This idea started out as a way to provide the Prius PHEV (aka "PIP") with a heater that doesn't rely on the gasoline engine starting and running, but I soon realized, as I imagined a more portable version, that it can also work for the Leaf. It's basically a portable (as in "You can move it" not "You can easily carry it") heating system that would save the considerable drain on the Leaf's battery pack from the car's heaters in cold weather. The Leaf heaters are designed to provide substantial heat almost instantly. This system should provide enough heat to both warm the driver quickly, and warm the whole cabin eventually, which means it can use substantially less energy for this purpose than the car's built-in heaters. It consists of:
* The power source. A sealed deep cycle 12 volt storage battery of at least 60 amp-hours (AH) in a marine type battery box. If a marine battery is used the maximum safe drain is only 50% of capacity, so I'd suggest a 75AH minimum capacity for that type. Otherwise assume that you can use 80% of the battery's rated capacity, although 60% is best. Do NOT use an automotive starting battery, as these are meant for high current but low drain situations, and will soon expire in deep-cycle use. While you don't necessary need them, I suggest a couple of marine-grade accessory sockets be installed in the lid of the battery box.
* The heater. While you could use a 12 volt automotive type interior heater, reviews of these heaters suggest that they are a waste of time, providing little actual heat. You can also simply plug them into the car. Instead, I suggest a ceramic type (for safety) 120 volt, personal-sized space heater. Lasko makes a 200 watt unit that I have personally tried in a cold indoor environment; it provides surprisingly warm air, with a modest but adequate airflow. Its biggest advantage is its low power consumption, but it also has disadvantages: no thermostat, and a shape that is "tippy" enough that it would have to be secured to a more stable base for use in a vehicle. I have seen listings for another heater, by Holmes, I think, that has both a 1500 watt setting that could be used for preheating the car with house current, and a 375 watt setting that would seem to be ideal for heating a car. I have not, however, tested this heater. There may be other, better choices available.
* The inverter. A good quality inverter is used to convert the 12-14 volt output of the battery to 120 volt house type current. It must be remembered that when you multiply the voltage by 10, you need 10X the rated current of the device to be drawn from the battery. Thus the 200 watt heater, which draws about 1.7 amps at 120 volts, would draw 17 amps from the 12 volt battery. (This is why I suggest a fairly large, heavy battery. While a 12 volt lithium battery pack would be great for this application, most people would opt for the much less expensive lead-acid type, so I'm concentrating on that.) The inverter does not have to provide pure sine wave output to run a simple heater, it just has to be well-made and provide its rated output. If using a 200 watt heater I'd suggest a 400 watt inverter, as you don't want to run an inexpensive inverter at or near 100% for extended periods of time. For a 375 watt heater I'd suggest at least 500-600 watts for the inverter. That's 500 watts *continuous*, not "peak" which can be maintained only briefly. If you use a good inverter you can also use it for things like picnics in warm weather.
* Battery charger. While it is theoretically possible to keep the storage battery recharged from the car's own electrical system, either through the "cigarette lighter" / accessory port or from a hardwired connection, the safer option is to use a dedicated 12 volt deep cycle charger. The charger should be at least 10 amps, and more would be better, as the battery will get drained substantially with each trip in which the heater is used, and if recharged too slowly it will both be impractical and possibly suffer sulfation damage. If the charger is carried in the car, then a compromise between size and power will likely be needed.
* Wiring. While a 200 watt heater could be run with standard 12 volt accessory plugs and sockets (assuming marine grade components, not low quality), it would be better and safer to use quick-disconnect high amperage connectors, like Anderson Power Pole or the more ubiquitous XT90 or XT60 (for smaller heaters) plugs. A separate plug for the charger would facilitate fast, safe recharging. Do NOT attempt to run higher wattage units using 12 volt accessory plugs. Do use a fuse or circuit breaker in the positive lead from the battery terminal. Amperage of the fuse will depend on the power required for the heater.
A word about safety: it's sometimes easier to assemble components quickly and sloppily, but when working with high amperages, even at low voltages, short circuits can VERY easily start fires. Use only quality wiring and connectors, properly assembled with shrink tubing at the ends, and electrical tape wherever needed. Don't route wires where they can tangle in feet or rub against metal or sharp edges. Make sure that the heater is secured to a stable base that keeps it away from all combustibles. Ceramic disk heaters are fairly safe, but nothing is perfectly safe. Finally, while sealed batteries generally only vent gas under extreme heat caused by over-charging or excessive discharge rates, don't assume that venting will never occur. This means don't put the battery in a sealed box!
As you can probably tell, I haven't yet built a prototype unit. Logistical and health issues will slow the process for me, so I'm putting the idea out here for you Leafers to try as well. Good luck, and *be careful*.
Last edited by LeftieBiker
on Wed Jan 08, 2014 4:25 am, edited 1 time in total.
2013 "Brilliant Silver" SV with Premium Package and no QC, and 2009 Vectrix VX-1 with 18 Leaf cells.
The most offensive, tasteless phrase in use here is "Pulled the trigger." I no longer respond to posts that use it.