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Old May 17, 2003, 05:24 AM
Registered User
Los Angeles Industry, California, United States
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LiPo vs Nimh

ok, so i've got an Airwave Sukhoi almost ready to fly, just need a battery pack, I have a Razor 2500A (similar to Hacker B20+18L geared series), and a Phoenix 25, I was going to buy some hecell 1100 8 cell packs but after reading about these LiPos which I dont know much about im wondering what the draw backs are, are LiPos more expensive? last fewer cycles? less power?

i need to make a decision, LiPo or Nimh, need the packs and the charger..

is there a LiPo FAQ anyone knows of?
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Old May 17, 2003, 06:02 AM
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coventry uk
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i'm using e-tec 1200's 3s2p and they are shorter in lenght than my 10 cell hecell packs, the li-poly's weigh 6 oz the hecells 7 3/4 oz, but the li-polys last twice as long.
as for cost, $100.00 for the li-poly's
the hecell's about $30.00.
really the hecells win due to cost, more robust, faster charge rates. and for most people the 8-10 min flight times with the hecell's is long enough.
i use a triton charger as it doe's all current battery type's
also if you wait a bit the li-poly's will come down in price as the market for them evens out. demand keeps them artificially high.

t.n
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Old May 17, 2003, 10:50 AM
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Check the specs of the KAN950's before you buy a 1000mah NiMH battery. They are capable of delivering a higher amperage than the Hecells. A search should find you the discharge charts.

http://www.unipros.com/battpacks/des...960&item=00AA1

Are you willing to "take a chance"? Check out: http://www.batteryspace.com/product.asp?3=272

Unless the weight is critical, NiMH are far more cost effective than LiPo's.

hoppy
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Old May 18, 2003, 06:21 PM
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Indianapolis, IN
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Hoppy: Great find! Have you 'taken a chance'? Any reports?
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Old May 18, 2003, 06:42 PM
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I think it depends what you are flying. If you are able to use a 2 cell lithium 7.2V pack on something that draws about 6-7 amps, lithium is either the same price or cheaper than NI-MH.

It even rivals Ni-MH at 3 cell 10.8V although it maybe a little more. Keep in mind what you are comparing, are you comparing mAH per dollar or max amp draw?

t.n. I agree that 2p packs can get pricey, but at the same time you are flying at least twice as long.

It depends on the application, I truly think there are many applications where Lithium is more cost effective.

Just my take on it, unbiased for sure

-Dave
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Old May 18, 2003, 10:31 PM
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OK, let's play with the numbers.

A high grade 12A 1000mah NiMH can be bought for $2 each.

For a 12A application, you would need a 2S2P Lipo for about $60.
This would give you 12A for 12min. Or you could buy 30 1000mah NiMH and make 5 6x1000mah packs which would deliver 12A for 25min.

At 6A draw:
One 1200mah Lipo at 6A runs 12min and costs $32.
Or you could make 3 6x1000 NiMH packs and get 6A for 30min.

OK, shoot the numbers down Are they wrong??

hoppy
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Old May 18, 2003, 11:29 PM
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First off most people do not make their own batteries, I would like you to show me where I can buy 3 premade packs of 1000mah Ni-Mh for $32?

You are also not considering the weight savings gained by using the poly cells. 1:1 thrust is achievable in planes where it was not before.

I agree if you build your own packs Ni-Mh depending where and how you buy is cheaper per mAh, or ever per max amp draw. But you can't argue that paying a little more for more energy density is not worth it.

Lets say your plane only draws 6-7 amps, you'd be better off getting Lithiums since they are much lighter and would be similar in price. I don't think you are the typical hobbyists buying your cells for $2 each and making your own packs. Go see what the same packs costs at the hobby shop and compare that to the lithium packs. You also do not consider the costs of heat shrink, connectors, and wire.

3x 6 cell pack at $2 per cell Ni-Mh = $36
2x 1 cell at 14.80 per cell = $29.60

I don't know how inclined I would be to buy Ni-Mh batteries that only costs $2 per cell. How well do they actually work? What sort of voltage do they deliver? When I do use older battery technology I tend to stick with Sanyo 500's or 600's due to their higher voltage and abusable characteristics.

Now there are lithiums that handle much more current than ever. It is only a matter of time before Ni-Cad and Ni-Mh is completely obsolete.

Lets compare the weight of the 2/3A batteries you speak of and the Li batteries.

2/3A = .75 oz per cell x6 (7.2V 100mah) = 4.5 oz or 127.6 grams

2 x 1200mah E-tecs x2 (7.2V 1200mah) = 1.8 oz or 52grams

The Ni-Mh is 2.5 times heavier and has 20% less capacity assuming it delivers the full capacity at 6 amps.

The less weight you have the easier the battle goes against gravity. Better flights more powerful and lighter with lithiums.

It seems to me even if you do build you own packs as cheaply as possible there are still a number of factors that favor the Lithiums, and they should not be written off so easily. Let me know if I am missing something?

-Dave
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Old May 19, 2003, 12:59 AM
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for my application i'd be pulling about 10-15amps or so, i need to run a Razor 2500A with a 11x4.7S APC prop.. at least thats the prop thats recommended. they just recommend 8-9 cell nimh.
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Old May 19, 2003, 01:41 AM
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I'd run 2p3s Etec 1200's, Lithiums can get pricey when paralleling however. You have to weigh out weight duration and cost and see what is best for you in your application. I don't mean to come accross as a Lithium pusher. I used nicads to some degree untill the E-Tec 1200's came out.

Regards,

-Dave
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Old May 19, 2003, 01:43 AM
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Hecells for now, i think, is one of the best options.
but,
Etech or similar lithium polys, although, expensive but do have weight advantage...
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Old May 19, 2003, 08:30 AM
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Quote:
Originally posted by LightFlightRC


I don't know how inclined I would be to buy Ni-Mh batteries that only costs $2 per cell. How well do they actually work? What sort of voltage do they deliver? When I do use older battery technology I tend to stick with Sanyo 500's or 600's due to their higher voltage and abusable characteristics.

-Dave
The capabilities of the KAN950 at 18A delivery and it's capability to deliver it's rated capacity are well documented here on ezone. As to the price, this dealer has them for $1.75 each. http://www.edogfight.com/Catalog_page/ezone.htm

On a $/mah or $/amp basis, the NiMH cells are cheaper than lipo's.

On a A/# or mah/# basis, the lipo's win.

Don't get me wrong, I think ETec LiPo's are great cells. They are the leader in the LiPo world and have delivered performance up to their stated specs. There is however, still a spot for the NiMH cells on the basis of cost for amps and mah delivery where weight is not the driving factor.

On another topic, I didn't know that most modelers don't make their own packs. That surprises me as you'd think that anyone that can build an airplane could put a battery pack together, and the money they would save could pay for more planes.

hoppy
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Old May 19, 2003, 09:04 AM
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United States, CA, Bear Valley Springs
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Quote:
Originally posted by LightFlightRC
I don't know how inclined I would be to buy Ni-Mh batteries that only costs $2 per cell. How well do they actually work? What sort of voltage do they deliver? When I do use older battery technology I tend to stick with Sanyo 500's or 600's due to their higher voltage and abusable characteristics.
You might want to consider studying up on KAN950s here on Ezone before making such a statement. If you are still using 500ARs and 600AEs, you're considerably behind the curve on the advancements in NiMh technology. I can't justify the use of LiPo yet due to cost and the fact that NiMhs are still a very viable energy source for our uses, are relatively inexpensive and hold up to the abuse that would kill LiPos.

My $.02.

mw
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Old May 19, 2003, 09:42 AM
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I'm agreeing with Mark here. The newer Lipos out have a tremendous usability. I still think they are 20 to 50% overpriced per cell. I'd would have loved to use lipos in some 400 applications but, the cost involved was too high as compared to KAN 950s. For what I needed in Lipo, I can build 3 to 4 packs of KAN 950s.

Dave...
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Old May 19, 2003, 10:14 AM
Balsa Flies Better!
Stamford, CT
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Bang for the buck...

Seems to me that somebody that put a nice Razzor motor in an airplane is willing to part with bux for better performance. It's silly to spend the $$ on a high performance motor, and then use batteries that are only moderate performance. You could probably get better performance from a Mega/li-poly combo for example, than a Razzor/NiMH matchup.

From what I've seen li-poly compared to NiMHs (admittedly, haven't run KANs- don't plan to at this point) the li-poly weight advantage alone (and that's using older generation Kokam packs)makes the choice a no-brainer. I've been swapping li-polys in for either nicads or NiMHs in over half a dozen planes so far- in every case performance has improved due to either lighter weight or more power- sometimes both. Given the description of the power system- i.e. 11 x 4.7 prop and 40 watts- most any airplane this is going in is going to be extremely weight sensitive. (OK, a WWI fighter that needs noseweight is an exception.) therefore, the li-poly batteries make a lot of sense. (no, I don't sell any of this stuff)

I'd point out that in the 6-7A amp draw range- the performance boost from li-poly is at least roughly comparable to going from ferrite to brushless- and at much lower cost- several of my applications have been in this range. I haven't got much experience in the 10-12A range- older li-poly certainly improved duration, but it sounds like the newer generation batteries should improve performance dramatically as well. (Have packs on order.)

Sam

PS- I'd rethink your prop though- props with pitch/diameter ratios of less than 0.5 are really inefficient.
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Old May 19, 2003, 12:49 PM
DNA
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It really depends on the application and the plane as to which
cells are better, lipo or nimh. The nice thing about nimhs, other
than their lower price, is the ability to add an extra cell to boost
performance.

In a plane I have, I was using 6 Kan950 cells. I wanted a little
more performance, so I added an extra cell for $2. The effect was
just what I was looking for, increased performance. The 7 cell pack
weighed 5.2 oz and the plane balanced fine. In this instance I was
drawing 10 amps or less from the nimhs with no problem.

I then tried a 2s pack of lipos in the plane, but at 3 oz less weight
for the pack, there was no way I could get the plane to balance. No
matter how I arranged the lipos, I would have to add lead ballast to
get it to balance and that is just dead weight. So unless the battery
pack is on or near the CG, it will be a problem getting the plane to
balance properly. It's not a design issue, as many models I have
require the battery pack to be in the nose to get the balance right.

The 7 cell Kan950 pack's cost was $14.00. I made it myself as many
other modelers do. It is capable of supplying 18 amps if necessary.
The 2s lipo pack's cost was $35 and could supply up to ~9 amps if
pushed hard. The 7 cell nimh pack had 7.7 volts under load, while the
lipo pack showed 6.7 volts under load. The loss of 1 volt meant the
plane would again fly like it did with 6 nimhs. The weight difference in
the packs may have made up for the voltage loss, but only if I could
have balanced it without the extra lead ballast.

In this case the nimhs were the clear choice. They are less expensive,
can handle more amps, are easy to add an extra cell, and the capacity
was not that much different than the lipos. If weight was the issue then
the lipos may have been a better choice, but not for this particular model.
I've used lipos in other planes where the weight savings was noticeable,
as was the extended flying time, but the extra expense was noticeable too.
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