Powering a car amp

I'm installing a subwoofer into our boat (also happens to be my first car audio installation, so I'm kind-of unsure on some things). First, the speaker is a 12" 8-ohm Rockford Fosgate Punch Z. Not that good, but it works. The amp is even cheaper, it was a $40 Baja so-called 400W 2-ch MOSFET Amp (heatsinks look like they belong on a 100W amp though) running in their version of a bridge mode - invert one amp and not the other, which is correct, but don't send the same signal to the amps, but instead still send left to one amp and right to the other! Their logic is it sums both left and right channels, except when a sound is different on each channel, there goes half of the power!

Anyway, I have the power antenna going to the remote in, RCA cables going from the radio to amp, the crossover set to low pass at ~60hz.

All thats left is to run power from the battery to the amp. I figured I would need roughly 20ft of wire (goes from about the middle of the boat to the back then all the way across to the battery), and the manual suggests I use 10-12 guage wire with a 40A inline fuse.

But, the manual says connect the ground to the chassis, assuming it is a car. Since the boat is different, the chassis isn't even connected to the ground. What I need to know is can I just run positive to the positive on the battery, and ground to the ground on the battery?

Also, how much power do amps usually draw when they are off waiting for a signal to turn them on? The boat isn't used anywhere near as much as a car, so I'm worried that when it sits and doesn't have an alternator going to keep the battery charged the amp might drain it.

Thanks!
 
To answer the first question yes you can hook up straight to the negative side on your battery, but you don't want to run a ground that far. The general rule in car audio is to keep the ground 12 in. or less (some say 18 in.) I'm not that familiar with boats but if it has gauges then there should be somewhere to ground the amp where the gauges and other electricals are grounded. And also for your power and ground wire I would suggest moving up to 8 AWG for a length of 20'.

As far as current draw I would get a resettable circuit breaker and use that to disconnect the power when not in use. You can find these at most car stereo shops. They are not too expensive and serves as a switch/fuse. I know Stinger and Phoenix Gold make them, but I'm sure there are several other companies.

And a side note I would cross that sub over a little higher maybe 90-100hz.
 
Thanks for the reply.

The amp is mounted right behind the head unit, so could I just ground it directly to the metal on the head unit, or the ground connection on it?

What would happen if I had to run it to the battery? Is that just a risk of a ground loop, or am I risking damage to the amp or electrical system in the boat?

I will probably plan on getting one of those breakers then. Just out of curiosity, how much power do most amps drain when they aren't on?

Thanks again,
Mike
 
Yes power is going through the ground. Actually on D/C power flows - to + in a circuit. So you need to use the same gauge wire for both the ground and power. Yes the only real problem with running your ground that far is the ground loop.
As far as current draw I can't give you a hard number because there are a lot of variables involving battery, amp, etc.
BTW don't ground it to the actual ground wire on the head unit. It needs to be a metal contact obviously so check around screws, bolts, etc. and you should find something. Good luck and let me know what happens.
 
darth_audio said:
Yes power is going through the ground. Actually on D/C power flows - to + in a circuit. So you need to use the same gauge wire for both the ground and power. .............It needs to be a metal contact obviously so check around screws, bolts, etc. and you should find something. Good luck and let me know what happens.

The screws/bolts, if they are grounded, are probably grounded using thin wire, which will be to small to handle the current.
 
Is this a glassfibre boat? If its steel, then normaly one don't connect the body to ground. (Has to do with corrotion.)

You should run 2 heavy gauge wire from battery to amp, one for + and one for ground. (The current in the groundwire are allways exactly the same as in the + wire, so both wires should be of the same gauge.)
Get ground (and +) for det headunit from the amp. This will depress groundloops for the soundsystem.

To check the currentconsumtion during off-state, just connet the ground on the amp to a powersource (battery), and use a multimeter (is this what you call the testinstrument? (english not being my native language)) sett to current measurement and connect it between the + of the amp and + powersource. A good idea would be to use a wire between the +'es and then removing it before you hook up the multimeter. This to prevent charging the caps inn the amp throu the multimeter which posibly could take out the fuse in the multimeter. I suspect a powerconsumtion well below 100ma. Thoug the currentconsumption are small it is, as sugested earlier in this tread, smart to disconnecting the powersource trough a autofuse. Smart, easy and safe.

space
 
Thanks.

So, if I understand you correctly, as long as I run both the amp and the head unit off of the same two wires coming from the battery, I wouldn't have to worry about ground loops?

The only other thing I'm worried about is the amount of power it will use. The fuse blows at 40A, so it could almost draw that much, and I'm worried the battery won't be able to keep up with it. What do you guys think?
 
Yes, if you hook up the ground of the headunit directly to the amp-ground, there should be no problems with groundloops.

At maksimum power (for audio) the peak powerconsumption will probably be close to just under 40 A, but the average will probably be well under 10 A, more like 5A, which will be LOUD.
There has been quite some hyping as to the size of the powercables to caramps. If you follow the instructions in the manual you won't be dissapionted.

space
 
space said:
use a multimeter (is this what you call the testinstrument? (english not being my native language))
space
Test instrument is a tool with which you can test something. Multimeter is a test instrument, so as oscilloscope.


space said:

At maksimum power (for audio) the peak powerconsumption will probably be close to just under 40 A, but the average will probably be well under 10 A, more like 5A, which will be LOUD.
There has been quite some hyping as to the size of the powercables to caramps. If you follow the instructions in the manual you won't be dissapionted.

space

If one has 10A max of current allowed for measurements with multimeter, should it be even attempted to measure 10A average, 40A peak power source like that?
 
If one has 10A max of current allowed for measurements with multimeter, should it be even attempted to measure 10A average, 40A peak power source like that?

I said he could use a multimeter to measure the currentdraw when the amp is connected to a voltagesorce but not turned on (off-state), not at on-state at maksimum power. But it probably wouldn't do much harm.

space
 
battery drain with car audio

i run my car audio system off marine deep cycle gr24 with great success with a new gr24 i can run a kenwood 2x70w amp for a good 7-8 hrs and shut down just as the batt hits around 11v i posted elsewhere looking for a simple way to regulate that power to a solid 14.8 {like an alternator voltage} as the 12-11 seems a bit low using two batt in series to get 24v to start is no problem but regulating that with the current the amp needs is way outside the value of regulator s i have used to get smooth dc in smaller projects any ideas there?
 
...looking for a simple way to regulate that power to a solid 14.8 {like an alternator voltage} as the 12-11 seems a bit low...

12-11 seem at bit low for what? The amp? Do you want 14.8V so to get maksimum power from the amp? It probably isn't a cheap way to do this. The best would probably be to buy an amp with regulated PSU. They don't care if the supply is 14.8 og 10.5 V. "Higher quality" amps usually have (at least should have) this.

Isn't the amp giving you enough power at 11V supply? Or does it shut down at powerpeaks? If it does, do you have a large cap (1F) on the supply? It could probably help you get some more playtime of the battery.

Even though you've got a deepcycle bat., going much below 11V probably isn't the best thing to do.

space
 
deep cycle sound

thanks space! yes i figure starting at 12v and stopping at 11v {min voltage stated on the amp} was not at all optimum i am trying to get the power and clarity up with voltage close to the spec max {17v} i also want to get more running time out of the batt i will usually bring 8-12 batt for a whole weekend to run two amps and an inverter the less batt i need to bring the better so what does a high quality amp so inside to regulate voltage at 14.8 i wonder or an alternator or a battery charger i find so many instances of devices cranking out high current 14.8v that i am finding it hard to believe my query is soooo obscure i have asked so many people at so many places there has to be a solution to put inline with my batt to get 14.8 i will just keep hunting for it