# "Waste" motor heat.....



## DIYguy (Sep 18, 2008)

OK, so I spent some time searching this and came up with next to nothing. My search "meter" was running close to "frustrated"...so I bailed out and decided to post a new thread. Excuse me if I missed something of significance.... as I'm sure this has been bashed about a time or two..

So, the cabin heater is something I have not finished up yet on my truck. I, like many I'm sure, like to ponder the details as I move fwd. (not too fast! lol  ) While I am trying to learn more about the "identity" of my new toy... (like checking a multitude of things after every run) I always let the motor blower run after parking and put my hand on the motor to feel the temp and add to my almost empty, but slowly growing, mental database of "symptoms" an EV...or rather, my EV... has. Now, I haven't calculated efficiency of the motor and how much power I am pushing through and what should be available as heat.... but I must say, there is always a steady flow of nice warm air exiting out those DE air ports. (its a 9 inch GE DC motor in a Mazda B4000... 192 volt nominal, Soliton1 with AGM's) At first I figured that the higher amp jaunts were the only times when much heat would pour out these ports. . . but u know, even after some pretty "normal" driving... I think there is enough heat available for what I would call "low level" or supplemental heat. My cabin is not huge and on a cool day, I think it would be enough. On a cold day, it would definitely need to be "boosted" by other means. 

In a world of power conservation such as ours, seems a shame to let it "blow away". Perhaps a removable, winter shroud connected to the heater blower?

This is an early pic...when I was still rigging things up...... That's a 3" SS blower and pipe.

Thoughts?


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## JRP3 (Mar 7, 2008)

I suppose you could calculate the average amount of watts your motor is using, multiply it by 15% or so and that's how much heat energy you have to play with. I'd guess it won't be much. Concentrated in a small area blowing out of the motor it may feel warm but once dissipated through the cabin I'm not sure you'd notice, but as you say it is free heat, as long as ducting isn't restrictive causing overheating.


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## Kelmark (Oct 26, 2009)

DIYguy said:


> OK, so I spent some time searching this and came up with next to nothing. My search "meter" was running close to "frustrated"...so I bailed out and decided to post a new thread. Excuse me if I missed something of significance.... as I'm sure this has been bashed about a time or two..
> 
> So, the cabin heater is something I have not finished up yet on my truck. I, like many I'm sure, like to ponder the details as I move fwd. (not too fast! lol  ) While I am trying to learn more about the "identity" of my new toy... (like checking a multitude of things after every run) I always let the motor blower run after parking and put my hand on the motor to feel the temp and add to my almost empty, but slowly growing, mental database of "symptoms" an EV...or rather, my EV... has. Now, I haven't calculated efficiency of the motor and how much power I am pushing through and what should be available as heat.... but I must say, there is always a steady flow of nice warm air exiting out those DE air ports. (its a 9 inch GE DC motor in a Mazda B4000... 192 volt nominal, Soliton1 with AGM's) At first I figured that the higher amp jaunts were the only times when much heat would pour out these ports. . . but u know, even after some pretty "normal" driving... I think there is enough heat available for what I would call "low level" or supplemental heat. My cabin is not huge and on a cool day, I think it would be enough. On a cold day, it would definitely need to be "boosted" by other means.
> 
> ...


I am just starting my first conversion, but I had thought of doing the same with the controller somehow. My kit car is on a VW chassis which had ductwork that ran from the rear engine compartment anyhow. I was thinking of channeling the waste heat to a custom built heater box then into the cars dash. Then use fans that can be reversed during the summer to draw air out of the cabin and cool the controller.

 
Some might say that the energy saved wouldn't be worth the effort but if efficiency is your goal then I think it’s worth it.


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## EVfun (Mar 14, 2010)

The motor air may stink from Ozone when the motor is under a good load (when it's making the most heat.)


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## DavidDymaxion (Dec 1, 2008)

Electric motors can make ozone. In an extreme case, it can make smoke. You wouldn't want to be blowing those things into your car. You could make a heat exchanger to safely harvest the little bit of heat. A heat exchanger can be as simple as a fresh air hose inside of a hose that is exhausting the motor heat (or vice versa), kind of the like the heater on an old VW bug or Porsche.


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## peggus (Feb 18, 2008)

Ozone and carbon dust! Getting black lung from driving an EV would be rather sad.


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## bipole (Sep 8, 2009)

Can you measure the temperature of the intake and (so called) 'exhaust' air from the motor?


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## Tesseract (Sep 27, 2008)

Kelmark said:


> I am just starting my first conversion, but I had thought of doing the same with the controller somehow. ...


Most dc motor controllers are going to be 96-98% efficient without even trying hard so they really aren't a worthwhile source of cabin heat. I suppose in this case DIYGuy could run a coolant loop through the Soliton1 first and then through a heat-exchanger sitting in the blower exhaust from the motor because...



DavidDymaxion said:


> Electric motors can make ozone. In an extreme case, it can make smoke. You wouldn't want to be blowing those things into your car. You could make a heat exchanger to safely harvest the little bit of heat. A heat exchanger can be as simple as a fresh air hose inside of a hose that is exhausting the motor heat (or vice versa), kind of the like the heater on an old VW bug or Porsche.


...David makes a good point here! From seeing what goes on in the motor during dyno tests I definitely wouldn't want to be breathing the exhaust from one! Big clouds of black dust when I unload the motor and crank up the RPM (the point being to do just that - clear out all the carbon dust that had built-up from running at high-amps).

That said, the motor will dump about 1.5-7.5kW of waste heat on average, which is right in the middle of what the average vehicle's heater core can handle. The air -> liquid heat exchanger is the way to go, IMO, because the heater core - that uses liquid, duh - is already in place so no tearing apart the dash. 

Another advantage of this setup is that it is easy to insert an inline engine heater after the motor's heat exchanger but before the cabin's. This will help out on extra cold days and/or when the motor is delivering a low average power (because the roads are icy or the like). Something like that 1500W job they sell at Northern Tool (KAT is the brand, IIRC?).


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## DIYguy (Sep 18, 2008)

Thanks for the feedback everyone. I hadn't considered ozone or other contaminants.... Tesseract is right, heat exchanger would be way to go. As for available energy, I wouldn't consider capturing anything from the controller...it just doesn't generate anything appreciable. The drive motor though, definitely does. I would say it is blowing the equivalent of at least that of a 1000 watt heater. Using some numbers off the top of my head...even at 125 amps and with the chopper an average of say 90 volts (??) and a motor efficiency of 90 % (likely conservative numbers) thats the equivalent of 1125 watt heater. Drop a little for the exchange process and shouldn't I be able to get about 1000 watts out of it? Not bad I'd say.

I already have a 1500 watt in-line engine heater installed (not finished wiring yet).

As for measuring the air in vs out.... ya, I probably could. I like to do what I call the "sanity test". (stems from homework with the kids lol) Just a practical way to determine if you are in the "ball park". Like feeling the motor heat with my hand on it, and the temp of the air coming out of it. Compare it to a heater blowing in your car. It's not all that different. Now contrast that with the controller. I ran my truck up to 85 mph the other day (still had more ) and the controller was barely warm. After normal driving, it is not much different than ambient. I know it's cool out now in Canadian spring weather...but when it's hot out, I won't need this heat anyways.

The way the weather is right now, it would make a lot more sense to figure this out than run that 1500 watt heater and pump. 

kewl...


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## bipole (Sep 8, 2009)

I did some comfort experiments this winter with my girlfriend's 2001 diesel jetta in 30-45 degree weather. I tried driving her car for few days with no heater, only the heated seat. I was very surprised at how comfy I was.

I ordered a heated seat kit from Jegs for about $75 and it only took about two hours to install and wire it up in the GTM. It draws 3 amps on the high setting at 12 volts. In my opinion this is the best 36 watts spent on comfort by far. You just can't beat direct contact heat.


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## DIYguy (Sep 18, 2008)

bipole said:


> I did some comfort experiments this winter with my girlfriend's 2001 diesel jetta in 30-45 degree weather. I tried driving her car for few days with no heater, only the heated seat. I was very surprised at how comfy I was.
> 
> I ordered a heated seat kit from Jegs for about $75 and it only took about two hours to install and wire it up in the GTM. It draws 3 amps on the high setting at 12 volts. In my opinion this is the best 36 watts spent on comfort by far. You just can't beat direct contact heat.


Good point bipole, thanks. Of course one needs a heated blower of some description to clear the windshield as well as safety check/compliance.

Cheers,


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## GerhardRP (Nov 17, 2009)

Tesseract said:


> That said, the motor will dump about 1.5-7.5kW of waste heat on average, which is right in the middle of what the average vehicle's heater core can handle. The air -> liquid heat exchanger is the way to go, IMO, because the heater core - that uses liquid, duh - is already in place so no tearing apart the dash.


What percentage of the heat is generated in the field coils? 
I ask, because if the system already has a liquid loop, couldn't you wrap cooling coils around the motor directly and then the air cooling takes care of the comm and armature.
Gerhard


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## Tesseract (Sep 27, 2008)

GerhardRP said:


> What percentage of the heat is generated in the field coils?


I don't know, but an optimized design would split the losses evenly between the field and armature.


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## dimitri (May 16, 2008)

Have you considered how long you'd have to wait before you get any cabin heat from the motor? I have a temp gauge attached to my Warp 9 and it takes good 10-15 minutes before the motor "heats up". By that time you are half way to your destination. Not worth the hassle , IMHO.

Most heat is around commutator, outside casing is much cooler, which complicates things even more. Just wrapping heat exchange pipe around the casing would be useless, you won't even feel it by the time it comes to the cabin.

Just get a KATZ heater and fugetaboutit....


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## EVfun (Mar 14, 2010)

We have some waste heat and it's hard to capture because temperature is not that high and the air itself stinks (literally.) Perhaps it would be a good source of supplemental heat to improve the efficiency of a heat pump system to heat the cabin. The GM EV1 used a heat pump heating and cooling system.


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## DIYguy (Sep 18, 2008)

dimitri said:


> Have you considered how long you'd have to wait before you get any cabin heat from the motor? I have a temp gauge attached to my Warp 9 and it takes good 10-15 minutes before the motor "heats up". By that time you are half way to your destination. Not worth the hassle , IMHO.
> 
> Most heat is around commutator, outside casing is much cooler, which complicates things even more. Just wrapping heat exchange pipe around the casing would be useless, you won't even feel it by the time it comes to the cabin.
> 
> Just get a KATZ heater and fugetaboutit....


Hey Dimitri. I do have an in-line electic heater. I'm interested in capturing the motor heat. I did the "sanity-test" several times. There is just no arguing with the heat coming off the motor. There are lots of ways to look at it.... but I must say, I've seen more frivilous things pursued... lol 

Right now, I'm thinking to get a small heater core and capture the air exiting the motor to force through it. The liquide loop would be in series with the electric fluid heater as Tesserac described. I don't think I would pursue the tube wrapping the motor casing. (this is how some heat is captured from waste drains in engergy efficient homes though)

By the way, the electric fluid heater is not particularly fast heating up either. I tested it with 120 volts ac, I expect it will be faster/better with my pack dc power though.


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## DIYguy (Sep 18, 2008)

At the risk of highjacking my own thread....

As an aside and related to fluid heater... I was thinking about the whole fluid expansion (it does want to burst when hot...lol) in-line rad cap with overflow tank issue. (recall, I have an electric fluid heater). All my searching for in-line filler/pressure caps came up with units for rad hose size connection. Then it hit me.... liquid cooled motor cycles! I called a local one who boasts of a large scrap part supply. Beauty... 

Take a look. For $30 bucks even.... perfect!


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## JRP3 (Mar 7, 2008)

This one comes with 3/4" removable barbs that should fit the larger heater hose perfectly http://www.siliconeintakes.com/product_info.php?products_id=1064










$25 bucks.


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## dimitri (May 16, 2008)

DIYguy said:


> By the way, the electric fluid heater is not particularly fast heating up either. I tested it with 120 volts ac, I expect it will be faster/better with my pack dc power though.


I'm sure you already read all threads on the subject, but I will mention it just in case you missed it. DO NOT use this heater on DC without modifying thermostat curcuit. Thermostat in the heater was not meant to handle DC current. Open it up and wire thermostat thru low voltage into the heater relay.


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## DIYguy (Sep 18, 2008)

JRP3 said:


> This one comes with 3/4" removable barbs that should fit the larger heater hose perfectly http://www.siliconeintakes.com/product_info.php?products_id=1064
> 
> $25 bucks.


Yup, that's what I was looking for....lol Thanks! lol
I paid $15 for mine ($30 was for both), no shipping and I didn't have to wait which is nice.

We get shafted shipping stuff from US for customs cost...which really burns me too.


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## DIYguy (Sep 18, 2008)

dimitri said:


> I'm sure you already read all threads on the subject, but I will mention it just in case you missed it. DO NOT use this heater on DC without modifying thermostat curcuit. Thermostat in the heater was not meant to handle DC current. Open it up and wire thermostat thru low voltage into the heater relay.


Yes I did re-wire mine that way, but thank you for mentioning it here Dimitri, as you never know who may pick up on it.


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## DC Braveheart (Oct 12, 2008)

dimitri said:


> I'm sure you already read all threads on the subject, but I will mention it just in case you missed it. DO NOT use this heater on DC without modifying thermostat curcuit. Thermostat in the heater was not meant to handle DC current. Open it up and wire thermostat thru low voltage into the heater relay.


Hey Dimitri,

I'm thinking of going the Katz water heater route - I asked that question about the thermostat on another thread but never got a reply. Any chance you can post details on how to modify it to control the DC relay instead of the pack voltage?

Thanks


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## DIYguy (Sep 18, 2008)

DC Braveheart said:


> Hey Dimitri,
> 
> I'm thinking of going the Katz water heater route - I asked that question about the thermostat on another thread but never got a reply. Any chance you can post details on how to modify it to control the DC relay instead of the pack voltage?
> 
> Thanks


Hey DC, just open up the heater, remove the thermostat wires from the high voltage. Put this thermostat in series with the 12 volts going to your contactor control side...which switches the high voltage. It's pretty straigh fwd. So, if the thermostat is closed (normally open) and your heater switch is on, the contactor will get 12 volts which will energize the high voltage and presto! When water gets to temp..... thermostat will open, causing contactor to open.


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## DC Braveheart (Oct 12, 2008)

DIYguy said:


> Hey DC, just open up the heater, remove the thermostat wires from the high voltage. Put this thermostat in series with the 12 volts going to your contactor control side...which switches the high voltage. It's pretty straigh fwd. So, if the thermostat is closed (normally open) and your heater switch is on, the contactor will get 12 volts which will energize the high voltage and presto! When water gets to temp..... thermostat will open, causing contactor to open.


Thanks for the reply!


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## Yukon_Shane (Jul 15, 2010)

I'm pulling gems out of the DIYForum vault today

DIYGuy, did you ever pursue this "waste" motor heat recovery strategy? The approach makes alot of sense and I've been thinking about something simliar.

Like you, I'm using a Kat's fluid heater so if this air/water exchanger worked for you I might follow your example.


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## DIYguy (Sep 18, 2008)

Yukon_Shane said:


> I'm pulling gems out of the DIYForum vault today
> 
> DIYGuy, did you ever pursue this "waste" motor heat recovery strategy? The approach makes alot of sense and I've been thinking about something simliar.
> 
> Like you, I'm using a Kat's fluid heater so if this air/water exchanger worked for you I might follow your example.


Hey Yukon. No, I didn't build this system. That said, after a few years of driving I must say, that I haven't changed my opinion of it at all. In fact, I still think it is a great idea. I've designed it in my little brain, but side tracked with bigger things. My fluid heater works great and have had no issues with it. The control system of it is lacking though and I will pursue a way to reduce it's output as full on is just too much heat after several minutes. The waste motor heat would be perfect to maintain temps on most days. 
Capture the heated air with a plenum around the motor, duct through a smallish radiator in your fluid heater loop.


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## DJBecker (Nov 3, 2010)

It's not clear that it's a good idea.

You have less "waste" heat than you might think.

The temperature difference is doing useful work of moving the heat away from the hot spots. You have to be careful that you don't reduce the longevity and efficiency of the parts trying to move that heat into the cabin.

You often see this in the PC space, where someone has a "new" idea to use the waste heat from the CPU or GPU to run a thermoelectric generator or Stirling engine. Except that this runs counter to all of the effort spent trying to keep the parts cool. The trivial power they recover is more than offset by increased leakage current from the overheating silicon.

ICEs have lots of high quality waste heat. The combustion chamber metal surface temperature might be 350C. Coolant at 90C still has a big temperature difference to transfer lots of heat. In contrast, you wouldn't want to run your motor or electronics at a case temperature of even 90C. 60C might be a reasonable number, and that would result in a coolant outlet temperature of 30C-40C. Far from warm enough to heat a cabin with a stock size heater core.


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## DIYguy (Sep 18, 2008)

DJBecker said:


> It's not clear that it's a good idea.


perhaps not to you. Do you have an EV with a DC motor than you can check?



DJBecker said:


> You have less "waste" heat than you might think.


REad earlier in the thread, it's documented. It's enough to make a difference in most vehicles.



DJBecker said:


> The temperature difference is doing useful work of moving the heat away from the hot spots. You have to be careful that you don't reduce the longevity and efficiency of the parts trying to move that heat into the cabin.


The idea would be to move the exhaust air through a radiator and capture the heat. It's true that the air flow velocity/volume should not be reduced or you could run into cooling issues. As long as the air keeps flowing, the motor doesn't care what happens to the exhausted air or heat that may be in it. In my case I have a aux blower as well as the motor fan.


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## iti_uk (Oct 24, 2011)

DIYguy said:


> The idea would be to move the exhaust air through a radiator and capture the heat. It's true that the air flow velocity/volume should not be reduced or you could run into cooling issues. As long as the air keeps flowing, the motor doesn't care what happens to the exhausted air or heat that may be in it. In my case I have a aux blower as well as the motor fan.


What about just using a water-cooled motor? That would be one fewer energy transfer to lose efficiency through.

I agree that the motor temperature may not be as high as that of an IC engine, but it would certainly be better than nothing.

Maybe one could design a combination heat exchanger, where air is first passed through the coolant-circuit heat exchanger, then over an electric heater element. I'd imagine that this _could_ be more efficient than using an electric heater element on its own.

How about battery pack heat? Would liquid cooling the pack be worth a shot?

Another more advanced method would be use a heat pump system. The low pressure side would cool the motor while the high pressure side could be used to heat the cabin, just like an inverted A/C system. Of course, the pressure and working fluid choices would have to be calculated for the ideal running conditions of the motor and the cabin heater requirements, but I'd imagine that it could work...

Chris


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## lithiumlogic (Aug 24, 2011)

I think this is easier to do if you got an AC motor, since then there will be no arcing brushes, and no ozone - you can just duct the cooling air that has been through the motor into the cabin. After all, the air coming out of a hoover is warm but doesn't stink of ozone, just the nasties from the dust bag.

Since you're using air, things should get warm quicker than with a water circuit.

Of course, a greater portion of the heat is dissipated in the controller in an AC system, so you'd want to capture this as well.

EV waste heat is lower grade than ICE waste heat of course, but i think a recirculate function could help here. For example, if it's -15C outside and you blow this air over motor coils at 40C, you get "heated" air at 15C - which still feels damn cold, and that heater fan is just making a wind chill factor in the cabin. You dont want the motor coils hotter than 40C when driving gently in the winter, in case it gets dangerously hot when goosing it in the summer.

But, if you recirculate the cabin air it should get up to a tolerable temp after a few passes through the cabin. I don't know what climatic conditions you experience in other parts of the world, but in the UK frosty mornings are generally pretty dry. On my ICE car, i find myself using recirculate mode for the first 20-25 minutes to get temperatures bearable, fogging is only a problem if i keep it on after that, by which point the engine is hot enough to warm up even sub-freezing outside air.

My "back of an envelope" scheme for doing this -

1. Air Intake in cabin (footwell?)

2. Diverter valve for recirculate function. When you're cold, 100% of the cooling air for the motor comes from the cabin, when you're warmer, it can be fresh outside air.

3. Air ducted through the controller heatsink

4. Air passed through the motor

5. Blower fan - speed is controlled by a thermistor on the motor or controller.

6. Another diverter valve. If you've got recirculation turned off and are still too warm, you can start dumping the heated air overboard, otherwise it continutes on to 7..

7. ceramic heater element. For the first couple miles, even with 100% recirculate the air coming out of the vents might still feel too cold, so you can turn on your ceramic heater

8. air distributed to cabin vents


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## DJBecker (Nov 3, 2010)

DIYguy said:


> perhaps not to you. Do you have an EV with a DC motor than you can check?
> 
> REad earlier in the thread, it's documented. It's enough to make a difference in most vehicles.


Where is it documented? There are posts where people think it might be a good idea, but no one talking about staying toasty warm while silently cruising past polar bears in a blizzard.

Ours is a series DC motor with a MOSFET controller. Everything is air cooled. We haven't seen a good way to use waste heat without a heat pump.

We made up a test cold plate using copper tubing pressed into a milled channel, but didn't put it into use. That was partially motivated by the lack of useful heat, combined with the hassle of liquid cooling while still experimenting with our controller. We're more motivated to add fan speed control to keep it cool during hot days than try to gather the minimal warmth when it's cold.


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## DIYguy (Sep 18, 2008)

DJBecker said:


> Where is it documented? There are posts where people think it might be a good idea, but no one talking about staying toasty warm while silently cruising past polar bears in a blizzard.
> 
> Ours is a series DC motor with a MOSFET controller. Everything is air cooled. We haven't seen a good way to use waste heat without a heat pump.
> 
> We made up a test cold plate using copper tubing pressed into a milled channel, but didn't put it into use. That was partially motivated by the lack of useful heat, combined with the hassle of liquid cooling while still experimenting with our controller. We're more motivated to add fan speed control.


No one said toasty warm. It was a discussion based on something considered to be worth doing. 
Tesseract made comments on the amount of useful heat. 
"That said, the motor will dump about 1.5-7.5kW of waste heat on average, which is right in the middle of what the average vehicle's heater core can handle. The air -> liquid heat exchanger is the way to go, IMO, because the heater core - that uses liquid, duh - is already in place so no tearing apart the dash. 

Another advantage of this setup is that it is easy to insert an inline engine heater after the motor's heat exchanger but before the cabin's. This will help out on extra cold days and/or when the motor is delivering a low average power (because the roads are icy or the like). Something like that 1500W job they sell at Northern Tool (KAT is the brand, IIRC?)."

It's not too hard to calculate either. Now capturing controller heat is not worth the effort. . . I agree with that.


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## Yukon_Shane (Jul 15, 2010)

The "back of the envolop" calculation seems pretty promising to me. 

If you figure you cruise down the highway using anything over 100 amps at 150 volts thats 15kW of power being used through a motor that's probably less then 90% efficient which means it produces atleast 1.5 kW of heat.

Most conversions that have cab heat installed seem to get by with 1.5 kW ceramic heaters. That's not to say that this would be enough to meet all of your heating needs but it's certainly atleast 50% and it's going to save you 1.5kW of battery power on cold days. 

Besides cabin heat you've also got to consider battery heat on cold days. Not only do I need to be kept warm but my battery back needs to be maintained at probably something close to 0C which can be a challenge when the outside temperature is -30C. If I can insulate my pack and use the waste motor heat to help bring the pack up to 20-30C over the course of my commute it might just stay above 0C while I'm at work.


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## Yabert (Feb 7, 2010)

Yukon_Shane said:


> Most conversions that have cab heat installed seem to get by with 1.5 kW ceramic heaters. That's not to say that this would be enough to meet all of your heating needs but it's certainly atleast 50% and it's going to save you 1.5kW of battery power on cold days.


Number seem impressive (1500-2500w of heat) but this one can be realy hard to entirely transfer inside cabin by the heat exchanger.
I think you can waste many time and money to recover only fraction of heat lost by the motor.


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## Ziggythewiz (May 16, 2010)

Yabert said:


> Number seem impressive (1500-2500w of heat) but this one can be realy hard to entirely transfer inside cabin by the heat exchanger.
> I think you can waste many time and money to recover only fraction of heat lost by the motor.


I think the biggest issue is where you're sourcing your air from. A cabin heater works by recirculating the same air over and over, while heating it. It has to get warmer.

A motor cooling system works by taking fresh air (presumably cooler than your cabin before you start heating it) and pushing it through in large volumes to remove some of the heat. I really doubt that in one pass it will become warm enough to warm your warmer cabin.

Let's say its 0F outside and your small heater makes it 40F inside. Good chance the air blown through the motor comes out 10-20F, so is that going to heat, or cool your 40F?


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## DIYguy (Sep 18, 2008)

Ziggythewiz said:


> Good chance the air blown through the motor comes out 10-20F,


I just love it when ppl pull this stuff out of their hat. More typing urself smart. Here's a tip. Don't do it!  
I think the hottest air is coming from you.... lmao


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## DJBecker (Nov 3, 2010)

DIYguy said:


> I just love it when ppl pull this stuff out of their hat. More typing urself smart. Here's a tip. Don't do it!
> I think the hottest air is coming from you.... lmao


Throwing it back at you: have you measured it? The output CFM and temperature rise? And how much useful cabin heating you can get out of it?


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## DIYguy (Sep 18, 2008)

DJBecker said:


> Throwing it back at you: have you measured it? The output CFM and temperature rise? And how much useful cabin heating you can get out of it?


Ur asking the wrong guy. I didn't quote temp rise numbers. My claim was simple. Enough energy to supplement cabin heat. You two fine gentlemen are disputing the claim. That's fine, free country. However, don't pull numbers out of ur hat to do it. 
Look, we know motor efficiency. We know energy input. We know that most of the heat comes out the air discharge holes. If it didn't, how long do you think the motor would last? I've felt mine at least a hundred times. Even with heat exchange efficiency losses it would still be an awesome supplement. Here in Canada, I crank on 4.5kw of heat. After about 7 minutes, I have to turn it off. 1 kw would be fine to maintain temps on most days. 
Another interesting thing is that lower ambient temps don't seem to effect the motor temp all that much. (yes, I measure it  ) I've heard others comment on this also.


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## Yukon_Shane (Jul 15, 2010)

Ziggythewiz said:


> I think the biggest issue is where you're sourcing your air from. A cabin heater works by recirculating the same air over and over, while heating it. It has to get warmer.
> 
> A motor cooling system works by taking fresh air (presumably cooler than your cabin before you start heating it) and pushing it through in large volumes to remove some of the heat. I really doubt that in one pass it will become warm enough to warm your warmer cabin.
> 
> Let's say its 0F outside and your small heater makes it 40F inside. Good chance the air blown through the motor comes out 10-20F, so is that going to heat, or cool your 40F?


Any cabin heater I've seen takes air from outside and runs it through the heater core and circulates it through the car. I've never heard of the heating system using recirculations to increase the heat of the cab air. That's typically something used in air conditional systems to keep the cab cool by recooling the air that's already at a lower temperature then outside.

I wouldn't say this definitively but I think that recirculating hot air within a cab on a really cold day would result in a lot of moister building up causing your windows to fog up.

It's unseasonable warm here right now (-2C) but I'll try my recirculation setting the next time it gets cold and see if I can confirm this suspicion.


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## somanywelps (Jan 25, 2012)

I've considered this and it appears to me that it will only be effective on Water-cooled BLDC and AC motors, where a radiator diverts the heat into the cabin from just dumping it.


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## JRP3 (Mar 7, 2008)

Something to consider, and it can probably be calculated, with a DC motor you need one heat exchanger to get the heat out of the motor cooling air and then you'll have another heat exchanger in the heater core, what are the transfer efficiencies of those two devices? If you have 1.5kw of motor heat how much is actually usable after the heat exchangers and plumbing? Plus as someone mentioned earlier it's going to take some time for the motor to warm up before you get any usable heat from it.


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## Ziggythewiz (May 16, 2010)

DIYguy said:


> Ur asking the wrong guy. I didn't quote temp rise numbers. My claim was simple. Enough energy to supplement cabin heat. You two fine gentlemen are disputing the claim. That's fine, free country. However, don't pull numbers out of ur hat to do it.


I was making up numbers to illustrate the point. The numbers aren't measured, but they will be relative. I thought that better than saying, temp in will be something, out will also be something...etc.

My ultimate point is that if you're getting air from the outside, and putting 1500W of heat into it (from motor or heater doesn't matter) it's the equivalent of driving with the window down and a hair dryer going.


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## Ziggythewiz (May 16, 2010)

Yukon_Shane said:


> I've never heard of the heating system using recirculations to increase the heat of the cab air. That's typically something used in air conditional systems to keep the cab cool by recooling the air that's already at a lower temperature then outside.
> 
> I'll try my recirculation setting the next time it gets cold and see if I can confirm this suspicion.


So you've never heard of a heater with recirculation, but yours has it?

Most cars I've had have a recirculation option, it will make it heat or cool faster. Yes, it will get stale and may increase moisture, usually you don't use that setting with the heater because an ICE has so much heat to waste anyway.


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## Yukon_Shane (Jul 15, 2010)

Ziggythewiz said:


> So you've never heard of a heater with recirculation, but yours has it?
> 
> Most cars I've had have a recirculation option, it will make it heat or cool faster. Yes, it will get stale and may increase moisture, usually you don't use that setting with the heater because an ICE has so much heat to waste anyway.


I didn't say I hadn't heard of recirculation I said I'd never heard of it being used for heating.

With all due respect I've been driving in arctic conditions for 20 years and I don't know anyone who uses there recirculation during heating. I can confirm definitively that it is not required and probably counter productive due to increased window fogging.


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## JRP3 (Mar 7, 2008)

I always start out using recirculation with heating, I figure it's better to use the warmer cabin air recirculated than the cold outside air, until the motor warms up, or I start fogging up, whichever comes first. Usually fogging is not a problem.


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## EVfun (Mar 14, 2010)

A lot of modern cars involuntarily turn on the AC if you switch any defrost setting. That allows recirculating air to work a lot longer. I often deliberately do that in the mornings when I drive my Toyota to work. Many older cars have no recirculating air option but I've never heard of a car with no fresh air option.


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## JRP3 (Mar 7, 2008)

Yeah I hate that automatic A/C engagement on defrost since it's often not needed and wasteful, luckily I can override it in my car.


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## tomofreno (Mar 3, 2009)

DIYguy said:


> The idea would be to move the exhaust air through a radiator and capture the heat. It's true that the air flow velocity/volume should not be reduced or you could run into cooling issues. As long as the air keeps flowing, the motor doesn't care what happens to the exhausted air or heat that may be in it. In my case I have a aux blower as well as the motor fan.


 I agree with JRP3 that losses will reduce the amount of heat introduced into the cabin significantly, plus in cold weather my motor only gets into the mid-30's C at most, and barely warms on short trips. If you wanted to capture the heat, I think it would be best to use a water-cooled motor and run the output through your existing heater with well-insulated motor jacket and lines then into the core, then through an outside heat exchanger to cool it further before sending it back to the motor. Similar to using solar to pre-heat water to your normal hot water heater in winter. The heater loop could be bypassed with solenoid operated valving for summertime operation, and the outside heat exchanger could be bypassed for winter operation as long as the motor did not get too hot. You could do similar with air, but I think it would be easier to insulate water cooling than air cooling from the cold breezes under the hood while driving and heat transfer to liquid should be more efficient so it would have less effect on motor temperature, although in winter I don't think that would be an issue. 

I'm not sure it is worth the cost/effort, but it would make use of some of the otherwise wasted energy.


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## DIYguy (Sep 18, 2008)

OK, its a dumb idea and it wont work. It wont work because its not a water cooled motor (big hint here, it wasn't about water cooled motors). . . and it won't work because of heat exchanger efficiency loss.. . never thought of that, (btw, u really only have to worry about the first heat exchanger loss. . . cause the second one is in a close loop and u get to circulate it as long as u want) and it wont work because the motor doesn't heat up right away (I'm glad someone thought of that. .. because I had no idea). . . and it wont work because of a bunch of other reasons that someone hasn't thought of yet. However, if we keep typing long enough, I'm sure we can come up with enough other reasons to keep anyone from doing it....  or not. We have figured out worse case on everything so far. . . hmmmm excellent. 

No shortage of sarcasm here guys..  keep er comin'.


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## iti_uk (Oct 24, 2011)

I'm sure it would be a sound idea to supplement an HVAC primarily heated by an electric element. Obviously this would only be useful once the motor is up to temperature, but a little useable otherwise-waste-energy is better than nothing, especially if the motor is water-cooled anyway - better to have the option to at least contribute to the heating of the cabin instead of dumping any coolant heat to the outside atmosphere...

I just think that this would require a water-cooled motor instead of an air-cooled motor, and not on it's own - the electric heater would be required, I believe.

Alternatively, just have the motor un-ducted but un-partitioned from the main cabin space. Direct heating of the air would result, but you'd have to live with high power electronics close by with no firewall or similar.

Chris


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## JRP3 (Mar 7, 2008)

DIYguy said:


> OK, its a dumb idea and it wont work.


I guess it depends on what you define as "working". Every time I open my hood on a cool day and feel the motor and controller heat I think "Damn, it would be nice to put some of that into the cabin." Then I think about what is involved in doing so, and how much it might actually change the cabin temps, and I move on. But I understand the temptation to tap into the free heat.


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## DIYguy (Sep 18, 2008)

JRP3 said:


> I guess it depends on what you define as "working". Every time I open my hood on a cool day and feel the motor and controller heat I think "Damn, it would be nice to put some of that into the cabin." Then I think about what is involved in doing so, and how much it might actually change the cabin temps, and I move on. But I understand the temptation to tap into the free heat.


Good point. Now u should feel mine. u run an AC set up in a small car. I run a 9" dc (for now) in a 4200 lb truck. I can tell u that mine pumps out some heat... lol The unfortunate part is, the 13" will have a much longer delay than the 9" so.... different again. Point is... there are different size shoes here feet... er um I mean people. 
With my current set up, I don't think it would be a huge amount of work as it has this nice flange around the DE and adding a capture plenum would be pretty easy. If I was leaving the 9" set up, I would give it a go, just to poke fun if nothing else. Not sure it's worth it with the 13". A lot more work too I think. Oh well, someone may find it helpful . . or perhaps inspiring is a better term..


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## TigerNut (Dec 18, 2009)

One could use a small air to air intercooler core to preheat the cabin air using the output from an aircooled motor... That would avoid one round of efficiency losses.


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## JRP3 (Mar 7, 2008)

Assuming you can fit ducting large enough to transfer a significant amount of heat.


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## lithiumlogic (Aug 24, 2011)

Thread necromancy! Well only 6 months' worth of necromancy..

I guess we'll just have to wait till someone builds an AC system with recirculated cabin air for cooling. So long as they post every few months to let us know they still have no respiratory diseases.

I don't get with the "your motor takes 15 minutes to warm up, by which time you're nearly there anyway". 

1) If you're concerned about still having to use resistive heat for the first 15 minutes of your journey, can you rig a cabin heater circuit to come on an hour before you set off for work in the mornings, that will largely take care of the first 15.

The corollary of this argument is that recycling motor heat only helps on the last 15 minutes of your daily commute.

2) Indeed, and your daily commute uses less than half the pack anyway, so who cares? 

My daily commute is 50 miles, so i could afford to do it with the heater blazing, windows wide open, at 80mph in a string vest and a pair of Y fronts.

The crunch time for an EV would be the annual driving home for christmas scenario. 180 miles in the winter, at night, on the motorway (say 55mph in the slow lane).

If I can save 1.5 Kw on heating each hour for the 3hours of this journey, and keep my cells warm, that's significant. Even if i have to use a resistive heater for the first 15 when the motor is cold.

I'd also want to make sure i'm using HiD lights, perhaps.

OTOH, it's also a scenario that makes the choice of AC motor questionable.

I can manage my daily commute without regen. The Xmas drive is highway, and only has opportunity for regen on the first and last couple of miles. An AC 50 setup isn't significantly different in price to a Netgain 9" & Soliton combo, but is lower peformance.


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