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  #31  
Old 02-06-2018, 12:24 PM
F1R F1R is offline
 
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Originally Posted by bobnoffs View Post
i would be hesitant to use a ''heat gun''. they get literally red hot.
a hair dryer has safer temps. also hair dryers can be had up to 1850 watts. that's a lot for an elec. heat source.
had my experience with a heat gun. trying to preheat a skidsteer. gun never left my hand and before it was over i melted a fuel line anyway.
Even a hair dryer or light bulb can and will blister the paint on a your nice fiberglass cowl very quickly if not used with care and attention. Heat guns are much hotter than that.

The stick on low wattage oil sump heaters and purpose made ceramic self regulated temp limit hot air heaters are much safer and gentler to your aircraft

YMMV
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  #32  
Old 02-06-2018, 03:07 PM
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Dugaru Dugaru is offline
 
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This is super useful info, many thanks.

So I've got a Reiff standard system - four 50-watt band heaters and a 100-watt HotStrip. If I'm reading the Odyssey specs correctly, the 1-hour AH rating for the 925 is 20 amps:

http://www.odysseybatteries.com/pc925_series.htm

So I'm guessing the system is giving the 925 about all it can handle, maybe a bit more, which makes my inverter beep. On the other hand, perhaps I'm getting pretty decent heating anyway. Time to test it out for a few hours.

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Originally Posted by lr172 View Post
a 150 watt heating element will draw approximately 12 amps at 12.5 volts. The inverter will likely have a 70% efficiency rating, ultimately requiring around 17 amps at 12.5 volts. Compare this to the AH rating on your battery. Be advised that AH ratings are typically given for low current levels (a 20 hour rating). You want the 1 hour AH rating for this application. These are quite a bit lower than the 20 hour rating, which is why they aren't adevertised.

Larry
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  #33  
Old 02-06-2018, 03:20 PM
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Sam Buchanan Sam Buchanan is offline
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Originally Posted by alpinelakespilot2000 View Post
I can raise temps about 10-15F in less than 30 minutes with a hair dryer, extension cord, and cowl blanket (old thin sleeping bag that doubles as survival gear). Just need to be able to find an outlet. That seems to be faster than a stick on pad/band system, it heats the whole engine, and is thus my current strategy while away.
But has the crankshaft been warmed up in 30 minutes? That is one big hunk of steel buried deep in the engine with a huge heatsink bolted to the end of it hanging in cold air. Those crank journals are the biggest concerns during a cold start.
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  #34  
Old 02-06-2018, 04:15 PM
alpinelakespilot2000 alpinelakespilot2000 is offline
 
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Originally Posted by Sam Buchanan View Post
But has the crankshaft been warmed up in 30 minutes? That is one big hunk of steel buried deep in the engine with a huge heatsink bolted to the end of it hanging in cold air. Those crank journals are the biggest concerns during a cold start.
Good question, Sam. My CHT's show similar temperature rises, so I know the heat is soaking into the cylinders at least but I don't know what the internal temperature of the engine would be.

I agree that longer is probably always better but, rationalizing out loud, when one has an FBO do a preheat using a blower is it generally on long enough to heat the crankshaft? My suspicion is that unless heated for a long time, a lot of aircraft get heated up a bit unevenly.
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  #35  
Old 02-07-2018, 12:27 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by Dugaru View Post
This is super useful info, many thanks.

So I've got a Reiff standard system - four 50-watt band heaters and a 100-watt HotStrip. If I'm reading the Odyssey specs correctly, the 1-hour AH rating for the 925 is 20 amps:

http://www.odysseybatteries.com/pc925_series.htm

So I'm guessing the system is giving the 925 about all it can handle, maybe a bit more, which makes my inverter beep. On the other hand, perhaps I'm getting pretty decent heating anyway. Time to test it out for a few hours.
Your pulling around 30 amps from that battery, which is a lot for it's size. It's no surprise that the voltage is dropping quite a bit and that is triggering your inverter to complain. You'll need to watch the low voltage cutoff on the invertor, as it might be high and would prevent you from drawing to the rated capacity of the battery.

Larry
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  #36  
Old 02-07-2018, 12:36 PM
lr172 lr172 is offline
 
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Originally Posted by Sam Buchanan View Post
But has the crankshaft been warmed up in 30 minutes? That is one big hunk of steel buried deep in the engine with a huge heatsink bolted to the end of it hanging in cold air. Those crank journals are the biggest concerns during a cold start.
Wear to the crank (it's usually the bearings that wear, not the journals) during cold starts is due to oil starvation and is unrelated to the temp of the crank itself; it's all about the oil temp. Cold oil gets thick and is much harder for the system to pump through the small galleries. This creates a delay in getting oil to the crank interface after start. As you may know, the crank rides on an .002" thick film of oil and that film layer cannot be maintained without positive oil pressure. Any engine rotation with power pulses without that layer will create wear to the bearing. The longer it runs before the oil film arrives, the greater the wear. The residual oil from last run slows down the wear for a bit, which is why you don't see much wear even with all of the starting.

Larry
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Last edited by lr172 : 02-07-2018 at 12:39 PM.
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  #37  
Old 02-07-2018, 03:23 PM
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Sam Buchanan Sam Buchanan is offline
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Quote:
Originally Posted by lr172 View Post
Wear to the crank (it's usually the bearings that wear, not the journals) during cold starts is due to oil starvation and is unrelated to the temp of the crank itself; it's all about the oil temp. Cold oil gets thick and is much harder for the system to pump through the small galleries. This creates a delay in getting oil to the crank interface after start. As you may know, the crank rides on an .002" thick film of oil and that film layer cannot be maintained without positive oil pressure. Any engine rotation with power pulses without that layer will create wear to the bearing. The longer it runs before the oil film arrives, the greater the wear. The residual oil from last run slows down the wear for a bit, which is why you don't see much wear even with all of the starting.

Larry
I don't have any interest in arguing the point, but here is a link to a Mike Busch article about how crank and cam bearing clearance is the biggest problem with a cold start:

https://www.avweb.com/news/maint/182846-1.html

This is a good read for anyone who needs to start a cold engine and wants more info on preheating. I suspect that many times the engine has not been heat saturated sufficiently after a brief session with a heater.
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Last edited by Sam Buchanan : 02-07-2018 at 03:26 PM.
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