Fuel fired heater woes

[jdr2710]

Now that it is getting cold & snowy here in colorado I decided to try to figure out why my arctic heater doesn't heat. I've got a Benmar I got off ebay a while ago. To make life easier I pulled it off the truck so I could work on it on the bench.

Much to my amazement it actually fired up on the first attempt on the bench (it never has worked while in the truck). After I let it run for a while I shut it down, then tried to restart it the next day, and no joy. After some poking around I pulled the igniter. The top metal coil going into the ceramic is not attached at the ceramic end, it must've just had a lucky short for the one time it worked.

Does anybody know where I might find a replacement? Or can you think of an alternative means of igniting?

Thanks,
Jeff

 

[m-35tom]

just re weld it, or replace the nichrome wire by measuring the diameter. i got mine on ebay from somewhere in eastern europe.
looks like you may have a very old heater, i would find one from 1985 or newer.

 

[jdr2710]

Unfortunately the wire broke off flush with the ceramic.

I wondered about using nichrome, but was hoping for the easy solution of a replacement part...

I checked out some of the specs on nichrome and found a diameter that is about what I've got now. But I'm not sure what temperature I'll need the wire to reach to ignite the fuel as it blows by. Does anybody know what temperature I should shoot for? I'm thinking I'd want to be a bit hotter than that since the fan blowing will cool it down some. The size wire I looked at can reach 2,000 degrees F with 12 amps. That wire is about 1 ohm per foot, so I'd need a couple feet or so to get to that temperature. I'm guessing that the wire would probably last longer at a lower temperature tho, so if I can get a guesstimate of the right ignition temperature, then go a fair bit warmer to compensate for the fan I could make it run a bit cooler, and draw less amps. As a W.A.G. I'd go about 1/2 the difference between the required ignition temp and the 2,000 degrees the wire is spec'd for. That should give plenty of heat, but keep the wire from burning out.

Thanks,
Jeff

 

[moving chicane]

The auto-ignition temperature of #2 diesel is 494°F Not sure if that helps.

 

[jdr2710]

494F hopefully that means an igniter running somewhere around there will suffice, I'll shoot for a deal hotter tho, since that shouldn't bother the wire or cause any ignition problems. I may have to experiment a bit before I seal up the repaired igniter. I did manage to get the burned up ceramic out of the old one, so I can weld in the new nichrome when I get it (that should be some interesting TIG fun). I've got some 3200 degree refractory mortar on the way too so I can insulate the new coils from the body of the igniter.

If somebody with a working Benmar heater could measure the resistance from the igniter to ground that would help too. The igniter is right beside where the fuel line goes into the main body. I'm guessing it will be around 2-4 ohms. The undamaged section of wire I removed was about 0.03" in diameter, about a 20ga wire. It was actually broken in a couple spots, I'm not sure how it ever managed to fire the one time. Based on the wire I removed it is around 2' in length, which is pretty close to what I was guessing, but confirmation of the resistance from a working unit would be nice.

Thanks,
Jeff

 

[m-35tom]

since you are replacing the wire, you should start from scratch with the resistance. most heaters have a resistor so the ignitor coil is close to 12 volt. you can measure the resistor and using ohm's law calculate everything else. resistance of the wire will probably go up as it gets hot. is your heater made to be multifuel? it looks old and may have been for gas.

 

[jdr2710]

I got heat!

It took a little experimentation, but I got the igniter fixed.

I ended up using 20ga nichrome wire. I initially tried 40 wraps around a 1/4" rod, but that seemed to be too cool with the air blowing by it (took forever to fire, and didn't like to stay fired), so I shortened it to 30 wraps to make it run hotter.

I discovered that it works better with quite a bit of the coils exposed at the open sections at the top and bottom of the igniter, plus it really liked having some of the refractory on the bottom end, to act as a heat sink.

I ran it a couple times and it fired up correctly, taking a couple minutes or so in the start position.

It was a little tricky to get it welded up, being so thin, but after some experimentation on a bit of scrap wire I learned that if I twisted the new wire to the old one I could get the tip of the twist welded with some very low amps, around 30-40 is all from the TIG. I left a section of the original wire at the top of the element so I wouldn't have to try to weld inside the igniter. At the bottom I just welded to the side of the igniter tube, then filled the end with some of the mortar.

For the section inside the igniter tube I slathered on the refractory mortar by hand with the element still wrapped around the 1/4" rod, masking the ends to keep them clear. This refractory mortar (good to 3100 degrees) is some tough stuff, once it cured it was quite solid. I did drill a 7/16" hole in another bit of material so I could trim off any excess mortar. Then once it was cured I cleaned up the masking and slid it inside the igniter.

All-in-all not a tough repair, but required some special materials I didn't have on hand. But now I can have some instant heat when plowing, bring on the snow!

Jeff

 

[Storm 51]

Glad to hear you got it fixed, jdr2710!

Sorry I could help you out with that one.

Storm 51

 

[cattlerepairman]

Ingenious fix! Very industrious.