Parasitic Drain Specs
I just want to put this out there for general discussion. I have found that factory specs for acceptable parasitic drain often times are much higher than what is actually observed on a good vehicle.
Case in point, I recently repaired a 2006 Honda Odyssey for a battery that would go dead if parked more than a day. Honda says anything under 50ma is normal. I measured 43ma even after a couple hours. According to honda this is good but it is far different from actual after i repaired the vehicle. The right side sliding door wouldn't stay latched which caused the drain. After repairing the door I rechecked parasitic current and it was only 1ma.
I have seen this on many other cars over the years. Actual measured current is always much lower than factory limits on good vehicles. I guess my take away from this is that when you measure a drain that's close to or just under the factory spec, don't be so sure that it's ok. Normal is usually much lower.
Thoughts, comments? Have others had similar experiences?
Great find, how did you catch the sliding door not latching, was it visual or scan tool live data. Those years Odyssey’s are also known for bad ac clutch relay stay on causing battery draw and blowing over pressure out of ac compressor relief valve
I think I'll do a separate post on the actual diagnosis and repair but just to sumerize, when shutting the right rear door it would latch and then 3 seconds later it would unlatch and it would be slightly ajar.
I compared pids on the scan tool left versus right and I was able to see that the ratchet switch never changed state. I had to repair the ratchet switch issue which is part of the latch.
Keep in mind that acceptable parasitic draw is a spec for the battery. If the manufacturer gives you a spec for acceptable draw it is for the vehicle with the correct battery installed.
I saw several BMWs and Benz vehicles with a walmart battery that had way too small of a Reserve Capacity rating. The current draw was acceptable for the vehicle, but the battery couldn't handle it and the vehicle would kill the battery.
I'm just curious why they don't publish a more realistic spec of what the actual current drain is on the car under normal circumstances.
Because 50ma is realistic enough that with that draw on a decent sized battery, the vehicle can sit 3-4 weeks and still start(weather plays a role into this as well)
Again, a 43 ma draw was not your primary problem....
Rudy, you are correct of course, I failed to move a decimal point. See my reply to Dave.
Still though on my original point, once the problem was fixed I was measuring around 6-10ma which is a bit lower than 50ma. I suppose the spec is more about the limits of what the system can handle versus a typical real world number.
My guess is the spec they list is the maximum range(even if they dont specify that)
Its the only logical conclusion,IMO.
Good topic Bob, I think there may be a few reasons. They may be anticipating the installation of aftermarket equipment or like Richard suggested, inferior batteries. Also they could be accounting for older batteries.
Funny how you had the same car and year with the same drain that I helped a coworker on this week. Are you saying that your 43 ma draw killed the battery over night ? Thanks
The van was sitting a lot because the owner had it up for sale but I believe if it started out with a fully charged battery it could take 2 days to go dead. I was surprised only 43ma would drain it that quick but that's the most I ever measured and it was going dead consistently.
It's possible maybe other modules were waking up overnight but I didn't do any overnight drain tests.
However, what I was most surprised at is that once the door was fixed, the parasitic draw dropped to approx 1ma.
43ma will not drain a normal sized,healthy car battery in 2 days. Either your reading was wrong or your battery was bad.
Thanks for the reply. I’m not at work but that car should have a group 35 or 24 battery and the reserve capacity on those batteries should be somewhere along the lines of 100 -120. Now if you divide that by 4 then you got 25 to 30 ma of acceptable draw. You were at 43 ma. Which is fine and in spec. Honda is right in my opinion. I just can’t see that drawing the battery overnight. I think your missing a zero and yours was 430 ma possibly ??? This week on the same car ....Mine had 2 issues. One was the rear latch not locking. It Would latch then pop back open like yours. The other was the module not going to sleep. All on the passenger side sliding door. Now I’ve seen a bunch of those modules causing draws and they were always between 300-500 ma. Mine was right around 400 ma. This was done inline with a vantage pro. I get about the same with a current clamp. The only time the latch was an issue was when it would pop open enough to let the door ajar switch not close and then it would be over an amp as the lights would all come on. The module fixed the car but it also got a new rear latch. I’m just trying to wrap my head around your car with 43 ma killing the battery. I think the interior lights were coming on and off from the ajar switch. Either way your car is fixed And the customer is happy
Dave, you and Rudy are correct, my reading, or rather my interpretation of the reading was in error. I was indeed off by one decimal place. I was preparing to take a photo of my setup while current ramping a test light when I discovered my error. I've used my current probe with a multimeter many times in the past for this but for some reason, this time I forgot to move the decimal. I'm going to claim a severe case of CRS.
Of course it makes total sense now that only 43ma would not drain the battery very quickly but 430ma sure will. It's a little embarrassing to have made such an error but it is what it is. I won't forget again, I think, wait, what were we talking about again?? ;-)
Anyhow, that doesn't change the fact that the door fault was the cause of the drain and after the repair I measured 6-10ma. See picture below. Battery was still fully charged this morning and OCV measured 12.9v.
Thanks for straightening me out on the meter reading. I'll put together a post this weekend on the door repair.
Honda also had a bad issue with these vans and sticking A/C compressor relays causing the compressor to stay on. That drained the battery very fast. I'm sure you guys have seen those before but just thought I'd put that out there. Was working for Honda when we first started encountering this issue.
I would say we should be able to come up with our own "specs"
Each customers situation is different. One may drive more or place higher demand on their vehicle. If we question the customer properly and evaluate their situation we should be able to decide how much is too much. Through record keeping we can Know what is normal if we keep good records. This way we could make recommendations on battery usage, change in driving habits, or how many accessories they may be able to use. We can use math for their situation as follows.. A battery with a reserve capacity of 110 and a draw of 0.030 amps or 30mA would be dead in…..110 reserve capacity x 0.4167 = 45.837 amp hours… 45.837 amp hours / 0.030 amps = 1527.90 hrs.. 1527.90 hrs / 24hrs (1 day) = 63.66 days. Adjust math as needed for each situation.
Hi Bill,how did you come by that formula?
To be honest Rudy I do not remember.
I take notes and document anything that is useful. I just pulled it out of my battery reference file when I saw this subject.
Fair enough. Do you know that it, in fact, works?
I have never tested it.
Seemed to be fairly logical math and I think I cross referenced with some other info at the time like approximate depletion time of batteries. Can't say that I have every thought to test it and that would be the only way I would know.
and GM says multiply by 'aprox 0.6' I would go with your 0.4167
Hi Bob. This is a pet peeve of mine. GM vehicle parasitic draw is calculated a 25% of the reserve minutes listed in SI for the vehicle in the battery usage chart. So, for a 115 reserve minute battery, the allowable maximum drain is 28.75 milliamps.
However, the actual draw when measured on a vehicle using this value and I'll use the 2002 up Trailblazer/Envoy platform as an example, is less than 10 mA, usually around 7mA or even lower.
So, blindly following the published maximum allowable value will net a dead battery unless the vehicle is used more frequently than the same vehicle with a normally operating system. The classic scenario is that the vehicle operator experiences no issues until they take a trip and leave their vehicle at the airport long term parking lot. Upon return, the vehicle will not start due to a dead battery condition that might never have presented in more frequent use.
I would rather see a vehicle typical draw listing accompanied by a chart identifying how many days a battery will remain above the minimum threshold to start a vehicle, with various mA draws. It makes so much more sense than following the battery reserve minutes / 4 method and blindly accepting that inflated value as an acceptable measurement, when in fact there is an abnormal draw and the tech errantly believes that all is well.