Re: DMM Question. Have I done something wrong?

["darren_karp2001" <darren@xxxxxxxxx>]

Thanks for the replies!

Bit confusing for me I think. I'll stay clear of measuring current!



--- In ukha_d@xxxxxxx, "James Hoye" <yahoo@j...> wrote:
>
> > I bought myself a new DMM from B&Q (A rapitest MAS830L) which
seems
> > fine. I went to try and measure the current of my cordless phone
by
> > connecting the probes to the battery whilst the phone was on. I
got a
> > reading but a few seconds later the phone went dead and the
batteries
> > were very warm! I let them call down and all was well. Was I
doing
> > something wrong whilst trying to test the current?
>
> Well, to test current, your meter needs to be in SERIES with the
device you
> are measuring.
>
> You need to effectively break into one of the leads powering the
device, so
> that the power flows THROUGH the meter.  The ideal current meter
has zero
> resistance, ie. it appears "transparent" so that it does not
alter
what it's
> measuring.
>
> It sounds like you connected it ACROSS the battery thereby
creating a short
> circuit - hence the batteries getting rather warm.  You use this
method for
> measuring the VOLTAGE (since an ideal voltmeter should have an
infinite
> resistance).
>
> Please don't try this on mains unless you are absolutely certain
of what you
> are doing!
>
> James
>