Lipo Mumbo Jumbo

[gangster]

Inspired by an earlier thead about charge rate I emptied a bag of lipos on my desk and not one of them gave any info about charging.

I then realised how vague and incomplete some of the info written on them is as stand alone information.

E.g all one had on it was 3S-2200 35C

.That means nothing at all unless you know a little about the nomenclature, these are consumer items, packaged and plugged up for toy aeroplanes not something from a nuclear submarine that we are using and are used by those in the know.

2200 what is that, the number of people working in the factory of the height of the managind director? I would be a rich man if I had a pound for every time I got no marks at school for not including the units.

At least some of the manufactures had the decency to add the mAh.

3S what does that tell us . Oh yes it means three seconds in SI units.

If I buy a battery for my car I buy a 12 Volt battery not a 6 cell one, imagine asking the lady in Tescos for a 4S battery for my torch , Wot? we got 6 volt ones. Different cell chemistrys give different cell voltage so what happens in two years time when the dear old Lipo is displaced by a new technology with 3.5 or 4.5 volts per cell.

30C what does that tell up, oh it must be the temperature of something!

Only one of my batterys tells me that it is designed 115.5 amp continuous and 231A burst. Even then its confusing to many people My motor tells me it is rated for 50A max not 50000mA and my ESC 80A not 80000mA

Top marks to Gliders their battery tells me its 3300mAh 11.1 Volts and the max current in Amps. As well as the other stuff.

 

 

Edited By gangster on 08/11/2016 11:59:14

[Allan Bennett]

How far do you go? If you try to include all the information that's even remotely relevant, you'll need larger batteries simply to give enough space for all the instructions and specification!

For example, even if you say it's a nominally 11.1v battery, don't you need also to mention that it could be as high as 12.6v, and that charging any single cell above 4.2v is asking for trouble? Also, there's quite a few people that think that a "115.5 amp" battery will force that many amps into the motor and, thus, burn it out. How do you deal with that in the labelling?

I think it's fair that the manufacturers should be allowed to assume that the end-users have a basic knowledge of the terminology; but I agree that your first example, with no units given, is unacceptable for a loose battery -- as opposed to one that's built into a device like a mobile phone, which has its own dedicated charger. What we need is for the end-users to be better educated, and that starts with the shop assistants who sell the stuff, and then continues with organisations like the BMFA, local clubs, forums like this one, and magazines like RCM&E.

My beef, in a similar vein, is motor suppliers who don't give full information. Sometimes they give only maximum watts, without quoting maximum amps or volts, or either.

[Geoff S]

Do you expect servos to give details of maximum torque (in imperial and metric units?) as well as the maximum applied voltage on the body or glow engines to tell you that the 40 means 0.4 cu ins or 6.5 cc? I'm afraid this is a technical hobby and you have to do a little work for yourself. There's lots of information on line about just about all aspects of the hobby as well as fora like this one.

As Allan says, there isn't room for everything to be written on the battery without cluttering it all up with tiny print so there's a recognised shorthand. The big number (2200 in your case) is the battery capacity in mAh, 3S is the number of 3.7v cells in series (ie 11.1v nominal but about 12.6 fully charged so a voltage isn't all that useful) and the other number 35C is the output current rating expressed as value compared to the capacity (C) so 35 x2.2 amps = 77 amps.

Whether the units are expressed in mA or Amps is a convention. I use either. It's like a 40 size glow engine isn't called a 0.4 engine - or 6.5 cc come to that.

Interestingly one thing car batteries don't tell you is their capacity although they do give a figure for the maximum current draw.

I certainly agree with Allan about motor data. Whilst the power rating is useful what I really want to know is the safe current - much more useful if you want to keep the smoke inside. The power rating has more to do with the physical characteristics ie how strong it is.

Geoff

[MattyB]

This hobby is full of items that come with next to no instructions and require knowledge to be used correctly. Linkages, servos, engines, retracts, plans, even some ARTFs come with next to nothing. These are not mainstream commercial products like washing machines or computers, so you cannot expect them to be packaged as such - knowledge will always be required to use them correctly.

Ps - I just checked a few, and all my batteries from HK and Gens Ace come with the nominal voltage, max discharge / charge rates in C and capacity marked reasonably clearly. I do agree that some packs do leave a bit to be desired on these fronts though.

[gangster]

 

Some very interesting and valid comments chaps

. I totally agree with the issue regarding the motor labelling, even some of our most respected suppliers are guilty of that one . When they just state a power and say voltage 3S to 6S and prop 10x7 to 13x6 or such like Come on guys give us a clue and a ball park figure. I have two identically sized , identical numbered motors on my bench both 600 + watts. However one will safely give me that power on a 4S within its 50 A max current but the other is after you trawl the web for the spec would need a considerably higher voltage to give the same power within its 34A max. A modeller could quite easily make that mistake.

As for car batteries, I must admit I thought they did quote their capacities , I did buy a tractor battery recently that quoted its capacity and a cold cranking current. Looking on Halfords web site they quote capacity's, and tell you what, the one I looked at was 44Ah not 44000mAh! Just looked at my own car battery and there was very little written on it apart from a few Japanese hieroglyphics, what it did tell me was 12V which is clearly incorrect as it would be as flat as a pancake at 12 volts, but hey we are happy to quote a car battery as 12 volts, we are happy to recognise our receiver packs as 4.8 volts when we know that fully charged they will be a bit more. So why not accept our lipos as a nominal 11,1V or 14.8 etc etc.

the other number 35C is the output current rating expressed as value compared to the capac ty (C) so 35 x2.2 amps = 77 amps. That sir is what my whole post is about 35x2200 is actually 77000. Notice no units as there are none on the battery. This has confused many people and that confusion has reared its head on this very forum a few times. I agree many people would automatically know, from being told to divide that 2200 by 1000 but why should they have to . Anyway is that 77A continuous or burst! nobody will ever know. I have to admit that is a purely hypothetical question the flight would be might short.

 

I disagree with the comment that you would need to fill the battery with small print it would hardly take much room to say 3S (11.1V) 2200mAh 35C continuous XA burst YA Gliders do and looking at MattyBs post so do HK and Gen ace.

So glad my glow motors are not quoted in cubic centimetre in some places and cubic mm in others Even that is better that a .40 being quoted in cubic feet or cubic yards. Anyway must go and put my field charge battery on charge its 110000000 uAh you know yes last couple of points were in jest but my whole point is it could be made way simpler for the average guy who is not versed in scientific notation to understand, and at the same time give all the relevant info.

 

 

 

 

 

 

 

 

 

 

 

Edited By gangster on 09/11/2016 16:04:19

[MattyB]

For those of you wanting to estimate the max amps for cheap motors from the like of HK, 4-max etc (more expensive ones from Hacker, Axi, OS etc. tend to have accurate specs provided that include this info) here is a rough method that should help...

1. For your motor find out the mass in grams and nominal voltage for operation.
2. Ignore any quoted max wattage. Instead take the mass in grams and multiply by 3. This is your (conservative) max power in watts.
3. Take the calculated max wattage and divide by the nominal pack voltage*. This will give you the max current in amps.
4. Size your ESC a minimum of 15% or 10A above this calculated max motor current, whichever is lower.
5. Prop to give yourself slightly less than the max calculated MOTOR current.

* - If the motor is quoted to be used on multiple pack sizes i.e. 3 or 4S always use the higher of the two voltages when doing this calculation, as it will give you a lower maximum current.

Yes this method is conservative, but it works - you are almost certain never to burn out a motor or ESC if you use it. Besides, in most models we need a bit of weight up front to get it to balance, so running a larger motor rarely causes an issue and will be more efficient.

Important point - the 3W/g rule of thumb only applies to prop models powered by cheap motors. Better quality items from Hacker etc will do more providing the cooling is right, and even cheap EDF motors can output far more watts/gram because of the enhanced cooling intrinsic to an EDF installation. I do not have a similar rule of thumb, but if forced to guess I would imagine it is at least 6W/g.

Edited By MattyB on 09/11/2016 16:47:27

[Trevor Crook]

Wow, never seen your rules of thumb before Matty, but just applied them to a couple of my setups and they are certainly in the ballpark. Useful info.

[Geoff S]

As I said earlier this is a technical hobby and you must expect to do some work to understand it. You're not buying a simple consumer item designed for ignorant users (I don't use the term 'ignorant' perjoratively. We're all ignorant about lots of things). You're buying something to be used by an 'expert' in an intelligent way. A level of understanding is required and you get that knowledge by reading either in books/magazines or here, on the internet. All activities have their shorthand and jargon and the things you're complaining about are the ones related to our hobby

I started playing with and riding motorcycles back in 1956 when every rider had to be a mechanic - an 'expert'. No-one left home without a toolkit. Cars of the time could be repaired by the user quite easily, but most took them to a garage. Most motor cyclists I knew did 90% of their own repairs/maintenance (sometimes at the side of the road!) and were proud that they knew how. That's aeromodelling now, even with ARTF and RTF models and that's what makes it interesting.

Geoff

[PeterF]

3S as an SI unit is 3 Siemens, unit of conductance (1/ohms), therefore does the 3S battery in fact have a resistance of 0.3333 ohms. Seconds is shown in lower case s to add to the confusion, i.e. 3s.

[John Privett]

Posted by gangster on 09/11/2016 16:00:37:

the other number 35C is the output current rating expressed as value compared to the capac ty (C) so 35 x2.2 amps = 77 amps. That sir is what my whole post is about 35x2200 is actually 77000. Notice no units as there are none on the battery. This has confused many people and that confusion has reared its head on this very forum a few times. I agree many people would automatically know, from being told to divide that 2200 by 1000 but why should they have to . Anyway is that 77A continuous or burst! nobody will ever know. I have to admit that is a purely hypothetical question the flight would be might short.

Ok, so the problem (if it is a problem) is that the capacity is generally stated in mAh when it could just as easily, and maybe more sensibly, be stated in aH. So 2.2Ah rather than 2200mAh. But a 35C battery means it's 'good' for 35x2.2 A, ie. 77A or 35x2200 mA, ie. 77,000mA. Just depends what units you want to use. Perhaps we should be grateful that we don't quote LiPo capcities in μAh !

As for whether it's continuous or burst, it's whatever the battery manufacturer (or more likely the company that sticks a label on it) wants you to believe. It's not much more than a marketing term - unlike capacity you can't readily measure the C rating.

 

[gangster]

Precisely John So we have the situation whereby the battery capacity is quoted in mA and the max current of the esc is in amps, the motor in amps, the meters which we should all use measure in amps and the chargers measure in amps. And in the case of the battery I quoted we have to assume its mA cos they dont tell us but most other manufactures do so.

Whether we like it or not these are consumer items for consumer products for ordinary people and not specialists or geeks.

Also agree with the "C" comments