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'[EE] Voltage for electromagnet'
2012\04\06@225702 by

Hi all,

as part of a project I need to energise an electromagnet to
repel a permanent magnet. The pulse will be fairly short,
probably a few 10's of milliseconds, at a rate of about 0.5Hz

The electromagnet is 200 turns of 0.7mm enamelled copper
wire on a 7mm soft iron rod. DC inductance is 65uH. To
energise it I'd have the coil as the high-side load for a FET
or BJT (eg power Darlington, TIP12x) driven by a PIC

Need to make a decision re PSU and reservoir caps to use

Would I be right in thinking that a higher voltage would be
better for the switching component and the PSU because the
amperage will be less for the same pulse wattage or is the
inductance going to play some part in this ?

TIA

Jo

Oh, and coil's DC resistance is about 0.5 ohm

Hi Joe,

I guess it's going to depend on the amount of current you need to get
enough repulsion. 5V will give you 10A max, 12V will give you 24 etc.

If you use the equation V=Ldi/dt then for 65uH and 5V supply, the
current will initially increase at 5/65 A/uS or about 76A/mS. This
will be  ultimately limited by the DC resistance to 10A  but the field
may be further limited if the core saturates. If the core does
saturate, the inductance will drop and the current  will increase even
faster.

So no, for a 10mS pulse, the inductance will not be a significant
factor. Pick a supply voltage that gives the performance you need.

Richard P

On 7 April 2012 14:54, IVP <joecolquittclear.net.nz> wrote:
{Quote hidden}

>

> So no, for a 10mS pulse, the inductance will not be a significant
> factor. Pick a supply voltage that gives the performance you need.

Thank

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