Battery & motor amp draw questions - RC Groups
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Sep 09, 2003, 07:24 PM
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soundman's Avatar

Battery & motor amp draw questions

I've been flying rc for a year or so now - mainly small stuff. I've just moved onto speed 400/480 powered planes & have a few questions regarding battery choice/useage.

The cells I have available are: 8x800AR (Sanyo), 7x750 NIMH AAA (vanson) & some kokams - one 2x1040, three 2x750, one 2x640 & two 2x540.

The motors available are: graupner speed 400 (6v & 7.2v) & jamara 480.

Available props: gunther zagi prop (125mmx110mm), graupner 6x3 (folding)......I have others as well, but I'd like to use one of these.

The questions:
1) What is the maximum current draw that these cells allow.
2) Can you use AAA Nimh in parallel (like kokams).
3) What sort of current draw will I get using a Gunther zagi prop & a Graupner 6x3?

The reason for asking these questions is as follows....I've nearly finished building a plane from a plan (shrike), & I don't think the 8x800AR packs will fit in the plane (as well as being quite heavy). The obvious answer is to go & buy some new cells (eg Kans), but due to a rather dodgy financial situation I unable to buy anything new at the moment. So I'm trying to find a workable solution from the packs that I already own.

I have done some searching on rcgroups but it didn't give me the answers that I was looking for.

Any help will be greatly appreciated - links to other sites with relevant info....anything useful at all.


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Sep 09, 2003, 08:47 PM
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Dr Kiwi's Avatar
This is pretty much off the top of my head - but for current draw on a 400 with a Zagi prop or the 6x3 I reckon you are looking at maybe 8-10A. Your 800AR's will handle that but not many of your other packs will make the grade. 750AAA are probably only good for 6A max and even your 1040 Kokams are not going to supply much more than 6A either. Your smaller Li Poly's haven't a chance.

Look at the motor calculator to get an idea of current draw, with both your motors

and go to any of a number of battery suppliers to get info on current draw limits of your packs.

Cheers, Phil
Sep 09, 2003, 09:02 PM
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Dr Kiwi's Avatar
Its worse than I thought - with the 400 6v on 8-cell 800's with a 6x3 the current requirement is over 15A, and with the 480 over 13A. Using 7-cell 720AAA NiMH its still over 7A - too much for those cells. The Zagi prop (5x4.3) is only a little less hungry - you will still need to supply 8-10A to your 400 or 480 and only your 800's can do that.

Cheers, Phil

Cheers, Phil
Oct 05, 2003, 07:10 AM
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farnboro flyer's Avatar
I have just put together an 8 cell block of the VANSON 750 cells.
I intend to use them in my MM Switchback, however on checking the current draw on the C drive 300 motor(GWS) and an 10x8 prop, the amp draw is about 8 amps.
I'm guessing that this is far too high for these little AAA cells!
anyone got an idea what the max that they will take without making their life short?

Oct 05, 2003, 09:04 AM
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Dr Kiwi's Avatar
I really think that for AAA even 6A is not good in the long term. Next time you win at bingo I'd suggest you get some KAN 650's and acquire some more, matching Kokams - at the moment you have an eclectic collection of LiPolys which you cannot mate up in parallel packs to get higher capacity and thus current draw. A possible el cheapo solution would be to get a D pinion and spur for your g/box - then you could run the same prop (10x8) at lower current draw. Otherwise - would a 9x6 on your C g/box, with, again, lower current draw, provide enough thrust for that plane?

Cheers, Phil
Oct 05, 2003, 02:34 PM
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headless's Avatar
I have been wanting to ask this question for a few days but didn't feel it needed it's own thread, and this is the best related to it --
I have a E-Starter with a 350C motor and 7cell 730mAh NimH packs. I have been running a 10x8 for a few flights and have been noting that my packs are getting very hot during flight. They come out of the plane so hot i can't hold them, i have to hold them through multiple paper towels. They are not hot enough, however, to melt the shrinkwrap surrounding them (which i had heard was the 'dangerous' point).

The 10x8 prop came WITH the e-starter. Is it the case that a 350c simply pulls much less current than the 400 you are currently talking about?

The GWS Table supplied at

for the 350c - C gearing (5.33:1) shows almost every single prop listed pulling over 6amps! Does this mean that the 350c requires me to buy better than 7cell 8.4v nimh packs? Only TWO prop/voltage combo's listed actually draw <6amps

Also, on the motor calculation program at

Which motor should i choose for a GWS 350C? I thought that they were made by Mabuchi but i don't see a mabuchi 350, and i only see EM 300, 400...

What is the closest match?
Last edited by headless; Oct 05, 2003 at 02:37 PM.
Oct 06, 2003, 03:45 PM
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Dr Kiwi's Avatar
Don't quote me but I've heard that the GWS 350 is simply a Speed 300, so plug in a Graupner Speed 300 6v motor and that should equate with your 350C. Apparently, they are all made by Mabuchi!

On batteries, I suspect your problem is not so much the number of cells (7 = 8.4v), or the capacity (730mAh), but the physical size and constitution of the cells (I assume AAA). You should use something like the 800 5/4AAA pack or better the 2/3AA KAN 650's - these will allow you to draw 8-10A - but will not be much heavier than what you are now using. [One very useful chart I have ( puts AAA at 13g, 5/4AAA at 15g and 2/3AA at 13-16g].

Cheers, Phil

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