Thursday, April 19, 2012

FlySky FS-TH9X Battery Upgrade

Rechargeable battery upgrade for FlySky transmitter

The manual for my FlySky radio shows a nice picture of a charger and rechargeable NiMH battery pack.  But it doesn't come with one.  And there isn't one available as an option from the seller.  Instead it comes with a battery holder for 8 AA NiMH batteries.  It works well enough but NiMH batteries have limited capacity, discharge relatively quickly, don't hold their charge even when not in use, and don't recharge very well.  Luckily we can easily swap out the 8 AA's for a much better LiPo battery pack.  With increased capacity, the LiPo pack will last a lot longer than a bunch of AA's and it can be recharged over and over again. There are just a few things to consider when purchasing a replacement pack.


Battery Size
The dimensions of the battery compartment are 112 x 32 x 25mm.  Make sure the pack you order will fit your receiver.

Your best NiMH batteries can provide around 2500 mAh.  But your typical AA is more likely to be rated at around 1200-1500 mAh.  Get the largest capacity LiPo that will fit for the longest run time.

Discharge Rate
This one is important.  Standard LiPo batteries can discharge 30-40 times their capacity.  That means a 2000 mAh battery can output 60-80 amps at one time.  Obviously your radio will never draw that much current but the pack is capable of supplying more than enough current to fry your transmitter.  Select a battery made for radio transmitters with a low (1C) discharge rate.

Eight AA batteries can supply 12 volts.  But they discharge quickly, so you never actually run at 12v for long.  More realistically they run at about 1.2 volts per cell or 9.6 volts total.  A 3 cell LiPo is only rated at 11.1 volts (3.7 volts per cell).  That is plenty to run your transmitter, especially since it stays at that level for a long time.  However, when fully charged, a 3 cell LiPo can provide up to 4.2 volts per cell (or 12.6 volts max).  12.6 volts may not damage to your transmitter, but just to be safe you should undercharge your battery.  You can do this by setting your smart charger to charge the pack as a LiLo battery.  That should charge it to a max of about 4.1 volts per cell, or 12.3 volts total.

charging as a LiLo

I ended up ordering this battery from HobbyKing.  It is a Turnigy 2650 mAh, 11.1 volt, 3S 1C LiPo pack.  I just needed to make a few changes to get it to work.  It comes with three leads.  The four wire lead is the balance plug.  Leave that alone.  The white plug is a battery lead for JR or Spektrum radios.  It won't fit the FlySky so I cut it off to save room and prevent someone from accidentally trying to plug it in.  Heat shrink the remaining ends to prevent a short.  The black plug is for Futaba radios.  That one will fit in the FlySky battery plug but DON'T PLUG IT IN YET!!!  The wires are in the wrong order and you will short out your radio.

extra lead removed

battery plug color coded

Plug in your AA pack and note the location of the black and red (negative and positive) wires.  I used markers to color code the battery connector.  The black wire on the battery needs to be moved to the opposite side of the Futaba connector.  Some careful prodding with a tiny screwdriver will free the tabs and let you remove it.  Then just slide it in the correct hole and it should lock in place.

cramped leads

With that done, the LiPo pack will plug in but the battery wires get pinched between the plug and battery pack.  I removed the leads from the plug again and cut away some of the plug so that the leads could comfortably bend up without being pinched.

plug cut for clearance

much better

And that's it.  Select a suitable battery, check your connections carefully (fix if needed), undercharge, and you are ready to go.  Your transmitter will run a lot longer and you will save money on batteries.

running on LiPo (11.6 volts)

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