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This may be helpful for those dealing with parasitic draw issues... recently was working on a 2018 GLA 250 which would have a hard time starting after sitting a few days. First crank either nothing or very slow, labored cranking... usually took multiple attempts before firing up. This car was already at dealer for engine harness repair (mouse damage) and subsequently for the hard starting which was diagnosed per a TSB as related to HERMES software (known issue causing high parasitic draw). However problem of hard start has persisted...
Quick parasitic current measurement with car off after a few minutes only indicated a 10-20 mA draw, totally normal. Hooked up a DMM capable of recording (OWON B35T+) and let it run for 5 hrs (randomly picked) with car off and locked. Sure enough there was draw/activity and even a large spike to 5.5 A indicating module/s were waking up. The large spike at the end was in the middle of the night and not related to unlocking the car or touching recording the equipment.
Spoke with a friend who indicated there's CAN monitoring built into vehicle and it can be read with Xentry. Sure enough, in Xentry we were able to see the interior CAN was active (not normal). In this case, the car will need to go back to dealer and have a CAN bus recorder installed. The recorder logs all activity and is used to further diagnose why certain modules may be waking up. Definitely a complicated issue and unfortunately a lot of time to figure out.
I looked at my '11 E350 and it doesn't appear to have the same "level" of monitoring, but it does have a feature recording the last two events that kept the BUS awake. For this W212, Navigate in Xentry: Central Gateway (CGW [ZGW]) > Actuations > Bus keepawake unit detection
Informative post, thanks. Is it possible to re-flash the ECU with a stock ROM with Xentry? Then run this test again?
I tune my Maxima ECU with RomRaider and a laptop. I've got several edited ROMs I switch back and forth between. I might be feeling the need, the need for speed one week +20% base fuel map, then have to pay for it the next with the economy ROM.
Can I ask -- where did you connect to measure the amps?
you hook an ammeter up in series with whatever you want to measure. if you want to measure the whole car, you would disconnect the positive lead from the battery, and connect the meter to the battery + and to the positive cable. make SURE the meter is in amps mode when you do this, and make SURE you switch a multimeter OUT of amps mode as soon as you're finished with doing this.
if you want to measure the stuff on a single circuit, you can remove that circuit's fuse, and connect the ammeter between the two fuse terminals.
Door opening on my car is 11 amps worth for like 5 seconds seconds and has 14 amps spike for 1 second, and 9 ish amps for 10 seconds or so,
probably all these with courtesy light set to light with the door open, I forgot.
So when using an amperage meter function of a digital voltmeter aka "in-series", be careful because usually 10 AMPS is the fast fuse value in say a Fluke and some
have 400mA ones also, to read the finer amperage. Fluke 10Amps fast fuse is expensive.
What I have not tested is , let say car is locked for say 2 hours and then the FOB key I bring closer to the car.
I wonder what will wake up when I do so.
It takes at least 30 minutes for my car to really "sleep" and and draw the sleeping mode power consumption.
When you want to read very low values of say 20 milliamps or less, you can use a 2A capable clamp-meter, but do be careful when near metal or how not-in-the-middle one position
the wire in the clamp sensor region. One way is to lengthen the jumper wire you want to sense and lift it up and away from the car metal at least 50-70cm. This is because DC we are reading and
its a pain in the azz at such low milliamps when using clamp meter, unlike AC voltage even at same 6 milliamps which its switching poles type magnetism at 50 or 60 hz is not easily replicated by us and thus the
clamp sensor which reads magnetism won't be fooled.
See below how a clamp amperage meter, el-cheapo one but very good for 2Amps and lower current value, can finally read close to a in-series multimeter accuracy
The same clamp meter when exposed to the magnetism surrounding the battery post, read 300mA ...LOL, by which it should be under well below 50mA even if I was not recording the video past 30 minutes after engine off and door locked and hood also locked. I know this meter auto off is like 10-15 minutes only.
Behind the Uni-T clamp meter is the yellow Fluke 381.
See even Fluke at such low amperage reads 400 mA LOL due to its huge claw......worse than the red Uni -T baby claw.
However this Fluke a 2,000 amps DC/AC wireless clamps. So below 1 amps, best not to use it, but I need its wireless function and its high DC amperage capability.
Last edited by S-Prihadi; 03-01-2021 at 10:29 AM.
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Can I ask -- where did you connect to measure the amps?
Between the negative battery post and negative battery cable. You could also do it between the positive terminal and cable... though I like the negative in case it slips and touches the body, which is already grounded (no sparks). In both cases your measuring the total draw from the battery.
I've also found running Xentry, various cars '11 thru '18 all draw around 20-30A when just running diagnostics (no activations or tests). Something to consider if your doing it for a while. I built a dedicated power supply capable of 70A at 14 VDC (not complete) as my pro-logix charger was only capable of 20A in PS mode and it was barely cutting it. When it came time to run tests, the voltage would drop into the low 12s as the charger couldn't keep up.
I built a dedicated power supply capable of 70A at 14 VDC
I did the same thing for car stuff, car stereo stuff, and general bench testing. Good deals on ebay for these things! Also, I got these fancy header things on ebay too, where did you get yours? Or did you build it?
That's a nice piece of kit, bmwpower! Love seeing stuff like that! I'm all about it. So you pulled the casing and bumped up the voltage with the pot, I did that too. Love your meter/shunt! Good stuff!
I did the same thing for car stuff, car stereo stuff, and general bench testing. Good deals on ebay for these things! Also, I got these fancy header things on ebay too, where did you get yours? Or did you build it?
I struggled with how to properly connect a large gauge wire to the PCB pad of the PS. With the header, I soldered two large copper bus bars and then to those connected the wire with ring terminals. Still a work in progress and I'd like to "package" it better.
That's a nice piece of kit, bmwpower! Love seeing stuff like that! I'm all about it. So you pulled the casing and bumped up the voltage with the pot, I did that too. Love your meter/shunt! Good stuff!
I used a couple resistors to increase the range of adjustment and to increase OVP. Used this, among others, as a guideline:
Very cool! Thanks for the info! Eventually I'm going to relocate the battery to the trunk and delete the under-hood battery. I bought 12 of these LiFePo4 cells from China. I'll be using 4 cells in the Benz and the other 8 are going into my Maxima car stereo project.
Thanks. I think this is the best way to go (negative side)
(I was wondering if you separated the cable or used a clamp-on.)
For small draws, I find a clamp-on not as accurate. I have the same Uni-T (clamp-on) as in S-Prihadi post, which I really like it. The OWON unit with onboard recording is a typical DMM. I know with scopes you can get amp clamps... I've never seen one used in conjunction with a DMM that wasn't a clamp-on to begin with.
Very cool! Thanks for the info! Eventually I'm going to relocate the battery to the trunk and delete the under-hood battery. I bought 12 of these LiFePo4 cells from China. I'll be using 4 cells in the Benz and the other 8 are going into my Maxima car stereo project.
I do hope you are using a BMS on each of those setups, and that you test the hell out of the built battery on the bench with several full charge, 50% discharge cycles before installing in your car, as the failure rate of aliexpress stuff is a little higher than brand name retail stuff. a good 20A load would be a couple 100W 12V halogens in parallel properly mounted to be fire safe (they get hot as hades).. 200AH batt, so 5 hours at 20 amps will take it down 50%.
as long as the car alternator puts out 14.4-14.6V but absolutely NO more than 14.6V, you're good enough. once the batts are 100% charged (current drops to zero at 14.6V), then a lower voltage like 13.6 will maintain the charge, most car alternators do something pretty close to this.
You will rely on the car's alternator and its charge regulator for charging those ?
Yep. 4 cells for this car and I'm adding the other 8 cells to an 18 cell Lithium Titanate battery I'm building for the Maxima. I have a DC Power Inc. 270amp billet aluminum alternator to feed the Maxima cells and I'm having them build me a 300amp alt for the Benz.
I do hope you are using a BMS on each of those setups, and that you test the hell out of the built battery on the bench with several full charge, 50% discharge cycles before installing in your car, as the failure rate of aliexpress stuff is a little higher than brand name retail stuff. a good 20A load would be a couple 100W 12V halogens in parallel properly mounted to be fire safe (they get hot as hades).. 200AH batt, so 5 hours at 20 amps will take it down 50%.
as long as the car alternator puts out 14.4-14.6V but absolutely NO more than 14.6V, you're good enough. once the batts are 100% charged (current drops to zero at 14.6V), then a lower voltage like 13.6 will maintain the charge, most car alternators do something pretty close to this.
Alt set point is 14.8 and I can throw a pot in the sense lead and adjust to a range 14V-16V. Thanks for the tips, been doing this lithium stuff for a while now though.
02-27-2021, 11:20 AM
