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I got 40 DC solenoids (12 V, 2 A) and each solenoid may be turned on for max. 5 seconds every couple of minutes or even more. Does this implementation require that an overheat protection should be provided for each solenoid? if any, what do you suggest, please? a heatsink or a fan? and how many fans could be used for the 40 solenoids?

Moreover, does a simple microncontroller circuit (including relays) require a fan or a heatsink?

In addition, I read that a flyback diode should be connected backward in parallel with each solenoid to prevent back EMF from flowing back to the circuit; what kind of diode do you recommend, please?

Is 1n4007 good enough?

Voltage Spike
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Doua Ali
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  • Without datasheet nobody can tell you how much heat solenoid can dissipate. And one of the way to reduce heating is to apply full voltage on begining just to move mechanism and reduce it. To hold it requires smaller current. – user263983 Feb 10 '21 at 23:07
  • @user263983 Thanks a bunch for your info. What about the PIC microcontroller and relays, do you think they need overheat protection or something? – Doua Ali Feb 11 '21 at 01:03
  • I am using PICs, never used overheating protection. Electromagnetic relays also works without heatsink. SSR may need it, but not for 2A.. – user263983 Feb 11 '21 at 01:36

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Let's see:

12V * 2A is 24W

It really matters what the duty cycle of these solenoids are, because 5 seconds averaged over 1 minute would look like a 2W load (5/60*24W = 2W) and over 2 minutes would look like 1W.

So with 40 of these solenoids that would be somewhere in the 80W to 40W of thermal power that needs to be dissipated, which would probably mean a fan of some sort, just from experience I'll bet you'd need 30 to 50 CFM (cubic feet a minute).

If you want to reduce the thermal/electrical burden of the solenoids a hit and hold strategy can work (look in the datasheet and it should tell you the holding current).

A good circuit for hit and hold is right here: How do I use a hit and hold circuit with a solenoid?

1N4007 will work if it can handle the current when the solenoid shuts off.

Voltage Spike
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  • Thanks very much for your tips. Excuse me, will a PC case fan with min. 30 cfm work for this purpose? and what about the PIC microcontroller and relays, do you think they need overheat protection too? Thanks a lot. – Doua Ali Feb 11 '21 at 01:12
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    A pc fan would work anything to get the heat out. The PIC shouldn't dissipate much heat way less than 1W. See this: https://meta.stackexchange.com/questions/126180/is-it-acceptable-to-write-a-thank-you-in-a-comment – Voltage Spike Feb 11 '21 at 05:28
  • Ok, thanks. Can a pc fan be controlled by the PIC MCU to be turned on only when the solenoids are being triggered? – Doua Ali Feb 11 '21 at 06:19
  • And will a heatsink do the trick just the same way as the fan, please? – Doua Ali Feb 11 '21 at 06:34
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    Yeah, if you search for fan switching circuits or use a PWM fan you can turn it on/off. You can use heatsinks for the solenoids, but moving air usually works better. – Voltage Spike Feb 11 '21 at 06:44
  • Great. And should I install a separate heatsink fot each solenoid or 1 big heatsink for them all? – Doua Ali Feb 11 '21 at 06:51
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    Which ever works best for you. – Voltage Spike Feb 11 '21 at 06:52
  • Oh unfortunately, the board is already finished and I can no longer add more connections to the microcontroller, so it's okay to only add a heatsink for all tgr solenoids along with a fan that is turned on after the system is powered on? Sorry for asking many questions. – Doua Ali Feb 11 '21 at 06:55