Keeping car electronics alive while changing battery - homebrew approach?

A cigarette lighter adapter and a 9V battery ought to work with most cars, IIRC.

Joe

I had to do this on my father in law's cadillac where the whole car gets a brain transplant when you disconnect the battery. I just connected it up to my car with jumper cables, swapped the battery and hooked it back up. Just be careful not to let anything short out. This caddy has a "jumper" terminal away from the battery so the hookup was easy. I just put the terminals in heavy leather work gloves because I had that handy.

Set the voltage at 14.0 +/- 0.25V and you should be fine. Like you indicated, just keep the polarities correct.

I've heard of using a battery jumper pack. Put that on the front floor, and plug in a double ended lighter plug cord. Maybe you or a friend has a jumper pack with a "charge the pack from your lighter socket" cord.

The DC 13 volts should work, also.

That will probably work well if you make sure that opening a door doesn't turn on interior lights and suck down the battery.

Charlie

On 3/25/2010 5:00 PM hr(bob) snipped-for-privacy@att.net spake thus:

Sounds like way overkill on the precision (and voltage) to me. Someone else here said to just use a 9-volt battery plugged into the cigarette lighter socket (does this car even have one of those???). 9 volts might be a mite low, but I'd say just use a 12-volt supply and be done with it. Remember, you're not charging the battery, only powering the radio's NOVRAM stay-alive power.

Keep in mind that when you start a car, the voltage can dip to 8-10 V under heavy load. So a 9V battery proly could do the job, as long as there wasn't much current drain on it.

I think lantern batteries are 6V (basically 4 D cells), so two of those in series would work as well. Mebbe even the battery packs from 12V drills, etc.

Better yet get the codes. You can get it from either a dealer (w/ a copy of title or other proof), or radio manufacturer with a sales receipt. If codes are unavailable, seriously consider dumping the unit It is an accident waiting to happen.

On 3/25/2010 6:49 PM Existential Angst spake thus:

Any of the above will work. You certainly don't need 14.0 +/- 0.25V.

=3D=3D Your best bet would be to phone a dealership for the make and year of car, talk to the service manager and get some FREE advice. =3D=3D

Any auto parts store, and probably even the auto section of Walmart sell an inexpensive device that plugs into the cigarette lighter and is powerd by 9 volt batteries for just this purpose. Not hard to find at all.

The codes will get the radio working, if it needs codes, but it won't restore the radio pre-sets. Some radios have 20 of those.

I would wait until the accident happened.

I use a little 12v gel cell, thats what I had handy.

Jimmie

"Charlie" wrote in news:hoh59l$ugm$ snipped-for-privacy@news.eternal-september.org:

what if your car turns off the cig lighter outlet when the car is off? Will the 9v fixture still hold the memory?

Most don't turn off the cigar lighter. Although I do question what happens when the door is opened and the little 9v tries to power the interior lights?

all 3 of my cars do: a 90, 94, and 96.

re: "cigarette lighter socket (does this car even have one of those???)"

They don't call them "cigarette lighter sockets" anymore.

They're called "Automotive Power Ports" or some variation of that.

Many vehicles have multiple "ports" such as additional ones in the trunk or hatchback or backseat to power portable DVD players, cell phone chargers, etc.

re: "Most don't turn off the cigar lighter"

Some do...some don't. Can't say if it's "most" or not.

The wife's 2005 Taurus doesn't, my 2004 Odyssey does. There are pros and cons for both.

My Dodge conversion van used to turn off the "Automotive Power Port" in the dash, but not the one in the "way back".

When I added another one in the passenger area, I made sure it stay powered on all the time.

What I'd like to see...and maybe they have them...is this:

A set-up where I can push a button once the car is started so that the Power Port will stay "ON" after the car is shut off, but default to shutting "OFF" with the car if I don't push the button. An extra bonus would be to be able to turn the Power Port on without starting the car, but would still default to shutting "OFF" with the car once it was started and then shut off, assuming I didn't press the button again.

That way I can decide if I want the Power Port energized with the car off, but I wouldn't be in danger of killing the battery if I accidentally left something on. When we had the Conversion van, the kid's would sometimes leave something powered on and kill the battery. It would be nice to prevent that, but still be able to *choose* to run something with the car off.

(The Traction Control in my Honda can be turned "OFF" once the car is running, but defaults to turning to "ON" every time the van is started. I'd like similar logic for the Power Port where I can override the default, but still have it default to "safe mode" if I don't take any action.)

This sounded a little like overkill, but is sounding better all the time.

No worry about cig lighter is on, or door is open for lights. And (not mentioned except by you) disconnected hot battery terminal can't be grounded.

Temporarily connecting a 9V battery to 12V doesn't do anything?