# Ceramic heater wiring



## jackbauer (Jan 12, 2008)

I'm looking for a little advice on wiring up a few of these ceramic heaters. They are rated at 120v and 1500w. Five connections. Resistances are as follows:
1-2 = 133R
4-5 = 125R
2-3 = 207R
3-4 = 833R

I just want to run them at full power from a 153v pack. Any advice much appreciated!


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## Jan (Oct 5, 2009)

What's wrong with the idea of connecting them all?


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## jackbauer (Jan 12, 2008)

That's the plan. Just need to figure out how


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## Jan (Oct 5, 2009)

Polarity doesn't matter. So 1, 3 and 5 together and 2 and 4 together to the other pole? Or are you thinking serial, due to the higher voltage? As far as I know they work on any voltage, just get hotter faster.


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## dtbaker (Jan 5, 2008)

here's mine.... runs at 120v nominal. Higher voltage should be fine and draw LESS amps as the elements self-regulate by temp.


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## Rational (Nov 26, 2011)

jackbauer said:


> I'm looking for a little advice on wiring up a few of these ceramic heaters. They are rated at 120v and 1500w. Five connections. Resistances are as follows:
> 1-2 = 133R
> 4-5 = 125R
> 2-3 = 207R
> ...


P = (V^2)/R so R = (V^2)/P
R = (153^2)/1500 = 16 ohms.

You need to somehow parallel these high value resistances to get 16 ohms. How many separate resistors do you have and of what value?


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## Jan (Oct 5, 2009)

The resistance curve of these things is very odd. I've not really measured it, but I believe they start with this relatively high resistance, which drops if the get warmer, to be able to produce the Watts they prommise, and finaly end up with a very high resistanse at their max temperature. Just perfect. Little inrush current, and self maximized temperature. I've added a temperature switch in my heater for security. I had it laying around. But in hindsight I think it's nonsens.


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## jackbauer (Jan 12, 2008)

Thanks guys. Any ideas on mounting these things as the outsides are conductive?


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## Jan (Oct 5, 2009)

I used parts of the original mounting, otherwise you have to make something yourself. I first thought of using fermacel.


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## dtbaker (Jan 5, 2008)

I have a series of pix starting here:
http://www.envirokarma.org/ev/gallery/091104_heatduct01.htm

I think if you use some plastic washers or make a non-conductive surround to hold the elements away from anything conductive you'll be fine.


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## tomofreno (Mar 3, 2009)

I posted on mounting two of these cores in parallel in a teflon holder here (scroll down to second paragraph):
http://www.diyelectriccar.com/forums/showpost.php?p=203777&postcount=599


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## skooler (Mar 26, 2011)

I know I'm not answering the question here...

Have you considered using 12V ceramic heater such as below?

http://www.maplin.co.uk/in-car-ceramic-heater-48775?c=froogle&u=48775&t=module

Two of these should work reasonably well and it also avoids bringing pack voltage into the cabin.

Cheers,

Mike


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## dtbaker (Jan 5, 2008)

skooler said:


> I know I'm not answering the question here...
> 
> Have you considered using 12V ceramic heater such as below?
> 
> ...



seeing as how these have a 15amp fuse, they probably are rated at only 150 watts or so..... so you'd need 10 (or 20) of them to get to equiv of one of the 120v elements people use; which means you'd ALSO have to add several dc-dc convertors to support them.

watts are watts regardless of voltage.  1500 watt heater is minimum for anywhere that gets down to freezing. 3000 watts are probably required for effective heat in colder places.

much more cost effective to run that kind of power off the high-voltage pack than multiple dc-dc convertors at 12v.


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## skooler (Mar 26, 2011)

dtbaker said:


> seeing as how these have a 15amp fuse, they probably are rated at only 150 watts or so..... so you'd need 10 (or 20) of them to get to equiv of one of the 120v elements people use; which means you'd ALSO have to add several dc-dc convertors to support them.
> 
> watts are watts regardless of voltage.  1500 watt heater is minimum for anywhere that gets down to freezing. 3000 watts are probably required for effective heat in colder places.
> 
> much more cost effective to run that kind of power off the high-voltage pack than multiple dc-dc convertors at 12v.


Hi dtbaker,

Makes perfect sense  diddn't realise they let out so little power, I should have done the maths but I assumed they would be capable otherwise they're more or less pointless!

Thanks for that,

Mike


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## notailpipe (May 25, 2010)

You probably decided what you want to do by now, but I really recommend starting over at your Irish Walmart-equivalent and get another one so you can reuse the case it came with and just screw that in. Here they're like $20 so might save you some time than fabricating some material that you'll always question if it's flammable...

You can check out this part of my build thread here (scroll to post #14). Not to toot my own horn, but I think the way I mounted it was pretty good, with it inside the blower duct instead of in the heater core like many have done. I list the many advantages on the link. 

One final advantage of starting over, is you can reuse the safety switch it came with too, JIC. I'm a little safety paranoid though...


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## dtbaker (Jan 5, 2008)

notailpipe said:


> .... the way I mounted it was pretty good, with it inside the blower duct instead of in the heater core like many have done.



I put mine in the duct too.... heater core would have required removing entire dash which is many hours of screwing around I would like to never do.


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## notailpipe (May 25, 2010)

Dang... so much for my patent application!


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## dtbaker (Jan 5, 2008)

notailpipe said:


> Dang... so much for my patent application!


only worth patenting if you plan to sell. 

anywho.... as an EE type, what do you think about putting two elements in there basically 'in parallel' to get 3000 watts? I would like to use one relay and one set of wires from traction pack, but am a little leery of the start-up amps.

I know that I kept blowing 30a fuses with the one element (running at 96v with my old pack) at startup.... but they might have been fast rather than slo-blow. I am a little ashamed to admit I am still running with the 'penny in the fusebox' and put some thin 24 ga telephone wire in place of fuses when I ran out and have never gone to get more real fuses....

I am thinking that 'next time' if I use two heater elements I should try a 20 or 40 amp DC rated CIRCUIT BREAKER and a more self-enclosed substantial relay/contactor. I don't particularly like that open relay I got needing to solder caps and resistors together and all that...... if I get a more substantial contactor, what would I need to do to 'soften' that initial hit as elements heat?

....just for background... I use the fan switched power to 'key on' the relay that closes circuit for heater elements to insure that elements cannot power before fan is running.....


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## notailpipe (May 25, 2010)

Wow, what perfect timing for this thread for me... I am rethinking my heater relay/contactor right now. 

What I did was a similar circuit that you're describing where for the heating element to be on, the dash "heat" switch had to be flipped AND the blower setting had to be 1, 2, 3, or 4, but if the fan was OFF then it would override the heat switch. 

Well, long story short, my design worked perfectly but the piece of sh1t chinese SSR I bought to control the heater fused its output after about 30 seconds of testing. Good thing I was there and it failed during the test because it failed in the on position! The SSR was rated for 40A of 250VDC which should have been plenty for the ~15A at 144VDC, so I dunno...

I've recently been looking into getting a small contactor instead, but then when I read about those, it looks like I'd want magnetic blowouts because that's the only way to reliably break current under load (which it would ALWAYS be, since it's on before I shut it off..) but then by the time a contactor has magnetic blowouts I'm back to the price of a non-chinese SSR (maybe that's what I should just do). The other part of me thinks it's just 15A how can a little contactor not handle breaking it... 

Anyway, getting to your question, why are you worried about startup amps from the pack? The batteries have to be accustomed to a sudden 15A surge, right? I'd think it'd be nothing to them, compared to stomping on the accelerator. Maybe you've been thinking too much of your DC/DC brake pump issue you were having.


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## jackbauer (Jan 12, 2008)

Thanks for the tips guys. Found the perfect material. FR4 pcb board! I actually plan to run 2 or 3 of these elements as the one i have currently installed barely works. I use a kilovac ev200 contactor (overkill i know) to control the hv to the heater. Tried just about everything else and its the only part that can take the power.


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## Jan (Oct 5, 2009)

Are you controlling these with a sensor, because of the relay?


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## dtbaker (Jan 5, 2008)

notailpipe said:


> I've recently been looking into getting a small contactor instead, but then when I read about those, it looks like I'd want magnetic blowouts because that's the only way to reliably break current under load


I got the heater contactor kit from kta-ev.com . The stuff they sell has not been the cheapest, but HAS been bulletproof. It has a magnetic blowout, and came with two little caps and resistors and a diode that you have to assemble. Apparently, they have figured out that heaters have some wild zap when contacts close and this stuff is required for the life of the contacts..... hence me wondering if similar setup would 'soften' the startup of the vacuum. I'm not worried about the batteries in this case, I just didn't like the extra time to solder this stuff together, and then have to enclose it in a splash-proof spot with main contactor.



notailpipe said:


> Anyway, getting to your question, why are you worried about startup amps from the pack?


because I kept blowing 30amp fuses with ONE heater element, and I would like to go with two I think. So, I think I may spend a little more and go with a re-setable circuit breaker instead of fuses.


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## Jan (Oct 5, 2009)

I don't understand why you want to use relays for heating? What's wrong with a ordinary switch. Or the switch the heater came with in the first place.


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## dtbaker (Jan 5, 2008)

Jan said:


> I don't understand why you want to use relays for heating? What's wrong with a ordinary switch. Or the switch the heater came with in the first place.



because AC switches will not handle the make/break under load. They arc and either burn contacts back open, or weld themselves shut.


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## Jan (Oct 5, 2009)

dtbaker said:


> because AC switches will not handle the make/break under load. They arc and either burn contacts back open, or weld themselves shut.


The load of the heater isn't that high due to the relative high starting resistance. Unless ofcourse you connect all the connections together like Jack wants. The starting resistance of the first position is someting like 6-800 ohm. Which is in most cases less than half an amp inrush current. Why is that a problem?


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## dtbaker (Jan 5, 2008)

Jan said:


> The load of the heater isn't that high due to the relative high starting resistance. Unless ofcourse you connect all the connections together like Jack wants. The starting resistance of the first position is someting like 6-800 ohm. Which is in most cases less than half an amp inrush current. Why is that a problem?


well.... try it and find out.

All I know is that a substantial DC rated contactor is strongly recommended for turning the pack voltage on/off to the heater.


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## notailpipe (May 25, 2010)

Jan said:


> I don't understand why you want to use relays for heating? What's wrong with a ordinary switch. Or the switch the heater came with in the first place.


I agree with Dan that they are not meant to handle the make-and-break arcing of such a high-voltage DC load. But pretend for a second that doesn't matter... how with a regular switch do you ensure nobody ever turns on the heater without the fan being on? Because to do that you need some sort of isolation device like a relay/contactor/SSR to control the enable. Or are you just trusting that the device will self-limit itself and not overheat? I assume there's a reason all those heaters come with a safety thermal switch.


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## Jan (Oct 5, 2009)

notailpipe said:


> I agree with Dan that they are not meant to handle the make-and-break arcing of such a high-voltage DC load. But pretend for a second that doesn't matter... how with a regular switch do you ensure nobody ever turns on the heater without the fan being on? Because to do that you need some sort of isolation device like a relay/contactor/SSR to control the enable. Or are you just trusting that the device will self-limit itself and not overheat? I assume there's a reason all those heaters come with a safety thermal switch.


I've added an even bigger savety switch. I was planning to turn the fan on the other way around. Doesn't make much difference, only a cheaper relay is needed. And I've got a few of those lying around. But before that, I will test the heater from a battery pack to see if you're right. 'They' say a lot. But if it's true, is often the question. I wonder if 'they' take the strange, yet perfect resistance curve of a ceramic heater into acount.


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## tomofreno (Mar 3, 2009)

> I don't understand why you want to use relays for heating? What's wrong with a ordinary switch. Or the switch the heater came with in the first place.


 Because it is running off the pack at around 120VDC. The heater switch is made for AC and would likely arc.



> The load of the heater isn't that high due to the relative high starting resistance. Unless ofcourse you connect all the connections together like Jack wants. The starting resistance of the first position is someting like 6-800 ohm. Which is in most cases less than half an amp inrush current.


 You apparently didn't read my post: 


> Resistance of the two heaters in parallel was 11 Ohm at room temperature of about 85 F, and after heating with a heat gun briefly, 5 Ohm.


 So one of my heaters is about 22 Ohm at room temperature, and a bit less than half that when operating, so ~ 9 Ohm, ~13A, ~ 1500W. With them in parallel I measured about 3100W input at operating temperature.


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## notailpipe (May 25, 2010)

Jan said:


> I've added an even bigger savety switch. I was planning to turn the fan on the other way around. Doesn't make much difference, only a cheaper relay is needed. And I've got a few of those lying around. But before that, I will test the heater from a battery pack to see if you're right. 'They' say a lot. But if it's true, is often the question. I wonder if 'they' take the strange, yet perfect resistance curve of a ceramic heater into acount.


Here "they" doesn't mean scientists in a lab that I just made up to be right, it's the specs on the hardware!  I used to think like you did, why not just put any old relay or switch in there? But when i started looking around for something that could stand 144+VDC of isolation voltage, even at 20A those relays started to be upwards of $90 on digi-key. 

I do think, for example when I drive my car to the DMV this weekend to register it (yay!) that it's okay to put like a light switch in there (just for now) to turn the heater ON/OFF, so my windshield doesn't fog up when I'm driving. But long-term I don't want the heater on if the fan is off and I know of no way to do that with a manually operated switch that is actuated through mechanical force vs. some sort of circuit which performs the conditional-fan logic.

If you know a way, I'd love to hear it. Are you saying that you sortof reversed the operation, like if you flick the switch to turn on the heater, the fan automatically comes on at least low? I'm not sure how I'd make that work with my original heater fan wiring, but it's an interesting idea. You could definitely make that work if you only want the fan OFF or HIGH with no speed variability, but that seems limiting for comfort/battery drain.


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## Rational (Nov 26, 2011)

notailpipe said:


> not meant to handle the make-and-break arcing of such a high-voltage DC load.


Alternating current extinguishes the switch arc several times each second so AC contacts don't need to be as hefty. It's as if the switch is run through fewer cycles.

The worst case is a DC inductive (motor) load with high voltage (switching arc can jump farther) and high inductance/current with fast switching time.

The voltage across the arc is e = -L dI/dT. With large L, large I and small switching time dT the voltage goes very highly negative.
I've seen practical switching times of 15 mS but I've heard that mercury-wetted reed switches can switch in a 1/4 pS.

A heater is a resistive load and that should be the easiest. If you want to stay with the switch you have there are contact protection networks which are mostly just a resistor and a cap, the cap being there to quench the arc.


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## notailpipe (May 25, 2010)

dtbaker said:


> I got the heater contactor kit from kta-ev.com . The stuff they sell has not been the cheapest, but HAS been bulletproof. It has a magnetic blowout, and came with two little caps and resistors and a diode that you have to assemble. Apparently, they have figured out that heaters have some wild zap when contacts close and this stuff is required for the life of the contacts.....


Dan, would you mind posting a picture and model number on the contactor from kta-ev, including diode wiring? A lot of these companies are just reselling things available for less on the internet and I'm already too overbudget to justify spend $90 on a relay. Let your sunk cost benefit us all.


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## dtbaker (Jan 5, 2008)

notailpipe said:


> Dan, would you mind posting a picture and model number on the contactor from kta-ev, including diode wiring? A lot of these companies are just reselling things available for less on the internet and I'm already too overbudget to justify spend $90 on a relay. Let your sunk cost benefit us all.



well, I have a couple closeups
http://www.envirokarma.org/ev/gallery/090301_final_assy00b.htm
http://www.envirokarma.org/ev/gallery/091103_heatcon1.htm
http://www.envirokarma.org/ev/gallery/091103_heatcon2.htm
and the parts 'loose'
http://www.envirokarma.org/ev/gallery/081109_heaterkit01.htm

they did not list the mfg/part no for the relay, but it shows on my kit invoice as $42 down toward the bottom, (the heater core was overpriced at $80 though. )
http://www.envirokarma.org/ev/080307_eparts_big.jpg

this might be one of the times when you might want to consider spending just a few extra bucks to support a Vendor that has been around for a LONG time and continues to give expert advice with quality components. I would suggest giving them a ring..


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## notailpipe (May 25, 2010)

dtbaker said:


> this might be one of the times when you might want to consider spending just a few extra bucks to support a Vendor that has been around for a LONG time and continues to give expert advice with quality components. I would suggest giving them a ring..


Hmmm, well it won't be the first time I buy from them. But it actually looks more complicated than I thought. I'd probably pay $42 if they gave it to me for that, but not $85 like it's listed now... maybe I'll give them a call. I'm still trying to get my money back for this faulty SSR I bought off eBay first! Thanks.


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## Jan (Oct 5, 2009)

tomofreno said:


> Because it is running off the pack at around 120VDC. The heater switch is made for AC and would likely arc.
> 
> You apparently didn't read my post:
> So one of my heaters is about 22 Ohm at room temperature, and a bit less than half that when operating, so ~ 9 Ohm, ~13A, ~ 1500W. With them in parallel I measured about 3100W input at operating temperature.


I was nowhere talking about your post. I said what I've measured. My core has just like Jack's several elements, with a all having a different resistance at room temperature. And the resistance is high. If I use the original 4 position switch, I see no problem. But that's tested from DC with a bridge rectifier and some prety big caps. Not from a battery pack. I'm going to test it more because all you guys make me scared.


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## dtbaker (Jan 5, 2008)

safely turning high voltage on and off is the hard part of what we do with EVs..... unfortunately the expensive part too. If you try cheaper solutions I have found that things tend to burn up.


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## tomofreno (Mar 3, 2009)

> And the resistance is high.


 Not sure where you are measuring Jan. I had B+ to two leads, B- to three. Measured at room temperature, 70 F, and after heating the core with a heat gun, as I described. I didn't see anything approaching the resistance you report. Must be a very different heater or different measurement points. You might check it's resistance after heating it. It will need to be around 10 Ohm or so to get much current through it and much heat out, depending of course on battery pack V.


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## Jan (Oct 5, 2009)

tomofreno said:


> Not sure where you are measuring Jan. I had B+ to two leads, B- to three. Measured at room temperature, 70 F, and after heating the core with a heat gun, as I described. I didn't see anything approaching the resistance you report. Must be a very different heater or different measurement points. You might check it's resistance after heating it. It will need to be around 10 Ohm or so to get much current through it and much heat out, depending of course on battery pack V.


My core is already placed in the heater house. So I can't do any easy measurements. No that's not true. I still can on the switch terminals. I'll do that. But from memory Jack's resistance measurments in the first post are prety similar of what I remember. The lowest more than 125 ohm and the highest over 600 ohm. The total resistance was someting around 50 ohm at room temp. I think it gets lower when it heats up, and extreemly high when it reaches its designed destination temp. And this high end curve is extreemly sharp. With 125 ohm and 300V the current is still no more than 2.5 amp. And that's the max for every position in the switch. There's no smoke, no smell, no funny sound, nothing extraordary happens when I turn the switch. Not if I turn quickly from off to position three. And not if I wait a while between every step to let every segment heat up. Because of the poor blower setup I hear the thermal switch break the circuit in position three after a while. And after a minute or so close it again. And again no sparks, funny noices etc. I will keep on testing if I've got the time, and report any explosions. If I don't report anything within a month or so, the explosion was prety big.


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## Jan (Oct 5, 2009)

Not really important, but I grabbed the first wire I saw to connect the heater to my charger setup for testing it from DC. And this wire had a switch, designed for a normal light. That switch defenitly wasn't able to break the circuit at this current and voltage. Lots of arcs, and a little smoke.


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## bjfreeman (Dec 7, 2011)

I am not sure if posting a link is against the rules, since mine were deleted but others have posted.
so here goes
http://www.waynesev.com/ev/heater.html


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## notailpipe (May 25, 2010)

All this talk about this issue made me wondering if I was just being too paranoid about safety and overthinking the heating switch.

Decided instead of all the theorizing and posturing I would try this with a standard light switch and put it to rest. No, they are not rated for this high voltage DC, but neither are the other solutions being proposed (like a normal relay). Here are my findings:

When turning on the heater (I'm using the standard 1500W ceramic heating element we're all talking about), it turned on fine, with a non-cool arcing sound though, and worked fine conducting the current for several minutes. 

When I tried to turn it off, I could FEEL the current pulling against me, trying to keep the switch closed (this is why they invented magnetic blowouts in a good contactor). As it finally turned off there were loud pops, arcing, and cracking sounds coming from inside the switch. The entire switch glowed blue as it caught on fire from the inside, and I blew out the flame. 

My heart was racing a mile a minute.

Here's the inside of the switch:









I think I'm going to save my money and buy something designed to do this, whether it's the switch from KTA-ev or a quality SSR from Digikey... But I think it's case closed whether this is just a simple resistive load. It's something to be taken seriously.


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## jackbauer (Jan 12, 2008)

This is why I use a kilovac. Might only be a heater buts its dc. You can switch the 12v supply to the kilovac any way you like. I use a little aftermarket illuminated rocker switch.


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## dtbaker (Jan 5, 2008)

cool, that pretty much is the proof of the puddn' right there. I never did try that, but have been tempted just to see what would happen. Now we know!


this also explains what happens to the 'soil warming cables', that are intended for AC, if you wire them to DC. I would imagine that the built-in thermostat/switch would look a lot like this switch ...


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## Jan (Oct 5, 2009)

Tested the original switch again today, kept the heater running for a half an hour or so, to keep my room nice warm. Switched like a mad man on off, slowly, quickly. Nothing, extraordanary happens. No sound, no arcing, no smoke. All at 310VDC. It works fine, and I'm getting more confident it will keep working forever. 

Heard today that manual ac and dc switches are constructed differently, but nothing really high tech. My switch could be a dc switch, since they work on booth ac and dc. I stop testing, and time will tell. I can always redesign it if it fails.


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## m38mike (Dec 27, 2008)

Thanks Notailpipe for that demonstration! 

I've decided that I'm going to use a Kilovac EV200 as my HV switch. I'm also putting a midget fuse in the HV line right before the EV200. I just took my 1500w ceramic heater apart. I took the 120v fan out and replaced it with a 120mm 12vdc fan. I also took the switches out of the circuit. I want mine to be a simple on/off operation. It'll be controlled by a 12v switch on the dash. When the EV200 is closed, the fan will be running. I'm putting the EV200 and the fuse inside a 6"x6"x4" plastic junction box. That should keep them protected.


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