Switched radio, constant memory with reducer

[Sergio]

There is no such a thing as "memory signal" on typical radios, all power comes from the constant +12v, the switched +12v is only used as a trigger signal.

I know, low blow on the chinese amps comment, but typically those are overstated numbers and just like power ratings on amps, your have very high distortion at the upper limit.

Are you using special head units that still use a separate low current +12v just for memory settings retention?

[kraftchick]

Sergio, hadn't looked at the drawing when I just replied...after looking at it now, thanks again....that is precisely what I was after!!! Just didn't know if a 48v coil relay existed, nor what to call it...awesome work!

[Cart Sports]

Originally Posted by kraftchick

Original poster here...fortunately my DC/DC converter does have the switching control wire, so I should good to go on parts by just picking up that 48v coil relay. Thanks Sergio!

Yes, in that case, using a normally closed relay should work fine. You need to make sure that it doesn't close when the key is on, or you could still lose your presets in the switch. Admittedly, I don't know much about how the head-units use the power and if you have either the switched or main power on, whether it would still store the presets.

[kraftchick]

No...I had referred to the "memory wire" based on a wiring diagram I saw for this radio. i do believe as you originally stated, the red wire (smaller gauge) is +12v for switching the radio on. The other +12v input to the radio (heavier gauge) is what I believe needs the constant +12v to maintain presets, etc.

[Sergio]

Just to be clear, the relay is Normally Open.

You need 2 power connections from the Radio to the Converter.

1) The +12v Constant large gauge wire from the radio (the one with the fuse), goes to the Constant Output Section.

2) The +12v switched wire (smaller gauge) from the radio goes to the Output of the Relay so it only gets power when the Key switch is on.

Edit: You got it, our posts overlaped.

[kraftchick]

Found this one with a basic Google search, what do you think? Do you know if Auto parts stores carry these generally? http://www.homanndesigns.com/store/i...products_id=88

[kraftchick]

Quick question I didn't pick up on. I realize all "grounds" need to terminate to the negatives...if 48v, then negative of battery back, if 12v (accessories), then negative of 12v side of converter. In the drawing, does the negative from the 48v coil relay terminate into the 48v negative? Basically just tying it into the -48v that's "feeding" the 48v side of the DC/DC converter?

[Sergio]

I ussualy buy my parts from Mouser electronics, this is their part# link

Digikey is another good place to get electronic parts, here is their part# link.

Make sure You get the 30amp version (your link was for the 20amp)

Yes, the negative side of the relay coil goes to pack negative (the -48v feeding your DC/DC Converter).

Most likely the 12v negative is the same as the 48v negative, there are a few converters on the Market that have isolated outputs, but the most common ones share the same negative.

[Cart Sports]

Uh, It's been a while since I've done stereo stuff, but the large fused Red wire is normally the main power, which needs to be on the switched side. The smaller, Yellow wire is the signal, needs to be constant, and doesn't carry much amperage.

[Cart Sports]

And yes, the conversion is normally done via the + side, so negatives are normally common.