1978 650 yamaha voltage loss - Page 3

 
I pretty much had the same impression as you did Rob, Kim doesn't know
how to measure what's going on, and he might or might not have a problem
with his bike or simply has a bad battery.  This is not a slam against
you, Kim.

Look for a forthcoming post saying 'when I put the meter across the
battery in the amp measuring mode, it blew the fuse, why is that?'...

All I can offer is, if you don't understand simple electrical circuit
concepts and at a minimum, Ohm's law, (not to mention Kirchoff, Thevenin,
Bios-Savart, Faraday, and all those other guys' laws...) don't expect
to do meaningful electrical troubleshooting.

--
'01 SV650S  '99 EX250-F13  '98 ZG1000-A13
OMF #7

 Mark Olson wrote:

connected.


My guess is that there'd be way less than an amp draw with
the key off and any autoranging digital meter ought to be able
handle that. Given that he's reporting .2 volts, I'd bet that's
what he's got.

In thinking about this, I'll bet Kim's getting his advice from
Clymers. I've seen Clymer slammed before for giving this same
advice about reading voltage on BMWs.

You can actually get a sort of meaningful reading if you use
a cable as a shunt and measure voltage drop. I once cobbled
up a fairly meaningful ammeter reading on a photovoltaic
system that way.

Clymer though wants you to disconnect the cable and look for
voltage between the disconnected cable and battery and with
modern meters, this is foolishness.


Volts times amps = watts. What else is really needed here ?
We already know volts too.

 Rob Kleinschmidt wrote:

Sure, if he put an ammeter in series with the battery (+) and
the starter relay.


It's the only reasonable way to measure high currents, and it's
far more useful for finding the typical wiring fault in bike
wiring which is poor connections which are low Ohms, but still
enough resistance to add up to a significant voltage drop.  Too
often people with a little knowledge think they should measure
a circuit's resistance when they really should measure voltage
because the readings they will get on a typical voltmeter are in
a reasonable range whereas a cheap meter won't accurately measure
Ohms to a precision of less than one Ohm.


Again, most of the time you are trying to spot the worst offender(s)
in a series of more or less working connections, and voltage drop
measurements are the best way to do that.

--
'01 SV650S  '99 EX250-F13  '98 ZG1000-A13
OMF #7

 
Kim Neubert wrote:

Be aware of the pitfalls of digital readouts.

It is amazing to see how many people trust the readout of a digital
scale.
The meter says 12.3 so my battery holds 12.3 Volts.

WRONG.

People (like myself) tend to throw away the badly translated Japanese
specs*) that came packed with the meter.
That spec says something about the accuracy of the device (and the
accuracy differs with the range setting too).

My spec may have told something like:  "at 20V range; +/- 2% +/- 1
digit".

Doesn't sound too bad eh? 2% isn't much. Well let me do some
arithmetic.

It means that with a real 12.3V inside your battery, the meter may
display something between 12.3 minus 2% and 12.3 plus 2%.
Which is 12.05 and 12.55
And the last digit (cypher) may then be off '1' too,
leaving any reading between 12.04 and 12.56 possible.

It is even worse. Most cheapos only have a three-digit readout,
and the above then becomes 12.1 through 12.6 with an accurate
last digit, but 12.0 though 12.7 with that last digit unreliable.

Especially those people that read 12.0 at their battery start
complaining
about a draining battery. "I just charged my battery, and all by itself
it drops back to 12.0 Volts."

So: What do you mean by: "My battery gets drained". Does it mean you
read a
low voltage with your meter, or does it mean that your bike will not
start.

If the bike happily starts when you read a low voltage, you need a new
meter.

The idea of a measuring voltage drop over the wire was not really a bad
idea for a quick check, but it tells you nothing.
True, when your battery is being drained, and the wire has some
resistance (which
it has) there will be some voltage drop along the wire.
- But because you have no idea what resistance the wire has, it does
not
  tell you how fast the battery is being drained (IF it is being
drained at all).
- But because you -probably- have a cheapo meter, that .2V reading
  can be off, and the voltage drop across the wire could be 0V or 0.4V
  You simply don't know.
- But because you are connecting different materials (tinned probe
  and [probably] lead-cladded battery post) you basically create what
is known as
  a battery, and measure the voltage that that tiny battery generates.
  Take two coins of different materials, spit on one, place the other
on top
  and measure the voltage between them.
  That is how a battery works.

Now, what can you do?
Switch off everything on your bike.
Unhook the negative post of your battery.
Set your meter to the highest amp setting (probably like 10Amps).
Hook up your meter probe between the negative post of your battery and
the wire that you just disconnected from it.
Read the meter.
If it says 0, you safely can set your meter to a lower amp setting
(probably 3Amps)
Reread and go to a even lower setting if you still read 0Amps.

I would be happy if my meter would read something like 1 milli-Amp.
I have a 12Ah battery, and draining 1mA would mean it takes about 500
days
to get a flat battery. Even if my cheapo is off by displaying '1',
while
meaning '3' it would take 166 days.
I don't know how long it takes for a battery to self-discharge, others
may
tell you that. But I certainly let not sit my battery unattended for
166 days.

If you read something in that 1 to 3 milliamps region, and your battery
gets
flat in a jiffy to the point that your bike won't start, you need a new
battery.

Rob.

*) The spec told me not to unscrew the
   back panel. How the hell am I supposed
   to insert a fresh battery in that thing?