computer power during cranking

jdc753 · 06-27-2008, 11:38 AM

I was reading a carputer post on another forum where the poster mentioned having the turn on lead wired to a remote door lock trigger. This got me thinking to some sort of early turn on system, like door chime or interior light or door locks or something that would go the second I open the door. However one of the deals in my truck is that during cranking everything inside the truck dies. I know the diesel takes a lot of cranking amps, 2 factory batteries at least 800cca minimum each.

What I was thinking could I get a small motorcycle or lawn tractor battery and wire it inline just before the psu to allow it to fire up and boot while I get into the truck and start cranking over the motor? Something like this here I would need some sort of isolator going to this batter too wouldn't I? Just trying to think of a way that I can feed the computer with a seperate source during cranking and then when the truck is up and running it will get its juice from the overall electrical system.

Alanh · 06-27-2008, 12:21 PM

You'll want an isolator to make sure your extra battery doesn't try to supply current to the starter. With that it should work fine. I need to do the same thing for an amateur radio transceiver that doesn't seem to like the lower voltage in my Toyota PU when starting. (The computer supply works fine at the lower voltages.)

You'll need to have adequately sized wire and isolator etc. to supply the total current which would be the current needed by your system plus the current needed to charge the aux battery. That will depend how low the aux battery is discharged which probably won't be a whole lot for much time if you only use the battery for hold-up voltage during starting.

I'd look into an isolator like the Hellroaring or similar solid state isolators myself because they're simple to install in a mode that automatically prevents reverse current flow from your aux battery back to the main battery and starter. They have a smaller voltage drop than a simple diode which means smaller heat sinks, etc. on the isolator. (At a higher price though.) You can wire an optional switch so the aux battery can provide current to the main battery, but I don't think it will be big enough to help start the engine if the main batteries are discharged anyway.

A diode should work in this case too though because you don't need maximum voltage to your aux battery to fully charge it like you'd want if it was a backup starting battery or powering a winch or something like that.

jdc753 · 06-27-2008, 04:19 PM

cool I'll look up that hellroaring you mentioned. Currently for electrical I have 1/0 running from the front secondary battery to the back where I am planning on splitting it with 1 1/0 to the sub amp, 1 4awg to the front stage amp, and 1 4awg to the small battery/carputer. The computer PSU is an OPUS 320w.

I'm thinking I may have to run a second run of 1/0, also in the future may add a third battery dedicated to the stereo/additional features.

I will admit I enjoy building computers and installing audio equipment and such and building most things (pretty much limited to component selection) but electronics just always seems to slip right through my brain. Its even worse cause my dad was a master electrician and lives on this sort of stuff. He just doesn't have that much experience in putting together these sort of systems or what components are available these days.

Thank you for the help.