Thread: Brief power loss between ACC and start

There will be a line somewhere in the car that is powered while the car is cranking and when it is finally running. The ECU and other computers need such power. Get a service manual, and you will probably find several places where you can connect your HD. If necessary, use a relay to switch a direct connection from the battery.

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Aaron Cake
London, Ontario, Canada

Player: Cyrix 200, 32MB RAM, 10.2Gig Quantum HD, Onboard EtherNet/Sound/Video, Custom Lexan Case, Arise DC-DC, Win95 Kernal w/Custom Player
Car: '86 Mazda RX-7 w/Basic Performance Upgrades

Put a relay in series with your battery line and your external hard drive. Control the coil of the relay by diode OR'ing the START and ACC lines. This will do it.

Ok, we tried the relay thing and it did not work out as expected. It did keep the power on during start, but the relay caused the engine to continue running untill ACC power was cut off, which is not acceptable. I did not do this myself (I had a pro do it) so I'm not sure exactly how he hooked things up. I do know he used two relays, one for ACC and one for "start". The relays contacted power from a second battery to my MP3 equipment. How do most of you out there deal with this power loss? When you listen to music with only ACC power, and want to start your car, do you shut down first? ... Still looking for the solution...

I have the same problem.It seems like battery voltage drops to 10-10.5v during the engine start,and my HD "goes to sleep" at these 3 seconds,although he's connected to the battery by the relay.I think I'll maybe use a small 12v battery,about 5-10 Ah as backup for engine start time.These are actually backup batteries for car alarm systems.Also using powerful (2A at least) flyback regulator will solve this problem.You know where I can find one? I tried LM2587...it only gives 1.2A-not enough for HD spinning.

The problem is not really where you connect to the car power, ( even if it is the ACC line) it wont mater if you run direct to the batery because the batery just cant supply a steady curent while cranking. the best solution I can think of ( im working on a schematic , and will post it as soon as I can) but hwere is the theory :

1. you need a seprate batery to power the computer while the car starts
2. you need a way to recharge the batery ( remember if just plug it into the car electrical system with no limiting circuit, the car will just suck the cranking power from both baterys.

use a relay with the coil conected to the IG line so when the ignition line (car starting) is hot, the relay will close a connection for the computer to run from the AUX batery, at the same time the relay will break contact from the computer to the regular car batery.

Then I would also recomend you get a voltage regulator ( around 1 amp ) or some resistors to limit current to use to charge the AUX batery. you should also hook this up so it only tries to charge the AUX batery when the car is running.Hook the charge circuit to one of the ACC lines ( hot when car is running ) If you dont do this you will notice it's hard to charge your AUX batery when your car batery ( without the car running is only about 11 volts) but with the car runing its up around 14v. the curent limiting is importiant because your car batt and/or alternator will put out 35 or more amps of power, that will fry the 1 or 2 amp AUX bat if hooked up directly.

It sounds complex but hte parts are like 10 bucks or so, and the wiring is not to hard if you know what to look for. Ill post a schematic as soon as I can.

why not get a time delay unit, and just have the system boot up, AFTER the engine is started.

Ryan212, Thanks for your suggestion, but that would defeat what I aiming for here. I want to have music in ACC as well as while the engine is running. My system is currently set up so that when power is on (ACC) the external drive wakes my PowerBook from sleep. This works well, and music automatically resumes play in about 10 seconds (No boot time). It will also wake from sleep properly if I start the car quickly. The problem I have is when I let it wake from sleep in ACC mode, listen to music, and then attempt to start the car. That brief power loss screws things up by putting the PowerBook to sleep again, even while the external HDD is powered. I can wake the system from sleep by pressing the power button (on the dash), but this defeats my goal of a totally automatic system - no buttons necessary to turn things on or off. By the way - My web site is in the works now, and I will have it up (I hope) in about a week. I have installed a PowerBook in my 2001 Nissan Pathfinder, and It came out pretty clean. --gizmomkr, I'm very interested in seeing your schematic!

I have come across a simple build kit from Altronics (aussie company as far as i know). This diy kit controls two batterys, your main one, and a backup. This backup charges when your car is running, but when you stop it, the second battery is isolated.

Have a look at the description at: http://www.altronics.com.au/cat.asp?...=430&id=K+4330 and see what you think.

Cheers

Destin -

What powers your external HD right now ( 12 V or plugin to 110 AC Inverter ?

In any case, The weather got warm this weekend and I was able to get into my dash to rewire my circuit.
It worked just like I planed, and the parts were about 8.00$ from radio shack.
Im about to install Visio so I can make a schematic.

Hornet - the device looks great for people with dual car bats, One thing I noticed was - based on the description, it outputs a pretty high amperage. A lot of people dont use a full second car bat, they use like a 10 amp alarm back up batery. If the charger was designed for high amp baterys, it would melt down a 10 amp batery.