Making the UPS transition faster

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moonshineJ

Member
Location
USA
A 1500 VA UPS works fine while on normal power coming from the utility or from the service diesel generator. If this power secured (either the utility line breaker or generator breaker trips), the UPS works correctly, providing backup 115 VAC to loads plugged into it. The only scenario in which the UPS does not work is when generator is secured using the remote shut down pull handle, which secures the fuel to the generator (this not a normal generator shutdown, which opens generator breaker first and then shuts the engine). It takes maybe about half a second that shut fuel slows down the engine, and the generator breaker is tripped by undervoltage relay (UV). For some weird reason the UPS cannot distinguish between these two conditions. It doesn't "recognize" decaying voltage (even this happens in a less than a second!), and just shuts itself down.

We reviewed a few options (e.g. followed the manufacturer's tips to change some hardware and software settings; no luck..), but here is what I'm looking for in particular.

Is there any outlet plug-in device or maybe a hardwired standalone module, which upon sensing decaying voltage (when generator "choked" on fuel, voltage decays from 115 VAC to maybe 80-90 VAC, before the UV trips generator breaker) would shut power to UPS immediately? Say, something quick-acting, which would trip power supply to UPS may be at 105-110 VAC?

Any help would be greatly appreciated.
 
mgookin

mgookin

Senior Member
Location
Fort Myers, FL
Have you tried a different UPS?

I don't ever use any software with a UPS of that size. The alarm is enough to tell me to do what I need to do to prepare for the power problem. If you have unattended functions I can see how your situation may be different. I'd still try another UPS.
 
ron

ron

Senior Member
Location
New York, 40.7514,-73.9925
The UPS might not be very good detecting power quality issues other than an outage.

You might need to set the UV pickup higher, so it switches over earlier in the process. This may lead to false transfers to battery.
 
Jraef

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Most likely it's because the frequency is drifting out of spec, and that UPS is not meant to be used on systems where this can happen. It's not an uncommon issue in larger UPS units, but rarely seen on small 120V versions. Simple on-line UPS units often take their control power for the electronics from a power supply board connected to the line source and have a separate internal battery or capacitor to keep it active when power fails. But often that line connected power supply is sensitive to frequency changes and will have a crowbar circuit to turn itself off in order to protect the electronics on the board. You may not be able to fix this inexpensively. A line voltage monitoring relay with frequency sensing could work, but is there an input on your UPS that could command it to change over to battery without waiting for its own sensors? If it's not to be able to be used on a backup generator, it's likely not going to have that command input to get a signal from any external relay either.
 
mgookin

mgookin

Senior Member
Location
Fort Myers, FL
Jraef said:
Most likely it's because the frequency is drifting out of spec, and that UPS is not meant to be used on systems where this can happen. It's not an uncommon issue in larger UPS units, but rarely seen on small 120V versions. Simple on-line UPS units often take their control power for the electronics from a power supply board connected to the line source and have a separate internal battery or capacitor to keep it active when power fails. But often that line connected power supply is sensitive to frequency changes and will have a crowbar circuit to turn itself off in order to protect the electronics on the board. You may not be able to fix this inexpensively. A line voltage monitoring relay with frequency sensing could work, but is there an input on your UPS that could command it to change over to battery without waiting for its own sensors? If it's not to be able to be used on a backup generator, it's likely not going to have that command input to get a signal from any external relay either.
Click to expand...

Could he daisy chain two of them? Let the first one fail and the second holds. They're cheap enough to try it.
 
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moonshineJ

Member
Location
USA
mgookin said:
Have you tried a different UPS?

I don't ever use any software with a UPS of that size. The alarm is enough to tell me to do what I need to do to prepare for the power problem. If you have unattended functions I can see how your situation may be different. I'd still try another UPS.
Click to expand...

Nope. At this time they don't want to buy a new UPS, because the new model may have the similar issues. I actually had a hard time explaining to tech rep from company who makes those what's wrong with it. Perhaps later...

"You might need to set the UV pickup higher, so it switches over earlier in the process. This may lead to false transfers to battery."

I was thinking about this for a brief moment recently. And we may return to this idea. I'm not sure if this UV relay within the generator breaker is adjustable or not. Another problem could be that this breaker may need to replaced with a newer model to get the right type UV. And once again - setting it to 110 VAC may cause unnecessary breaker trips, while 100 VAC ..the UPS may stay dormant as it is.

"Let the first one fail and the second holds"
I tried a few units, including a brand new one. No luck.
 
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moonshineJ

Member
Location
USA
Jraef said:
Most likely it's because the frequency is drifting out of spec, and that UPS is not meant to be used on systems where this can happen. It's not an uncommon issue in larger UPS units, but rarely seen on small 120V versions. Simple on-line UPS units often take their control power for the electronics from a power supply board connected to the line source and have a separate internal battery or capacitor to keep it active when power fails. But often that line connected power supply is sensitive to frequency changes and will have a crowbar circuit to turn itself off in order to protect the electronics on the board. You may not be able to fix this inexpensively. A line voltage monitoring relay with frequency sensing could work, but is there an input on your UPS that could command it to change over to battery without waiting for its own sensors? If it's not to be able to be used on a backup generator, it's likely not going to have that command input to get a signal from any external relay either.
Click to expand...

Jraef, this UPS is quite primitive. Well, it has serial DB-25 + USB port, and perhaps there is an option to command the UPS via these ports to change over to battery. But, you are right, even if there is such an option, the interface would come at price.
I looked for voltage monitors:
http://www.icmcontrols.com/Digital-...ing-80300-VAC-24240-control-VAC-Prodview.html
This particular model has SPDT contact which can handle 10 A resistive @ 277 VAC. The UPS draws some 3-4 A 115 VAC, so in theory I could run the power to UPC via this SPDT contact. If this voltage monitor is fast enough, it could make a trick. Or may not.

Now my next question: you mentioned voltage monitor which actually monitors frequency rather than voltage. For a "dying" generator - what's better: frequency monitoring, or voltage monitoring, and why? Do I need some type of event logger so I can capture VAC vs time, and Hz vs time during securing fuel to the generator to make a decision?
 
Chamuit

Chamuit

Grumpy Old Man
Location
Texas
Occupation
Electrician
If you can't change the UPS, how about an ATS? We have one at a site that is really sensitive. Detects all kinds of utility problems.
 
gadfly56

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
Chamuit said:
If you can't change the UPS, how about an ATS? We have one at a site that is really sensitive. Detects all kinds of utility problems.
Click to expand...

If they won't look at a different 1500 VA UPS for a couple hundred bucks, I don't think a new ATS is in the picture. :happysad:
 
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