# How to actuate a solenoid for maximum power without damaging it?

I want to activate the solenoid. See specs for 34 AWG solenoid here:

I am powering the solenoid with 12V. Which of the following two ways would give the most power?

1. Powering the solenoid for 100ms without PWM, and off for a very long time
2. Powering the solenoid for 100ms with 100Hz PWM signal of duty cycle 25%, and off for a very long time

I think the first one is the most powerful, but could it damage the solenoid? 100ms is below the maximum on time of 5s so I don't think it will damage it. Could some one please confirm that my thought process is correct?

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Dan - I found the question and response to this interesting. Can you outline what you are trying to achieve, as I cannot envisage why maximum power is a goal with a solenoid. –  Cybergibbons Jun 8 '12 at 19:34
I am using the solenoid to move a light object, and I am having margin results, i.e., some solenoids are not able to move the mass or seem to be dead. I am troubleshooting the issue, and am exploring the possiblity that I am not delivering enough power to the solenoids. –  Dan Jun 8 '12 at 20:56
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## 1 Answer

The following summary is based on the supplied table and the derivation is explained below. The table is based on a common solenoid frame which has various coils available. Wire sizes range from 27 awg (27g) to 37 awg (37g) with number of turns and coil resistance varying with wire size.
"Power" for the purposes of solenoid activation force is taken as ampere-turns in the solenoid coil (see below):

• At 12V with the specified 34 gauge winding you can power the solenoid on for up to slightly over 5 seconds and then need a 15 second pause to achieve a 25% duty cycle.

• You could run the 34g solenoid on up to 20V for up to 2 seconds and achieve more power than you can get at 12V, or ...

• You could run a 32g version of the solenoid at 12V for up to 2 seconds to achieve more power than you can with the 34g solenoid. With your desired 100 mS on you can apply 12V for 100 mS and then repeat again after 300 mS and repeat that cycle indefinitely.

• For maximum power with a 34g coil and 100 mS on you could run at 20V and 100 mS on followed by 300 mS minimum off. The 12V/32g and 20V/34g arrangements produce the same solenoid power)

• The design limit is to not exceed an average dissipation of 3 Watts, with an instantaneous dissipation of up to 30 Watts for 2 seconds allowed, followed in all cases by a long enough pause to reduce the average to 3 Watts.

The following is derived by rearranging the data supplied and applies to all coils:

• ton max = (60 / Watts_on) seconds

(Watts max = 30)

• Tcycle >= (Watts_on x t_on_actual) / 3 seconds

The table is saying that to get maximum allowed power for up to 2 seconds (and your 100 mS is a subset of this) you can operate the solenoid at 30 Watts at 20 degrees C, with 847 amp turns of drive.

No other condition provides more power and no higher instantaneous power level is shown as allowed.

A.t = Amp.turns = Amps in coil x number of turns.

The 34 awg entry says DC resistance is 13.1 ohms,
so at 12 V you'd get I = V/R = 12/13.1
= 0.916A.

Turns for the 34g version are shown in the table to be 567
so Amp turns would be 0.916A x 567t = 520 A.t.
This is below the allowed 847 At for 2 seconds.
It is about equal to the allowed 536 At for 5 seconds.

At 12V Wattage = V^2/R
= 12^2/13.1
!= 11 Watts
which is well below the allowed maximum.

This means that if you want genuine maximum power for the solenoid frame provided, based on table data, you can either

• Run the 34g solenoid at 20V

or

• Run a 32g version of the solenoid at 12V. (Actually 11.9)
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