Hi all,

I have a 1970 small block that I have been fighting a draining battery for years. Even though I just put in a batter tender, I wanted to find out what was causing it. So I put a volt meter in-line with the positive battery lead and saw it was drawing 6.8mA. I then dislocated both shoulders crawling down to the fuse block and before I started pulling fuses I noticed a few wires "poked" in. One of the wires had an in-line fuse and seems to be running to the back of the after-market stereo the previous owner installed. It is also marked with a tag about connecting to positive battery for memory.

When I removed the in-line fuse, the draw went to 0.1mA...so I think that has been the issue. My question for you all is this...is 6.7mA a typical draw for a stereo "memory" to basically store radio station pre-sets? The stereo is probably 20 years old. I will likely replace it with an "original" someday anyway...but just wondering if that is a draw I should expect?

Second question - should I chase that last 0.1mA? To be honest, my volt meter is not super accurate...so I'm not sure how much stock to put into a 0.1mA reading...but still. If your car is not running, no keys in the ignition...do you expect 0mA, or is 0.1mA expected?

Thanks!

 

I can not comment on the value of amp draw on your stereo because you did not give any specifics about it. Kinda hard to answer a question that is so generalized. Old stereos...who knows...you can have a problem inside that is powering up 'stuff' that normally would not be powered up when it was new.

AS for chasing down that last 0.1 mA. It is pointless. It is more than likely the factory clock.

I get concerned when the reading it getting over 0.2 mA. At 0.3mA...I am really concerned. At 0.4mA...I know I have a problem that will eat a battery over night.

DUB

 

Door switches , stupid alarm horn, stupid alarm switches , light sockets , cig lighter , center console window switches.....the ever present clock drain.

I d unhook these one at a time let the car sit .....I found a weird short in a door switch that was messing up my batt.

The on off switch can go bad on a radio ...but rarely leaving the unit in the on position.

I d bet the interior lighting or alarm circuit has a minor short or bad component

Also make sure the connection are like new , I solder new connections on to all the wires at the alternator.

So that the max current can flow to recharge the circuit.to the battery

If maintaining wiring to a C3 is hard ......think what trying to fix all the millions of circuits in a C 6 in 45 years...nobody will want to do that.

 

You don't think they will build a "painless" wiring harness?

 

I believe you are chasing ghost. The factory clock in my 69 pulls much more than that. You are going to have drain from the clock and aftermarket radio and mine is around 25 ma which I believe is normal. I am not sure what meter you are using but it does not sound like you are getting good readings. 1 ma is 1/1000 of an amp, not many meters I know of have that kind of resolution. I used a Fluke 87 and would recommend it for testing. Set it on ma and connect the leads in series with the negative battery cable.
I have a disconnect on the battery of my 69 and leave it totally disconnected when not in use. The drains you are talking about are nothing to worry about unless you have the car stored form months. If you drive it every few weeks and the battery and charging system are performing correctly you should have no issues.
Based on my experieince do not trust the auto parts testers to tell you the condition of your battery if you have a standard lead acid battery. Purchase a cheap hydrometer $1.99 and check each cell. They should all float the same number of *****, 4-5 is adequate charge and if all show this the battery is charged and all cells are good. If not try charging the battery. If some of the cells float 4-5 and some only 1 or 2 you have dead cells, replace the battery then check to make sure the charging system is functioning properly.

 

Hi DUB - thanks for your insight. I apologize for not sating the stereo model, I figured it was so old! Anyway, it is a JVC KS-R7...AM/FM with cassette!

 

Thanks for everyone's comments. I should have added that I no longer have the clock in the car. The previous owner removed it and replaced it with something else. I also don't have a factory alarm. The previous owner put an aftermarket alarm in it that had a pager and stuff...that was giving me fits, so I removed it a few years ago.

It sounds like I shouldn't bother chasing down the last little bit? If the car sits unused, how long might it take for a 0.1mA draw to deplete the battery?

 

A VERY LONG TIME....depending on condition of your battery itself...I could easily state that you should get a month ....if not more. BUT that does not matter anyway...because you should be cranking and driving/moving the car and getting it up to operating temperature at least twice a month.....and without a doubt...do it once a month. I would not be worried about the battery as much as other components that need to stay lubricated that are much more important than the battery....not writing that the battery is not important....but allowing your engine to run dry on oil film on parts due to sitting several months and then crank it and have any oil film pretty much gone off of lifters ...thus having a metal on metal issue is more catastrophic than a battery....in my opinion. Other systems of the car suffer due to not being used...and one of them is the brake system.

DUB

 

Im with TX-Techman on this one. I think were having a problem with scale here. .1mA is NOTHING. Typical key off draw on a modern car is .008-.050 amp/8-50mA.
Im guessing you had a 6.7/6700mA amp draw(alot, enough to kill a battery overnight) and now its .1 amp/100mA(still a good amount, enough to kill a battery in a week or so.). If the radio is indeed pulling 100mA, check to make sure the power wires are connected correctly(constant power to consant power and switched 12v to switched 12v) and if so get a new radio.

 

Hi guys - thanks for the comments. My meter is no Fluke (I mean that in a good way), that's for sure. It is inexpensive...but it's better than putting both leads on my tounge and seeing how high my hair sticks up!

Anyway, I put my meter on the 200m setting...which I believe means that it in that setting, it can only read draws up to 200mA, if the draw is more than that, then I need to turn the dial to the next seeting which is 2A and the last one is 15A. When it's in the 200m setting, the display read 6.8....so I assume that is 6.8mA?

 

Sounds logical to me. If that is the case then good news, 6.8mA isnt bad at all, should take weeks for a good battery to go dead. Bad news is, might be a problem elsewhere, Id suspect a bad/weak battery. Check the static battery voltage after sitting overnight, should be in the 12.5-12.7volt range. Better yet, get it load tested.

 

Yes I agree, no worries about something draining your battery with that little load. For sure have the charging system checked, but I do not trust the battery load test you get from the dealer, Autozone, or AAA. They all told me the battery and charging system in my C6 was just fine, but it was very erratic and left me strained several times over a few days. I suggest a cheap hydrometer, $2 at Walmart. If all the cells float 4 to 5 ***** the battery is good. If all are below 3 ***** recharge the battery and retest. If a few of the cells only float a ball or 2 and others 3 to 5, you have a bad battery with dead cells.

 

Yup, I agree with what dugsgms74 has posted. Up to 50mA can be typical on newer cars and they can typically be able to be sit 3-4 weeks with that much current. If this sitting time was too short the manufacturer would be covering too many roadside boosts and dead battery complaints under warranty. So, the 6.8mA current in your car is nothing to worry about and you should easily be able to start it after a month of sitting if the battery is still good.

 

A bit unrelated I know.....
I have no issue with battery drain because I use a quick disconnect and for safety reasons leave the battery disconnected when I am not driving it.
(at least until 100% of the old nasty wiring is replaced by me.)
Am I the only guy who does this?

 

Nope, I have a disconnect on my 69 as well and also a Battery Minder. I highly recommend it for safety reasons as well but need to get in a better habit of disconnecting it when driven. It also eliminates all possibility of drains, but does not insure your battery will be ready to go when you are. I am on my 3rd Red Top Optima in less than 6 years.