W124 wiring advice

[shanksy]

ok, after double checking the diagrams I realised i'd connected the 12V feed to the one next to X4/1 so i've now corrected that.
Still no voltage at seat connector though so I checked the fuses. Upon removing them one basically crumbled in my hand so i'll replace them tomorrow then try again.

 

[shanksy]

Right, 2 x new fuses and i'm now in business, I finally have feeds to the seat connectors.

I've wired pad 1 to pins 1&2, pad 2 to pins 3&4. The pads are heating up but not as much as I was expecting.
Touching the pads you can barely tell they are on, its only when you apply pressure with hands on both sides you can feel a little heat.

Is this to be expected or should the pads just feel hot to the touch ?

Is there any way I can do a test to see if they are getting 1.5A or 5A when they are switched on to make sure both settings are working?

 

[mejermy]

Mine take around 3-4 mins to feel the heat. Leather in a W124 as yours, but not an MB loom or relay. They are never as hot as my old W126 is, or my W211, which is the hottest and quickest to warm up of any I have had. My wife's W169 seats warm up quickly also, but they're cloth.

If you place your DMM in series (in line) between the active connections so the current flows through the DMM you should see the current passing when set to amps.

 

[brigadier]

I don't know how warm yours get, but don't expect them to get hot. Maybe try sitting on them for a while?

The amp test as above will tell you as well

 

[shanksy]

Ive just checked the power under both settings, i'm getting 1A on setting 1, 2A on settings 2 ?
The aftermarket pads are designed to receive 1.5A and 5A respectively which is why they are not feeling too warm I guess.

What current is the relay supposed to provide to the OEM pads ?

 

[shanksy]

Just tried with the engine running and now i'm getting 2.5A on High and 1.25 on Low

 

[brigadier]

Pads draw the power required by essentially making a short circuit between 12v and ground. You need to check voltage drop under load - as in measure voltage at pads switched on both settings.

 

[shanksy]

Pads draw the power required by essentially making a short circuit between 12v and ground. You need to check voltage drop under load - as in measure voltage at pads switched on both settings.

Thanks Brigadier, is that just a case of connecting the DMM to a ground connection then the positive wire on the pad ? (whilst engine running and pads on)

 

[shanksy]

Not sure if that was correct or not but I tried the DMM positive on the Pads positive wire and the DMM negative on a chassis ground but I get no reading,
Got some nice blue sparks though

 

[brigadier]

Did you plug your test leads correctly for voltage reading? Voltage needs to be measured at pad connection - pin1 and pin2

 

[shanksy]

No
Just realised I still had them plugged in the DMM for the Amp reading.

Now i've corrected I get nothing. I don't even get a volt reading at the seat connector end either now. Could I have fried something ?

 

[shanksy]

Luckily I only fried one of the fuses, i've now got 2.5A power again.

Think i'll leave it alone for tonight, not having a good day

 

[shanksy]

I gave in and had another go, amazing how easy things are when you do them properly

So, with load applied, heat setting 1 gives 7V and setting 2 gives 14V.......??

 

[shanksy]

All my readings seem to indicate that heat setting 2 gives double the power of setting 1.
I can't quite fathom how I am supposed to get 5A on high and 1.5A on low ?

 

[brigadier]

voltage seems ok. could it be that 5A supposed to be both mats - one seat.
edit: if supply is at 14 volts - the pad is getting all the power it can carry. Just to make sure can you check the resistance (ohms) of the pads (resistance setting - between pin1 and pin2), then it's easy to check how many amps it takes at 14V using good old ohm's law.

 

[shanksy]

Don't know really, this is the ebay ad...........
2 Pairs Carbon Fibre Element Heated Seat Retrofit Kit U.K. seller | eBay

Wouldn't have thought so, it would seem strange to quote it that way and wouldn't be consistent with getting 1.25 on the low setting.

If the voltage across the pads is fine, and the pads determine the current drawn, I think i'll email the ebay seller and ask them to clarify.
It might even be that the pads are duff.

 

[brigadier]

What you get on low setting depends on relay unit you use. Mb relay maybe gives more power on low setting than what they use. If you measure resistance of the pad we can clarify this.

 

[mejermy]

Lee - just picked up on your latest travails. I checked the spare set of pads I have here and they have a resistance of 5.5 ohms, which gives only 2 - 2.5 amps at battery voltage.

Thought this might give you a cross bearing on yours.

 

[shanksy]

I've just checked and the resistance is 6 Ohms for all pads, just googling Ohms law now ......

 

[shanksy]

Well thats quite a simple calc
So the pads are only drawing just under 2.5A

@Malcolm - remind me again were your spare pads the Waeco carbon pads or generic carbon ones like mine ?