To get the same "holding force", you need to maintain the same current.
I'm guessing that because this is a 120V coil and you are talking about inv=
erters, that it is designed for 120VAC.
That means you need to measure impedance, not merely ohmic resistance.
It's much easier to just measure the current through the coil with the sole=
noid fully assembled and energized with 120VAC.
Once you have that current value, you merely need to get that same current =
with your 12V coil.
Depending on the solenoid, if it is 12VDC, like I think it is, the DC may m=
agnetize the slug.
Hopefully it won't make any difference.

Hope this helps,
Robert

----------------------------------------
> Date: Tue, 21 Apr 2015 14:13:51 -0600
> Subject: [EE] Solenoid coil rewinding
> From: microbrix@gmail.com
> To: piclist@mit.edu
>
> Some things seem to get harder to find as time goes on. Things like this
> used to be done all the time, probably from paper nomographs that never g=
ot
> enwebified.
>
>
> I have a solenoid coil that I'd like to re-wind from 120V to 12V.
> The complication is that I need to keep the amp-turns and the inductance =
to
> similar values.
>
> The original is 70 ohms, 19 layers of 176 turns or 3344 turns. I wasn't
> able to measure the inductance due to high series resistance.
>
> Seems like this should be possible, and yet I've found precious little in
> data on how to rewind for different voltages.
>
> I tried re-winding for amp-turns and had limited success, but the output
> energy was very limited.
>
> The device in question is a BD-10AS from ElectroTechnic products.
> The magnetic field of the solenoid opens a switch which is integral to th=
e
> function, and so I need about the same level of flux. I am theorizing tha=
t
> the reason for low output was the lower inductance of my 400 turns of #19
> vs
>
> I need to use it far from an outlet, and powering it with an inverter is
> almost certainly going to result in a smoked inverter. I thought of a
> series pack but the idea of a battery at 120V with any real output curren=
t
> is pretty scary.
> --
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> View/change your membership options at
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