Electric "Heater In a Box" System

This is from the Leaf forum, originally. It should be equally applicable to the PIP.

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, and provide the PIP with an alternative source of heat for short to medium length trips. The Leaf heaters are designed to provide substantial heat almost instantly. This portable 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 for regular use. 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, to power things like 12 volt coolers and electric blankets that would put excessive strain on the car's smallish accessory battery.

* 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, with both tip-over switch and thermal cutoff switch for maximum safety. 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 or bracket 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 about 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. The smaller and lighter the battery, the easier it would be to remove and charge it outside the car. Again, there is a capacity vs size/weight tradeoff involved.

* 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 200 watt heater would require a 20 amp fuse, while a 375 watt heater would need a 40 amp fuse.

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 or bracket 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! Marine battery boxes have built-in vents in the lids.

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 and PIP folks to try as well. Good luck, and *be careful*.

 

A heater for the engine coolant that got it hot enough to provide heat as well would be nice, but I'm not sure it would be practical to get that much coolant that hot.

 

I've decided to go with two of the 200 watt Lasko heaters for the prototype, because they are so well reviewed, and apparently produce more usable heat (each) than the 375 watt Vornado (not Holmes) unit. I will mount them on a support of some sort, with the option to run one heater or both at once. I also dug out an 800 watt inverter I've had sitting around for years. I hope to have it all assembled and ready to test at the end of next week. I will be using them at floor level in the driver's area, below my legs in front of the seat, because I have poor circulation and feel heat the most when it's on my feet and legs. The power cords will run through a protective plastic tube to the battery/inverter setup, in one of the rear foot wells. I want to be able to reach the power switches while driving, without taking my eyes off the road.

 

I'm not sure what you mean. The charging station? Maybe, with an extension cord. If you elaborate I can give a better answer.

 

No. These are 120 volt heaters. Most cars' accessory outlets can't handle the amperage needed to provide real heat. Even *one* of the 200 watt Lasko heaters will draw 17 amps at 12 volts (through the inverter) and most accessory outlets are rated at 10 amps max. The separate battery, PITA that it is, prevents several problems, from melted wiring to a damaged car accessory battery. If you want to avoid using that, the inverter should be hardwired directly to the accessory battery, and that battery should be upgraded to a larger, true deep cycle one.

 

That's exactly what this system should do: provide a little supplemental heat while driving. It isn't a preheater, although it could serve as one.

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That's correct. The battery and inverter would reside on the rear passenger floor on one side, with the heater(s) being safely placed for best effect. Why else use a battery instead of house current...?

 

As long as it's in a marine battery box it should be fine. It has to be the sealed type.

 

The heaters arrived today, the day after I ordered them, so I did some preliminary testing of components. After testing each heater in an outlet to make sure it wasn't defective, I then tested each one with a 300 watt inverter, plugged into a modest-sized deep cycle battery in a box that I have in the house for power failures. The Lasko 200 watt heaters do very well with inverters, apparently: I was expecting them to run slower than on household current, but they seemed to run exactly the same. Smooth and quiet, with lots of heat output. I then brought one onto the front porch, where I have an outdoor outlet. The temp outside was about 34F, so I plugged the heater in and let it run in the cold to see if it produced enough heat rise in cold air. It does indeed. The air coming out felt about 100F, even in the cold. I'm guessing that the ceramic disks are regulated to produce a fixed output temp, and will do so to the best of their ability. If there is a deficiency, it will be with airflow, and I may be able to fix that with a booster fan in front of or behind the heaters. Hopefully that won't be necessary. I'm into my work week(end) now, so it may be next week when I put everything in the Leaf and test it with the 800 watt inverter and both heaters.

 

There are several factors, but a store brand Chinese or Mexican-made battery can be had for about $75 for a 100AH size, on sale - $100 full retail. An American made similar sized battery is about $150, while a true deep-cycle battery would run from about $150 to $300. With a true deep-cycle battery you can use a smaller capacity, lighter unit because they will withstand deeper discharges. I'm using a 31AH high quality (but old, now) deep cycle battery that weighs about 25lbs, to test.