9th January 2017, 05:21 AM
So, does someone want to explain this lipo stuff? I am looking to switch to lipo batteries for strattologgers CF and I don't follow this number scheme they have. What do you recommend? Looking for a charger as well.(would like to charge my altus metrum batteries as well) I know I need at least 1 Amp for the charges.
9th January 2017, 05:33 AM
Chris, for the charger, I strongly recommend a 'smart charger', like the one shown below. Yes, they are pricey, but they help prevent incorrect configuration/charging that will destroy the battery (and which may result in a fire). I have one of these and at least twice it prevented me from stupid human errors.
A good rule for rocket experimenters to follow is this: always assume that it will explode.
— Astronautics, issue 38, October 1937.
9th January 2017, 05:34 AM
Here is a recent thread on the topic of the Li Po choice http://www.rocketryforum.com/showthr...-StratalogerCF
The charger I use, and this is my second, is the iMax B6AC V2. I picked this one up because it does a single step storage charge, whereas my previous one you had to discharge it first then charge it up to storage. http://www.skyrc.com/index.php?route...product_id=217
NAPAS, URRG, MARS, CRC
L1 May 18th, 2014 NAPAS Club launch (PML 3" Bull Puppy)
L2 Jun 26th, 2015 LDRS34 (Madcow 54mm Carbon Fiber Tomach)
L3 Currently targeting 2019...lots of challenges to work through.
9th January 2017, 06:03 AM
Originally Posted by Worsaer
wonder why the search didn't find that one...found one from 2013 though. Thank you, this should fix me up.
Originally Posted by mpitfield
10th January 2017, 11:51 PM
For the strattologger CF & the missle works 2+ I use the turnigy nano-tech 2s 180 mAh lipo & the Turnigy P606 AC/DC Lipo charger. It can charge three 2s Lipos or six 1s Lipos simultaneously. They are both available from hobbyking. Hobbyking has USA based warehouses so the items are usually received within 3 to 5 days. Each lipo is currently $4.19 and the charger is around $35. The lipos weigh less and are smaller than 9 volt batteries and last for multiple flights on one charge.
11th January 2017, 06:48 AM
Part of the problem is that we're still using nomenclature that dates back to when one had to parallel sets of LiPoly cells together to get acceptable discharge characteristics for the airplanes/cars we were using them in when they were first introduced to modeling (about 15 years ago). It was not uncommon then to have a pack that was described as, for example, "3s2p" which was a six cell pack with two strings of three series cells in parallel with one another. Now you mostly see "1s", "2s", "3s" and so forth and that's just one cell, two cells (in series), three cells (in series).
Using the same sort of nomenclature, a nominally 12V lead-acid battery is a 6s battery, or the 4 AAs in an Estes Electron Beam launch controller is a 4s pack of alkaline cells.
LiPolys are nominally 3.7v per cell though they are actually well discharged when down to that voltage at rest. A full cell is 4.2V, so a 2-cell pack ("2s") will be 8.4V when fully charged. You can see, then, how 2s packs get substituted for "9V" transistor radio type batteries (which are internally 6 tiny alkaline cells in series). And you can see, then, how a 3-cell pack ("3s") can stand in for a 12V battery in a launch system (or a jumper pack for your car) with a fully-charged voltage of 12.6V. Recent ones have such a low internal resistance that they don't sag much under load and so can deliver LOTS of current. This is another reason why a small LiPoly pack works well in dual-deploy sort of application.
But when they first became available, their internal resistance was quite high which is why they were paralleled. One of my first big LiPoly packs for an RC airplane was a 4s3p pack (3 strings of four series cells in parallel). It was as large and as heavy as the 14-cell NiCd pack it replaced, but it had FOUR times the capacity and therefore four times the flight time. This was for an airplane power system that drew around 30A at full throttle.
You also see them rated in terms of "C" - as in "20C". That means the cell can safely deliver current of 20 times the rated capacity number. A simple example - a 20C 1000 mAh (1 Ah) pack can deliver 20A (20 times 1A) without significant cycle life reduction. That also means you can discharge it in 3 minutes (1 Amp-hour - or 60 Amp-minutes/20 Amps = 3 minutes).
Clear as mud?
Another thought: It is painfully common to see the units of capacity (milli-ampere-hours - mAh) or ampere-hours (Ah) used interchangeably with current (mA or A) when talking about chargers in particular. It's just sloppy and I don't know how it got that way, but it has. It's just the same as confusing total impulse of a motor with thrust, and just as wrong.
Last edited by BEC; 11th January 2017 at 06:54 AM.
NAR 89040 L1
11th January 2017, 09:09 AM
I once saw a 'boom box' advertised as having 7200mw per channel.
11th January 2017, 02:25 PM
Thanks guys, I got some batteries and a charger on the way.
11th January 2017, 04:49 PM
There has been some very good information on the thread; but I wanted to also introduce the concept of........
MINIMUM VOLTAGE FOR LIPO BATTERIES
To start, I don't fully understand it. But Lipo batteries become "damaged" if their voltage gets too low. Soooooo................
The first thing a Lipo battery charger does, when you plug in a Lipo battery, is check the voltage of the battery. If the voltage of a cell is below 3.3 volts, the battery is considered BAD, and the charge will not charge it.
Consequently, in the RC community, most speed controls (and other voltage regulating items) will shut down motor power at 3.5 volts (per cell).
"Lock S-foils in attack position....."
11th January 2017, 05:33 PM
3.5V per cell should be considered the absolute minimum. I prefer to keep them a bit higher when I can. Note that the discharge curve is nearly flat until they are almost totally dead, so the difference between even 4.0V and 3.5V is quite small compared to total available energy in the cell. For things we use around here like altimeters and tracking transmitters, that means sizing them properly and just accepting that they might die early if we don't recover the rocket in time, but it is something to keep in mind. We don't want to add a ton of mass to make sure we don't kill the cells, but we don't want to replace them after every flight either.
12th January 2017, 06:17 AM
If you get a higher capacity battery, as long as the rocket is recovered within a few hours you should be fine. Since a 400-500 mAh battery isn't all that more expensive than a lesser capacity one, I'll take a little extra weight knowing I'm not going to be replacing a battery because it takes me an hour or two to get a rocket down out of a tree or other hard to get at location.
But get a good charger. I can't say 100% that it was the charger, but I had a brand new battery discharge below 3v after being hooked up to a cheap charger. Since it was only about .1v low, I was able to recover the cell (there are ways of doing it with a B6 style charger, just be cautious) and it seems to be OK now.
12th January 2017, 07:57 AM
I have brought low voltage lipo batteries back from the dead by fudging the charger settings and letting it run hog wild up to a low but usable level, then correct the settings to finish the charge. I am not recommending this as best practice, and I am not certain how well it will hold up over time, but I have not had any problems at all so far.
Originally Posted by Crawf56
Most of the various IMAX and B6 chargers are all the same; the ones with a blue screen above four buttons get repackaged in all kinds of colors and names.
- punishing the punishers -
lunar #26 / tripoli #15480
12th January 2017, 08:05 AM
+1. Hit the LiPo with a couple of 12V recharge cycles for 30 seconds or so. About half the time it will come out of the "under voltage" state and work fine. If it doesn't recover, just pitch it and buy another.
Originally Posted by watermelonman
12th January 2017, 12:17 PM
More info on how to do the 12v hit please?
12th January 2017, 02:58 PM
... and be aware that if it's physically damaged in a way that you didn't notice, you might have a lithium fire on your hands. First sign is heat, second swelling; then hissing, smoke, flames.
Originally Posted by dixontj93060
Don't do this unattended, and consider a charging bag for your lipos. This concludes your regularly scheduled paranoid safety broadcast.
13th January 2017, 04:22 AM
What do you use to charge them with?
13th January 2017, 01:52 PM
I use this one Tenergy TB6AC
Originally Posted by Lowpuller
L3 NAR 98225
13th January 2017, 02:04 PM
There are more details on YouTube, but in short, you change the settings on the charger to act like you're charging another kind of battery so it ignores the low cell voltage.
Originally Posted by Lowpuller
If you do it, keep a very close eye on it. I put mine in a Lipo safe and only charged it for about 15 seconds at a time at the lowest rate the charger would charge at. Mine didn't even so much as get warm, but as I stated earlier, it was only about .1v below what the charger considered low anyway.
13th January 2017, 05:58 PM
While force-charging a lipo to get it above the required voltage CAN work, be very careful and use the minimum time to get it there. I would also recommend doing a couple capacity tests to ensure it still stores a similar amount of power and can source sufficient current. Lipos that are discharged too far are damaged internally. How much depends on how far below the minimum voltage and how long it stays there. If it starts to puff up, stop charging and treat it like it might catch fire at any moment. I know a few people in the RC world that charge lipos in cinder blocks with a sandbag over the top. If there's a fire, it melts the bag and dumps the sand on it. Not only stopping the fire, but preventing smoke damage.
I'm not quite that paranoid, but treat them with the respect they deserve or you're asking for them to burn. Most of the lipos we would use have no protection like the ones in laptops and cell phones. Those have little PCBs that prevent over-discharge and disconnect if they overheat or pull too much current. That would not be a great thing for us, so it's generally not there. But that means you have to protect them. And even with protection boards, we had the Note 7....
While warning might seem overstated, people have lost their homes and been injured due to lipo fires. It's not very likely if they are not mistreated, but it can and does happen. The little ones we would use in rocketry for altimeters and trackers are so cheap that I would consider them disposable if they are damaged rather than try to force charge. A big 6s pack I might try it on, with caution, but a 500mAh 2s? That's about $6. https://hobbyking.com/en_us/turnigy-...lipo-pack.html
14th January 2017, 05:26 AM
14th January 2017, 06:05 AM
Yeah, really do not smash them, stab them, etc...
18th January 2017, 08:34 PM
Yeah, apparently there are different connectors as well. Mine don't fit the charger. This crap sucks.
18th January 2017, 08:50 PM
Yeah, tons of different connectors. I standardize on a couple and either buy batteries with those connectors, or just cut off the ones I don't want and replace them. I just buy packs of connectors from Hobbyking to solder on to whatever I want to use. XT60 mostly for me.
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