Use of accessary sub-woofer, with car not running, results in batter discharge


#1

I just installed the Honda sub-woofer system in my 2006 Odyssey. Factory add-on harness plugged right in to the sound system harness. When I attempt to use this sub-woofer system without the engine running, the battery gets totally discharge. How do I detect if there is a short in the component or a short in the new wire harness? What else could be contributing to the battery discharge caused by this new accessary?


#2

What does the kit consist of? I suspect there is some sort of amplifier, which probably uses a built-in inverter to get higher voltages needed to power a subwoofer. It may just be that the subwoofer system is a power hog and draws a lot of current from the battery.

Also, how old is your battery? Maybe you need a new one. A load test would help to find out.


#3

OK, I see it’s a 2006 Odyssey, so the battery can’t be too old. Still, have it load tested.


#4

You nneglected to tell us how long it takes for battery discharge.
This is important.


#5

Yes, and excellent point. How long were did it take to kill the battery?


#6

I suspect there is some sort of amplifier, which probably uses a built-in inverter to get higher voltages needed to power a subwoofer…

It’s WATTS not volts. If the battery is actually draining then it’s drawing a lot of amps to get the amount of watts the sub needs to play at a high sound level.

Some speakers are very innefficient and need a LOT of power. I suggest either leaving the van running or you get a more efficient woofer. A woofer that has a efficiency rating of 95dbs will use less then half the power for a woofer rated at 90dbs.


#7

" I suspect there is some sort of amplifier, which probably uses a built-in inverter to get higher voltages needed to power a subwoofer…

It’s WATTS not volts. If the battery is actually draining then it’s drawing a lot of amps to get the amount of watts the sub needs to play at a high sound level."

Well, yes, it’s Watts, but how do you get more watts out of a 12V power source? You either have to have a very low speaker impedance, or you have to get higher voltage. Watts = I*E (amps * volts) the only way to get more current is to either lower the impedance or raise the voltage. High power amps for cars have to use inverters to get much higher than 12V levels to make higher wattage possible. Car speakers generally are in the 2 to 8 ohm range.

My point was that those inverters suck a lot of current.


#8

What is the brand and model of the subwoofer? How many watts does it draw? I suspect that it’s just a power hog. You bought it so you could have a fat, honkin’ bass, and that requires power.


#9

It’s probably a high current consumer and those kinds of things will run even a new battery down pretty quickly.

The son of a friend of mine used to work babysitting some oil wells at night and he installed some high tech audio setup in his vehicle.
He wanted that booming bass out there for company but quickly discovered that 30 minutes max and he was out in the boonies with a dead battery.
His dad finally convinced him to leave the amperage eater gear off while he was parked and use it “normally”.


#10

Unless you want to install numerous additional batteries, or a compact generator, then you’re SOL for engine off audio operation.

How many watts is this setup rated to put out? Assuming you have at least a thousand watts worth of amp, try to figure where all these watts COME from. A 1200 watt system will need to pull out about 100 amps with the engine off. That battery is designed to apply a 100 - 200 amp burst of power to the starter for a few seconds. 30-45 seconds of starter operation can sometimes be enough to cripple a battery. Your stereo is overtaxxing the battery. If you continue to run the battery dry, you’ll completely ruin the battery.

I suggest that you take this as a warning, and be sure to check your alternator amperage output. Most alternators are designed so that if you’re driving on a rainy day, with MAX A/C, lights, and the whole of everything electrical turned on, to have approx. 10 - 15% reserve. If your alternator can’t keep up with your audio system, as well as the rest of your car’s drain, the battery has to make up the deficit. The battery can run out of power even though the car is running because you’re taking more than the alternator is making. One day you may find yourself on the side of the highway after your battery drains and your electrical system overloads. You may also find yourself in the market for many new electrical components, which are always expensive.

These are the kinds of things you need to review before you install major electrical add ons.

-Matt


#11

[/b]The subwoofer unit is a standard Honda accessary with the amplifier embeded in the speaker unit. It is a 12 volt unit and the standby current is 2mA and the nominal is 4.5 A which does not seem like that big a draw. Power output if 80 watts max and normal at 50 watts max. This is a small supplemental unit compared to the huge monster units that folks buy at car audio places.


#12

[b]Battery discharge occured after about 15 minutes.


#13

[b]This is a Honda std accessary draws 4.5 amps at most.


#14

[b]Thanks Matt. Since this Honda audio add-on accessary is such a low 4.5 amp draw on the system and only 80 watts max output there has got to be another circuit path or possible short that is siphoning the juice out of the battery.


#15

Like it or not, a 4.5 amp draw is huge and no battery in the world is going to stand up under that for very long.

Something as puny as a trunk light bulb (a tiny fraction of an amp) can kill a battery overnight so do the math.
Just how long does it take for the battery to run down?
Have you considered unhooking the subwoofer and see if the problem goes away?


#16

Have you tried measuring the actual current being drawn with the system running? Comparing that value with the amp-hour rating of your battery will help you determine if there is a problem with the sound system, or if you just have a weak battery.


#17

50 Watts is a lot. Typical headlights draw 55 Watts on low beam. How long can you leave your headlights on without draining your battery? Double that, and you will have approximately how long your subwoofer alone can go at “normal” levels. Don’t forget the head unit and other speakers are also using some watts. Basically, this is like leaving your headlights on.


#18

I think your battery is getting weak. Have it tested, but as I said above, running this system is like leaving your headlights on and that runs the battery down pretty quick.


#19

You either have to have a very low speaker impedance, or you have to get higher voltage.

HUH??? My home speakers are NOT low impedence (8 ohms) and my amp draws a LOT of amps when I want to crank it up…My amp is NOT increasing the voltage to increase wattage…In fact it’s a LOT easier controling sound quality by increasing amps then increasing voltage.


#20

Your home system is starting with a 120V AC power supply, not 12V DC. It’s basic Ohm’s Law. E=IR (volts equals current times resistance (or impedance in this case)). If you want to push more current through a given impedance, you have to raise the voltage. This is why most car head units are limited to 20 Watts per channel at 8 ohms. 12/8=1.5 (volts divided by impedance equals current) W=I^2R (Watts equals current squared times impedance) 1.51.58=18 (rounds up to 20 because most cars actually have slightly more than 12V in practice).

In fact, your home system is lowering the available voltage because to drive an 8 ohm load at 50 watts doesn’t take anywhere near 120 volts. But it’s much easier to raise or lower the voltage with AC than with DC. A simple transformer is all it takes, though lots of modern equipment uses switching power supplies instead.

Trust me, I used to repair stereo equipment (both home and car) and you have to either raise the voltage or lower the impedance to increase current. It’s the Law :wink: