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HomeAircraftHelicopterMain Discussion › Building your own TX battery pack.
01-18-2010 10:05 AM  8 years agoPost 1
Popadel

rrNovice

Johannesburg

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I’ve been trying to build my own power pack for the TX, so I used 8 Nm Hi rechargeable 2500mah batteries in series and i also striped the original Spectrum 1500 mah pack from the DX7 to use the resistor in there which runs in series and seems to be there to ensure you can charge it via trickle charge with the OEM charger. Seems without it you can’t charge it.

Problem is that the batteries were all flat (as in 0V) when i soldered it together and now it won’t charge and the TX binding button light just keeps flicking on and off when i switch it on but there is nothing showing on the screen.

What could I have missed? Or should i have charged the batteries first before soldering them? Removing that little white diode that runs in series from the original pack makes no difference to the power output, but it does not allow the charger to work.

Thanks in advance.

Srimok 90 - OS 91 HZ PS ; Trex 600ESP 12S 560 scorpion; Trex 450 Pro Scorpion 222-6; Trex 250 SE

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01-18-2010 10:10 AM  8 years agoPost 2
hootowl

rrProfessor

Garnet Valley, Pa.

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Double check all your positives and negatives on your build. Be sure you have the correct polarity at the plug. Try charging the pack without using the radio.

Wolves don't lose sleep over the opinions of sheep

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01-18-2010 10:32 AM  8 years agoPost 3
Popadel

rrNovice

Johannesburg

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I have read in another forum today that Spectrum use the reverse order on polarity for their batery pack and i never really checked that, i just assumed red was positive and the other was negative.

anyway...more testing coming up.

Srimok 90 - OS 91 HZ PS ; Trex 600ESP 12S 560 scorpion; Trex 450 Pro Scorpion 222-6; Trex 250 SE

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01-18-2010 11:05 AM  8 years agoPost 4
wzak29

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Lake Peekskill NY USA

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You can’t have a resistor in series with the batteries without a diode or the resistor will limit the current and voltage to the tx. What is the value of the resistor? If it only has color bands please tell what they are

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01-18-2010 12:22 PM  8 years agoPost 5
copperclad

rrElite Veteran

NY

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I have read in another forum today that Spectrum use the reverse order on polarity for their batery pack
Hi
i just popped the battery out of my DX7 and checked , the red lead off the battery is positive and the brown lead is negative , HTH

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01-18-2010 12:49 PM  8 years agoPost 6
JRjoe

rrElite Veteran

Jonesville , IN USA #1

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the red lead off the battery is positive and the brown lead is negative
+1..... i'll agree with that

It's the way they wire the charge plug on the side of the TX that's opposite Futaba...


JRjoe.....
Indoor plumbing??? No, we don't need that!!!

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01-19-2010 03:38 AM  8 years agoPost 7
w8qz

rrVeteran

Grand Rapids, MI - USA

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You may need to charge the cells with a 'dumb' power supply, the first time - if these are brand new cells, sitting at 0 volts to start. My experience has been that new cells take several cycles to come up to full capacity. NiMH cells (of the type we use for our radio gear) seem to work better with initial charges at a low rate - i.e. 1/10 C charge for at least the first few times.
Some new 'HydraMax' NiMH flight packs I purchased recently took 6 charge / discharge cycles to come up to capacity, but once there, they've worked great.
I don't understand why a diode would be installed to prevent charging - those normally are there to prevent an accidental short (a.k.a. discharge) on / to the charging jack from causing a fire. (I bypass those on my transmitters, so that I can cycle the packs more easily). Is it possible you've wired the diode the wrong way around? But then, normally the diode is not part of the battery pack itself. I don't understand either what purpose a resistor in the battery pack would serve. Are you confusing the two?
Remove the pack from the transmitter, remove any diodes or resistors from the pack, and work on cycling it a few times by itself - that should eliminate a couple of possible problems.
Unless Spectrum has done something very unusual with their OEM 'wall wart' charger, it should be pretty basic - a transformer, a rectifier, and an LED to sense current draw. It doesn't care what it's hooked to, or whether or not it has some special resistor installed in the battery pack.

"The helicopter is much easier to design than the aeroplane, but is worthless when done."

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01-19-2010 03:54 AM  8 years agoPost 8
dkshema

rrMaster

Cedar Rapids, IA

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i also stripped the original Spectrum 1500 mah pack from the DX7 to use the resistor in there which runs in series and seems to be there to ensure you can charge it via trickle charge with the OEM charger.
There is no series resistor (or other element) between the battery and its plug. Eight cells wired in series, and a plug. Red is positive, brown is negative.

The CHARGING JACK is wired opposite the Futaba version. JR has CENTER PIN negative, Futaba has CENTER PIN positive.

There is a 3 amp fast blow fuse inside the transmitter case. If it blows (and it will if you hook up the charger backwards), you need to replace it.

A trip to Radio Shack will get you a pack of them...

http://www.radioshack.com/product/i...&origkw=%3Cspan

And a couple of different ways to wire your battery:

A diode is installed in some transmitters to prevent you from accidentally DISCHARGING the battery if you short out the charging jack. I don't believe JR/Spektrum uses them.

-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz

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