truck electric leak

On Wed, 22 Apr 2009 19:16:43 -0500, the infamous "Karl Townsend" scrawled the following:

That'll drain a battery in no time.

Soak it overnight with Kroil and try -tightening- it first, then loosening it tomorrow. Sometimes it loosens easier the wrong way.

Reply to
Larry Jaques
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On Wed, 22 Apr 2009 19:16:43 -0500, the infamous "Karl Townsend" scrawled the following:

I forgot to ask if the alternator turns easily on the bolt.

A hammer on the end of the bolt can help loosen it, too, so try a few taps there now that you have the radiator out, Karl.

Reply to
Larry Jaques

On a friend's Hyundai with a Mitsu engine, I had the tube that the alternator pivot bolt went through splint lengthwise and come off. I took the car sans alternator to a welding shop. He ixnayed that, as the other side of that alum. front/side cover was the oil pump.

I cleaned both halves, wrapped a pencil in teflon tape and used JB Weld, then rubber bands to hold it in place to set. Four days later, we put the alternator back it, and it held. I heard later it lasted the three years until they sold the car.

(Remember, it's a goat for a SCSI chain, but the correct sacrifice for a rusted bolt and bracket is a Norway rat...)

Reply to
David Lesher

It's not likely to be the starter! A failed diode in the alternator is more common than most may think.

Steve R.

Reply to
Steve R.

If you know much about electrical circuits, and electronics, it's pretty hard to do a bad rebuild. I did my own for a couple of decades. Then I did it for a living for a while. There was not one bad rebuild in the lot!

Steve R.

Reply to
Steve R.

Over the years, I've had questionable results from rebuilt altenators from auto parts stores. Someone on a forum I happenned across in a search for something else mentioned that a junkyard unit was usually a better unit, since it at least hadn't failed once already like the "rebuilt" ones. Since I've switched, I've not had a bad replacement, so they may be on to something...

--Glenn Lyford

Reply to
Glenn Lyford

Follow up. JOY! Got it out with the torch. melted AL on the alternator I had it so hot.

Now I really really hope this is the cause of the current drain.

Karl

Reply to
Karl Townsend

Hey David,

I grok that it doesn't matter where the ammeter is in this 'series' branch of the network but I wonder what advantage there is in placing the meter in series with the ground side of the battery in relation to placing it in series with the hot side of the battery?

Is it a safety thing, to prevent bad stuff from happening should one of the wires slip and find ground?

--Winston

Reply to
Winston

You got it. The first bad thing is when you loosen the Hot terminal with a socket set, and the handle hits grounded metal.

The second is when you burn your hand on the now-hot wrench.

The third bad thing involves getting the acid and lead chucks washed out of your eyes.

Disconnecting the ground side first is just smart. It makes no difference in measuring.

Reply to
David Lesher

I'll disconnect the ground side first and use it for current sensing, from here on in.

Thanks!

--Winston

Reply to
Winston

"David Lesher" (clip) Disconnecting the ground side first is just smart. It makes no difference

^^^^^^^^^^^^^^^^^^^^^^^ Same safety precaution should be followed any time you are disconecting or reconnecting the battery, whether for measurement, replacement, cleaning or stealing ;-)

Reply to
Leo Lichtman

I shall leave a note on the air cleaner for Señor Herrera. (Wouldn't want him to hurt himself. That would make me feel badly.)

--Winston

Reply to
Winston

As others pointed out, the ohm meter reading isn't very reliable. My bad.

Harbor Freight has a centec multimeter that will read 10A DC. Slow response, yada but what do you expect for 4 bucks. If there is a HF near you, get one and check current with battery in circuit then get back to us.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

Reply to
Wes

There are several reasons to avoid the ohmmeter approach. First is you are asking to screw up and toast the meter. Even if it is a Harbor Fright $3 special, it's still a bummer.

But the bigger is this. The ohmmeter applies a test voltage to the circuit. It's going to be far less than the 13-15v a running car has. One of several failure modes for semiconductors is to leak, and the leak is proportional to the voltage drop... and not just linearly. Raising the voltage from say 5 to 10v might get you 10 or 100x the leakage, not just double.

Result? You do NOT see the leakage with an ohmmeter. You will see it in ammeter mode.

Reply to
David Lesher

"David Lesher" wrote: (clip) the leak is proportional

^^^^^^^^^^^^^^^^^^^^^ Basically what you say is right, but I have to correct you on this small nit: Proportional *IS* linear.

Reply to
Leo Lichtman

An Ohmic resistance is linear but semiconductor behavior is often exponential or logarithmic. A good example is the drop across a diode:

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down to the part about kT/q. The effect is that the voltage drop rises with the logarithm of the current.

This one shows how the forward drop changes inversely with temperature:

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In the 1980's 4-1/2 digit DVMs were very expensive and I built my own, using a constant-current source for the resistance function instead of the usual MickeyMouse shortcut that obscures the actual voltage and current passing through the resistor. Mine forced 1uA, 10uA...10mA and showed the true voltage. It would clearly demonstrate the logarithmic VI curve of a diode, from ~400mV to ~700mV. Unfortunately my ex used it to check her car and fried that circuit with 12V.

Jim Wilkins

Reply to
Jim Wilkins

diode:

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Scroll down to the part about kT/q.

So, could you do the usual electronics fault finding thing of using the diode check function on the output lead of the alternator? - (then reverse, repeat, see difference or none) even cheap DMM have them now

- (BTW - was yours a SABTRONICS kit?)? - or is it getting too complicated and as Karl has identified the Knuckle Crunching Alternator as being the culprit....

And I would humbly disagree re ohmmeters vs ammeter's - its all to easy to fry an ammeter, the 10a range on most DMM's is rated for a few seconds only, then the copper wire shunt disengages itself....besides,

10a is leakage current in a vehicle...and DMM's are now cheap, throw away items, but a decent ammeter is still expensive....

Andrew VK3BFA.

Reply to
VK3BFA

I just wanted to back up a minute and point out what was happening. 43 days with a decent battery is believable. The problem is that a shorted diode in the alternator is causing the leakage and is also preventing the battery from being fully charged.

I've seen this on one of my vehicles. A drain disproportionate to the discharge rate because of inadequate charging.

Reply to
Jim Stewart

(...)

You could do that if you could access the inside of the alternator. I guess that you could sort alternators with shorted diodes from the outside, by comparing the forward drop of the 3 phase rectifiers. The shorted units would have ~0.7 V less forward drop than the good units. A unit with two shorted series diodes would have ~1.4 V less forward drop, at least theoretically.

What vehicle normally experiences as much as 10A of battery drain, with the key out of the ignition and the lights off? Are there any?

Note that Karl revealed the high value of leakage current to be well within the range of his DMM:

The 10A current shunt built into the DMMs I use are 100% duty cycle and will tolerate 20A for 30 seconds without damage.

No fear that any of my DMMs will be damaged if used properly.

The DMM ammeter in series with the negative battery terminal is a safe and effective method for troubleshooting leakage current.

--Winston

Reply to
Winston

Yep, quite true.... I've also had ordinary diodes "go zener" instead of behaving.

But Leo seems to think proportional == linearly proportional. I disagree but decided it wasn't worth arguing about.

Reply to
David Lesher

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