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Old 12-15-2008, 06:38 PM   #1 (permalink)
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Electric car heat! Liquid?

Hey EVeryone!

I got my Electric Geo Metro back on the road today!

Unfortunately, it was really cold out! - 2 degrees at my place this morning!

I have minimal heat in the car right now.

I have experimented with just placing an oil-filled electric radiator in the back of the car, and having it set on a timer to start heating in the morning an hour before I would leave.

This seems to work fairly well in that the interior of the car is already warm. The seat, steering wheel, and glass is already relatively warm, and none of the battery capacity was used to create that heat.

Since the car was originally designed to use heat from the engine, transported by liquid, exchanged into the interior of the car, I was thinking it should be fairly easy to do a similar heat system in my electric conversion.

If I installed an insulated coolant tank in the car, it could have an AC electric heating element inside it. The n, coolant could be heated in the tank from wall power, using a time, while the car is parked in my garage.

A 12V heating element could also be in the coolant tank, to heat it while driving, or on the return trip home at the end of the day when the car wasn't plugged in.

I know most EVers use some form of electric heat for defrosting a car, as it is simple and compact. However, my car has a relatively small 72V battery pack. By using a liquid system, I would be able to carry with heat that came straight from the wall, instead of from the battery pack.

I have followed some information on a similar thread on an EVer forum, but I want to get YOUR input.

Any thoughts on this idea? How to make it simple and inexpensive? Let me know! It's cold outside!!!


EDIT:
Here is roughly what I am thinking.

I don't know the exact size needed for the tank, maybe 2 gallons or so? Can't be too big to fit in the car!

I am also not sure if it needs a pump, or if the system could be driven by convective currents. Reading about in-line heaters on this forum seems to indicate that they are typically installed to circulate coolant using convection.

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Last edited by bennelson; 12-15-2008 at 06:52 PM..
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Old 12-15-2008, 07:28 PM   #2 (permalink)
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The system will have to use a pump if you want a decent thermal exchange rate. It won't need to be much of a flow rate though, so a low-power pump or even a hand-operated pump will do fine.

A hand-operated pump would make "crank up the heat" a rather literal command.

Last edited by captainslug; 12-15-2008 at 07:51 PM..
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Old 12-15-2008, 07:49 PM   #3 (permalink)
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A setup like this would hold a lot more energy than adding a few batteries for an electric heater. Its not a simple setup, but it would be a good one IMO.
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Old 12-15-2008, 08:42 PM   #4 (permalink)
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Call me crazy, but I believe a large, insulated, container with a built-in AC heater element is the definition of a church coffee pot!

Maybe I can dig one of those up at the thrift store and put a 12V pump on it!!!
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Old 12-15-2008, 08:49 PM   #5 (permalink)
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Yeah, they're called Coffee Urns, ironically. 2 gallons is more than your original coolant system held, so it's probably sufficient.

What are you using to bleed heat from the e-motor you have?

If you're already bleeding heat from there, you could always duct it back through the cabin air filter housing and have semi-free heat, since it's heat that's already being generated.

If you're not bleeding that heat off the motor, maybe a motor cooling system is in order? You could use the circulation of your coffee urn cooling system to help cool the motor too, I would say, and that would add a little extra heat to the coolant, making it warmer for the occupants.

Food for thought.
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Old 12-15-2008, 09:05 PM   #6 (permalink)
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No need to "bleed heat" from the motor.

It doesn't get hot. Period. Especially in winter.



OK -back to experimental mode!

A Mr. Coffee Brand Tea Maker

Holds about a quart, and will heat that water to just under 200 degrees f. in about 5 minutes.

On the bottom, it's marked as 700 watts. It was confirmed as 680 watts with my Killawatt.



Of course the tea machine is a bit small to use by itself for an EV heater, but seems like 700 watts would be plenty of power.

To go bigger, something like this could be used.



That's my mother's coffee urn (used for tea) which I had borrowed for the weekend. She loves it, her only complaint is that it gets TOO HOT. I looked on the bottom of the urn. Guess its power rating. 1000 watts!

We are definately talking block-heating power!

Just imagine that coffee urn, unsulated, with a circulating pump! Sounds like a liquid heating system to me!


PS: No, I can't actually use that particular urn,...my mother would kill me!
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Old 12-15-2008, 09:06 PM   #7 (permalink)
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Quote:
Originally Posted by bennelson View Post
A 12V heating element could also be in the coolant tank, to heat it while driving, or on the return trip home at the end of the day when the car wasn't plugged in.
Or maybe two insulated tanks? Large tank & small tank both heated by power from the grid. When car has sat unplugged for a long, long time = no heat stored in insulated reservoir tanks, close valve to take large cold tank out of loop? 12V heat element in small tank. Haven't really thought out the plumbing.
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Old 12-15-2008, 09:12 PM   #8 (permalink)
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Coolant will presumably be some sort of anti-freeze so boiling point will be above 212*F
Automotive cooling systems are normally pressurized, which also pushes up boiling point.
Needless to say, the more heat you can store, the better.
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Old 12-15-2008, 10:13 PM   #9 (permalink)
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Of course you realize that I now have to take Mr. Tea apart (I pity the fool!)

The bottom uses square drive screws to discourage tinkers from taking the pot apart, electrocuting themselves, and suing the company.



Fortunately, I have a set of square drive bits!

Once the heating element is removed, you can see there are only a few parts inside- the heating element, a light, and some sort of a thermo-switch.





The two short pieces of rubber tube you see connect into either end of the "horseshoe" of the heater. The whole thing is one piece of aluminum with the heating element on one side, which conducts heat into the tube the liquid goes through.

Pressure from the weight of the water in the pot pushes down into the bottom of the horseshoe, where it is heated. When it gets hot, it has no place to expand to other than out the other side of the horseshoe, up a tube, and out the pot into the carafe you set next to it.

Now I have to test the heater out to see it in action without all that white plastic in the way. I loaded the heater tube with water using a kitchen baster and plugged the device into a GFI-protected outlet. (Kids, don't try this at home!)



The heater VERY quickly boiled off the water. This made lots of steam and frightened my wife. ("You might want to step back....") But once it boiled off, the thermo-switch popped and the red light turned off.

This makes me think that the switch is a temperature safety of sorts. You plug the tea pot in, and it cooks the water until it's all gone, at which point the temperature sky-rockets, causing the thermo-switch to kick out.

Does anyone know of resistive heating elements like this care what voltage is going through them? Or if it's AC or DC? I don't think it matters, but I am far from positive.

Anywho! I don't see why I can't just plumb an insulated container of coolant to run through this heater, through the heater core, and back into coolant tank. I think it could be set up so that convection moves the coolant while it heats. While running the heater in the car, I would need a pump to circulate the coolant to exchange heat to the heater core.

While just parked and running the heater, some heat should radiate out the heater core and pre-warm the cabin.

Sound workable? Your thoughts?


PS: The resistance of the heating element was 19.3 Ohms.


EDIT: YOWZA! I just thought to stick my kitchen instant read thermometer directly into the heating element. It instantly spun all the way twice around the 200 degree F. scale. It must be about 450 degrees inside the heater!
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Last edited by bennelson; 12-15-2008 at 10:42 PM.. Reason: thermometer test!
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Old 12-16-2008, 02:11 AM   #10 (permalink)
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Hmm, Mr Tea. Put a cup or so of COLD water (that's what the direction in the new package will call for) in the reservoir. Hit the power button. The element heats water sourced from the reservoir and emits it through a tube to the external (out of loop cup). As the reservoir nears empty the heating element becomes so hot that it triggers the safety cut off switch.

Suggest you (at your own risk of course) put the heater back in the pot. Fill the pot with 50/50 antifreeze. Hit the button. Using two cups keep pouring partially full hot cups into the reservoir - to simulate recirculating closed system. What temperature does the reservoir reach when the safety switch turns off? That's assuming it does shut off before AC cord becomes uncomfortably warm (definitely monitor) or you pop a fuse/circuit breaker.

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