Is a direct connection to the battery strictly necessary?

**Lum** · 01-22-2005, 10:04 PM

I'm looking at the M1-ATX supply sold on this site, which has a 10 amp fuse so presumably will never be drawing that much.

In addition to this, I'm going to build a small cheap amp using a pair of TDA1554 amplifier ICs, maximum load will be 8-10 amps, call it 10 to be safe so that's 20 amps total.

I would like to make the unit self contained and easilly transferrable, so wiring it to the standard ISO connector would be preferred.

I have checked the wiring diagrams for my car and the audio circuit is rated at 15 amps and the accessory circuit which also feeds into the ISO plug has 15amps available to me.

I was thinking, the PSU has to be permanantly on so that will go to the audio circuit, and the amp that I build can go to the accessory circuit since it doesn't need to be on all the time, and everything will be fine.

Has anyone done this, any reports? any fires?

**Chairboy** · 01-22-2005, 10:08 PM

Biggest prob will be RFI. If you don't mind hearing engine whine/static over the music (which increases in probabillity with this), then go ahead.

**Lum** · 01-22-2005, 10:11 PM

Is that RFI caused by the motherboard sound being affected by the power source, or RFI caused by the amplifiers being affected by the power source.
How do head units get around this?

**Chairboy** · 01-22-2005, 10:20 PM

Caused by things like the ignition system, not stuff in the computer. HU's have lots of filters.

**Lum** · 01-22-2005, 11:30 PM

Originally Posted by Chairboy

Caused by things like the ignition system, not stuff in the computer. HU's have lots of filters.

What I meant was, which bit is going to suffer from the interference, the motherboard audio or the amplifiers?

ie. where do I put the filters to fix it?

Edit: the audio circuit only shares with the electric mirrors and the heating controller, my head unit used to get interference with radio reception while the electric folding mirrors were used but was otherwise fine. I guess the amp will need some protection?