DIY Electric Car Forums banner
1 - 20 of 28 Posts

·
Registered
Joined
·
17 Posts
Discussion Starter · #1 ·
I am trying to figure out a cabin heating solution for my conversion and am having a bit of trouble finding a definitive path to take. In my situation there is no making any use of the original HVAC housing or related components. They are archaic and cannot house both heat and AC. The aftermarket HVAC systems available don't appear to be suitable for swapping the wet heater core with a PTC core for various reasons. This leaves me with creating a closed and isolated loop of heated coolant to make use of the wet core in the chosen aftermarket HVAC. What I am having trouble figuring out is:

1.) Is a Tesla battery heater sufficiently powerful enough to heat the coolant in a completely isolated loop to use for cabin heat? Ideally around 180 degrees fahrenheit?

2.) If the Tesla battery heater is not sufficient, what other high voltage coolant heaters are out there that would be?

Efficiency is not a top concern as the climate the truck will be operated in would only make occasional use of the cabin heater. It just has to be there as an option when needed. I found a coolant heater that Borg Warner makes but it does not appear to be able to be purchased by the public. Has anyone used a HV coolant heater to heat the cabin? What did you use and how well did it work?
 

·
Registered
Joined
·
103 Posts
I am investigating/experimenting with using a common high voltage (~400V) water heater element to heat the "heating" loop that would heat the water through the stock heater core (we will also use this same water to warm the batteries for charging in the cold). You have to use a GigaVAC contactor to control it so you can open the circuit under high ([email protected]) load, but you also need this for typical PTC heaters too. It may work, it may fail miserably...
 

·
Registered
Joined
·
17 Posts
Discussion Starter · #4 ·
The Leaf and the Bolt EV both heat coolant for their cabin loop. Everything doesn't have to be "Tesla" 🤦‍♂️

The rest of my EV components are Tesla and I happen to have a battery heater in hand already which is why I singled out that unit. I am aware there are other manufacturers and if one of their parts suits my application better then I am not opposed to using it. Really I am just trying to keep this project as simple as possible while achieving the best end product.
 

·
Registered
Joined
·
70 Posts
EVTV has an expensive hot water heater system. Uses a contactor and a solid state relay for the repetitive on/off. Are there any oem heaters that can be operated without can control?
 

·
Registered
Joined
·
124 Posts
How about a heated windscreen to take care of fogging and ice? Then a set of heated seat inserts to keep you warm. Would you really need to heat the cabin air? If your in a really cold climate, deal with regular snow etc, then possibly? But if your in a temperate area, heating the cabin air isn't necessary if other heat sources are available. Its also quite inefficient to heat all that empty space, that directly takes range from your battery. In my car (260z) a heated windscreen is around $800 and the seat heater inserts are $300 for the pair. I wasn't planning on having any sort of airbox at all, I wasn't even going to bother with AC though, I can just open the windows.

If you need to heat coolant though, I would suggest using an OEM part first, Tesla, Leaf, Bolt etc. They are essentially just an inline heating element in the coolant loop thats already designed and packaged to work in an automotive environment. Definitely keep it separate from the battery/inverter loop, they don't get hot at all and heat like you'd want for a cabin would be really bad for them. Other options for heating coolant that require some level of diy and research, Use an immersion heater element in a container of coolant, the element could be from a water heater, jug(kettle) or various items like that. advantage is that you have a resevior of heated coolant, it'll hold its temperature a lot better. Downside is it'll take a few minutes to heat all that coolant and there is more weight from all the liquid volume.
Another option for an inline heater, would be the inline water heater from a dishwasher. Its essentially a heating coil wrapped around a coolant pipe. It may get 'too' hot though and need a bypass to run parallel with it to mix hot and cold if you can't control the element temperature.
Downsides to those options is the voltage. If your running 400v, you may be able to overvolt them to some degree, But if you sourced a dishwasher heater from a 120v unit, it'll probably break pretty fast. a 240v unit might be a better option, or possibly even an industrial style 3 phase unit (360ish volts)
Controlling the element 'should' be pretty easy, in theory your just turning it on and off constantly to maintain a roughly constant temperature. If you using a contactor to do that (load rated) the constant clicking on and off may get irritating. A lot of the time in an appliance setting, they dont really control the element temperature, they just run it full power with it 'tuned' for the expected operating voltage, then using coolant flow as the 'regulator' to prevent it overheating. That won't really work well in a car, the coolant flow varies, the required heat output varies, the voltage between a full and empty battery can be quite large.

An electric PTC heater would be best though, they can usually be fitted into an original airbox in place of the old heater core and they are instant hot air. They typically have a high current draw initially until they get to temperature, then they naturally have an increase in resistance that lowers the current drawn into them.

Check this out, he talks about PTC heaters and shows one thats already fitted into a classic Mini airbox.
 

·
Registered
Joined
·
3,100 Posts
While you can always add a cabin heater later, I can say that despite having heated seats and heated steering wheel and a determination to max out efficacy and range, when it gets really cold, the heater comes on, 7kW be damned (it settles at ~2-4kW in cold weather).

The reality is that your lungs transport heat/cold to your core and being miserable by choice makes you ask why you're doing this? Being miserable from your build choices makes you wonder why you did this.

The big problem is most of these OEM heaters are CAN controlled, the nice part being that the on/off control is easy, and I'm not sure that anyone has cracked that nut yet.
 

·
Registered
Joined
·
124 Posts
While you can always add a cabin heater later, I can say that despite having heated seats and heated steering wheel and a determination to max out efficacy and range, when it gets really cold, the heater comes on, 7kW be damned (it settles at ~2-4kW in cold weather).
This is where I think it pays to make the determination based on the climate that your using the car. I've seen on the news some of the crazy iced up roads in the US, or videos of people opening their front door with it half packed with snow, or how common it seems for the average US citizen to own a snow blower or have had to shovel a driveway. If I were somewhere like that, I would definitely heat the whole cabin, range be damned.

Where I am in the world, We get sub zero mornings and iced up windows, but it usually only lasts for 3 months of the year at most and typically by lunchtime its quite pleasant. The heated seats in my wife's car were all we ever used through winter. Heating the whole cabin would be pointless here.
 

·
Registered
Joined
·
17 Posts
Discussion Starter · #13 ·
Did you look at some of the offerings from VintageAir or Oldair? I'm hoping to fit a Tesla PTC element in one of those for my build
Today is your lucky day my friend because that was my intention going into this project but after a couple days digging in it became apparent very quickly that was not going to be a viable option. Not without copious amounts of re-engineering and possibly junking the HVAC unit in the process which isn't a cheap date.
With Vintage Air boxes they have designed it so that nothing internal to the box is serviceable. They glue the housing together when assembled. Their intention is for the whole box to be replaced if anything internal fails. The Restomod Air units are built in the same fashion so you run into the same road blocks. Additional road blocks are the way the cores are positioned inside the box and the use of blend doors which further add to size constraints.
Old Air looked promising initially but once I found an image of the internals my hopes were dashed. Their housings clip together and can be separated quite easily. Unfortunately It appears they have one modular cube shaped core that makes up both heater core and evap core. One would have to swap in both the PTC heater and an evap core to make it work. If you found an evap core with side plumbing and a PTC heater core that were the same relative size it could be doable with some engineering. There are no blend doors inside the unit so the core temps would need to be regulated. In my application the box that was slated for the vehicle also protruded quite a bit below the dash which was highly unappealing.
 

·
Registered
Joined
·
17 Posts
Discussion Starter · #14 ·
How about a heated windscreen to take care of fogging and ice? Then a set of heated seat inserts to keep you warm. Would you really need to heat the cabin air? If your in a really cold climate, deal with regular snow etc, then possibly? But if your in a temperate area, heating the cabin air isn't necessary if other heat sources are available. Its also quite inefficient to heat all that empty space, that directly takes range from your battery. In my car (260z) a heated windscreen is around $800 and the seat heater inserts are $300 for the pair. I wasn't planning on having any sort of airbox at all, I wasn't even going to bother with AC though, I can just open the windows.

If you need to heat coolant though, I would suggest using an OEM part first, Tesla, Leaf, Bolt etc. They are essentially just an inline heating element in the coolant loop thats already designed and packaged to work in an automotive environment. Definitely keep it separate from the battery/inverter loop, they don't get hot at all and heat like you'd want for a cabin would be really bad for them. Other options for heating coolant that require some level of diy and research, Use an immersion heater element in a container of coolant, the element could be from a water heater, jug(kettle) or various items like that. advantage is that you have a resevior of heated coolant, it'll hold its temperature a lot better. Downside is it'll take a few minutes to heat all that coolant and there is more weight from all the liquid volume.
Another option for an inline heater, would be the inline water heater from a dishwasher. Its essentially a heating coil wrapped around a coolant pipe. It may get 'too' hot though and need a bypass to run parallel with it to mix hot and cold if you can't control the element temperature.
Downsides to those options is the voltage. If your running 400v, you may be able to overvolt them to some degree, But if you sourced a dishwasher heater from a 120v unit, it'll probably break pretty fast. a 240v unit might be a better option, or possibly even an industrial style 3 phase unit (360ish volts)
Controlling the element 'should' be pretty easy, in theory your just turning it on and off constantly to maintain a roughly constant temperature. If you using a contactor to do that (load rated) the constant clicking on and off may get irritating. A lot of the time in an appliance setting, they dont really control the element temperature, they just run it full power with it 'tuned' for the expected operating voltage, then using coolant flow as the 'regulator' to prevent it overheating. That won't really work well in a car, the coolant flow varies, the required heat output varies, the voltage between a full and empty battery can be quite large.

An electric PTC heater would be best though, they can usually be fitted into an original airbox in place of the old heater core and they are instant hot air. They typically have a high current draw initially until they get to temperature, then they naturally have an increase in resistance that lowers the current drawn into them.

Check this out, he talks about PTC heaters and shows one thats already fitted into a classic Mini airbox.
Thank you for all the info! It gives me a lot to consider. If I wasn't after having AC in the vehicle I would try and reuse the old heater unit and retrofit it with a PTC heater. I do want to avoid installing two separate climate systems in the vehicle. Right now I am eye balling the Bolt water heater. I am looking into what it will take wiring wise and also how to control it. It will be integrated with a Vintage air system and I would like to make use of only that control panel if possible. This has been an incredible learning experience so far. I have not done this amount of research on anything since high school lol!
 

·
Registered
Joined
·
1,767 Posts
Btdt, leaning towards a 4way valve and different refrigerant with higher efficiency and pressures in the existing AC unit.

Flip the 4 way valve and You basically just exchange the condensor for the evaporator and use the heat of compression. I also use 220 volt water heater elements in 2"metal pipe plumbed into the old coolant lines with a coffee maker pump on 12v because this system is only good to about 40 using propane as the refrigerant. And NO my other car has not caught fire yet, or exploded, or torched holes in various systems from it's factory propane system. R290 I believe.
 

·
Registered
Joined
·
17 Posts
Discussion Starter · #16 ·
Btdt, leaning towards a 4way valve and different refrigerant with higher efficiency and pressures in the existing AC unit.

Flip the 4 way valve and You basically just exchange the condensor for the evaporator and use the heat of compression. I also use 220 volt water heater elements in 2"metal pipe plumbed into the old coolant lines with a coffee maker pump on 12v because this system is only good to about 40 using propane as the refrigerant. And NO my other car has not caught fire yet, or exploded, or torched holes in various systems from it's factory propane system. R290 I believe.
Reversing the AC system is not a bad idea! I would however, be concerned about the performance of the system with an ambient air temp close to or below the condenser turned evap cores cold temperature.
 

·
Registered
Joined
·
1,767 Posts
This is why you up the system pressure and change refrigerant. My house Mitsubishi heats down to -14f on 300 psi static R410, however today at 0 degrees, it's spending lots of time defrosting the outside unit.

You will probably still want coolant powered supplement heat
 
1 - 20 of 28 Posts
Top