1500VA smart ups tolerant of Generac whole house 11kw generator

[dave_power]

Hey all, post covid I moved my small business to my home.  I took with it my APC SMT1500C and it seemed to play reasonably well with my Generac whole house 11kw generator.

When the batteries dies I chose another brand UPS and unwittingly downgraded in performance.  This UPS while it has the capacity I need ($400 ups) it will not survive the power restored event.  When power is restored from the utility and the generator turns off, the UPS goes dead regardless of remaining capacity.  This power event happens fairly often.  So it's a mad dash to power the server devices down when we're on generator.  

I remember my SMT1500C of years ago handling this without issue, but I was hoping to get some feedback about this.  I don't really want to go with a double conversion ($) unless I need to.  Thank you!

[Teken]

It’s not clear to me what you’ve done with the old APC SMT1500C?!?! If you still have it then simply replace the individual cells or purchase a new RBC.

If the unit was sold or thrown out than obviously you need to provide a lot more information regarding the current replacement brand and model UPS.

Regardless, there are four types of UPS but will only call out the most common UPS Topologies:

Which provide either Modified Sine Wave (PWM) or Pure Sine Wave.

Standby - Offline, Line Interactive, Double Conversion - Online . . . 

Generally speaking and at a high level the only UPS that operates fine with a specific generator is the one you’ve tested and validated with!

There are no guarantees if a Line Interactive vs Double Conversion topology UPS will fair better then another. ☝️

It comes down to the available sensitivity setting and transfer voltage ranges.

The sensitivity setting determines when the unit will engage and go into battery only inverter mode. The upper and lower transfer voltage determines when the AVR circuit will engage and in what voltage range.

In some enterprise systems there is a third option to offer more fine tuning called Power Quality. 

The vast majority of times if this option is available this setting acts like a global filter for the sensitivity option. Depending upon the vendor it can focus more on THD, Slew Rate, Frequency, etc.

Sometimes it’s just a glorified clock / timer, or a line voltage detector. I suggest you review what the options are for this third party UPS and adjust both sensitivity and transfer voltage to the widest range.

Then report the outcome once generator power is called upon during the next grid down / lights out event.

Questions Ask . . . 👍

[dave_power]

Thanks the APC ups was deaquired it was an older unit.  Of course I wish I didn't go with the cyberpower I have now that is a 1350va home grade unit.  It does have a sensitivity adjustment and I have it set to lowest.

I am aware of the different techs.  As this is a quiet home office, and not a server room I don't want a 60 decibel fan running all the time, nor do I want the big electric bill of 24X7 double conversion.  Really what I need is a long delay after power restored I think.  I think the UPS switches back too soon and is getting a dose of dirty power as all of my other home equipment is browning/surging.

It may be worth the risk of getting another SMT1500c and trying it out.  I was trying to find some other soul here that says "yeah that isn't a problem on my generac" not a guarantee.

[Teken]

Sound like the generator is either under sized or is not maintained to operate correctly.

The vast majority of generators when called upon start up, achieve operational state, then transfer over.

If the generator has a manual ATS then insure the system is fully operational and up to speed and outputting clean power.

Than, engage the ATS to transfer power to the load centre / service panel.

None of the above will matter if the generator is not operating as intended and outputting dirty power. 

During the monthly cycle tests the output should be measured and validated to see how clean / not so clean the output is.

Dollars to donuts the unit is outputting dirty power whether it be fluctuating voltage, frequency, or THD.

Basic maintenance would detect if the unit is hunting and timing is out. Whether it be as simple as dirty / old spark plug, timing, governer, etc.

How many hours are on this generator? When was the last maintenance performed and what was done?

Have you validated the power coming out of the generator if so what are the values?

Questions Ask . . . 👍