More Power from a AC coil

[zak07]

I have a AC coil that I'm trying to get more stroke out of, any suggestions...I cannot add any diodes or rectifier circuits. I was hoping that I could add more windings? or something that I could do to make a new coil. Any help would be great.

 

[Skogsgurra]

Reducing the winding impedance often helps. It cannot be done by increasing the wire area, since the impedance is mostly inductive. Reduce the number of turns instead. That usually increses the pull - up to a point where the reduced number of turns means reduced pull. You may need to limit the duty cycle so your coil doesn't let out the black cloud. It is not good for it.

You can often get good results by having a PTC thermistor and a resistor in series with the coil. Or a simple timed switch that shorts the resistor and opens after about 100 milliseconds. There are many possibilities.

If you can think of adding a rectifier and a capacitor, you can get very efficient coils. Just design it so that the capacitor applies two or four times more voltage than the coil was designed for. That will pull it in quickly and with great force. The capacitor shall be chosen so that it has been discharged down to nominal voltage after the core has pulled in. A series resistor then reduces current to holding current.

Gunnar Englund

http://www.gke.org

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[sslobodan]

Can you give more details?

 

[Skogsgurra]

More details? For your information or for the OP?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[sslobodan]

From him more details about the application.

 

[Skogsgurra]

OK. We probably have to wait till they wake up on the other side of the pool.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[zak07]

Thanks guys, I have been required to operate a mechanism by this AC coil powered at down at 13VAC. The nominal source is 120VAC. At 13 VAC, it does not effectively trip the mechanism 90% of the time. I'm been tweaking some mechanical advantages but really up againest this barrier at such low voltage. The coil specifics is 1.5 ohms, .0334 dia. copper wire.

 

[Skogsgurra]

Good morning!

I see the dilemma. Rewind the coil. Use a wire with about ten times that area and wind as much wire there is room for. That's the simple solution. You may need to do a few tests before getting it right.

There are mathematical formulae for this. But let's KISS.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[zak07]

Gunnar,

Do you mean a wire of size of .33" diameter? That is a big wire, I may can get a few turns, if I can find this wire size and fit it on the nylon bobbin.

 

[Skogsgurra]

Area ten times larger. Means diameter 3.16 times old diameter.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[electricpete]

I think Gunnar gives good advice. Just to give a rough analysis:

3x the diameter per turn
10x the area per turn
1/10 the turns
1/100 the impedance (I am assuming the impedance is primarily inductive, NOT resistive, which gives inductance proportional to turns squared)
1/10 the voltage
I = V/Z = (1/10)/(1/100) = 10 times the current (assuming your power supply doesn't droop under the heavier current).
Phi = L*I/N = 0.001 * 10 /0.1 = 1. Should roughly recreate the same flux and force.

Check of Current density:
Current / area per turn = 10 / 10 =1. Should create roughly the same I^2*R heating.

You mentioned you are exploring the mechanical aspects. Also the magnetic aspects deserve consideration. In some cases halving an airgap is equivalent to doubling the current.

There are I'm sure quite a few considerations for a successful design. Like for instance does it drop out when you want it.

I would mention that there are people who know a helluva lot more than me that design coils and put a ton of thought into it. A lot of them hang out in the magnetic forum.

If it were me, I would be looking for an off-the-shelf relay to meet my needs. Why reinvent the wheel?


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[electricpete]

Correction:
Phi = L*I/N = 0.01 * 10 /0.1 = 1.
(stop laughing, you knew what I meant)

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[electricpete]

I backed up and read the dc suggestion. Another good one. It might be that the coil as wound now for ac would pull in fine if you put a simple filtered rectifier in front of it. Do a simple resistance check with a meter to estimate the resistance (neglecting temperature effects) and you can estimate the current you'll draw to see whether it is more or less than the ac current. If more, you have to think carefully about the thermal performance... still may not be a big deal if you only have momentary energziation

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[electricpete]

Correction:
"In some cases halving an airgap is equivalent to doubling the current."
should have been:
"In some cases halving an airgap is gives twice the force per current drawn."
The effect of decreasing airgap can be to decrease current draw, but if you don't change volts/turn you don't change flux.

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[Laplacian]

Could you use a 24VAC rated coil, or is this a custom or unique part that is not readily available? This method is used for some medium voltage motor starter contactor coils and circuit breaker trip coils. The key is you either have to incorporate an "economizer" circuit to reduce the voltage down to rated after the coil is energized (motor starter), or the coil has to be deenergized quickly after it operates (breaker).

 

[itsmoked]

There may actually be commercial, "economizer chips" available now. Google "Solenoid controller" or "solenoid driver." They generally allow a current profile to be created to the coil.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com