I know with these "newer" cars with tons of electronics, some modules have constant power and will draw current constantly. Does any in the automotive industry know how much constant current is acceptable without risking battery drain?

 

Any current will eventually drain the battery.
The drain is kept low enough so that the battery does not significantly discharge until the next typical time it is driven.
I should think they would design for a least a month of drain with perhaps only a few percent reduction of the battery's Ah capacity.

 

Any current will eventually drain the battery.
The drain is kept low enough so that the battery does not significantly discharge until the next typical time it is driven.
I should think they would design for a least a month of drain with perhaps only a few percent reduction of the battery's Ah capacity.

Yes I understand any current will eventually drain the battery but what is the norm? I want to hook up something that will draw about 160 miliamps and not sure if that is too much.

 

I want to hook up something that will draw about 160 miliamps and not sure if that is too much.

I was working on a car this week. The computer is on all the time and pulls 200mA.

What is the amp hour rating on the battery. It probably will not say. Many car batteries will hold 50A hours.
That is 50A for 1 hour, or 5A for 10 hours or 312 hours at 160mA or 13 days.

 

Yes I understand any current will eventually drain the battery but what is the norm? I want to hook up something that will draw about 160 miliamps and not sure if that is too much.

Just run some numbers and see what kind of ballpark you are in.

If we are talking about a car with an internal combustion engine and a 12 V battery, then it likely has a capacity between about 40 A·h and 60 A·h. Let's use 50 A·h for illustration. At 160 mA, the battery would be (nominally) depleted after 312 hours, which is less than two weeks. But the real question is how long would it take before there wasn't sufficient energy to start the vehicle, and I wouldn't want to rely on it to start a car even after just one week.

A lot of it comes down to how long the vehicle sits between uses (and not the 'typical' time, but what is the 'longest' time). If it's no more than a day or two, it's probably fine. If it sits for a week from time to time, I'd be concerned.

For my vehicles, this kind of draw would be unacceptable. Even the two cars that we drive the most will occasionally sit for over a week if we just don't have anywhere we have to be.

I had a car that I put in storage (just an outside fenced-in lot) while I served a tour of duty. I just parked it there, turned off the key, and walked away, no prep at all (just didn't have time). Three years later, I got in and it started right up (which surprised the hell out me). Imagine that happening with any car today.

 

Next question: how low can you routinely draw down an automotive lead-acid battery before you significantly shorten its life?

 

Next question: how low can you routinely draw down an automotive lead-acid battery before you significantly shorten its life?

My guess is that this is a very complicated question with the answer depending on a lot of the fine print about the profiles and time scales involved.

 

most car i worked on the computer go's to sleep it will draw 20ma to 32ma mostly gm car. it takes about 15 min after key off for the computer to go in to sleep for the 15 min it can pull up to 300ma why the computer still active.

 

If your Car will not be driven for more than ~3 to ~4 days,
it would be a good idea to permanently install a "Battery-Maintainer",
INSIDE the Car, NOT under the Hood,
and permanently attached to the Cigarette-Lighter-Socket,
( or hard-wired into the wiring harness if You know how ).

Plug it in with an extension-cord from the House every time You park the Car,
then You won't need to worry about the Battery.

They are available from Walmart or any Auto-Parts-Store.

Short-Trips, especially with the AC/Heater-Blower on "High-Speed", and with the Headlights On,
is very hard on the Battery,
AND, very hard on the Engine-Oil, so change your Oil more often.

A Battery-Maintainer will alleviate any Battery problems caused by infrequent, short-trips,
and may help the Battery last for as much as ~5 to ~6-years.
.
.
.

 

If your Car will not be driven for more than ~3 to ~4 days,
it would be a good idea to permanently install a "Battery-Maintainer",
INSIDE the Car, NOT under the Hood,
and permanently attached to the Cigarette-Lighter-Socket,
( or hard-wired into the wiring harness if You know how ).

Plug it in with an extension-cord from the House every time You park the Car,
then You won't need to worry about the Battery.

They are available from Walmart or any Auto-Parts-Store.

Short-Trips, especially with the AC/Heater-Blower on "High-Speed", and with the Headlights On,
is very hard on the Battery,
AND, very hard on the Engine-Oil, so change your Oil more often.

A Battery-Maintainer will alleviate any Battery problems caused by infrequent, short-trips,
and may help the Battery last for as much as ~5 to ~6-years.

That's what I was going to suggest - a battery maintainer.

On the comment about a battery lasting 5 to 6 years - - - I have some old batteries, already seven years old when I put them on a maintainer. They still work well, hold charge and deliver (near as I can tell) full current when needed. They're over 10 years now. Two of them are. AND resting voltage, not just after a start after being on the charger, the voltage is 12.6V. That's a good sign the battery is healthy. A weakening battery will have lower and lower resting voltages. 12.5, 12.4, 12.3, 12.2 - and at this point I start worrying about a battery. 12.1, 12.0 and confidence is low. 11.9 resting voltage - yeah, it's time for a new battery. At least that has been my experience. And been driving since 1974. GEEZ! Driving 50 plus years now.

 

This seems to be the third thread on what seems to me to be the same topic..

 

This seems to be the third thread on what seems to me to be the same topic..

DEFINITELY!

 

I was working on a car this week. The computer is on all the time and pulls 200mA.

That seems very high. What model year is that vehicle? Sleeping current consumption requirements have been significantly upgraded in recent years.

When I last worked in the early 2010s in automotive electronics, the industry in general and semiconductor vendors in particular, were working extremely hard to dramatically reduce power consumption. There were dozens of strategies, including that the CANbus transceiver could fully power off the subassembly to which it was connected, and itself going into a deep sleep mode.
If I recall correctly, the roadmap was for individual peripherals to consume below half a milliamp during sleep.
I ignore how much current the ignition switch module requires, since this module must be alert at all times and provides the main wake up command for the remaining modules and computers.

 

What model year is that vehicle?

Toyota 05 van. The online help 'I should see about 250mA draw from the battery'.

 

Toyota 05 van. The online help 'I should see about 250mA draw from the battery'.

I can't imagine what this computer is doing that needs so much current when the vehicle isn't running and has had time to completely cool down.

So, does the owner's manual say anything about the maximum time you should let the vehicle sit to prevent the battery being drained to the point where it won't start?

 

‘05 model, that explains it.
Nowadays the consumption may be 20X lower, even with a far higher electronics complexity.

 

‘05 model, that explains it.
Nowadays the consumption may be 20X lower, even with a far higher electronics complexity.

I have a 2005 Chevy Trailblazer and I can leave it parked for well over a month without worrying if it will drain the battery so much that it won't start. I've done that many times. I just did a quick check online and found a couple of sites that both say that, for my vehicle, that the parasitic draw should be under 25 mA.

I'm still curious whether the owner's manual of a vehicle that has a parasitic draw of hundreds of milliamperes warns owners not to let their vehicle set for more than so-many days without charging the battery. On numerous occasions I've gone to activities in which my car sat parked for a couple of weeks. Some of these were in the back country. I never once thought to disconnect the battery to prevent the it from being discharged over a time scale like that -- I've had cars that fired right up after years of sitting idle. So if I had bought a brand-new 2005 Toyota and drove to a back-country site and camped for a week and then been stranded because the normal parasitic draw was expected to be that high, I would not have been happy, especially if the owner's manual didn't have a pretty prominent warning about how quickly the battery would be drained on that vehicle.

 

A car that you cannot leave sitting for a month without the battery dying is not a car I would ever want to own.

 

A car that you cannot leave sitting for a month without the battery dying is not a car I would ever want to own.

And I would have thought that such critters didn't exist, at least not right of the manufacturer's lot. So now I'm wondering how prevalent they are and whether the owner's manual calls this out in any way. The next time I buy a car (which are typically at least ten years old) I don't want to get blindsided by this.

 

Not all vehicle batteries are so very new!! A few years back there was one nationally marketed brand that would go weak sitting on the shelf for a month or two. And certainly towards the end of life battery charge does tend to vanish much sooner. There are also some after-market sound system products, subject to incorrect installation, that will seriously increase the "off-state" current draw. And some USB outlet devices as well. Understand that some products are JUNK even while totally new, still on the shelf.