Honda Car Forum

In article <Xns987B77E803509jyanikkuanet@129.250.170.84>,
Jim Yanik <jyanik@abuse.gov> wrote:

> BTW,if you want to extend the DC amps range of your inexpensive DMM,use a 1
> ohm resistor in series with what you want to measure(use short heavy leads
> soldered to the 1 OhmR),and the DMM measures across the 1 ohm R.
> Since I=E/R,1 volt across 1 ohm= 1 amp.
> If your DMM has a 2V range,that's 2 amps full scale.
>
> I'd use a 10W 1 ohm WW resistor.

....and be careful. If you by some mischance get it across the battery it
will try to dissipate I^2*R W. One ohm at 12V passes 12A, so thats 144W,
well in excess of the 10W its rated for. It will get red-hot and fail in
some interesting way, quite suddenly...

Nigel Spon <not@spum.invalid> wrote in
news:not-B71A34.12205515112006@kyle.snap.net.nz:

> In article <Xns987B77E803509jyanikkuanet@129.250.170.84>,
> Jim Yanik <jyanik@abuse.gov> wrote:
>
>> BTW,if you want to extend the DC amps range of your inexpensive
>> DMM,use a 1 ohm resistor in series with what you want to measure(use
>> short heavy leads soldered to the 1 OhmR),and the DMM measures across
>> the 1 ohm R. Since I=E/R,1 volt across 1 ohm= 1 amp.
>> If your DMM has a 2V range,that's 2 amps full scale.
>>
>> I'd use a 10W 1 ohm WW resistor.
>
> ...and be careful. If you by some mischance get it across the battery
> it will try to dissipate I^2*R W. One ohm at 12V passes 12A, so thats
> 144W, well in excess of the 10W its rated for. It will get red-hot and
> fail in some interesting way, quite suddenly...
>

So,if you're that inept,put a 3A fuse in series with the resistor,like many
DMMs that are fused for the current ranges.

Of course,any ammeter would also be a short across the 12V.


--
Jim Yanik
jyanik
at
kua.net

Hello again, I was the original poster of this thread. I'm posting an
update to the problem, for those who are interested.

After disappearing mysteriously, the parasitic load was back again last
night. Today I've finally found the problem. It's the *alternator*. I
found it by disconnecting the alternator ground. It was very hard to
find before because it was intermittent, but it's definitely the
alternator.

Bad alternator diodes..? I recall the problem started just after an
engine wash..

Thanks.

UPDATE:

For those interested, the problem is finally resolved. I was the thread
starter, asking about an intermittent parasitic drain that can't be
found. I finally isolated it to the alternator; and today, after a day
of trying, finally got the alt off. Brought it to a shop, and they
diagnosed the problem as "grounded rotor". Regulator, diodes all
checked out fine. They replaced the rotor with an identical (Nippon
Denso) rotor, and now there is optimal current drain and no parasitic
load. Total cost, including labor (if converted to US$): $24.

Thanks to jim, TeGGer, Earle and all the others who replied. More power.