Battery Heater?

[Kyle Boatright]

Does anyone use a battery heater on their RV? We're probably headed out of town on one of the very cold upcoming days (<20F, unheated hangar), and i was considering adding a battery heater (remotely controlled) to warm the battery before departure.

I have a 25W silicone heating pad, and I figure I could glue it to a piece of aluminum and wrap that halfway around the battery. Making a few assumptions, that would give me about a 2C rise in battery temperature an hour if there were no heat losses, which there certainly would be. So if I turned it on 10 hours before departure, I figure I might get a 10-20F increase in battery temperature, which is enough to make a difference.

Thoughts?

 

[Rallylancer122]

Never tried a heater but I have removed batteries and brought them inside on cold nights when I had to leave the next day.

 

[alpinelakespilot2000]

Does anyone use a battery heater on their RV? We're probably headed out of town on one of the very cold upcoming days (<20F, unheated hangar), and i was considering adding a battery heater (remotely controlled) to warm the battery before departure.

I have a 25W silicone heating pad, and I figure I could glue it to a piece of aluminum and wrap that halfway around the battery. Making a few assumptions, that would give me about a 2C rise in battery temperature an hour if there were no heat losses, which there certainly would be. So if I turned it on 10 hours before departure, I figure I might get a 10-20F increase in battery temperature, which is enough to make a difference.

Thoughts?

Another option… A 60-75w light bulb in a safety cage would likely work just as well with the added benefit of heating up the entire engine, especially with cowl plugs and a blanket over the cowl

 

[Kyle Boatright]

Never tried a heater but I have removed batteries and brought them inside on cold nights when I had to leave the next day.

The unfortunate thing about the -10 (which is the airplane of interest for Monday's trip) is if you use the stock battery location, you have to remove the baggage bulkhead to reach the battery. That's a rotten job. Reinstalling the battery and bulkhead on a 10F morning would be awful...

One of my planned modifications is to add a small door in that bulkhead to make it a bit easier to quickly access the battery for heating, charging, or disconnecting...

 

[AlexPeterson]

Kyle - could you put the heat pad under the battery? Perhaps also put a thin (1/4"?) insulation layer under the pad? Maybe construction foam is available that thin, not sure. (I don't know anything about the stock battery mount system.) Be sure to attach the ground wire to the plane in case any of the wires decides to short to the airframe.

 

[Kyle Boatright]

Kyle - could you put the heat pad under the battery? Perhaps also put a thin (1/4"?) insulation layer under the pad? Maybe construction foam is available that thin, not sure. (I don't know anything about the stock battery mount system.) Be sure to attach the ground wire to the plane in case any of the wires decides to short to the airframe.

Under the battery is a recommended location for a battery warmer, so that's a consideration. As far as insulating it goes, even a cut-to-fit piece of baffle material would reduce the tendency of the airframe to act as a big 'ol heat sink.

 

[bobnoffs]

i would cut a piece of .063 alum. to the battery size and stick the heater to that. if you do or don't use the plate you will need insulation under the heater as it has quite a bump at the cord end.
for reference i have one [25 watt] under a plate in an insulated box in my shop and it will keep a cup of coffee hot. not quite as hot as right out of the coffee maker. the plate by itself would get hot, you can't keep a finger on it. maybe stick the heater to the plate first and play with it a bit, see what you think.
let us know how it works after an hour, i will make one too!

 

[lr172]

It is known that as temps drop, the battery output drops. However, not sure that batt heaters are necessary. I have started my 320 at 0F maybe 10 times and never had issues. I use a 250 watt sump heater and cowl plugs to keep the heat in. This get the whole under cowl area temp up quite a bit and have never found my battery too weak to get the engine started and it often takes a couple of attempts, as you need a LOT of prime at 0F. I have probably started at 20F 25 or 30 times and is a non-issue.

Battery heaters definitely work, but you must exercise caution to be certain you don't OVER heat them. I would invest in a blanket with necessary straps to hold it on and cowl plugs over a batt heater. Equally effective with no risk.

Larry

 

[Kyle Boatright]

Battery heaters definitely work, but you must exercise caution to be certain you don't OVER heat them. I would invest in a blanket with necessary straps to hold it on and cowl plugs over a batt heater. Equally effective with no risk.

Larry

Remember, this is a relatively stock -10, so sump heaters and the like won’t warm the battery.

The thing that differentiates the -10, at least in my life, is that if the whole family is loaded aboard on a 10F morning, ready to go somewhere, the engine *has* to start. Way different than me or me and a buddy bumming around on a Saturday morning in the -6. So over preparing to make that happen is a good investment on my part.

 

[MacCool]

It is known that as temps drop, the battery output drops. However, not sure that batt heaters are necessary. I have started my 320 at 0F maybe 10 times and never had issues. I use a 250 watt sump heater and cowl plugs to keep the heat in. This get the whole under cowl area temp up quite a bit and have never found my battery too weak to get the engine started and it often takes a couple of attempts, as you need a LOT of prime at 0F. I have probably started at 20F 25 or 30 times and is a non-issue.

I wouldn’t give temps of 10-20° F a second thought…based on decades of having to start cars, tractors, snowmobiles etc in temps down to -30° F. That said, I confess I’ve never tried to start my airplane in temps less than 0°, but my situation mirrors Larry’s. I think that if you’re starting your airplane in the safe engine temps that Lycoming recommends (pre-heat recommended at 10° F or warmer), a healthy fully-charged battery would have no problem.

Put a 100-watt light incandescent light bulb on a drop cord inside your cowl, throw a sleeping bag over it, and put the battery on a float charger the night before.

 

[David Z]

I start cars down to -40. Battery output lowers with cold. A weak battery first shows up in the fall when cranking power is weak. That means it's time to get a new battery. Some people put fancy battery blankets around car batteries, but that's basically nursing along an old battery and delaying the inevitable...dead battery, won't start. It also hints that battery capacity isn't what it should be. If battery capacity is utilized for anything important, be wise to replace it. On a car, you'll just get stranded at the grocery store when the battery blanket isn't plugged in. An airplane has higher consequence.

 

[bobnoffs]

when this thread started i was thinking lipo. a good agm i think is good as is way below the temp. i want to go out and get my airplane flying. 20 deg. with a good engine preheat is as cold as i want to go. hundreds of starts in my car at -25 deg. f
i still haven't figured out what to do with an earthx in the winter for a 20 deg f start though. i get conflicting info from the web, the factory, and the battery charger mfgr.

 

[Moshonsk]

I wouldn't be too concerned about anything above -20. Although battery capacity is lower, as long as the engine has been preheated and the oil is warm a decent battery should have no problems cranking the engine over to start it. Instead of installing a battery heater, why not put your time and effort into installing a ground power plug? I installed one on the rear baggage bulkhead of my -10 very easily and then if the battery is too low, or if someone left the master on or whatever, it's an easy fix to get the engine started.
And where we live we routinely start up preheated engines down to -40 and as long as the engine is 'warm' and the battery is decent, there are no problems. It does, however, weed out marginal batteries very quickly.

 

[lr172]

Remember, this is a relatively stock -10, so sump heaters and the like won’t warm the battery.

The thing that differentiates the -10, at least in my life, is that if the whole family is loaded aboard on a 10F morning, ready to go somewhere, the engine *has* to start. Way different than me or me and a buddy bumming around on a Saturday morning in the -6. So over preparing to make that happen is a good investment on my part.

That is true. However, the 10 has two batteries and the 6 cyl likely only requires marginally more amps to crank than the 4 cyl. Sure, a battery may lose 20% of of it's output capacity at 0*, but the 10 has WAY more capacity than my 6 has at ANY time. If you have a permanent magnet starter like the NL series, this also makes a big difference.

I have started the 10 several times at 30* or less and had absolutely NO noticeable drop in performance cranking it over. Sorry, but just don't remember the coldest that I have started it below 30 and unlike the 6, have not yet done so at 0*, though I have no concern that it will crank over just fine.

I did my phase I in Jan and Feb in Chicago. There were some wicked cold days that I flew. Always used an engine heater, but the hanger was insulated but not heated, so don't have a real good idea what the temps were inside, but confident that battery temps were at least as cold as 30* on a few occassions.

Remember that the engine internals are all going to be around 50* so you are not dealing with the same issues as starting your car at 0*. You aren't fighting all of that resistance, so the ampacity required is no higher than starting in spring or fall. The challenge of starting a car at 0* is NOT just due to the battery being cold.

If I were to do something to warm up the batt, I would rig up a milk house heater to a 3" dryer duct, then pull one of the insp plates off at the elev attach area and stick a few feet of it in there pointing forward. That should easilly bring up the battery temp overnight. Several here have made engine pre heaters like this, so plenty of posts and pics to copy from.

 

[nedricher]

I too, have started air planes and other vehicles at very cold below freezing temps with no consideration given to warming the battery. A good battery will not have a problem doing the job in the cold. This applies to lead acid batteries (flooded, gel, and arm). Having said that, the new lithium ion batteries can be damaged or destroyed if charged or used in cold temps.

 

[togaflyer]

Bring your power on but don’t crank your engine right away. Give it about a minute before putting a large demand/cranking the engine. I have a charger connection accessible via the baggage area. If you have access to hooking up your charger, that also helps keep the battery warm.

 

[akschu]

Kyle,

I think the comments about cars starting in -15 is pretty bad advice as my wife's car uses 0w-20 oil, is water cooled, and almost nothing in that engine is splash lubricated. Airplanes are a different animal.

One of the biggest problems is breaking the oil friction on start. After 25 years in Alaska, I've learned a few things about starting airplanes and diesel trucks in extreme cold.

First, you want the oil warm enough to not fight with you. If you run 50w year around, you must use a pan heater and it must be running for 8-10 hours depending on wattage. Also, I like to turn the prop over by hand a few times to get a feel for how hard the starter is going to have to work and how loose the engine is.

Second, the engine tolerances are much tighter at extremely cold temps, a good pan heater should warm the block to some degree as well, I use a cowl blanket to keep the heat in the engine. It's the same idea as a 100w bulb with a blanket.

Once the engine and oil are warmed up enough to that the battery doesn't have to work extremely hard to start, it will probably work if it's not -20 and in good shape, but I like to use a trickle charger/maintainer to keep the battery warm. It makes sure it's topped off and the charging makes a little heat in the battery. (Note, this is all lead/AGM batteries, you can't float charge a lithium battery).

As long as you have the engine ready to start, and the battery is warmish and topped off, it will light right off.

In AK I used the trifecta on my diesel trucks, battery maintainer, oil pan heater, and freeze plug heater. I could power it up 3 hours before leaving and start my truck in -35F with no issue and at those temps it wouldn't warm up in the driveway idling, and stopping for fuel would take my water temp from 205F to 160F and the fast idle would kick back on half way through the fill up.

Read more about cold airplanes here: https://backcountrypilot.org/featur...ports/welcome-to-the-ice-world-of-lake-george

 

[lr172]

Kyle,

I think the comments about cars starting in -15 is pretty bad advice as my wife's car uses 0w-20 oil, is water cooled, and almost nothing in that engine is splash lubricated. Airplanes are a different animal.

One of the biggest problems is breaking the oil friction on start. After 25 years in Alaska, I've learned a few things about starting airplanes and diesel trucks in extreme cold.

First, you want the oil warm enough to not fight with you. If you run 50w year around, you must use a pan heater and it must be running for 8-10 hours depending on wattage. Also, I like to turn the prop over by hand a few times to get a feel for how hard the starter is going to have to work and how loose the engine is.

Second, the engine tolerances are much tighter at extremely cold temps, a good pan heater should warm the block to some degree as well, I use a cowl blanket to keep the heat in the engine. It's the same idea as a 100w bulb with a blanket.

Once the engine and oil are warmed up enough to that the battery doesn't have to work extremely hard to start, it will probably work if it's not -20 and in good shape, but I like to use a trickle charger/maintainer to keep the battery warm. It makes sure it's topped off and the charging makes a little heat in the battery. (Note, this is all lead/AGM batteries, you can't float charge a lithium battery).

As long as you have the engine ready to start, and the battery is warmish and topped off, it will light right off.

In AK I used the trifecta on my diesel trucks, battery maintainer, oil pan heater, and freeze plug heater. I could power it up 3 hours before leaving and start my truck in -35F with no issue and at those temps it wouldn't warm up in the driveway idling, and stopping for fuel would take my water temp from 205F to 160F and the fast idle would kick back on half way through the fill up.

Read more about cold airplanes here: https://backcountrypilot.org/featur...ports/welcome-to-the-ice-world-of-lake-george

While I agree that 0 weight oil makes a difference in starting effort, water cooled engines get just as cold as air cooled engines if they haven't been run in several hours. In fact, air cooled engines tend to have larger clearances than water cooled engines. Splash oil has no real bearing on how difficult an engine is to crank.

All that said, the norm for auto engines was 10Wxx for many decades and they were not meaningfully harder to start than 5 or 0 weight. That migration to thinner weights was not for cold starting ability but for mileage improvement in the ongoing battle with the regulators. They have been less and less forgiving of efficiency reductions during the warm up period over the years.

I would hope NO ONE would try to start an engine with 50W oil in these type of temps. 20W50 is not that much thicker than 10W oil at 20* and I doubt anyone on this forum would start an aircraft engine at 0* without preheating the oil, kind of taking that out of the equation.

 

[rocketman1988]

Temps

“…Second, the engine tolerances are much tighter at extremely cold temps,…”

That’s interesting. Can you give examples?

Aluminum, for example, will change about 0.0000128” per degree F so a 50 degree temp change is about 0.00065”. Considering the manufacturing tolerance is around .005”, a 50 degree temperature change is a very small number and likely inconsequential compared to other factors.

 

[Kyle Boatright]

“…Second, the engine tolerances are much tighter at extremely cold temps,…”

That’s interesting. Can you give examples?

Aluminum, for example, will change about 0.0000128” per degree F so a 50 degree temp change is about 0.00065”. Considering the manufacturing tolerance is around .005”, a 50 degree temperature change is a very small number and likely inconsequential compared to other factors.

I've seen this claim elsewhere, and from a source I trusted (but didn't try to verify). Obviously, Aluminum moves more with heat and cold than steel, and the claim was that in very cold temperatures, the bearing clearances between the case and the crank get very tight.

Anyone know the standard bearing clearances off-hand?

 

[rocketman1988]

I've seen this claim elsewhere, and from a source I trusted (but didn't try to verify). Obviously, Aluminum moves more with heat and cold than steel, and the claim was that in very cold temperatures, the bearing clearances between the case and the crank get very tight.

Anyone know the standard bearing clearances off-hand?

Couldn’t find a Lycoming specific chart but typical clearance is about .001” per 1” journal diameter. I think the journals are about 2.5” so around 0.0025”…

 

[lr172]

I've seen this claim elsewhere, and from a source I trusted (but didn't try to verify). Obviously, Aluminum moves more with heat and cold than steel, and the claim was that in very cold temperatures, the bearing clearances between the case and the crank get very tight.

Anyone know the standard bearing clearances off-hand?

Most rod journals for engines of this size are in the neighborhood of .0023-.0028. Main journals closer to .003. The tolerance range is usually .0005 - .0007. That is total clearance (bearing ID - journal OD). The typical gap between the parts is half of that amount when moving. The lyc published range for rod bearing clearance is .0008-.0038 with a service limit of .005

Alum vs steel doesn't apply with any of these clearances. All the parts are steel and expand and contact at similar rates (excluding the soft bearing shell, which has very little alum-mostly tin and copper). When dealing with cylinders, it does apply. Need to be cautious with heat, as the alum expands faster and greater than the steel barrel. Opposite when cold; piston is contracting more than the barrel and therefore clearance grows. You almost never have meaningful friction from the piston to wall anyways (Lyc has max of .018-.021 clearance at skirt, the thickest part). The friction is from the rings dragging on the wall and the friction is due to springed rings and not clearance, which is ALWAYS 0.

A lot of this is moot, as the greatest resistance to spinning an engine that the stater is fighting is the compression. Not saying that oil viscosity doesn't matter, it does, and that is why heating oil is the most common method of helping to start an engine in cold temps. Remember that engine is normally compressing air that is around 100*. A cold start at 0* and you are compressing air that is 0*. It is MUCH denser and therefore harder to compress. Exact same reason you will climb twice as fast at 0* ambient vs 100*; That dense air is both producing more power in the engine and producing more lift on the wings. Some diesels with almost double the compression rate deal with this when cold by opening the valves a bit (to stop compression) in order to let momentum and RPM build without the affect of compression before attempting to start.

EDIT: sorry, forgot that the case is the shell on a lyc and is alum. That clearance is .0015-0045 with an .006 service limit. I do not believe that the differences in thermal expansion will tighten that clearance to anywhere near a point of 0 clearance therefore no issue. Don't know the numbers off hand, but expect that the difference in thermal expansion rates between alum and steel is less than .0001" for a 100* temp change. WAY less than the clearance.

Larry