UPS and frequency variations

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gregoryfast

Member
Location
Alaska
I am hoping someone can help me with this. We had some equipment burn out during a power outage. There were 6 touch pad computer screens, POS (point of sale). Each protected by an individual UPS. The UPSs were plugged into their own transient surge suppressor. Each had an individual circuit. I POS had smoke coming out if it. A hard drive on another UPS stopped.

We suspect frequency may be the culprit. The utility is on a small island 100% isolated from the grid. Ocassionally there are spikes of 70 to 80 Hz. but only for a few cycles.

Our questions are:
1. Do UPSs make their own frequency or do they allow the system frequency to pass through with out modification?
2. Are some UPS units better for frequency protection than others?
3. Are there any other products which can protect equipment from frequency variations?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Re: UPS and frequency variations

It sort of depends on the type and brand of UPS you have but USUALLY, if the incoming power is not of acceptable quality (either voltage or frequency out of spec), the UPS will create the correct voltage/frequancy power from the battery.

If it is an online unit, it does this continuously. If it is a standby unit, it will switch from mains to battery in a few milliseconds.

In any case, I doubt the UPS or power issues caused your problem since in general the power supplies on your POS do not care what the voltage or frequency is, and the UPS would have supplied them appropriate power in any case.

There is a possibility that some kind of transient appeared on your ground wire and somehow damaged the POS units, but this is pretty remote.

POS equipment is often of poor quality, and you may have gotten a bad batch.
 

derf48

Member
Re: UPS and frequency variations

Did the burn out occur during the power outage? If so, then you probably barking up the wrong tree! If it happened on start up, then a high surge on the supply side could have been present.
I had a similar case where six PC's were destroyed. All were protected with plug in tvss strips. Long story short, ground fault occurred in the building, main bonding jumper missing, current looking for path to source (grounded conductor) found a connection between grounding and grounded in the tvss strips and entered the computers and burned up circuit boards. Many times in troubleshooting we assume an event must have been caused by ... and therefore we don't find the real cause. Good luck!

Fred
 
Re: UPS and frequency variations

Originally posted by gregoryfast:
Our questions are:
1. Do UPSs make their own frequency or do they allow the system frequency to pass through with out modification?
2. Are some UPS units better for frequency protection than others?
3. Are there any other products which can protect equipment from frequency variations?
 
Re: UPS and frequency variations

Sorry for the previous "slip", new reply below:

Originally posted by gregoryfast:
Our questions are:
1. Do UPSs make their own frequency or do they allow the system frequency to pass through with out modification?
2. Are some UPS units better for frequency protection than others?
3. Are there any other products which can protect equipment from frequency variations?
[/QUOTE]

UPS, including the better smart-UPS, do not alter or adjust incoming utility frequency, they simply pass it through to the loads. Some upper end UPS add voltage regulation to the incoming utility power, and all have some degree of surge protection. You must add power conditioning equipment to regulate utility frequency. This should not normally be an issue for computer and POS equipment.

When a back-up UPS is providing power in the absence of utility power, it "estimates" a sine wave. The is within tolerance of frequency requirements of comuter equipment - barely. Electric motors and many sensitive commnications systems will not tolerate this estimated sine wave.

Smart-UPS's produce true sine wave when providing power in the absence of utility power. For sensitive data systems, you might be better served with true sine wave. You might also be better served with good line-to-neutral (normal) transient voltage surge protection, and leave the cheap power-strip protectors where they belong, connected to cheap equipment!

Jack Painter
Virginia Beach VA
 
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