Testing for parasitic draw, particularly overnight or intermittent?

[not null]

What tools do you folks use to test circuits for parasitic current draw? Especially if it happens overnight or seems to happen intermittently.

Thanks

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[AVC]

Intermittent draws are very tedious to catch and then locate the offender. Predicable draws; constant or at specific events; key-on, xx minutes after key-off, are easier as you can repeat conditions. As for actual troubleshooting, a DVM that reads DC millivolts for drops across fuses, a DC amp clamp (for draws >100mA) and a DVM that can measure DC milliamps. Helpful to have two DVM's to measure volts and current simultaneously. Then good electrical diagrams to understand topology and where modules are located in the vehicle.

There are a variety of work flows for troubleshooting. Pine Hollow Diagnostics just posted a good video tutorial on YouTube.

 

[AVC]

If you own a logging DVM, that can be connected to a PC app, you can capture long term, overnight draws. I have a Picoscope which is good for that.

 

[First Sergeant]

I grabbed this from A.I., but this is what we did in the 70's. All we had was a regular multi-meter. I have not tried this in years, since haven't had any issues (not counting the Maverick which we know has some draw). Not even sure if this old method would work correctly on these newer computer cars! Good luck!

To check for parasitic draw, set your multimeter to DC Amps (10A or mA) and connect it in series between the disconnected negative battery cable and the battery post. A normal draw is below 50mA (0.05 amps); higher readings indicate a drain. Isolate the circuit by removing fuses until the draw drops.

Edit: Sorry, did not read your post correctly. Yeah, overnight and intermittent draw will be very hard to catch, especially pulling fuses at 0200 hrs in a cold garage! Best of luck my friend!

 

[Ray_B]

How do you know you have the drain? I.e., is your battery dead in the morning?
If so, and you don't have the meter(s), try pulling a couple fuses per test run until the drain stops. Then replace one fuse at a time to ID the circuit. (The Navy called it "Binary isolation" when troubleshooting 'black boxes').

 

[HeyBales]

Have you seen the normal processes for doing so?

You can do the pushing locks closed on doors & hood and locking truck with fob with doors/hood open.
Need to wait upwards of 75 min while things go to sleep. 60 for 25/26MY.
But good to measure during that time too. Just in case something is going overboard until sleep mode. Like AC turning fans on...

Then 25-50 mA during sleep mode.
If you have Forscan Lite or Forscan on computer - you can look at the PID the next morning for what was recorded for average current draw during the prior sleep period.
That'll tell you if there is even something to catch.

Otherwise the process of checking fuse milli-voltage in lookup table - will be hampered.
Because you can only get to the BdyCM fuse box in passenger foot well.
But not that many circuits from there, though some of the common ones that start having issues.

The main fuse box under the hood, disconnects from the 12V circuit when it's pulled to look at the fuses - making it impossible to do the same check. Our forum techs have confirmed Ford has no solution to get around that issue.
They pull the power/connections from the modules from that fuse box, then leave unhooked.
If you hook them up again - they can turn on other modules.
So you'd have to get the service instructions as to required order, or dig thru circuit diagrams to disable in the best order to really find something.

But if you merely want to confirm overall draw and have it logged over multiple nights to catch something - then ditto to above posts on the devices to use.

Vast majority of mornings & leaving work (and other shorter stops where it goes into sleep mode), I note the prior sleep period avg draw if it happened - shorter it was the closer to 80 mA it is, the longer it is the closer to 20 mA it is. Unless it was a night I think the BMS Relearn occurred - than back around 70 mA.

Sadly I've found no such PID for what was the draw during the go-to-sleep window.

I'm about to install a shunt with monitor since my multimeter turns off too soon for that 60-75 min period. I've sat in there for 30 min doing clamp current draw every 5 min. Or was it 60?
And I have no garage so relying on seeing the figures thru the window since you shouldn't unlock/open the door.
I didn't want to buy the expensive ones with bluetooth to phone app monitoring - though that would be nice. It appears all the Android apps are side loaded straight from China instead of the app store. Didn't like that.

 

[ZABSMAV]

What tools do you folks use to test circuits for parasitic current draw? Especially if it happens overnight or seems to happen intermittently.

Thanks

Get yourself an Ancel BM-200 and put it on your battery. You can get it from Amazon like we did. It's very inexpensive and logs the battery temp, SOC and voltage.

This is the device on Amazon:

https://a.co/d/0h5hB3AH

 

[AVC]

The main fuse box under the hood, disconnects from the 12V circuit when it's pulled to look at the fuses - making it impossible to do the same check. Our forum techs have confirmed Ford has no solution to get around that issue.

I encountered that Ford ***holerly when I modified my cig lighter outlet for constant power. I imagine a handy DIY'er could build an umbilical to jump 12v to the fuse block, either from the mating contact on the receiving box, or directly from the battery.

There's also nothing preventing one from putting a DVM in series with the 12V battery to monitor/log sleep current, to at least confirm whether there is a parasitic draw in the 12v equipment. I wouldn't personally use the 10A range, unless you have a 4.5 digit (20,000 count) or better DVM to reliably read <100mA.

 

[HeyBales]

I encountered that Ford ***holerly when I modified my cig lighter outlet for constant power. I imagine a handy DIY'er could build an umbilical to jump 12v to the fuse block, either from the mating contact on the receiving box, or directly from the battery.

There's also nothing preventing one from putting a DVM in series with the 12V battery to monitor/log sleep current, to at least confirm whether there is a parasitic draw in the 12v equipment. I wouldn't personally use the 10A range, unless you have a 4.5 digit (20,000 count) or better DVM to reliably read <100mA.

And since schematics would be needed eventually anyway, if really tracking down what it is, one could see what of the main cables leaving the underhood fuse box are doing what - and at least get an amp clamp on them.
I really wonder about accuracy of that down below 1A though. Not looked at like a Klein manual for the table of specs.
Because one draw at 0.5A could be that 2 day drain, or at least bad enough if only 1 day occurred because intermittent.

I think the tools you mentioned would be better.

 

[not null]

Thank you all for the info, especially @HeyBales for the deeper dive. I was hoping there was a "Good, Cheap & Easy" tool I just wasn't aware of. I've been chewing on the idea of trying to build something.

Basically a logging multi-meter. Plug it into a couple of fuses at a time, use a microcontroller to do the measurements, log the data, and then see what I find.

The devil is in the details of course.

 

[MavGator]

if you have the time to manually watch it, a DC clamp on amp meter is your friend. Very handy and noninvasive.

 

[johnDeere]

You can use one of theses.
Or this one.
Very helpful.

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