24v-12v solution?

[RUFF]

I'm currently working in a truck(although it's more s piece of machinery) it has a 24v system but it has a 12v set up for lights etc. Prob is it was never built with the intention of having a radio(cd player) installed. It's had one fitted aftermarket. Prob is when the key is off the 12v shuts down with it so all memory in the radio is lost. Now I know I could just run a wire back to one battery but that's a massive job in this machine that I'm not willing to take on. But I have a constant 24v supply 6" from the radio. Is there a cheap way I can reduce the 24v back to 12v right there just to supply the memory back up on the radio when the key is off?

[KUSTOMV840]

The only way to set it down is with a transformer. I had to build a little unit to charge my psp, phone etc off a 24V AC supply a few yrs ago. I put the supply into a bridge rectifier to make AC to DC then used a transformer to step it down from 24 to 12V. The transformer cost me about $120.

But now there is cheaper options... http://www.electusdistribution.com.au/p ... UBCATID=71 This should do the trick for you.

[RUFF]

Thanks I wonder how that would go being energized at all times though. Would it drain much power while the truck is turned off? I don't want to turn up for work at 1am Monday morning to find flat batteries.

[KUSTOMV840]

It will only draw as much current as the radio wants. IE just like a normal car, so you will not end up with a flat battery.

[DamTriton]

A direct (unswitched 12v) line for the memory (standby power) for the radio is what is needed. One of the wires on the radio should be marked as "memory","clock", or "standby power", this is what usually supplies the inbuilt clock they usually have. These usually only require a few milliamps (10 tops) and should be able to be supplied using a resistor and a zener diode

http://www.reuk.co.uk/Zener-Diode-Voltage-Regulator.htm" onclick="window.open(this.href);return false;

Using 12 v out and 26 volts (running motor) supply with about 10mA would mean using a 12 volt zener, and a 1400 ohm resistor (1500 ohm/1.5k ohm will be fine) will work to supply the aforementioned memory/clock/standby wire only.

Borrow the switched 12 volts from your lighting circuit for the main power.

[RUFF]

A direct (unswitched 12v) line for the memory (standby power) for the radio is what is needed. One of the wires on the radio should be marked as "memory","clock", or "standby power", this is what usually supplies the inbuilt clock they usually have. These usually only require a few milliamps (10 tops) and should be able to be supplied using a resistor and a zener diode

http://www.reuk.co.uk/Zener-Diode-Voltage-Regulator.htm" onclick="window.open(this.href);return false;

Using 12 v out and 26 volts (running motor) supply with about 10mA would mean using a 12 volt zener, and a 1400 ohm resistor (1500 ohm/1.5k ohm will be fine) will work to supply the aforementioned memory/clock/standby wire only.

Borrow the switched 12 volts from your lighting circuit for the main power.

The radio is allready installed and works. I know how to install a radio and why it needs a constant 12 volts. I only want a simple solution to convert the 24-12 so I can keep a constant 12 to the memory. Not an explanation on something I never asked.

[RUFF]

I ended up buying one of these out of china- http://cgi.ebay.com.au/ws/eBayISAPI.dll ... K:MEWNX:IT" onclick="window.open(this.href);return false; Cost me $7.80 delivered. Will just split it open and rewire it for the positive supply only.

[mickyd555]

I ended up buying one of these out of china- http://cgi.ebay.com.au/ws/eBayISAPI.dll ... K:MEWNX:IT" onclick="window.open(this.href);return false; Cost me $7.80 delivered. Will just split it open and rewire it for the positive supply only.

Im farly confident in saying it wont work hooking up the positive only. you will need to connect both negative wires to the frame/chassis and then the respective positive wires to 24v and then the stereo. when you get it ill have a look if you want.

[stilivn]

You could just fit an old radio with the nob style tuners

[Shadow]

I ended up buying one of these out of china- http://cgi.ebay.com.au/ws/eBayISAPI.dll ... K:MEWNX:IT" onclick="window.open(this.href);return false; Cost me $7.80 delivered. Will just split it open and rewire it for the positive supply only.

Im farly confident in saying it wont work hooking up the positive only. you will need to connect both negative wires to the frame/chassis and then the respective positive wires to 24v and then the stereo. when you get it ill have a look if you want.

yeh it will definately need the grounds hooked up aswell, its a switch mode step down power supply.

Can just hook them both to any good ground

could have just used one of these http://www.jaycar.com.au/productView.as ... BCATID=320" onclick="window.open(this.href);return false;

hook left pin to +24volts, middle pin to ground, right pin is +12volt out (for your radio).

[suggy126]

Make the current 24v - 12v transformer stay on permanently. Then hook the stereo up to it like you would to the battery, the "accessory" side needs to have a relay put in line (use a 24v switched relay). Then switch the relay off accessories. The switching and contact circuits in relays are seperate, so using a 24v relay to switch 12v doesn't matter. If you want a diagram pm your email address.