While at Toledo last week George Joy mentioned the fact that the E-Tec cells were quite good, even better than the Kokam. As I recall he indicated that you were selling the E-Tec cells as well.

From : Don Stackhouse

We've been doing a lot of testing with Li-poly batteries lately. I'm planning to send a post to the slowflyer and e-light lists soon relating our results.

First of all, the Kokam cells:

Two cell packs of the little 145 mah cells don't seem to have the power output and the necessary max current capacity, except for the most efficient MPS-1A models that don't need more than about 40% throttle for cruise. The Cub, A6M2 Zero and the Curtiss-Wright Junior may be OK based on this. Flight times might be acceptable, as long as you're willing to put up with a significant loss of full-throttle power. The weight reduction helps a lot, but the power loss more than offsets this. The max current limits on the Kokams indicate that on models that use higher power settings than that for a significant percentage of the flight, the cells might be damaged. We're still investigating that, but so far it appears that the best application for the Kokam 145 cells is as a single cell in an RFFS-100 equipped plane, or similar.

Two cell packs of the larger 500 mah KoKam cells do OK in our twins and MPS-2A powered models, about the same performance as the 230 mah NiMH cells but with more flight time. The shorter-winged models with a single MPS-1A do not seem to like the weight of the KoKam 500 mah cells. The Me109 Joe's son Terry was flying at Bowling Green had an MPS-2A with a pair of Kokam 560 cells. It's lighter than the same airplane with a 230 mah NiMH pack but with nearly the same power at full throttle, and as you could see it's a very happy airplane with that setup. However, read on.

Regarding the new E-tec cells that are just now becoming available: These seem to have more current output than the Kokam cells, both in terms of what they can tolerate without damage and in what they will actually produce in service (officially about 4-5C max continuous and up to about 7C for brief periods), and come in sizes that seem better suited to our company's current models.

A two cell pack of the E-tec 250 mah cells is fully 1/2 ounce lighter than a 7-cell 110 mah NiMH pack (our standard NiMH recommendation for indoor flying with a single MPS-1A). Full-throttle power at the beginning of the run is slightly less (about 90%), but with the weight savings the overall performance seems to be about the same or slightly better, and the flight times are far better. Power at cruise is about the same as good 110 mah NiMH cells, and power available at all throttle positions near the end of the flight is a little better. I recently flew the Junior with a 2-cell 250 mah E-tec pack outdoors in measured winds averaging 10 knots with frequent gusts to 12 and occasional gusts to 15. This required about 75% on the throttle stick position (we can normally cruise the Junior at about 1/4-1/3 throttle stick position in calm air), and with the old 110 mah NiMH pack I would have expected about 7-8 minutes at the most at these power settings. The E-tec cells lasted a very solid 22 minutes! It appears that the E-tec 250 mah 2-cell pack may be the best presently available all-around choice for most of our models powered with a single MPS-1A.

I also have logged a fair amount of time recently on the Ryan ST prototype with an MPS-2A twin-motor system and an E-tec 2-cell 700 mah pack. This is the same plane we flew at Bowling Green, and we had the same powerplant setup in the FW-190A. Both planes flew the entire night on the same charge I'd given them two days before, without any re-charging between flights. This pack weighs 0.1 ounces less than a 230 mah NiMH pack, but provides a HUGE 55% increase in power compared to the 230 NiMH pack at full throttle (5800 static rpm vs. 5000, after the initial peak burns off and the rpm stabilizes about a minute or so into the run), and provides flight times in excess of 35 minutes. I'm not sure how much in excess, I haven't had a chance to run one all the way to the end yet, but end-of-flight voltage measurements suggest another 10-15 minutes or so. In the tests at the Ft.Wayne, IN golf dome they started turning the lights out 35 minutes into the flight, and at that time the pack still had 7.2 volts. In comparison, the 230 NiMH pack goes about 8-9 minutes at those power settings. Note, that's not 35 minutes of "economy cruise", but rather it's regular sport flying with periodic takeoffs and landings to a full stop, and loops and other maneuvers throughout the flight. There is no question in my mind that this is the best available option today for models with the MPS-2A or a pair of MPS-1A's. I'm really looking forward to trying this setup in a P-38, or the super-efficient Electra. BTW, the MPS-2A is also available as an upgrade for any of the single-motor RK models except the Junior (it doesn't need it, and there isn't enough prop clearance above the tailboom for the MPS-2A's 6-5 prop), and the MPS-2A should work especially well in the single-motor WW II warbirds.

I've done static tests of a 2-cell E-tec 1200 mah pack in the Boeing B-17. Full-throttle power was 20% better than we get from the 6-cell 600 mah NiMH pack we normally use in this airplane, and the 1200 mah E-tec 2-cell battery is 0.9 ounces lighter. The Boeing currently flies extremely well on a 6-cell 600 mah NiMH battery, so I anticipate it will see roughly double the flight time in addition to the big increase in available max power. It should be interesting.

We sold out of our 250, 700 and 1200 2-cell E-tec packs at Toledo, except for one 1200 pack. The smaller packs were all gone by Saturday afternoon, including the batch I brought up around lunch time that day. We've ordered more along with some E-tec chargers and hope to have them available for sale in the next week or so.

The Castle Creations Pixie 7 can be programmed for an appropriate cutoff voltage for Li-poly cells, although in our experience it's only necessary as a backup. There's a pretty big voltage drop between fully charged and fully discharged, and the resulting rpm drop due to the combined effects of voltage and Kv leaves you with only about 30% power at the point that the cells have reached a nominal unloaded level of 2.7 volts. I've also heard that numbers under load of 2.3 volts per cell will result in 2.7 after the throttle is closed, which would correspond to an rpm of only 57% and a power output of only 19% (remember, power absorbed by a given prop is proportional to the cube of its rpm). In any case, by the time the voltage got low enough to damage the cells, the available power would probably be insufficient to sustain flight in all but the most efficient or grossly overpowered models. Still, it's a good idea to have that ESC low-voltage cutoff as a backup. A good charger protects from overvoltage during charging, so there is no need for a voltage protection circuit in the battery itself (which is good, since such a cutoff would also kill power to the radio!). As far as charging, I've charged individual cells one at a time, but I don't bother with that any more. I do occasionally check individual cell voltages with a voltmeter, but so far they've always matched with each other within 0.01 volts, even on packs that see high discharge rates such as in the Ryan ST during one of my aerobatic workouts.

As I mentioned above, the presently available Kokam cells seem to be good products, but just not quite the best fit in size and power characteristics for our particular models. At Toledo Fred Marks told me about some new approx. 300 and 600 mah Kokam cells that should be available soon, that are supposedly capable of discharge rates up to as much as 20C! I'm reserving judgement until we actually test them, but if they do even half that well they should be awesome. I see quite a battle brewing between the E-tecs and Kokams, but it appears that us modelers should come out ahead either way.

The actual cells I saw at the Peak Electronics booth were indicated as coming from Mikro Designs. They were matched cells. I believe Mikro has something to do with Don McGlauflin, the fellow that founded Sirius and then sold the business to George.

I'd like very much to get some more info on E-Tec? both the charger and the cells? Who are they? Got an e-mail address for me?

Also I just finished writing up a review on the Peak Sirius lithium charge. I like it much better than the Kokam LIPO-402 and the Plantraco, mainly because of the LCD screen instead of LED indicators. I believe as you do, if George Joy is involved, it is going to be good. The only problem is the $150 list price. For $180 I can buy the Orbit Microlader which can handle a lot more cells and current. Remember, right now we are seeing 1000 and 2006 MAH Li-Poly cells. But not too far away are cells up to 6000 and 8000 MAH. A charger limited to only 1500 mA current is soon going to be left at the starting gate.

For folks who are pulling massive amps with huge batteries in larger electrics, yes, they need something with more current. However, remember that the slowflyer list is about slowfliers, and those are not using 6000 mah cells! Also, the folks who are using those huge cells are spending big bucks on cells, and so they aren't going to expect to use a super cheap charger.

I have nicad/NiMH chargers that put out lots of amps for my bigger electrics, but for my park flyers and smaller I typically use a Sirius 200. It's cheap, small, light and easy to carry, and does a better job on 110 mah cells than most of the big, heavy, expensive chargers. The Plantraco fits a similar niche for Li-poly cells. At under $60 retail it's a much better fit for someone flying little cells in a relatively cheap parkflyer. This was one of the things that was holding us back from endorsing Li-poly batteries for our Roadkill Series models before now. I personally found it repugnant to have to tell a customer they would have to spend hundreds of dollars for a charger to charge the little bitty batteries in their $50 RK model! Also, a lot of customers are intimidated by fancy screens and LED alphanumeric displays. For them, something with just two LED's that give you the status of what's happening, plus a SIMPLE chart printed on the case telling how to interpret them (like the Plantraco's) is preferable to something that leaves them with the impression that they need dual degrees in both rocket science and computer programming to properly set up and use. You'd be surprised how many of our customers feel just that way about things with fancy screens.

The Sirius 200 is a good, simple, bulletproof $60 charger that any untrained beginner can use to safely and successfully charge their 110 mah 7-cell NiMH packs, and we've sold a lot of them for exactly those reasons. The Plantraco LPC-400 and presumably the new E-tec charger should fill exactly that same role for Li-poly batteries. I expect to be using them for my indoor, backyard and park flyers long after I've acquired a Microlader or bigger and fancier charger for the larger more exotic stuff.

By the way you do know who is behind Plantraco don't you? Remember Dave Abbe?

Regardless of what he's done before, I am VERY happy with what he's doing now.

I also have a new Plantraco receiver I'm planning to try in one of our Triplanes soon. It's four channel plus has a built-in 10 amp speed controller with a 1.5 amp BEC! I'm not sure if that means it's a 4-channel without using the ESC and 5-channel including the ESC, it's not entirely clear from the instructions. It does have digital signal processing that filters out the glitches, and an automatic throttle shut-down if it goes for more than 1 full second without a valid signal. According to my slightly pessimistic digital scale, it weighs 9 grams with the case on and 7 with the case off, including the motor leads and antenna.

Speaking of neat new receivers, I also have a Berg Microstamp 4-channel. It has the slimmest construction I've seen yet (even the connectors lie flat in pairs to reduce the height without increasing the width!) and has digital signal processing. It also has a glitch counter built in and an LED that tells you how many glitches it filtered during the course of the flight. I'm really looking forward to the next round of prototype model tests, when I'll have a chance to try out all these new electronic widgets!

Don Stackhouse
DJ Aerotech