Acceptable current draw (parked up)

[MrOizo]

Hey peoples,

What's an acceptable current draw for a car that's sitting, parked up?

Just measured mine and it's 0.25 amps - that's expected?

I pulled fuses from under the dash and nothing changed so it's most likely the alarm?

Cheers.

[DeeCee]

0.25A sounds about right and the alarm will still draw power

[MrOizo]

Oh ok, thanks! I was thinking that was on the high side for just sitting there going by what others online have been saying.

Some say 80mA is about right for a clock, ECU and radio presets.
It ok that an alarm is using ~150mA?

[KinLoud]

Adrian - I made a few intelligent guesses along with your current drain into this formula I found!
It explains your current drain almost exactly!

Using the formula I get
Current drain = 0.24266447793776 amps
8460 minutes (6 days) since your previous work session on your car
Working on your car average of 0.5 days per week over the last year.
Amazingly accurate result!

Direct quote from USANYPCA website...
(USA Not Yet Completed Project Car Anonymous)

"Unexplained battery drain in your project car.
Frequent posts/topics on this topic has sent me on a journey of scientific discovery.
I contacted as many members who have current project cars. I arranged to visit them to chat about their project and measure accurately the battery current drain.
Using my Extech 380560 bench micro ohm meter (High Resolution Precision Milliohm Meter (110VAC)
Benchtop meter provides resolution down to 0.01mOhm), I measured the resistance of the earth cable (between battery and chassis). Then with the earth cable reconnected to the battery I measured the voltage drop across the earth cable using my Keithly 2182A Digital Nanovoltmeter
This enabled me to accurately measure the current drain with minimal interference to the circuit.
NOTE - electrical formula I=V/R, I current, V volts, R resistance ohms

During my chat with the project car owners I found out how often they worked on their cars and how many days since they last did any work.
When I got home from my 2 week scientific road trip I put all the data into a scientific spread sheet for data analysis.
I then searched for some sort of correlation between the data.
I was surprised by the what I found!
THE RESULTS
I developed a formula that can explain the current drain

A=(((Last/Pi).Ave)/(Q/k)).C
Where
A (current drain) = amps
Last = minutes since previous work session (prior to session in which current measured)
Pi = 3.141592653589793 (approx)
Ave = days worked on car per week averaged over last year
Q (number of free electrons per cc of copper) = 8.5*10^+22
k (work ethic constant) = 10,000,000,000,000,000,000
C (correction constant) = 1.5

In plain English...
The more recently you last worked on your car and the more often you work on your car the lower the unexplained battery current drain.
Hope this helps everyone"

[gepsk8]

Don't want more than 0.05amps. Or battery will go flat over few days or less.
Some cars take up to 30mins to drop current down after battery is reconnected.
Try using clamps that hold battery stud and termal. So can slide it up with out disconnecting circuit.
Set any alarms. Keys in your pocket, bonnet switch disconnected.
Start with disconnecting aftermarket accessories, and then fuses until u find problem.

[Crucible]

Yeah 0.05 amps or 50 milliamps, dont want much more than that. On some cars it takes a while for modules to go to sleep so leave the ampmeter on and keep an eye on it.

0.25 is 250 milliamps which is a bit high..

[MrOizo]

Adrian - I made a few intelligent guesses along with your current drain into this formula I found!
It explains your current drain almost exactly!

Using the formula I get
Current drain = 0.24266447793776 amps
8460 minutes (6 days) since your previous work session on your car
Working on your car average of 0.5 days per week over the last year.
Amazingly accurate result!

Direct quote from USANYPCA website...
(USA Not Yet Completed Project Car Anonymous)

"Unexplained battery drain in your project car.
Frequent posts/topics on this topic has sent me on a journey of scientific discovery.
I contacted as many members who have current project cars. I arranged to visit them to chat about their project and measure accurately the battery current drain.
Using my Extech 380560 bench micro ohm meter (High Resolution Precision Milliohm Meter (110VAC)
Benchtop meter provides resolution down to 0.01mOhm), I measured the resistance of the earth cable (between battery and chassis). Then with the earth cable reconnected to the battery I measured the voltage drop across the earth cable using my Keithly 2182A Digital Nanovoltmeter
This enabled me to accurately measure the current drain with minimal interference to the circuit.
NOTE - electrical formula I=V/R, I current, V volts, R resistance ohms

During my chat with the project car owners I found out how often they worked on their cars and how many days since they last did any work.
When I got home from my 2 week scientific road trip I put all the data into a scientific spread sheet for data analysis.
I then searched for some sort of correlation between the data.
I was surprised by the what I found!
THE RESULTS
I developed a formula that can explain the current drain

A=(((Last/Pi).Ave)/(Q/k)).C
Where
A (current drain) = amps
Last = minutes since previous work session (prior to session in which current measured)
Pi = 3.141592653589793 (approx)
Ave = days worked on car per week averaged over last year
Q (number of free electrons per cc of copper) = 8.5*10^+22
k (work ethic constant) = 10,000,000,000,000,000,000
C (correction constant) = 1.5

In plain English...
The more recently you last worked on your car and the more often you work on your car the lower the unexplained battery current drain.
Hope this helps everyone"

Ahhhh - this explains a lot! Wonder how the results will change with a different work ethic?

[MrOizo]

Thanks for input guys. Going to have another go and diagnosing the thief of amps over the weekend hopefully.


Keeping on the topic of batteries, one thing that i am not sure about is the advice from the big cheese at HCB (Harbour City Batteries) where i got my Ultra AGM battery from.
The manager at HCB said that these AGM batteries are not to be left on a charger, even the CTEK 'intelligent' ones. Instead monitor and charge when voltages are below certain values (have the print out some where).

I had my battery on charge (from flat) during the day and was lucky when i checked on it as it was bulging at the sides and the relief valves on the top were bubbling and fizzing and very hot.

What do people know about this? Am i using the wrong charger?
This is the one i have, It listed as being compatible with AGM:
http://www.cteknz.co.nz/tabid/319/Produ ... fault.aspx

I should add that this is the SECOND battery i have had do this! First one replaced under warranty.
At the request of HCB i took my charger into the workshop/lab and they tested it fine.

Could it be that when charging with a 0.25amp draw from the car, this screws with the charger and battery?

Cheers.

[Grrrrrrr!]

I'd take him at his word, he should know his stuff, we used to get AGM batteries by the pallet load from him, and they were good batteries.

Since your car is still a garage queen , the easiest thing to do is just to disconnect the negative terminal when you finish working on it, will stop all discharge problems and flat batteries, then just charge it once the battery voltage gets down a like he says. Or option B.. finish the car and take it out for a burn every weekend.

Easiest way to kill any lead acid battery is to let is discharge right down to nothing then leave it sitting a for a few weeks. You almost always get one dead cell.

I better go take the toy for a burn this weekend, its been parked for a few weeks.

[Mr Ree]

I run an AGM Full River battery, and did a LOT of research and asked a LOT of questions before buying it, as my car is used very infrequenty too, and I hate having to deal with removing battery cable and the ECU needing to relearn all its shit every time I drive it.

I bought a battery tender, and simply connect it up to the cables coming from my battery, when I put it back in the garage.

It floats it between 12.65 and 12.80, to ensure it doesnt lose any charge, as the AGM's dont like that one bit.

I wouldnt charge one on a conventional charger.

[rollaholic]

you shouldnt have a problem leaving the CTEK connected for as long as you like so long as its set correctly (ie setup for AGM charging). as i understand it they are sensitive to over charging, so your old fashion chargers can ruin them but the CTEK is supposed to only charge when the voltage drops below a specified point (as indicated in your link too!)

i have to say since the brand i work on switched to AGM we have been replacing alot more batteries, often after only 2-3 years while the slightly older cars with lead acid are still going strong at 5+ years.

we are talking about batteries with a retail cost of 600 or more too.

as the others say less than 0.05A is where it should be at on the current draw side of things.

[Dell'Orto]

Interestingly, my bike has an AGM battery, and I charged it using a CTEK battery charger, set in AGM mode, and had no ill effect?

[matt dunn]

Could it be that when charging with a 0.25amp draw from the car, this screws with the charger and battery?

If you are using a clever charger like a Ctek or similar you must disconnect the battery.

They go through different modes of charging and use a voltage/current program to tell when to switch changes,
so if you have current drawing off the charger assumes that the battery is still absorbing it and that it needs more.

We strike it a lot with campervans where people use multi-step chargers on the house batterys and wonder why they are always dry,
and dont last.
It's because the chargers dont switch off bulk mode.
To charge a battery while connected or having power drawn out of it you need a charger with a power supply mode,
so they just put out a straight voltage mo matter what the current,

or in your case a battery maintainer not a charger if you just want to stop it going flat.

Also we dont look for current draws less than .25A or 250ma, as that can be quite normal on a lot of cars.