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lipo battery heat

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Stan Waters23/10/2018 15:54:07
13 forum posts

Hi All, I was wondering how you more experienced people deal with the heat from lipo's when in use.

Do you have to protect the mounting on which it held whilst flying, I appreciate the need to ventilate both the esc and the lipo, but is the heat generated enough to do something extra with the mounting area.

The plan does not show any information as to mounting as the aircraft was designed for ic. power ( Ben Buckle mini super).

Any thoughts will be appreciated.

Stan

Biggles' Elder Brother - Moderator23/10/2018 16:04:10
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15748 forum posts
1460 photos

Hi Stan,

to be honest it isn't generally that big an issue - or it shouldn't be! If you have to protect the mounting you have big problems mate!

What's needed usually is just a sensible size air intake at the front, and an exit air hole at the back of approximately twice the area. What's a sensible size? Well about 1.5 times the crosssectional area of the battery is usually fine or a little more to be generous. It doesn't have to be one single inlet - you could have two and add their areas.

Rememeber it not just the battery that can get warm, so will the motor and the ESC so they must be in that airflow too. But if you have epec'ed these well, with plenty of "headroom" there should be no issues.

BEB

Edited By Biggles' Elder Brother - Moderator on 23/10/2018 16:06:21

Geoff Sleath23/10/2018 16:28:33
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3133 forum posts
247 photos

I've never had LiPos anything more than warm to the touch when flying propeller driven models. It might be different for ducted fans that draw lots of current a lot of the time. My most thirsty model (a quarter scale Mew Gull) draws a maximum of 70 amps but only for a few seconds on a vertical and it's mostly around 18/20 amps straight and level according to the telemetry.

Not really a problem as BEB says. It's the esc that's most likely to need good cooling. It's tempting to use the flat side to mount it on the fuselage side but that's the heat sink and needs a flow of air so use the other one. If your esc is well over specced as it's likely to be in your vintage build then even that is unlikely to be much of a bother.

Geoff

Simon Chaddock23/10/2018 16:39:22
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5286 forum posts
2777 photos

Stan

Is your LiPo really getting that hot that it can damage its mounting?

In general if you discharge a LiPo over a flight at about half is rated C i.e at a 10C discharge for a 20C rated battery then it should not get too hot. The rate at which heat can be dissipated from a LiPo is limited, particularly from those of 3 or more cells as the 'middle' ones have no external surface. In addition each LiPo cell is encapsulated in a thick layer of plastic which is a pretty poor conductor of heat.wink 2

In practice you rely on the thermal mass of the battery to absorb the heat generated from discharge and aim that that the discharge will be complete before any of the cells have reached a critical temperature. A LiPo's life will be significantly shortened if it gets too hot.

The ESC on the other hand has very little thermal mass so it can over heat really quickly so adequate cooling is essential. To a slightly lesser degree the same condition applies to the motor although it does generate more heat.

Edited By Simon Chaddock on 23/10/2018 16:41:36

David Mellor23/10/2018 16:45:44
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1231 forum posts
602 photos

If your battery is getting hot then there is something wrong somewhere.

Without more info, it is hard to tell what might be amiss, but on the face of it, perhaps your motor is demanding more current than the battery is capable of delivering comfortably.

Usually it is best to have some measurement of actual current draw, measure voltage sag (the voltage drop under full load) and then check that the C rating of your battery is up to the job. It sounds like your battery is either to small (not enough mAh and/or too low a C rating) or that it has become knackered - which they all do eventually unless well looked after!

Chris Walby23/10/2018 17:21:22
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765 forum posts
148 photos

I have a couple of EDF's that hammer the lipos if you fly at full speed and the batteries are usually very warm to hot to hold. The down side is flight time can be less than 3 minutes so the lipo is normally out of the model and left to cool in ambient air.

As the guys have already mentioned above, cooling for ESC and motor will be needed and you don't need to push the lipo that hard to achieve something that will fly so I don't think you will have an issue with a little ventilation.

Could be wrong, but I think the competition glider guys actually heat the lipos in the aircraft as they perform better above normal ambient air temperatures to get the best out of the lipo (extreme use, but it is a competition!).

Stan Waters23/10/2018 17:27:10
13 forum posts

Thanks for your help, I am still building the model so I do not know how hot it will get, It was from another modeller who told me that the lippo gets hot, so I thought I would ask the question at this stage rather than have problems at a later date.

Thanks for putting my mind at rest, this is my first electric aircraft so it is a leaning curve, I will watch out for the esc. though and provide cooling.

Stan

Nigel R23/10/2018 18:04:54
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2297 forum posts
387 photos

I can quote what I've done on similar size / power model to the mini super -

1/2" x 1" air inlet at the front of the cowl

Motor and ESC both in cowl area.

1" x 1" hole in the firewall

lipo directly behind firewall

1.5" x 1.5" hole for air out, a few inches behind the trailing edge, on fuselage underside.

Keep the inside of the fuselage nice and open - no solid formers.

An 800W model with those kind of sizes, the lipo is warm and no more than warm.

On a 300W model with those sizes, the lipo comes out cool.

Hope that helps

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