Charge rate and other settings

[sambo60]

Hi guys
How do you know what settings to charge your lipos at? What voltage? What current? What is the relationship between 1C 2C etc and mAh? I'm not sure about these things and I'm trying to understand it all so I don't burn my house down... :lol:

[kgfly]

Sambo,

Lipo batteries are rated by the number of cells in series (which defines the pack voltage), the total capacity and the maximum continuous and burst discharge rates.

A lipo cell is nominally 3.7V (4.2V fully charged, should not be discharged below 80% capacity or 3.0V at rest). So 2S = 2 cells in series = 2 x 3.7 = 7.4V. 3S = 3 x 3.7 = 11.1V etc.

The capacity is the amount of energy that can be delivered in 1 hour. So a 2200mAh battery will notionally deliver 2200mA = 2.2A non-stop for 1 hour (= 60 min). This is defined as 1C. A battery with a 20C continuous discharge rate can be discharged totally at 20 times the nominal rate and will got flat in 60/20 = 3 minutes.

So a 3S 2200mAh 20c/30c battery is 11.1V nominal (12.6V fully charged) and can be discharged at up to 44A continuous with short bursts at up to 66A.

By default you should never charge a lipo above 1C. For a 2200mAh battery that means no more than 2.2A charge current. You tell the charger either how many series cells (eg 3 for 3S) or the nominal pack voltage (eg 11.1V for 3s) and either the pack capacity (2200mAH) or the max charge current (2.2A) and away you go.

A few safety rules:

* Never leave a lipo charging unattended
* Never use anything expect a dedicated LiPo charger or the LiPo program on a multichemistry charger
* Never short circuit a LiPo (= fire)
* Never overcharge a LiPo (= fire)
* Never puncture a LiPo (= fire)
* Always charge in a fire proof container (eg pyrex dish, ceramic dish, terracotta pot, saucepan, ammo box, LipoSack) and preferably in a fire safe location with nothing flammable overhead/nearby.

For maximum longevity:
* Never discharge more than 80% of nominal
* Never allow operational temperature over 140F (60C)
* Balance frequently

----------------
What charger do you have ? If it is a cheap one without decent features and a display that tells you what it is doing, what the cell voltages are and how much charge went back into the battery then I would recommend an upgrade. The best chargers around (IMO) for smaller packs like those used in a TRex450 are the FMA CellPro4S (~$75 + a DC bench supply) and the eStation BC6 (~$160 with ac/dc supply built in). These are both excellent integrated intelligent balance chargers that are as safe as possible. With these advanced chargers it is possible to safely charge lipos above 1C once you know what you are doing.

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Hope that helps.

[WhirlingBladesOfDeath]

With these advanced chargers it is possible to safely charge lipos above 1C once you know what you are doing.
Do you have any info on cycle life compared to charge rate? IE, at 1/2C I will get X cycles from the battery, compared to Y cycles if charged at 1C, compared to Z cycles if charged at 1.5C?

Normally if I'm waiting for the battery so I can go fly again, I charge at 1C. If I have plenty of time, I charge at 1/2C. Just curious if I'm gaining anything by charging at 1/2C, or if I'm just wasting my time! :roll:

Thanks,
Jason

[Jermo]

If you're using an active balancing charger (like a Cellpro 4s) you won't notice any reduced cycles (according to their documentation and documentation from some of the battery manf.)

They keys are being able to monitor individual cells during charge, balancing, and being able to adjust the charge rates dynamically during charge in response to cell conditions.

Most chargers can't do that. Especially if they use passive balancing..ie..balancer is seperate from the charger with no data/control path back to the charger.

Examples of good chargers/balancers..ie
Cellpro 4s
TP 1010?? I think that's it..

Example of a bad setup:
Jamara Peak 3 plus with a blinky balancer.

[WhirlingBladesOfDeath]

WOW! I just checked out FMA's website now, and it looks pretty cool! (as far as battery charges go) I've read you talking about your Cellpro 4S before, but didn't pay much attention since I already had my Multiplex charger.

So if I understand correctly, with the new 4amp charger, I could charge my TP 2070 at about 2C and probably have a full charge in 30-40 minutes. Is it really as simple as the instructions make it look, just set the C rating and it figures out the rest? That's pretty cool that it can sense the difference between a 800mAh and a 2100mAh battery.

Do you happen to know if they plan to release any higher Amp Cellpros? It would be cool to be able to charge a 2100 mAh at a full 3C.

One thing that confused me though was on page 2 of the manual http://www.fmadirect.com/support_docs/item_1242.pdf where there is a warning about using 2 chargers from the same power supply. Just to be clear, would I be OK using my 5A power supply to power a Cellpro at say 3A and my Multiplex at 2A, charging 2 completely different batteries at the same time? That would REALLY cut down on my charging time. :)

Thanks,
Jason

[kgfly]

jason,

There are a number of high quality chargers that can safely charge above 1C including:

Cellpro4S
eStationBC6/BC8 or e902+PB6
Hyperion 12010i+LBA6
TP1010+V210

I suggest downloading the manuals for these and reading them carefully to see what they can do.

Different battery manufacturers make different statements about fast charging. FlightPower for example say Fast Charging: In conjunction with Enerland, the FlightPower EVO 20 range has been qualified for 2.5C charging as a combination of cell technology and matching by FlightPower at the point of manufacture. This means that an EVO 20 1800 mAh pack can be fast-charged at 4.5 Amps (or 4500 mAh). This will result in a pack that is 90% full in around 25 minutes. (All) fast charging of rechargeable chemistry results in a reduction in cycle life, it is therefore recommended that fast charging be done when time is of the essence.
Any packs made with Enerland cells (FP, Polyquest, Hyperion and others) would be similar. As you have seen, FMA claim their technology allows fast charging any lipo without detrimental affects. I know I would be tempted to charge above 1C with the right charger. The other option is to use the feature some of the chargers offer to charge to only 90/95%. The last 5 to 10% of charging can take up to 30% of the time so you can trade off a little capacity for a lot of time.

The warning about using two chargers from the same power supply only applies if the two packs are still connected to each other. For example if you had two 3S packs connected in series to make a 6S pack. So long as you disconnect the packs from each other you can safely charge them from two chargers on the same power supply.

[th3tick]

And the Cellpro still falls back on the "only charge above 1C if the manufacturer of the battery says so" (paraphrased). Thunder Power's battery instructions say 1C. I'm SO tempted to do it, though.

And thus I just bought two of the FlightPower 2170s which DO say 2C is ok.

[Probedude]

Another good charger that can charger up to 10A and 6S and balance at the same time is FMA's BalancePro. No LCD though like the Cellpro.

[kgfly]

Yep, the BalancePro falls short for me due to it's lack of onboard display and limited controls. It has a PC interface but I don't want to have to boot up a PC everytime I need to charge. It is cheap (about $115 including the PC cable).

Many of the leading chargers (eg CellPro4s, eStationBC6/BC8 or e902, H1210i etc) also have optional PC interfaces so that you can monitor/log the charge/discharge cycles but since they have on-board displays you don't need the PC just to see what's going on.

[Probedude]

Many of the leading chargers (eg CellPro4s, eStationBC6/BC8 or e902, H1210i etc) also have optional PC interfaces so that you can monitor/log the charge/discharge cycles but since they have on-board displays you don't need the PC just to see what's going on.

True.

Back in I think January FMA said they were working on the LCD version of the BalancePro as their top priority. Hopefully it's near completion. There's a guy on RCG that built his own BalancePro external display by parsing the datastream coming out of the PC port, only cell voltages and current if I remember correctly (I don't think mAH's charged comes out the serial port).

[kgfly]

I think if FMA add a decent UI and the features of the CellPro4S to the BalancePro it will become a leading contender for 2S-6S LiPo/LiFe charging. I hope they do :)

[sambo60]

So what rate should I charge my 2200mah batteries at? I'm getting a new charger that can do .5A up to 2.0A, so what's safe to charge at? I would like to have my batteries charge in about half an hour if possible.

[Jermo]

Sambo if you're using a balanced charger like the Cellpro 4S you can safely charge at up to 3C.

[sambo60]

What does 3C mean in terms of mah? Would that be 6.6A for a 2200mah battery? I'm not sure I have all these concepts down yet.

[kgfly]

Jermo - That seems a bold statement to me. I would not agree that all balance chargers or all charger+balancer combinations are safe to use at 3C with all brands of lipo, which is what your comment seems to suggest, even though you mention the excellent CellPro4S as an example.

Sambo60 - The fundamental safety guideline for LiPo batteries is to never charge above 1C. For a 2200mAh battery 1C = 2200/1000 = 2.2A. Most LiPos discharged by no more than 80% will take from 60 to 90 minutes to complete a balance charge cycle. Since the charger you are considering is only capable of max 2A it won't have the ability to charge even at 1C let alone above 1C.

To acheive a 30 minute charge cycle requires the use of one of a handful of top-quality charger/balancer solutions and even then can only be done with great care and proper fire precautions. Only some battery manufacturers rate their packs for >1C charging (eg FlightPower, Polyquest and Hyperion and maybe some others) and even these highlight that charging above 1C will shorten the life of the pack.

From the brief description of the charger you are getting it sounds like a low end device. It is not a good idea to try to save money on a LiPo charger, it's simply too dangerous and will not get you the maximum lifetime from your packs, ultimately costing you more in the end.

I agree with Jermo that if you are on a tight budget then the best choice by far is the FMAdirect CellPro4S charger (~$70). I strongly recommend you do not buy the cheapo charger and order one of these instead. This charger is capable of charging most LiPos at above 1C (according to FMA's claims) and has an excellent reputation amongst users.

[Jermo]

Ken,
You're essentually correct. Let me clarify a bit. Most battery pack manf are now coming out and stating you can charge up to 3C rate with a balanced charger. This isn't globally true with all packs. It's not just the charger manf making these claims. It's pack manf.

The new Cellpro is good up to 4Amps. Because it's a balancing charger it's safer. If I had to go bigger I'd be looking at the bantam or thunderpower chargers.

[kgfly]

What does 3C mean in terms of mah? Would that be 6.6A for a 2200mah battery? I'm not sure I have all these concepts down yet.Yep, 3C would be 6.6A for a 2200mAh pack. Looks like you have got it sorted :)

BTW - charging at 3C is not much faster than 2C. This has to do with the charge algorithm for LiPo which is "CCCV" = Constant Current then Constant Voltage. While most of the charge is delivered in the CC phase, most of the time is spent in the CV phase. The higher the current, the faster you get to the CV transition, without necessarily pumping in as much or more total charge before getting there. Hence there are diminishing returns for high-C charging. There are excellent tutorials on the FMAdirect site if you want to learn about lipo technology and charging solutions.

[sambo60]

The charger I have right now is this one here http://www.helidirect.com/product_info.php?cPath=116&products_id=1038

I have this one coming in the mail https://www.unitedhobbies.com/UNITEDHOBBIES/store/comersus_viewItem.asp?idProduct=2055
I figured its so cheap and it has good reviews so why not try it out.
If I were to get the CellPro charger, should I get the 3A or 4A one (I see those 2 at FMAdirect.com) and also, what are those clips that I see in the picture? I imagine they connect to a power supply, but I prefer to just have it plug into the wall socket like my current charger does. I don't know how the 25 dollar charger gets its power, but for 25 bucks, I can't go wrong. If the new one needs some other kind of power supply, what do you guys recommend? Anyway, you guys are a big help as always, helping me understand all this stuff. I'm in LA and I still feel like I have the only rc heli for miles around.

[th3tick]

Jermo: what ones are saying 3C is ok? I've got Align, Thunder Power, Flight Power, and Air Thunder (I think I'm missing Air Power and Thunder Thunder in that list), but all are 1C excepting the Flight Power, which is still only 2C.

[kgfly]

Sambo60 - The majority of chargers require a DC input and hence need an external DC bench supply or a 12V battery. A small number come with built-in ac/dc power supplies like that Align one. The best fully integrated charger on the market is the eStation BC6 which has an built-in ac/dc supply, multichemistry charger and balancer all in a single unit.

That charger from UH and the CellPro4S both require DC input and so you will need a DC bench supply for them. I recommend nothing under 100W output (eg 12V/8A). A good 13.8V/20A DC supply is about $60 and will allow you to run multiple chargers in parallel if needed.

If I were you I would cancel the charger from UH or sell it on eBay and get a CellPro4s(4A) it really is far superior in every way and will charge at (or above) 1C safely.

[sambo60]

Can you recommend a specific DC bench supply? Ugh, I'm gonna have to spend a lot more money and I'm addicted :( I may get a cellpro eventually, we'll see how much money I can make this summer (I'm only 18).

[th3tick]

While there are other threads on the power supply, one recommendation was:

http://cgi.ebay.com/Tekpower-13-8V-12V-30A-Linear-DC-Regulated-Power-Supply_W0QQitemZ190112268745QQihZ009QQcategoryZ582 86QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

I followed that recommendation, and have one now. Plenty of power for multiple chargers, and a good price for 30A.

[kgfly]

That's $100 delivered, a bit hefty and a bit pricey for someone on a budget. This one lwill certainly do the job (13.8V/20A) and may be more affordable: http://www.hobby-lobby.com/powersupply.htm

[sambo60]

I guess I just have to resign myself to the fact that I'm going to be spending a $hitload of money on RC heli stuff unless I give up the hobby which I really enjoy. I am just getting started actually (I started in October to be precise). So I guess if the power supply from ebay will work with my trex5000's batteries/chargers then I am better off getting that one. Also, I want a PS thats not an eyesore, since I charge them in the house. That may factor into my decision in the end. As I was saying, I better make a helluva lot of money this summer to support my addiction...

[kgfly]

It's not a cheap hobby, that's for sure. The cost of the power supply will pale by comparison with the many other costs to come. So long as you go ahead with your eyes open you won't be discouraged.

If you need budget batteries check out the Hextronik D9 3s 2200 20c packs from unitedhobbies.com. While not on par with the premium packs, they are good value and many folk have been quite happy for them. Definitely good for a beginner IMO, better to mangle a $30 pack than a $70 or $90 one! Other money saving tips:

* Fly Align Pro 325 woodies or TechMP 325 woodies. Anything else will cost more for not much benefit. Do NOT fly the blue/white "fibre" blades. They are too strong and will cause massive damage to your heli when you crash. Believe it or not, you want your blades to break when you crash.

* Broken frames and other plastic/CF parts can often be repaired by whipping with cotton then soaking the cotton in thin CA glue. Not suitable for something like a blade grip or head block, but works on many other bits.

* If you break your horizontal fin simply trim it neatly so that it can still be used to mount the tail boom clamp for the boom supports (or make a little bracket to do that job) and don't bother spending money to replace it. Also, reinforce the leading edge of your vertical tail fin with some 0.6mm aluminium or something else of your choice. This will allow it to survive many tail taps that would otherwise snap it off.