still confused on testing for battery draw

albosma · 07-31-2006, 07:10 AM

One person says I need to put my ampmeter between the positive cable and the positive terminal (after disconnecting cable of course), and someone else says it's the negative cable and the negative terminal?

Also, I have other wires coming off my positive cable. Would I need to take those off before testing?

thanks!

rick-l · 07-31-2006, 07:14 AM

It doesn't make any difference where you measure the flow in the circuit. Current flows from the positive terminal and an exactly equal amount into the negative terminal.

albosma · 07-31-2006, 07:26 AM

well, I'm getting zero draw putting the meter between the negative terminal and the negative cable (after disconnecting). with an alarm and a clock, I should be getting something right? I even had my ampmeter on 2 milliamps and still showed zero.

equality72521 · 07-31-2006, 07:28 AM

Are you sure you have your meter cables plugged into the proper jacks? Black to common and red to the milliamp jack? It's common for people to have the cables plugged wrong.

albosma · 07-31-2006, 07:32 AM

I actually read the manual! yes, black to common andred to the Ampmeter hole. maybe I'll try the positive terminal to the positive cable.

Rot 911 · 07-31-2006, 07:32 AM

You can put the meter either way between the pos. terminal and pos. cable or neg. terminal and neg. cable. It will show a drain (if there is one) either way.

albosma · 07-31-2006, 07:39 AM

thanks. my battery keeps dying if I don't drive it for more than 1-2 weeks so there must be a drain. I'll try the positive side.

Zeke · 07-31-2006, 07:51 AM

First off, try your meter turned to voltage to verify continuity. Then switch it over to ampre readings. Do go too low at first, you don't want a load going thru milliamps. Work your way down. Now, the clock in my car "rewound" itself every minute or so. There is no constant draw. If your alarm is not set, no draw.

albosma · 07-31-2006, 07:54 AM

I just read somewhere that 0.3 Volts = 300mA. My regular mechanic (not a Porsche mechanic) said they got 0.3V when they tested for draw. That would be 300mA. My ampmeter only goes up to 200mA. I wonder if I blew my ampmeter fuse. 300mA would be way too much draw right? Does 0.3V = 300mA?

Wil Ferch · 07-31-2006, 08:38 AM

volts is not amps..... !!!

think of volts as potential energy ( the energy a bowling ball "has" at the top of a cliff, relative to ground if it should fall).

Think of "amps" as current draw or "flow"...a completely different concept. Pardon my bluntness....but people who don't understand electricity ( "basics") shouldn't be allowed close to their cars with electrical tools...it can get very dangerous. Bone up on the basics...then have at it.

- Wil

911pcars · 07-31-2006, 08:43 AM

Check the fuse in the multimeter. It might be a goner if it doesn't display any current flow. The voltmeter itself has high internal resistance and doesn't need/use a fuse.

You're connecting correctly to the battery.

Sherwood

albosma · 07-31-2006, 08:47 AM

hey, I know volts are not amps. What I'm asking is if I see a 0.3V draw across my multi-meter when I do a draw test, would the corressponding amerage be 300mA? Anyway, don't bother responding. It seems I was testing it correctly and I'm guessing my draw is too high for my ampmeter to register. I'm going to get a ampmeter with a higher scale and try it again.

911pcars · 07-31-2006, 09:13 AM

Quote:

Originally posted by albosma
hey, I know volts are not amps. What I'm asking is if I see a 0.3V draw across my multi-meter when I do a draw test, would the corressponding amerage be 300mA? Anyway, don't bother responding. It seems I was testing it correctly and I'm guessing my draw is too high for my ampmeter to register. I'm going to get a ampmeter with a higher scale and try it again.

No. The 0.3V reading represents the voltage drop or loss as a result of the meter connections between the negative cable and negative bat. post- fairly typical of a temporary elec. connection.

Most multimeter ammeter circuits have a current capacity of 10amps - more than enough to measure parasitic current loss. If your system is leaking more than 10A at rest, there would be an accompanying smell of burning car and tell tale smoke (in other words, not the case). I'd guess either the ammeter portion of your gauge is lunched or the ammeter fuse needs replacement.

Sherwood

Wil Ferch · 07-31-2006, 09:16 AM

Well...I certainly don't know "what you know"...and you were asking !

who knows if this v=a correlation works at *one* reading??? Best to measure "Amps" if that's what you're chasing.

You don't mention your car.... for reference, a mid 80's Carrera spec stand-by draw is 16mA... a 964 is more like 65 mA. Common convention for all cars is to start worrying at 100 mA ,at least ......

Cheers,
- Wil

rick-l · 07-31-2006, 09:48 AM

Quote:

You can put the meter either way between the pos. terminal and pos. cable or neg. terminal and neg. cable. It will show a drain (if there is one) either way.

Make sure the other cable is connected however!!!!!

Do not try to measure the current from + to - with your meter.

I can not imagine what the .3 volts you are reading is. Are you putting another voltmeter across your meter and reading the voltage on the current shunt in your meter?

albosma · 07-31-2006, 09:52 AM

thanks to everyone. I'm going to check my ampmeter - I could swear the highest setting was only 200milliamps, but seems like it should have a higher setting than that. I'll check it when I get home and buy a "bigger" one if I have to.

Tom '74 911 · 07-31-2006, 01:08 PM

sorry in advance for hijacking - kind of related though:

Can someone recommend a resource (book) to learn about the electrical system etc... in these cars. Mine is a '74 911. I know I don't know enough to foll w/it, but want to learn and would love some suggestions.

Thanks,
Tom

911pcars · 07-31-2006, 01:22 PM

Metric electrons are pretty similar to American electrons. The only difference is the way Porsche lays out their electrical diagrams - that is, compressed. Avoid the black and white versions of the electrical diagrams. You'll shoot yourself eventually.

Obtain the color versions of the diagrams that conveniently match the wire colors to your car. Purchase an inexpensive digital multimeter and read/study the included instruction manual and/or the many websites that attempt to simplify how electricity and automotive circuits work. In addition, there are many, many excellent textbooks on basic automotive electricity fundamentals.

Sherwood