Checking for a parasitic battery drain....

[rothsean]

So I had a battery go bad and I got a free replacement. I installed the new one but I want to make sure that there is no parasitic drain when the car is off.

I have a multi-meter clamp tester and I clamped the tester to the positive cable of the batter when I was inside with the key off and the doors closed. The lowest setting for my digital tester is 20. I set it to 20 and it showed 0.00 when connected. I tested it by turning on the headlights and it had a quick jump to .17-.44, then back to 0.00.

Is all that normal or did I miss anything?

[Bitsyncmaster]

You won't be able to read the low currents of standby currents with a clamp on 20 amp meter. You will have to pull one wire off the battery and use a milliammeter connected to that removed wire and the battery terminal you removed it from.

[rothsean]

You won't be able to read the low currents of standby currents with a clamp on 20 amp meter. You will have to pull one wire off the battery and use a milliammeter connected to that removed wire and the battery terminal you removed it from.


So do they make a clamp milliammeter ?

[Bitsyncmaster]

So do they make a clamp milliammeter ?

I have not looked for one with a low range. Mine has 20 amp and 200 amp ranges.

[Farrar]

If you have a multimeter, see if it might have a low amp scale. Some of them do.

[David T]

Most multi-meters have a low amp scale but you can easily blow any fuses in it just by opening a door and turning on the light. A cheap and easy way is to just stick a small light bulb in series with one of the leads going to the battery. If the bulb is bright you have a big drain and if it is dim you are probably OK. If you can measure you should see less than 50 MA. I do not believe there is a clamp-on meter that measures in that range. When testing for drains you must disable the interior lights but remember that you are not testing that circuit and it could be the problem! I like the old fashioned analog meter with a scale so I can see how a drain is and if it is steady or it rises and falls. You can't do that with a digital display.
David Teitelbaum

[rothsean]

Most multi-meters have a low amp scale but you can easily blow any fuses in it just by opening a door and turning on the light. A cheap and easy way is to just stick a small light bulb in series with one of the leads going to the battery. If the bulb is bright you have a big drain and if it is dim you are probably OK. If you can measure you should see less than 50 MA. I do not believe there is a clamp-on meter that measures in that range. When testing for drains you must disable the interior lights but remember that you are not testing that circuit and it could be the problem! I like the old fashioned analog meter with a scale so I can see how a drain is and if it is steady or it rises and falls. You can't do that with a digital display.
David Teitelbaum

I have one with a scale too. It goes down to 10 amps on the selections.

Even when I selected 20 on my clamp multi meter is still showed 0.00. I would assume that a small drain would at least be 0.01 or something like that.

[Elvis]

A digital measuring device can't be accurate at the lowest end of its measuring range.

it's always +- some % and additionally +-1-2 digits.

It's like using a yardstick to measure the tiny parts inside your watch.


Is it even a DC clamp ? The cheapest ones measure just AC !!!!!!

[Exolis]

You can get clamps that will measure mA, but the probe itself is probably 2-3k then the oscilloscope will cost another 5k+. As for a Multimeter, like everyone has said, using it as Ammeter is your best bet and accurate.

Parasitic current or Dark Current as we call it at Nissan, is essentially going to always exist since your do have things such as radio with memory. Granted the DeLorean doesn't have much things for Dark Current, but anything connected to B+ has potential to add on to Dark Current. Long as you are about 15-20mA or under, you should be good and shouldn't discharge the battery much if left a few weeks off.

If so desired, you can purchase a small solar panel and hook it up to B+, that way it essentially gets rid of any dark current while the car is off.

[rothsean]

You can get clamps that will measure mA, but the probe itself is probably 2-3k then the oscilloscope will cost another 5k+. As for a Multimeter, like everyone has said, using it as Ammeter is your best bet and accurate.

Parasitic current or Dark Current as we call it at Nissan, is essentially going to always exist since your do have things such as radio with memory. Granted the DeLorean doesn't have much things for Dark Current, but anything connected to B+ has potential to add on to Dark Current. Long as you are about 15-20mA or under, you should be good and shouldn't discharge the battery much if left a few weeks off.

If so desired, you can purchase a small solar panel and hook it up to B+, that way it essentially gets rid of any dark current while the car is off.



Ok, so this conflicts with some other people. So the multi-meter that I have will work or not? When I hook it up it shows 0.00 at the 20A selection, which is the lowest that my meter goes down to.

[Exolis]

Ok, so this conflicts with some other people. So the multi-meter that I have will work or not? When I hook it up it shows 0.00 at the 20A selection, which is the lowest that my meter goes down to.

With the clamp and using it on the battery terminal cable, you should see something way higher. Theres a good chance you might have it in AC and range off since it was probably just picking up the Current spike with the headlights.

It maybe possible to still use the clamp you have for dark current measurement, but with it being so small, it's most likely not to be very accurate at all.

Though if you have extra cash, something like this would work. http://www.amazon.com/GTC-CM100-Current-Clamp-Meter/dp/B001TCWL1E/ref=sr_1_11?ie=UTF8&qid=1371141800&sr=8-11&keywords=amp+clamp+meter But for cost efficient, a cheaper DMM will work by using the Ammeter function. For a non-clamp DMM, you just leave the terminals connected, place one clip on terminal and other on cable and then pull away cable (while on High Amp Fuse, check to make sure it's asleep(or low enough that you can switch to Smaller Fuse), connect cable back then switch probe to smaller fuse. You will want to avoid disconnecting the battery while doing this so you don't get any in rush current reconnecting or reset anything(for accurate measurement).

Sorry if anything is unclear, I'll try to explain more if needed.

[Dangermouse]

So the multi-meter that I have will work or not? When I hook it up it shows 0.00 at the 20A selection, which is the lowest that my meter goes down to.

We don't know which meter you have so it is hard to say. Model #


When you say "clamped the meter to the cable", I assume you mean "clamped the meter around the cable"??

[Bitsyncmaster]

Most multimeters have a 10 or 20 amp fused range and a lower milliamp range fused at 1/2 amp or so. So what Exolis is trying to say is keep the battery connected along with the meter connected so when you remove the battery cable you don't get a momentary open circuit.

My tape deck will initialize when power is applied so I get a larger current for the first few seconds when connecting the battery. My meter on the milliamp range will handle that current without blowing it's fuse but some meters may not.

The stock standby current on our D is about 20 ma. That drain will let you go about one month (good battery) and still start the car. But then your battery is half dead so you need to do a long drive or put a charger on it or it will not go another month.

[David T]

The following creates the standby power drain (aka parasitic or "dark" power) when the car is not running:
Radio (keeps the presets and if the ASI radio, the clock going)
Console clock (if the earlier Craig radio)
Door lock module (there is a mod to reduce it's standby draw)

That's IT! Nothing as compared to the newer cars with all of the computers. In them you won't go 2 weeks without draining the battery so much that if it is cold or the battery is a little old the car won't start! Most of the time any problems are caused by either junk that was added to the car (mainly car alarms), interior lights that don't go off, or a bad battery. You must remember the lights on the bottom of the door can be on and you will never see them so if you have the 2 interior lights off and for some reason the door switches are not shutting that circuit off, that can kill the battery pretty fast, especially if you still have the filament type (not LED) bulbs. A very good investment is a battery master switch. On my car I have one and I added an in-line fuse ahead of it to power the radio circuit to hold the presets and keep the clock going even with the master off. I also use a Battery Tender for 1 day once a month if the car is not being used and I use it the night before I know I am going to be using the car so I have a fully charged battery all of the time. Makes life much easier for the alternator and the battery also lasts longer. A solar panel is a good idea to overcome standby power loss but not if the car is kept in a garage!
David Teitelbaum