Choosing a Battery Pack

piker · January 04, 2013, 04:29:59 PM

O.K., here's a simple question that I'd like your opinion on:

I'm shopping for battery packs for a couple of my new planes that I hope to have flying in the Spring. As you know, there are several "C" ratings available these days, generally from 25C to 45C. I'm looking at 5000mah packs which would provide a current capability of 125A for 25C to 225A for 45C. I've never run more than 60a in a plane and generally would prop for about 50A max.

Besides the good prectice of taking into account "safey margin" room, why would I need to even consider 45C when 25C would give me double the current capability that I need. I think I know the answer... "that I don't need 45C for my application and that the 45C batts are only for high current applications", but I'd like to hear what you guys have to say on the subject.

Thanks.

Robert

Ededge2002 · January 04, 2013, 05:15:35 PM

Ive found that the higher the "C" raiting the higher the voltage is under even much lower loads. No noticable performance drop throughout the duration of the discharge. If you brake this down you get more volts at the same pack capacity. The higher C packs usualy do not heat as much as the lower value ones do as well. Less risk of developing puffy cells. The final "bonus" to the higher C packs ive found is cycle life. Provided they are stored properly I have found that I get a lot more cycles on even packs that im pushing quite hard at times.

I admit that I shop around and buy the best packs I can find at the best deal.... But perormance is over value to me.

flying saucer · January 04, 2013, 05:30:04 PM

Quote from: Ededge2002 on January 04, 2013, 05:15:35 PM
Ive found that the higher the "C" raiting the higher the voltage is under even much lower loads. No noticable performance drop throughout the duration of the discharge. If you brake this down you get more volts at the same pack capacity. The higher C packs usualy do not heat as much as the lower value ones do as well. Less risk of developing puffy cells. The final "bonus" to the higher C packs ive found is cycle life. Provided they are stored properly I have found that I get a lot more cycles on even packs that im pushing quite hard at times.

I admit that I shop around and buy the best packs I can find at the best deal.... But perormance is over value to me.

+1 to everything Ed said regarding holding voltage/packs staying cooler etc..

BUT, when you're dealing with a known 60A draw power system, and your 25C pack is rated for over 100A, I see less reason to go up to a 45 or 65C battery, as the pack isn't anywhere near it's performance limit and will likely hold up well. You also have to consider the fact that with higher discharge lipo's you will see shorter flight times when flying near full throttle.

piker · January 04, 2013, 05:48:16 PM

Good points guys. I recall the voltage drop and general happier lifestyle of the higher C packs. I've had my head in balsa dust too much lately and forgot how these electric airplanes work

My 5000mah 45C packs were great until I bent them. They may still be O.K., but I havn't tried yet.

Robert

wollins · January 04, 2013, 06:39:18 PM

IMHO if these were just for your new WW1 Bipe they (the 45C) would be way overkill. I mean we're talking 225A continuous or almost four times your requirement at burst! In my big Decathlon, I've been using 5000 20C packs and I have tons of power to spare, and I pull about 85A in that plane.

Having said that ... if you're buying for general use for more than just that plane ... in other words if its not application specific I'd say go for the higher C rating for sure. ESPECIALLY since the prices of these packs nowadays are so low ... even relative to the lower C packs!

One other thing to keep in mind though is that the higher the C rating the heavier the cells are ... in other words a 20C 5000mah pack will be considerably lighter than a 45C 5000mah pack. My 20C 5000mah packs are 20 ounces each, the ones you're looking to buy are almost 26ozs each. If you're running ten cells that's three quarters of a pound of extra weight, so if weight is an issue you have to take that into consideration.

Just my .02 cents.

Colin

Bobmic · January 04, 2013, 06:55:14 PM

Hi Robert,

It really depends on the type of flying you expect - keep in mind that these two guys are not "Normal" flyer. One is flying rockets and the other tries to break the sound barrier each time he takes off

Unfortunately C rating is based on the manufacturer and you will end up with different readings for same C rated batteries which are manufactured by different manufacturers. the problem is that no one mentions the voltage drop under load so the stated rating can only be used as a reference between batteries.
If you want high acceleration you have to have high C rating but if this is not the most important factor, you can save money and weight if you go with a 25-50C.
Attached are readings from my Sundowner which was flying with a 35-45C 5s Compact Zippy 2700mAh, in theory this battery should be good for 95 to 120Amp but as you can see the voltage dropped about 2 volt at 50Amp and 3 volt at 80Amp. I am not sure what will be the results with a Thunderpower or a NanoTech with a high C rating but you get the point, for a plane that does not need to accelerate supper fast you will not notice a big difference (even though - I can not comment about packs holding longer etc. )

Bobby

piker · January 07, 2013, 10:01:01 AM

Hey guys,

Just wanted to say thanks for your help and input.

Although I'm sure the lower C rating batteries would be fine for my application, the thought of having higher C rated batteries that would be "cruisin'" in my application, would potentially hold a higher voltage, and potentially live longer, and also be available incase I do want to go hot rodding at some point, is worth the little extra cost.

So, despite logic, I'm gonna go for the 45C's

Thanks again!

Bobmic · January 07, 2013, 02:44:28 PM

Agree with the "incase...

"
Same as driving a >300HP car and spending extra for high grade fuel when the speed limit is 100kph ...

flying saucer · January 07, 2013, 03:50:13 PM

Quote from: piker on January 07, 2013, 10:01:01 AM
Hey guys,

Just wanted to say thanks for your help and input.

Although I'm sure the lower C rating batteries would be fine for my application, the thought of having higher C rated batteries that would be "cruisin'" in my application, would potentially hold a higher voltage, and potentially live longer, and also be available incase I do want to go hot rodding at some point, is worth the little extra cost.

So, despite logic, I'm gonna go for the 45C's

Thanks again!

Good choice, I recently received a 45-90C 2200mah 3S pack, and after using many 20 and 25C 3cell lipo's, I can tell you this one is a different animal. Way more power and stays cooler.

I think another benefit of these is the odd time when you forget to set your timer or you just run them down way below 3.7V/cell, they take the abuse and recover much better than 20-25c packs.