Question about parallel car batteries...and amp meter usage...

Discussion in 'General Electronics Chat' started by kazlx, Jan 9, 2008.

  1. kazlx

    Thread Starter New Member

    Jan 9, 2008
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    Forgive my ignorance...and registering here to get an answer to what may be a stupid question, but it's driving me crazy.

    My diesel f250 is my first vehicle with 2 batteries, so I want to make sure I'm not screwing up my readings and coming to the wrong conclusions.

    I have been having a problem with the batteries dying. I think it is from the stereo (2 amps: 1 speaker amp, 1 sub amp, all 'professionally' installed). The weird thing is that the problem is recent and the stereo has been in for almost a year.

    Do I need to isolate one battery to check for amp draw with a meter? The stereo is fed from the driver (aux) battery with 1/0 cable through a 150A fuse to a distribution block with 4ga to each amp. Disconnecting the main amplifier cable and inserting the meter, I get about a 1.6A draw with the truck completely off and the key out. This seems wrong to me.

    I took it to the stereo shop and they told me it isn't the stereo. He told me they checked the stereo with one battery disconnected and it is fine, but there is getting a draw somewhere that stops when they pull a fuse under the hood (a 50A maxi) that the owners manual says is the junction box fuse. I am guessing this is the main battery feed to the junction box, so that doesn't really isolate anything. I just have a feeling I am getting BS'd with excuses by the stereo shop because they don't want to take the time to figure it out because the system has already been sold and they don't want to work on it and not make any money.

    I am pulling my hair out because I don't trust driving the truck anywhere. The amp power lights are not on with the truck off, but it seems to me that with the batteries wired in parallel, it shouldn't matter that the amps are only fed from one battery. I should still be able to check amp draw from the main stereo wire and it should read either 0 or milliamps with the truck off......The pair of batteries would only increase the amp-hours for a longer load time and give the necessary amps to start the diesel.

    I guess my main question is do I need to isolate one battery to test amp draw by pulling fuses? I was just about to start pulling fuses, but I blew the fuse in my meter and all the stores are closed....

    Any help is appreciated....I only know enough about electrical to get myself in trouble....
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Divide and conquer. ;)

    No, I don't think that the amplifier should be pulling 1.6A with the ignition off.

    The most drain you should see with the key removed and all lights off (including interior lights) is but a few milliamps to keep the radio's clock running and the station memory alive.

    Disconnect the aux battery from the main battery. See if there is any current draw from the main battery to it's harness. If not, the problem is on the aux battery side. If there is, start pulling fuses (replacing them immediately if there is no change) until the draw goes away. Once you find a fuse that has a major effect on the current draw, look at what that fuse is supplying power to, and start unplugging those components, plugging them right back in if there is no marked improvement.

    Same thing on the aux battery side. Pull fuses/disconnect stuff until the power drain goes away.

    Check your battery voltage. A fully charged battery will have 12.7V across the terminals. If one of your batteries has significantly less than that, it may have a shorted cell. This can drain the other battery.

    One of the best ways to check the charge of your batteries is to use a specific gravity meter, called a battery hydrometer. These things generally are moulded plastic, with a rubber/plastic hose on one end and a rubber bulb on the other, and they're under ten bucks. You stick the hose in a battery cell, suck up the acid, and a weighted flap or ball(s) will indicate the specific gravity of the acid in the cell. They should all be about even, and around 1.265. If you read 1.225 or below, your batteries' plates are being subjected to sulphation; the plates are getting coated with gook that will soon kill it. This starts happening when your battery voltage drops to 12.4. Keep your batteries charged and they'll last much longer.

    If you find just one or two cells that are significantly lower than the others even after charging, those cells are damaged by sulphation or by the plates being shorted. When the plates corrode, slag falls to the bottom of the cell, eventually building up enough to short out the bottoms of the plates.
     
  3. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    I am willing to bet that the cause of your problem is your alternator and / or batteries.

    All modern stereos and amplifiers know when your car is off, then they draw very little current. The problem is that most audio shops won't tell you how abusive having a high power stereo is on your vehicle's electrical system. It severely loads your alternator and wears your battery out much faster.

    The solution, of course, is an extra battery with a high performance alternator. High value caps will make life a bit better on the system too, the usual 1/2 to 2F will do nicely.

    I had a car when I was a bit younger and thought it would be 'cool' to install a 1200W sub amplifier and a 55W X 4 deck. After about 6 months, I noticed my lights dimming and the battery gauge fluctuating more than usual. It got worse and worse, then I just ditched the system. I had my batteries topped up and alternator rebuilt. Good thing my dad is a mechanic!

    Steve
     
  4. kazlx

    Thread Starter New Member

    Jan 9, 2008
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    The problem for me is that the amps should know when the car is off, but there is still a 1.6A draw to the amps when it is off. That is with both batteries connected and measuring in-line in place of the main fuse. There is nothing wired to the aux battery besides the stereo. Everything is wired to the main battery and the aux battery is tied to the main.

    The truck came stock with dual batteries.

    I do need to check voltage across the cells and get a hydrometer to check the cells, except I *think* the batteries might be sealed....but I popped the 10A fuse in my meter last night....
     
  5. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    I'm working from memory here, but isn't there an enable signal going to the deck? I believe this signal shuts down the amplifiers. Do you have this signal attached?

    Steve
     
  6. kazlx

    Thread Starter New Member

    Jan 9, 2008
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    0
    Yes, there is a small 22ga or so trigger wire that turns the amps on. The power lights on both amps turn on when the truck is turned on and go off when the truck is off, but there is still a draw through the main power wire when the truck and amps are off.
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Do you have a wiring diagram for the truck? By now, it's a matter of pulling fuses until the mystery current draw stops. After that, use the diagram to see what devices are on that branch, and see how to isolate each one to see which is causing the current flow with the ignition off. If you have a fuse panel under the hood and under the dash, it could be a long day.
     
  8. kazlx

    Thread Starter New Member

    Jan 9, 2008
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    I do have a wiring diagram for the truck. I am planning on pulling fuses, but the stereo is ran on it's own circuit, plus it is the only aftermarket wiring on the truck. To me, it is the first thing to be suspect of and I want to verify if something is wrong there or not before I start pulling fuses...
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
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    If there is a fuse leading to the amp, pull it first. Lacking that, cut the power lead & splice it later. It's just a process of elimination.
     
  10. rusirius

    Member

    Jan 9, 2008
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    Forgive me for sticking my nose in where it doesn't belong... But one question... You mentioned you blew the fuse in your meter? Not that it doesn't happen in other instances, but GENERALLY when I've seen this happen it's because somebody configured the meter to measure current and then connected the probes across a source with a voltage differential. I mean no offense by this, but is it possible you're not using the meter correctly and that could explain seeing the 1.6a?

    Otherwise, yeah, it's just a matter of elimination... Measure current going straight into the amp itself when the key is off... If the amp is powered down and you're still seeing current, then the problem is in the amp... Otherwise, check the current at the batteries and as suggested start pulling fuses till it goes away, then just work forward from that fuse on to figure out exactly what it is that's drawing it...
     
  11. kazlx

    Thread Starter New Member

    Jan 9, 2008
    6
    0
    Yea, no offense taken. I know I screwed up with the meter. It was me forgetting to move the probe to the right configuration. Combination of it being late, me being in a hurry and irritated because I'm trying to do all this in the dark at night with a flashlight....

    When I got the 1.6A reading, the meter was configured correctly and setup in place of the main fuse for the stereo...
     
  12. Externet

    AAC Fanatic!

    Nov 29, 2005
    761
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    Ahhhh... the typical laziness to write properly ...
    The readers have to figure out when the f@#$% amp means amplifier or when it means ampere :mad:
     
  13. kazlx

    Thread Starter New Member

    Jan 9, 2008
    6
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    Maybe a little context and reading comprehension...?:) If you are going to complain about laziness, how about some complete sentences and periods?

    Maybe I should use 'current'.....
     
  14. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    Kalzlx grammar and usage are proper when taken in context. Ad hominem commentary is not in keeping with the posting guidelines. Nothing here to get amped about.:D
     
  15. FredM

    Senior Member

    Dec 27, 2005
    124
    1
    if you amputate the amp, you should get ample proof that it is the amp which is sucking your amps, but if you dont get ample proof, because the wasted amps continue to be wasted after you have amputated your amp, then it is probably not your amp to blame, and probably time to review the current situation.
    I still wonder about having 1.6 amps in your truck - I have never found a way to have a non-integer number of these running simultaneously in a vehicle! - must be one (or 1.6?) of these new-fangled DSP floating point amps, class D or something - like these tiny PC amps which provide 50W PMPO but sound about as loud as my first tranny back in the 60's which only gave 0.5W RMS .. How times change!!;)
     
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