How to use a power drill battery to run power seat in JY? - PeachParts Mercedes-Benz Forum

Mölyapina · #1 07-21-2014, 06:42 PM

I have seen some people mention doing this. How is it done?

lorainfurniture · #2 07-21-2014, 07:50 PM

All you need is a 12 volt battery and put leads on it.

jay_bob · #3 07-21-2014, 07:56 PM

Depends on the chassis but most of these cars use 5 dc motors total per seat.
- cushion front up/down
- cushion rear up/down
- seat traverse forward/aft
- backrest tilt forward/aft
- head restraint raise/lower

And of course the basic theory of a dc motor is that if you flip the polarity the motor will change direction. In order to do this, both motor terminals are brought to the control device. One motor terminal is switched to +, and the other is switched to ground, to make the motor move in one direction. The switching connections are reversed to make it go the other direction.

The control methodology varies widely.

Some cars have direct control of the motor voltage via the door switch. This method is used mainly on older models that do not have memory control. This is the easiest to hack, you just have to find the pair of wires from the switch that go to each motor, apply voltage from the tabs in your drill battery, and get the seat to move.

124s and 126s with memory seat use a control box underneath the seat. The door control sends commands from the various switches, to relays in the box, that actually control the motors. The motors have 3 extra wires, these are the feedback sensor that tells the memory box where the motor is at in its travel. This sensor is just a variable resistor like a slider on a sound mixer board. On these type boxes you have to get in between the control box and the motor. Unfortunately you might have a chicken and the egg problem here, because you can't get the seat up enough to get to the box. On this type you might be best served to find the thick red wire that is the power feed to the control box. Be sure to disconnect this wire from the seat box, and apply power to the terminal on the control box, and try to move the seat using the door switch.

By the time you get to the W210/W140 the interface between the door switches and the seat control box is CAN bus. Yet more complexity to deal with since the door switch and the seat box get powered from different circuits. Very difficult to hack in the yard.

Your best bet, especially if you are on the prowl for older models (like 123/124/126) is to get a copy of the wiring diagram and print off the pages for the power seat before going to the junk yard. Put the diagram pages in a notebook with sheet protectors.

mach4 · #4 07-21-2014, 08:01 PM

Make up a couple of small cables with decent size alligator clips to connect the positive on the battery to the positive cable on the car and the negative to a ground or the negative cable in the car. Make sure there is a fuse in the appropriate circuit for the seat motor and hit the seat switch. Any decent size battery with about 12v will work. Might be easier to use one with leads rather than contacts.

jay_bob · #5 07-21-2014, 08:06 PM

Quote:

Originally Posted by mach4

Make up a couple of small cables with decent size alligator clips to connect the positive on the battery to the positive cable on the car and the negative to a ground or the negative cable in the car. Make sure there is a fuse in the appropriate circuit for the seat motor and hit the seat switch. Any decent size battery with about 12v will work. Might be easier to use one with leads rather than contacts.

I had considered suggesting that approach, but after seeing the way people hack up wiring in the yards I was concerned about having him try to energize the entire vehicle's bus that way.

You can try that, but I would be observant when hooking up. If you see big sparks, or your cable starts getting warm, then be ready to disconnect it.

Some yards may not like it if they see you powering up the entire bus on the vehicle in their yard due to liability reasons. They remove the batteries for safety (and so they can make a few bucks on the batteries).

Jeremy5848 · #6 07-22-2014, 12:55 AM

I recommend building a cable to plug into the accessory connector in the driver's footwell. That allows you to bypass the ignition switch and energize the seat circuit or whatever other accessory you want to test.

dude99 · #7 07-22-2014, 01:40 AM

You could also use alligator clips and energize a specific circuit via the fuse box.