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Discussion Starter · #1 ·
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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Discussion Starter · #2 ·
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:
> 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
>
>
>
>_______________________________________________
>For subscription options, see
>http://lists.sjsu.edu/mailman/listinfo/ev
--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
What do you call 4 Blondes in an Abrams? Air Tank.

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Discussion Starter · #3 ·
Hi, Neon! Welcome back!

Neon John wrote:

> 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.

Please forgive my ignorance, but is this really an "economizer"?

In other words, does the combination of contactor coil plus economizer
use less power than the contactor coil alone?

Compared to a PWM economizer like the Kilovacs have, I'd expect the
big resistor to use more power.

<snip>

> 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.

It just looks too good to be true!

>
>
> John (I'm baaaaaaaaack! :)


> --
> John De Armond
> See my website for my current email address
> http://www.neon-john.com
> http://www.johndearmond.com <-- best little blog on the net!
> Tellico Plains, Occupied TN
> What do you call 4 Blondes in an Abrams? Air Tank.
>

--
Doug Weathers
Las Cruces, NM, USA
<http://www.gdunge.com/>

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Discussion Starter · #4 ·
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
> use less power than the contactor coil alone?

Yes, it definitely is an economizer. You're putting additional
resistance in series with the coil, so it will take less current.
Therefore, less power.

> Compared to a PWM economizer like the Kilovacs have, I'd expect the
> big resistor to use more power.

True; a PWM economizer should require even less power, but it's also
much more complicated than a resistor and a capacitor.

-Morgan LaMoore

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Discussion Starter · #5 ·
Doug Weathers wrote:
>> 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.
>>
>
> Please forgive my ignorance, but is this really an "economizer"?
>
> In other words, does the combination of contactor coil plus economizer
> use less power than the contactor coil alone?
>
> Compared to a PWM economizer like the Kilovacs have, I'd expect the
> big resistor to use more power.
>
Thanks Neon John!

It sure does use less power. I hooked up a test today. Using a 10000uF
cap and 100 ohm resistor I get my Albright to pull in strong and stay on
using just 100mA at 12.7V. My Albirght normally uses 1.5A at this
voltage. So while the resistor dissipates 0.1^2*100=1W overall the whole
system is using much less power.

12.7V*1.5A = 19W without economizer
12.7*0.1A = 1.3W with this economizer

100mA might not be quite enough to be reliable in a car though. My
Albirght would drop out at about 65mA. So if someone is going to use
this without a DC-DC then the voltage will drop and it could drop out
the contactor.
>> 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.
>>
>
>
It just looks too good to be true!

I guess in this case looks are deceiving!

--

-Jon Glauser
http://jonglauser.blogspot.com

http://www.evalbum.com/555

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Discussion Starter · #6 ·
Doug Weathers <[email protected]> wrote:

>Hi, Neon! Welcome back!
>
>On May 17, 2008, at 2:23 AM, Neon John wrote:
>
>> 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.
>
>Please forgive my ignorance, but is this really an "economizer"?
>
>In other words, does the combination of contactor coil plus economizer
>use less power than the contactor coil alone?

Yes, absolutely. The particular contactor I was working with drew about an
amp at 12 volts so it has about a 12 ohm coil. With 50 ohms in series, that's
62 ohms or 190ma. 190ma * 12 volts = 2.32 watts. That compares to 12 watts
(1 amp, 12 volts) for the un-economized coil.

>
>Compared to a PWM economizer like the Kilovacs have, I'd expect the
>big resistor to use more power.

But it doesn't because the loop current is reduced to around a tenth of the
non-economized level. Various contactors will need various hold-in currents.
The fork-lift contactor that I was using remained actuated at almost 200ma
even over very rough terrain so that's all I fed it.

Re: Kilovac. I have an EV250-2A Czonka II Kilovac here on my desk. I just
tested its characteristics with a Watts Up DC power analyzer. (This is the
one aimed at RC modelers and not the totally different product with the same
name that works with line voltage.) It captures the peak inrush (measuring
interval unknown) amps and watts and displays the running amps, watts and a
few other parameters.

Averaged over several tests, the peak inrush is 0.93 amps and the sustaining
current is .34 amps, 4.1 watts, with the supply voltage of 12.3. Our values
are quite similar. (They obviously chose a higher sustaining current than I
did, probably to make it more vibration-resistant) IOW, all their fancy PWM
doesn't gain us anything for typical applications. Only where the contactor
has to cycle relatively rapidly MIGHT the PWM provide some benefit.

The RC time constant of 62 ohms and 2200uF is only 0.14 seconds so unless we
need to cycle the contactor more than a couple of times a second, the
theoretical added speed of the PWM simply doesn't matter.

In return for perhaps a longer cycle time, my simple little circuit is
practically bullet-proof, with no semiconductors at all to be subject to
surges, static discharges, reverse polarity and all the other things that fry
electronics.
>
><snip>
>
>> 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.
>
>It just looks too good to be true!

Yep it does but it is true. Try it yourself in the privacy of your home! :)
Just cuz a corporation is large and fancy, nothing sez they can't complicate a
BJ! :)

To be clear, I didn't invent this. This is an OLD method of economizing the
250 volt DC coils of the huge relays used in industrial plants and power
plants in earlier times. These relays were huge, perhaps 6" to a side and
4-6" deep in the panel board. There might be as many as 8 high current
contacts. It took a LOT of force to move that armature. Yet, since there
might be hundreds of these relays in even a small plant, supplying full
pull-in current continuously wasn't considered practical. Thus the
economizer. Many relays had the economizer made into the case. Or an
external Bakelite (or similar material) module could be attached. All I did
was co-opt the concept for EV use.

John
--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
Save the whales, collect the whole set!

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Discussion Starter · #7 ·
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
> power analyzer. (This is the one aimed at RC modelers and
> not the totally different product with the same name that
> works with line voltage.) It captures the peak inrush
> (measuring interval unknown) amps and watts and displays the
> running amps, watts and a few other parameters.
>
> Averaged over several tests, the peak inrush is 0.93 amps and
> the sustaining current is .34 amps, 4.1 watts, with the
> supply voltage of 12.3.

The EV250-2A datasheet specifies a 2.8A inrush over a 200ms interval and 0.34A holding current. It seems your Watts Up measurement interval is probably a bit long for this, though it seems to measure accurately otherwise.

> Our values are quite similar. (They
> obviously chose a higher sustaining current than I did,
> probably to make it more vibration-resistant) IOW, all their
> fancy PWM doesn't gain us anything for typical applications.

Perhaps, perhaps not. I bought the EV250-1A, which differs from the -2A version in not having the built in economiser. The datasheet for this model states the coil resistance at 3 ohms, which jives with the 4A pull-in/hold current I measured with 12V applied directly to the coil.

The datasheet also states that this contactor needs the continuous voltage held between 3.8-5.1V, which works out to 1.2-1.7A of hold current.

If one chooses to observe these recommendations, applying 4V to the coil results in 1.33A of current and requires a 6 ohm resistor dissipating 10.7W to drop 12V. The cap required to supply 4A for at least 200ms for pull-in probably gets a bit larger too.

The PWM circuit can apply the same 4V @ 1.33A to the coil and draw less than 0.5A @ 12V.

Also, consider what happens as the 12V supply voltage varies. With a DC/DC on, the voltage could be as high as 14.7V, raising the current to 1.63A, the coil voltage to 4.9V (still OK), and the 6 ohm resistor's dissipation to 16W.

Without a DC/DC, or with a failed DC/DC, the 12V supply could sag to 10V (or less), dropping the current to 1.11A, the coil voltage to 3.3V (below manufacturer's spec), and the 6 ohm resistor dissipation to 7.5W.

If I were buying a Kilovac today, I'd just pay the extra for the internal economiser and be done with it, but at the time I bought 3 without and so built my own external isolated PWM economisers (isolated because the contactor drive from my controller is referenced to the traction pack). Mine are based on the TI/Burr Brown DVR101/DRV102 (don't remember which) PWM solenoid driver (e.g. <http://focus.ti.com/lit/ds/symlink/drv102.pdf>). A useful feature of this part is that the duty cycle increases as the duty cycle command voltage decreases, so simply making the duty cycle command an appropriate fraction of the 12V supply results in the duty cycle being varied to hold the coil voltage more nearly constant vs changes in the 12V rail.

The circuit gets a bit more complex to satisfy the Kilovac's 4A pull-in current and its desire to not have a freewheel diode across the coil despite needing one there for the PWM, but if one wanted to use one of the DRV-10x parts for an Albright or other contactor needing less than about 3A to pull-in, the circuit becomes trivial and one can then take advantage of the part's built-in thermal protection and status output features.

Of course, with less demanding applications, the RC slugger/economiser is still simpler and cheaper.

Cheers,

Roger.

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