mini solenoid heat on trinket 5v

Breakout boards, sensors, other Adafruit kits, etc.

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
Locked
User avatar
czaram
 
Posts: 45
Joined: Sun Jan 04, 2015 11:40 pm

mini solenoid heat on trinket 5v

Post by czaram »

I am pulsing the mini solenoid on and off for one second. I'm testing this with a 5v 2a adapter and using a TIP 120, 2.2K resistor to pin 1. After a short amount of time, the solenoid and the TIP120 heat up.
I'm using the circuit shown on https://core-electronics.com.au/tutoria ... duino.html (but with a Trinket 5v @ 8mhz and a 2.2K resistor).

Any suggestions?

User avatar
Franklin97355
 
Posts: 23911
Joined: Mon Apr 21, 2008 2:33 pm

Re: mini solenoid heat on trinket 5v

Post by Franklin97355 »

With the 2.2K resistor, you may not be turning on the transistor fully and that can cause heat. Try the recommended 220 ohm resistor.

User avatar
czaram
 
Posts: 45
Joined: Sun Jan 04, 2015 11:40 pm

Re: mini solenoid heat on trinket 5v

Post by czaram »

No, a 220 ohm doesnt help with the heat. I've tried this with two brand new mini solenoids, so I dont think it is the hardware. Something about the circuit I'm missing. The TIP120 also gets warm, but not as hot as the solenoid.

User avatar
Franklin97355
 
Posts: 23911
Joined: Mon Apr 21, 2008 2:33 pm

Re: mini solenoid heat on trinket 5v

Post by Franklin97355 »

You are pulling 5 watts through the solenoid and that will make it hot.

User avatar
adafruit_support_bill
 
Posts: 88093
Joined: Sat Feb 07, 2009 10:11 am

Re: mini solenoid heat on trinket 5v

Post by adafruit_support_bill »

Solenoids by nature are not especially efficient devices. Once the coil is energized, they become purely resistive devices and whatever power you put into them is dissipated as heat.

User avatar
czaram
 
Posts: 45
Joined: Sun Jan 04, 2015 11:40 pm

Re: mini solenoid heat on trinket 5v

Post by czaram »

I'm bit out of my depth here. Would a mosfet be better than the TIP120? Or is there another solution for reducing heat? Thanks in advance.

User avatar
Franklin97355
 
Posts: 23911
Joined: Mon Apr 21, 2008 2:33 pm

Re: mini solenoid heat on trinket 5v

Post by Franklin97355 »

If the solenoid is the major heat source there is not much you can do other than reduce the voltage or current supplied to it. If the transistor is heating you can make sure you are driving it fully or get something that has a lower internal resistance when on.

User avatar
BryonMiller
 
Posts: 222
Joined: Fri Mar 04, 2016 10:34 am

Re: mini solenoid heat on trinket 5v

Post by BryonMiller »

I think you would find that the solenoid requires more power to pull in than it does to be held in. So you might consider driving the solenoid transistor with a PWM output. You could pull in the solenoid with 100% duty cycle. Then you could (after a short time, maybe 100ms) lower the duty cycle. I'd guess it would hold with the duty cycle down to 50%. You might have to experiment with both the 100ms number and the 50% duty cycle number. If you could really get away with 50% that would cut your long-term heating in half.

User avatar
adafruit_support_bill
 
Posts: 88093
Joined: Sat Feb 07, 2009 10:11 am

Re: mini solenoid heat on trinket 5v

Post by adafruit_support_bill »

I think you would find that the solenoid requires more power to pull in than it does to be held in.
Good advice there. That is a common technique for reducing current draw and the associated heating in solenoids. Depending on the solenoid and any load that might be attached to it, you can typically reduce the holding current to just a fraction of the actuation current.

User avatar
czaram
 
Posts: 45
Joined: Sun Jan 04, 2015 11:40 pm

Re: mini solenoid heat on trinket 5v

Post by czaram »

Thanks Byron and Bill. Good idea -- I"ll go the analogWrite route and see how hot things get. (My first time playing around with a solenoid!)

Locked
Please be positive and constructive with your questions and comments.

Return to “Other Products from Adafruit”