# Choosing AWG coil size for solenoid

Discussion in 'The Projects Forum' started by jellytot, May 20, 2014.

1. ### jellytot Thread Starter Member

May 20, 2014
72
0
A question about Coil AWG for solenoids. I need a tubular solenoid for a project. But there are multiple coil awg size options. How do I choose the one ideal to my project? For example, a solenoid has coil awgs available from sizes 27-37. My project requires a solenoid duty cycle of less than 10%. It seems the 27 is ideal as it has the lowest voltage and resistance, so why would anyone ever want size 37? A link to a solenoid with the awg options: http://www.ledex.com/ltr2/access.php?file=pdf/Tubular_0.5x1_Push.pdf

Jul 18, 2013
10,266
2,268
I would think the first thing you need to establish is the field strength required to operate the relay, this will have a bearing on the current required and in turn the wire gauge.
Max.

3. ### alfacliff Well-Known Member

Dec 13, 2013
2,449
428
also, you need to decide how much room you have for windings on the solenoid you have decided on. magnetic field depends on ampere turns, larger wire means less turns than smaller wire in the same area.

4. ### ronv AAC Fanatic!

Nov 12, 2008
3,222
1,070
It all depends on what you want to do. Lets say you want to use 12 volts to switch it. You would want to choose one that could run on 12 volts. If you don't want to waste power you would pick the one with the highest resistance to drive your load.

5. ### wayneh Expert

Sep 9, 2010
11,920
2,855
It's actually a very difficult optimization, if you want the "ideal" one. You have to figure out how many turns you'll get within your specified dimensions, and how long the total length will be. Depending on what you're doing, you can calculate the expected inductance and thus how it will behave at various frequencies. This bears on the current flowing and thus the field strength. Little things like the enamel thickness, winding efficiency and so on all come into play.

Gladly, it's unlikely you need truly "ideal" performance, you just need it to work. The main trade-off is between turns and amps. Fat wire gives less turns but more current. Thin wire allows more turns but less current. Maximum field is when the product of ampsturns is maximum. So the answer depends in part on the rest of your circuit.

6. ### Bernard AAC Fanatic!

Aug 7, 2008
4,140
393
Just for exersize I picked a coll bobbin 1.5 in long X 1 in dia, with 1/4 in bore, guessing it could disipate 1 W, but at 10% maybe 5 W. R= E sq/ p, or about 30 ohms. Pick a wire size for trial say 27, .051 Ω/ ft..017 in dia. Ave winding dia. .625 in or 36 turns X 88 turns/ 1.5 in; 3168 in. or 264 ft. X .051 = 13.5 Ω, [ came out to 27 Ω before which indicates 27 a good choice ]. At 13 Ω coil might run hot, so try one number larger & try again.

7. ### jellytot Thread Starter Member

May 20, 2014
72
0
I'm a electronics newbie. But this is my take on the advice given:

Choose a voltage I want to trigger the solenoid. Then choose a corresponding awg for that voltage (higher voltage = lower amperage = higher awg = thinner wire). Luckily, they include a chart in the PDF that lists awg/VDC nominal.

But what if my selected voltage is between 2 values? For example, let's say I want to drive the solenoid with a 24V power supply. In the chart:
awg 31 = resistance 9.56, turns 795, VDC nominal 19.6
awg 32 = resistance 16.54, turns 1068, VDC nominal 25.7

In this case, do I use 31 or 32, and why?

8. ### wayneh Expert

Sep 9, 2010
11,920
2,855
I don't want to register at that site just to look at the pdf. Can you attach it (or the relevant portion of it)?

Just off hand, I'd say you want one rated for a voltage below your available voltage. You can limit the current with an external resistor as needed but you cannot easily give it more voltage. The 32 works out to 1.55A while the 31 is 2.05A. Hmmm...

9. ### jellytot Thread Starter Member

May 20, 2014
72
0
Sorry, I didn't realize you needed to register to see the PDF. Here is the data in the PDF:

PERFORMANCE
Maximum On time (sec) when pulsed continously (at 100%/50%/25%/10% max duty cycle)= ∞ / 50 / 5 / 2
Maximum ON time (sec) for single pulse (at 100%/50%/25%/10% max duty cycle)= ∞ / 140 / 30 / 8
Watts (@20 deg C) (at 100%/50%/25%/10% max duty cycle)= 4 / 8 / 16 / 40
Ampere Turns (@20 deg C) (at 100%/50%/25%/10% max duty cycle)= 497 / 704 / 994 / 1573

COIL DATA (Coil Options for Solenoid Purchase)
awg 27: Resistance=1.43, Turns=306, VDC nom (at 100%/50%/25%/10% max duty cycle)= 2.4 / 3.4 / 4.8 / 7.6
awg 28: Resistance=1.95, Turns=342, VDC nom (at 100%/50%/25%/10% max duty cycle)= 2.8 / 3.9 / 5.6 / 8.8
awg 29: Resistance=3.84, Turns=508, VDC nom (at 100%/50%/25%/10% max duty cycle)= 3.9 / 5.5 / 7.8 / 12.4
awg 30: Resistance=5.29, Turns=572, VDC nom (at 100%/50%/25%/10% max duty cycle)= 4.6 / 6.5 / 9.2 / 14.5
awg 31: Resistance=9.56, Turns=795, VDC nom (at 100%/50%/25%/10% max duty cycle)= 6.2 / 8.8 / 12.4 / 19.6
awg 32: Resistance=16.54, Turns=1068, VDC nom (at 100%/50%/25%/10% max duty cycle)= 8.1 / 11.5 / 16.3 / 25.7
awg 33: Resistance=22.6, Turns=1194, VDC nom (at 100%/50%/25%/10% max duty cycle)= 9.5 / 13.4 / 19 / 30
awg 34: Resistance=37.41, Turns=1547, VDC nom (at 100%/50%/25%/10% max duty cycle)= 12.2 / 17.3 / 24 / 39
awg 35: Resistance=60.71, Turns=1976, VDC nom (at 100%/50%/25%/10% max duty cycle)= 15.6 / 22 / 31 / 49
awg 36: Resistance=96.19, Turns=2475, VDC nom (at 100%/50%/25%/10% max duty cycle)= 19.6 / 28 / 39 / 62
awg 37: Resistance=141.93, Turns=3060, VDC nom (at 100%/50%/25%/10% max duty cycle)= 23.8 / 33.7 / 47.6 / 75.3

10. ### alfacliff Well-Known Member

Dec 13, 2013
2,449
428
I would go with the lowe resistance one if it were to e held in for a very short time and needed to operate fast. if it were to hold in for a long time, I would go for the higher resistance one. if you need a stronger pull, use a limit switch that limits the current when the solenoid is pulled in. pinballs use two coils for flippers, one with heavier wire for a strong pull, and another with finer wire for holding. the switch shorts the higher resistance coil at end of stroke to limit heating the solenoid. a similar thing is used on overhead cranes brakes, a switch opens when the break is completely released which limits the current and heating of the brake coil.

11. ### jellytot Thread Starter Member

May 20, 2014
72
0
Yeah, the duty cycle for my purpose would be around 2.5% Basically, the solenoid needs to hit a button every 10 seconds. So when the solenoid is energized, it's only energized for less than a second (about 0.25 seconds) for the button press.
Assuming a power source that feeds 24V into the solenoid, I'll request the awg 31 coil option for this project (VDC nominal 19.6), though it seems a coil with a lower awg than that may be OK or better.

12. ### Bernard AAC Fanatic!

Aug 7, 2008
4,140
393
If the 24 V source is current limited, might try a capacitor discharge ckt, then wire size can have wide range.

13. ### ronv AAC Fanatic!

Nov 12, 2008
3,222
1,070
That should work if you need that much force. But keep in mind that if you forget to turn it off that one will smoke.

14. ### Bernard AAC Fanatic!

Aug 7, 2008
4,140
393
Power depends on the solenoid, value of C, charge V, recharge current, & ?. Left idle, C charges to V & wates for a command --ie no smoke.