# Advice on getting heat into the cabin?



## dougingraham (Jul 26, 2011)

I bought a couple of ceramic space heaters and reused the elements. In my case I put them where the AC evaporator was in the original fan flow. I had two easy choices at my pack voltage. About 1000 watts and 4000 watts. I decided to try the 1000 watts first. 1000 watts is barely enough to clear the fog off the windshield. It takes 15 minutes of driving to take the edge off the cold which is about how long my commute takes. I have been considering increasing my pack voltage which would automatically increase the heater wattage. I probably wont do that until next summer so I may pull it out and rewire it to get 4000 watts.

I believe I had some photos in the what did I do to my electric car today thread a couple of years ago. This is DIY low budget stuff as I spent about $50 on a contactor and $30 for the two space heaters. Oh, I have a fuse on it too. I think that was another $30.

Unless your temps never get below 40 F you will need more than 1000 watts.

Best Wishes!


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## bigmotherwhale (Apr 15, 2011)

If i were you i would get the most compact and powerful storage heater you can find or make, and connect it to a system that powers it up when you are on regenerative braking, this way you wont waste power.

you could even use pettier elements to extract heat from your power train and heat the cabin if you were so inclined, it would be more efficient than simply resistive elements.

the other option is to use a refrigerant and a compressor and run it in reverse, this system would be the most effective and efficient you could make especially with a well set up scroll from a prius etc, you can also use the cold side to cool your power train. 

speaking of which i know there wont be much heat from your motor or controllers but could you plum the cooling lines into a heat exchanger in the cabin?


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## Duncan (Dec 8, 2008)

Hi Glndwr
The most efficient use of electricity is to get some seat warmers
In a comfort v watts comparison seat warmers are the winner!


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## Moltenmetal (Mar 20, 2014)

Logical thing is to preheat your car whenever possible using line voltage. If you use it for a commute, a line voltage driven heater on a timer would greatly increase your comfort without a major drain on your batteries. Otherwise a ceramic heater is a typical solution. Just be aware that whatever contactor you use will need to be able to extinguish an arc from your rather high DC voltage, and the protective equipment in that ceramic heater (thermoswitch and thermal fuses are typical) will NOT be up to the job of stopping a 230 VDC arc. My 105VDC pack melted a 230 VAC 40A relay while trying yo stop current through a a 700W hairdryer. The contactor I have in there now has two sets of contacts in series and a very long throw, so it works great at stopping the arc.


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## glyndwr1998 (Apr 27, 2013)

Thanks for the replies gentlemen,

Molten metal, great info there in the DC arc, something to consider.
I have a few weeks before I need the heat here in the UK, although we are a warmer climate than others, in winter the screen will require defrosting many times, otherwise the seat warmers would have been an ideal compromise, it's a shame the Prius didn't come with a heated front screen, I did hear somewhere that ford has a patent on heated front screens?

Thanks again, any quick easy solutions out there I'm still eager to,listen?

Thanks.


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## glyndwr1998 (Apr 27, 2013)

Hi bigmotherwhale,

This project is for my plug in Prius, I have a 16kwh battery fitted to it so most of my miles are in ev mode, hence the heat requirement.
Also, most of my journeys are short ones, maybe 4 miles, so even if I was to drive in hybrid normal mode by the time I get to the destination the engine is still not hot enough to generate heat.
I realise they are short journeys and some will say man up and wear extra clothing gloves etc..... But it's more for the defrosting of the screen and when it's wet to demist, and it does get very wet here in the UK, so de misting is more of an issue than heat, if it was only heat I would definately get the seat warmers.
Is there an easy way to turn my Prius existing air con ( that is working very well) into a heat pump?

Thank you





bigmotherwhale said:


> If i were you i would get the most compact and powerful storage heater you can find or make, and connect it to a system that powers it up when you are on regenerative braking, this way you wont waste power.
> 
> you could even use pettier elements to extract heat from your power train and heat the cabin if you were so inclined, it would be more efficient than simply resistive elements.
> 
> ...


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## Duncan (Dec 8, 2008)

Hi Glynd

Your air con will be very useful in de-misting your screen as it can dry the air out before blowing onto the screen
I don't think you can simultaneously use it to dry the air and heat the air so you should use the air con for the largest energy requirement which is to dry the air,

You then need to heat the dried air before blowing on the screen


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## piotrsko (Dec 9, 2007)

Here in the US, someone was making defrost replacement grids. A company called j.c.Whitney had then for order. Stick one on the front glass.


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## Moltenmetal (Mar 20, 2014)

I have a Prius base model gen 3 and a Prius C, and I'm not sure about the C but I was quite sure that I read that the gen 2 DOES have electric heaters for windscreen defog- fair sized ones, around 400 W each.


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## bigmotherwhale (Apr 15, 2011)

Yes there is a way of using the air conditioning to heat the cabin, quite simply turn the system around so the condenser (the hot part) is on the inside
and the evaporator (cold) is on the outside preferably somewhere where it can cool something that gets hot like a motor or controller. 

In a system like this you will pump at least four times the amount of heat than the electricity needed to generate it. you wont need to run the system for very long to heat the cabin, you should be dissipating a few KW of heat. Turn the AC on and see how hot the condenser gets.

I would advise speaking to a refrigeration genius, go find a forum and tell them what you want to achieve, it may be a case of simply reversing the flow so the expansion valve is used in reverse and refilling the system. It is possible to make an air conditioner with valves so you can choose which side is hot and cold so i see no reason why it cant be done here. 

http://www.heatpumps.co/About Heat pumps/files/page3-coolingheatingcycle2.jpg

In my greenhouse i have an old fridge insides with the evaporator buried outside in the ground, i used to run a resistive heater to do the same job, now i use alot less power as heat is being moved around not created by simply wasting power using a resistor.


Another thing, i live in the UK also and i know what its like with the windows, especially with a leaky car, I saved all the little packs of silica gel that you get in shoes and electronic stuff and put them in a sock in the car. it did actually help now i see they are selling something exactly the same in halfords, might be worth a go. 

You know the old VW beetles used to run a heater from the exhaust, they were the only car ive seen that you can get heat a few seconds after starting it, didn't smell to nice however!


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## glyndwr1998 (Apr 27, 2013)

Hi all, 

I saw on eBay a defa termini 1350 heater these are designed to preheat a cabin of a vehicle in very cold climates, 230v AC 1350watts, it was cheap but here's the thing. I was going to just plug it into my 250vdc pack with an inline fuse, and give it a go, ...... Until......
I watched a video on YouTube of switching high voltage DC, and to be honest it frightened the pants off me. A guy with a knife type switch videoing th arc with 220vdc, it was an eye opener watching the arc with the switch away from the contact by about an inch, and the arc was terrific.

So, won't b doing that then.

Is there an easier way to switch DC.

I Do like this little heater, it's compact, made to work inside a car so that's also good, but I'd need to find a way to switch it on safely, or buy a 12v to 1500w DC to AC inverter and connect that to the 12v battery, only then that poses another question, can the small 12v battery in the Prius take to load of a 1500w 12v inverter.
something that sounds so easy to do, in reality is a difficult task, that could cost a fair chunk of money

Anthony.




Moltenmetal said:


> Logical thing is to preheat your car whenever possible using line voltage. If you use it for a commute, a line voltage driven heater on a timer would greatly increase your comfort without a major drain on your batteries. Otherwise a ceramic heater is a typical solution. Just be aware that whatever contactor you use will need to be able to extinguish an arc from your rather high DC voltage, and the protective equipment in that ceramic heater (thermoswitch and thermal fuses are typical) will NOT be up to the job of stopping a 230 VDC arc. My 105VDC pack melted a 230 VAC 40A relay while trying yo stop current through a a 700W hairdryer. The contactor I have in there now has two sets of contacts in series and a very long throw, so it works great at stopping the arc.


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## Moltenmetal (Mar 20, 2014)

If you use the little AC heater from the AC mains (on a timer, to preheat your car before you drive), it will work great.

If you try to operate that heater off DC, you will need to:

1) Verify that the fan unit will operate off DC. The hairdryer I'm using has a DC motor with a diode, and operates from a reduced voltage by means of a tap in the resistance coil of the heating element, so it works fine off DC. However, a small ceramic space heater will have a shaded pole motor which will NOT work from DC- you would in that case need to replace the fan and/or motor in the unit 
2) Remove the thermostatic switch, and any low-high type switch, as these will NOT shut off a DC current.
3) Operate the heater with a proper, DC-rated contactor or DC-rated solid-state relay, fed by a correctly sized DC rated fuse to protect your wires.
4) Provide some other means of temperature control, i.e. one that operates that relay, preferably with a great big temperature deadband so that you don't have it cycling on and off too frequently and cooking your relay's contacts.

Note that some fan-type heaters want the fan to be kept running while only the element is switched on and off for temperature control. Wiring that kind of arrangement up is more complex, but not that difficult.

The right contactor WILL shut off a DC arc, so no need to be scared about it. My surplus relay, although it did not have a DC rating, definitely has no trouble snuffing a DC arc of 105 V. But the AC rating of a contactor gives you no useful information about what, if any, DC voltage and current it is safe to use.

If you use a DC rated solid state relay, you will need to be careful here too- those relays do have a finite probability of a 100% on-state failure. You need to protect against that to prevent a fire. The nice thing about solid state though is that they'll have no real problem with cycle life.

The heater itself probably also has a thermal fuse mounted somewhere near the heating element, which may or may not be up to the job of shutting off a DC current. A thermal fuse on a mechanical contactor's coil is a good overtemperature protection circuit for this application.


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## piotrsko (Dec 9, 2007)

Chevy Volt packs use a 400v 400(?) Amp relay from panasonic as an emergency disconnect or possibly the mains disconnect. P/n AEV14012 M05. I have seen them on fleabay for about 100 USD. If I recall correctly they are rated 10,000 operations, hydrogen quenched contacts. If that isnt big enough your Google foo is very weak.


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## z_power (Dec 17, 2011)

For HV switches you can snip Prius main contactors (400V, at least 60A continuous) from ~$25 at eBay... search term "prius relay" or "hybrid relay".


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## bigmotherwhale (Apr 15, 2011)

I used to run a 1000w inverter driving a hair-dryer to defrost demist the windscreen on cold days, it does work for a short while enough to demist even from the small battery in a micra.
it did the job, but terribly wasteful. 

using a prius contactor would work great but seems overkill to me, a small solid state relay or even a pre charge relay could do the same job?


did you consider the idea of trying to plumb a 4 was reversing valve into your air conditioning system?


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## piotrsko (Dec 9, 2007)

Every solid state relay I have EVER used failed at about 30% rated watts. Didn't matter how well heat sunk, they either failed at rated voltage or rated current.

Had a 480 v at 100 amp fail on 120 v at 2 amp.

Didn't know the prius ones were that cheep. Thanks


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