Does leaving a multimeter on the battery posts to monitor battery voltage drain the battery at all ? Should I turn the meter off and disconnect it between checks ?
Quick multimeter question
- Thread starter Rusty67
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6Stang7
New Member
The internal resistance of a multimeter is very high (mega ohms), so you're drawing very little current. Still, if you left it on there long enough then it would technically drain the battery.
How are you using the meter exactly and how long is it being left on for? Are you using it for you car's charge/discharge gauge?!
How are you using the meter exactly and how long is it being left on for? Are you using it for you car's charge/discharge gauge?!
LOL
Something like that. My dad's car has this perpetual battery drain and I'm trying to find the problem. It is definitely in the radio circuit but I'm trying to figure out where in the circuit it is. I think the battery itself my have an issue as I had the meter on it early at is was at 12.28-12.27 and I came back later without having started the car and the meter was reading 12.35. I may need to put a new battery in before I can reliably check the voltage and narrow it down.
Something like that. My dad's car has this perpetual battery drain and I'm trying to find the problem. It is definitely in the radio circuit but I'm trying to figure out where in the circuit it is. I think the battery itself my have an issue as I had the meter on it early at is was at 12.28-12.27 and I came back later without having started the car and the meter was reading 12.35. I may need to put a new battery in before I can reliably check the voltage and narrow it down.
6Stang7
New Member
Was that a typo or did the voltage go up???
Depending on how long later was, dropping a tenth of a volt or two wouldn't surprise me.
If you want to make sure that you have a perpetual battery drain when the key is off, what you can do is set the meter to amps and disconnect the battery. Place the meter is series with the circuit (so if you disconnected the negative cable from battery, and then place the + probe of the meter on the disconnected negative cable and the - probe on the negative terminal of the battery). If there is a drain, the meter will let you know it and how much.
Depending on how long later was, dropping a tenth of a volt or two wouldn't surprise me.
If you want to make sure that you have a perpetual battery drain when the key is off, what you can do is set the meter to amps and disconnect the battery. Place the meter is series with the circuit (so if you disconnected the negative cable from battery, and then place the + probe of the meter on the disconnected negative cable and the - probe on the negative terminal of the battery). If there is a drain, the meter will let you know it and how much.
That was not a typo, the voltage went up.... really wierd.
The voltage was steady at 12.35 all day for the rest of the day. I'm wondering if the battery has been drained and recharged too many times. Its an optima but all batteries can only take so much abuse with charge/discharge cycles.
The voltage was steady at 12.35 all day for the rest of the day. I'm wondering if the battery has been drained and recharged too many times. Its an optima but all batteries can only take so much abuse with charge/discharge cycles.
6Stang7
New Member
You know, now that I think about it, there probably should be a slight drain on your battery. If you have an after market stereo in your car, then even when the key is in the off position, your stereo should be drawing a slight load for the flash memory. I'd check the drain with the meter to make sure it is just that.
Its the stock radio and I have the head unit disconnected right now. I also have the stock amps disconnected. The car will sit all week so if it has the same voltage on Saturday as it did when I left I'll know I eliminated the cause. I'll just add pieces in 1 by 1.
kilgorq
Member
Actually there is a regulator but it is built into the alternator. How long does it have to sit before it will not start?
Yes, I know the 3G alternators have an internal VR but again I know this isn't the issue.
Car can usually sit between 2 and 5 days until it wont start.
Car can usually sit between 2 and 5 days until it wont start.
kilgorq
Member
If it were me I would try the battery first. Especially if it is lasting a couple of days.
The voltage going up a little is not out of the norm. As the acid eats the lead in the cells there will be Minor variations in the voltage.
Tim65GT
Active Member
You really don't even need a multimeter to find a slow drain. Get a brake light bulb and socket and put it in series with the battery. Make sure the ignition is off and the doors are closed.
If it lights up, something is drawing too much current. It takes over 2 amps to light the bulb which is way more than the normal amount of current (300 ma or less) that the system draws from the battery when the car is off.
Pull each fuse one at a time, and see if the light will go out. If so, you found which circuit is drawing too much current.
If not, disconnect the alternator connections and see if it that does it. If it is internal the light should go out.
View attachment 242576
If it lights up, something is drawing too much current. It takes over 2 amps to light the bulb which is way more than the normal amount of current (300 ma or less) that the system draws from the battery when the car is off.
Pull each fuse one at a time, and see if the light will go out. If so, you found which circuit is drawing too much current.
If not, disconnect the alternator connections and see if it that does it. If it is internal the light should go out.
View attachment 242576
kilgorq
Member
It sounds like you are on the right track. I am curious as to how much current the stereo is drawing. It may be that one of your amps is not shutting off. I have seen that a few times.
Right now I have the fuse in and the amps unplugged as well as the head unit. As far as I can tell there is no drain. I think its actually the head unit but I'm going to try to verify that this weekend.
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