The core is 12.5mm diameter?

Apologies - I misread your reply. The core is 12.5mm meaning I have 6.25mm for the coil to make 25mm total diameter yes

 

The core is 12.5mm diameter?

so do the calculations ,
chose a wire diameter
calculate how many turns , and thus wire length
calculate resistance
calculate power disipation

a spread sheet is ideal for this,

 

The trick to use is to have VERY SHORT pulses of current to move the steel plate.AND a few more turns. The temperature rise is caused by the WATT SECONDS of power (AMPS x Volts x Seconds)

 

The trick to use is to have VERY SHORT pulses of current to move the steel plate.AND a few more turns. The temperature rise is caused by the WATT SECONDS of power (AMPS x Volts x Seconds)

Ok, thank you

 

Ok, thank you

Depends how complex you want to get,
Solution I've done when need an electromagnet , that needs a big pulse to initially pull , say 1 Amp, but can hold with a lower current , say 100mA , is to use a constant current source and a capacitor .
Charge the capacitor via cc , it stops charging at a given voltage .
When switch closes, coil is powered by the cc source and the capacitor, resulting in big current , lots of pull. But capacitor quickly discharges, current in coil is now just the cc source
When switch opens , capacitor is charged up again .

 

hi Annie,
As I said earlier you have to empirically determine the Ampere-turns required that will provide the 'force' required to actuate the 'blink' operation.

The easiest method I would use is to wind on 100 turns of 32SWG onto the 12.5mm core, then use a variable power supply to determine what voltage and current is required to 'blink'

E

 

hi Annie,
As I said earlier you have to empirically determine the Ampere-turns required that will provide the 'force' required to actuate the 'blink' operation.

The easiest method I would use is to wind on 100 turns of 32SWG onto the 12.5mm core, then use a variable power supply to determine what voltage and current is required to 'blink'

E

I think the op stated that voltage was fixed , all they can change is wire .

 

I think the op stated that voltage was fixed , all they can change is wire .

I know.

But the required actual Ampere-turns should be measured, then we can possibly add a resistor in series to give that current from a 48v source.

 

I know.

But the required actual Ampere-turns should be measured, then we can possibly add a resistor in series to give that current from a 48v source.

Good point.

 

Even just measuring the actual current of a short pulse is not really simple. An analog meter movement always has inertia , and most digital multi-meters have conversion times and lack a peak-hold function. So " the required actual Ampere-turns should be measured" is not an easy thing to do.
BUT if the actual total circuit resistance can be measured, the math is not so terribly complex.

My guess is that coil heating will be the big problem unless the on-time of the pulses is rather short. The charged capacitor pulse scheme is a good choice, but that brings up a quuestion about what is being used to swiitch the current on and off??

 

Even just measuring the actual current of a short pulse is not really simple. An analog meter movement always has inertia , and most digital multi-meters have conversion times and lack a peak-hold function. So " the required actual Ampere-turns should be measured" is not an easy thing to do.
BUT if the actual total circuit resistance can be measured, the math is not so terribly complex.

My guess is that coil heating will be the big problem unless the on-time of the pulses is rather short. The charged capacitor pulse scheme is a good choice, but that brings up a quuestion about what is being used to swiitch the current on and off??

AARGH! So this magnet is driving me insane!
We have used an old coil as a blueprint, and created a new one to identical specs. Using identical larger core 15.9mm (5/8”), smaller wire 0.19mm, the damned thing is getting just as hot where as the original doesn’t.

We have wound the coil to the same diameter as the original and same length along the core.

Any suggestions guys? ‍

 

Can you determine the minimum current the magnet requires to perform its function?
From that you may be able to add a series resistor to lower the current to that level, and reduce the heating.

 

Can you determine the minimum current the magnet requires to function.
From that you may be able to add a series resistor to low the current to that level, and reduce the heating.

We don’t have the equipment to do that unfortunately. We are complete novices.

We tried a 12v supply which powered the magnet but it didn’t allow the core to discharge quickly enough and drop the magnetic connection quickly. It didn’t get anywhere near as hot with 12V.

 

We tried a 12v supply which powered the magnet but it didn’t allow the core to discharge quickly enough and drop the magnetic connection quickly.

What do you mean "drop the magnetic connection"?
That should be faster than when applying a higher voltage.

 

What do you mean "drop the magnetic connection"?
That should be faster than when applying a higher voltage.

So when we quickly hit the switch with 48V - to switch power off - the magnet instantly drops the small bolt it has attracted (as a test).

With 12V it attracts the bolt a fraction slower, but when the supply is switched off, it holds the bolt for a few seconds.

 

Didn't read EVERY post, got antsy and am jumping in.

A heavier gauge wire will drop the resistance and increase the amperage and wattage (it will be even hotter). You want to use as small a gauge wire as possible. Calculate the resistance of the new coil (or measure it) and divide 48 by the new number. This will give you the amperage. You can also square the voltage and divide by the resistance to get the wattage. In the end you want enough power to move the lip without having to use an overkill of current (amps).

 

Didn't read EVERY post, got antsy and am jumping in.

A heavier gauge wire will drop the resistance and increase the amperage and wattage (it will be even hotter). You want to use as small a gauge wire as possible. Calculate the resistance of the new coil (or measure it) and divide 48 by the new number. This will give you the amperage. You can also square the voltage and divide by the resistance to get the wattage. In the end you want enough power to move the lip without having to use an overkill of current (amps).

Thank you for the advice. I guess I’ll need to get a multimeter?

 

So when we quickly hit the switch with 48V - to switch power off - the magnet instantly drops the small bolt it has attracted (as a test).

With 12V it attracts the bolt a fraction slower, but when the supply is switched off, it holds the bolt for a few seconds.

Don't switch off the power supply. Just disconnect the wire between the power supply and the coil.

Also, in order to experiment with different current values, you can put a resistor in series, ideally a variable power resistor of about 100Ω, or use many 1W resistors in various combination of series and parallel to arrive at a desired series resistance and coil current.

 

There is a "cheating trick" sometimes used to get an electromagnet to "release instantly" when required. That uses what is called "an H bridge" to apply a very short burst of reverse current to cancel the magnetic field and rapidly release whatever was attracted. Of course, for that to work you MUST NOT HAVE a reversed DIODE across the coil, which is used to prevent the buzz when an electromagnet is powered with unfiltered rectified AC.

 

What I think it seems like youbare doing is switching off the power supply, BUT NOT disconnecting the electromagnet. SO OF COURSEthe release will be slower!