# Ceramic Heater Relay



## EVfun (Mar 14, 2010)

Those work for the heater on cars up to about 156 volts. They are actually being pushed a bit past their ratings but generally seem up to the task. A snubber across the contacts would be a good idea. I've used this relay before for heaters, in my case 2 for 2 ceramic cores in a Rabbit Pickup (I could run myself out of that thing.)

Oops, that relay doesn't have a 12 volt coil so it wouldn't be a good choice. The P&B KUEP-3D is the right type, with the 150 volt *DC* rated contacts. A local EVer bought a bunch of these in a surplus clearance not long ago and is offering them for a reasonable price. I'd buy them from him!


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## omonoid (Aug 30, 2009)

ok thanks. would you suggest 2 ceramic heaters for Washington weather (im from spokane)

I was planning on using a snubber and im at 120v so it should work fine


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## EVfun (Mar 14, 2010)

I would for eastern Washington because your winters can be more brutal. My '66 Datsun has only one, but doing better than the stock (afterthought) tiny heater in that thing is too easy. I like to see EVs match or better their gas counterparts 

I just noticed something -- that 110 VDC rating is the relay *coil* voltage. That won't do!


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## omonoid (Aug 30, 2009)

What is coil voltage vs regular voltage? What should it be?


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## EVfun (Mar 14, 2010)

It should be a 12 volt coil. The relay coil is operated by your 12 volt system through whatever switch system you set up. It will provide 12 volts from your cars regular electric system to turn on the relay on when you want heat.

My setup was to get power for the heater element switch by tapping the low speed heater wire. In most vehicles this wire only has power when the heater fan is on, so the elements cannot be turned on with the fan off. It will have 12 volts at any fan speed with most systems because in most cars the heater fan speeds below high speed are created by passing the fan power through a power resistor first (the resistor is generally somewhere in the heater box assembly so the fan cools it.) I put a slide switch in the heater controls so the temperature lever would change it from off to low to high.


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## omonoid (Aug 30, 2009)

oh yeah that makes since. so i want a 10-15 amp relay rated for around 120 vdc with a 12v coil.

Do you by chance have a wiring diagram of your heating system. Im trying to make one of my own, but it would help to see one


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## sjc (Oct 28, 2008)

EVfun said:


> Oops, that relay doesn't have a 12 volt coil so it wouldn't be a good choice. The P&B KUEP-3D is the right type, with the 150 volt *DC* rated contacts. A local EVer bought a bunch of these in a surplus clearance not long ago and is offering them for a reasonable price. I'd buy them from him!


Would you recommend that for a 144V system, or is that getting too close to the rating on the relay?


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## EVfun (Mar 14, 2010)

That relay has been successfully used on enough 144 and 156 volt EVs that I really can't recommend against it. I would recommend a snubber across the contacts as those ceramic heaters can pull 15 amps, even a bit more at just the right time as they warm up.


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## EVfun (Mar 14, 2010)

omonoid said:


> oh yeah that makes since. so i want a 10-15 amp relay rated for around 120 vdc with a 12v coil.
> 
> Do you by chance have a wiring diagram of your heating system. Im trying to make one of my own, but it would help to see one


I don't have one. I converted an '81 Rabbit Pickup to a 120 volt EV and installed 2 ceramic heaters in a sheet metal pan built to fit in place of the heater core. Those heaters usually have 5 connectors on the side. I had 2 and 4 from each hooked together, then through a 30 amp fuse (with appropriate DC rating) to pack negative. I had 1 and 5 of each hooked together wired to one KUEP relay. The center (3) connection of each element was hooked together and wired to the other relay. The other contact on both relays was hooked together and through a 30 amp fuse (with appropriate DC rating) back to pack positive. 

The control side was a simple tap into the fan low speed power wire, that went to the heater low and heater high switch. Coming out of the switches that power went to the 2 relays. The other side of the relay coils where connected to frame ground.


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## omonoid (Aug 30, 2009)

ok that makes sense. 2 cores 2 relays 2 fuses and some wire is really all i need. plus a snubber on both relays


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## Roy Von Rogers (Mar 21, 2009)

Try looking at this....

http://cgi.ebay.com/Solid-State-Rel...773?pt=LH_DefaultDomain_0&hash=item3a5e44af35

Roy


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## EVfun (Mar 14, 2010)

Warning - solid state relays generally fail ON when they fail. It is also worth noting just how much of a heatsink they require to handle 15 amps! Clearly they less efficient that a good old mechanical relay.


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