# Wiring Ceramic Heaters



## lowcrawler (Jun 27, 2011)

So I am trying to avoid running expensive, heavy, HV cabling though the passenger space of my car, so where I locate my heaters depends on how they get wired.

How do you wire up ceramic heaters? 

From what I can gather it sounds like you wire pack voltage to the load side of a relay and from the relay directly to the heater(s). So for this 'loop' it would be PackPostivie->RelayLoadIn->RelayLoadOut->Heater->PackNegative. These wire would only needs to be of appropriate size to handle the amperage going to the heaters, something like 10ga wire.

Then on the 'coil' side of the relay you would connect a switch of 12V power that also was running your fan. Do I understand correctly? I read a lot about diodes, snubbers, etc and it's all very confusing and I"m not quite sure the point.


I'm going to put 2 elements blowing through my defrost vents and 1 element in the footwell. I was thinking I could hook it up such that I'd have 3 different 'settings' -- one with just one element 'defrosting', one with one element defrosting and one element heating the footwell, and then another that gave a 'super defrost' (2 elements defrosting) and one element heating the footwell.

This was the circuit I put together. This is the first circuit I've ever tried to make, so please let me know what I did wrong and why my car will catch on fire.  (seriously, i'm going to put this in my car unless someone says I shouldn't... I'm honestly asking for help here.) I went with simple 'on-off' switches for the fans, figuring that I wouldn't need variable speed on them.










Edit: Why do I need 4500W of heating (plus seat heaters)? I live in MN and refuse to have a car that can't keep me warm. I assume 3 heaters will keep me warm, right? Should I go for more? It's not like I need to use them all all the time...

Edit #2: So, anyone know where to get some solid state DC-output relays? Would this do the job? http://www.futurlec.com/Relays/SSRDC200V40A.shtml

Edit: #3: I assume a standard 120V Ceramic heater element could take my 48x3.2=153nominal pack voltage? If not, is there an efficient way to bring the pack voltage down?


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## lowcrawler (Jun 27, 2011)

Fuses!! Dho!

I _think_ this is where I would put them? What kind of rating would I want on said fuses? My gut says something like 12-15A @ 150V ... ?

Would it make sense to fuse the 12V line too? Where - just at the start of the entire circuit, or do it for each intermediary location? Without knowing what my fans pull at this point (haven't looked for fans yet) it'd be hard to size, I suspect.

New diagram:


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## dtbaker (Jan 5, 2008)

My setup I only have one element, right in the main duct downstream of the fan. when I turn on the fan (any speed) the heater comes one. The relay I used is not solid state, but pretty substantial with a magnetic blowout as recommended for 'fairly' high voltage and reasonable amps.

with multiple elements you may need something more substantial. sometimes you can fins deals on heavy contactors on ebay.

fuse-wise, you need more than you might expect. The initial hit is very high until the element heats up and resistance self-regulates. Probably 10 seconds. i was blowing 30 amps fuses at 96 v, the spike on my analog meter zapped up to about 50 amps, but only for a second when I turned on heater. (with a 1500 watt rated element)

I have whole section with pictures on my site for the heater installation I did...
http://www.envirokarma.org/ev/03.Interior.shtml
http://www.envirokarma.org/ev/gallery/081109_heaterkit01.htm
http://www.envirokarma.org/ev/gallery/090301_final_assy00b.htm


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## lowcrawler (Jun 27, 2011)

Yeah, you page got me thinking. 
I'm thinking about pulling out that first switch and just setting it to have the heater and fans 'linked' to the same switch. I'll never run the fans w/o the heaters so it doesn't make sense to separate them. One less switch on the dash = good deal.

Other than that -- what's up with snubbers, diodes, etc. Do I need any of that junk, or am I find with this setup just as-is?


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## mora (Nov 11, 2009)

I didn't use any extra diodes or resistors. You can find SSR's from ebay too. I paid about 15$ each (used two of them) including shipping. 220VDC / 40A. Use heatsink on these as they might get warm in use. I'd put fuses before relays, but maybe it's only me.

I have four of those heating elements connected, hehe. Two SSR's and two switches to control them, much like your plan. I'm only at 96V now but am in progress of upgrading to 144V. I hope those 120V elements can take 144V or I have to come up some new ideas too. 4 elements at 96V didn't produce as much heat as I expected but it is enough to warm up whole car, even at -30C temps.


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## dtbaker (Jan 5, 2008)

lowcrawler said:


> Yeah, you page got me thinking.
> I'm thinking about pulling out that first switch and just setting it to have the heater and fans 'linked' to the same switch. I'll never run the fans w/o the heaters so it doesn't make sense to separate them. One less switch on the dash = good deal.
> 
> Other than that -- what's up with snubbers, diodes, etc. Do I need any of that junk, or am I find with this setup just as-is?



my understanding is that relay lasts a lot longer with the extra stuff, and reduces the amp spike that would otherwise blow fuses. I dunno about solid-state alternatives, so I don't really know what to look for on ebay.


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## mizlplix (May 1, 2011)

The purpose of fuses are to protect the entire circuit. Place them as close to the source as possible.

Yes, eliminate any components that you can. One switch to do everything.

Unless you have a large cabin interior, try one element. Put it into the upper circuit, then maybe have a recirculating fan for the footwell.

Electric elements will be slower to heat the area than the water heated original as you are dealing with reduced BTU's. 

Really, all you want is to keep the windows clear and to just stop shivering. Comfort is reducing your range.....Think about it.

Miz


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## gdirwin (Apr 7, 2009)

lowcrawler said:


> Why do I need 4500W of heating (plus seat heaters)? I live in MN and refuse to have a car that can't keep me warm. I assume 3 heaters will keep me warm, right? Should I go for more? It's not like I need to use them all all the time...


I am even a bit farther North of you - I drive summer and winter, and have 2 x 1500W heaters. The first 15 minutes of a drive is better than an ICE car (I pre-heat the car with an AC interior heater, then crank the heat while I am driving, plus use 12V seat heaters). Beyond this, 3000W of heat is not as good as the heat thrown from an ICE...

I had a fancy PWM temperature controller (compared measured temp to a set-point, then adjusted the ceramics with PWM through solid state relays) but found that I basically wanted an on-off switch - when it is cold, you want as much heat as you can get... I do not drive for hours at a time, so the car temperature never really equalizes (short drives to work and back each day).

If you have long drives, have you considered adding insulation to doors, firewalls, floorpans etc ? ICE cars are trying to get rid of excess heat, while EVs need to retain the heat - fundamental difference.

I have a friend who drives his converted BMW EV about 60 miles on the highway every day (summer and winter) - he eventually ended up with 4 ceramic heaters (6000W) to keep himself warm on the highway...


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## mizlplix (May 1, 2011)

I live in Arizona......sorry, I couldnt help myself.....

I once converted a southwind gasoline heater to propane. It was so good that I almost never used it. Lol 

Used a barbecue regulator and soldered up the fuel discharge pipe. Redrilled.it several times to where it didnt trip its high temp cut off.

Miz


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## tomofreno (Mar 3, 2009)

> Comfort is reducing your range.....Think about it.


 Yes, the less comfortable I am in the car the less I drive. 

My experience jives with gdirwin's. I also have two 1500W heaters. I just use a simple on/off switch to control - run them until I am warm, then off till I start feeling uncomfortable, turn them back on...They worked well last winter in temp's around 20F and above. It was warmer than normal last winter so didn't get to test them in colder temp's. My feeling is they would not keep you very warm in temp's around zero and below without adding insulation to the vehicle and preventing air infiltration - particularly at highway speeds. 

My pack is nominal 115V and I also have blown 30A slow blow fuses like dtbaker, but only occasionally, so they seem borderline. I recently ordered some 35A Ferraz-Shawmut time delay fuses to try.
http://www.discountfuse.com/A2D35R_p/a2d35r.htm?gclid=CI-Fi-KWlagCFUoZQgod9jltCQ


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## dillond666 (Dec 27, 2010)

Re snubbers and diodes etc.
The snubber (R/C) or diode would be to absorb any inductive spike when switching the relay off. You could put one on the load side but as the heater element is mostly resistive I don't think you really need to bother. If you put a diode on the relay coil side it will help the longevity of the dashboard switch contacts. Use something like a IN4004. Put the diode across the relay coil connections with the stripe at the positive terminal.

Derek


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## rfhendrix (Jan 24, 2011)

Living in southern California I think a 1500 watt 12 volt unit should keep me toasty. Any thoughts on my idea before I buy one?


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## EVfun (Mar 14, 2010)

1500 watts at 12 volts would require 125 amps! Can your 12 volt system keep up with that plus the regular car 12 volt system loads.


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## rfhendrix (Jan 24, 2011)

Good question. 

I am thinking about a 75 hr deep cycle battery. Would that work? Or do you think I could get away with a smaller wattage heater? I need it mostly for defrosting and to take the chill off the cab. The 12 volt system runs a vacuum pump for the brakes and the usual accessories. No power windows etc. My commute to work is only 5 miles.


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## rfhendrix (Jan 24, 2011)

Thinking about this 12 volt 50 amp unit: http://www.sportsimportsltd.com/us-made-polymer-composite-12-24-36-or-48-volt-quartz-heater.html


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