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Voltage of UPS

fixit7

Member
I have a UPS for my computer.

With no power supplied to the battery backup, the voltage showed around 80 volts when I was expecting around 115 volts AC.

Is that because I do not have an RMS meter?
 
Unless you are using a "true RMS" voltmeter, you will always get a reading between 80 and 88 if the power supply is working 100%.

I'd say your UPS is working as it should be. If you want further confirmation just go to the APC website and find the FAQ.
 

audioguru

Well-Known Member
Most Helpful Member
115VAC electricity is a sinewave with a peak of 163V. Maybe the cheapo meter simply peak-detects then reduces the reading to the RMS value of 0.707 times less.
80V/115V= 70% so when a cheapo inverter produces a squarewave with the same power as a sinewave then its peak voltage is 70.7% the peak voltage of the sinewave.
 

audioguru

Well-Known Member
Most Helpful Member
Amazon, Banggood, AliExpress and ebay do not have a clue about the cheap Chinese junk they sell. Most is no-name-brand.

Why buy a new meter? Buy a good inverter that works properly instead.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Amazon, Banggood, AliExpress and ebay do not have a clue about the cheap Chinese junk they sell. Most is no-name-brand.

Why buy a new meter? Buy a good inverter that works properly instead.
Why?, when his existing one looks to be perfectly fine - you wouldn't expect a pure sinewave from a UPS, there's no point.
 

audioguru

Well-Known Member
Most Helpful Member
Many electronic products use a linear power supply that relies on the peak voltage of a mains sinewave. A cheap squarewave inverter has a peak voltage that is 0.71 times what the sinewave had. Then there is a sudden reduction in the power supply voltage when the UPS begins supplying the power, unless it has a modified or pure sinewave.
 

fixit7

Member
Why?, when his existing one looks to be perfectly fine - you wouldn't expect a pure sinewave from a UPS, there's no point.
I was going to wait till it breaks.

I think it was only $10.

The dial is very hard to turn.

The wire gauge of the probes is much less than on my ElectroMate UEI DM200.

It can't read resistance higher than 200 ohms and does not measure current.
 

gophert

Well-Known Member
Most Helpful Member
I was going to wait till it breaks.

I think it was only $10.

The dial is very hard to turn.

The wire gauge of the probes is much less than on my ElectroMate UEI DM200.

It can't read resistance higher than 200 ohms and does not measure current.

Here, this one is $15 and does most everything my Fluke does on low-res setting (high res has rarely (Never?) been needed.

It has true RMS, min/max, auto ranging,, auto power off, delta voltage, - even sends dc, sine or triangle waves for continuity test. Please tell me how well it works. Ships free with prime but not sold by amazon. It is sold by the "manufacturer" but that seller has 99% rating so I think you are safe. The most you can lose is $15.

 

Nigel Goodwin

Super Moderator
Most Helpful Member
Many electronic products use a linear power supply that relies on the peak voltage of a mains sinewave. A cheap squarewave inverter has a peak voltage that is 0.71 times what the sinewave had. Then there is a sudden reduction in the power supply voltage when the UPS begins supplying the power, unless it has a modified or pure sinewave.
You seem to be mising the point?, that it's a UPS - not a general purpose inverter. A squarewave would probably be perfectly fine, but it's quite likely to use a modified sinewave anyway.
 

fixit7

Member
I get several power outages per month and it has never failed me. I replaced the 8 ah battery with an 18 ah one extending its run time to 30 mins.
 

Reloadron

Well-Known Member
Most Helpful Member
I have a UPS for my computer.

With no power supplied to the battery backup, the voltage showed around 80 volts when I was expecting around 115 volts AC.

Is that because I do not have an RMS meter?
I would say yes. Both of the below meters are connected to the same source, a UPS with a MSW (Modified Sine Wave) output.
118366

The meter on the left is an inexpensive average responding RMS indicating meter while the meter on the right is a true RMS responding RMS indicating meter so what you see makes sense to me.

Years ago a good RMS responding meter was an expensive proposition. Today they are relatively inexpensive and loaded with additional useful features. Just find one with the features you want at the price you want to pay.

Ron
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I get several power outages per month and it has never failed me. I replaced the 8 ah battery with an 18 ah one extending its run time to 30 mins.
Yes, it's an easy upgrade, stick a much bigger battery on your UPS to make it last longer.

Sounds like your mains power isn't very good though?.
 

Reloadron

Well-Known Member
Most Helpful Member
I get several power outages per month and it has never failed me. I replaced the 8 ah battery with an 18 ah one extending its run time to 30 mins.
When I get several a month I start thinking about the merits of a backup generator. Then too, it depends on the duration of an outage I guess.

May I just say, I hate the name of the left hand meter! :D

Nice comparison though - and as you say, true RMS meters are freely available now for very little money.
Yeah, but it was a free giveaway. :)

Ron
 

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