randyoo@gmail.com wrote:
>> #1. learn how to use a meter properly. you do /NOT/ measure a dc
>> voltage with the meter set to ac.
>
> Before I go any further, I want you know that I'm grateful for your
> help. That said... I'm pretty sure I know how to use a multimeter. My
> intention was NOT to learn the DC voltage, but rather the amount of AC
> ripple, which exists in any DC generated by a rectifying circuit.
> Obviously, since I measured pretty much the same thing on another
> "good" vehicle, either my meter was wrong, or I'm not using it right,
> but I'm going to blame the sub-$10 digital multimeter, unless you tell
> me there's a different way to measure AC ripple on a DC voltage.

i doubt a meter that cheap will give you ripple since it'll need to
"offset" the dc. also, the ripple should be something of a funky
waveform since the alternator is 3-phase - it'll be 3 full-wave
rectified bumps, superimposed at 120 degrees each - so a cheapo r.m.s.
approximation will be off too. if you have one rectifier out, waveform
will be real ugly - ugly enough to cause noise on the audio system.
borrow an oscilloscope if you want to get serious about that stuff.

in the mean time, measure the dc voltage at idle, no load and at idle,
full load. if the readings are within spec, it's probably just brushes
giving you that startup flicker. also, check the gotcha of belt tightness.

>
>> #2. suspect a crock from autozone. there's no way an 80A alternator is
>> going to output 175A, even intermittently.
>
> I'm leery of what they told me, but I'm confused as to how two
> different stores, 6 months apart, managed to measure the same thing,
> and make the same diagnosis. I'd believe you over them any day, but
> I'm still curious as to what they're measuring...
>
>> #3. check the brushes on the alternator. they're cheap to fix. the
>> rest of the honda alternator is good for 300k miles very often.
>> #4. re mileage, check for gotchas like brakes stuck on, dying oxygen
>> sensors, etc.
>
> This is great advice. I never even considered the brakes/O2 sensors,
> either of which could be faulty by 150k miles, and would definitely
> impact fuel economy. Hmmm, O2 sensors... Maybe that cheap-***
> multimeter will come in handy, after all! At least I know how to get
> DC voltage readings from it, for sure!
>
> Thank you again for your time and help.
>
> -Randy
>
>

 

"Earle Horton" <apodo@gracioso.usa> wrote in
news:BNydnfMdVZVIipbbnZ2dnUVZ_ternZ2d@comcast.com:

><randyoo@gmail.com> wrote in message
> news:1175121753.078339.8680@b75g2000hsg.googlegrou ps.com...
> ...
>>
>> By the way, I measured 30 volts AC across the battery with the
>> engine running, and then went and measured another vehicle, and
>> got nearly the same reading, so I assume that most likely, that's a
>> normal reading.
>>
> I admit I never thought to measure AC across a vehicle battery. The
> alternator is supposed to have diodes in it, which filter out the AC,
> but I suppose you are going to get some fluctuation with the
> alternator making output. What is the DC voltage?
>
> Earle
>
>
>

his meter could measure pulsating DC on the AC mode,especially if it's a
True RMS meter. 30VAC seems odd.

DCV is more important,though.

--
Jim Yanik
jyanik
at
kua.net

 

"loewent via CarKB.com" <u10197@uwe> wrote in news:6fe61a42fbc3e@uwe:

> With regards to your crazy speedo, I had the same problem recently on
> my 98 Civic LX. Here are pics of what I found was wrong. The short
> blew my #15 fuse, which is for the Alternator and BOTH O2 sensors.

Wouldn't that turn on the CEL and set a code or two?

> If
> you've been driving around with this fuse blown, it would make sense
> that your mileage is in the pooper.
>
> My car runs like a top now, mileage back to high 30s. (and it has
> almost 300k kms on it)
>
> Pics have been uploaded to
>
> http://www.tegger.com/hondafaq/misc/..._mil%26fuse15/
>
> t
>
>
> randyoo@gmail.com wrote:
>>> #1. learn how to use a meter properly. you do /NOT/ measure a dc
>>> voltage with the meter set to ac.
>>
>>Before I go any further, I want you know that I'm grateful for your
>>help. That said... I'm pretty sure I know how to use a multimeter. My
>>intention was NOT to learn the DC voltage, but rather the amount of AC
>>ripple, which exists in any DC generated by a rectifying circuit.
>>Obviously, since I measured pretty much the same thing on another
>>"good" vehicle, either my meter was wrong, or I'm not using it right,
>>but I'm going to blame the sub-$10 digital multimeter, unless you tell
>>me there's a different way to measure AC ripple on a DC voltage.
>>
>>> #2. suspect a crock from autozone. there's no way an 80A alternator
>>> is going to output 175A, even intermittently.
>>
>>I'm leery of what they told me, but I'm confused as to how two
>>different stores, 6 months apart, managed to measure the same thing,
>>and make the same diagnosis. I'd believe you over them any day, but
>>I'm still curious as to what they're measuring...
>>
>>> #3. check the brushes on the alternator. they're cheap to fix. the
>>> rest of the honda alternator is good for 300k miles very often.
>>> #4. re mileage, check for gotchas like brakes stuck on, dying oxygen
>>> sensors, etc.
>>
>>This is great advice. I never even considered the brakes/O2 sensors,
>>either of which could be faulty by 150k miles, and would definitely
>>impact fuel economy. Hmmm, O2 sensors... Maybe that cheap-***
>>multimeter will come in handy, after all! At least I know how to get
>>DC voltage readings from it, for sure!
>>
>>Thank you again for your time and help.
>>
>>-Randy
>



--
Jim Yanik
jyanik
at
kua.net

 

If fuse 15 blew, CEL is on. If its not, its probably burnt out. It has to
go on as this is the fuse for the alternator and the O2 sensors. no power to
O2 sensors = P0135 and P0141.

t

Jim Yanik wrote:
>> With regards to your crazy speedo, I had the same problem recently on
>> my 98 Civic LX. Here are pics of what I found was wrong. The short
>> blew my #15 fuse, which is for the Alternator and BOTH O2 sensors.
>
>Wouldn't that turn on the CEL and set a code or two?
>
>> If
>> you've been driving around with this fuse blown, it would make sense
>[quoted text clipped - 43 lines]
>>>
>>>-Randy
>

--
Message posted via CarKB.com
http://www.carkb.com/Uwe/Forums.aspx...-cars/200703/1

 

jim beam wrote:

<snip>

> i doubt a meter that cheap will give you ripple since it'll need to
> "offset" the dc.

Plenty of cheap meters (including my $7.99 no-name digital DMM) will
read the ripple on top of a DC voltage. On the AC setting, the input
signal is AC coupled (through a capacitor).

Regardless, both the poster's car and a known good car measure 30V
ripple. This simply isn't so. There is something wrong with the meter or
the method.

<snip>


> in the mean time, measure the dc voltage at idle, no load and at idle,
> full load. if the readings are within spec, it's probably just brushes
> giving you that startup flicker. also, check the gotcha of belt tightness.

With the caveat that on some cars (like my '94 Civic) the set point for
the voltage regulator is lowered while at idle (if a few other
conditions are met). Bumping the RPMs up a tad from Idle makes the set
point return to 14.5V (nominal).