Battery Powered Block Heater

Foxpaw · 08-18-2004, 10:13 PM

This is a bit in advance, but it's occurred to me that I may need to brainstorm a plot to allow me to safely start my car in the winter.

I can plug the car in at my house, so that is not an issue. However, I will be parked at the University during the day and I won't be able to plug the car in there. I live in Manitoba and it can periodically get very, very cold during the winter. Last year there were a few days that dipped below -50 degrees Celcius, and I am concerned that starting the car at this temperature without the benefit of having the block heater plugged in may be very bad for it.

So far, my scheme is to have an additional battery setup in the hatch which will run the block heater. That battery could be recharged when I have the car plugged in at my home. I do not want to use the IMA battery pack to prevent undue cycling, unless the amount of energy used by the block heater is very small.

So, my questions are, how much power does the block heater draw, and approximately how long does it take to warm the block sufficiently to start it safely? (if I can put it on a timer, I'll be able to conserve a lot more energy)

sunhunter · 08-18-2004, 11:13 PM

The forum topic "engine block heater" suggests that the power is about 400W. I have no idea what the thermal mass of the engine and cooling system is or what the thermal transfer rate to atmosphere would be so I don't know how long it would take or what temperature rise would be achieved. I think you may need to plug in the heater and measure the temperature rise over a period. I guess is would be best to do the test in the temperatures you are talking about. My guess is that at those low temperatures, you may need to power the heater continuously.

Another thing, at those low temperatures, the battery you use won't release as much power. This may not be an issue since you will need a bunch of batteries any ways. A string of 10 deep cycle lead acid to get the 120V. Fuse for 5 amps using dc rated fuse and use a disconnect switch or circuit breaker. Use 14AWG wire. I think 70 amp hour batteries might get you 8 hours at those temperatures, just a guess though. $500 - $1000 US

Maybe I am wrong and it only takes an hour of heating. I think you will need to test.

b1shmu63 · 08-19-2004, 12:11 AM

Under those conditions I think your car will start better if you have 0W20 synthetic and an oversize 12 volt battery. The car will start using the 12 volt battery any time you get really cold temps.

Since the engine is completely uninsulated trying to keep it warm by supplying heat is a loosing battle. If you used one or more thermos bottles to hold a quantity of engine antifreeze it would help on restart. I'd like to do this myself but it is not a trivial project. Then again a battery powered block heater on a timer is a little involved too.

Armin · 08-19-2004, 07:55 AM

I have been using the standard Honda block heater for two winters in New England. The lowest temperatures here were around -20 C.

For most times, I found I needed to run the block heater about 2.5 hours before I start the car. In this time, the core temperature increased about 35 C above ambient. After that the heat losses take over so the core temperature doesn't increase much anymore. This is pretty independent from the outside temperature. If I leave it on for several hours, it levels off at about 45 C above ambient.

Anyhow, that means you need about one kWh to heat the engine. That's pretty close to the total capacity of the 144V battery, just to give you an idea of the amount of energy required.

In Europe, gasoline-powered block heaters are popular. They don't need much electricity (just enough to run a water pump and a fan), so they happily run off the battery. They are more efficient than idling the engine, but obviously dirtier than electric...

Corey872 · 08-19-2004, 09:01 AM

In general, batteries aren't very good for resistance heat...they just don't have that much power. (From memory) A "Group 31" battery, which is a fairly large "truck" battery will have about 75 amphours capacity. So that is about 0.9 Kwh. Of course that is rated at 77 degrees and 20 hours discharge time. Drop the temp and discharge time and it could easily be less than half of that capacity.

If you are worried about just getting it started, I would think the 0W20 synthetic oil and possibly a larger 12V battery would help. If you are more concerned with engine wear, another option may be a "pre-oiler". This is a device that holds a small quantity of oil under pressure when you shut the engine off, then releases it just before you start the engine the next time. This (in theory) gets oil into the system and hopefully to the top end before you crank it over.

If I had to deal with -50 temps, I know what I'd do...but moving 1000 miles south may not be an option for everyone

Good Luck...stay warm!

Aaron Cake · 08-19-2004, 09:22 AM

You could build a thermos like the new Prius. It is used to quickly warm up the coolant. I have been thinking about this. Make a heavily insulated bottle of about 4 gallons or so, and coil about 15 feet of copper tubing inside. Fill with wax and connect in series with the radiator. Shouldn't effect normal engine operation, but when the car is cold started, the warm coolant will begin to circulate...

Just a thought. Lots of room in the Insight engine bay for such a thing.

Guillermo · 08-19-2004, 12:31 PM

Like it was mentioned before, a battery powered engine block heater is not a good option. Use synthetic engine oil and try to find a 120V AC outlet for the engine block heater. To make sure you don't get stranded at work on the coldest days, keep a spare 12V battery in the office in case your little 12V battery is so cold that it has trouble starting the engine.

To start ice racers at -40C many people make a low sheetmetal table that fits under the engine compartment and they put a camping stove under there for 1 or 2 hours to heat up the engine compartment.
I wouldn't do that at the office everyday... but hey they are ice racers after all!

b1shmu63 · 08-19-2004, 02:42 PM

I know that the Insight starts fine at -26 C. Haven't experienced below that.

Foxpaw · 08-19-2004, 06:59 PM

Well, my concern isn't particularly getting it started, since I'm confident that it will. Rather, I started my Tempo in -50 degrees Celcius last winter when it wasn't plugged in. I did it once, and the engine has been noisy and prone to stalling since. So, I don't really want to risk causing such damage to my Insight. I'm not sure what exactly causes this damage, but the noises started immediately when I started the car, which suggests to me that at that temperature maybe things have contracted sufficiently that they are siezed right up and were "broken" (literally, perhaps) free by the starter.

If the car started under IMA power, would this be easier on the engine? Heating the passenger compartment instead of the engine is likely a much more practical possibility, as it has much better insulation.

Quote:

Originally Posted by Aaron Cake

You could build a thermos like the new Prius. It is used to quickly warm up the coolant. I have been thinking about this. Make a heavily insulated bottle of about 4 gallons or so, and coil about 15 feet of copper tubing inside. Fill with wax and connect in series with the radiator. Shouldn't effect normal engine operation, but when the car is cold started, the warm coolant will begin to circulate...

Just a thought. Lots of room in the Insight engine bay for such a thing.

I like this idea, but I don't see what the wax is for? I'm guessing that the wax is used to store the heat energy inside the thermos, though I'm curious as to why wax would be chosen as a good material for this.

b1shmu63 · 08-19-2004, 09:44 PM

Wax acts as a phase change medium. There is much more energy stored when a solid turns to a liquid, therefore it takes longer for it to cool down than straight liquid. As I see it the main problem would be head escaping through conduction of the copper pipes entering and exiting the thermos. I'm thinking of using something like sections of fibreglass fishing rod for the transition, or perhaps just plastic tubing. By using two thermoses in parrallel I hope to double the flow rate. This mod has to be thought through carefully. I intend to foam the whole thing into a rectangular container to furthe reduce heat transfer and put a 15 watt heating element in there with a thermal cuttoff switch.