Li Poly batteries, fantastic

try

I checked into your web site and I believe the batteries there are basically of the smaller types, right? See if this is not more comprehensive?

I should have said the website you presented. Thanks. Perhaps you may have done some testing on these batteries?

It's just that I am awed by the rapid progress made in the field of batteries. Who knows what else technology may bring forth?

Wan

The cells are good enough: More work needs to be done to make them less l=iable to explode under abuse, and to make theme cheaper.

| 10S3P, 78amp (nominal) li-poly 7800mah 37 volt pack $873.60

And in case somebody wasn't paying attention, this is exactly why we don't see many large electrics yet.

This battery pack puts out up to 2900 watts, or 3.8 HP.

This would be comparable to an OS FX 1.6 engine, which puts out up to

3.7 HP. And costs $270.

This battery pack will put out that much power for 6 minutes *at best* (since it's a 10C discharge rate.)

And this is just the battery pack -- there's no ESC, no motor (with this much money going inot just one battery pack, it's silly not to get the best brushless motor you can find. And of course, it won't be

100% efficient, reducing the actual power you get.) You're looking at many hundreds of dollars more for that.

And of course, you usually want at least two battery packs ... the costs add up very fast. Some say that it all evens out in the end, that you're essentially buying all your fuel up front. There's some truth to that, but it still seems that large electrics still cost a lot more, both up front and over all.

The `sweet spot' for electrics is still the Speed 400 and smaller sizes. Once you get larger, the price goes WAY up. If you double the power, you basically double the price. (Compare this to glow, where if you double the power, you add maybe 20% to the cost.)

That said, I bought some Li-poly packs for my smaller electrics, a XE2 with an Astroflight 020, and an Electrifly with a geared Speed 400. Both got two cell packs, the first was a Tanic 2200 pack, and the second a 1700 mAh pack of some sort. They're quite nice, though I wish I had a three cell pack in the XE2 -- it has less power now, but a lot more duration.

Someday (hopefully soon!) these batteries will come way down in price. That will be a very good thing!

I am also waiting for the cost to come down. The fuel arguement is only valid when thinking long term. I don't know anyone who paid for all the gas their car would use at the time they bought the car.

Another thing to consider is the charger for such battery beasts!

However the FX puts it out at a not too useful RPM. To be fair that pack and a motor is probably nearer a 50cc motor.

No, but it will be approaching 90% overall. How efficient is your glo prop?

Its true. Get into the big sizes and the cost does rocket.

But you are not being totally fair here.

There are more variables than you account for.

Actually I'd slightl;y take issue, and say that the sweet spot is

100-500W, whicgh is speed 400 up to roughly 40 sized glo equivalents. In teh smaller planes, the radio gear has to be light, and that gest expensive, but planes around the 15-25 glo equivalent are not too expensive to electrify and not too small to need specialised gear.

And you don't need a brushless motor to enjoy kithoum - the excess power and duration means rather les efficient (and much cheaper) motors still deliver good performance.

I think it will be sooner rather than later. Ther are a lot of applications becomeing more sensible using lithium technology. I think there will be a huge incrase in use of these cells everywhere. Even current small cars would benefit from knocking a few ounds of teh wight by replacing the lead acid cell. If the price was right...

>

Heck, not many people pay for the car upfront!

Lease those lithiums. Theres a new business oopportinity for you Paul!

Not particularly hard to engineer. 8A at 40V or so.

| Doug McLaren wrote: | | > In article , | > Wan wrote: | > | > | 10S3P, 78amp (nominal) li-poly 7800mah 37 volt pack $873.60 | > | > And in case somebody wasn't paying attention, this is exactly why we | > don't see many large electrics yet. | > | > This battery pack puts out up to 2900 watts, or 3.8 HP. | > | > This would be comparable to an OS FX 1.6 engine, which puts out up to | > 3.7 HP. And costs $270. | | However the FX puts it out at a not too useful RPM. To be fair that pack | and a motor

A high quality, and expensive motor. For example, an Aveox 1415/1.5 with a 3.7:1 gear ratio and a 14x10 prop can use 2500 watts (36 volts or so, 70 amps), giving a useful output of about 1700 watts, and costs about $250 for the motor and $300 for an appropriate ESC. (Are the ESCs really this expensive for larger motors?)

(Maybe my choice of motor is very poor -- I've never actually really investigated putting together an electric plane this large before. At least not once I realized the small fortune I'd spend on batteries alone.)

| is probably nearer a 50cc motor.

Actually, that HP rating is at 9000 RPM. That's not that unreasonable

-- certainly, it's not some screaming 0.049 engine. I doubt you'd need to go to 50 cc (3 ci) for similar performance.

It depends on what you want. If you want speed, you want high RPMs and a small prop. If you want to do 3D, you want low RPMs and a big prop. Electics make the latter easier to do.

| > This battery pack will put out that much power for 6 minutes *at best* | > (since it's a 10C discharge rate.)

Don't disregard this. If you're using this much power, it won't be a very long flight.

| > And this is just the battery pack -- there's no ESC, no motor (with | > this much money going inot just one battery pack, it's silly not to | > get the best brushless motor you can find. And of course, it won't be | > 100% efficient, reducing the actual power you get.) You're looking at | > many hundreds of dollars more for that. | | No, but it will be approaching 90% overall.

Probably not even too close to 90%, even for a brushless. And even less if you're running at the maximum output of the batteries. Run it through Motocalc ... it's very upsetting. 70% seems more realistic, and that's for a good motor.

| How efficient is your glo prop?

As for props, at some level, props are props. Gearing your motor down can give you more prop efficiency for slow flying, but you're still losing energy at the prop, glow or electric.

| > And of course, you usually want at least two battery packs ... the | > costs add up very fast. Some say that it all evens out in the end, | > that you're essentially buying all your fuel up front. There's some | > truth to that, but it still seems that large electrics still cost a | > lot more, both up front and over all. | | Its true. Get into the big sizes and the cost does rocket. | | But you are not being totally fair here. | | There are more variables than you account for.

Like? I guess you do need to add a throttle servo to the glow setup

-- $10 or so.

I don't think it's really reasonable to add the cost of chargers and starters and such to the prices when making comparisons.

| > The `sweet spot' for electrics is still the Speed 400 and smaller | > sizes. Once you get larger, the price goes WAY up. If you double the | > power, you basically double the price. (Compare this to glow, where | > if you double the power, you add maybe 20% to the cost.) | | Actually I'd slightl;y take issue, and say that the sweet spot is | 100-500W, whicgh is speed 400 up to roughly 40 sized glo | equivalents.

A 0.40 sized glow engine can do a lot more than 500 watts. The OS FX

0.40 is rated at 1.36 hp -- 1033 watts. Yes, it's at a higher rpm than most need, but still, you're going to have a hard time getting similar performance out of an electric system that peaks out at 500 watts. Especially when the power system weights more than the glow power system. And I believe that power rating doesn't take into account the energy lost in the motor (and gearbox, if there is one) -- but the BHP rating of a glow/gas engine does. (Of course, IC engines are only like 25% efficient at best, but that's another matter entirely.)

| In teh smaller planes, the radio gear has to be light, and that gest | expensive, but planes around the 15-25 glo equivalent are not too | expensive to electrify and not too small to need specialised gear.

No, it's not too bad, but you'll still end up spending hundreds of dollars on batteries. It would take many many flights to run even $100 worth of fuel through a 0.25 glow engine plane.

I've never found my (e-power) batteries to last (the internal resistances just seem to go up too much after that) more than a year or two, and I spend far more on batteries now than glow fuel. Of course, I also fly the electrics more than my glow planes ... | And you don't need a brushless motor to enjoy kithoum - the excess | power and duration means rather les efficient (and much cheaper) | motors still deliver good performance.

When you're spending $900 per battery pack, it just makes good sense to spend a few hundred on the best motor you can get. Getting a better motor will save you money on the battery pack, because you can use a smaller (and cheaper) battery pack and get the same performance. For a $20 8 cell NiCd pack it's not a big deal. But for a $900 battery pack ...

(For larger motors, doubling the power rating doesn't seem to double the cost. A brushless motor setup with 0.40 performance doesn't cost that much more than one with 0.09 performance.)

| If the price was right...

That's my beef. If I could get Li-poly cells for like 20% of the current cost, I'd go all electric tomorrow.

Yes. To date its been a narrow market with low volume sales. There is no real reason they should be tho - the majority of the electronics is teh same for a 10A ESC as a 100A one, you just need a lot more power FETS stuck on teh back, and some way to drive them harder maybe added.

Agreed. All out speed you will generally find a tuned pipe IC screamer is still the best. But for 3D work teh electric is more controllable and far more efficient overall as a a power train.

Mmm. The point is that that sort of power train is mostly used at or near max eficiency current, only peaking to full power for short bursts.

You use full power really only when going for max rate of climb (keep that up and the model is out of sight soon) or absolute max speed. The rest of the time its throttled back a lot.

So flight times are often surprisingly longer. Even EDF models with lower weeight lithium packs suddenly don't need full power all the time.

Once you come down a few notches from flat out efficiency is better, current its lower and suddenlt flight times ae much longer.

That is a misleading statement. An ungeared motor putting teh prop tips close to mach 1, and being strong enough at the root to cope with the centrifugal and torque pulse loads imposed by an IC motor, and heavy enough to act as a flywheel, is nowhere near as efficient as a thin bladed larger one geared down to the correct RPM for your model.

This is teh MAJOR reason why people are surprised at how little E-power they need to fly a given glo airframe.

Only in the case of >75mph models does teh glo engine start to match teh overall prop efficiency of the geared electric.

Well, what kind of kit do you need to take to the field for a glo motor.

- spare gloplug

- glo starter battery

- electric starter.

- fuel pump

- bag of baby wipes

The field battery of course is commoon for both sorts.

Additional model cost include

- throttle servo

- hefty engine mount

- maybe custom muffler for the plane

- fuel tank and plumbing

- fuel proofer and generally strong firewall construction.

And of course, fuel. Not irrelevant in a big model by any means.

Well I disagree. For reasons stated above. Execpt when you DO need that extra RPM.

Its actually fairly close. Especially with a custom designed E-plane with all the beefed up structure to take engine vibraion removed, along with the fuel, tank, heavy prop and engine mount, muffler and servo.

As I said, the gains on the prop outweigh the efficiency losses in the box, or people wouldn't be using them.

I am not trying to maintain teh E-planes are xcheaper at higher powers, bu they are not as expensive, or heavy, when costed out over a season or two, as you are making out.

They also have some advantages in terms of reliability and ease of starting and very predictable throttle response that make them ideal for aerobats and multi-engined models.

That is where the cost is worth bearing. Bigger aerobats, and multi-engined models.

Also in the sub .25 type of sport model, where the costs are comparable.

Only a big single engined sport or speed plane - 40 and up - is it really a bit enthisiastic to go electric.

Well, I have spent $70 on a pack that will do 200W, about equivalent to .19 power wise by my estimation. Certainly .15 power. I can. and will, split that amongst several different models. I cannot reasonably unbolt an engine and swap it amongst two or three models in the same day.

But I can only fly one plane at a time, and two such packs as that will allow me almost continuous back to back flying with short breaks in between on an unlimited number of models.

Because the pack is light, and powerful, for general purpose sport models I can spend very little on the motors - cheap inefficient ones do just fine for average flying. Sure I have a 200W brushless setup that cost in excess of $100, but hat is not what I have to fly all the time, Thats reserved for planes that need to go straight up!

Again, there is a positive feedback mechanism. With Nicads, to fly at all, we needed to thrash the packs and motors just to fly at all. I've got some 2 year old packs that haven't been thrashed too much, that are still fine.

All the signs are that the lithiums will be up there after two years as well.

The key thing is to rememebr they are going to die of old age anyway whether you use them or not, and simply use them to the full, by splitting them amongst several models. You do NOT need to buy one pack per model. I've got one 100W pack and one 200W pack. That, plus a charger, is $200. Those will power ALL my planes built and on the board

- about 7 in all. So that works out at $30 per plane or less.

In the speed 400 sized cans, which are good enough for scale and modest planes cost is less than $50 per motor/ESC/box combo, and the 200W 480 class motors are not much more. Even the 480 class brushless is only $120 or so. So typically each model is costing me between $80 and $150 for the power train capital cost.

Contrast that with an IC engine, servo, tank, mount etc. etc. and add fuel costs and its not very different.

In general with two fully charged packs charged at home before flying, I can expect 40 minutes of continuous flight of the packs inclding general stuff like getting them packed up and checked out prior to flinging in the air, and the landing approach etc etc at low power. Then a 20 minute hiatus to recharge the packs, followed by 20 minutes flight/forty minutes wait AT THE VERY WORST WITH A FLAT PACK which they seldomn are. Its more like 15 minutes flight 10 minutes wait in practice. The amount of time glo planes seem to spend being started and fiddled with makes it very little worse. If you have three packs and two chargers its pretty much constinuous flying no breaks. Or indeed three packs and one charger will allow you to take 45 minutes of continuous power to the field ready to go.

More than most glo pilots except the chopper boys seem to actually spend in the air anyway.

Apples and oranges. Unless you MUST have a 40 powered or bigger plane, electrivc is cheap, and convenient. Why have a 40 powerd plane? Because that is the 'sweet spot' for IC. That's where its at its cheapest really. Slightly smaller is the sweet spot costwise for electrics.

Once you have enough packs, you don't need to buy more for new models. Just unplug them, charge, and use on the next plane...onbce you have enough packs, you don't even need to field charger them...pre-charge them all, and fly them till they run out and go home. If you want different power levels, parallel or series up packs (fully charged of course to make sure discharge times are matched) and you can save on buying another pack.

People on a tight budget have even been known to swap receivers, motors and ESC's between planes at the field. Unplug a few connections and unscrew two or three bolts, and away you go...

Of course all this requires a change in the way of doing things and thinking. If you 'think glo' and do the sums you will never go electric. You have to 'think flight times and planes' and work out an overall budget for the type of flying you do...but in many cases, if you DO do this, you will find its not half so bad as the critics make out. How many planes do you take to the field anyway?

I don't see that at all. I run a $70 pack and a $18 gearbox on a $7 motor. All in $50 plane. Split amongst several models its not a silly thing to do.

Look at the cost breakdown of a speed 400 plane. Kit cost $50 Glue, paint, covering, odd bits - $15 Motor $7 Gearbox $15 Prop $5 Receiver $50

4 x feather servos $80

Thats $222 already ...

Now add ESC, at maybe $25, and we have a $250 plane without the battery.

Since as I said the battery is costing (because its shared between three models at least only about $11 per plane), its a $262 plane at this point.

Now if I drop the $25 ESC and add in a brushless+ESC at maybe $100 I am adding $75 to the plane cost. A 30% hike in cost.

Besides which, that model is a scale jobby, and will potter around doing mild aerobatics for the best part of 40 minutes on the one charge.

I simply don't need to spend $75 to extend that to one hour.

Ive done the calculations over and over, and the way that makes sense is to buy lithium batteries, and share them between models. Motors I cosndeier more disposable, and cheaper than, servos. ONLY if I want the last ounce of performance will I bother forking out for a brushless.

I mean, not every plane you have runs a tuned pipe high performance motor, does it?

Stop thinking 'one plane, two packs' and start thinking 'oow packs, infinite planes' or whatever, and suddenly the cost benefit equations stand on their heads.

You both present points of view that are valid. WHEN the prices come down, not IF, we would all benefit. The costs of Li Poly batteries for larger aircraft seemed high indeed, But as the demand for them becomes high, then mass production will make for lower prices.

Take the example of digital cameras. I bought a Nikon Coolpix 5000 for about $1,000. In less than 6 months an improved version was selling for around $700 (The Nikon Coolpix 5700, you may check it out). Most things electronic or otherwise kind of work that way price wise.

This is my humble opinion.

Wan

The,

Speaking of speed 400 motors, I've got one of those new Great Planes Douglas DC-3 Speed 400 EP Twin ARF ($159.99) on back order. It uses a Speed Control: Electronic with (BEC) battery eliminator circuitry and dual motor harness, and recommended battery pack is 9.6V 8 cell 1800mAh (AA cells).

With Li-Po's at 3.7/7.4/11.1 volt, what Li-Po combination would you suggest for it?

--

Jim L.

Using - Virtual Access(OLR), ZAP 4.5, & WinXP Pro w/SP1

Not knowing how many amps the dual sp400 will draw, I'd use a 3S3P Kokam

1500mah pack(actually three of the 3S1P packs) That would be good to about 36A and almost triple the flight time. Just don't run it at full throttle for long or the motors could fry. Then again, depending on the sp400s they might be fine with higher voltage.

PCPhill

Don't ask how much I spent on batteries this morning. Really, don't ask......

----- Original Message ----- From: "Jim Lilly" Newsgroups: rec.models.rc.air Sent: Saturday, February 14, 2004 9:54 AM Subject: Re: Li Poly batteries, fantastic

Paul, you know that the same battery pack may be used in different planes, don't you? Then you would not have to think about paying for

100 gallons of fuel each time you want a new plane.

I know you have a lot more experience with model planes than I, but I still believe electrics are do-able now cost wise. Witness the hundreds of electric flyers whose .40 to .60 sized planes that are performing as well and flying even longer than some gas powered planes now.

With my limited experience on Li Poly, I'm hoping somebody would be able to illustrate my point.

Wan

Wan,

I completely believe that electrics will continue to grow in popularity, but not become dominant until something is done about the entry fee. You can get a VERY nice .50 size glow powered model, ready to fly, for under $250. That includes plane, radio, engine and fuel, etc. To get equivalent performance with electrics still costs much more. Some of the examples here talk about near $1000 just for one battery which has the potential for performance in the 1.5 glow power range. Add in the cost of motor, speed controller and charger! And yo have ONE flight. Want two? Wait while your battery charges or spend another $1000 for a second battery.

Unless they are race motors, they won't draw more than 10A apiece. Trouble is you can't gear EDF down, so they may get a little hot and bothered on 3sLIPO.

The safe option is 2s2p, which will probably run at 15A or so. My choice would be Irate 1100 or thereabouts, but 3s2p of larger cells may be quite lively.

Its a hard call. Its no aerobat, and may well run fine on the lighter

2s2p packs.

We all had to fork out for radio transmitter, and charger tho? you don't start out in electrics on 40 sized models either. You strat out with a 50 dollar LIPO and a 3o dollar charger at the worst...

Some people sepnd $1000 on transmitters. So wahts the odds with a pair of $500 packs?

You cam get a ready to go firebird for under $100. Its perfectly possible to get an sub 250 dollar leccy plane, it just isn't '40' sized.

THAT is what 'entry level' leccy flyers start with.

They can always get greased up later on...:-)