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Post by cschrein on Jun 13, 2011 7:19:57 GMT 1
I've had a SuperCub LP for about a month now. I've apparently killed two batteries and am just wondering what replacement battery I need and whether I need to get a new carger and/or a voltage meter. I'm not interested in doing any modifications - I just want to be able to help my daughter learn to fly. Did I kill the batteries by flying until they died? I'm reading that I should just time my flights and not let the battery completely dishcharge. My stock charger just flashes red three times and the batteries no longer work.
Sorry for the newbie questions but I'm just looking for simple solutions at this point!
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Post by Dillzio on Jun 13, 2011 8:36:54 GMT 1
First thing you need is a balance tester, it's a little LED panel on a circuit board that plugs into the battery's balance port and tells you the voltage of each cell. They're dirt cheap, and available from ebay or hobbyking www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=6589Once you get it, start using it regularly, at the beginning, during, and at the end of a flight (obviously, you will have to land half way through the flight for a quick check, I don't recommend checking your battery voltages in mid-air). If you want your batteries to last, you should be landing when each cell is about 3.7, give or take 0.1v. Pretty soon you should get a feel for how long you can fly for, and then you set a timer just as you take off (I use my phone) to warn you to land before your battery gets too low. In terms of a replacement battery, you should go to hobbyking and get a 3S 20C battery. I would recommend a Zippy 1600mah, only 9 bucks plus postage. www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=6539 You will need to modify the battery box to make it fit, but that's something you really should be doing anyway, the stock battery box poses a known fire risk. |
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Post by flydiver on Jun 13, 2011 15:24:11 GMT 1
On the stock charger once the voltage goes below 3.0v on any cell it won't charge anymore. This is a 'safety feature'. Of course the ESC low voltage cut-off is set BELOW that level (smart, eh?).
Your 'killed' lipos may be fine with a better charger that can bring the voltage back up as long as it doesn't go TOO LOW. A little low is not good for them, too low does permanent damage and may render them dangerous. That's why you NEED a proper voltage checker.
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Post by cschrein on Jun 13, 2011 16:52:23 GMT 1
Thanks for the info! I will definitely get a balance tester. Any recomendations for an improved charger?
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Post by Dillzio on Jun 13, 2011 23:50:48 GMT 1
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Post by renard80 on Jun 16, 2011 23:05:52 GMT 1
. . . . If you want your batteries to last, you should be landing when each cell is about 3.7, give or take 0.1v. . . . On Dylan's advice I have just bought one of those testers (from the ever-helpful john66 ;D) . My SC batteries are 11.1v 1300mAh. My Mini Cub batteries are 7.4v 300mAh. When they are fully charged, the tester shows the oldest 1300 at 4.02 each cell. My newer 1300s are around 4.14. The 300s (fairly new) show around 4.17 each cell. Do all those values sound right? I ask because Dill says I shouldn't go below 3.7, and that doesn't seem like a lot of airtime from 4-ish. (I can't test this in flight at the moment - the southern UK is socked in with gusty winds and heavy rain. Bummer.) |
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Post by toff on Jun 17, 2011 7:12:32 GMT 1
On full charge, each cell should be ( irrespective if its 2 or 3 cell ) at 4.20 volts. This is the top line for a lipo cell with each being a nominal voltage of 3.7 volts. So... an 11.1v lipo is actually a 12.6 v lipo, 14.8 v is actually 16.8v, etc.....
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Post by ginginho on Jun 17, 2011 9:04:12 GMT 1
Renard, as Toff has said, 4.20 is the cell fully charged. The little battery testers are useful but not always completely accurate. Your values suggest that your charger isn't taking them to full capacity, is it the stock HZ charger you are using? I believe these aren't the best available and hence maybe why you are getting the reading you see. It's not a big problem as at least you have a safety margin (taking packs over 4.20 can be pretty dangerous), and you packs will be 90+% charged. Fly posted a table on here years ago that lists various voltages and what they equate to in charge in a cell, I think he got if from RCG but I could be wrong.
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Post by john66 on Jun 17, 2011 12:30:08 GMT 1
The little battery testers are useful but not always completely accurate. Reseller disclaimer! Though as agreed by most, Nick included I believe (after all he reccomended one to me originally  ) ? They are I believe, accurate enough for knowing whether you have another flight left in your batts, but not for a bang on accurate balance reading. But hey Renard more than happy to give a full refund upon return if you want one of the more accurate field testers. I have some on order but they are alot more expensive (20-40 quid I believe off the top of my head) John |
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Post by ginginho on Jun 17, 2011 12:38:59 GMT 1
The little battery testers are useful but not always completely accurate. Reseller disclaimer! Though as agreed by most, Nick included I believe (after all he reccomended one to me originally ) ? They are I believe, accurate enough for knowing whether you have another flight left in your batts, but not for a bang on accurate balance reading. But hey Renard more than happy to give a full refund upon return if you want one of the more accurate field testers. I have some on order but they are alot more expensive (20-40 quid I believe off the top of my head) John Ooooh, getting nervous John? I should have stated that they can be out but only a little, mine reads the second cell always 0.02v lower than the others (IIRC). It's not a major difference and Renard shouldn't need more accuracy that what these give. |
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Post by john66 on Jun 17, 2011 12:54:37 GMT 1
Ooooh, getting nervous John? Absolutely Nick, you know me always like to give 100% satisfaction!  John |
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Post by renard80 on Jun 17, 2011 13:05:01 GMT 1
Hey, John, I'm perfectly satisfied with the tester I bought from you! Clearly it is adequate for my needs.
I was just after reassurance that my batteries were OK for adequate flying time at the charges shown, if it is recommended that I stop flying at 3.7.
And, Nick, yes - I use the stock chargers which came with my HZ SC and Mini. I take your point about their possibly limited efficiency.
Thanks to everyone for the valuable advice.
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Post by flydiver on Jun 17, 2011 17:24:52 GMT 1
All batteries sag (drop) voltage under load. The 3.7v/cell is the BOUNCE BACK voltage after the load is removed. Take a look at this graph: www.rcgroups.com/forums/showpost.php?p=10981333&postcount=1Essentially the lipo is empty below 3.0v/cell. Taking it that low starts damaging it. The lower and the longer > the worse. LVC - Low LVC Damages High C LiPolys !!! www.rcgroups.com/forums/showpost.php?p=4904168&postcount=1The chart I posted (not home this week-gone windsurfing) is an approximation. You can't be entirely precise as a look at those graphs will indicate. As cells age their internal resistance goes up and performance goes down. This is reflected in their ability to sustain a load and even hold on to a charge. This deterioration is a function of initial cell quality (very difficult to actually determine as it's SUCH a moving target) and treatment by the pilot. |
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Post by renard80 on Jul 31, 2011 0:21:27 GMT 1
Any replies to this will probably baffle me with science, so please can you keep it simple for this simpleton . . .
Today was an example of how I get confused about battery life and whether it's safe to go up again.
After flying for a while, my little balance tester showed each cell at about 3.8. As I understand the safe level to be not less than 3.7, those readings would be enough to prevent me trying another flight.
However, a pal then used his more expensive tester, which showed my battery had "45% remaining". Well, surely 45% is a heck of a lot, so I put her up again and enjoyed another flight.
I am now confused. Should I trust my little tester and stop flying when it approaches 3.7 - or by doing so am I losing flight-time as the bigger tester indicates that the battery remains nearly half full?
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Post by flydiver on Jul 31, 2011 5:00:23 GMT 1
I am now confused. Should I trust my little tester and stop flying when it approaches 3.7 - or by doing so am I losing flight-time as the bigger tester indicates that the battery remains nearly half full? Did you test it again after that flight? You should have. The goal is to have 20% remaining. So, you only had 25% remaining....maybe, for cell longevity. Voltage on rechargeable cells is not completely accurate on gauging CAPACITY remaining due to the discharge characteristics. It is NOT linear. Take a look at the graph I posted above. Those little testers are not terribly accurate either. For that matter I have 2 FMA Cellpro 4S chargers that do an analysis of the battery before it starts charging. It reads out voltage and % remaining. Both of them will give different % on the SAME voltage on the SAME battery. So, 2 approaches - be conservative, lose some flight time and (hopefully) keep your batteries in good shape for a long life. Or - don't worry about it, they're cheap. Go for it and have fun. Replace when necessary. You've been flying > a year and have over 300 posts here. How have you been doing so far? |
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) ? They are I believe, accurate enough for knowing whether you have another flight left in your batts, but not for a bang on accurate balance reading.