Automotive electricity

Having problems with a HAM radio, someone suggested I check the input
voltage, while xmitting. Since I was in the motorhome, and it was plugged
in to shore power, (at home), after checking the DC voltage, which was as
expected (12.6 VDC), I put the meter on AC voltage and checked. Well, it
read 27V!!!! So thinking that maybe there was some leakage, or somehow the
AC was leaking onto the DC circuits, I disconnected shore power, and took
another reading: 27V on the ACV scale, and this time measured directly at
the battery!!! Not to be outdone by such a little problem, I took my
volmeter to the car, lifted the hood, and checked directly on the battery of
the car, not the motorhome, and the car was not running: 27V!!!

What am I reading? I could understand some pulsating DC being read as AC,
when the alternator of the car is going, but the engine was not running and
there was no outside poser applied to the vehicle.

As it seems to be normal, I am not overly concerned, but I am really
curious. Does anyone have any idea?

VA2JTM.

I think I'd try another meter.

--
Steve
=======================
Remove the not dot from my address to abuse my email box
"JTMinQC" <jtminqc(remove)@************> wrote in message
news:bhu3b2$37pde$1@ID-76207.news.uni-berlin.de...
> Having problems with a HAM radio, someone suggested I check the input
> voltage, while xmitting. Since I was in the motorhome, and it was plugged
> in to shore power, (at home), after checking the DC voltage, which was as
> expected (12.6 VDC), I put the meter on AC voltage and checked. Well, it
> read 27V!!!! So thinking that maybe there was some leakage, or somehow
the
> AC was leaking onto the DC circuits, I disconnected shore power, and took
> another reading: 27V on the ACV scale, and this time measured directly at
> the battery!!! Not to be outdone by such a little problem, I took my
> volmeter to the car, lifted the hood, and checked directly on the battery
of
> the car, not the motorhome, and the car was not running: 27V!!!
>
> What am I reading? I could understand some pulsating DC being read as AC,
> when the alternator of the car is going, but the engine was not running
and
> there was no outside poser applied to the vehicle.
>
> As it seems to be normal, I am not overly concerned, but I am really
> curious. Does anyone have any idea?
>
> VA2JTM.
>
>

Well Georges, based on the limited information I gave, I understand your
skepticism. However, here goes: When checking the DC voltage (on the DC
scale), while xmitting, I had weird noise coming out of my mobile speaker.
It sounded like 60Hz hum. Then, I immediately disconnected the radio, and
switched the scale to ACV, just to see. This is when I read 27V. I even
checked with a second meter, and had exactly the same reading. Since I was
connected to shore power, I suspected some AC leak into the DC side. I then
disconnected the RV from shore power, and still had the same reading.
Really curious at that time at how come I should read AC voltage on a
vehicle with absolutely no AC anywhere, I took my meter to the car, and did
the same. First DC scale, which read normal, and then, switched to AC
scale, which also read 27V. At that time, having checked two vehicles each
with two different voltmeters, and had exactly the same readings, I knew
something was amiss, and suspected strongly that I was reading something
other than AC, but what. Thanks to Dennis Lee, I now have a very clear
explanation.

Yes I do know that to read DCV, one should use the DCV scale. If you had
read the original message completely, you would have seen that I first
switched to AC scale because I suspected I may have had some AC leak into
the DC side of the RV.

My conclusion is that both vehicle are OK, both meters are OK, it is just
the way they are designed. And again thanks to Dennis Lee.

VA2JTM

"George E. Cawthon" <GeorgeC-Boise@worldnet.att.net> wrote in message
news:3F42F42B.EBFC5D2D@worldnet.att.net...
> Well since two different vehicles were checked it is
> unlikely that both would be wrong so it is more likely your
> voltmeter. But you discussion explains exactly what is
> wrong. You used the ACV scale and you should have used the
> DCV scale since vehicles use direct current not alternating
> current.
>
> Just switch to the DCV scale. Excuse me for the skepticism
> but you are a ham?
>
> JTMinQC wrote:
> >
> > Having problems with a HAM radio, someone suggested I check the input
> > voltage, while xmitting. Since I was in the motorhome, and it was
plugged
> > in to shore power, (at home), after checking the DC voltage, which was
as
> > expected (12.6 VDC), I put the meter on AC voltage and checked. Well,
it
> > read 27V!!!! So thinking that maybe there was some leakage, or somehow
the
> > AC was leaking onto the DC circuits, I disconnected shore power, and
took
> > another reading: 27V on the ACV scale, and this time measured directly
at
> > the battery!!! Not to be outdone by such a little problem, I took my
> > volmeter to the car, lifted the hood, and checked directly on the
battery of
> > the car, not the motorhome, and the car was not running: 27V!!!
> >
> > What am I reading? I could understand some pulsating DC being read as
AC,
> > when the alternator of the car is going, but the engine was not running
and
> > there was no outside poser applied to the vehicle.
> >
> > As it seems to be normal, I am not overly concerned, but I am really
> > curious. Does anyone have any idea?
> >
> > VA2JTM.