Parasitic Battery Draw

[STB2000]

I'm trying to diagnose a battery drain and want to ensure I'm going about it correctly.

Using an analog multimeter with the negative probe on the battery's negative terminal, and meter's positive probe on the battery's negative wire, I've set the DC selector 50, and the gauge's needle goes to 50.

I'll attach a photo if someone can help me with the instructions using this interface on a PC.

I've removed all of the fuses and still see 50 on the gauge.

Appreciate your help.

[corvair500]

Do you have multimeter set to read DC-Volts ? Do you have one of the battery terminals disconnected from the battery ? There is no way that I am aware that you would read 50 volts anywhere on the car .

[STB2000]

Negative cable removed from battery. Meter dial is set to the side with a V and a symbol that looks like a m.

[STB2000]

Sorry, meter is reading 10, not 50.

[corvair500]

So , you have nothing on negative battery terminal and are measuring from positive batt term to the neg cable ? There should be no voltage . Maybe you have multimeter set to measure resistance in Ohms ????

[STB2000]

Measuring from the negative terminal to the negative cable. Meter is set on DC volts.

[bbodie52]

I'm confused and uncertain as to what testing method and scale you are using. Perhaps the face of this sample multimeter will help you to describe your meter settings?

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Are you using a digital camera? Can you copy or transfer your image files to your PC hard drive or to a thumb drive that is plugged into an USB port and has a drive letter assigned to permit file access?

To upload a file image to a new post, scroll down in the new post editor and click on the Attachments tab. then click on the Add files button below that and navigate to the file(s) you wish to upload.

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Sample Image

I hope this helps!

[bbodie52]

There are two wires coming from the positive battery terminal. The thick (6B, 6 gauge, Black) cable carries voltage only to the starter solenoid, to power the starter motor (and boost the ignition coil spark) when the key is turned to START. The thinner wire, (labeled 12R, 12 gauge, Red) provides power to everything else in the car via a wiring JUNCTION point next to the battery, attached to the perimeter frame in the engine compartment. The voltage regulator and alternator art tied to the battery at this point. You might try further isolating the alternator by disconnecting the connections to the alternator (at the alternator terminals). A shorted diode in the alternator could result in a battery drain.

How would a shorted diode affect alternator output?

Leaky or shorted alternator diodes can cause rapid changes in the output voltage of the charging system. In addition, bad diodes can also allow current to leak from the battery back through the alternator to ground.

For shorted diode testing procedures, see page CHARGING SYSTEM 6Y-7 in the attached 1965 Corvair Chassis Shop Manual - SECTION 6Y - ENGINE ELECTRICAL



https://ssl.corvair.com/user-cgi/catalo ... ow_page=84

Not all circuits are fused. The headlight switch, for example, is not fused by the fuse block. The wiring schematic included below can help you to follow the various circuits in the car.


Left-click the image to enlarge it for better viewing or "Pan & Scan" Click a second time for maximum enlargement...

1965 Corvair Monza Full Schematic

CORVAIR COMBINED WIRING SCHEMATIC DIAGRAMS
viewtopic.php?f=225&t=12968

[STB2000]

Thanks for the tip on the photo! Here's the setting and the reading.

[STB2000]

No change to the reading after removing the wires from the alternator terminals.

[joelsplace]

If it has an aftermarket radio disconnect it.
Check the heater duct over the starter. They will rub on the positive terminal and drain the battery.

[gbullman]

There are 2 approaches to see what sort of draw you have with nothing on; either measure resistance with no battery or current with the battery.

Your meter has pretty low capacity for measuring Amps (250 mA max or .25 Amps) so I would measure resistance to be on the safe side.

Disconnect both cables from the battery and use the ohmmeter to measure the resistance between them with red lead going to the positive cable and black lead to the negative cable. The amount of ohms you read will allow you to estimate how much current is flowing when the battery is connected.

Basic Ohms Law is
Volts = Amps x Ohms

You want to know how much current is being drawn so you would use this form
Amps = Volts / Ohms

I would use 13 for the Volts, divide that by how many ohms you're reading and that is roughly the current that is being drawn when the battery is connected.

If your ohms are greater than 52 then you can actually measure the current with your meter without damaging it. To do that you connect the positive cable to the battery, the red lead of your meter goes to the negative cable and the black lead goes to the negative battery terminal.

If you have a modern radio that will draw a tiny amount of current and if the clock is trying to wind that will show up as heavy load until it winds.

I always do these checks before connecting power to a car that has been disconnected for a while. I have the advantage of a 10 Amp meter so can read a pretty decent load without hurting the meter. With nothing on I would look for Amp readings well under 100 mA (.1 Amps), the lower the better as far as draining the battery.

Hope this helps.

[STB2000]

Thanks! I’ll try that approach.

[STB2000]

Culprit was the heater hose on the starter. Thanks all for your help!

[bbodie52]

Those pesky, wire-wound heater hoses can cause damage if they are not properly supported! In your case the metal reinforcing wire apparently created a periodic or partial short to ground that drained your battery.

A silver heater (air) hose is missing its strap and hangs down to rub on the passenger side axle. It looks like the rusty exhaust pipe is doing the rubbing, but that's just a bad angle in the photo. The rust is on the surface of the axle, not transferred from the exhaust pipe.

Years ago I was working on a neighbor's Late Model Corvair, and I discovered that the heater hose on the driver's side was hanging down and was rubbing the left half shaft. This had been going on for some time, as the hose reinforcing wire had cut like a metal lathe a wide notch in the center of the shaft, reducing the thickness of the shaft tube considerably!