Hi All,
…. And wow, there is a lot to cover here. Sounds like we have planes trains and Automobiles?
First let me start with why would you buy a Fromeco Pack?
You would buy a Fromeco pack because they are made by us, (Mike and I) here in the States. Each pack is glued, welded, soldered, and shrunk by us. We take a lot of pride in what we build. We understand that there is upwards of 15k (in some cases) riding on these packs and electronics, and we take it very seriously. The cells we choose to use (we are constantly testing new cells) are tested and approved by us, testing includes Vibration, Environmental, Shock, and of course discharge profiles. We are very picky, this is why we haven’t taken the newer larger size Lithium Ion cells as of yet.
Other reasons to buy Lithium Ion over Poly (RX & IGN only)
They are lighter
They are Safer (we don’t usually push this, however it is a topic in this discussion)
They are more robust (mechanically)
Why do they cost so much?
Because they are made HERE by us. We will never be able to compete with Hobby King 12.95 LiPos shipped direct from Shenzhen City, at least not until the paradigm changes, which it will eventually.
Let me answer some of the questions I saw here.
8Ball and Poly.
Yes you can do this, however…. a polymer has less internal resistance than a Lithium Ion pack. This means you are going to get less of a voltage drop, which means you need to cheat your number up slightly. For anybody that wants to do this I suggest that you discharge your pack all the way to the basement 6.0volts. Then put in 300mA (or whatever you want for a safety margin) and then do a 1 amp load test for 7 to 10 seconds, whatever your number is, is your new NO FLY voltage. Larger packs capacity wise will have different numbers than smaller packs.
8Ball and our cells, we came up with through testing, we know that under a 1amp load for 7 to 10 seconds we have a certain amount of capacity left (that I will not state) at 7.0vdc.
Are Lithium Ion Cells safer than Lithium Polymer cells
Yes. (Again we don’t push this unless asked)
To use the Car analogy we need to switch out the GT500 and replace it with a Tesla, the Honda can stay a Honda but it needs to be a Pius I mean Prius. Technically the Tesla should be using LiPos, because they can provide more power with less voltage drop. Being a sports car this would be very advantageous. They use 18650 Lithium Ion Can cells similar to what we use, in very large controlled arrays for safety purposes.
Lithium Ion cells (from a reputable Manufacture Samsung, Panasonic,LG(sometimes), Sanyo,Molicell) have 3 safety features built into them.
1. VENT ~ CID (Cell Interrupt Device)
2. PTC (think thermal fuse) Positive Temperature Coefficient
3. SHUT DOWN SEPARATOR (SDS)
The PTC is the first line of defense. The PTC engages when a Lithium Ion cell is subject to an over amperage situation for a set time period. In our case if you take a 2600 Relion and put it under a 12 amp load, at about the 4 min mark the pack will PTC out. At which point the battery will go to close to 0 volts until the load is removed from the pack (note the if the PTC ever gets engaged it changes the characteristics of the battery it increases its resistance slightly). If the PTC was to fail this is when the SDS would come into play. The SDS basically goes opaque (phase change) in the sense of Electrons can no longer pass. If this happens it is final, the battery is a brick. The SDS is activated by temperature, this temperature is based on Thermal Runaway profiles of that particular cell. Then you have the VENT~CID, which is sort of a catch all. So if you put a 24vdc 6amp charge into a single cell, it will probably vent, and vent with some fire, however the intent is, it doesn’t explode. The VENT~CID works off of cell pressures, cell pressures usually increase due to a Temperature issue.
Polymers have none of these attributes. There was talk a few years back of adding a retardant to the polymer matrix to try and make them a little less volatile whether this has been implemented I don’t know.
So are Polymers more powerful than Lithium Ion?
Yes. But how does that relate to powering a 40%.
About 6 years ago Mike and I went out and data logged our 40% Patty Wagstaff Extra 3W. Mike built a 4khz logger, basically this thing took a data point 4000times a second for about 5 minutes. I am a fair pilot, and I put the Patty through the ringer in a controlled pattern over and over and over again, I flew the plane hard enough that I stripped out a double stack of 8711s on right elevator(high speed walls). Basically start data logger, fly canned routine which incorporated Heavy 3D (walls, blenders etc.) and IMAC (Rolling Circle, Humpties etc.). We tested Lithium Ion (ours), Polymers(Thunder Power), A123 (ours). This test was done to prove the efficacy of the DCUP. What we found was pretty shocking. Yes there were 40amp spikes, but they were milliseconds long, and the same magnitude across all packs. What was interesting was the (what we call the Hotel Load) nominal amperage was very stable between 4 to 6 amps, and the nominal voltage was stable as well. The Lithium Ion did have nominal voltage that was lower than the Polymers, however it wasn’t dramatic. One thing to note, this was on a Regulated system (A123) regulators were bypassed. Unfortunately the data for this testing was lost on a Hard Drive that took a dump, years ago some of it was posted on GiantScaleNews. Another interesting artifact of this testing was the IMAC flying was harder on the batteries than the 3D in nominal terms. The spikes were not nearly as high but the Hotel was. Keep in mind I can't fly like Daniel H. which would probably return different results.
We have done a lot of testing on Polymers. We have the equipment to run Batteries up to 30C and further. The one thing I have noticed when testing a 30C polymer at 30C is, it is HARD ON THEM. Really hard on them. Does it do 30C, yes, can it be rated at 30C, yeah I guess it does 30C, but how many times? One thing to remember is, about the only thing these batteries are used for is our hobby, yes there are some outliers but... It is important to note that it is very hard to find a Technical cut sheet on the cells that are used in a Polymer packs, it is impossible on a 12.50 pack from Hobby King. I AM NOT BAGGING ON LIPOS here, I only bring this up because in this thread there is mention of percentages of pack being used. And yes the the Lipo is going to do better in this department, but the results may not be as lopsided as it is made to appear. An example of this on the Lithium Ion side is ongoing as I type this. Right now we are testing the Panasonic 3400mAh cells. These cells are rated at a 5amp per cut sheet, ours only 4amps. However when tested head to head with our Samsungs the Panasonics do miserably, even at 1 amp. When pushed into the 6, 8 , 11 amp area it is no contest. So here is an example where even a cut sheet and documented SPC controlled battery doesn't quite cut the mustard for our standards. Does it work yes, and just doing quick napkin calculations should prove it to be better but it is not. Is this a bad battery, NO, just designed to do a different duty than the Samsung.
Do our Lithium Ions last longer?
This is could be up for debate when proposed on the general population. Much like how effective a diet is. Problem is, everybody tells you they stuck to the diet but you don't really know how many times they jammed 10 Snickers bars down their throat. Same with batteries. In theory our Lithium Ions should last longer if treated properly. This would be because they have more traceable manufacturing method using SPC (Statistical Process Control), Six Sigma etc. NOTE: This does not apply to all Lithium Ions.
Storage Charge
All Lithium Base batteries benefit from bring the cells into a Nominal voltage range. Is this needed in the middle of season, between the weekend? I would say NO, but they will benefit if you do. What really needs to be expressed is, it is very hard on the batteries to store them on a full charge in very hot conditions. This kills them. So if your storage is a hot area, it is best to have them at nominal voltage. Higher temperatures drives degradation from the 3% area to 25%. So if it is hot where you store, you need to use the storage charge method. We have a KB article on our site about this.
I hope this helps a little.
I just whipped this up and I am an enginerd, which means I suck at the English Language. So if you're a spelling Nazi who drives a Pius I mean Prius you're probably pretty pissed off right about now.
Kurt Cook
Fromeco Scale Avionics LLC
