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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