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Rhondas
11-09-2005, 06:08 AM
Im useing a 15 astroflight motor and 10 sub c 1400mah battery pack, its on the heavy side but flies nice 5 minutes, I just got into nimh batteris and found out these are little power house's , If I change to 10 AAA 2500mah nimh and also change the heavy astroflight motor to a speed 400 geared to use my 9x4 prop Im now useing, will I get longer flights and maybe just maybe faster speed because of the lighter motor set up. what do you suggest?

Matt Kirsch
11-09-2005, 03:27 PM
The 2500mAh AA cells aren't good for running motors. They're only capable of very very low discharge rates, not even enough to run a Speed 400 motor without overheating and sustaining damage. AA cells in general should be avoided because they're designed for maximum capacity, not good discharge characteristics. The electrical "creme filling" that gives the pack its capacity is stuffed in there so tightly that the electrons have a hard time getting out (simplified).

When converting from NiCd to NiMH, you want to stick with the same size cells as a general rule. Sub C NiCd? Use Sub C NiMH.

In your case, you can use "A" size NiMHs because your current draw should only be around 25 Amps. You'll get both reduced weight and increased flight times. Look at cells like the Sanyo HR4/5FAUP 1950mAh cell.

As far as replacing the Astro 15 with a Speed 400 geared, that's a dramatic drop in power. I don't think the drop in weight will be equally dramatic, or dramatic enough to compensate... I'm not sure you'd be happy with the results. The Astro 15 is doing 300 Watts (not sure where they get 400 at astroflight.com), but a Speed 400 is really stretching to do 100 Watts. If you cut power by 2/3, you need to cut the weight by 2/3 to maintain similar performance.

Twmaster
11-09-2005, 03:34 PM
It sounds like that plane is just screaming for a SP400 geared and 3s 1350 Lipo.

I'll echo hat Matt said. The AA and AAA cells will not handle the discharge current of that power set up. A cells will do well. I have a bunch of 1800 NiMH 4/5A cells from surplus cell phone battery packs and they work great on SP400 applications.

Matt Kirsch
11-09-2005, 03:36 PM
One thing I failed to ask was, what plane is this? How much does it weigh now? We can figure the approximate weight drop by using the lighter components and see how much performance you'll loose by going with the Speed 400 setup.

Steve
11-09-2005, 05:11 PM
Hey there,

Do you have a source(s) for those batteries?

It sounds like that plane is just screaming for a SP400 geared and 3s 1350 Lipo.

I'll echo hat Matt said. The AA and AAA cells will not handle the discharge current of that power set up. A cells will do well. I have a bunch of 1800 NiMH 4/5A cells from surplus cell phone battery packs and they work great on SP400 applications.

Twmaster
11-09-2005, 05:26 PM
Hey there,

Do you have a source(s) for those batteries?

Sorry Steve but no source any longer. the fellow I got mine from has gone belly up. I have a bunch left if interested in some of them. I originally got them to repower a laptop battery pack but that project kinda fizzled. Just got lucky as they do work well in some model applications. I was even using them in a speed 400 powered micro boat!

:D

Steve
11-09-2005, 07:03 PM
Sure....whaddaya want for them? I need to build or buy some new batts for my Slow Stick. Do you have solder bars and heat shrink and all of that stuff?


Sorry Steve but no source any longer. the fellow I got mine from has gone belly up. I have a bunch left if interested in some of them. I originally got them to repower a laptop battery pack but that project kinda fizzled. Just got lucky as they do work well in some model applications. I was even using them in a speed 400 powered micro boat!

:D

Rhondas
11-10-2005, 12:25 AM
The 2500mAh AA cells aren't good for running motors. They're only capable of very very low discharge rates, not even enough to run a Speed 400 motor without overheating and sustaining damage. AA cells in general should be avoided because they're designed for maximum capacity, not good discharge characteristics. The electrical "creme filling" that gives the pack its capacity is stuffed in there so tightly that the electrons have a hard time getting out (simplified).

When converting from NiCd to NiMH, you want to stick with the same size cells as a general rule. Sub C NiCd? Use Sub C NiMH.

In your case, you can use "A" size NiMHs because your current draw should only be around 25 Amps. You'll get both reduced weight and increased flight times. Look at cells like the Sanyo HR4/5FAUP 1950mAh cell.

As far as replacing the Astro 15 with a Speed 400 geared, that's a dramatic drop in power. I don't think the drop in weight will be equally dramatic, or dramatic enough to compensate... I'm not sure you'd be happy with the results. The Astro 15 is doing 300 Watts (not sure where they get 400 at astroflight.com), but a Speed 400 is really stretching to do 100 Watts. If you cut power by 2/3, you need to cut the weight by 2/3 to maintain similar performance.

Thanks Matt I get the picture you explained it very well with the cream filling Thanks.:p