10CG Power Mod Could be relevant to 10C 10CAG 10CHC

[Brett Armstrong]

Hi, I just got myself a 10CG and being an electronics tech I couldn't help have a poke around. I found the main voltage regulator to be a surface mount version of an old skool 7805 resistive voltage regulator.

This type of reg is about 50% efficient and the higher above 8V the worse it gets the rest is turned into heat(note for those running 3S lipos).

The R-7805 is a modern switch mode reg with an efficiency of 97%. The use of 3S lipo shouldn't be a problem as this guy can handle 30V max. It is larger and needs to be mounted away from the original spot but doesn't need a heat sink so that's easy. I haven't done a before and after current reading as my meter was playing up.

I didn't have much time so I haven't explained the whole dissemble process.

The first pic shows the stock voltage reg.

[IMG]http://i1129.photobucket.com/albums/m513/brettarm/LM7805.jpg[/IMG]

The second pic shows the heat pad and wires to move the reg.

[IMG]http://i1129.photobucket.com/albums/m513/brettarm/Wires.jpg[/IMG]

The third pic shows the pcb back in place and the regs new home and the red lines are where the battery compartment is once reassembled(avoid getting wires in this area).

[IMG]http://i1129.photobucket.com/albums/m513/brettarm/R-785.jpg[/IMG]

I ended up covering the whole reg in shrink tube and cable tying down. Have fun modding.

[Djay]

Thanks for the post Brett, but can you tell us a bit about why you changed it and what would be the reason for changing it etc.

Darryl

[Brett Armstrong]

The 5V supply runs most of the transmitter if you swap from a 50% heat loss to a 3% heat loss there will be much improved battery life. The R-7805 will also provide better high voltage performance with 3S lipo. Just added the photos for ease of viewing.

[Brett Armstrong]

Update

I have been using some video goggles powered from the trainer port on the 10CG, the added current draw goes close to the 0.5A limit of the R-7805.

I have found a new switch mode supply that is capable of 1.5A. The Murata OKI-78SR-5 is smaller and cheaper.

I have also done some current readings with the 10CG transmitting with a stock NiMh battery at 10.4V.

LM7805 fitted 170mA

OKI-78SR-5 fitted 120mA

It's not the 45% saving I had hoped for but it is about 30%.

If your transmitter normally lasts 5 hours this should give it about another 1.5 longer life on the same battery.

Happy flying.

[Frank Skilbeck]

I must admit I always found it strange that manufacturers persisted with using higher voltage packs than needed and then used a voltage regulators to drop the voltage when a lower voltage battery would have done the same thing, I suppose they wanted to be compatible with the chargers already supplied.

[daddycool]

Hi

found this interesting reading, but when a lipo comes to its end it has a steeep voltage drop and the low voltage warning probably would not function. This wouldpossibly cause quite a nasty accident even if failsafe is operational. and would you be able to realise that you have no power to your tranny.

just trying to work through this scenario and that seems probable.

does anyone else agree or not??????

[Martin Harris - Moderator]

Many of us do - including Manny Williamson of the BMFA who raised this very topic recently.

[Olly P]

Indeed - this is something to be aware of, especially on sets where the LV warning cannot be adjusted.

If you are using LiPo for the Tx, then I would advise keeping a note of the time used for and testing the max safe power time period, same as electric fliers do for normal battery use.

You could also get a voltage warning device on the balance lead to chime at 3.2v per cell - plenty for the Tx, but a good time to land to protect the battery.