# Lipo Help

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#### tbonerocketeer

TRF Supporter
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.

#### Worsaer

##### Amateur Propulsionist
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.

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#### tbonerocketeer

TRF Supporter
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.

Thank you.

Hi Chris,

Here is a recent thread on the topic of the Li Po choice http://www.rocketryforum.com/showthread.php?137650-Battery-for-a-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/product&product_id=217
wonder why the search didn't find that one...found one from 2013 though. Thank you, this should fix me up.

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#### FMarvinS

##### Well-Known Member
Hi Chris,

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.

• Regards,
Fred, L2
KG4YGP
ROSCO member

#### BEC

##### Well-Known Member
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.

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#### Rex R

##### LV2
I once saw a 'boom box' advertised as having 7200mw per channel.
Rex

#### tbonerocketeer

TRF Supporter
Thanks guys, I got some batteries and a charger on the way.

#### Crawf56

##### Pig Soooiiieee!!
TRF Supporter
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).

#### ttabbal

##### Well-Known Member
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.

#### byoungblood

##### Well-Known Member
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.

#### watermelonman

##### Well-Known Member
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).
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.

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.

#### dixontj93060

##### Well-Known Member
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.
+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.

#### dhbarr

##### Amateur Professional
+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.
... 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.

Don't do this unattended, and consider a charging bag for your lipos. This concludes your regularly scheduled paranoid safety broadcast.

#### Lowpuller

##### Well-Known Member
What do you use to charge them with?

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#### byoungblood

##### Well-Known Member
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.

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.

#### ttabbal

##### Well-Known Member
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-500mah-2s-20c-lipo-pack.html

#### ttabbal

##### Well-Known Member
Yeah, really do not smash them, stab them, etc...

#### tbonerocketeer

TRF Supporter
Yeah, apparently there are different connectors as well. Mine don't fit the charger. This crap sucks.

#### ttabbal

##### Well-Known Member
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.

#### jd2cylman

##### Still not Carl... ;-)
TRF Supporter
Do you leave them on the charger all the time? Or do you charge them up, then take them off the charger and recharge them before you use them?
Help.....

#### timbucktoo

##### Well-Known Member
Staff member
TRF Supporter
Global Mod
I charge mine before launch. Once charger says they're full, I remove from charger. If not using for any length of time, I have charger put them in "storage mode".

#### jd2cylman

##### Still not Carl... ;-)
TRF Supporter
OK, more Lipo questions if the OP doesn't mind me piggy backing on this thread.
On the 750mAh 1S 35-70C battery I have, there are two plugs. A red one that I'm sure is the Jst power plug, and a white one with a red and black wire. Is this a balance plug? Since this is a 1S battery, I assume that the balance plug isn't really needed? The P405 charger I got (without any adapters to actually charge the battery they didn't mention that...) has a balance board, but the smallest plug is only for the 2S batteries...
Thanks.

#### Rex R

##### LV2
I have seen Nimh batteries vent...sounded like a firecracker. the balance plug is to bring all the cells (in the pack) to the same voltage, if you have only one cell there is nothing to balance, but some chargers use the balance plug to charge the pack. my hyperion charger gets all nanny mode when I charge a 1s pack.
Rex

#### MikeyDSlagle

##### Well-Known Member
Chris, what batteries did you get? And what plugs are on them? I recently started using 2S LiPos along standard 9v. If you haven't got it worked out by next launch, maybe I can help. I'm no expert but it's not too bad when you get past the numbers and bs. My charger doesn't have the right plugs either, I use alligator clips for now... Never think about that stuff until I am charging my batteries.
Nothing else, we can hook my charger up and at least get your batteries charged, depending on your plug that is. My charger is 110 AC or 12 DC.

Mikey D

#### cerving

##### Owner, Eggtimer Rocketry
TRF Supporter
Single-cell LiPo's for R/C helis typically come with either a single JST-RCY (the red JST plug we're all used to) or a JST-XH plug (the little white plug). Most chargers have a JST-XH connectors so if your battery comes with a JST-RCY then you'll need and adaptor to charge it.

Most multi-cell LiPo's for R/C use have two plugs, a high-current plug and a low-current "balance connector". You charge them through the balance connector, which is a JST-XH connector with one socket for every cell +1; a 2S LiPo has a 3-pin connector. That JST-XH is practically universal, but the high-current plugs vary, depending on the current draw; you can't push 60A through a JST-RCY connector (the red ones that we all use) so the larger batteries will use a "T" connector or XT-60. For our use, you can simply cut them off and solder on a JST-RCY pigtail instead, since you know you're not going to be running a lot of current through them. Just make sure you get the polarity right...

#### ttabbal

##### Well-Known Member
I'm not a fan of the JST-RCY. It comes apart with very little force, low enough that I'd be fine using it as a break-away connection for a staged rocket. I think there are locking varieties out there, or locking servo style connectors. You can and should secure them of course, but it just feels like one more failure point that's easily avoided. I use XT60 on my RC stuff, very solid. Overkill for little stuff, but there is a smaller XT30 that might be a good choice. I will say it's entirely possible this is overkill, that's just how I do things with power connections.

Most larger chargers charge via the high-current connection, using the balance port to adjust any cells that are too far off. Some low-current chargers do charge via the balance connection, I have one, it's limited to about 2A, which makes sense for those little JST-XH and thin wires. My faster charger can push 200W into the battery, the balance port can't handle that. I can't imagine much use on a rocket for a battery that uses that much charge power, but for RC it's pretty common.

Sadly, there's a lot of attempted vendor lock-in in the RC world. One of the reasons every company seems to have their own connectors. Thankfully, the balance port is almost always JST-XH though. So you might have to change the high-current connector out. Many batteries come with no connector, just heat shrink over the wires. You add your own connector as needed. That's why I have a pile of XT60s around, I just swap out anything that's not my "standard". And they are pretty cheap online.