First off, I am aware that plugging an UPS into an inverter is a bit redundant. The only situation I can think of it being useful is in a car when you want full amps for cranking over the motor but still want to run equipment. Anyhow, besides the silliness of why would you plug a UPS into an Inverter, my question is why it will not work. I have been using a motor master 3000 watt modified sine wave inverter with an APC Back-UPS RS 1500VA. When it is plugged in the UPS gives a wiring fault error. I was thinking it may be that the Inverter is not grounded properly so I tied the earth ground pin from the UPS to the buildings ground and still the UPS say’s there is a wiring fault. I heard people say that UPS’s do not like inverters in the past, but the troubling part that I have is that I had the ups working off a Robin Subaru R1700i inverter series generator without any issues. Anyone out there have any thoughts on this matter?
Electronic – Plugging a UPS into an inverter
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Electricity isn't simply on or off... you're missing the quantity of electricity which is measured in Amperes (Amps for short).
So, while your UPS is charging, it's using lots of electricity to charge your UPS storing a large amount of power as well as the relativity small quantity of electricity powering your house.
When the power is switched off, your UPS is just providing the relativity small quantity of electricity for your home appliances.
So, in the space of time it takes to charge your UPS, your electric company will charge you the cost of 8 hours worth of electricity, plus 2 hours of normal use, plus a tiny bit extra for the inefficiency of your UPS.
If you do this, it will likely cost slightly more than you are paying now, due to the UPS inefficiencies.
This is a YMMV / Caveat Emptor / DTTAH / ACNR type question and answer*:
ie the following may help but you MAY blow things up.
Is the buzzing because of the capacitor is bad or that a different component could be failing and having a secondary, audible effect on the capacitor?
Could be either. Capacitor is possible but I've not heard one do this. You may get a better idea by using a 'sound transfer unit' eg a wooden ruler or length of solid plastic bar or similar. ENSURE it is not electrically conductive to the extent that applying 600 VDC on one end and your ear on the other will not cause "problems" [tm]. You may wish to use a piece of rubber glove on one end as well BUT in practice even touching the capacitor outer SHOULD be safe.
Place one end of STU (sound transfer unit) against object to be tested and other end against ear or bone of head near ear. Sound can be localised and heard much better this way., Try on surrounding objects as well. Applying EHT to far end is to be frowned on - you should not have any EHT in a UPS.
I thought the AC capacitors didn't have electrolytes in them and hence can't understand why they would be buzzing loudly when they did not previously
AC capacitors will probably contain two x electrolytic capacitors of twice the target capacitance each, connected in opposed polarity.
Should not both these caps be interchangeable in this application?
There is a "reasonable chance" that the cheap fan cap WILL work OK here. Also, used or dead fans may be cheaper again.
I am thinking of plugging out the 20uF 250V pedestal fan capacitor and putting this capacitor into such a fan instead, to confirm if the cap itself is causing the noise - sounds like a good idea?
Yes. Sounds good. Always a risk that the fan will stress it worse than the UPS does but if it is good it should work OK.
I am not sure why the fans use 250V caps but my assumption is that these Chinese makers just stock up on one variety of the caps since most of the world are at or below 250V.
Many countries are 230 VAC. Some nominally 220 VAC. Voltages can be and are sometimes higher than nominal. 250 VAC is saying it will work anywhere.
Hence, for this experiment, using a 150V cap instead of the 250V one for the fan (in the US) should not damage either fan or cap?
Probably. Cap MUST be AC rated and suitable for whatever class of service it sees. X rates is phase-phase or phase-neutral or line-line. Y rated is phase-ground. Such ratings allow for surges, spikes etc. 250 VAC cap in 110 VAC system should be fine.
If it's confirmed that the cap's at fault, could I put in the 20uF 250V pedestal fan capacitor on the APC UPS board and expect it to have no detrimental effect on the UPS?
You can always EXPECT :-) ... .
But, yes, it will probably be OK BUT no guarantee.
My understanding is that this is a power cap and as long as the capacitance and voltage rating is good, other cap chars like ESR don't matter?
See above re X and Y rated. Also, some designs pass high currents at all times and some don't and a cheap cap may get sadder quicker.
*YMMV / Caveat Emptor / DTTAH / ACNR =
Your milage may vary
Let the buyer beware.
Don't try this at home (you can but ...)
All care, no responsibility
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I ended up trying a true sine inverter, and that seemed to do the trick. I guess the ups did not like the square wave from the inverter.