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Discussion Starter #1 (Edited)
We have a 1999 Subaru Legacy which often sits for 3-4 months at a time without use. When we put it in service again, the battery would be drained, so I've been removing the cable from one side before it sits. I've recently installed a new battery.

Now I have a meter that measures amps, but have almost no experience using it. It's a PT (brand) meter. (pic)

One of the YouTube videos I watched says all you need to do is put the meter in line on the positive side and read the 10 amp scale. I did that and the meter read 0.00, showing no draw. Is it really that simple? Does that really mean there is no significant draw? Thanks.
 

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the standby drain for a lot of vehicles will probably be around 10 mA. the 10 amp scale will not show anything that small, switch the DVM down to the 200 mAmp range, it should then give you a reading in the 5 to 20 mA range.

Worst case, go to the lowest scale, but I think that will peg out as "Over Range"
 

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Discussion Starter #3
the standby drain for a lot of vehicles will probably be around 10 mA. the 10 amp scale will not show anything that small, switch the DVM down to the 200 mAmp range, it should then give you a reading in the 5 to 20 mA range.

Worst case, go to the lowest scale, but I think that will peg out as "Over Range"
Thanks, John.
 

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On the 200mA scale the amp reading is .02.

Does that seem normal?

Do you think that would drain a fully charged battery over, say, 4-5 months?

Thanks.
 

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On the 200mA scale the amp reading is .02.

Does that seem normal?

Do you think that would drain a fully charged battery over, say, 4-5 months?

Thanks.
That is exactly what I expected, yes, that is normal.

that is 20 milliAmps and over the space of 4-6 months, will kill the car battery.

So, I advise you to do one of two things.

Lift the Negative Terminal ( far safer, if the wrench touches the car chassis, no sparks )

Or, install a huge breaker like we use on airplanes and big diesel trucks.

turn it to OFF, and the battery is disconnected.

My gl1800 has a Voltmeter wired HOT to the battery terminals.
That VM has a small drain of about 3 milliAmps.

but, the bike already has a Standby drain of about 10 milliAmps.

I noticed immediately, that if I did not keep a Battery Tender on the bike, that in six weeks time, it would not start.

-------------------

To put this into context, I used to work for a rural telephone company in Utah.
We covered the whole state servicing little tiny communities and mining camps.

The miles to get from the NW corner to the SE corner of the state is astronomical, so we used airplanes to get around. We had two of them, one for the boss, and one for me.

at each of the little airstrips we used, we had an older car, usually a Ford Ranchero because of the inline six, and the PU bed can be used to haul stuff.

We removed the batteries, and locked them up in a storage unit on site.
There would be times that the cars sat for 6 months or more, before we had to use the car again.

Install the battery, spray a whiff of Ether in the air filter housing, click, varoom!!!

those batteries held up over the winter months at -59 degrees, so we had to use Ether to keep from ruining the battery trying to pump gas from the tank up to the carb. the Ether allowed the engine to crank immediately, and the high RPMs made the fuel pump work great.
 

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Discussion Starter #6
AZgl1800;5861209 that is 20 milliAmps and over the space of 4-6 months said:
John, thanks for the explanation. I need a little more education:

1. On the 200 mA scale, isn't a reading of 0.02 two one hundredths of a milliamp?

2.What would a reading of 1.00 be? Not 1 mA?

3.Or does the reading mean .02 of full scale, which would be 4mA. I'm confused.(Obviously)

In any case, I think I'll just pull the cable from the negative terminal, as you suggest. I've been using a breaker that apparently died, and I've been advised by a couple semi-knowledgable people to scrap it. Thanks for your help.
 

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John, thanks for the explanation. I need a little more education:

1. On the 200 mA scale, isn't a reading of 0.02 two one hundredths of a milliamp?

2.What would a reading of 1.00 be? Not 1 mA?

3.Or does the reading mean .02 of full scale, which would be 4mA. I'm confused.(Obviously)
I would need a picture of the meter while it is showing you that display.
IF, it actually shows a period in front of the '02', that would be in the MicroAmp range, and if that is true, you should be able to switch down to the 200 MicroAmp scale and then you would see 20.0 or close to it.

on the 200 mA scale, 20.0 would be 20 mA
I never saw a DVM that displayed 0.02 on the larger ranges.
maybe some do now?? mine is 20 years old now.
 

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John, thanks for the explanation. I need a little more education:

1. On the 200 mA scale, isn't a reading of 0.02 two one hundredths of a milliamp?
Back to question #1.

you are correct, if the display is showing 0.02

2/100 of 1 mA is 20 uA

0.02 actually means 0.020 as the scales go by a 3 digits at a time,

you want to keep switching the meter down scale until you are getting a display in Positive digits.

e.g. use the 200 uA range to cause it to display 20.0 or 20 microAmps
that will verify your thinking.
 

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Discussion Starter #9
Thanks, John.

.02 amps doesn't sound like much to me. I'll try the scale that has the next higher resolution in the morning. Won't change the parasitic draw, but will be more accurate. Sure do appreciate your help.
 

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if it is actually 20 uAmps,

it should not make a difference if the battery is left connected.

was the top of the battery clean and free of corrosion?
and are you using a protective battery terminal paste to coat the terminals to prevent corrosion? I use an old toothbrush to scrub it good.

I do... usually it is red in color. I first take the terminals apart, clean every thing in a baking soda solution, rinse, and do it again until no fizzing can be seen.

Dry it off well, put on a light coat of terminal grease on the battery post.
[ame]https://www.amazon.com/Permatex-22058-Dielectric-Tune-Up-Grease/dp/B000AL8VD2[/ame]

tighten it all up, and liberally coat the whole thing with the protector coating.

https://www.crcindustries.com/products/battery-terminal-protector-7-5-wt-oz-05046.html

most auto parts stores carry it, as well as Home Depot.
 

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Let's take a step back. When you put the meter in line, did you actually disconnect the cable, put one meter lead on the battery and the other meter lead on the now disconnected battery cable? I recommend using the negative side as John noted, for the same reasons. It isn't really likely that your ECU only draws 20 microamps. That would make it the most efficient ECU I'm aware of. I would suspect something in the low 100 to 300 milliamp range.
 

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the standby drain for a lot of vehicles will probably be around 10 mA. the 10 amp scale will not show anything that small, switch the DVM down to the 200 mAmp range, it should then give you a reading in the 5 to 20 mA range.

Worst case, go to the lowest scale, but I think that will peg out as "Over Range"
Well, worst case would be blowing the fuse in the meter.
 

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I'd find 0.02A (20mA) a whole lot more believable than 20µA.

Just my 02¢ :ROFL:
 
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Discussion Starter #14
John:

Yes, I cleaned off all the corrosion with a wire brush, then steel wool, and then used dielectric grease. Never thought to use the baking soda solution, but I will next time.

ToniMax and DW:

I thought 20 micro amps sounded awfully low. I tried it first on the negative side, but the reading kept bouncing around. Maybe I was on the wrong scale. I'll do both sides today and take a couple of pictures. Thanks for your comments.
 

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I suggest you make ALL current measurements in the Negative lead cable.

Why? the Positive lead cable usually has several wires coming off of it,
1. starter motor
2. ECU
3. Accessories

it is difficult to keep all of those tied together and get an accurate reading of the standby current.

whereas, using the Negative lead only, has just one (1) cable/wire going to frame ground. that ensures that you can measure all of the total current drain.

Rule of using Ammeters.
ALWAYS START ON THE MAXIMUM SCALE AVAILABLE.
then note what is displayed.
? too low to measure? switch down to the next lowest scale.

Repeat as necessary to get a valid meter reading.

as mentioned, 20 MicroAmp is totally ludicrous for the standby current of any ECU that has ever been manufactured. ( for cars anyway )
 

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I suggest you make ALL current measurements in the Negative lead cable.

Why? the Positive lead cable usually has several wires coming off of it,
1. starter motor
2. ECU
3. Accessories

it is difficult to keep all of those tied together and get an accurate reading of the standby current.

whereas, using the Negative lead only, has just one (1) cable/wire going to frame ground. that ensures that you can measure all of the total current drain.

Rule of using Ammeters.
ALWAYS START ON THE MAXIMUM SCALE AVAILABLE.
then note what is displayed.
? too low to measure? switch down to the next lowest scale.

Repeat as necessary to get a valid meter reading.

as mentioned, 20 MicroAmp is totally ludicrous for the standby current of any ECU that has ever been manufactured. ( for cars anyway )
Thanks, John, for the information.

Below are pics of the meter inline on the positive side and the negative side. The scale for both is 200m on the meter. The readings on both sides are in the 60s, i.e. ~62.X, as you can see. Do you think this mean that it's worth pulling fuses to chase the link?

FWIW: I hear a fast ticking sound when the meter is hooked up, but not when the cables are attached. What's with that?
 

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Yes,
you need to pull fuses until you find what circuit has that much standby current.

that is enough to kill the battery in a matter of a few weeks, depending on the CCA size of the battery. If that were on your bike's battery, it would be dead within a week.
 

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FWIW: I hear a fast ticking sound when the meter is hooked up, but not when the cables are attached. What's with that?
I would anticipate, that on the 200 mA scale, the meter is too much resistance for whatever is trying to pull current. to me, sounds like a relay is trying to pull in.... a relay would explain that much current.

So, since you hear ticking ( relay ), the standby current is going to be more than the meter is showing, since the "relay" or whatever cannot stay engaged?

does the car have an aftermarket stereo with a power amplifier?
maybe the power off function is not working now?
the radio goes off, but the power amp stays on?
 

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FWIW: I hear a fast ticking sound when the meter is hooked up, but not when the cables are attached. What's with that?
It probably has a relay that comes on temporarily when the battery is connected then after a short time goes off. Set the meter to the 10amp range and see if it has a higher draw for a short time then drops. It is normal to have a small residual current and the only way you can prevent it from killing the battery is disconnect it or use a battery tender.
 

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Discussion Starter #20
It probably has a relay that comes on temporarily when the battery is connected then after a short time goes off. Set the meter to the 10amp range and see if it has a higher draw for a short time, then drops. It is normal to have a small residual current and the only way you can prevent it from killing the battery is disconnect it or use a battery tender.
Thanks, Dave, I'll try that. Just continuing to disconnect it when we leave is probably the answer.
 
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