Anyone an electrical engineer? I have a question. Thanks

[Shawn01754]

Ive figured my Mercedes power seats are DPDT power switch. Straight forward and simple. I can run DPDT rocker switches to accommodate the functions as the original switch is of lower voltage. What I'm curious about is a multi DPDT relay like below. My question is can I use my low voltage switch and incorporate a relay like below. I'd like to use my stock switches if I have the capability.

https://www.amazon.com/ELECTRONICS-SALON-Signal-Relay-Module-version/dp/B00M90SR3G

[Jerems]

I'm a little confused on what you are asking, if your switches are just regular toggle switches you can use this relay board without issue. The board states it need a High (12V) signal to activate the corresponding relay. As long as your switch toggles between from an open contact to closed when you push/toggle them you can use this board. Just run 12V to one side of the switch and the other side to the IN X of the board.

Be careful with that board it, states the contacts of the relay are only good up to 1A each, which is very low power handling. I'm guessing your power seats will pull a lot more amperage than that. You will need more heavy duty relays is my guess. You try to run your seats off that you might let out the magic smoke or worse start a fire.

And 1 DPDT switch (For example seat forward and backward) will need two of those relays one forward and one for reverse of the motor.

Hope that helps, maybe you can explain your issue a bit more. I'm also not sure what you mean by your original switch is of lower voltage. You mean lower than 12VDC as in a 6VDC system?

[Shawn01754]

Thanks for your response Jerems, Here's what I'm thinking.
Option 1) simply use 1 DPDT Mometary rocker switch with (on) off (on) per motor as described below
http://www.instructables.com/id/HOW-TO%3a-Wire-a-DPDT-rocker-switch-for-reversing-po/?ALLSTEPS

Option 2) incorporate a multi DPDT relay and use my switches out of the 2008 Mercedes. I'm not sure if the switches ground to complete the circuit. I'm old school when it comes to wiring. I remember 12v at the switches. How's it work these days?

Option 3) use 12v positive switches out of a 1995 Mercedes. Again would need lots of relays

[H2Ogbodies]

Switches are usually one of several things:

a switch can be normally open at rest or normally closed at rest

Having said that, with each flip of direction, if switch is normally grounded, then one contact receives power while the other stays grounded. If the switch is normally open, then typically there is a ratcheting type movement whereby on contact goes to ground while the other gets power-this all pertains to any reverse polarity wormgear style motor drive.

You need to sit down with a multi meter set to OHMS and decipher exactly what your switches do in each direction and at rest before contemplating any type of relay wiring since it will depend entirely on how the switches behave-I hope this made sense....I build a wide array of late model features in older harness designs as new replacements in older vehicles so if you have questions along the way ask anytime!

[Shawn01754]

Switches are usually one of several things:

a switch can be normally open at rest or normally closed at rest

Having said that, with each flip of direction, if switch is normally grounded, then one contact receives power while the other stays grounded. If the switch is normally open, then typically there is a ratcheting type movement whereby on contact goes to ground while the other gets power-this all pertains to any reverse polarity wormgear style motor drive.

You need to sit down with a multi meter set to OHMS and decipher exactly what your switches do in each direction and at rest before contemplating any type of relay wiring since it will depend entirely on how the switches behave-I hope this made sense....I build a wide array of late model features in older harness designs as new replacements in older vehicles so if you have questions along the way ask anytime!
Awsome !!!

[Jerems]

H2Ogbodies worded it perfectly.

Your Mercedes switches should be polarity reversing switches just like you would see on power window switches.

As H20gbodies suggested sit down and check how your switches are wired using an ohm meter. I found this simple diagram to give you a visual reference:

136006

the center pins will connect to the top or bottom pins swapping the positive and negative terminals on the power supply to the motor depending on which way you toggle the switch. This isn't how all switches are wired so your switch may have the pins in different locations but the basic theory is the same.

Good Luck!

[Shawn01754]

H2Ogbodies worded it perfectly.

Your Mercedes switches should be polarity reversing switches just like you would see on power window switches.

As H20gbodies suggested sit down and check how your switches are wired using an ohm meter. I found this simple diagram to give you a visual reference:

136006

the center pins will connect to the top or bottom pins swapping the positive and negative terminals on the power supply to the motor depending on which way you toggle the switch. This isn't how all switches are wired so your switch may have the pins in different locations but the basic theory is the same.

Good Luck!

136012 136013 new switches have a printed circuit and only 8 wires, I got my hands on an older 1995 Mercedes switch and one wire comes alive with each motion and positive and negotiate are feed right to the switch

Maybe a few of these with my older switches. https://www.amazon.com/gp/aw/d/B00X9HVHLM/ref=mp_s_a_1_14?ie=UTF8&qid=1484351898&sr=8-14&pi=AC_SX236_SY340_QL65&keywords=dpdt+relay

[Shawn01754]

I Understand basic DPDT switching, however it's not that simple unless I use rocker switches. Here's my latest thought, I will test this theory tomorrow. 1995 switches and 2008 motors. Stay tuned.
136019

[Jerems]

new switches have a printed circuit and only 8 wires, I got my hands on an older 1995 Mercedes switch and one wire comes alive with each motion and positive and negotiate are feed right to the switch

Maybe a few of these with my older switches. https://www.amazon.com/gp/aw/d/B00X9HVHLM/ref=mp_s_a_1_14?ie=UTF8&qid=1484351898&sr=8-14&pi=AC_SX236_SY340_QL65&keywords=dpdt+relay

This is interesting. What model of Mercedes are these from?

With the older switches you say one wire becomes live with each movement...When you do a seat tilt backwards / forwards does it reverse polarity when touching the output to the motor? On your multi meter it will go from +12VDC to -12VDC.

The newer switches might plug into a computer / controller of some sort, if you can find wiring diagrams for switches it would give a better idea on how it's working.

For relays, you don't need a DPDT relay, a regular Bosch style automotive SPDT relay will work because you can only use one relay per movement. If the switches are rated for the amperage you might not even need a relay but it's always safer to use one.

Let us know how it goes!

[blitzer454]

You're picture is really small and hard to read. But I think you have it wired incorrectly. You will need to reverse GND and power on one of the relays in order for this circuit to work. The problem with this type of circuit is that you can damage the motor if the switch remains pressed after the motor has reached its stopping point. You will need to confirm if the motor has some kind of protection built into it to prevent such damage. For example window motors generally have some kind of over-current protection circuit or they may have a some kind of slip clutch hardware mechanism that allows the motor to continue to run after reaching the stop point.

The Mercedes switch connector most likely goes to a motor driver module that uses motor controllers instead of driving the motors directly. This module would also provide the over-current protection.

In short, if the original circuit uses switches to directly power the motors then you're okay with implementing a similar circuit or one using relays, but if the motors were originally being driven by a motor controller circuit, then beware that you may not be providing the motors the protection they need which will result in the motors wearing out prematurely or possibly causing a gear to strip.

[Shawn01754]

Great news! The seats work terrific with the 1995 Mercedes switches. As far as holding the seat powered for to long in any given direction, that's a simple fix.
Not entirely sure, but I believe With an amp meter test the draw with me (200lbs) in the seat going up position.That would be max draw generally speaking. Should be somewhere around 7 amps. Wire a 10 amp cut out really on the ground side and the relay will cut out as the motors are maxed. Found something like this https://www.brillman.com/store/product_detail/d100-cutout-relay-1331

[blitzer454]

Max current draw will occur when power is applied to the motor and the motor is not turning. This occurs when you first start the motor or when the seat mechanism reaches the end of travel and the motor is forced to stop turning. When you first start the motor there will be a high current spike which won't last very long so it's not as much of an issue, but applying power to a motor that can't turn is the bigger problem. Adding a fuse or circuit breaker to your circuit is a great idea to protect against a dead short, but it doesn't really protect against stripping a gear as it can't react fast enough plus you would need to find a circuit breaker with just the right current limit to trip. The circuit breaker you found is rated at 25A which is way to high.

Your current rating of 7A seems too high to me as well. I would have expected somewhere between 2 to 3 amps.

[H2Ogbodies]

On your wires, with power on, check to see if every wire other than the power lead is grounded at rest. I assume you've isolated a ground wire? If so, probe that wire and every other one in OHM position to verify if it is open or closed. If they all show continuity that's good because it means it's a reverse polarity type circuit and it is essentially the same as a GM power window design.