Keeping Power On to Alpine Head Unit Through Crank

Have a 1998 Dodge Ram diesel and I hate it when starting you turn the key to 'run' then 'wait to start' (none of that is a problem) but then when turning to crank the power is cut to the Alpine and it is forced to reboot and start all over. Is there a way by using capacitors and other things to keep the Alpine powered(and maybe other things like gauges). I got to think rebooting the head unit halfway through initializing is not good for it esp when it happens every time you start the vehicle. It is a computer after all. I'd appreciate a wiring diagram and parts necessary to do this greatly.

A 3 amp diode and a 3300 microfarad (at least 25 volt) capacitor. Insert the diode between the truck switched wire and the radio's red wire. Banded end of the diode toward radio. Positive lead of the capacitor connects to the banded end of diode. Ground the capacitor's negative lead.

I have not done this in a long time. If you are having to order this stuff, maybe get 2 of the capacitors. If the on time is not long enough, parallel the second capacitor with the first one.

If you have access to two 1 amp diodes you can do this instead, Same diode configuration as listed above. A second diode banded end to the banded end of first diode. Other end of that diode to the Dk. Blue ignition wire at the key cylinder.

Thank you very much for the reply. I'm not a electronical engineer so describing the process the way you did is much appreciated. The power off time is very short on these Cummins engines. I'd say less then 3 seconds. I bought a assortment of capacitors and diode on Amazon so I should be able to get something to work. Now to get lucky and dust off my old soldering skills...and not start my truck on fire. Thanks again 'i am a idiot'

EDIT: I got this wired up and installed today and it works perfectly. Thanks again IAAI

How much capacitance did you use?

i am an idiot wrote:

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How much capacitance did you use?

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I timed the power off time and it was 1.5 seconds. I used a 4700uf 50 volt capacitor. When I turn the truck off the Alpine stays on for 4 seconds so I think I have enough storage to make it work long term.

Well, that didn't last very long. I'll have to dig into the dash when I have time but it seems the capacitor failed.

Highly unlikely. Maybe a broken leg, but I doubt the cap failed.

Well I'm highly confused. The capacitor/diode assembly worked perfectly for 3-4 months in my truck then failed. I removed it, tested and couldn't find anything wrong with it. I made a new one identical to the first and it won't work either. Tried a couple different capacitors of various sizes and nothing. Sooo, I'm going to try the '2' 1amp diode configuration suggested in the third post and see if that works. Very frustrating. Glad I choose a career other then electrical related.

Post a picture of the caps and diode installed on the wire.

Sorry for the crude text. Best I could do on my phone.

That appears to be a 1N4148 or similar. Not near enough current capacity, for sure not enough to charge the 4700 mic capacitor. Replace that diode with only 1 of the 3 amp devices, you will be golden.

I believe (and was sold) it was a 1N4751A. I will make the change you suggest and report back.

That is a zener diode. When you get the other one, let us know if it works.

Success, eventually. I think there was damage to the 4700 capacitor pictured with the first install using the small diode as I changed to the new 3 amp diode and replaced the 4700 single capacitor to two (2) 3300 capacitors wired in parallel and it works perfect. I'm so thrilled. I'm just puzzled why the first attempt worked for at least 4 months, many start cycles and then failed. I'm just glad it didn't fry something in the Alpine head unit that warranty probably would have a issue with. Thank you for the help 'i am a 'genius''. It was very important to me to have success with this.

I'm on my 8th or 10th Alpine head unit right now (from over the last 20 years or more) and no matter what car it was in, every one of them shut off momentarily when the engine was cranking. Not sure HOW you stop that from happening. They never "reboot", but just go off for a few seconds. I hook mine power and memory wires together and run them straight to the positive battery terminals and the deck STILL shuts off on crank. Not sure the scientific reason why, but every deck I've owned, no matter what brand, did this. I'd love to find a way to stop it, but for now it's just annoying. At least nothing resets itself. I'm going to follow this post and see if there is some remedy, but I've never heard of one.

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kenwood_nut wrote:

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I'm on my 8th or 10th Alpine head unit right now (from over the last 20 years or more) and no matter what car it was in, every one of them shut off momentarily when the engine was cranking. Not sure HOW you stop that from happening. They never "reboot", but just go off for a few seconds. I hook mine power and memory wires together and run them straight to the positive battery terminals and the deck STILL shuts off on crank. Not sure the scientific reason why, but every deck I've owned, no matter what brand, did this. I'd love to find a way to stop it, but for now it's just annoying. At least nothing resets itself. I'm going to follow this post and see if there is some remedy, but I've never heard of one.

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Once I used the proper diode this has worked perfectly. My issue was a issue on my diesel. With Dodge diesel trucks when you turn the key to the start position all power is cut except that going to the starter and ecu/pcu. This forced the head unit to re-start and it was not only annoying but in the long run I didn't think it was good for the stereo. I don't know why manufacturers can't build/design this into the unit. It cost me less then a dollar to fix this and didn't change a thing about how the truck starts.

Glad you got it working. I missed your post from July.