Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Which is better -- amp ground connected to frame or battery?

  1. Feb 16, 2017 #1
    There is this debate in car audio forums of this question whether it is better to connect your amp ground to the frame of the car or the battery.. basically they haven't came to a conclusion so I was curious what you guys think...

    Basically what I mean is that when you hook up an amp in the trunk of your car to power speakers should you connect the ground for the amp to the frame of the car or should you run a thick 1/0 ofc copper wire back to the battery...

    I could see pros and cons to each situation-
    Frame:
    Pros: very large so it can handle heat well, R=rL/A... resistance should be low since there would be a large surface area, good conductor since it is so large
    Cons: car frame material has a larger resistivity than a copper wire, car frame has many materials connected such as rubber so ground current may have to bounce off several materials to make it back to the battery ground, other devices are using the frame as the ground so maybe it could cause some interference.
    Battery:
    Pros: going straight to the battery seems like the most direct path, copper has low resistivity, copper wire also has a large surface area since it is made of many small wires, avoid interference since it's a dedicated ground
    Cons: could be a worse conductor than the frame, could wear out faster than the frame, can't handle heat as well as the frame can

    So what do you guys think?
     
    Last edited by a moderator: Feb 16, 2017
  2. jcsd
  3. Feb 16, 2017 #2

    Averagesupernova

    User Avatar
    Science Advisor
    Gold Member

    If this is the sort of thing floating around on car audio forums? Seriously? Having worked in automotive electrical some years ago my recommendation is to not hook anything to the battery except the battery cable(s). Hook the amp to the chassis and make sure there are good conductors that tie the chassis and the engine block together. BTW, this debate will likely never die on car audio forums.
     
  4. Feb 16, 2017 #3
    I think unless your audio draws current ~ in the class of the starter then simply there is no point in hooking it directly to the battery.
     
  5. Feb 17, 2017 #4
    Thanks for the response. I know that is the general rule of thumb, especially since most car audio systems installed at car audio shops aren't very big and wire is expensive but in terms of electrical theory what would you say...
     
  6. Feb 17, 2017 #5
    The amplifier should draw current, right? A noticeable amount considering that an average size good amp is around 3000 watts rms
     
  7. Feb 17, 2017 #6
    Something to add is that wouldn't you want your circuit to have the same size conductor on both sides of the battery or amplifier? When you use the frame or chassis as a ground the electricity flows from the battery through the copper wire and then back to the negative side of the battery through the frame of the car which is substantially different than a wire. When you guys create a circuit, don't you generally have the same size wire/metal throughout, excluding components.
     
  8. Feb 17, 2017 #7

    davenn

    User Avatar
    Science Advisor
    Gold Member

    I doubt that there is a car amp out there that can really produce that sort of power ... It is another audio amplifier sales farce to the unsuspecting and unknowledgeable

    3000W / 12V = 250 Amps ..... and even if you wanted to say there was a couple of more volts
    3000W / 14V = 214 Amps

    seriously ?? :rolleyes:

    a genuine 300W to maybe around 800 - 1000W, I could believe
     
    Last edited: Feb 17, 2017
  9. Feb 17, 2017 #8
    Interesting. Okay would you say it would be better to use the frame? Would it be bad at all to go straight back to the battery, because I wanted to do that since I'm running a lot of extra electrical equipment in the interior and I get weird noises when I turn the devices on sometimes
     
  10. Feb 17, 2017 #9
    The car chassis counts as conductor far thicker than the copper wire on the + pole.

    3000W rms is marketing. If it comes with a gigantic puffer cap then it's a kind of short time peak value. If there is no puffer, then it's only a dream sold at high price.

    The most you can do is to use a thicker wire at the - pole of the battery to the chassis and 'reinforce' the chassis with some thick copper, from the battery connect point to the amplifier ground point (you should connect it to the chassis on both points!). It'll do ~ nothing, but you will feel better I think... This class of load is just not for 12V systems.

    A battery is not enough. It's a common problem with such beefed up car audio systems. You need a bigger generator, a bigger battery, many rewiring, a gigantic puffer cap and at the end you can't use it at night because when you turn up the bass the lamps starts blinking and the dogs around starts wooooooooooooo...
    :nb)
     
    Last edited: Feb 17, 2017
  11. Feb 17, 2017 #10

    tech99

    User Avatar
    Gold Member

    If you connect the amplifier negative lead directly to the -ve battery terminal, then if the thick negative lead from battery to frame becomes broken, the starter current might flow through your own amplifier -ve lead. This could happen of the amp has an inadvertent ground somewhere, such as via an antenna cable. Such a condition might cause damage or fire. So it is best to connect your amplifier lead to the frame end of the thick battery cable.
    I think the reason for connecting close to the battery, if any, is to reduce noise and interference, rather than current capability.
     
  12. Feb 17, 2017 #11

    jim hardy

    User Avatar
    Science Advisor
    Gold Member
    2016 Award

    Good advice.
    Actually battery negative, chassis and engine must be tied together by heavy conductors .
    Look for wide braided cables and make sure they are intact, not corroded, and not left off by some previous owner.
    A kilowatt of audio ?
    If you don't see wide braided grounding cables but instead little skinny ones or corroded ones, replace them.

    On some Fords the negative battery cable goes down to engine block near starter, and it has midway along its length what looks like a simple mounting tab that bolts to the inside fenderwell.
    That is more than a mounting tab, it's the grounding tab that ties battery negative and engine both to chassis sheet metal.
    When somebody replaces that cable with one not having the grounding tab it causes electrical troubles - lights dim, electrical accessories don't work, because current has to find its way back to the alternator and battery through accidental routes like the speedometer cable and instrument wires . Sometimes those will melt.

    A friend's Chevy truck recently quit when the braided wire just behind passenger side front fender connecting cab to frame corroded in two. That left all body sheet metal essentially disconnected from battery. It'd pass just enough current through the rust to barely run the fuel pump. Truck would idle but not drive, and turning on any light stopped the engine because fuel pressure dropped too low for the injectors to function.

    So if you're adding a hundred amps or so of load to the grounding conductors in your vehicle, it would behoove you to know where those conductors are and to inspect them to be sure they're up to the task.

    That was the point of my two boring anecdotes.


    old jim
     
    Last edited: Feb 17, 2017
  13. Feb 17, 2017 #12

    Averagesupernova

    User Avatar
    Science Advisor
    Gold Member

    For the record, a couple hundred amps current draw is not at all uncommon for one or for sure several amplifiers combined. If you doubt me do a quick Google for db drag racing. Dimming headlights is not at all uncommon.
     
  14. Feb 23, 2017 #13
    Interesting. So if you were to fuse the wire that goes from the amp ground to the battery ground would that eliminate the worry? or do you think it would just be safer to ground to the chassis/frame?
     
  15. Feb 23, 2017 #14

    Averagesupernova

    User Avatar
    Science Advisor
    Gold Member

    If you fuse the main ground wire and it blows, where do you have think the current will find its way through then? My guess is someplace you don't want it.
     
  16. Feb 23, 2017 #15
    When you say "main ground wire" are you talking about the ground wire from the amp to the battery?
     
  17. Feb 23, 2017 #16

    Averagesupernova

    User Avatar
    Science Advisor
    Gold Member

    Yes. This is what you suggested right? Fusing this wire?
     
  18. Feb 23, 2017 #17
    Ya
     
  19. Feb 23, 2017 #18
    So you think if the ground fuse blew the current would still travel through other things?
     
  20. Feb 23, 2017 #19

    Averagesupernova

    User Avatar
    Science Advisor
    Gold Member

    If there is a path, why would it not? I don't recall if some (or all) amplifiers have the shield on the RCA connectors isolated from the main power ground or not. I am pretty sure the RCA outputs on most headunits DO have continuity between the RCA connectors shield and ground. I would take the side of caution and do everything possible to be sure that continuity is not broken on the power cable.
     
  21. Feb 23, 2017 #20
    Interesting. Do you think the same thing could happen when the ground is connected through the frame since there's so many other electronics connected to the frame and wires near the frame? Or are you concluding that the safest option is to connect it to the frame/chassis?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Which is better -- amp ground connected to frame or battery?
  1. Which is better? (Replies: 7)

  2. Amp limit of a Battery (Replies: 2)

Loading...