Li-Po

Cell phones don't need to be able to dump the battery charge in 6 minutes flat.

That single fact - high discharge rates - makes all the difference to safety, that and the weight factor.

If you want excplosive power, sometimes it explodes. You wouldnt wander around an open tank of gas with a lit cigarette either. Well most wouldn;t.

Yes, but for how loing, and at what voltage droop, and will they really do it for 100 cycles, or even one cycle packed inside an airless foam fuselage on a hot day in the Mojave Desert?

The short answer is they really won't do 15C at all. Probably 5C is safe, and 10C in bursts will merely shorten the lifetime to < 100 cycles, but 15C for the full four minutes in the above conditions will just be another fireball over Roswell etc. :-)

As will you if you try to pull 15C out ofthose packs for any length of tme.

That is NOT so. That is tantamount to saying that you shpuld only refuel a gasser inside a fireproof container, equipped with fuel vapour sensors and an automatic fire extinguisher, when in reality the only thing you need to do is make sure you don't do it indoors with a lit cigarette hanging out of your mouth.

The cost issue is transparent to real modelers.

No it isn't.

Exactly. 17 hour flight. Not 17 minutes.

ANY series resistance of any switching rear saps top power, and any circuitry adds weight and cost.

Its early days. It will get better.

Well they do, and thats teh thing.

The problem is not so much that attitude that real men don't read manuals, as real men only read glossy brochures.

Hey D.H., My remarks were based on a report from a known and respected engineer who is extremely conversant with batteries of all types. I stand by those and reject your continued stupidity that implies possible injury to others through carelessness. In the words of another, you sir be an idjet.

The cost of safe operations is transparent to real modelers since most of them are not interested in injuring others. How about you?

| Brings up another point not often mentoned in Glow Vs. Elec. shootouts. If a | gallon of fuel goes bad (almost never happens) you are out $14. If a Lipo | pack goes bad (happens very very often), you are out much more. It's | something I don't often see in the equation in those types of threads.

To be fair, you can also screw up and run your glow engine too lean and ruin it that way. And I've heard of cases where glow fuel ignited and burned up very nice planes.

Expensive (and even fiery) mistakes aren't restricted to LiPoly cells.

| >>You need about 4000 mA/h to fly that plane RELIABLY. | > | > Actually, Kokam has a 2000mAh pack that can do 15C, or 30 Amps. I've | > got four of them. | | Yes, but for how loing, and at what voltage droop, and will they really | do it for 100 cycles, or even one cycle packed inside an airless foam | fuselage on a hot day in the Mojave Desert? | | The short answer is they really won't do 15C at all. Probably 5C is | safe, and 10C in bursts will merely shorten the lifetime to < 100 | cycles, but 15C for the full four minutes in the above conditions will | just be another fireball over Roswell etc. :-)

I've got some Tanic and iRate 2000 mAh packs (the use the same cells) that are rated at 10C continuous and 12C for short periods. They

So much for the `you need about 4000 mA/h to fly that plane RELIABLY' claim. Looks like 2000 mAh will do it, as long as you don't mind a six minute flight.

| Only shortcoming I found is in the length of those temp sensors | wires (about 6" leads), but Futaba servo extensions are a direct | connection, so extending them is easy.

Do be careful with that. Those sensors work by altering the resistance based on the temperature, and by adding an extension you're increasing the resistance -- so you're introducing a systemic error into the system.

If the resistance of the probe is high and the extension (and connectors) is low, then the error will be small. But if not, it could be signifigant. You might want to see what kid of difference the extension makes ...

The point I was trying to make is that I CAN put them on the charger, lock up the mission module, and go home for the night. No fireproof box, no baby sitting, no worries. Granted, the circuitry is rather large but so is the application. Scaled down to our size, I really don't think it will add more than 3-4 grams to existing packs. The circuitry and the chargers that will handle them would make these things almost as carefree as the older NiCd or NiMh are. In our litigious society, anything that will keep the lawyers out of the pool is a plus. Unfortunatly, people here DON'T take responsibility for their own actions and blame whoever has the deepest pockets. I would hate to see a large law suit put a stop to this developing technology over a few bucks worth of circuitry. If it is good enough for cell phones and the like, it's good enough for us.

BTW, my UUV only travels at 3 knots underwater. If I increase the speed to only 5 knots, my "flight" goes from 17 hours to about 5. These batteries not only power the propulsion system but also 2 onboard computers, a side scan sonar, and various other sensors used for navigation and communication. When running at 3 knots the system draws 6-7 amps per battery. That's without the sonar running so I would imagine the load goes up to 10-15 amps at depth with everything on. Eventually I'll take some pics and post them on the binaries site. The vehicle itself weighs in at 750lbs dry and around 1200 lbs when flooded. Fun stuff.

Jim W

I would have thought that any measuring temperature would have to be based on a CHANGE in resistance rather than the measurement of it in an absolute sense - otherwise the charger wouldn't be able to accommodate a range of batteries, or a variety of ambient tmperatures. But then I don;t know much about the subject, just using common sense logic.

David

Doug McLaren wrote:

acknowledgement

D.H. an idjet? When did he get the promotion?

Hey! Congrats D.H.

Yah, and one more post showing the same low level of thought and intelligence, and he looses the promotion.

Al I said was that safety at ANY cost is NOT something ANYONE is transparent to.

You might as well ask why any motorist does not drive a $500,000 foam bubble at 2 mph only, in order to protect pedestrians.

The idiot, is, as usual, you.

Heres a new phrase for you.

Cost benefit analysis.

When you have sudied the concept, come back and we can have an intelligent conversation about it.

Until then stop parroting the perceived wisdom of others in a vain attempt to appear knowledgeable.

If I was soldely interested in avoiding all risk to others, I wouldn't drive a car, or fly a model plane, or light a fire, or indeed eat a hamburger.

In fact the only way that I can see to avoid the faint possibility of injuring another human being is to kill myself immediately.

I suggest you try it and make the world a safer place - for democracy. :-)

Do yo pack em in foam fuselages and fly in 40C ambient temps tho?

My Irate 1100's showed about 20 C rise in a foam fusealage at around 8C.

At 10C at 40C ambient I would estimate they are right on the limit of

It depends on what you want to mean by reliably. 'Redline' the packs constantly, and you will suffer reduced life, and possibly in adverse conditions catastrophic failure. Or you may not suffer anything more than a little shorter life.

I am reading of many premature failures of packs run at or near maximum. Those who seem to get long life are those who don't push their luck.

YMMV.

You're one to talk about making the world safer for democracy. Socialist pig that you are!

Sadly most socialist consider me a Tory, because I believe in individual freedom of choice, not an imposed socialist state, but then I don't believe in the Right either.

Never botherd to lable myself. Perhaps libertarian is right?

OTOH teh most accurate I can get is a post modern social pragmatist.

I know that will be all too much for your simple black-and-white vision of things, so lets leave it there huh?

or suck up gasoline fumes with a shop vac. Boy i'll never do THAT again....

In article , The Natural Philosopher wrote: ... | > I've got some Tanic and iRate 2000 mAh packs (they use the same cells) | > that are rated at 10C continuous and 12C for short periods. They | > *will* do 10C for six minutes with little problem, and I've got well | > over 100 flights on them and they still have almost the full capacity | > on them. They're about nine months old now, so it wouldn't surprise | > me if there's something new and better out now. | > | > So much for the `you need about 4000 mA/h to fly that plane RELIABLY' | > claim. Looks like 2000 mAh will do it, as long as you don't mind a | > six minute flight. | > | Do yo pack em in foam fuselages and fly in 40C ambient temps tho?

Yes. Though I have opened up some space around them so air flows around them in flight -- that helps a lot in keeping them cooler.

As for 40C ambient temperature, I do live in Texas, so I'd have to say yes, though when it's really 40C (104F) or more, I tend to not fly so much.

| My Irate 1100's showed about 20 C rise in a foam fusealage at around 8C. | | At 10C at 40C ambient I would estimate they are right on the limit of | 65C pack temps.

I also don't usually spend an entire flight at 10C discharge rates. Perhaps half of the flight, sure, but not all of it.

Either way, the packs are handling it very well. I'd call them very reliable, and yet I do push them up to the `redline' for at least some of each flight.

I think it's heat that really kills them, not high discharge rates. Of course, high discharge rates cause heat, but if you can keep them cool some other way (either via good airflow or by flying in the winter) then they'll last a long time.

| It depends on what you want to mean by reliably. 'Redline' the packs | constantly, and you will suffer reduced life, and possibly in adverse | conditions catastrophic failure. Or you may not suffer anything more | than a little shorter life.

Of course, that's true with any pack.

| I am reading of many premature failures of packs run at or near maximum. | Those who seem to get long life are those who don't push their luck.

Of course, that applies to pretty much anything. If you run your car engine at the redline all the time, it's not going to last long either.

Do tell:-)

I started a bonfire with gasoline one hot summers day.

Drenched the pile, stepped back a safe distance and was bending down to light a bit of balled up paper to throw at it from 8 feet away.

I realized later on the way to A and E that petrol vapour is heavier than air and runs a long way in a very slight breeze.

The resultant fireball wrecked my parka, eyebrows and the synthetic skin they sprayed me with made me look like something out of Dracula movie: Since I was driving to Belgium the following day, I can now confirm that this is a highly effective way to get almost anything through customs. The wouldn't even look at me...

I can also confirm that rolling around in a ball on the ground does put you out eventually, and dousing every bit of skin with cold water immediately afterwards reduces the damage and you may end up as I did with no scarring to speak of.