Question....is my Kill A Watt meter going bad... or is it not?So.. I have a Kill a Watt.. and it has seemed to work OK...Recently I was boon docking... I do not have an inverter in the RV, so I hooked my portable one up to the coach battery... and then ran a cord inside.It is the first time I have camped with a CPAP and wanted to run it...Plugged in the Kill A Watt to the power cord and then plugged in the CPAP....wow... voltage went from 120 to about 138 or so.... Yikes!!unplugged the CPAP... tried again.. same thing... weird..pulled out my digital volt meter...voltage at the cord (from the inverter) was reading 120v...plugged in the CPAP.. and carefully measured the voltage.....120V... no spike like on the Kill A watt.....So.. is my kill a watt dying... or.. another thought I had is the inverter is NOT a pure sine wave.It is a 1000w Black and Decker that has worked for quite some time...Thoughts?Exeter

Your inverter is probably not PSW and your Killawatt is probably fine. Try it with regular power.

I mentioned in my post that the inverter is NOT PSW....will this mess with a Kill A Watt?

MSW VS PSW. The sampling on the K_A_W is not rms, so it tends to report what it sees. That is not 120 on a MSW inverter.

exeter_acres wrote:will this mess with a Kill A Watt?I'm not familiar with the workings of a KAW, but yes, MSW is difficult to read for most voltage devices.

That is exactly why I decided to power my BiPAP directly with 12 volts right into the old pluggeroo. Your power brick on your CPAP will tell you what it does for a living among the 232 symbols and yadda-yadda. Look for the voltage in and out.

Strangness with a Kill A Watt | Good Sam Community

exeter_acres
Explorer
Aug 28, 2013
thanks for all the Great info re: the Kill a watt and the inverter......

appreciate it!
exeter_acres
Explorer
Aug 28, 2013
MEXICOWANDERER wrote:
That is exactly why I decided to power my BiPAP directly with 12 volts right into the old pluggeroo. Your power brick on your CPAP will tell you what it does for a living among the 232 symbols and yadda-yadda. Look for the voltage in and out.

when I picked up my CPAP the Dr. looked at me strange as the first thing I wanted to look at was the voltage...

24V...ugg... what's up with that?
AllegroD
Nomad
Aug 28, 2013
test it on a stable stick house line. KAW can go bad. I had a small surge set one permanently at 150 something.
tvman44
Explorer
Aug 28, 2013
I don't think it will damage the kill a watt but it will not read accurately. :)
wa8yxm
Explorer III
Aug 27, 2013
There was a poster some time ago who claimed that MSW inverters would kill a kill-a-watt... He said TSW's would as well but mine has yet to die from my true sine wave Prosine.

There can be serious issues with some voltmetes on MSW inverters. I do not know about the kill-a-watt, never tested it.
ScottG
Nomad
Aug 27, 2013
exeter_acres wrote:
I mentioned in my post that the inverter is NOT PSW....

will this mess with a Kill A Watt?

Yes.
Wayne_Dohnal
Explorer
Aug 27, 2013
My experience is that the KAW does give true RMS voltage readings with MSW power. That said, it could be that the CPAP machine doesn't play well with MSW and made the waveform even worse to the point of confusing the KAW. If the KAW gives good readings with PSW I'd blame the high reading on the MSW power.
camperguy99
Explorer
Aug 27, 2013
Yep, my KillAWatt craps out on my MSW inverter too. It's OK with the Honda EU2000i but not the MSW inverter. I would have thought the KAW would work since it is a true RMS reading device but not so.
K_Charles
Explorer
Aug 27, 2013
I had a Kill a Watt meter plugged in all the time. One day it said 174 volts so I unplugged it. When I got home I plugged it in at the kitchen counter and it said 180 volts so i junked it.
MEXICOWANDERER
Explorer
Aug 27, 2013
That is exactly why I decided to power my BiPAP directly with 12 volts right into the old pluggeroo. Your power brick on your CPAP will tell you what it does for a living among the 232 symbols and yadda-yadda. Look for the voltage in and out.