# High-Voltage Heating



## sailfish11 (Sep 15, 2007)

I'm looking for a ceramic heating element for my 312V system. I've found a few places that sell heating elements for EVs (e.g. here) but nothing that is rated to work above 240V. My question is, would a 240V element work (i.e. not get destroyed) if plugged into my 312V pack?


----------



## dogstar74 (Dec 6, 2008)

I wonder, wouldn't your heater be a just a large resistor? Then aren't you wasting energy sending it 312V? Would a DC/DC converter to 120V reduce the loss, i.e. increase the efficiency? Or perhaps since you need a DC/DC converter to run the auxilliaries such as batteries, stereo, lights etc, could you run a 12V Ceramic heater instead? All you would need to do is up the amp load that the DC/DC provides. Just a thought.

Here's a link to one the MAY work. I haven't done this so buyer beware!
http://www.roadtrucker.com/12-volt-heating/300-watt-12-volt-heater.htm

Aaron


----------



## dogstar74 (Dec 6, 2008)

ACtually, a little research answered my own questions. 

http://answers.yahoo.com/question/index?qid=20071025002258AASbOtc

Sounds like you need a 120V or nuthin.

Aaron


----------



## Twilly (Jan 22, 2008)

Could you use 2 in series, I ran one with 144vdc and it worked great...


----------



## sailfish11 (Sep 15, 2007)

I could run two in series, but since they don't make 156V elements I'd have the same problem (of not running the elements at their rated voltage). If the heater is just a large resister, than I should be able to run it at higher voltage without damaging it -- it would just run hotter, right? Then I guess I'd have to worry about it melting its casing or something, but otherwise it should be fine. Of course, I don't really know what I'm talking about here....


----------



## etischer (Jun 16, 2008)

Actually you are in luck because 110 VAC is 155.5 volts DC when it is rectified. The heater should draw the same power at 110VAC as it will 155.5VDC. Im doing a 312 volt system too, and plan to use 2 110vac heaters with 12v fans. 

I also have a simple circuit to vary the power to the coils. It uses a hobby kit 12VDC PWM Module and an IGBT. I will also have a mechanical contactor in series incase the IGBT fails and gets stuck on. The IGBT is rated up to 300A at 600V. 











Heres a pic of my circuit dimming some light bulbs. 12v goes into the PWM (yellow wires), chopped up PWM comes out (white wires) and goes into the IGBT pack. 




sailfish11 said:


> I could run two in series, but since they don't make 156V elements I'd have the same problem (of not running the elements at their rated voltage). If the heater is just a large resister, than I should be able to run it at higher voltage without damaging it -- it would just run hotter, right? Then I guess I'd have to worry about it melting its casing or something, but otherwise it should be fine. Of course, I don't really know what I'm talking about here....


----------



## mark1030 (Jul 28, 2008)

etischer said:


> Actually you are in luck because 110 VAC is 155.5 volts DC when it is rectified. The heater should draw the same power at 110VAC as it will 155.5VDC. Im doing a 312 volt system too, and plan to use 2 110vac heaters with 12v fans.


I was wondering how I was gonna find something I could hook up to my 160V pack. Cool!


----------



## Qmavam (Aug 17, 2008)

etischer said:


> Actually you are in luck because 110 VAC is 155.5 volts DC when it is rectified. The heater should draw the same power at 110VAC as it will 155.5VDC. Im doing a 312 volt system too, and plan to use 2 110vac heaters with 12v fans. [quote/]
> 
> Hi all,
> 110vac is not the same as 155.5vdc.
> ...


----------



## sailfish11 (Sep 15, 2007)

If i used two 240v elements, each one would only get 156v -- would they get hot enough?


----------



## Qmavam (Aug 17, 2008)

sailfish11 said:


> If i used two 240v elements, each one would only get 156v -- would they get hot enough?


 I calculate two 240v 1000 watt heaters in series would put out 422 watts each for a total of 844 watts. Kind of low.
I'm on the road and it's early, when I get to my destination I'll recheck
my math. And post the math so all can understand and check.
Later, Mike


----------



## Qmavam (Aug 17, 2008)

Qmavam said:


> I calculate two 240v 1000 watt heaters in series would put out 422 watts each for a total of 844 watts. Kind of low.
> I'm on the road and it's early, when I get to my destination I'll recheck
> my math. And post the math so all can understand and check.
> Later, Mike


 So we want to calculate the wattage of a heater with a different supply voltage.
First two formulas.

P= I x E is Power = current (in amps) x voltage

E = I x R is Voltage = Current x Resistance

Let's start with a 1000 watt 120v heater.

First let's find the current. 

To do this we need to 
rearrange the formula from P= I x E to I = P/E.
I = 1000/120 or I = 8.33amps.
So a 1000 watt heater draws 8.33 amps from a 120 volt supply.


Now let's say we want to find the resistance of the heater element.
We know the voltage and the current so 
we can rearrange the formula E = I x R to R = E / I
R = 120 / 8.33 or R = 14.4 ohms
So the heater element has 14.4 ohms of resistance.

Ok, what was the question? Oh, 240 volt heater on 156 volts.

I'll assume a 1000 watt 240 volt heater, but you can use the wattage of your heater.
First we can calculate the current draw of the heater.
I = 1000 / 240 or I = 4.16 amps, 
Then find the resistance.
R = 240 / 4.16 or R = 57.7 ohms

Then we can plug in the 156 volts. 156 / 57.7 = 2.7amps
and using P = I x E or 156 x 2.7 = 422 watts

So two 240 volt 1000 watt heaters in series would produce 844 watts on 314 volts.

Now for those that know their algebra,
I just ask my 17 year old daughter/math wiz how to combine the formulas.
You can use this formula to find the new heater wattage.

New heater wattage = (New E^2) /(OLD E^2 / P ) The ^2 means squared

(New (E^2) = New voltage for heater squared-- in this case 156 volts
(OLD E^2 / P) = original heater Voltage squared / original heater Wattage (P)--- in this case E = 240 and P = 1000

Soo... ((156 x 156) /(( 240 x 240) / 1000)) = 422 watts the new heater voltage.

I hope I gave you some information, it was more difficult to explain than it was to do.
If you have question, feel free to ask.
Later, Mike


----------



## Twilly (Jan 22, 2008)

So.... To use a 2 - 1500 watt 120 volt heaters, You would get 1950 watts of heat from each of the heaters ( in series ), for a total of 3900 watts of heat.


----------



## Qmavam (Aug 17, 2008)

Twilly said:


> So.... To use a 2 - 1500 watt 120 volt heaters, You would get 1950 watts of heat from each of the heaters ( in series ), for a total of 3900 watts of heat.


 Hi Twilly,
I get a different answer, I'll go over what I think are the voltages and wattages you are proposing to use.
We have two 1500 watt 120 volt heaters. 
We are going to wire them in series.
The battery pack is 314 volts.
Because we have a series connection we can calculate the problem 
two ways, one heater at a time or two heaters at the same time.
I'll calculate one heater, to do that we must divide the battery pack
voltage in half. 314 / 2 = 156
Using the combined formula below and pluging in the numbers.
New heater wattage = (New E^2) /(OLD E^2 / P ) 
New heater wattage = ((156 x 156) /(( 120 x 120) / 1500))
New heater wattage = ((156 x 156)/(14400/1500))
New heater wattage = ((156 x 156)/9.6)
New heater wattage = (24336/9.6)
New heater wattage = 2535
So, I see your 1500 watt producing 2535 watts, but not for long







.
And when placed in series with the second heater you would get
5070 watts of heat.
I checked this several times a couple of different ways and pretty
sure I have it correct.
Let me know what you think.







I wouldn't apply more voltage to a heater than it is designed for.
Later, Mike
PS. I just figured out how you got your 1950 watts. You figured that
156 volts is 1.3 times 120 volts so the wattage is also 1.3 times.
( or something similar)
That's not proper, voltage has a squared relationship to wattage.
Another formula P = E^2/ R 
P = watts
E = Voltage
R = Resistance
Note that E has a squared relationship to P.


----------



## peggus (Feb 18, 2008)

If we're talking about ceramic heater elements here you might as well forget the calculations, they are meaningless since R is not constant.

The ceramic heater elements have a temperature dependent resistance that looks something like this:


```
Resistance 
ohms 
    |                                        | 
 25 |                                        | 
    |                                        | 
 20 |---___                                  | 
    |      ---__                             | 
 15 |           --__                        / 
    |               --___                  / 
 10 |                    --__             / 
    |                        --__       _- 
  5 |                            --____- 
    |_________________________________________ 
   0        50        100          150      180 
             Temperature degrees Celcius
```
 The elements self regulate to a certain temperature. If it goes higher the resistance increases to limit the power. 

Your 240V element will probably work just fine on 320. We know it won't flashover since the peak of 240AC is 340V, and it should self regulate to a safe temperature. 

These ceramic elements are usually made up of several smaller heaters stacked in series.









So if you wanted to be absolutely safe you could take two 240V elements and power only the first plus half of the second element for a 360V heater.


----------



## Qmavam (Aug 17, 2008)

peggus said:


> If we're talking about ceramic heater elements here you might as well forget the calculations, they are meaningless since R is not constant.
> 
> The ceramic heater elements have a temperature dependent resistance that looks something like this:
> 
> ...


 Thanks peggus,

I looked for additional info and graphs about the nonlinear resistance vs
temperature of ceramic heaters. I found a little but not much. It is an interesting and a useful characteristic to be exploited for safety in electric heaters. If you have any URLs with data about ceramic heaters please post it.








I agree with you, everything I wrote about calculating power will apply only to a pure resistance heaters.

I would like to see a detailed graph to figure power from a ceramic heater, It looks like if you lower the voltage in, the heat output would drop even faster than a resistance heater. On the higher voltage side I'd need more 
info to calculate.
Do you know if the heaters are run at the sweat spot where resistance is minimum?

Thanks for the info, Mike


----------



## peggus (Feb 18, 2008)

They naturally gravitate towards the sweet spot. When you first turn it on and it starts heating up the resistance drops which increases the power. If it gets hotter than the sweet spot the resistance increases, reducing the power.

Exactly where on the curve it ends up operating depends on airflow though.


----------



## Qmavam (Aug 17, 2008)

peggus said:


> They naturally gravitate towards the sweet spot. When you first turn it on and it starts heating up the resistance drops which increases the power. If it gets hotter than the sweet spot the resistance increases, reducing the power.
> 
> Exactly where on the curve it ends up operating depends on airflow though.


 Hi All,
I woke up with ceramic heaters on my mind. I searched several hundred
pages and finally came up with the right term, barium titanate PTC.
Here are some URLs if anyone else is interested.
http://www.rotfil.com/en/product.asp?idprod=64
http://www.dbk-usa.com/products/ptcheaters/ptcheaters.htm
http://www.dbk-usa.com/products/ptcheaters/ptcheaterqanda.htm
http://www.scribd.com/doc/8358923/textchap9
Page 8 shows a nonlinear relationship between current and voltage in the 
ceramic. (just to confuse things







)
Note the barium titanate is altered with different dopants, this will change the slope and sweet spot, so the graphs may not match your heater.
Later, Mike


----------



## sailfish11 (Sep 15, 2007)

I guess they would have chimed in by now, but is there anyone out there using a ceramic heater at a higher-than-rated voltage? It looks like it might be possible.


----------



## piotrsko (Dec 9, 2007)

my $.02, and I hate to say this, BUT;

seems to me that you are in the steep portion of the learning curve perhaps by yourself, much like Beshire and his motor. 

that being said, sounds like you need to get into cheap experimentation mode to generate data. get a couple of extremely cheap heaters and proceed to blow them up in a safe and controlled manner. Be advised that they may not self destruct and function as exactly desired.

Please publish your results good or bad and help someone else out.


----------



## Twilly (Jan 22, 2008)

sailfish11 said:


> I guess they would have chimed in by now, but is there anyone out there using a ceramic heater at a higher-than-rated voltage? It looks like it might be possible.



I am putting 144vdc to a 1500 watt heater rated at 120vac... But this is really not "higher than rated voltage" because the 120vac wave peaks at higher than 144v...120v is the RMS or average voltage... But anyway, it works great


----------



## Qmavam (Aug 17, 2008)

Twilly said:


> I am putting 144vdc to a 1500 watt heater rated at 120vac... But this is really not "higher than rated voltage" because the 120vac wave peaks at higher than 144v...120v is the RMS or average voltage... But anyway, it works great


I'm not giving any advice about ceramic heaters because of the nonlinear
resistance with temperature.
I will say that 144 vdc is "higher than rated voltage" of 120 vac.
I agree, the 120 vac peaks higher (170v peak) than the 144 vdc, but it is also near 0 volts during some of the cycle.
Also RMS and average are not the same. In fact, 120 vac equals 120 volts rms but equals zero volts average. (this assumes a sinewave)
Also 144 vdc is equivalent to 144 volts rms and that is equal to 144 vac.
(assumes sinewave)

The average of one alternation* is 0.636 x peak.
*alternation is 1/2 cycle from 0 volts to peak and back to 0 volts.
Later, Mike


----------



## ElectriCar (Jun 15, 2008)

My ceramic heater works as described on page 2. Running around 150V and varying the fan speed varied the heat output. The slower the fan the lower the amperage thus lower heat output. 

On low speed in my S10 my heater only put out about 1100W I think. At full fan speed it put out right around 2kw. See link where I posted the results of my heater/fan speed power calculations. 

It's dead at the moment but I think it's the connectors. We debated whether to solder them on or just use the crimp on spade lugs. It lasted maybe a total of an hour of run time, mostly at medium speed putting out about 1600W.


----------



## Qmavam (Aug 17, 2008)

ElectriCar said:


> It's dead at the moment but I think it's the connectors. We debated whether to solder them on or just use the crimp on spade lugs. It lasted maybe a total of an hour of run time, mostly at medium speed putting out about 1600W.


 It sounds like a fun experiment to measure the power output of a ceramic heater with a variable speed fan. Looks like it could put out a great deal of power if the air flow was large enough. However, the problem could come up that you have wiring and connections that are not in the airstream so they don't stay cool.
Regarding just the ceramic portion of the heater, if it was -20 degrees and you had an enormous air flow you might be able to use two, three, or even four times overvoltage on the ceramic.
Let us know what the fault was on your heater.
Inquiring minds want to know







.
I rented a car for a trip to Michigan, the car had electric seat heaters, 
I would like to say they were great and electric seat heaters are a good idea for an EV!
Here's an aftermarket seat heater http://www.heatedseatkits.com/
These are 12 volt heaters so your going to need a dc to dc converter.
Mike


----------



## sailfish11 (Sep 15, 2007)

Qmavam said:


> Here's an aftermarket seat heater http://www.heatedseatkits.com/
> These are 12 volt heaters so your going to need a dc to dc converter.
> Mike


This is exactly what I'm putting in my EV -- but you still need a conventional heater, if you plan on driving into the cold months, to act as a defroster for the windshield.
Since I'll have the seat heaters, I'm not too concerned if my ceramic heater is a little under powered.


----------



## Qmavam (Aug 17, 2008)

sailfish11 said:


> This is exactly what I'm putting in my EV -- but you still need a conventional heater, if you plan on driving into the cold months, to act as a defroster for the windshield.
> Since I'll have the seat heaters, I'm not too concerned if my ceramic heater is a little under powered.


 Yes on the conventional heater. 
How are people handling this?
Are they heating water to circulate through the heater core?
Any links to aftermarket EV waterheaters? 
Or do people replace the core with an electric heater.
Even if your dressed for a cold ride you still need the defrost function.
(well I don't, I moved from Michigan to Florida 14 years ago) 
My favorite line: 
"You don't need to brush the sunshine off your windshield."
Mike


----------



## JRP3 (Mar 7, 2008)

Qmavam said:


> Are they heating water to circulate through the heater core?
> Any links to aftermarket EV waterheaters?


That's what some people are doing and what I'm planning. A 120 volt block heater and circulator pump. http://www.amazon.com/gp/product/B000BQUUR6
http://store.solar-electric.com/100-00-21.html

There are a number of threads here, search liquid heater.


----------

