Opti-power fully charged at 4.18v per cell

[cjcj1949]

It would be useful if the lipo manufacturers would give us an easy to understand figure that will tell us how good the packs are. We basically want the volts to drop as little as possible when we increase the current. Internal resistance can be used to give us that figure, but as internal resiistance is calculated from voltage drop, why not give us the voltage drop directly. I would suggest voltage drop at 20 amps and 20 Centigrade. The 20 Amps would be a short pulse which raises the current from 0 to 20 Amps. Easy to understand for all users who can then decide if they need a punchy battery or not and they have the option of getting their battery tested to see if it comes up to spec. New products could demonstrate how much better they are than the competition with numbers that mean something instead of the current C ratings.

[Guest]

CJCJ1949 makes some very interesting and useful observations here, plainly this is someone who knows a lot about lithium. We wressled with C ratings for ages as having done the work in testing I think 17 different manufactures cells (this cover all brands prety much) we soon relaised there is a massive difference in lithium quality from close to dangerous to very good at the other end of the scale and mostly very average.

During testing one of the critical issues is voltage hold, in fact the critical issue coupled with heat. In structured testing which is what we did and it took a considerable time to do, we would take a cell charge it at 1C and monitor the charge in terms of time taken, IR activity of each cell (divergence) in the pack during the charge, capaicity acceppted by the cell and end voltage plus temperature.

A fully charged cell is then discharged on a purpose built rig designed to discharge at a given rate. The cell is attached to the discharge conductors by copper tags as think as your finger directly, no EC5 or Castle bullets in sight. The software is given its instructions the cell is then set to discharge at 1C during which we monitor voltage hold, temperature and capacity withdrawn from the cell.

Then the cell is recharged and again the details recorded and again discharged this time at 5C, then 10C then 15C and so on. This was done for a wide variety of manufactures cells and this allowed us to build a REAL picture with REAL facts about the cells tested no guessing or gut feelings involved. Its expensive to do and takes a lot of time but as the new boys on the block and knowing little about how different manufactures products compair we felt we had to do this.

CJCJ is perfectly correct in the fact that the IR and voltage hold go together and if you have a very divergant IR in a pack that is the weak cell and pack is only as good as that cell. If you pack is cold or very cool at the end of a flight then it is likely to have low IR's and good voltage hold and that is indicative of a good C Rating. Most helicopter pilots do not pull more than 9C anyway (very transient bursts to higher levels do occur).

Lower IR will generate less heat during charge and discharge but this is not linked to the maximum capability of the cell to take or release charge, that is down to the chemicals used in the pack and the manufacture quality. Low IR is a good thing as less heat means the pack will last longer under normal use as heat is one of the major contributors to lower cycle life but whilst there is a correlation between low IR and the overall capability of the pack this is more down to the heat generated than the chemical capability of the cell.

The testing we did does not give you any real indication of cycle life however. The cellpro PL8 and soon to arrive PL6 do have some functionality built in which does record the pack charge data and part of that is the IR activity and over time can give you an indication of cycle life but the only real way to monitor this is by recording the flights discharge and the cells charge data. This being the case this is what we did and still do!

The test pilots were given a PL8 preproduction packs and told to abuse them. Each machine had a Castle Creations HV Ice (foutunately not the exploding type) as these have built in logging, this was downloaded after a set of flights and the cells recharged again using the CellPro data link and the charge data collected for all flights this was sent to us for periodic analysis. 3 of the UK top fixed wing pilots and 7 of the UK top 3D Heli pilots were involved, this has been scaled down now but we are continuing to do some work with selected pilots to understand cycle life better and charge C better.

We are now well past 100 cycles of 'Masters' level 3D flight on some of the larger packs and there are some very slight signs of stress as you would expect. We compared the data to when the packs were new and on average each cell is running at 0.13 volts below where they were as new. At maximum stress (peak amp points) the packs are showing around 1.8V difference to a brand new. This is pretty convicing stuff as the pilot cannot actualy feel this in flight. Packs will degrade with time as the chemisty is consummed as it were and over time even the best packs will swell a tiny bit after use and as they degrade heat slightly more. The information we would indicate that in sport use 200 cycles should be possible perhaps more!

We are doing similar work in the USA at this time again with selected pilots and you will find more data on voltage hold etc on the forums over there where OPTI is involved. Early days but I think around 70 cycles over there.

As CJCJ notes quite correctly the C Rating is not really the issue its the actaul pack performance and chemistry quality that determines the pack quality. Before anyone asks we will not release the data we have for all sorts of professional and commercial reasons, the point is we did the work and continue to do it. I might do as CJCJ suggests at some point and discuss voltage hold in more detail.

We currently do 100% QA on cells coming into stock, this is only a simple test to check that each cell is "alive" and that there are no DOA's, this takes a lot of time and so far the fail rate is less than 0.001%.

We are the new boys on the block and to that end we are keen to understand how the client base finds the cells and support as much as we can that client base. As lithium is used ever more widely more and more questions will be asked, we will try to answer as best we can.

Sorry to bang on so much but it is important that the community understands the work behind the brand, that we do take this very seriously and that quality and commitment is a very important factor. Yes we could have sold a poor quality cell at lower cost but thats not where we want or need to be. We wanted to produce the best cell we could at a reasonable price and be able to offer good customer support and have confidence in the product.

Andy

[NEAGRON]

Andy,that makes good reading,it would be great if you could may be inform us of all the usefull information required for us to monitor our cells,May be Stuart would allow you to have a sticky.I personally am using A Cell Pro PL8,and all I can say is its one hellifull piece of kit,over kill for me as at presant only chargeing 3s-2200 packs.The packs im usuing are not optifuel but test assure my next pack's will be after your responce on here. Andy one final question for you,what is considered a good IR figure and also how difference btween cell's are considered acceptable.
Many thank's for the time you have taken to answer question's on this post,your's Marty.

[Guest]

Marty,

Indeed an interesting question, what is a good IR. I guess it will be no surprise that theres not a simple answer, firstly the lower the better but what is low?

IR (internal resistance) is a function of a number of aspects of the pack the size and design of the tabs on the foil parts internally the size of the wires used, the quality of the wires used, the solder type etc. Then there the chemistry itself so its difficult to compair one manufactures cell absolutely with anothers however the fact remains the lower the better!

You tend to find IR's on big packs tend to be lower as they are easier to control during the manufacturing process so the chemisty is better proportioned one cell to another and the physical cell is bigger so easier to work on. As a rule of thumb only on big cells IR of <5 is OK 5 to 10 not so good and <2 good. On smaller cells say like your 2200 3S IR's of 5 to 10 would not be unusual.

The real issue is IR divergance and this is often a good indication of a cell starting to fail. If you watch a cell charging and you see this:-

2700 6S pack 3 cycle 6 IR.JPG


Then you would have to say this is not a good cell and is U/S even thought it would still charge and operate but the whole pack is compromised to the worst cell, in this case cell 6.

If you saw this:-

2700 Pack 5 6S cycle 1 IR.JPG


Then you would be looking at a very good cell with no issues at all a very nice pack indeed.

As I noted above it's not all about IR but about how the chemistry gives up its energy over time and how the voltage holds during that discharge period.

IR's do vary during a charge see below:-

850 3S pack 64Cycle 8 IR.JPG
Here you can see that cell 1 IR value varied during the charge but in fact it's divergence was good at the end of the charge cycle, on a small cell like this this sort of divergence is fine.

Hope this helps a bit in what is a very complicated subject.

Andy

[NEAGRON]

Many thank's for that Andy,my packs which are galaxy 40c are giving a IR reading od between 4.7 and about 6 off the top of my head,so as they are small 3s-2200's,I take that as being classed as good pack's,will monitor them even more now,I am chargeing my packs on the PL8@2c accurate charge.

Andy as stated in my previous post it would be great if you could maybe talk to Stuart and do a sticky on the best practices for chargeing lipo batteries and what to look out for.Im sure there would be a lot of happy bunnies on here if you did that,I know youre a busy man,but maybe you could do this for the forum.your's Very Gratefully,Marty.

P/s that has improved my knowledge base no end.

[ChrisB]

Thats what you call service!

I would like to see that from HK with a Turnigy pack!

But they are a Up to a third of the price so works for me.

[jamiem]

But they are a Up to a third of the price so works for me.

Horses for courses Optipower isnt going to compete with turnigy on price, but they will on pretty much every other variable (power, support, temperature, longevity, weight, availability etc etc). You pay yer money and make yer choice as the saying goes If price is ultimately the deciding factor, them I'm sure you are happy with the HK packs

[LaurenceGough]

All four of my nano tech packs have made it to 20 cycles and are twice as wide as they first arrived - Twice the value for money!

[cjcj1949]

I don't know much about Lithium Batteries because very little is published. Internal resistance is a variable which depends strongly on how it is measured. I use the Wayne Giles meter to measure effectively how much the volts drop at 17 amps on discharge. It is then no surprize to find that it predicts how much the volts drop in use. There may be a good correlation between charge ir and discharge ir but as the reactions are different I am not sure that would always be true. The only thing I know is that there is a simple way of predicting how well a cell will behave without using it. It does usually seem that one cell goes before the others and it is a shame that we cannot buy individual cells, especially for Sport use. Space isn't that much of a problem for 450 3S 2300 battteries and separation would give better cooling.

[Guest]

Laurence,

With all that gas in there won't they be lighter!!!

[LaurenceGough]

Only when discharged . Electrons are heavy.

[Ashley Davis]

Space isn't that much of a problem for 450 3S 2300 battteries and separation would give better cooling.

Not really if you look at the make up of a lithium pack, the surface areas generating heat within the pack are massive compared to the outer surface area of the pack that can be used for cooling, so cell separation offers very very little in terms of additional cooling.

[AcidDrink]

Thanks for good reading everyone. I have very high hopes for Optipower lipos, I think UK market desperately needs a reasonably priced consistent quality packs everyone can trust. Being transparent about testing process and QC process helps a lot.

[sacko]

Talking of IR values.

The Optipower packs I have are the only packs I have ever had, where the IR values decrease the more you use them!

When bought, the IR was matched on all cells at 2.2 according to the Cellpro, they have now dropped to 2.0 across all cells.

[cjcj1949]

Not really if you look at the make up of a lithium pack, the surface areas generating heat within the pack are massive compared to the outer surface area of the pack that can be used for cooling, so cell separation offers very very little in terms of additional cooling.

That is just wrong isn't it. Look at any heatsink. Heat loss is proportional to external surface area. Heat generation has nothing to do with heat extraction.