Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Tech Help

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 12-23-2005, 05:39 AM
locry's Avatar
I love this place!!! :)
 
Join Date: Nov 2003
Location: Philippines, ...recently submerged, AGAIN
Posts: 1,011
Electric Relay experts please help

I installed powerseats in my 124 which did not originally come with power seats, i have just recently acquired the powerseat switches. I'm missing all the wiring and the control box. It's very difficult to acquire parts where i live, so i think it would be easier if i just made my own "relay box"

anybody have ideas on how to make one from scratch?

my main concern is how to wire the relays and how many relays do i use? i'm thinking 4 for each motor, 2 would turn the motor one way and the other two would turn the motor the other way. for a total of 20 realys?!?!?!

although the switch by itself is constructed in such a way that when toggled it reverses polarity to the motors, thereby turning the motor both ways. I don't want to have to wire the entire thing through the switches. That's why i need to install relays, but i don't really know how to go about it. The original mercedes control box uses just 10 relays, i'm guessing that's 2 relays per motor, as there are 5 motors. I just can't see how they made it work using just 2 relays per motor. HELP!!!!

__________________

85 190E 2.3(SOLD)
86 230E (-->300D)
87 300D (-->300TD)
68 250S w/ a 615 and manual tranny (RIP)
87 300TD (SOLD)
95 S280 "The KRAKEN" (Turbo 2.9 602 transplant)
Reply With Quote
  #2  
Old 12-23-2005, 08:10 AM
Geezer
 
Join Date: Aug 2000
Location: Holland, MI
Posts: 1,316
Relays are used to switch higher currents. It's easier to switch 15A with a small switch energizing a coil with a beefy set of contacts than to design a switch that has a light touch and 15A contacts.

A starter solenoid is an example where a very small contact in the key tumbler switches very high current, on the order of 100A-400A. Without the solenoid, the switch would have contacts so big you probably could not turn the key using both hands!

You need at least two relays for each motor.
-One (forward) is wired +/+, -/- (battery positive to motor positive) to spin the motor one direction.
-One (reverse) is wired +/- and -/+ to run it backwards.

You wire battery positive to the common of the switch. Pressing in one direction closes the 'forward' contact and energizes the 'forward' relay. Pressing in the other direction closes the 'reverse' contact, and energizs the 'reverse' relay.

I don't know how the W124 seat is wired, but this is a general overview of the theory.

I hope this helps.
Reply With Quote
  #3  
Old 12-23-2005, 12:11 PM
locry's Avatar
I love this place!!! :)
 
Join Date: Nov 2003
Location: Philippines, ...recently submerged, AGAIN
Posts: 1,011
thanks for replying.

i don't get the part where using two relays would turn the motor forward and back... wouldn't energizing a relay just close one circuit? Positive OR negative, NOT both positive AND negative?

therefore wouldn't i need 4 RELAYS? 2 Relays for forward, and 2 more relays for reverse?

for example: Relay 1 supplies + to the motor WITH
Relay 2 supplying - to the motor = FORWARD rotation

then Relay 3 supplies - to the motor WITH
Relay 4 supplying + to the motor = REVERSE rotation

i would be triggering/energizing RELAY 1 & 2 with the same current by using the switch forward position, ditto with RELAYS 3 & 4 by using the switch reverse position... at least that's what i think with my LIMITED knowledge of relays... HELP!!!!

this is what i THINK i know of relays: there is a contact that when ENERGIZED(supplied with positive current) closes a switch, which completes a CIRCUIT... this circuit is INDEPENDENT of the energizing contact, which means i can assign a POLARITY to the CIRCUIT. am i making sense? so sorry.

I hope i'm missing something here coz i don't want to use 20 relays total... I hope i can get away with using just 2 relays per motor which i think is supposed to be the case...

help!!!
__________________

85 190E 2.3(SOLD)
86 230E (-->300D)
87 300D (-->300TD)
68 250S w/ a 615 and manual tranny (RIP)
87 300TD (SOLD)
95 S280 "The KRAKEN" (Turbo 2.9 602 transplant)
Reply With Quote
  #4  
Old 12-23-2005, 01:37 PM
Registered User
 
Join Date: Sep 2004
Location: Seattle
Posts: 1,947
Relays are like switches. They come in single pole, double pole, triple etc. This is how many circuits it can switch. Then each pole is either single throw or double throw. Single throw has just "normally open" contacts (only closed when the relay is energised). Double throw has both normally closed and normally open contacts (3 contacts with the "wiper" being connected either to the NO or NC contact). Single throw is sometimes called "form A" and double throw is sometimes called "form C". Some relay coils are polarized but many are not. You need to make sure the contact rating of the relay can handle the motor load.

Jim H is talking about using double pole relays.

You would probably be better off finding the original wiring.

Mike
__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra
Reply With Quote
  #5  
Old 12-23-2005, 02:27 PM
Moneypit SEL's Avatar
Now what?
 
Join Date: Jun 2005
Location: SE PA
Posts: 525
Two relays per motor. Wire it this way.

Use two 5-pin relays per motor.
Pins 85 and 87a wire to ground
Pins 87 to Battery positive
Pins 86 connect to switch
Pins 30 to either motor connector

When the relays are not energized, both motor connectors are grounded.
When the switch is moved, one relay switches from ground to battery positive and the motor runs.
Moving the switch the opposite direction will reverse polarity at the motor and the motor runs the opposite direction.

__________________
1989 300 SEL that mostly works, but needs TLC
Reply With Quote
  #6  
Old 12-23-2005, 07:41 PM
locry's Avatar
I love this place!!! :)
 
Join Date: Nov 2003
Location: Philippines, ...recently submerged, AGAIN
Posts: 1,011
thanks for the replies guys!!!!

moneypit,
thanks for the diagram, now i understand how using 2 relays would work.

i never thought of grounding both poles at the same time, that's the one i missed. thanks man!

__________________

85 190E 2.3(SOLD)
86 230E (-->300D)
87 300D (-->300TD)
68 250S w/ a 615 and manual tranny (RIP)
87 300TD (SOLD)
95 S280 "The KRAKEN" (Turbo 2.9 602 transplant)
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 03:37 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page