German SAW 2016 in Munich

[dmitry100]

About house temp so around 60-70*F

I was charging them at 7 amps

[martin]

General opinion on IR readings should be taken at 72 F .

[Darin Jordan]

General opinion on IR readings should be taken at 72 F .

Wouldn't you be more concerned about what they would be at operating temp? I know I would be...

[martin]

The 72F is used as a standard guide to compare lipos against one an other, otherwise the numbers will be all over the place. For example if you test a given battery at 72f & get say 2 ohms per cell & you test the same battery at 60f you will see a much higher figure reading.

[Fluid]

The internal resistance of various cell types is not linear over temperature changes. Cell "A" may give the same IR as cell "B" at 72*, but raise the temperature to 115* and it may have a significantly lower IR value. As a result, listing IR at 72* is of limited value for many of us. Yes, you can compare all cells at one temperature - but it may have little to do with cell performance at the temperatures seen in high performance FE boats.

I'd rather see IR values measured at 110*. Personally, I don't care what my pack's IR is when it's sitting in storage.



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[longballlumber]

So how do you control temp? During a discharge cycle the temp is going to fluctuate based on several variables. Wait isn't cell temp a bye product if IR... lots of variables that don't allow anyone to justify much; unless both parties are using the same equipment AND the same test procedure

[Darin Jordan]

So how do you control temp? During a discharge cycle the temp is going to fluctuate based on several variables. Wait isn't cell temp a bye product if IR... lots of variables that don't allow anyone to justify much; unless both parties are using the same equipment AND the same test procedure

Not that complicated... You wrap a heating blanket around the pack... when their temp reaches a certain point, you discharge them.

[dmitry100]

Darin, do you normally check IR during discharge or during charge?

CellPro seems to only allow me to see IR during discharge...

[MarkF]

To many people look at IR when it's not really giving you all the info. IR measurement is the pathway from the lipo to the tab. It doesn't take into account the quality of the lithium being used. Manufacturers see how many people are looking at IR numbers and now build packs that have low IR to fool people, but use cheaper lithium. You'll know if your lipos have a short life cycle or loose their good punch in a short period of time. To me, this make IR a useless tool. Most of you can tell when your packs are going bad when you run them.
Lipo optimum running temperature is 86 to 104 deg F. Basing your opinions on IR at 72deg is kind of pointless. Voltage under load and cycle life is whats important.

Mark

[properchopper]

To many people look at IR when it's not really giving you all the info. IR measurement is the pathway from the lipo to the tab. It doesn't take into account the quality of the lithium being used. Manufacturers see how many people are looking at IR numbers and now build packs that have low IR to fool people, but use cheaper lithium. You'll know if your lipos have a short life cycle or loose their good punch in a short period of time. To me, this make IR a useless tool. Most of you can tell when your packs are going bad when you run them.
Lipo optimum running temperature is 86 to 104 deg F. Basing your opinions on IR at 72deg is kind of pointless. Voltage under load and cycle life is whats important.

Mark

You get a good start. Second place, lane 2 and begin to chase down first place. He bobbles on a turn and you slide past. The CD's voice coming from the speakers utters the most beautiful words ever to a racer's ears : " YOU just put a move on so-and-so." You hold first until lap 5 and then on the back straight you start to slow down, imperceptibly but enough to be overtaken. The CD says : "First Place is slowing down for some reason".

Choose batteries wisely, this "slow down" will be unlikely and you can be a winner. Believe/wallow in numbers bantered about by keyboard pilots and zoom-zoom rookies and revel in their Kabuki Theater nonsense.

[dmitry100]

Do you guys use any sort of thermal pad (like the ones we use for PC's) between your Lipo Heater and the lipo's for improved heat transfer? since the lipo's are an uneven surface and all

[Fluid]

My LiPo heater is a standard "medical" heating pad from WalMart. I wrap it around the packs, it heats from both sides trapping the heat inside. I put it all in an insulated pizza bag, others just wrap it in a towel.



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[dmitry100]

ahh ok nice. Is there any accurate way of determining internal temp of the lipo's during/after a heating session?

[Fluid]

IR gun, the packs heat from the outside but 15-20 minutes seems like plenty. With some experience you'll find a blanket setting to match you target temp.

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