Sunday, December 28, 2008

Building the heater

Money has been tight after ordering the batteries and the holidays so progress has been rather slow lately. This is technically the second heater but I will only fully document the final design.

I first built a water heater utilizing the existing heater core. It used a 1500 watt engine block heater and pump to circulate the water. I decided not to use this setup for a few reasons. First and least important was the noise I could hear from the pump circulating the water. A few people recommended a pump that was very quiet but after further thought I didn't try it out. The second reason was the amount of heat I noticed on the outside of the heater unit itself. I figured if all that heat was on the outside it was wasted energy especially while driving if air was passing over the heater. The hoses also get very hot on the outside which again means energy lose. Last I figured this gave me a fluid that could leak, and therefore something that needed to be checked from time to time.

So, as many others have done, I went for the ceramic heater setup which replaces the water heater core with an electric version. Mine, however, well be quite different from the typical basic ceramic install as you'll see later.

The first part in building a ceramic heater is removing the heater core and this is not an easy task, especially with newer vehicles. As I've mentioned before, get the service manual for your vehicle as it will really save you time during your build.

I won't go into boring details of the dash removal but figured I'd still post a few pictures to give you an idea.

Here is a pile of plastic trim, air bags, steering column, etc which is well over a foot tall. There are a few things in the picture to give some perspective. Of course also not shown is the full dash itself.


Here is a picture after removing the dash. I thought I was home free at this point. I was wrong. From the middle to the passenger side you can see the heater box, blower assembly and condenser unit. The blower and condenser needed to also be removed to get to the heater box. This really wasn't that much more work but meant the refrigerant needed to be evacuated. I was hoping to avoid that.



A slightly closer picture with the heater box finally out! Look at all those wires! Most of them are attached to the dash so this is really nothing.



At last the heater core itself is removed.



Here is a shot of the heater core itself. It's a lot skinnier than I thought it would be.



OK on to building the new heater core. I purchased this ceramic heater from Kmart for $30. It was the cheapest ceramic heater they had. First I purchased a $20 heater which was not ceramic and just used five coils of wire. I doubt these would hold up well with the vibrations of a car. It was so cold in the garage I just kept it for a shop heater :)


Here I am testing the temperature coming out of the heater. 231 Fahrenheit, hopefully that will do the trick on the cold mornings. It rarely gets below 40 where I live so this should do just fine.



Now for a test to see how much power this heater really draws. It bounced around quite a bit while running but it's drawing right around 1500 watts as advertised.



Here is the ceramic heater element itself.



Here is the first place my heater will be different than most others. Instead of destroying my original heater core which I hope to sell to get some cash back I'll build my own. I'm using aluminum 1/8" thick for all the pieces. The main frame is 1" square tubing.


Below I've cut out a recess for the heater to set in with my plasma cutter. It was cut slightly higher and angled in to allow clearance for the outer terminals.



I messed around to see if I could weld this assembly but aluminum is a huge pain to weld with a MIG welder. To be honest I was suppose to use 100% argon gas but was only trying it with my 75% argon 25% CO2 mix so it failed horribly. I couldn't afford to get another cylinder for the argon gas so fell back on self tapping screws to hold it together.


Here you can see on the left a piece of flat laid across the side and end pieces using the self tapping screws to hold it together.



Here is one side assembled. The screws go into the side pieces and the end pieces.



I drilled a 1/2" hole on the top for the wires and put a couple of grommets in there to protect the wires from the rough metal holes.



Now I need to make some plates to fill in the gaps where the ceramic heater doesn't cover. I used a piece of metal clamped down to the plating I was cutting to act as a guide for my plasma cutter.



Here is the bottom plate installed.



It's hard to see here but I've cut some slits into the side pieces to allow me to bend them in. This will give a solid piece on the sides a good distance away from the ceramic heater element to allow about a 1/4" of silicone.



I originally cut out small pieces of plastic (from a coolant reservoir I used on the water heater setup) to keep the ceramic heater from touching any metal. This is very important not to short out the heater element to the frame. However, the plastic couldn't withstand the high temperatures if the airflow was too low so I removed these and replaced the gap with more silicone.


I used a high temp (650 Fahrenheit) silicone gasket sealant putting about 1/4" on both sides and bottom. I then cut and installed the top plate. Both of these plates will force all the air to pass through the heater element and not be able to bypass it.



Here is a side-by-side of the water and electric heater cores.



Next I added a foam stripping to all sides and the top. This not only keeps the element from being able to move a little inside the heater box but adds a little more sealing to keep air moving through the element and not around it.



Here is the completed heater being installed back into the heater box. Now that the new core was complete I also did a quick continuity check with my multimeter to make sure that none of the elements were grounded to the frame.

Here is a shot in the housing with a wiring harness built for it. There are five seperate 12 gauge wires inside the harness coming from each section of the element.
Later I will show the electronics and wiring side of the heater. The five wires actually allows for more than the two heater settings (low/high) that they give you and I will be taking advantage of this to allow for more levels of heating. This will not be done, however, through any switches. I will use the existing hot/cold knob and build a circuit to detect changes to this and convert that into a desired temperature setting. Then depending on the temperature differential I will determine how much heat to output. This should end up a lot better than a simple on/off switch on the dash and will use less power when only a little heat is needed without completing shutting down which would then be shooting cooler air out the vents.

I reinstalled the dash and did a quick AC test with the heater. My garage was around 47 F and so was the inside of the car when I started. I was able to get the car up to 80 F. I also measured the vent temperature and I was getting 115 F. I compared this to my truck after it heated up which was putting out 140 F. I'm not sure what my original temp would have been in the car but figured this was at least some reference point. In addition I'll be running the heater on 144v DC so it will actually get hotter than the AC test.

4 comments:

Rob said...

Brian,

Man, you do nice work! The installation of the ceramic heater looks great.

I'm very interested in how you will control variable heat output using the existing dash control. I would like to do this as well.

My climate is much colder (Canada) and I'm considering twin ceramic units. Not sure of the space requirements though.

One question about the aluminum frame... Is there a chance the al might conduct enough heat away from the ceramic that it may over heat the plastic housing? Would a shut down thermostat be necessary? Better make certain the fan is running when the element is on.

Is there some sort of equivalent to a rheostat that would work for this application?

Regards,

Rob (RKM)

Brian said...

Hey Rob,

Thanks for the compliments. I was originally worried about the plastic getting too hot as well but there are a couple things that I believe make it safe. First off the original heater core was also aluminum so it would be able to transfer the heat quite well also to the plastic although the ceramic could reach higher temperatures if you didn't pass air through it. The silicon actually doesn't allow much heat to transfer from the element to the frame so this helps out a lot as well. Additionally the element will not be allowed to run if the fan isn't on and from testing I've done even the lowest of my fan settings still moves a lot of air from what this element got in the original heater case.

These elements are self regulating on how many watts they will draw based on temperature. So for example if I don't pass any air the element will only draw around 300 watts compared to the rated 1500. On low setting in the car I'm drawing 1300 and if I crank it up to high it's actually pulling over 1800 watts.

I've installed a temperature sensor on the heater element before I installed it so I'll be able to use this as well to make sure things aren't getting too warm in there. More on all this later though. :)

gdirwin said...

Can I ask if you have any window fogging problems due to the silicon
(around the ceramic elements) "gassing"?

I put 2 ceramic elements into my EV (replacing the heater core) but sandwiched them between a lot of silicon (also high-temp stuff).

I get a film built up on the windows after only a few days...

Just curious if you see something similar (looks like you did a neater job with less silicon then me).

Garth

Brian said...

Yes I get fogging, but it's not from the silicon. Just as with a gasoline car you'll need to run the A/C compressor to remove the moisture. The temperature difference draws the moisture to the windshield while running the heater. Running the compressor will remove that moisture. Sadly the two together really drains the battery and shortens the range.