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Discussion Starter · #1 ·
I went out to move my son's Chevelle yesterday (it's sat for a month or more)and only got a clicking from the solenoid. Thinking it was a dirty connection, I cleaned the cables, still no go. Got the Fluke and measured the voltage, 11.47 volts. That's too low, but it's a new battery. So I unhooked the pos. lead and checked the current flow with everything OFF, 35ma. Is this too much?

If it is, we'll start to disconnect the harness to isolate where the leadage is (inside or under hood), then go from there.

So, is 35ma acceptable? Obviously in a perfect world it'd be zero, but what about real world? I thought it was a new alt and reg but I'll check with him on that.
Thanks
 

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Shouldn't see any draw if nothing is on. Could be the start of something beginning to act up. I'd look at it a little further. Keep the positive cable off. Disconnect the heavy red wires on the horn relay. This will separate the main feed wire to the fuseblock from the alternator/regulator. Repeat tests attaching one these wires back one at a time.
BTW
Most guys just use a light bulb between the battery negative post and the negative cable. It's often easier just to watch the light instead of a meter. Also if you slip and short something the meter doesn't get messed up.
 

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Do you have an aftermarket radio with digital display if so the have a memory wire that will draw??
 

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I have read on a couple of different web sites that a parasitic load of 50mA is ok and on others that 25 - 75mA is acceptable depending on the vehicle.
I always figure 40 to 50mA is ok if you disconnect the battery when letting the car set for more than a few weeks.

:confused:


The quote below is not Chevelle specific and most likely dealing with newer vehicles.

Originally posted by Exide:

Here’s the simple formula to calculate the acceptable parasitic load a vehicle can have.
First and foremost, you must start with the proper battery in the vehicle. Regardless if it’s OEM or not, look for the Reserve Capacity in minutes.

You may have to reference a spec chart for some batteries that don’t have that information printed on the battery. Once you have confirmed the proper battery and the Reserve Capacity in minutes, you’re ready for the math. Multiply the “RC” minutes by 0.25 to give you a guideline, in milliamps, as to what the allowable parasitic load you could expect for that vehicle. For example, if the battery has an “RC” minute capacity of 100, you would multiply that by 0.25 to get 25 milliamps. Or, a battery with an “RC” minute capacity of 160 x .025 = 40 mA.
<a href="http://www.exide.com/products/trans/na/battery_care/electrical_parasitic_load.pdf" target="_blank">
Continued at Exide.com</a>
 

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Mine draws 'about' 20mA. Clock, CD changer (allows eject/insert motor sensing circuit), radio memory. Although it never sets longer than a couple of weeks with no problems starting. (Exide spiral cell, like an Optima)
 

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Discussion Starter · #7 ·
Thanks guys for the input. I know that some current is acceptable, he does have a never radio with memory and a clock in it...) but wasn't sure how much is too much current. When we first got it with teh original radio and etc. it was only 1 ma. But lots of changes since then that could affect the current (engine pulled/rebuilt/installed- we could have hooked something up wrong..., new alt., starter, modern radio...)
We haven't had a chance to look at it since, but I feel we have enough to go on to determine if it's under hood or inside, them if it's just maintenance current of the circuits needing it.
Thanks guys!!
 

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I think anything in the <100mA range is going to be fine. Yes, ideally it would be zero, but the more modern electronics you have, with memory requiring a small draw on the battery, the more draw there will be. Here are some common battery capacities:

Group 24
70-85 Amp hours

Group 27
85-105 Amp hours

Group 31
95-125 Amp hours

So even figuring a 100mA aka .1A draw, that would be about 700 hours or about 1 month, to drain the smallest battery "dead", which is usually considered 10.5V by the industry. When you start getting up into the 1 amp and higher draws, that is usually a light stuck or or something major.
 

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Well, somethings up for sure. I disagree that anything less than 100ma is okay necessarily. Even in modern cars with all kinds of sleeping electrical goodies, the typical parasitic drain is less than 30 ma! Typical drains look like this;

Old time clock - 100 mils (when actuation relay resets)/temporary
Digital Clock 3 - 4.5ma
Quartz Clock 7ma
ECM 6.5 - 8ma
ETR Radio & Clock 7ma

So, you can see that maybe 15ma continuous may be common at most for your application. My cars have modern electronics in them and I only see about 10ma sitting.

I would start to isolate the circuits by pulling fuses until the drain disappears. Perhaps your alternator circuit/field is draining your battery. Start your hunt with that device by disconnecting it since it appears you have changed it. Then go from there.

Even with a 35ma drain...the battery should sustain that drain for 100s of days! 12.65vdc is considered a fully charged battery. An acute discharge of the battery to levels as you have described points to a possible issue with the battery even tho the battery is new. I would retest the battery with load testing too.

This brings me to another point about batteries today. Lead-acid batteries are obsolete technology! New spiral-cell technology batteries such as Optima is worth it's price. Can be mounted in any position, sealed, doesn't gas, doesn't require a trickle charge because of it's long shelf life and will perform inherently and expotentially better under parasitic drain situations.

Just another take :D
 

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HOTRODSRJ...

Your disagreement is respectfully noted. There is going to be a wide variation for sure. I still feel that if you start adding a bunch of "sleeping" electrical goodies...alarm system, stereo w/memory, quartz clock, ECU, keyless entry, etc, it is going to start adding up. A single blinking LED for an alarm system could easily be 20mA.

With modern cars, I would suspect that they integrate the systems as much as possible to reduce the load, but if you start adding piece-by-piece to an older car the "sleeping load" may add up a bit faster.

I also agree with most everything you mentioned about the Optima and other spiral cell batteries. "Lead acid...obsolete technology!"...that may be pushing it a tad ;)

I am curious, though, how the spiral cell would perform better under parasitic load conditions? I agree that they would have a longer shelf life, but under parasitic drain conditions, it would seem that battery capacity would be the dominant factor. This is assuming that the parasitic load would drain the battery in a relatively short time compared to it's overall shelf life.

The specs I found for the standard Optima batteries at http://www.1st-optima-batteries.com/ show capacities ranging from 44-55Ah which is a notable amount less than even the smallest of the "common" (obsolete
) batteries I listed above.
 

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Corey, there is a difference as you pointed out with amp-hour numbers. Some of the Optimas are as high as in the mid 60s I believe. The reason I like the Optimas for storage issues/parasitic charges is that they do not need a trickle charger to keep the capacity up, unlike lead acid types that can loose their charges without a load and diminish the amp-hour numbers drastically just due to time. The self-discharge of a typical lead acid battery is about 40% per year which means about 15% in 90 days. That's big unless you trickle charge then this point is moot.

Spiral cell Optimas self-discharge rates are only a fraction of lead acid and moreover when you need to recharge the batteries because of the parasitic load, the Optima will take a fraction of the time as well to recover. That's my story and I'm stick'in to it :rolleyes:

YOu can use either but still I just prefer the newer technology for it's other features.
 
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