rated at 6v. To power it, I'm using 4 (new) AA batteries, which should provide 6 volts. The servo only comes on periodically, so to stop the batteries from going flat I've hooked up a solid state relay to turn power on/off to the servo.

The servo is running very weak (with fresh batteries) - is it possible that the solid state relay has a voltage drop or something that's causing this?
 

bigone5500

Apr 9, 2014
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Apr 9, 2014
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You could probably measure the voltage to the motor as it is running. This would show if you have voltage drop. I would think that a solid state relay would definitely have a small amount of drop.

Do you have a part number to the relay you are using?
 

bigone5500

Apr 9, 2014
712
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Apr 9, 2014
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Thanks for the reply Jared. The solid state relay is a HFS40 (http://pdf1.alldatasheet.com/datasheet-pdf/view/194494/HONGFA/HFS40.html) - I can't find anything about voltage drop in the datasheet, but maybe it's implied?

I'm turning it on/off with and arduino, which is why I went with a 5v solid state replay

I think I could be wrong about measuring the voltage drop. However, your relay has transistor output. So I am not sure about how much drop there will be in your circuit. I'll take a guess and say not more than .5 volts.
 

mikgol

Jul 6, 2013
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Jul 6, 2013
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I've got the 5v version. Hmm, judging by that post I'll try putting a 1n4007 diode across it to see if that helps.

Is it "bad practice" to use solid state relays to power motors etc? (sorry if that's a dumb question)
 

GPG

Sep 18, 2015
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Sep 18, 2015
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There's a max voltage drop of 1.5V in the datasheet.
 

mikgol

Jul 6, 2013
87
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Jul 6, 2013
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Ahh yep! I see it now :) That would explain it then. I'll chuck in another AA battery to compensate. Cheers for the help guys
 
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