Electrical "pop" when clutch disengages

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rednesss

rednesss

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An add on to my other thread, when the Sanden 508 style compressor clutch disengages, I get an electrical "pop" back through the speakers in my car. Is there anything I can do to suppress this electrical surge, like a diode or something in line with the 12V power wire to the clutch? Any electrical engineers out there?

Thanks
 
A condenser at the power supply connection might do it.
But it might be coming from that switch (right next to the radio)
 
Hi,

I'm a retired electrical engineer and to answer your question yes, you need a diode. The pop you hear in the radio is the magnetic field of the A/C clutch coil collapsing when it turns off and causing a voltage spike on the 12 volt system. Find a diode with a rating of something like 6 to 10 amps and 100 to 200 PIV or Peak-Inverse-Volts. Connect the bar or cathode end of the diode to the clutch coil connection as close to the clutch as you can get. Connect the anode end to a good ground. Ground ---- >|---- Clutch

Try a Radio Shack if you still have one open around you. If you can't find something locally PM me and I'll send you one.

In answer to your other thread question, OFF should be OFF. The A/C clutch gets its power through the A/C-Heater control panel, through a low pressure cut off switch on the receiver/drier then to the clutch coil. It sounds like something is not wired right or the control panel is broken.
 
So basically Y in a diode to the single wire running to the clutch, with one end going into the 12v connection, and the other to ground? Paying attention to the orientation of the diode.

As far as I know, the wiring is all original. It goes from the push button controls, down to the evaporator temp controller that cycles the compressor on and off, then out to the low-pressure cutoff switch, then to the clutch.

The clutch gets energized in "off", "Max a/c" "A/C" modes on the push button that I have. It does not, that I've seen, get energized on the "Heat" or "Def" modes. So maybe the push button switch is bad. Which is unfortunate because I just replaced it with a new one I got from eBay.

Am I looking for a Zener diode or a Schottky or????
 
Out of curiosity, does the diode shunt the voltage spike to ground or something?
 
Well, it's definitely the switch. It's letting power through even in the "off" position. Which is depressing since I just bought the switch in December. I'm not looking forward to buying another one.
 
rednesss said:
Out of curiosity, does the diode shunt the voltage spike to ground or something?
Click to expand...


Basically yes, When the magnetic field of the clutch coil collapses it creates an opposite polarity voltage spike from that of the supply voltage. This causes the diode to conduct and short circuits the voltage spike dissipating the stored energy.
 
rednesss said:
Well, it's definitely the switch. It's letting power through even in the "off" position. Which is depressing since I just bought the switch in December. I'm not looking forward to buying another one.
Click to expand...

Pry the little tabs back, crack that puppy open and fix it.
That's what I do. (if it's not literally broken)

I think it's interesting how voltage spikes for radio's, points and most other electrical and RF interference issue's we use condensers but for an electrical RF problem with of/off switching of an automotive AC unit we are switching to diodes?

I'm not an electrical engineer though, so...
 
Pete in NH said:
. Ground ---- >|---- Clutch.
Click to expand...

rednesss said:
So basically Y in a diode to the single wire running to the clutch, with one end going into the 12v connection, and the other to ground? Paying attention to the orientation of the diode.



Am I looking for a Zener diode or a Schottky or????
Click to expand...

Yes, and just about any silicone diode will do.
 
TrailBeast said:
Pry the little tabs back, crack that puppy open and fix it.
That's what I do. (if it's not literally broken)

I think it's interesting how voltage spikes for radio's, points and most other electrical and RF interference issue's we use condensers but for an electrical RF problem with of/off switching of an automotive AC unit we are switching to diodes?

I'm not an electrical engineer though, so...
Click to expand...

Condensers also work. AND the two devices in concert help and are used. But the larger the device the more energy you must dissipate. I'd guess a clutch, which draws a fair amount of current, can produce a fairly large, powerful spike.

But you don't want to put a fairly large cap across an inductive load such as the clutch, because, "if it's large enough" the cap / condenser acts like an instantaneous short when power is first applied.........making things harder on the switching circuit, thermostat or dash switch in this case.

On the other hand, the "go to" supression for ignition coils "for everybody" was always a condenser (capacitor) across the coil + wire.

"Our" cars have always had several. One at the coil, one in / on the alternator, one on the instrument voltage regulator on the cluster, and one or more in a RC or LC network IN the radio. This means a filter network of caps and resistors, or caps and inductors.

Variations on the following are likely inside your radio, on the incoming power conductor

http://www.murata.com/~/media/webre...20140424-p1/en-20140424-p1_img0003.ashx?la=en
 

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67Dart273 said:
Condensers also work. AND the two devices in concert help and are used. But the larger the device the more energy you must dissipate. I'd guess a clutch, which draws a fair amount of current, can produce a fairly large, powerful spike.

But you don't want to put a fairly large cap across an inductive load such as the clutch, because, "if it's large enough" the cap / condenser acts like an instantaneous short when power is first applied.........making things harder on the switching circuit, thermostat or dash switch in this case.

On the other hand, the "go to" supression for ignition coils "for everybody" was always a condenser (capacitor) across the coil + wire.

"Our" cars have always had several. One at the coil, one in / on the alternator, one on the instrument voltage regulator on the cluster, and one or more in a RC or LC network IN the radio. This means a filter network of caps and resistors, or caps and inductors.

Variations on the following are likely inside your radio, on the incoming power conductor

http://www.murata.com/~/media/webre...20140424-p1/en-20140424-p1_img0003.ashx?la=en
Click to expand...


Huh, cool.
Thanks for explaining Del

So the diode spike suppression is able to handle more power without causing a momentary shorted condition by directing the spike directly to ground instead of trying to absorb it then? (and without possibly causing a reverse polarity surge?)
 
The reverse surge is pretty much what the diode "shorts out." Another word is "clamp." Depends on the type of diode, but diodes do have a slight voltage drop when conducting, about .7 volt. So if the diode is good, the reverse spike can only "climb" to about .7V across the diode.

"For the math," most of which I never knew LOL and what little I've forgotten, "of course" there's a Wiki page LOL

http://en.wikipedia.org/wiki/Flyback_diode

"All sorts" of info

https://www.google.com/search?q=rel...ircuits.com%2Fvol_3%2Fchpt_3%2F9.html;583;118
 
67Dart273 said:
The reverse surge is pretty much what the diode "shorts out." Another word is "clamp." Depends on the type of diode, but diodes do have a slight voltage drop when conducting, about .7 volt. So if the diode is good, the reverse spike can only "climb" to about .7V across the diode.

"For the math," most of which I never knew LOL and what little I've forgotten, "of course" there's a Wiki page LOL

http://en.wikipedia.org/wiki/Flyback_diode

"All sorts" of info

https://www.google.com/search?q=relay++inductive+kick++waveform&newwindow=1&source=lnms&tbm=isch&sa=X&ei=NbBzVdTCO4f9oATjiYGQAQ&ved=0CAcQ_AUoAQ&biw=1138&bih=511#imgrc=a1T-9Ra9EOqS9M%253A%3BVGje6C7JvCkZYM%3Bhttp%253A%252F%252Fsub.allaboutcircuits.com%252Fimages%252F03271.png%3Bhttp%253A%252F%252Fwww.allaboutcircuits.com%252Fvol_3%252Fchpt_3%252F9.html%3B583%3B118
Click to expand...

This is actually the answer. MT:burnout:
 
FWIW for some more theory.... A coil (inductor) has the natural property of wanting to keep the current flowing through it at a constant level and in the same direction. When you interrupt the coil's current, the energy in the coil's magnetic field becomes the source of energy to try to keep this current flowing; the coil essentially becomes a battery. Since the current was flowing into the + end and out of the - end (+ current theory), when the coil becomes a 'battery', what was the - end has to become + to keep current flowing out of that end, and the + end of the coil becomes the - end. Since the coil 'battery's ' + end is grounded, the other goes negative relative to ground. The suppression diode is oriented to short this 'coil battery's ' current back through the coil itself.

This reverse spike suppression is a different issue that what we normally use condensers (capacitors) for; those are more typically used to absorb constant, lower level voltage spikes/noise riding on the +12 v system.
 
TrailBeast said:
Huh, cool.
Thanks for explaining Del

So the diode spike suppression is able to handle more power without causing a momentary shorted condition by directing the spike directly to ground instead of trying to absorb it then? (and without possibly causing a reverse polarity surge?)
Click to expand...
When the power is disconnected from the a/c compressor clutch coil the magnetic field the current created collapses. The magnetic field induces a reverse polarity spike in exactly the same way your ignition coil does when the ignition coil is switched off. Putting a diode in parallel with the compressor clutch coil just allows the spike to run around the coil windings until the residual energy is dissipated as heat by the resistance of the windings. Many GM cars with two-pin compressor clutch coil connections had the diode right at the connector or near the connector in the harness for just that reason.
 
As a side note, you can get an interesting "shock" just doing simple things like checking transformers with an ohmmeter LOL. "inductive kick"
 
So I was able to find 2 different ones in town, a 6 amp 400V, and a 6 amp 50V. I hooked up the 6 amp 400V and I still have a slight pop through the speakers. I know it was recommended to find one with a 100-200V PIV, but would the 50V one be OK? I just don't want to find any smoke. Thanks.
 
50v should be fine... It only sees the regulated charging voltage and that should not exceed 15v or so. Does the 50v one work better to suppress the pop?
 
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