Home Made A123 Receiver Pack

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Home Made A123 Receiver Pack

Postby RCMikeofIndiana » Thu Jan 27, 2011 2:28 am

I am very interested in making my own A123 receiver packs. Your youtube video was very informative. The only grey area for me is charging. I have a Hyperion EOS0606iAD-C charger that lists "1-6 Lipo - Lithium Iron (3.3V/cell types, inc. A123 brand cells / LiePO4 Cells)". Does this sound like a charger that will charge the A123's?

Thanks!
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Re: Home Made A123 Receiver Pack

Postby RCModelReviews » Thu Jan 27, 2011 8:49 am

Yes, that charger will do just fine.

A123 is a particular brand of LiFePO4 cells so you can just use the LiFePO4 setting on your charger and set the charge-rate to as high as 4C (up to 4 times the capacity of the cell -- so those 1100mAH cells can be charged at up to 4.4A (4,400mA).
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Re: Home Made A123 Receiver Pack

Postby RCMikeofIndiana » Thu Jan 27, 2011 10:56 am

Thanks! I plan on ordering the batteries from Hobbyking soon.
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Re: Home Made A123 Receiver Pack

Postby RCMikeofIndiana » Sat Jul 09, 2011 11:03 pm

I am still waiting for the A123 batteries from HobbyKing to be back in stock. In the mean time I have had several club members tell me I would need to do a little wiring trickery if I wanted to use the A123 battery pack as a receiver battery. They are saying that it puts out too much amperage and it would (potentially) fry my receiver and maybe a servo or two. They did not go into details. Are these home make battery packs safe "as-is" in my planes?
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Re: Home Made A123 Receiver Pack

Postby ergocentric » Sun Jul 10, 2011 12:42 am

Most receivers and servos are designed for use with up to five NiCad or NiMh cells - two LiFeP04 cells should put out the same voltage - 6.6Volts.

Perhaps they are confusing them with LiPo cells, 2s Lipo is 7.4Volts fully charged and could damage your receiver or servos.

What you do have to be careful of is not discharging any Lithium chemistry battery too far, as they may be damaged.
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Re: Home Made A123 Receiver Pack

Postby RCMikeofIndiana » Sun Jul 10, 2011 12:54 pm

Ergocentric,

I understand the voltage is safe. It is the amperage that they were referring to being to high that may cause the burning out of the receivers and/or servo's. Most commercial A123 pack sellers also talk of having a heavy duty switch & wiring to handle the high amperage.
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Re: Home Made A123 Receiver Pack

Postby John_Edward » Sun Jul 10, 2011 1:25 pm

RCMikeofIndiana wrote:They are saying that it puts out too much amperage and it would (potentially) fry my receiver and maybe a servo or two.


The easy way to remember is that Voltage is aggressive, it all goes to the device.
And Amperage is kind, and only the right amount goes to the device when needed.

A single A123 cell is rated for 3.3volts, and can give constant of around 70Amps, and a burst off 100Amps.
A two-pack would be 6.6volts.
The 70Amps is comparable to a LiPo C rating, it tells you how much power you can draw from it.
C rating to Amps is calculated: (C rating x mAh rating) / 1000
Amps to C rating is : (Amps * 1000) / mAh rating

So an 2xA123 2300mAh battery would be a 6.6v 30C battery.
A 2S LiPo with a C rating of 30 would be a 7.4C 30C battery.
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Re: Home Made A123 Receiver Pack

Postby RCModelReviews » Sun Jul 10, 2011 11:21 pm

RCMikeofIndiana wrote:Ergocentric,

I understand the voltage is safe. It is the amperage that they were referring to being to high that may cause the burning out of the receivers and/or servo's. Most commercial A123 pack sellers also talk of having a heavy duty switch & wiring to handle the high amperage.

Your friends are confused.

Current is the flow of electricity.

The magnitude of this flow (current) is determined by the pressure (voltage) and the resistance to the flow.

There's a formula called Ohm's Law which says: I = V/R (where I is current, V is voltage and R is resistance.

So, the only things that determine how much current flows into/through your RC gear is the voltage you apply and the resistance the servos, receiver, etc represent.

Think of it this way...

The battery in your car can deliver several hundred amps - which is more than enough current to turn you into a smoldering block of carbon.

However, if you put your hands across the terminals of that battery -- nothing happens. There aren't hundreds of amps surging through your body because there's just not enough voltage (pressure) to push that current through the resistance of your body.

The only way you'll get more current to flow is by either raising the voltage or reducing your resistance.

Now an A123 pack *can* deliver more current when it's asked to -- but that's a very good thing!

If you have a linkage that becomes stiff then the servo on that linkage will have to work harder to move the control surface -- that means it will draw more current. If your battery is a wimpy AAA or even AA -sized NiMH one, it may not be able to deliver the required current so its voltage will drop. The result could be a brownout that crashes your model.

By comparison, the A123 will deliver the required extra current and the servo will continue to move. If you regularly check how much current you're putting back into your batteries when you recharge them you'll soon spot the fact that something is using more current than usual and that might lead you to save your model by investigating and finding the faulty linkage.

The only time an A123 will fry anything is if you have a major problem such as a stalled servo or short-circuit in your wiring. In the former -- the servo will probably fry -- but the rest of your system will probably continue to work -- possibly saving your model.
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Re: Home Made A123 Receiver Pack

Postby ran riegler » Sat Jan 14, 2012 10:54 am

Does enny body know abaut the fake a123 chinese batteries?
they are two kinds one marked under the yelow heatshrink and one not marked
both of them are 2-2.4$ including shipping
the non marked is sepose to be better i think
it gives abaut 850mah, can work at up to 30c i think
how meny charges it will give ?
and what are the diferences in behavior
maybe il better look in ebike forums
thanks
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Re: Home Made A123 Receiver Pack

Postby ergocentric » Sat Jan 14, 2012 4:33 pm

ran riegler wrote:Does enny body know abaut the fake a123 chinese batteries?
they are two kinds one marked under the yelow heatshrink and one not marked
both of them are 2-2.4$ including shipping
the non marked is sepose to be better i think
it gives abaut 850mah, can work at up to 30c i think
how meny charges it will give ?
and what are the diferences in behavior
maybe il better look in ebike forums
thanks


Fake? no.
Same Chemistry? yes.
Same physical structure? no.

A123's claim to fame is higher current available with lower internal heating because there is more surface area on the electrodes

that being said, I also need to say that it seems you get what you pay for (but I keep buying the cheap batteries)
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