Large Scale Central

Li-pol Battery question

Electronics Power and Sound
#1

With Li-pol batteries all the rage in the radio-control model aircraft fraternity and now gaining a measure of credence amongst the model railroad crowd, should one entering this arena of R/C consider a li-pol as an alternative to ni-cad and ni-mh technology. I am aware of the apparent ‘dangers’ in charging these packs and it seems that a decent charger will individually recharge each li-pol cell, rather than treat the entire number of cells as one battery for recharge purposes. I am also aware that allowing the cells to go low-voltage may impart some grief, but I am assured that analogue charging will reinvigorate these under-voltage cells. It would seem that li-pol’s must always be kept in a ‘full’ charge state and not allowed to discharge fully, to prevent low-voltage hibernation.

One battery pack available as a dual pack, is individually rated, each pack, at approximately 14.4 volts per pack with 6600 mah discharge capacity per pack. Is this overkill for R/C trains as regards battery discharge capacity? To me the voltage of 14.4 is adequate, as I normally run at around 12 - 14 volts maximum and do not feel that I need the 21 volt capacity of the 2 amp Aristocraft standard dual li-pol battery pack.

#2

Hi Tim.

I would not touch any of them unless they have same sort of protection circuitry built into them that the Crest 21 volt batteries have.
Even then I want see them proven completely safe as compared to NiCd cells.

How about you become our test bed. So to speak.

#3

Tony,
a fellow model railroader here in Sydney, who competes with both R/C sportsplanes and sailplanes, uses li-pol’s exclusively, as do many other fellow aviation modellors. The general consensus is that they are extremely safe, with the only concern being that they will run under-voltage and then can become tempermental as regards being able to recharge them again. The main concern is that they are charged sensibly. My discussion today with a hobby store recommendeds that the cells be recharged individually and not treated as a single battery as we do with ni-cad’s and ni-mh. When questioned about safety concerns with use and recharging of li-pol’s the consensus was that they are safe to use.

    In model sports aviation,  the modellors are drawing up to 150amps discharge from these batteries during a climb to attain altitude in minimum possible time (around three seconds duration).  If there were safety concerns with usage then a battery with such a high rate of discharge, if suspect would not be used.  Similarly,  these model aviation sportsmen are recharging these cells in around 50 minutes,  not the overnight trickle charge that I would consider prudent.
#4

Tim.

Feel free to go ahead.

Personally, I still would not touch them.

Each individual Li-Pol cell is 3.6/7 volts so separating packs to charge them is not something I would relish doing. That would mean gaining access to the batteries. Not always easy in most locos.

#5

Tony,
the battery packs have a separate charging lead which connects to each individual cell. The charger will charge each cell independently of the other. There are five(possibly 6?) wires for a 3-cell 11 volt battery - positive, negative power wires and a separate charge wire to each cell. From memory the charging connection is a three pin (or four pin) connector. To charge the battery, one would need access to the charging lead, so it would need to be accessible without removing the tender shell, or boxcar body, etc. The attraction of the li-pol battery is it discharge capacity and compact size. Where a comparable size ni-cad or ni-mh maybe 2400mAh, a li-pol could be 6600mAh.

     I notice that the Aristocraft li-pol has a simple two wire connection that is used for both power feed/discharge and for recharging purposes.  This means that the battery is recharged as if it were a ni-cad,  with the total output voltage the consideration and not  the voltage of each individual cell,  as happens with a 'smart' li-pol charger.   By charging the battery as if it were one cell then maybe this is why the battery has received bad press.   Considering the punishment that the competition model aircraft hobby give to these batteries I am not inclined to dismiss them as a possible alternative.  Each time I have pointed out the apparent shortfalls/pitfalls with the li-pol, as a result of urban myth attained knowledge,  I have been put in my place by conflicting and supporting arguments from those who use the cells.
#6

I also use the lipos in my rc planes , but , I am very careful to follow the rules , and I charge them in a flame proof container , and store them in a flame prooof container when not in use . Yes I am a afraidy cat .
The lipos are very powerful batterys and light weight , and retain their charge a long time , right now after weeks and weeks , of them sitting in a can , I can grab a lipo and go fly .
Instead of having to recharge a other type battery .
I have seen enough videos of the lipos burning , that I am cautious .
BUT TIM , if you always follow all the rules with them , it will be safe , most likley .

I do not store the lipo batterys , with my cans of black powder , and the cans of gasoline for the lawnmower !
;- )

#7

Tim, except for an initial problem with the first batch of Crest Li-Po batteries, the Crest packs have since actually gained a very good reputation for safety and performance.
That is perhaps because each pack contains suitable safety circuitry.

Would you have have confidence that the LS consumer could remember to charge each cell individually?
I certainly wouldn’t.
I don’t know what the outcome would be if they didn’t remember to charge each cell and maybe missed one. My guess is it would not be pleasant.
Also, with at least 4 access points needed to charge a 14.4 volt pack, the installation would become very complicated.

The idea of being able to reliably charge one pack (of any voltage) of NiCd batteries appeals a great deal more to me.

#8

Tim, you have clearly done your homework. I don’t think you need to charge each cell individually, since you will not be working them as hard as the airplane guys.

I think if you would charge your packs as a unit, but check the individual cell voltage often, and watch for variations, you would be fine.

Charging each cell individually would definitely be optimum, but then to have any kind of convenience, you would need a charger per cell. That’s a lump of cash.

I would say you are not the typical user, and Tony is focused, rightly so, on the average guy, and bulletproofing the situation. Since you are walking into this situation armed with a lot of understanding, I would say try it out.

Regards, Greg

#9

Greg,
the li-pol packs that I have seen all have provision for individually charging each cell. It is not possible to treat the multiple cells as one battery for charging purposes. The smart chargers will treat each cell separately for charging purposes. All one needs to do is plug the connector to the charger and let the charger monitor each cell’s state of charge. The operator is not able to override the charging process. I am considering a twin pack 14.4 volt 6600mAh, which could quite possibly run a loco all day wiithout need for recharging.

    The model aircraft modellors assure me that there is no problem,  when treated with care,  as I am sure that a hobby which uses these exclusively,  for the reasons stated previously,  would be aware of multiple failures and take precautions against failure occurring.  I feel that the situation is like the Chevrolet Corvair controversy once the consumer activist Nader took on the case in the 60's.  For a generation afterwards the car was branded as a death trap.  I am sure there are those who still drive a Corvair and enjoy the experience.
#10

Tim,
I am not trying to teach you to suck eggs, but, are you aware that a 14.4 Li-Pol battery contains 4 individual cells wired in series?
So two 14.4 volt packs will require 8 different charge points

#11

Tony,
I have not disassembled a pack of li-pol cells, but every pack sighted so far (excluding the Crest li-pol) has contained a positive and negative power lead set and a separate multi-wired charging lead set, with a multi-pin flat connector on the end (number of pins determined by number of cells in each pack). This separate charging lead is connected to a matching receptacle on the charger. The charger then will charge each cell independently of each other cell. How it does this is unimportant to me at this stage. I do not see the charging as a problem as that is already sorted out with the attached/integral charging lead on each battery pack. Obviously if using a twin pack, each containing four cells, then either two chargers would be needed or each pack charged sequentially, using one charger.

    On another matter,  what do you think of using a smaller capacity battery pack (ni-cad, NIMH, li-pol) in say a tender,  for limited loco useage and then a larger battery pack in a trailing car for more intensive train operation?    I like the idea of a trailing power car,  but see the need for it to be permanently attached to the loco as a disadvcantage.  A DPDT switch,  mounted to the tender chassis, would select either tender onboard battery or trailing car battery (via a mu cable).
#12

OK Tim.

I think your nomenclature is wrong.
You said each “CELL” was 14.4 volts and had only two leads coming from it, and must be charged separately.
“Cell” is the wrong term.
I can assure you each 14.4 Li-Pol “cell” (as you call it) has four x 3.6 volt cells in it.
It is rightly termed a pack. Not a cell. A cell is the individual 3.6 volt part.
In which case, yes I do agree each pack of 4 x cells should be charged by an individual charger.

A 7.2 volt NiCd or NiMh pack contains 6 x 1.2 volt cells.
Unlike Li-Pol packs, you can charge as many cells in series as you like. As long as the charger can handle the voltage requirements. These NiCd and NiMh cells can be made up into a pack of any voltage.

The other matter.

Please read up on how my BIK-U3/6 installation kits work.

http://www.rcs-rc.com/accessories/rcs_bic_u3_6_inst.pdf

I think you will find I have been using just such an idea for many years.

BTW. I will never recommend AA NiMh batteries for our use. Not even for low power situations.
They do not last very long in terms of recharge cycles compared to NiCd and rapidly self discharge when not being used.
Stick to NiCd.
If you must use AA size because of space restrictions choose only the new hybrid chemistry made by sanyo and known as ENELOOP.

#13
Tony Walsham said:
[i][/i]If you must use AA size because of space restrictions choose only the new hybrid chemistry made by sanyo and known as ENELOOP.
I've just started noticing these show up on the market, but don't know much about them. I'll have to do some searching around and get some data. I've been using NiMh in my cameras and 2-way radios and other toys for about 4 years with good results, but I definitely agree that they don't hold a charge well. My camera is always dead when I go to use it.

Jon

#14
Jon Radder said:
Tony Walsham said:
[i][/i]If you must use AA size because of space restrictions choose only the new hybrid chemistry made by sanyo and known as ENELOOP.
I've just started noticing these show up on the market, but don't know much about them. I'll have to do some searching around and get some data. I've been using NiMh in my cameras and 2-way radios and other toys for about 4 years with good results, but I definitely agree that they don't hold a charge well. My camera is always dead when I go to use it.

Jon


Hi Jon.

The ENELOOP AA batteries made by Sanyo are guaranteed to hold 85% charge for 12 months.
They are a mixture of NiMH and Alkaline chemistry.
Sanyo are no longer making AA NiMh batteries.
Panasonic have an equivalent brand.

I had been using AA NiMh batteries which have increasingly been failing in customer installs.
I have now stopped using them in favour of the ENELOOP cells.
BTW. I can only get AA and SubC cells here at a reasonable price. Other sizes are available to special order, but the cost is prohibitive.

Even though the ENELOOP cells show much promise, I will never use AA size cells again where they can be avoided, as they have power output restrictions which if exceeded will drastically cutail their life.

Never use AA cells where the continual current draw is greater than 1/2 an amp. It is OK to have occasional drains of up to 1 amp. Above that and you will destroy the cells very quickly.

Who told me. A major SANYO distibutor in Australia.

#15

I love threads like these. Though not immediately relevant, one of those “file it away fore shore” beauties!

#16

Sorry this is a bit long-
The use of LiPo batteries is going strong in the RC air community. I have flown exclusively electric powered aircraft for the past 7 years and LiPo technology has been a real boon to the hobby. I would suggest that if you really want to learn more you go to http://www.RCGroups.com and check out the battery forum.

The major advantage of LiPo’s is that their energy density is considerably higher than that of NiCad or NiMh which is of major concern for flying because you want to keep weight down where ever you can. In model RR’ing this is not a major factor in operations.
There are four things to be careful of when using LiPo’s- damaged or misused LiPo’s can experience what is know as thermal runaway- read that as a real real hot fire!!!

  1. Physical damge to the pack- more likely when flying than when running a train.
  2. Over discharge of the pack- most modern flying ESC’s have a low voltage cutoff (LVC) that can be adjusted or is auto sensing depending the size pack you are using.
  3. Over charging of the pack- a good chargers are “LiPo aware” and stop charging at the appropriate voltage levels.
  4. Cells in a pack being out of balance- goes in conjunction with #3, in that a good LiPo charger is a balancing charger that monitors individual cells so as not to over charge any cells in the pack.

With that said here are some thoughts about LiPo use. Again check the http://www.RCGroups.com forum for tons of info, I’m not coming up with anything new here.

  1. Handle the LiPo’s with care. They are in a foil package not a metal can and can be damaged any number of ways.
    2.The speed control (ESC’s) we have available for model RR’ing are not LiPo aware and have not provisions for LVC. The only system that seems to have a way around this would be the RCS EVO speed controls. Because you use a surface receiver there is a possibility that the LiPo Shield available from Dimension Engineering (http://www.dimensionengineering.com/LipoShield.htm) would work with this speed control Basically it reads the voltage of the pack that is being used and cuts off voltage to the speed control when it senses that voltage has dropped to 3v per cell. I’m using this device on some of my older, non LiPo aware ESC’s in planes. I may try it on the EVO I’m running.
    3 &4- Buy a good balancing charger for LiPo’s. One poster mentioned charging each cell invidually. Most LiPo packs now come with a balancing plug. This plug is connected to the individual cells in the pack and a balancing charger charges each cell separately. The FMA CELLPRO 4 I use is really great in that it tells you what’s going on during the charge by listing individual voltages on its screen, slows charging cells that peak while continues charging cells that are not peaked (BALANCING the pack), has adjustable rates of charge up to 3C. A good balancing LiPo charger is an essential tool.

With all that said the major hurtle is #2. LiPo’s shouldn’t be discharged lower than 3v per cell. You can measure the amperage your loco draws and calculate run times (conservatively please). I do this on non LiPo aware ESC’s that don’t have a LiPoSheild connected.

I’ll say that LiPo’s are probably not going to be used in my loco’s. I’m most likely to use Lithium Ion packs with a protection circuit built in. (http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=1975) They have to be charged with a Lithium charger ( a Great Planes Triton is an excellent versatile choice, though it not a balancing charger). The protection circuit board on these keeps the pack from being over charged and over discharged. I’m trying to figure out if it also keeps the cells in balance.

My other choice is likely to be the cells contained in Dewalt 36v tool packs (collectively known as A123 or M1 cells). This is another Lithium technology with cells that are capable of delivering very high amperage, capable of quicker charging than LiPo, about the same size as sub C NiMh cells but lighter and each cell is something like 3.4v. With these cells you can replace a 10 cell NiMh pack with a 3 cell A123 pack thus saving space. These cells are becoming very popular in larger electric planes. Going to higher voltages you end up with a much smaller package than when using NiMhs or NiCads.

The advantage of Lithium technologies is greater voltage per cell so for a given voltage packs are considerably smaller and can fit into tighter spaces. In model RR’ing we don’t usually have to worry as much about amp draw as its a lot lower than in electric flying (my planes draw from 12A to over 40A). My two Porters and my friend’s Critter based on a Bachman 44Tonner power truck are drawing around 1A.

Enough said as this has gotten very long. Hopefully it will help.
Dave:

#17

Great post Dave.

Thanks.

#18

Thanks Tony. I just hope this helps people who are considering various battery chemistries.
BTW, the hiccup with the EVO hasn’t reoccurred, must have been a frozen gremlin sneaking from the cold outside.
Dave