airdale
Flight lieutenant
Posts: 42
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Post by airdale on Jun 13, 2009 3:46:11 GMT 1
I have a question about LiPo's that I'm sure is pretty basic, but I'm in the dark! I have 4 LiPo's for my SC 1-3S 1100MAH 15C-20C burst and 3- 3S 1800MAH 20C-25C burst. Why is the 1100MAH the best of all 4? They are all about the same age and the usage and charging is identical!
The 1800's run very hot while the 1100 gets just warm and when I "punch" it you can hear the motor winding up with the 1100 but not with the 1800's? I know they 1100 is lighter by a few oz's but the performance difference is HUGE!
I wudda thought that the 1800's would be the go-to battery but, not the case at all! I think I'm getting better performance out of the 1100 and can't figure out what I'm doing wrong? I've felt the ESC after landing and it's barely warm (on either battery). Why am I not getting any ZIP outta my 1800's?
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Post by flydiver on Jun 13, 2009 5:26:39 GMT 1
What brand---specifically? It's important. What use history---specifically, it's also important? Battery manufacturers or resellers can claim whatever they want. Almost all this stuff is from China. There are no rules really. Frankly I discount ALL performance claims of EVERYTHING RC from China at LEAST 20% until proven otherwise. Assume everything is from China until proven otherwise. This is directly from Todd's Models on top of his web page to ALL his batteries: [Todd's Battery Rule #1 - Whatever the manufacturer rates a pack's discharge rate at do 2/3rds and you'll have a battery that will last a long time. So if a pack is manufacture rated at 30C then run it at no more than 20C. If you run packs at the full C rating for the entire flight then expect a decrease in performance in 5 to 50 cycles.] Folks still learning about lipos might want to read the rest of his information. www.toddsmodels.com/Thunder_Power_Poly_Rc_Enerland_Polyquest_s/20.htmIf you have the SAME batteries with the SAME use history the 1800 should perform better, assuming weight is not a major issue (small plane, weight sensitive). In the Cub, that difference should not be a factor. But, different batteries, different story. If you have an 1800 eBay 'Mystery' lipo and an 1100 Thunder Power Prolite the Mystery is going to get it's volts kicked. TP is a WAY more expensive battery but is WAY better. Some of the PZ lipos are OK, some are marginal. Some lipos are frankly, crap. And occasionally even good manufacturers will end up with a bad batch of one variety or another. The difference there will be warranty satisfaction vs. 'eat it'. You pay your money....... Poor handling of even a good battery (excessive discharge, excessive heat, etc.) can take a good battery and ruin it in short order. A guy [everydayflier] in another forum that tests a LOT of batteries got a new model that was supposed to do 40C. So he did a 40C test. Ruined it in one test. Obviously the claim was bogus. I had a lipo that I was treating right well and it just crapped out on me. I have another I inadvertently drained to ZERO!!! volts. DEAD! I recharged it (don't do this at home kids), and d**ned if it still doesn't perform OK. I have it's identical twin to compare it to. It is just a tad puffy but I think that kind of abuse should have absolutely killed it. Usually does. I do expect it will have a shorter life. I have HUGE caution marks on it and am watching it carefully. If you believe LVC will save your lipos, well, you have a lesson to learn. |
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airdale
Flight lieutenant
Posts: 42
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Post by airdale on Jun 13, 2009 15:33:27 GMT 1
Thanks for the response. The 3 1800mah's are Transmetric (from eBay) and the 1100mah is the SkyArtek that came with another plane I bought. I have never run any of them below 11.2V (they'd probably MELT my plane) and I use a Balance charger when bringing them back up. I have a little Video Camera mounted on the SC so I'm VERY seldom above 1/2 throttle.
I was out this morning for some air time and after 6 minutes the 1800's were almost too hot to hold in my hand but the 1100 was just warm??
I thought maybe it was the length of my battery cables (I have the ESC mounted in the cowl) but that would effect ALL of them if they were too long!
Maybe the 1800's are just CRAP eBay batteries!
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Post by flydiver on Jun 13, 2009 16:25:00 GMT 1
The 3 1800mah's are Transmetric (from eBay) Maybe the 1800's are just CRAP eBay batteries! Are the wires really thin? This will make a huge difference, especially with longer wires. There were some that came out with stupidly thin wires and lousy performance. Maybe you got some? I think there is your answer. Proof is in the performance. Trouble with this kind of purchase is the HUGE variability on expectation, use, and actual quality. Some folks are happy, and some are not. My personal philosophy is that you have to know exactly what you are getting from eBay with RC or don't go there. Of course newbies don't have a clue and seem compelled to go there for the 'great deals'. Oh well. Like you they ask afterward. BTW-beware of excessively long battery cables. It can do very bad things to the ESC, like fire. |
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airdale
Flight lieutenant
Posts: 42
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Post by airdale on Jun 13, 2009 16:43:26 GMT 1
The wires are not exceptionally thin (16 awg) and I've felt the ESC after my usual 6 min. flight and it isn't even warm! I added a UBEC because of the brownout scare with Spektrum. I'm just not getting the same level of performance with the 1800's that I am with the 1100 and the HEAT Factor kinda worries me (especially after only 6 min.) I guess you get what you pay for! ($18.50 apiece for the 1800's) Time to look for another brand I guess!
Thanks for the help!!
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Post by flydiver on Jun 13, 2009 17:07:11 GMT 1
Internal resistance must be high. Bad chemicals. Warm is OK. Too hot to hold is destructive to ANY battery.
Like I said, they can claim anything they want. There are no official C-rating cops. That's OUR job on the forums. Do your part to ensure crap like this is boycotted into extinction.
You are likely lucky with the SkyArtek. They just buy in bulk from some vendor and repackage.
It does sound like your eBay lipos are really cheesy.
I got some ABF batteries that were cheap also, used them gently, and they seemed fine. After about a dozen cycles the balance started going whacky. More bad chemistry and poorly matched cells. These were KNOWN to not live up to their advertised C-rating but I didn't need that much 'room' so thought they would be fine.
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airdale
Flight lieutenant
Posts: 42
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Post by airdale on Jun 13, 2009 18:53:44 GMT 1
Does anyone have any GOOD experience with a particular brand of batteries? Good enough to recommend them to a fellow SC Pilot! I have been trying to avoid cutting the battery box but, that limits my choices of batteries to the "brick" style. I guess it's time to get out the exacto knife!
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Post by flydiver on Jun 13, 2009 19:46:56 GMT 1
The Hobby City fans will jump in about here. You might want to read this. www.ampaviators.com/index.php?option=com_content&task=view&id=74&Itemid=28It's the same type of battery I mentioned trying hard to kill and it wouldn't die. The Hextronic got a HORRIBLE (and well deserved) rap a couple years ago when the chemistry they use in 10's of thousands of lipos turned out to be bad and people were getting brand new puffed lipos, puffed after only a couple flights, etc. They seemed to have cleaned up their act. Loong Max, FlightMax, Zippy, and Rhino, all from HC seem to be doing fine. There are a few state side resellers for a bit more $$. If you are willing to pony up the Outrage lipos are VERY good. Thunder Power, Polyquest,and Maxamps are expensive and good. |
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airdale
Flight lieutenant
Posts: 42
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Post by airdale on Jun 13, 2009 23:02:11 GMT 1
Wow- lots of choices!! It seems like HC is always outta stock on the Zippys I want. I'll probably modify the battery box so I have some more options. Just out of curiosity I put 1 of the fully charged 1800's on the amp meter and Full Power draw was 32 amps (only kept it there for a second) the full power draw on the 1100 was 42 amps (just about snapped off the throttle pulling it back so fast!!). I'm not sure what this means but, I KNOW I won't be doing alot of full throttle hot-dogging with the 1100 (only have a 40A ESC!) You can definitely hear the difference between the 2! The 1800's just don't cut-it. I think I'll do some more reading b-4 I make my next battery purchase!
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Post by flydiver on Jun 13, 2009 23:26:34 GMT 1
What motor, ESC, and prop? Specifically - it matters with this stuff too.
That's a LOT of amps for the Cub. Stock is ~10A.
If stock motor you are WAY WAY WAY over propped.
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airdale
Flight lieutenant
Posts: 42
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Post by airdale on Jun 14, 2009 3:28:05 GMT 1
Oh yeah that would be WAY over!! I've got a Turnigy 35-36B (1300kv) with a SS 40A ESC. I'm propped @ 10X6 and I guess I still need to adjust, I'm not really comfortable with 42A even if I very seldom "open her up". I have to read a little more about the correct prop. to use.
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Post by patmatgal on Jun 14, 2009 5:44:32 GMT 1
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Post by flydiver on Jun 14, 2009 6:32:02 GMT 1
Spec for that motor:
Current capacity : 35A/30s
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airdale
Flight lieutenant
Posts: 42
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Post by airdale on Jun 14, 2009 11:30:24 GMT 1
patmatgal- Thanks for the choices! I've been trying to avoid the longer batteries because didn't want to cut up the BB but I guess I'll have to. What kind of flight times are you getting with the 450 BL? and is there a HUGE difference between the 1300 and the 1750?
flydiver-
"Spec for that motor:
Current capacity : 35A/30s"- Yep- I was kinda shocked at the draw, that was the first time I checked it!! Time to re-prop I guess -sheesh- 1 more thing to study up on!!
Well- it's 55 Deg and 0 winds- time to go SMOKE a motor!! (I've got a 2409-18T from Heads UP RC as a spare, probably a better choice anyway)
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airdale
Flight lieutenant
Posts: 42
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Post by airdale on Jun 14, 2009 13:40:03 GMT 1
I flew all 4 packs this morning and I LOVE that little 1100 mah. I ran it down to 9.4v cause I was having so much fun with the power! Even at 200 ft. up (give or take) you can hear the motor wind up when you hit the throttle where the 1800's just keep plodding along. I think I'll be in the market for some new batteries SOON!
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