Surges & Spikes produced by AC motors

[eetechie]

I cannot seem to find any information on the effects of hooking up a compressor or other AC motor to sensitive electronic equipment. I know the motor produces spikes and surges and is destroying switching power supplies in our products. Does anyone know if there are papers or information on the effects of these motors?

 

[dpc]

This depends on the type of motor. If this is a three-phase squirrel cage motor, it will not produce spikes or surges.

If it is a single-phase motor with capacitor start, you may see a transient when cap is switched out.

If it is a "universal" motor with or without SCR speed control, then it will create a lot of hash on your ac input.

But none of the above probably creates as much electrical noise as a switching power supply. I wouldn't blame the motor too soon. You could try some surge suppression on the input to the power supplies.

 

[tmahan]

Are you surge the problem is spike and surges. You don't say how big the compressor is but based on the limited information you are providing please consider that you may have the opposite problem, voltage sag caused by the motor starting.

 

[eetechie]

First, let me say that only one distibutor (out of 30) has a problem, and they connect the compressor with about 2' of wiring to the input of the switching power supply. The compressor is a very small, single phase compressor (Sears brand, $50, user supplied). There is no SCR control, it switches on and off with a pressure switch on a paint pressure tank. If there is a capacitor start is not known. The output is clean, checked with a scope and added spike protection. The switching power supplies are definately damaged on the AC input. Some power supplies have evidence of arcing on the other side of the input fuse. I do not think voltage sagging would be able to do this. We have recommended the compressor be hooked up differently and possibly add a surge supressor in front of the switching power supply.

 

[buzzp]

Remember that motors draw more than full load amps at start-up. Maybe this is causing the damage.

 

[electricpete]

I'm not 100% sure I understand whether the motor is on the input or the output of your electronics. Can you clarify whether
#1 this motor is served from the same ac source as your electronics

OR

#2 - this motor is powered from the output of your electonics

In any case there wil be some inductive voltage spike when the motor is switched off. Also dependent on exactly what kind of device is used to switch the motor off.

 

[eetechie]

This compressor motor is powered from the same AC input as the switching power supply. The output of the power supply is filtered and runs remote devices (spike protection was added to the output because of the devices turning on and off).

 

[buzzp]

For starters, I would not hook the compressor up to the input of the switching power supply. It should have seperate wire ran to the source. Depending on the rating of the input terminals to the power supply and exactly how 'they connect the compressor with about 2' of wiring to the input of the switching power supply'.
Does this one from this particular supplier always fail? Is it the only one to have failed? How many have failed? Besides my point above, I do not see any correlation to the compressor and the switching power supply. Is it the compressor or switching power supply distributor that is the only one having problems? If it is a certain switching power supply then change to one that works and don't buy from the other again because your getting junk. Check into any IEC tests that have been done on the power supplies and/or check for CE marking on the device.

 

[busbar]

Depending on how much money a failures are costing, you might try IEEE 1100, IEEE Recommended Practice for Powering and Grounding Electronic Equipment [Emerald Book]

Chapter 1 is on line at:

http://standards.ieee.org/colorbooks/sampler/Emeraldbook.pdf

 

[jbartos]

Suggestion: Often any sensitive electronic equipment is either connected to or has its built-in clean power supply. Alternately, the common bus may be treated to improve the power supply quality various ways. Some of them are already posted, others are:
1. Isolation transformers
2. Power line conditioners
3. DC power supply with an inverter for the sensitive electronics.
4. Etc.

 

[eewd]

The seperate source for the compressor and adding surge suppression to the electronics input is the best solution. If the compressor is connected to the same source and is putting out damaging transients or harmonics at other than startup or shut down, the surge suppressor will soon be depleted and provide no protection.
The alternative is to install the surge suppression and specify which compressors are compatable with your system.

 

[elecman]

My first reaction is that the switching devices for these motors sound like poor quality, resulting in spikes on switching, particularly switching off. Surge suppression is likely to cure the problem but is treating the effect, not the cause.

 

[jraef]

I would hazard a guess that a Sears air compressor running from 1 phase power, assuming 120V, is most certainly a capacitor start motor and could most definately cause problems on the switch mode power supply. If you cannot separate the power sources, install a line conditioner in front of the power supply. Ferroresonent are good for this application, small, inexpensive and reliable.

Air compressors tend to turn on and off quite frequently and the power quality during starting is extremely poor until the centrifugal switch on the motor takes out the caps. The problems are very breif, but the comopressor cycles very rapidly. If you dont kow, look for a "bump" on the side of the compressor motor. That is a tell tale sign of a capacitor start. The only other type of 1 phase motor would be a "split phase" starting version, no longer commonly used in machinery of this type. Some small comnpressors are using Universal motors (the type used on your power drill for instance) even though they are not using variable speed capability, but they are typically limited to fractional HP.

Actually, in reviewing you original post I see that this is a $50 compressor, so that may in deed be the case. A universal motor usesa rectifier and brushes going to DC windings, very poor power quality and very likely to do damage to your PS. Invest in a line conditioner. That which does not kill me, makes me stronger... and pissed off!

 

[buzzp]

As I stated earliar in a different manner, the motor could be browning out the power supply and thereby causing problems with that particular power supply on motor start-up.

 

[eetechie]

Jaref,
You mention "Ferroresonent are good for this application, small, inexpensive and reliable". I have never heard of this type of protection device. Can you give me some input on where I can get specs on this? I currently have several devices on order to check their supression capability on the AC input.
As for some more background information, the predecessor to this product has been in existance for approximately 35 years and had a linear regulator providing power to the remote motor. A problem it experienced was intermittent (every couple of years) destuction of the regulator. I believe this has been solved with the new product by adding protection circuitry to the output of the switching power supply.

Thank you for your help.

 

[jraef]

Ferroresonant power conditioners were invented by Frank Sola in the 1930s. The best source for them is still the company that bears his name, Sola Electric (now called Sola/Hevi Duty)

http://www.sola-hevi-duty.com/

Check out the CVS or MCR Series products under Power Protection and Conditioning.

That said, Sola lost their patent protection several years ago and there are now several other manufacturers on the market. Do a Google search on "ferroresonant line conditioner" (carefull, I had spelled it wrong in the first post) or "constant voltage transformers". Just be aware that not all power conditioners are ferro's, and some types of alternate technologies will be susceptable to the same problems as your power supply! Also remember that you only need the power conditioner in front of the power supply, not the compressor! "If it were not for electricity, we'd all be watching TV in the dark!" ...George Goebell.