Block heater problem

I have a sub compact tractor that has an engine 120 vac block heater the keeps burning out after two to three winter seasons.
I have so far replaced two and now I need a third.
I believe the problem is too much wattage for such a confined space , I've added a timer that only operates for twenty five minutes then off for five then cycles again.
This doesn't work so I'm thinking of dropping the 400 watt heater to 100 watts so my question is what would be the best way to accomplish this?

A block heater only works best for about 2 hours before startup. Running it longer is usually a waste of electricity. In extreme cold, maybe 3 hours runtime before starting. Running it longer tends to burn it out sooner.
A lower wattage like 100W will not provide enough heat to compensate for the cooling rate of the cold air around the engine block.
Another option may be to look into a coolant circulating heater. Those tap into the coolant lines and heat the coolant which is also circulated through the engine block. More complicated to install of course...
Finally, you could try some form of lamp "dimmer", to turn down the wattage of the 400W heater to about 200W-300W. But knowing how much heat it is generating may be a guess. Too low, and there is not enough heat. Most lamp dimmers will handle 500W-600W

I was just looking at a dimmer, 500 watt, 6 amps, even if I worked down to 200 watts I expect the element might last longer.
I thought the timer might help, I guess I could set it to come on for five minutes then off for two then cycle again.
Too tight for an inline hose heater.
Thanks for your response.

Timer going on and off probably stresses the heater more than just leaving it on. When the heater is cold, its resistance is a bit lower, causing a surge in current until it starts to heat up.

If you put a diode in series the heater power will halve.

You need a diode rated to the maximum current (4A) or more, and the peak voltage (150V) or more. Diodes like that are cheap and you should be able to find one that has a much larger rating.

You may find a bridge rectifier that does the job and could be easier to mount. You should use + and - on the bridge rectifier and leave the two terminals marked "~" disconnected.

I read about using a diode a few days ago but was waiting to hear from someone here, I can try that easy enough prior to installing the new heater and test the power of the element through the diode.
Thanks for that suggestion.

The power element is probably only specified to work when underwater. If that is the case, turning it on in air for more than a few second may damage it.

Edit:- I've noticed that some block heaters heat the oil, but whether the heater is designed to be in oil or water, there is far more heat transfer in liquids than in air.

I can submerge the heater in water to test it, I did buy a magnetic oil heater but my concern is it could get pulled off in the snow or possibly cook the oil on the bottom of the oil pan.
I really don't want to crawl under the tractor to disconnect it every time I use the tractor which is almost daily.
I'm looking at a 200 volt 5 amp schottky diode I can wire inline on the block heater cord depending on how much heat it dissipates.
I've also added a battery blanket that warms the battery.

Diver300 said:

You may find a bridge rectifier that does the job and could be easier to mount. You should use + and - on the bridge rectifier and leave the two terminals marked "~" disconnected.

Click to expand...

No. Connect the two "~" together. Use them as one terminal. Use either + or - (not both) as the other terminal.

If you want to go the half-wave rectifier route, then for better long term reliability double all of the requirements. For a 120 Vac, 3.3A circuit, use a diode rated for 400 V and 8 to 10 A. Average power dissipation in the diode could be around 2 W, so don't encase the diode in heat-shrink tubing. The body and leads act as heatsinks.

Separate from that, I like the idea of the lamp dimmer. There should be a sweet spot where the heater is on continuously (no cycle timer) at a power level just high enough to maintain the block at the temp you want.

ak

Diode bridge approach. Click on the schematic for a larger image.

ak

Diver300 said:

You may find a bridge rectifier that does the job and could be easier to mount. You should use + and - on the bridge rectifier and leave the two terminals marked "~" disconnected.

Click to expand...

This scheme is slightly simpler to implement but does result in more heat given off by the bridge rectifier.

Connecting both AC ("~") together and connecting them and + will give about half the amount of heating in the rectifier.

The heat given out by the block heater is almost exactly the same for either scheme.

Ok; I have an idea now what will work and I want to thank everyone for contributing, hopefully at $100 U.S a pop I can make this element last a little longer.

Diver300 said:

This scheme is slightly simpler to implement but does result in more heat given off by the bridge rectifier.

Connecting both AC ("~") together and connecting them and + will give about half the amount of heating in the rectifier.

Click to expand...

Disagree. The "heating" will be the same, but it will be spread out across two diode junctions instead of just one. Same total power dissipation, but lower junction temperatures. How much lower depends on the Vf matching between the two diodes. The current sharing between the two diodes will not be perfect, but probably no worse than 60/40.

ak

AnalogKid said:

Disagree. The "heating" will be the same, but it will be spread out across two diode junctions instead of just one. Same total power dissipation, but lower junction temperatures. How much lower depends on the Vf matching between the two diodes. The current sharing between the two diodes will not be perfect, but probably no worse than 60/40.

ak

Click to expand...

If current flows from the - to the +, there are two paths, each made of two diodes in series. As with two diodes in parallel, the sharing of the current in two paths won't be perfectly balanced.

The voltage drop will be about twice that of having two diodes in parallel.

Per the #11 schematic, I don't see any reason to run the AC through the other two diodes.

ak

Diver300 said:

If current flows from the - to the +, there are two paths, each made of two diodes in series. As with two diodes in parallel, the sharing of the current in two paths won't be perfectly balanced.

The voltage drop will be about twice that of having two diodes in parallel.

Click to expand...

Diver300
The bridge rectifier of analogkid is perfect as drawn. Any attempt to use more of the four diodes will result in more voltage drop, more heating without any better voltage blocking.

KevinW
Large bridge rectifiers are available for a few dollars and will work perfectly (many even have a nice lug to bolt on an heat sink. The design may drive some people batty because connections are left unused but not to worry, if it does eventually burn out, you can just flip it around and use the other two diodes another day.

I'll try the bridge rectifier and post the results in a few days.

I once lived where -30' C was a risk your car might not start, and -40 was routine for a week or two in February, so I learnt how to make it start reliably. (Yes, even in -40.) The only time I heard of a water heater failing was from a lack of fluid. The best water heater was the inline hose water heater, which did more to circulate the heat evenly. Rectifying AC to DC won't solve the problem.

All cars sold had 500W water block heaters, and outlets for employee parking at work were also standard. However, one of four timeshares was used, and they had an 800 amp transformer DC starter on a two-wheel truck for emergencies when the plug was not reliable.

All sorts of tools included a toaster + diode in snow and jumper wires line to + of battery and neutral to V- when I was a young poor engineer and had 2 kids. That would take a dead battery and get me started in about 20 minutes at -30'C if I put a hair dryer on the carburetor. Sometimes it took a little diesel starter spray.

We always carried jumper cables just in case of a weak cell or a burnt-out alternator diode that only ran on 1 or 2 phases out of 3. Americans were so appreciative when they got spontaneous help with a dead car in the parking lot, but in Canada, it's normal practice to stop and help anyone. Even hitchhiking to Uni was a normal practice and sometimes with door-to-door service from strangers.

My best advice is to check for leaks, your fluid level and get an inline water heater and follow the installation instructions. It has a thermistor for protection, unlike block heaters.


e.g. https://evwest.com/in-line-fluid-he...lFzmfsKkSohzqyGcyk8X4OIDOyYSq89hH9TasKiuE_av0

Tony from Winterpeg.

Most of the issues starting a car in cold weather is..
(A) the oil turning to honey or amber.
(B) battery losing cca at low temperatures.

Steel design care what temperature it's at and the antifreeze doesn't change viscosity much until -45°C.

The best strategy for starting a car in the cold is to buy a car that uses 0W20 engine oil. It will start like nothing happened even at -40°C. I'd recommend a Honda. Honda has their cold weather test track in Baudette, MN and rents it out to other parts makers and OEMs. They also use a very clever mix of alloys for cylinder wall sleeve, piston/piston rings that all have specific thermal expansion to allow increasing gaps between parts as temperatures decrease for cold weather starting, low oil consumption in summer and year-around low friction losses due to oil viscosity specifying 0W20 year around.

Note: The newer Camrys and most BMWs are using 0W16 and even 0W12 oil. These should start very easily as well at -40°C.