DIY $8 Lithium Transmitter Battery - Futaba FX18 ?

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Re: DIY $8 Lithium Transmitter Battery - Futaba FX18 ?

Postby RCModelReviews » Fri Jun 11, 2010 7:13 am

You can wire up a balance lead if you want, although I've not bothered for low-drain applications like a transmitter.

There's plenty of info on the Net as to how to wire a balance connector but if you want details I can do up a diagram.

Why 3 cells?



FBURDEN wrote:Very Rookie Question here?

If I solder 3 of these lithium batteries together how do I recharge them with the HK Accucell 6 or Accucell 8?

Besides the connection to the radio, what other connectors to I need to have to attach it to the Accucell? So that the 3 cells get properly balanced?

Thanks,
Ford
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Re: DIY $8 Lithium Transmitter Battery - Futaba FX18 ?

Postby ergocentric » Fri Jun 11, 2010 12:32 pm

Basically one wire each end and one wire between each pair of cells:

http://sites.google.com/site/tjinguytec ... connectors
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Re: DIY $8 Lithium Transmitter Battery - Futaba FX18 ?

Postby FBURDEN » Fri Jun 11, 2010 4:51 pm

Hi,
"Why 3 cells"? It's for a Futaba 6EX which needs 9.6 volts I believe. Currently has an 8 pack of Nicad AA's.
If the lithium is 3.7 then I need 3 of them.
I'd rather not change/add any resisters to the motherboard.

I'd be happy not to need to install balancing connectors. Is there a charger that you would recommend that only needs to be connected to the power leads. The HK accucell seems to need be connected to the balancer as well. (from reading the manual, I haven't bought one yet....)

Thanks!
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Re: DIY $8 Lithium Transmitter Battery - Futaba FX18 ?

Postby ergocentric » Mon Jun 14, 2010 4:59 pm

FBURDEN wrote:Hi,
"Why 3 cells"? It's for a Futaba 6EX which needs 9.6 volts I believe. Currently has an 8 pack of Nicad AA's.
If the lithium is 3.7 then I need 3 of them.
I'd rather not change/add any resisters to the motherboard.

I'd be happy not to need to install balancing connectors. Is there a charger that you would recommend that only needs to be connected to the power leads. The HK accucell seems to need be connected to the balancer as well. (from reading the manual, I haven't bought one yet....)

Thanks!


You have 8 nicads, you have a charger, so I doubt you would be saving much money through the purchase of new batteries and new charger.

Your radio may work well on a lower voltage if converted to 2.4, just the transmitter portion of most non 2.4 GHz radios need higher voltages because the transmitter designs were so old.

All of this also depends on the power dissipation capabilities of the voltage regulators inside the radio, but I think most Futaba transmitters will work fine at the increased voltage.

Fully charged:
1.25V x 8 = 10 Volts (NiCd)
4.2V x 3 = 12.6 Volts (LiIon or LiPo)

a 25% increase in battery voltage, for a five volt linear regulator that would be a 50% increase in voltage drop and power dissipation.
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Re: DIY $8 Lithium Transmitter Battery - Futaba FX18 ?

Postby FBURDEN » Tue Jun 15, 2010 12:21 am

Actually I'm now leaning towards using the Hobby King A123 18650 batteries. 3 of them, 3*3.3 = 9.9 (fully charged voltage of the 3.3 volt ones would be how high??) If I leave my browser open I get a popup offering them for about $8.00 each.
I need a new charger for my Lipos anyways ... I'm leaning towards the Accucel 8.

They should be safe eh?
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Re: DIY $8 Lithium Transmitter Battery - Futaba FX18 ?

Postby RCModelReviews » Tue Jun 15, 2010 12:28 am

Be aware that these cells are larger than AA so you can't fit three of them into the battery compartment.

Those LiFePO4 cells are the same size as the lithium-Ion cells used in the $8 modification and two cells are a "neat" fit when angled diagonally.

Two LiFePO4 cells won't produce enough voltage (6.6V) though.
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Re: DIY $8 Lithium Transmitter Battery - Futaba FX18 ?

Postby FBURDEN » Tue Jun 15, 2010 12:37 am

How about the Turnigy 1450mAh 3S 11.1v Transmitter Lipoly Pack with a diode or 2 to bring the voltage down.
http://www.hobbycity.com/hobbyking/stor ... oduct=9787

I apologize for may lack of electrical knowledge ...
I still think the A123's are the way to go for me (my Futaba is a 2.4gig 6EX).

Theoretically I'm interested in what a diode or 2 would do here.
The Turnigy 1450mAh 3S 11.1v Transmitter Lipoly Pack has a great price, under $8.00!!!

I get the impression from Bruce that the Lipo with the diodes is still questionable as to whether it now makes it safe for transmitters.

Would be nice to have a confirmation on that ... technically very interesting...
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Re: DIY $8 Lithium Transmitter Battery - Futaba FX18 ?

Postby FBURDEN » Tue Jun 15, 2010 12:41 am

for the LiFePO4 cells I would cut a small rectangle hole for each cell in the floor for the compartment, so that each cell rests in it lower by about 3 or 4 millimeters. I believe they are 3 or 4 mils bigger in diameter.... thank God for Dremels.
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Re: DIY $8 Lithium Transmitter Battery - Futaba FX18 ?

Postby RCModelReviews » Tue Jun 15, 2010 12:59 am

You can put a diode or two in series with the LiPoly pack but you'd have to make sure you didn't attempt to recharge through those diodes (or it wouldn't charge).
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Re: DIY $8 Lithium Transmitter Battery - Futaba FX18 ?

Postby FBURDEN » Tue Jun 15, 2010 2:38 am

hmmmmm this link tells all about the reasons for NOT using a Lipo, or anything which might give you too much voltage...
http://forum.myrc.biz/index.php?topic=283.0
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