Car "memory saver" for when working on cars

[eltax91]

Hi all

I was idly looking at some "how to" guides for jobs on the daily hack (Octavia PD130) and one of the jobs involved removing the battery for access. The guide showed a picture of a "memory saver", which was basically a 9v square abttery wired to a cigarette socket, plugged into the (permanent live) cig socket.

My question is, how would this keep power going to the ECU and/ or stereo, as suggested in the guide, if you have broken the circuit by removing the battery. I just can't fathom it.

Cheers for any help in advance

[Ozzie Osmond]

Devices attached to the battery are wired in parallel, not wired in series, so removing any device (including the battery) does not "break the circuit".

Think about it. If things were wired in series then failure of one lamp bulb would make all of the car's lights go out. In fact, if everything was in series the car would stop if a bulb failed. Just like old-fashioned Christmas lights.

[eltax91]

Ozzie Osmond said:

Devices attached to the battery are wired in parallel, not wired in series, so removing any device (including the battery) does not "break the circuit".

Think about it. If things were wired in series then failure of one lamp bulb would make all of the car's lights go out. In fact, if everything was in series the car would stop if a bulb failed. Just like old-fashioned Christmas lights.

Ah, that makes sense.

So, I could make myself a home brew one of these so as not to lose the radio code in future?

[KaraK]

eltax91 said:

Ozzie Osmond said:

Devices attached to the battery are wired in parallel, not wired in series, so removing any device (including the battery) does not "break the circuit".

Think about it. If things were wired in series then failure of one lamp bulb would make all of the car's lights go out. In fact, if everything was in series the car would stop if a bulb failed. Just like old-fashioned Christmas lights.

Ah, that makes sense.

So, I could make myself a home brew one of these so as not to lose the radio code in future?

Indeed - replacing the N/S headlight bulb on my car is a battery-out job (don't ask!) so last time it needed doing we just hooked up a little twelve volt battery to the postive and a grounding point on the block and it worked a treat!

[PoleDriver]

If you needed to ask that question, this will be the probable outcome!

[Deva Link]

eltax91 said:

..plugged into the (permanent live) cig socket.

I doubt many cars have permanent live cig sockets, although many of these things come with croc clips to attach elsewhere.

Merc's have a live and earth connection under the bonnet and a power supply is supposed to be attached before software updates etc are done as they take ages.

[eltax91]

Deva Link said:

I doubt many cars have permanent live cig sockets, although many of these things come with croc clips to attach elsewhere.

Merc's have a live and earth connection under the bonnet and a power supply is supposed to be attached before software updates etc are done as they take ages.

My Octavia does, it's live regardless of where the guys are, same with SWMBO's A3, my previous Mazda6 and my Defender 90...

[Deva Link]

eltax91 said:

My Octavia does, it's live regardless of where the guys are, same with SWMBO's A3, my previous Mazda6 and my Defender 90...

Fair enough - I didn't think it was on our Ibiza but don't think I've tried the Golf.

It definately isn't on our Honda, Merc or Mitsubishi - it's always a bit of a faff using the tyre compressor on those cars.

They're usually not perm live to prevent people draining the battery by leaving stuff plugged in.