Building a mini 12volt heater for model engine heating.

Hello to all! I am new to the forum and would like to ask for some advice.

I work with two stroke model engines and would like to build a heater to pre heat the motor to approximately 200F before starting the motor. Most of my motor wear ocurrs starting these engines cold, and preheating them will double there life.

Design musts:
1) MUST be able to utilize a 12volt power source.
2) I plan on machining a 3" in diameter aluminum sleeve with a 0.050 wall thickness to fit over the aluminum cooling head of the motor. The sleeve will be enclosed on one end. Through thermal transfer I hope to heat the motor.
3) I will be using a thermal insulator to keep the heat inside the sleeve.

The simplest method I know would be using nichrome wire to wrap the sleeve, and place the insulating material around the wrapped sleeve. Wrapping the sleeve with 1 foot of 30 awg nichrome wire yields a resistance of approximately 3 ohms.

I would like to have the sleeve reach an approximate temperature of 200 F, and stay there. If it takes 10 or so mins to gradually reach that temp would be fine. I don't really need to be able to regulate temperature.

Could someone help me with a circuit design? I thought about using power diodes to limit current which I think in turn should limit heat output, but are there better ways to accomplish this? I really don't know what current levels will be required until I experiment.
Anybody have any ideas? Thank-you in advance.

I would use this type of 50Ω 5W resistors. They transfer heat well to what they are bolted to. A 50Ω resistor will draw 0.25A and produce just over 3W per resistor when powered off a 12.6V battery. If one is not enough, then use two. If using two, wire in parallel. Your dissipating ~3W in a 5W resistor, so it is appropriately derated.

You should machine flat(s) onto your sleeve to mount the resistor(s). Use some thermal compound (like used on CPUs) between the base of the resistor and the sleeve.

MikeMl said:

I would use this type of 50Ω 5W resistors. They transfer heat well to what they are bolted to. A 50Ω resistor will draw 0.25A and produce just over 3W per resistor when powered off a 12.6V battery. If one is not enough, then use two. If using two, wire in parallel. Your dissipating ~3W in a 5W resistor, so it is appropriately derated.

You should machine flat(s) onto your sleeve to mount the resistor(s). Use some thermal compound (like used on CPUs) between the base of the resistor and the sleeve.

Click to expand...

Thank-you I will give them a try.

I was also wondering whether 12volt heater cartridges would be economical?

RayJ1 said:

Thank-you I will give them a try.

I was also wondering whether 12volt heater cartridges would be economical?

Click to expand...

What is the resistance of a "12volt heater cartridge"?

What is a "12volt heater cartridge"?

Sun electric company makes a cartridge heater. They also make them to run on 12volts. It's like a large resistor that generates heat.

I didn't know that they actually made resistors to generate heat. The 50 ohm resistors help solve my huge current problems.

Why heat the engine when all you need is oil that does not get thick when cold like synthetic oil?
Oh, a 2-stroke engine? It is an smoking oil-burner? It will be expensive to burn synthetic oil. Heat and burn the old cheap oil instead.

RayJ1 said:

Sun electric company makes a cartridge heater. They also make them to run on 12volts. It's like a large resistor that generates heat.

I didn't know that they actually made resistors to generate heat. The 50 ohm resistors help solve my huge current problems.

Click to expand...

All a heater cartridge is, is a resistor in a protective (usually metal) covering.

You could just go and spend $3 on one of those jet flame type general purpose lighters at the local home supply center. They will give you far faster warmups and are very hard to blow out.
Spend $5 more and get a butane refill cartridge and you are good to go for a very long time and for less than what any electrically powered device will cost.

Thank-you for all the replies. One of the questions that enters my mind is wattage that I will need to heat the head and aluminum sleeve, and also to reach a 200f temperature in a reasonable amount of time(15mins)

The amount of metal I will be heating is approximately 125grams of aluminum( 45g motor head + 80grams aluminum sleeve over the head which is the heating sleeve)

It seems the heater cartridges(12volt) will be a good option for me. The 12volt heaters I've looked at put out about 25 watts. I'm wondering if this even in the ball park of what will be needed.

I would appreciate any ideas.

Get you a FREE kitchen oven on craigs list. Hook it up set the temperature on 200 degrees and put the motor in the oven until it warms up.


You can also build you a metal or plywood box with ridgid type fiberglass insulator available at your local contractor heat & air conditioning shop. It comes on 4ft x 8ft pieces just like plywood 3/4 and 1" thick. Cut it with a razor knift to insulate your box. A 100 watt light bulb will heat the box to about 150 degrees pretty quick. I built one and used it as a food dehydrator. You might need to experement and use 2 light bulbs about 75 watts each. A thermostate would be nice to get the exact temperature you want.

Hi Ray,

I guess you're carrying owls to Athens.

I have used a lot of diesel and two stroke model engines and all of them were started with a rich mixture, supplying enough oil for the starting phase.

They don't have piston rings and therefor there is almost no wear and tear. They just start easier if they are preheated.

I also designed and built a 10.5ccm 7-cylinder radial engine with turbo charger which produced 3DIN-hp at 22.000 rpm and sequential ignition (7 ignitions per revolution).

None of the engines used suffered from early weakness but from the impact into hard surfaces.

For easy start at cold temperatures a gas torch used 20 seconds on the cylinder will heat the combustion chamber well.

Boncuk