Measuring battery drain

My Porto 20vt has long had a problem with a high drain on the battery that has killed several batteries in quick succession, not to mention failing alternators not helping either.

Armed with a new battery and remembering that I bought a new multimeter some time ago that measures DC amps, I connected it up and with ignition off, I seemed to be getting around 1 amp, yes 1000 mA! At least, I think so...I certainly always get a small spark when connecting the earth clamp to the battery, which has never felt right.

Despite being a clever engineer (well, maybe) I wasn't sure how to read the meter?

The red lead is plugged in to the terminal that says "10A = MAX FUSED" but on the rotary dial for DC amps I have a choice of 10, 200m, 20m, 2m and 200μ (that's 200 "mu")

So using the 10A connection, should I only use the "10A" setting, with the other lower settings needing the other connection labelled "200mA = MAX FUSED"?

Using the 10A connection and at the the "10" setting it reads 1.06 with a little "20" showing on the display, which I interpret as being 1.06 amps, which sounds huge, but would explain why the battery can be dead within a week or two.

At "200m" it read "10.6" with a little "200" on the display.

On "20m" it read "1.06" again (plus "20")

On "2m" it read ".106" (plus "2")

And on "200μ" (that's 200 "mu") it read "10.6" (plus "200")

But are all these other readings spurious because I should be using the "200mA" connection? I'm not going to do that however, since if the drain is realy 1.06A, that's 1060mA and will "blow" the 20mA "fuse"...

Whatever the reading, I will start pulling fuses to check, but my top suspect is the Apexi AVC-R (not installed by me), or one or both amplifiers and/or the head unit (which were installed by me, with permanent live). Otherwise its the old suspects of the boot light or Scorpion alarm. I've removed the Aquamist that was also installed (not by me) and other mods include a wideband lambda, direct feed fuel pump, a widget, early HIDs with relays for feed, and wiring for a couple of phone mounts/USB supplies...I think that's it?

Hey Dave

Hmm- sounds like a lot of info; but you've got the right methodology.

In short; multimeters tend to have the same core functionality;

volts AC
volts DC
resistance (across a few ranges, if they don't auto-range)
continuity
current AC
current DC

and some have diode testers, capacitance value and frequency counters and all sorts.

A good multimeter will have either autoranging current measurement (between milliamps & amps), or different sockets for either scale.

My own Fluke 75 (from back in the day) has a black COMMON socket for the negative lead for ALL functionalities, and then three red sockets.
One is for resistance, continuity & voltage, and the other two are for current milliamps and current amps.

It is common for 'less sophisticated' 'meters to show a '1' to denote some kind of reading or functionality. I have found however that this is often not actually a useable result or indeed a measurement value.
Sometimes it can be the device trying to tell you that the measurement is out of range.
Sometimes, at very low measurement points, you can get a '1' for no reason at all.

So in short; you are only looking for DC amps- or DC milliamps if possible. A larger scale (10A) can be less sensitive to smaller readings.
you should only have one (or two) sockets for current-test functionality; I have never seen a 'meter with a choice of 'many' current measurement sockets.

The '2m, 20m & 200m, scales to which you refer, must be for resistance measurement.

Can I ask what kind of unit of measurement was being shown on the right of the screen during your test..?

I shall post a picture of an 'ideal' test-configuration on my own multimeter, when I get to work tomorrow morning for you.

('200mu' but with a little tail on the 'u', would be 200 micro-farads; which would be a unit of capacitance- we don't need that for this test)

You've set the meter correctly and assuming you've connected the probes in series (NOT in parallel!) with the battery (ie. disconnect one of the battery terminals and connect the probes between that terminal and the now bare battery post) you're showing a 1.06A (1060ma) drain, which is quite high as it should normally be about 50-150ma depending on accessories.

Next step would be to pull each fuse to find which circuit the problem is on, or you can get a current probe for your meter that plugs right into the fusebox to test each circuit, like this :

that's clever Graham- I've never seen one of those!

The sealey one is cheap, eg. ebay # 390974354104 for standard fuse size like the coupe, or # 191412488490 for the mini fuses on newer cars.



You pull the fuse out of the fusebox, insert it in the side of the probe and then plug the probe into the fusebox.

Thanks both

@dante - the 200m, 20m, 2m and 200ua are definitely for the lower DC current readings. I'll post up a picture when I can.

@Graham, you've confirmed the high reading, I will look at getting one of those probes, where did you see that one on Amazon?

Sealey TA123 the is part number for the standard fuse size version, available on ebay or Amazon.

Here's a pretty crappy pic of the meter showing 1.06 amps (and yes, it was connected in series)

I connected the meter up again tonight, 1.06A as before, but then the indicators started flashing, driven by the Scorpion alarm (siren switched off). When I pressed the key fob to switch the alarm off, the current draw dropped to 0.70A. Repeatedly disconnecting and connecting the meter made the measurement drop to 0.45A.

I tried all the fuses in the engine compartment (apart from any that may be in the control box on top of the washer fluid reservoir, since I couldn't undo all of the silly little screws) but no change.

I then opened the door, pulled down the fuse box, and then noted that the reading was just 0.07A (that's still 70mA however). Removing the fuses one by one, the only one that made a difference was fuse 16 for the clock, courtesy light, alarm (maybe factory fit only?), electric aerial (the signal amplifier I guess), compact disc (? I thought that was powered entirely from the head unit via the DIN cable?) and anti-theft device receiver (remote fob receiver). Pulling out the fuse made the alarm LED come on, and putting it back switched on the courtesy light and make something click behind the glove box (the Scorpion ECU I guess since that's where it is). These are all things that should be on all the time (apart from aerial/amp and CD?) so I will test each one in turn to see which is the culprit. I switched on the ignition to check how many alarm LED flashes I got (7 = attempt to start the vehicle, but actually I just turned the ignition on) but that produced a huge current draw initially as everything started up, so I was reluctant to try the lower amp readings on the meter.

Checking the wiring diagram shows that I should have removed both of the 60A maxi fuses to cut off the supply to fuse 16, since they are wired up in parallel (to act like a 120A fuse?).

I'm a bit puzzled as to why the 1.06 dropped to 0.70 then 0.45 then 0.07. The higher figures could have been with the alarm in a "suspense" mode if there is such a thing? The alarm would have "known" the battery had been disconnected with the alarm on (in reality the battery drained down to be absolutely dead, measuring less than 1 volt), and when reconnected (via the meter) it was waiting to "go off"? The opening/closing of the door (and switching on/off the courtesy light) affected the readings as expected) and the 0.45 dropping to 0.07 might have been with the courtesy light on then off.

I've ordered one of those fuse adapter test leads, let's see what I find then. I guess a good test would be to connect the battery and check the current across that fuse connection when the alarm is on and the car locked (with interior alarm sensors either on or off). Maybe the alarm has "gone bad", the ECU in there might be a replacement for the original when something about the alarm stopped working a few (10+) years ago (the siren I think, I know I replaced that but can't remember if I replaced the ECU).

May be the rechargeable battery in the siren? Similar thing happened with the tracker in my coupe... when the rechargeable battery pack is working fine it draws very little power to keep it topped up, but when the battery eventually fails to hold charge it seems to draw a lot of power trying to charge it.

With the tracker it would drain a fully charged battery enough to cause a non-start in about 2-3 days, suggesting a 1A+ draw similar to yours.

Do you have anything non-standard that's connected directly to the battery or is everything going through the maxi fuses/fusebox?

Yes, could be the alarm siren battery, I can't remember why I replaced the siren all those years ago, but that could have been why. My old Peugeot 306 did the same thing, a massive current drain due the old siren. I'll take the old siren apart to see if the battery could be replaced somehow. I think I must have one of the oldest surviving Scorpion 918U alarms out there...

There are a few leads that I connected directly to the battery, I think they are the supplies for the two (audio) amplifiers which have their own inline fuses, I will check.

I ordered Gunson 77068 fuse adapter test leads. Unfortunately the fuse holders on the main fuse box have high "shoulders" around the sides of the fuse so that the tester barely makes contact before dropping out due to the high "shoulders" on the tester. Nothing that a sharp Stanley knife can't fix! However you have to trim to a good 5mm depth so that the "shoulder" is only as "fat" as the plastic case on the fuse, to the point where on one side there's a big hole now, I might trim a bit more so that the "shoulder" can drop down and then I can glue up the gap. Basically the tool is too chunky to fit easily in the restricted space around the fuse holders.

Anyway, once I got it to fit, it was showing 90mA which is more than the 13mA it's supposed to take when "armed" (and 9mA when "disarmed"). I think the earlier very high readings were spurious due to the alarm not having "reset " properly.

It was easier to remove the current siren rather than mess around finding the old one. Loosen the 2 x 10mm nuts each side and slide the siren out of the U shaped bracket and undo the 4way connector. Remove the 2 long screws and ease the siren part away from the casing. Undo the "nut" holding the cable where it enters the casing then slide the nut and the "gland" down the cable towards the connector. Push the cable into the casing, and the PCB should also get pushed out of the casing. Once outside the casing, you can see the battery pack in a thin card wrapper and the whole thing tie-wrapped to the PCB.

The battery pack is 5 x NiCd AA rechargeable batteries connected together to give 6V 600mAh capacity. Replacements look to be available, although the terminal "tails" are not both in the same place as on the originals. But the connecting leads are quite long and it looks like a simple soldering job that even I could do.

But I wondered about getting higher capacity like 2100mAh, would that be better, or will that just mean an even bigger battery drain even when new?

I will add some pics later so that you can see what I'm talking about...

This was my thread on a similar topic, while I think you've covered it, thought I'd post up incase there's any extra info that could be helpful to you Dave.

Hi Chris, yes I looked at that thread and several others first, but I'm not sure you ever fixed your problem did you, it seemed like it was the boost controller?

I'm thinking mine is the alarm. Unfortunately testing the drain by disconnecting a battery terminal and inserting a multimeter inbetween is unreliable because as soon as you disconnect the battery, the alarm loses power and seems to trigger something that interferes with the readings.

Mine was the boost controller for sure. Never got to the bottom of why, but it was one of the cheap HDI ones so presume it was just poor electrics?!

You could try a clamp meter. It measures current in a non invasive way

er...

can you get a clamp meter for DC..??

Yes you can, I bought one and found it was rubbish so got my money back. They mostly seem to have large "clamps" more suitable for measuring the power supplied from France to the UK every day (2 GW today, BTW) IMHO.

Maybe they work, but I couldn't get one to work, whereas measuring the current in place of a fuse does not seem that invasive, but I agree that removing a battery lead and inserting a meter is rather invasive, and can affect the result.

Edit: Yes, I know 2 GW is power and not current. That 2 GW is supplied at 270 kV so that's a current of 7400 amps by my simple O level calculation...

That's a shame Dave, when mine was misbehaving I borrowed one from my brother and it was quite accurate. I'll see if I can get the model number for info. I quite liked it as you can watch the car 'go to sleep' and go through lock cycles

Similar experience to mine. I still have my DC clamp meter but it's basically garbage.. I wish I'd sent it back for a refund, readings are all over the place even when the cable is in the supposed "sweet spot" right at the base of the clamp. The AC clamp part at least works, but I wouldn't call it reliable either.

Have seen reviews of even expensive Fluke clamp meters saying that the clamp part is more or less worthless if you want accurate, repeatable measurements.