# [EVDL] coil economizer



## EVDL List (Jul 27, 2007)

I'm trying to come up with a coil economizer to use on my 12V SW200
contactor. I've come up with this so far:
12 ohm
+V---+--------+--/\/\/\/-+
| |/ |
--- +-| 2N2222 |
1mF --- | |\* |
| | | |
+----+ +----------+---+
| | 3
/ diode ^ 3 (contactor coil)
\ 2k ohm | 3
/ | |
GND--+-------------------+---+


I've simulated it and it cuts the current in half after ~200ms. I'm just
not sure about the coil inductance (I assumed 1H and 12 ohms).

Am I on the right track with this? thanks!

-Jon Glauser
http://jonglauser.blogspot.com
http://www.evalbum.com/555



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## EVDL List (Jul 27, 2007)

Way too complicated. No semiconductor needed.

A simple capacitor paralleled by a resistor, both in series with the coil is
all you need. Roughly compute the capacitor size needed to supply the inrush.
Compute the resistor size needed to supply the hold-in current.

When power is applied, the cap's reactive impedance and the resistor are in
parallel feeding current to the coil. As the cap charges from the voltage
drop across the resistor, the current decreases until at steady-state, only
the resistor is conducting. When power is removed the cap discharges through
the resistor.

The only limitation of this arrangement is if the contactor needs to cycle
more rapidly than the RC time constant. Then something more complicated is
needed. But that's not the case with an EV main contactor. It MIGHT be an
issue for a contactor used in a non-solid-state contactor controller but
probably not. The R and C might have to be tinkered with a bit.

This is so simple that frankly, for the mundane application of a main
contactor, calculations aren't worth the energy involved. Simply grab a few
hundred microfarad electrolytic cap out of your junk box, hook it in series
with the contactor coil and see if it will pull in the contactor for a second
or two. If it won't, go larger. If it firmly pulls it in then add the
resistor and you're done.

To make this clearer, here is a photograph of one of my economizers.

http://www.neon-john.com/EV/EV_home.htm

Last photo on the page, click for a larger view.

John (I'm baaaaaaaaack! 


On Fri, 16 May 2008 09:42:30 -0600 (MDT), "Jon Glauser"


> <[email protected]> wrote:
> 
> >I'm trying to come up with a coil economizer to use on my 12V SW200
> >contactor. I've come up with this so far:
> ...


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## EVDL List (Jul 27, 2007)

Hi, Neon! Welcome back!



> Neon John wrote:
> 
> > Way too complicated. No semiconductor needed.
> >
> ...


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## EVDL List (Jul 27, 2007)

> Doug Weathers <[email protected]> wrote:
> > Please forgive my ignorance, but is this really an "economizer"?
> >
> > In other words, does the combination of contactor coil plus economizer
> ...


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## EVDL List (Jul 27, 2007)

> Doug Weathers wrote:
> >> Way too complicated. No semiconductor needed.
> >>
> >> A simple capacitor paralleled by a resistor, both in series with the
> ...


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## EVDL List (Jul 27, 2007)

> Doug Weathers <[email protected]> wrote:
> 
> >Hi, Neon! Welcome back!
> >
> ...


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## EVDL List (Jul 27, 2007)

> Neon John wrote:
> 
> > Re: Kilovac. I have an EV250-2A Czonka II Kilovac here on my
> > desk. I just tested its characteristics with a Watts Up DC
> ...


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