Reply With QuoteIt seems overly complex and you can get chattering using one relay to switch another. A simpler method is to use a "retaining" contact, like in this drawing.
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ChatterBox
SubscriberLast year when I reupholstered my seats, I installed the optional heating pads to both seats. I have not yet wired them up. The loom that comes with the heaters is a simple on-off relay circuit with a rocker switch. The problem I have with this is, if I or a passenger switch the heater on and do not switch it off when exiting the vehicle, the heater will again be on next time the ignition is switched on. I want it to switch off with ignition off and not come back on unless intentionally switched on.
I've sketched up a very simple circuit diagram and would like some feedback regarding whether there are any problems using relays in this manner. I've acquired a couple of small DPDT momentary switches with a Normally Open (N.O.) and a Normally Closed (N.C.) in each. I propose to use the N.C. switch to switch on, this will latch the first relay in and activate the circuit until either the NC switch is pressed to turn the heater off, or the ignition is switched off.
Anyone see any problem with this? And yes I do know to put fuses in.
seat heater circuit.jpg
ForumSage
SupporterIt seems overly complex and you can get chattering using one relay to switch another. A simpler method is to use a "retaining" contact, like in this drawing.
download.png
2005 D3 TDV6 Present
1999 D2 TD5 Gone
ChatterBox
SubscriberOk thanks for that; the diagram above shows a 415v circuit with a contactor, I've used those many times with machines in my workshop but I could not find the equivalent for a 12v circuit (also they are horribly expensive in 415v) thus my attempt to replicate the system in 12v.
ForumSage
Supporter
There's a way to do it with what you have, using -ve switching, excuse my scrawl.....
20250821_191933.jpg
2005 D3 TDV6 Present
1999 D2 TD5 Gone
ChatterBox
SubscriberThanks for that, just got your PMs, wife had a remote meeting on our only computer...
I see the difference to my diagram is that the NC 'stop' switch is on the earth side of relay 1 coil rather than the +ve side, and that the N.O. start switch is connected to both relay coils. Does this avoid the chattering problem that Randlover mentioned? It looks like an elegant solution. Thanks again for taking the time.
ForumSage
SupporterYes, ignore what I said about chattering, as at first I thought the switches were relay contacts.
2005 D3 TDV6 Present
1999 D2 TD5 Gone
ChatterBox
SubscriberThat's great, thanks. Now I need to figure out a location on each side of the dash for two little push-buttons, and a way to label them.
ChatterBox
SubscriberA little further to this project...I finally got around to wiring in one of the seat heaters a couple of weeks ago. I had an interesting time of it; I got hold of a couple of little momentary switches from Jaycar that have both a N.O. and N.C. circuit so I could use a pair of the same switch for on & off. I located them at the front of the 'Mud' under-cubby drawer thingy. Having done all the wiring according to Randlover's diagram, using the cables and connectors that came with the seat heaters, initially I got a continual buzzing from one of the relays, the relay got hot and then the N.O. circuit in the 'on' switch burned out. I checked and re-checked all my connections and coudn't see a reason for this. Happily the little switches had 2 parallel N.O. circuits so I transferred my connections across to the other pair and decided to try re-wiring according to my original circuit design as shown in the first post in this thread. This time the heater switched on and warmed up, but wouldn't switch off! It was not making any sense until I discovered this:
random wiring connector.jpg
The cable connectors that I had used from the supplied loom had the wires completely mis-matched across the connector. I didn't bother tracing what they were actually doing, just swapped them around so the Red went to Red, black to black etc and tried again. The heater now works perfectly as I wanted it to; press the ON switch with ignition on and it warms up, switches off with the OFF switch and when the ignition has been switched off, the heater remains off until switched on again. I left it wired according to my original diagram rather than swap around a third time.
I now have a further question for the electronics experts; I would like to add a temperature control. The heater gets too warm for anything but really cold weather. I'm thinking preferably a 3-position rotary switch to select low, medium and high, wired into the circuit between the power relay and the element. I don't know how to select an appropriate variable resistor; can anyone advise me on this please?
RoverLord
Figure out the max current of the thing, peak voltage and then goto jaycar or similar and get a DC motor control circuit with suitable ratings or a PWM controller, put it in after your relay trickery.Originally Posted by POD
Dave
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