Simple Radio on while cranking mod.

[oldtamiyaphile]

With newer car headunits, the radio turning off while the engine cranks no longer cuts it. While the ~20 second loading time of an MP3 playing off USB is annoying, it's worse if you're on a Bluetooth phone call and need to start your engine.

I've seen a few more complex solutions, but here's the easiest.

All you need is a big capacitor (I think I used a 2700uf and a 4700uf in my two cars), and a diode. The capacitor connects to ground and the accessory wire (switched live). The diode simply goes on the accessory wire to stop the capacitor feeding the rest of the accessory circuit. It's not 100% essential on some cars, but if you have say an old LCD clock, anything pluged into your 12v socket etc, you'll probably need it.

When you key off, the capacitor keeps the switched live on for a few seconds. Since the current draw on this wire is tiny, you don't need a massive cap. ~2700uf corresponds to around 8 seconds play time, 4700uf is around 20 seconds. I went with a big cap since I have excess electricity and a neat side effect is that you can still hear your music playing as you unlock your house door.

This won't work on all cars, I tried it on my Proton and Renault and they worked, doesn't work on my Jeep which apparently just sucks too much juice from the battery while cranking?

Hard to photograph, but every thread needs a pic, but frankly pretty self explanitory (the extra wire is for a radio switch):

[niky]

Neat.

[19bonestock88]

Does it matter what voltage the capacitor is rated for? I can’t find 12V/4700uf...

[samwichse]

Originally Posted by 19bonestock88

Does it matter what voltage the capacitor is rated for? I can’t find 12V/4700uf...

As long as the cap's max voltage is greater than you'll ever sink into it (~14.5V), you're fine.

[19bonestock88]

I’m actually more than a little looking forward to getting this mod done on my car, and based on how I drive it could drive FE up some...

As it is, I bump start the car approaching red lights and stop signs except at ones where I’ll be sitting for several minutes, just to avoid my crappy aftermarket radio turning off and having to reconnect my phone to it (BT)... sometimes when I’m cranking it over it resets the radio entirely and then I have to re-pair my phone and reset my clock... if I can avoid this major PITA by installing a cap and diode, it’ll make my car much more convenient to drive and I’ll be able to save some fuel by not idling at red lights

[hamsterpower]

I'm pretty sure the radio being turned off while cranking is by design. A relay disconnects it to keep the accessories from getting zapped by spikes.
You could disable that relay and take the risk.

[19bonestock88]

...or add a cap and diode and enjoy radio while starting the car...

[teoman]

Thank you forr this tip.

My grandma has a W210 1999 e200 MB. It was in pristine condition 3 years ago with very low miles. Then my 2 aunts (both of whom I consider of lower intelligence and situational awareness)borrowed it and basically dinged and scratched every independent panel on the car. They ran the battery dry, the radio reset (it is one of those thief protection ones where the code has to be reentered) so it was broken for them and they replaced it with a cheap LG unit that was probably wired in by apes. Every time the car restarts it switches off, it does not retain the stored stations in memory.

This mod could help me a bit, not for direct FE but not getting in to an accident while trying to restart the pos radio.

[BdK9001]

Love the idea behind this mod so much, I've directly ordered the necessary parts! But instead of a diode, I'll be using LED's which will be illuminating the footwells. Maximum comfort for minimal money

[teoman]

Neat idea!
It will probably pulse with the music. Especially the bases.
What is the voltage drop and max current of your led’s?
You may also need a bigger capacitor to avoid flicker. But give it a go!