V
FUTABA 9Z
THE UNOFFICIAL WORKSHOP MANUAL
WARNING:
THE INFORMATION IN THIS MANUAL IS FOR INFORMATION PURPOSES ONLY AND MAY BE INCORRECT, CAUSE DAMAGE
TO YOUR RADIO OR INJURY TO YOURSELF AND OTHERS. IF YOU USE THIS MANUAL YOU DO SO SOLEY AT YOUR OWN RISK.
www.jamesandtracy.co.uk
Copyright 2012 jamesandtracy.co.uk
Page 51 of 84
Figure 46 Poor design of the connection on Spektrum DSM module
4.7. Cycling and Fast Charging the Transmitter Battery Pack
The 9Z transmitter battery cartridge contains a diode to provide reverse polarity
protection for your transmitter. This is very unusual as these diodes are usually placed
within the transmitter, not the battery pack. As a result, it is not possible to cycle the pack
without ‘jumping’ this diode. Further, most modern chargers ‘sense’ the amount of
charge to put into a battery through monitoring its voltage during charging. With this
diode in the charge loop this is not possible, and so most modern chargers will ‘error out’
using this pack. Finally, if you’re unlucky enough to have a charger that does work with
the 9Z’s pack and you decide to charge at above 300mA, the result will be some melted
plastic and a non-functional pack, because the 9Z’s diode is only rated to 400mA (i.e.
about 1/2C of the original pack or 1/5C of a modern pack).
For all these reasons it’s a very good idea to upgrade the 9Z’s battery pack with a bigger
diode and build you a simple diode jumper. The total cost will be about £2. If you always
use the jumper for fast charging, the larger diode is not really needed. However, most
policemen would tell you that if they were faced with a gun they’d hands-down prefer a
“bullet proof vest” over “an almost bullet proof vest” for protection and I’d urge you to feel
the same way about the 9Z’s pack.
You can construct a simple diode jumper from 0.1” PCB header (cut to length) for the
9Z’s transmitter pack as shown in Figure 47. This is slotted into the five pin port on the
back of the transmitters battery pack during charging and shorts out the internal diode.