Parasitic Draw/Drain specification. 2

[Enoz28]

I've been told there is a Parasitic Draw/Drain specification vehicle manufacturers use. All vehicles draw some power from the batteries when the car is shut off, Parasitic draw/drain is used to describe this. I've scoured the SAE handbook(maybe I overlooked it) and have been told to look at an ASE manual(don't have access to one, but trying to get access). I've found ways to test for Parasitic draw, and a lot of supposed specs from different manufacturers, but I can't find any thing other than suggested values. My question is: Is there a spec that outlines Parasitic Draw/Drain that manufacturers design to, and/or utilize for error detection?

 

[LionelHutz]

I think you pick the allowed draw based on the battery capacity and the amount of time you want to allow where the vehicle will still start after sitting parked.

 

[IRstuff]

This is worth reading:

http://action.publicbroadcasting.net/cartalk/posts/list/1685810.page

TTFN

FAQ731-376

 

[Enoz28]

LionelHutz, so is there an industry standard that says the vehicle should be able to sit X amount of days without being turned on? What I'm looking for is the industry standard if there is.

IRstuff, I stumbled across that already, and was an interesting read. But it doesn't really point me to an accepted industry standard for parasitic draw.

Thanks for the replies though.

 

[LionelHutz]

I have no idea but I doubt there is a standard that says a car must start after sitting so many days. I think it'd be a manufacturers decision driven by attempting to keep the free roadside assistance calls down and not pissing off customers with dead cars. Also, you should account for the battery degrading a certain amount as it ages. I'm sure there are other considerations as well.

 

[Enoz28]

LionelHutz, you did give something else to think about though. Another way of approaching the problem. Thanks.

 

[TurboXS]

Anecdotally, we have had a 2001 WRX that couldn't go a week without flattening the battery. On the other hand a 20 year old car went for more than 3 weeks and still started with vigour.

 

[IRstuff]

Actually, if you look at the article you've already read, that's the basic postulate for the leakage numbers cited. an 80Ah battery with a 50 mA draw will last 66 days, which is a plausibly practical limit for leaving a car sitting.

TTFN

FAQ731-376

 

[WGJ]

My employer aims to have a successful start after 14 days parked with an 80% state-of-charge battery at the beginning of the park period. That obviously has to be evaluated for the vehicle platform with the smallest battery and the vehicle platform with the most electrical and electronic junk hanging on it.

Bill

 

[WGJ]

Ref "80% state of charge" -- Found this on the Web

% Charged Specific Gravity

100% 1.255 – 1.275

75% 1.215 – 1.235

50% 1.180 – 1.200

25% 1.155 - 1.165

0% 1.110-1.130



Bill

 

[jbkettler]

In the repair industry the rule of thumb is that the parasitic draw should be no more than 1/4 of the reserve capacity of the stock battery in mA (i.e. stock battery is 120 min reserve capacity, maximum draw is 30 mA). I have seen individual instances of published data per manufacturer, but it falls right in line with the rule of thumb in most instances. Also keep in mind that this is after all modules go to sleep - which can take over an hour in some instances.

 

[Enoz28]

great feedback all, I haven't had a chance to thoroughly investigate "state of charge" and "reserve capacity", but a cursory search on the internet looks very promising.

 

[DanEE]

Toyota's published specification for parasitic drain (published in their factory service manuals) is 50ma maximum..

(posted per TMS policy for educational purposes only)

http://home.4x4wire.com/deddleman/photos/elec_parasitic_load.jpg

 

[Enoz28]

Alright, I've done a lot of reading, and it seems that parasitic drain does not have a vehicle spec, meaning it varies from vehicle manufacturer to manufacturer. also, parasitic drain's upper limit is influenced by the reserve capacity of the vehicle's battery. The only other question I have: is there a spec as to how long a vehicle can sit before loosing the ability to start? I've read that it's typically 20 days, but that is only a rule of thumb.

 

[IRstuff]

Since you've already determined that every car has a different spec on parasitic draw, why would you expect a consistent answer for non-operational standby time?

TTFN

FAQ731-376

 

[Enoz28]

IRstuff: Good point, but if there is one, I'd like to know about it.

 

[MacGyverS2000]

<smack forehead>

Dan - Owner

http://www.Hi-TecDesigns.com

 

[WGJ]

Ditto

Bill

 

[dgallup]

I park my car for 3 weeks once a year. I would be extremely vexed if it did not start when I get back. I think 30 days is a bare minimum.