Electric "Heater In a Box" System

I keep seeing this mantra, but it's incomplete. It should read "In the case of using PIP to heat the net efficiency is higher *than it would be otherwise* BECAUSE you are using the waste heat as well as powering the car." The mere act of using some (not even most) of that waste heat does not magically change the equation from a minus to a plus. I also notice that none of the 'ICE heating' proponents seem to want to mention that gasoline usually comes from another part of the world, or at least the other side of the continent, or that it is a highly refined and processed product.

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I may test the 'box' in the Prius tomorrow, my back permitting. I consider the Leaf test a modest success. It would have been a total success, I think, if I had been able to leave both heaters running. The PIP has more interior space than the Leaf, though, and that's where most of the interest lies, so I want to test it in a PIP. I don't expect much if any rise in overall interior temp; I'm instead hoping for that 'bubble of warmth' around the driver.

 

I did get in a quick test (running late, so after dark). I taped the two 200 watt heaters together and anchored them to the driver's seat adjuster bar like I did with my Leaf. It was 23-24F outside, so the interior of the car was somewhere in that vicinity. I tossed a home weather station in the 'arch' storage area to get some sense of the temp in the vicinity of the driver's footwell, but didn't wait for it to reach ambient. I then turned on the inverter and both heaters, and went for a drive. The ICE came on for some reason (probably cold components) but I left the climate control off so it provided no heat, and it shut down several minutes later, to stay off for the rest of the roughly 8 mile drive. The two heaters together made my legs nice and warm in a few minutes, so I shut one heater off for the rest of the drive. I remained comfortable below the waist. My face, however, was cold, even with an open-face balaclava on. I kept the ventilation in floor/defrost mode, with the recirculate flap closed, opening it for a minute every 5 minutes or so, and just the air being pushed in then by the car's motion was enough to keep the windshield clear. I got home with virtually no range left, but feeling the cold only in my hands (bad circulation, plus no steering wheel heater!) and face. The weather station in the arch was reading 42F, so some heat does escape from the footwell and partially warms the interior. However, that configuration is inadequate, IMO, for more than a short drive. However...

I was only using one heater for the most part, and there is a space, on the left top of the dashboard, where the second heater would fit perfectly, without obstructing the view substantially. That second heater, secured to the top of the dashboard and aimed at the face area, should work perfectly to keep one's head warm, while the one in the footwell keeps the legs and feet warm. I'm not sure I'll be able to find a way to secure the heater to my housemate's car without doing any cosmetic damage at all, so I suggest that anyone who was waiting to see if this was worth a try, and who owns their PIP, take it from here. I'll summarize the components again later.

 

You're welcome. Unless I get an Inspired Idea on how to secure that second heater to the dash, though, I'm probably done.

So, what are the components again?

* Marine battery box. I think mine is a "Group 27" size, and it's much larger than my little 31AH (when new, years ago) storage battery. Group 29 would probably be better for a 100+ AH battery.

* DC to AC inverter. Get one with at least 1/3 more continuous (not surge) capacity than you'll need, and preferably twice as much. For one 200 watt heater, get a 400 watt inverter. It will likely have a surge capacity of 800 watts, but 400 is the important number for this application. For two heaters, 800 watts continuous. The inverter must be protected by a fuse (most are), and must have either a low voltage alarm (best for this application because you can hear the battery get overtaxed while driving, and just reach down and shut a/the heater off) or a low voltage shutoff no lower than 11.5 volts. An inverter with ring-type terminals that the power cables attach to is most convenient. I strongly suggest you use automotive battery cables with standard battery terminals on the battery end, and attach ring terminals or whatever type you need to connect to the inverter on the other end. I used the alligator-clamp cables that came with my inverter for this test, but that isn't a long-term solution. For multiple heaters and a large battery, use heavy duty battery cables.

* Heater(s). I like the Lasko 200 watt "My Heat" units because they seem to blow hot air even in a cold car. They also use safer ceramic disk technology. Their main flaw for household use can be a plus for this use: there is no tipover switch, just a thermal protection cutoff. So while you have to make sure it/ they are securely mounted, you can mount them in any position.

MyHeat™ Personal Heater Model 106 | Lasko Products, Inc.

* You will also need a battery charger. If the battery will be residing semi-permanently in the car (I put mine in the right rear passenger footwell) then you need to decide if you want a smaller charger that you can plug in away from home, or a larger, faster one to stay in the garage. The charger has to have a setting for "gel" or "deep cycle" batteries. Don't use a battery "maintainer" to charge a large depleted battery. Use an actual "smart" charger with two or three stages and a shutoff or float mode.
* Deep cycle battery. While you can get away with using a marine/starting battery, and these are least expensive, you will get longer life and more available amp-hours per pound with a true deep cycle battery. Capacity? One 200 watt heater will use about 17 amps in one hour. Two will use about 35 amps. Deep cycle batteries should not be discharged below 20% charged, and if they will be sitting that way for a while, 50% is better. So calculate how long the heaters will need to run, and get a battery with at least twice as many amp-hours capacity as the heaters will need. I can't personally vouch for the claim made by Greensaver that their batteries will not get sulfate buildup if left partially discharged, but that's what I'd use, in the hope that it's true. I do know that these batteries will sit for long periods with little loss of charge, indicating low internal resistance, which is good for a high-drain application like this.

PRICES:

Marine battery box: about $25. Less on sale.

800 watt inverter: $40 to $150. A pure sine waver inverter is not needed for this application, so a good inexpensive one will work. Make sure it has a low voltage alarm, or at least a cutoff, to protect the battery.

Heater(s): The Lasko heaters run from $20 (usually for the white ones) to about $35. Different colors have different model numbers.

Deep-cycle battery: anywhere from about $60 for a 75-100AH "marine" battery to several hundred dollars for a Greensaver or AGM type deep cycle in the 150AH range. A small (30AH or so) deep cycle battery will cost about $75.

 

I took a few quick ones of the components sitting on my porch. I was always pressed for time when testing, so there are none of the components in the car. I'll post one of the porch photos, but remember: "Prototypes ain't pretty." Maybe I should include the price of a roll of duct tape in the last post...