Installing an Audio Amplifier

[RocketDork]

I've done this quite a bit in the car world, but installing an audio amplifier (for a set of subwoofers) in a motor home presents a couple of challenges.

The amplifier will turn on ONLY when a 12 V signal is present from the stereo installed in the dash. Therefore, when the radio is switched on, it will cause the amp to switch on...and vice versa.

SO, the questions that I pose to you guys are these.

1. Do I wire the amp directly to the House batteries and run it from there all the time?

2. Do I wire the amp directly to the chassis battery and run it from there all the time (I don't think so...)

3. Do I wire the amp to the "main/aux" switch in the dash to power it off the same battery the stereo is running off of. I'd have to wire it up using a relay...it draws 30 amps at max, more than the switch will handle.

4. If I wire it though a 2 pole relay to the dash switch which switch position would I put on the NO and NC contacts???

I'm inclined to wire the amp directly to the house batteries (via a fuse) and just go from there...but I figure you guys may have some insight or reasons why I shouldn't do this.

[RocketDork]

I've done this quite a bit in the car world, but installing an audio amplifier (for a set of subwoofers) in a motor home presents a couple of challenges.

The amplifier will turn on ONLY when a 12 V signal is present from the stereo installed in the dash. Therefore, when the radio is switched on, it will cause the amp to switch on...and vice versa.

SO, the questions that I pose to you guys are these.

1. Do I wire the amp directly to the House batteries and run it from there all the time?

2. Do I wire the amp directly to the chassis battery and run it from there all the time (I don't think so...)

3. Do I wire the amp to the "main/aux" switch in the dash to power it off the same battery the stereo is running off of. I'd have to wire it up using a relay...it draws 30 amps at max, more than the switch will handle.

4. If I wire it though a 2 pole relay to the dash switch which switch position would I put on the NO and NC contacts???

I'm inclined to wire the amp directly to the house batteries (via a fuse) and just go from there...but I figure you guys may have some insight or reasons why I shouldn't do this.

[MrTransistor]

Hi Rocket,

I'd go with the relay, house battery, and ˜main/aux' or ˜engine/house' switch. Of course, place a fuse in the power line to the house battery and use wire of a sufficient gauge to keep voltage drops to a minimum. On the ˜engine/house' switch; parallel with the wire that feeds the radio so that when the switch is in ˜engine' position, the relay is de-energized to remove any drain on the house batteries.

[John Hilley]

I agree with MrTransistor, wire it to the Main/Aux switch on the common contacts to the coil of the relay. The switch switches between the "Coach Battery" when in Aux position and "Chassis Battery thru Ignition Switch" when in Main position. When in the Main position, amp would be controlled by the ignition switch. When in Aux position it would be on whenever the switch was in that position. Wire the amp thru the relay NO contacts to the "Coach Battery"

[RocketDork]

Let me restate to see if I understand correctly.

Wire the amp to the coach battery directly. Use a fuse close to the battery to prevent short circuits from causing a fire.

Then wire the amplifier control (power on, off) through a relay that is energized by the Main/Aux switch...use the NO contact to switch the amp to the coach battery, ie, the coach battery powers the amp on/off when energized. The relay does not actually provide any *power* to the amp, just acts to turn it on and off.

Is that correct?

[John_Canfield]

There are endless options for wiring your amp. Are you sure you need 30 amps? At the volume level you will most likely be using it, I'll bet your current demand will be considerably less.

(If you do pull 30 amps, I hope I'm in another campground down the road from you )

Having said that...

Keep it really simple:

Take your 12V from something that will be disconnected when you cut off your disconnect switch. The house disconnect solenoid would be a good candidate - wire it to the house side of the solenoid on the large terminal (*not* the coil.)

I wouldn't bother trying to find an ignition-switched source of 12V unless that is of particular importance to you.

I don't understand the need for a relay

Do a forum search for "wire calculator" - I think I posted several months ago a link to a web site that provides a wire size calculator to determine the proper wire gauge for 30 amps and your wire length. If you can't find the forum reference, do a google.

Always fuse right at the source like others have said.

[John Hilley]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Let me restate to see if I understand correctly.

Wire the amp to the coach battery directly. Use a fuse close to the battery to prevent short circuits from causing a fire.

Then wire the amplifier control (power on, off) through a relay that is energized by the Main/Aux switch...use the NO contact to switch the amp to the coach battery, ie, the coach battery powers the amp on/off when energized. The relay does not actually provide any *power* to the amp, just acts to turn it on and off.

Is that correct? </div></BLOCKQUOTE>


Not quite. The power from the coach battery to the amplifier has to be wired thru the NO contacts of the relay to power the amplifier. You should fuse the battery connection near the battery. PM me if you have more questions.

[RocketDork]

OK, I think I've got it.

The reason I was thinking a relay was to be able to power the amp from either the house battery or the chassis battery depending on what the position of the Main/Aux switch was.

The suggestions above indicate that I should just connect it to the house battery.

Its also been suggested that I connect it after the big relay that switches the house battery in and out.

Since the Amplifier has its own relay to power it when the stereo is turned on. I'll utilize it to power the amplifier. I'll include a 30 amp fuse to the amplifier at the house relay to prevent any short circuits from doing damage.

I've done a bunch of installations in cars, so I'll use large enough wire for current requirements and distance to the amp.

Its likely that I'll never run the amp flat out...just working to fill the anemic sound that comes from the house speakers. My kids on the other hand, may...although never when we are camping with others. We are very conscious of our noise "footprint" when we are around other campers.

Thanks for all the help! I don't think I would have connected it after the relay for the house power...not that it represents a drain when its powered off, but it is a good idea!

[MrTransistor]

Hi Rocket,
You got it now! Enjoy that powerful audio spectrum.