18 October 2009

Interior preheat

Several Mini E drivers have expressed range concerns due to colder weather in the North East and using the heater in the car. I have used an interior heater for years that I bought from Napa to preheat my cars so I don't idle them to warm them up, don't have to scrape the ice off, and don't freeze on the way to work while the antique combustion engine warmed up.

Now I use it to increase my range in the Mini E. Here is a link to something similar to what I have:

Kat's Automotive Interior Heater 120 Volts #37100 $64.45


My particular model might not be available anymore. It draws 6.75 amps, or about 825 watts, the rating is 900 watts as is the link above. I plug it in when I get up in the morning and by the time I am ready to leave the car can be pretty warm, usually over 80 degrees F. When the weather gets colder I will probably go back to using a timer to turn it on before I get up. Preheating the cabin lets me run without any heat for the first ten miles or so, and then use a lower setting than I would have.

I have added cabin temperature to my logs, as well as heater settings. The link is over to the right under "#458 trip log only". Sorry about the confusing layout of the spread sheet, I'll rearrange it someday. Recent entries are at the bottom, unlike these blogs.

Mini says they don't want accessories installed, so I have my heater sitting in a steel pan that is meant for baking bread. It holds the heater at a safe angle and allows it to be positioned such that it won't melt anything like seats or the dash board. There is a thermal cutoff switch and maybe another safety feature in mine, I hope the link I found is as well equipped but I don't know, it is just a suggestion. The instructions for mine explicitly say it should be screwed down in such and such a fashion, and I have put the required mounting in my GM car. Maybe can move it to the Mini, I'll have to check with the service guys for permission.

And don't underestimate the power of taking hot drinks on your drive to increase your battery range. Liquids are also good for your immune system during flu season. And you can often run the heater at a much lower setting.

The rain here lately has put a stop to using the recirculate button to reduce the heat setting. Others have observed this causes the windows to fog up. I doubt that using the AC and the heater would use less power than turning off the recirculate. That would be interesting to try to measure...

But I do have to make some more measurements on heater power consumption. If someone else doesn't post it first, I am going to park the Mini E in the cold with the heater on at maximum, windows partly open, and time how long it takes to draw the battery from 100% down to 30% or less. Probably at fan setting 2 to start, although I rarely have to use more than the lowest fan setting after preheating.

Was anyone besides me expecting Mini to have used a heat pump instead of a resistive heating element? Too bad, but maybe it is not practical yet.


  1. Jim, I did a similar test three times about three weeks ago. I ran the heater at maximum heat and the lowest fan setting for two hours. I only lost 8-10% of charge so I think you'll have to run it for a while to get down to 30%. However, when I did it, the outside temp was warmer than it is now and the batteries were performing much better than they are now. I'll look forward to your results.

  2. I wonder if a regular electric portable heater would work - I've got a tiny one at the office I might give a try - good idea.

    When you guys tested the heat were you driving? I have sat in the car with the heat on and it does not draw as much as when driving. Seems once you put load on the battery it really draws, especially if the batteries are cold.

  3. Chris - just be careful. Heaters that were not designed for use in a car can tip over and start a fire, or melt things. The ones designed for cars have maybe more safety built in.

    I'll comment on the heater drain tests in a separate post.