Re-winding solenoids.

Really? Explain how you came to that conclusion.

I started with known measured numbers. Worked backwards with a calculator to get the unknown. From there I went forward towards what I thought was correct.

Then asked if what I was doing sounded right. I.e. basing the requirements on ampere turns.

I even went so far as to include the calculator I used to determine the number turns based on the physical size, DC resistance and measured inductance.

So, and unfortunately VERY typical of Usenet, I've had to put up with unfounded personal attacks and a whole plethora of "How you should do anything except what you want to."

Jeff-1.0

Hi Jeff, I know nothing about power stuff or soleniod coils. I have made a few open air magnetics. (Usually Helmholtz things) If the size of both air coils is the same, then I believe your calculations are correct. It's only the magnetic field strength that you need to match and that's proportional to number of amp-turns. Wind away I say!

George H.

Driving home, I was thinking that since you're doing a pulsed thing you may care about the L/R time constant. (Is the pulse time much longer than that?) Did 'your' program spit out inductance values too? (Forgive me, I'm too lazy to look for them.) For 'thin' coils you'd expect the inducatance (for the low voltage coil) to go down by four and the resistance to go down by two, so a decrease of two in the time constant... hardly seems like it would matter, unless somethng else in the circuit is expectng it to take longer. For your fat coil the change in time constant is likely even less.

George H.

Oh

The pulse is mechanically derived. The small control relay energizes the solenoid. When the solenoid causes the transfer switch to actuate, the auxiliary contacts open the solenoid connection.

Jeff-1.0

Just for grins, Jeff 1.0 have you tried spice models of the rectifier solenoid at 480 and 240? It may help you see something you may have missed. BTW i expect you will replace the bridge with one appropriated rated for the solenoid?

?-)

It hadn't occurred to me to do that. It's pretty much of a static operation. You apply power, it pulls up on the armature. When the mechanism changes position, an auxiliary switch disconnects the solenoid.

The original bridge was dealing with 480 vac @ 5.2 amps. The new coil will present a load of about 4 amps @ 240 vac. It's not an issue.

Jeff-1.0

See where I mumbled: At 60Hz, that's 276 uF. 330uf 600VDC caps should work. I'm not very confident with my crude approximations. Therefore, I would feed the model to LTSpice and see what it's really going to do.

Look for current and voltage spikes.

You can specify an input pulse with:

Syntax: Ixxx n+ n- PULSE(Ioff Ion Tdelay Trise Tfall Ton Tperiod Ncycles)

There are also other circuit simulators that might work: (Java)

Make me rich and I'll do the recti-fire and sol-e-void model for you.

I expect you can learn interesting things looking at the current = waveforms in the various configurations.

That does not make sense for the ampere-turns argument. The number of turns drops dramatically thus the current must increase accordingly.

Jeff-1.0

Not as bad of a turns drop as thought. The new numbers make sense.

?-)

A follow up to this exercise.

Using 1/16" PVC for the ends and schedule 40 1/2" PVC for the core, I wound 2000 turns of #28 wire on the form and put things together to test them.

It works with 240 VAC across the bridge rectifier now.

And yes, the coil heats up. It's trying to dissipate

The contacts on the transfer switch disconnect the solenoid coil from power as soon as it starts to move. Inertia carries it through the sequence.

Jeff-1.0

You might want to add a thermal fuse in series with the coil. It the contactor gets stuck in the energized position, you might have a fire.

That happens it the actuator gets stuck or if the energizing voltage is unusually low? Duz it stick in the "on" state?

Worrying about the widows and orphans this might harm...

There is that. See below...

See, now this is where everyone got upset over nothing.

This whole exercise was to see _IF_ I could correctly wind a replacement solenoid for 240 V rather than the original 480 V.

Now that I've satisfied my curiosity, I'm going to sell it in it's original format (480 v 3-phase) as THAT is where it's value lies.

Jeff

So, this was all an academic exercise, with no practical purpose or monetary value? Had I known, I would have been less helpful and more insulting. You should feel guilty for having wasted my time. For penitence, please either flog yourself, or send me an appropriate percentage of the proceeds.

Fear not fearless leader, I'll remember to cut you in.

Jeff-1.0