Tuesday, November 8, 2011

Rolls Royce and Bentley seat memory batteries

In my last story I described replacement of the backup batteries in the Rolls-Bentley alarm controller under the dash.  This story sort of builds on that one . . . This time I’d like to look at changing the batteries in the memory seat units.

Each front seat has its own memory unit.  They are located under the seats.  Depending on the age of your car they may take one of several forms.  These pictures show the controllers found in the mid-1990s.

To get at them, you remove the lower cushion, unscrew the memory unit, and withdraw it to the front.  It comes out dragging a large tangle of wire as you can see.  The controller is the box on the floor, just to the right of the Fluke test meter.  I've removed the cover in that photo.

Looking at the cover you see these memory units are something of a homemade affair.  The label is something I could have made up on my own printer!  Looking inside you can see the single battery.  In this car, the battery is not corroded badly but in older cars it will leak and the acid eats away the circuit board, leading to failures.

In the photo above I point out the battery that we are about to change.  The new one will look different, but as long as we match the voltage and technology (don't mix ni-cad and lithium ion) we will be all set.  This particular battery is 3.6 volts.  The original one has a 100MA rating; we will fit a slightly bigger one because that's what they sell today.

These seat memory units cost $2,500 when they were available, and there are none left.  Consequently, we have a lot of incentive to preserve the ones we have.  Changing the batteries before they leak is the best way for you to do that.

We unsolder the battery from the board and remove it.

Then we fit a new battery.  This one is a 3.6 volt battery for a pet collar.  I found it at Radio Shack.  It’s a perfect functional replacement for $20.  It’s a snap to solder in place but you should note that the original battery had two positive wires and I had to add a jumper to replace that missing second positive lead.

The photo below shows the jumper I had to add


APIII said...

Greetings, I just had a customer send me one of these for replacement that had quit working several years ago. Suddenly, like the movie "Christine" the seat began to move forward, pushing Him into the steering wheel. Needless to say, that gave Him the inspiration to do something about it.


Used Cars Dealer said...

This is the good blog with good images and good details. Please keep on posting the more stuff. I will like to hear more from you.

gsmac said...

I had an old Korg PolySix keyboard on which the memory retention NiCd leaked and damaged the board just like you describe - it was a LOT of work to repair, with a lot of PCB traces to fix.

I skip the lowest-price-vendor Radio Shack batteries and use Digikey for replacements. You can find the correct voltage and capacity that you want, and they're usually much cheaper than anything you can get at retail.

One thing about installing larger capacity batteries - you need to make sure it's not so large that the charging circuitry on the board can't handle the charge current - particularly the initial charge current. I made that mistake once, thinking "more is better" but then watched at power-up as a transistor in the charge circuit let out its magic smoke.

John Elder Robison said...

Those are two excellent points. Digikey is a good vendor; we use them here. And if you go too much bigger, you can fry older circuits. Most newer charge circuits are current limited though, so they will not care. It would only be your older bipolar transistor series regulators that would smoke