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Old Aug 01, 2001, 02:44 PM
Time wounds all heels.
Phoenix, AZ
Joined Jul 2001
832 Posts
Can we start a thread on Lithium battery capabilities?

I will give all the links I have found relevant.

http://www.magtechinc.net/Tadiran.htm
http://www.tadiranbat.com/TL59C.htm
http://www.mentornet.org/electric.htm#Lithium

Li seems to be a kinda unknown, everyone seems tantalized, but a little intimidated.

It kinda reminds me of gas guys, looking at electrics for the first time. It looks cool, but you have suspicions of them being "weak" and "underpowered"

Can we start a thread to dispel the myths about Li and get some usable hard data about them instead?


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Old Aug 01, 2001, 03:12 PM
Our Daddy and Heli Junkie
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Lithiums are not up to the tast of anything but Slow Fly and RX packs for now. There are new cells coming out but availibilty and price are still the questions. EFI has covered a few of them.

NIMH are the best option now for duration and modest power.

This also may belong in the Science Forum, but this is just a general question and answer so far.

But don't give up, it will happen.
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Old Aug 01, 2001, 03:21 PM
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Walled Lake, MI, USA
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Many people have been using lithium cells in e-flight applications for many years. Most of the discussions have been in the Slow Flyers section, because slow flying has lower current requirements that are compatible with lithium cells. If you do an E Zone search for "lithium" you will find hundreds of messages with lots of useful information.
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Old Aug 01, 2001, 03:36 PM
Time wounds all heels.
Phoenix, AZ
Joined Jul 2001
832 Posts
err...

I read all the posts about Li.

I want to talk about new and exciting Li.

Cost is marginalized by use. If there are some cool new higher capacity cells, or if its possible to use cells for ultra-light or slowflyers, lets get some "facts" on the board.

It would be nice to have some figures and estimates in one thread, so newbies didnt have to spen 4 days pouring over old history to find a few gems of info.
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Old Aug 01, 2001, 03:50 PM
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What new and exciting Li batteries are you referring to? The ones I know about share the same major characteristic as the more commonly used Lithium Metal Tadiran brand cells. That characteristic being that they can only handle a very low amp draw and therefore are mainly practical for use in very small/low amp draw motors/applications. They can be used in parallel for higher amp draw applications like Speed 400 but most find this impractical due to charging considerations. The lithium cells I know of (and use) can only be charged at a very slow rate which means that they can't be recharged at the the field (this of course is partially compensated by the great duration to weight advantage that they offer for slowflyer/microflyer class models)like nimhs or nicads. If you know of new and exciting Li technology please fill us all in as we would be interested to know about it. Li to me means Lithium Ion - are you referring to something different or just lithium batteries in general?

Greg

[This message has been edited by greg morrison (edited 08-01-2001).]
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Old Aug 01, 2001, 06:02 PM
Time wounds all heels.
Phoenix, AZ
Joined Jul 2001
832 Posts
err, actually I was obliquely referring to Fred's new batteries, of which I was interested in hearing more.

I have heard( read ) at several sources about people using Li at 2.5-3.5A draws.

If you used parallel packs ( 2x2@3.6v) it may be possible to pull 6-7A out of a pack.

This may be enough to power a AF 010 at sufficient RPM to push a Red Flame Blaster in a Styro A-7.

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Old Aug 01, 2001, 08:11 PM
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Problem is, if you use parallel packs, you lose the weight advantage of lithiums. Double up the lithiums to get more current, and you might as well be using NiMH, which would offer about the same weight and capacity, but with faster charge rates and lower costs. There really aren't many facts available about the next-generation lithium cells that Fred mentions, or you would have already found something about them posted on the E Zone. When a new technology becomes available, someone on the E Zone is usually right on top of it. In the meantime, NiMH and NiCd technologies are also advancing.
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Old Aug 01, 2001, 08:53 PM
Time wounds all heels.
Phoenix, AZ
Joined Jul 2001
832 Posts
Just so I get this straight.

A 6v 4 cell pack of 1600mah Li weighs 68g

A 9v 6 cell pack of 1600mah Li weighs 102g

A 7 cell 850mah pack of the lightest Nicads I can find. 177.6g

Most are saying it is best to go with the 1100mahAA or the 1400mahAA non-Li cell.

3 packs of 2 Li cells, pulling from 1.5A to 2.5A per 2 cell pack. I believe it may be possible to pull as much as 3.2A per pack. ( 1.6A per cell) For a total energy budget of 4.5A-9.6A possible. Pretty big span. But if a 1.5-1.6A draw is feasable....

Motocalc claims a 8.4A draw on 6 Li-ion 3v cells for the 010 in a Red Flame DF unit. And a good duration.


Here is my latest Motocalc, check it to see if you think I am way off.

AF 010, 6-3V 800Mah Li, Dry weight 3.5oz, ( entered as 1.8oz on motor, and 5.5oz on airframe.) 2x.3oz servo, 1x.3oz rx, misc glue, hardware( 1.5oz) .5oz ESC. AUW estimated 11.6oz. 9.1oz thrust, with 8.4A draw.


At the high end of the draw scale, I meet my amperage requirement for the 010 motor with the 6 cell parallel pack, while maintaining a " not lunacy" draw rate. And I still save 77g over the 7 cell Nicad.


what do you think?

[This message has been edited by watersharer (edited 08-01-2001).]

[This message has been edited by watersharer (edited 08-01-2001).]
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Old Aug 01, 2001, 11:33 PM
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Panasonic now has some very interesting cells starting with the CGR17500 and going up. Unlike the Taradian cells they are 3.7V not 3.0V and are rated for fast charging over the full life of the device. Check Panasonic's website.
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Old Aug 02, 2001, 12:09 AM
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I dont know why you would want to try to use lithiums on anything other than a slow flyer. They do not have the power of nicads.
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Old Aug 02, 2001, 12:48 AM
Time wounds all heels.
Phoenix, AZ
Joined Jul 2001
832 Posts
Well Cue, it really comes down to power vs. weight.

The Li cells provide about twice the power, at about half the weight.

Several people have mentioned that Li cells are $$. But have you seen the price if a matched pack from SR? Plus the Li cells are much higher voltage per cell, meaning I can carry fewer of the lighter batterys, equalling lower AUW.

Isnt that the craft? Making it fly on less and lighter than the one before? It was mentioned that the AF 010 cant make the rpms to fly the jet. It only needs 12k, which seems fairly reasonable, not outrageous.

I realize that none of this is a BARF. But how many of you would leap on a 30 min flight time small jet? This does not seem to be completely unattainable. It may take some real tweaking to do it, but it doesnt seem impossible.

And who knows, if its doable, it might be BARF-able.

I mean, what if you could get the empty airframe down to 3.5, from 5.5.

And the Li's would push 2.6A per 2 cell pack (34g a pack)

Now I just need a 1-2 oz motor, that can push 12kRPM @ less than 9A. Thats not fusion technology. How can it be done? maybe a higer pitch fan could do it. If the EJF or WeMoTec small fans are even slightly more efficient than the Red Flame, it might be doable at 10k RPM and 8A. I want to go ligher/efficient, rather than bigger/more power.

Think Tim Taylor, with a bent for the small.
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Old Aug 02, 2001, 01:17 AM
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Quote:
Originally posted by watersharer:
Well Cue, it really comes down to power vs. weight.

The Li cells provide about twice the power, at about half the weight.

.
Lithiums do not have twice the power, they have less power than nicads.


[This message has been edited by Cue (edited 08-02-2001).]
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Old Aug 02, 2001, 02:56 AM
Time wounds all heels.
Phoenix, AZ
Joined Jul 2001
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I stand corrected.

The proper wording is:

About twice the capacity at half the weight.

My bad.
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Old Aug 02, 2001, 04:16 AM
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It seems like you have an intriguing idea here.

True, LI do have a higher capacity to weight ratio, which is usually a good thing. But the problem is the max amp draw. To get 9 volts and 1000mah of capacity, LI will be the lightest weight, no question. But if you need 9 volts and 8 amps worth of juice, then that 1000mah capacity doesn't mean squat if you can't support the amp draw.
This is where the comparison comes into play - for a given needed AMP DRAW, what cells are the lightest? Nicad, NIMH, LI, Smurf juice, whatever.
I know that LI technology is advancing, but seems to have "plateaued" somewhat. The basic technology has not changed, and it seems that the energy discharge limits have been reached.
I am not trying to discourage you or be a "naysayer", but just pointing out the traditional problems with LI technology. Yes, the capacity-to-weight ratio is superior to anything else, but what about current delivery (amp draw). This is why they have been only used in park and slowflyers - due to limited current delivery.
Question is, how do you overcome that problem?
If you figure out how to get those little LI to pull a C10 discharge rate, you'll make a million. I know "they" are working on this as we speak, but public information in this area is lacking.
Trust me, big power tool companies want this as bad as you do.

Shawn
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Old Aug 02, 2001, 05:19 AM
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Victoria, BC, Canada
Joined Apr 2001
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Quote:
Originally posted by watersharer:
A 7 cell 850mah pack of the lightest Nicads I can find. 177.6g
I have an 8 cell 650 mAh NiMH pack that is only 85 g (AAA cells). It can provide 4-5A and only cost $13.
The Tadiran LiMetal batteries provide the most current for the weight of any Li. You'd need 3 800 mAh LiM to get the same voltage at 50g and $50 but you'd only get 2-3A. If you parallel another 3 cell pack, you're now up to a substantial weight and a phenomanal cost.
Worse yet, one severe over-discharge or over-charge and your Lithium investment is ruined.

You're approaching this completely wrong. If you desparately want to use lithium cells, an EDF is the worst place to start. You could use an aerobatic slow flier like a Long Tiny or IFO. But lithiums are best for long flights at low currents. Sorry but that's the state of the technology.

If you want to fly the Flying Styro A-7, a Flame Blaster fan is almost certainly too weak, and there is no way you can then add the performance penalty of lithium cells.

If you need convincing, buy the LiM from Magellan and see if you can get them to work in a Blaster.

If you want to fly the A-7, use an EDF 400 fan, 020 brushless motor and 8 600AE NiCd. I think you'll find it challenging enough to be successful. Then you can experiment with something else.

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