Just recently I came across a thread concerning running a 8fg of a 3S Lipo, YES I did say 3S.
3S is 12.6v and a 8fg normally uses a 1700Mha 7.2v NiMh? Now we all know a lot of flyers use a circa 2200 2S Lipo for increased flightimes between charges (2S is 8.4V at full charge.) a little over spec but acceptable.
Those who use a EzUHF will know its meant to be run at 12v although it will happily run on 8-8.4v with an approx 50% reduction in range as I have done for ages..
The EzUHF incorporates an additional power jack allowing you to piggyback a separate 3S pack in these circustances but it is a little untidy and adds complication to an otherwise simple system.
At the end of last year Sander of Immersion fame acquired a 8fg himself and used it to address the Futaba variable frame rate problems combined with the EzUHF. He also did some testing of the 8fg running a 3S using a FLIR camera to look for hotspots. His conclusion was only a small increase in heat and it all appears to work within respectable limits. Immersion themselves have been using 2 of these Tx's for a while now without problem.
Anyway I did a lot of searching as people had apparently already tried 3S with the 8fg... Anyway I could find no confirmation of this anywhere. All I found was hearsay that its a 8v TX and it shouldn't be done. This does seems typical of forum speak, and that no one had actually bothered to try or test!.
NOW I'll be 100% clear neither I or Immersion are suggesting you go try this modification, your doing this at your own risk should you try.
Anyways, today I fitted a 3S Zippy 1500Mha. I had no way of testing other than to plug it in go, but all seems good so far on the bench. Weather prevented any flight tests today but over the next few weeks I will find out if this is doable. One other thing is my EzUHF is soldered directly to the 8fg as the trainer plug is a known weak point with any LRS.
Ice
The problem with running the Futaba from 3S is that it appears to work great, but eventually they blow their schottky diodes and your tx is dead instantly. During a flight this can be disastrous. I have had it happen twice previously on a 7C luckily both times on the bench
Eek, I run mine on 3s with my ezUHF. What's the solution? Not fully charge the battery?
Using diodes to drop the packs voltage down
ken to see the results on this over time as I'm not using my 8Fg just now for this very reason, was a pain using the external battery and I kept forgetting it so for now I've got all my EzUHF kit on my 10C running from a 3S, if it works well then I'll go the route of Iceman and wire the EzUHF internally and run from a 3S
Coyote I see you mention the Tx internals of the 7C.
Quoteschottky diodes
so obviously have considerably more electrical knowledge than I posses on this subject.
My question is the 8fg using the same diodes/board and liable to this issue you mention.
Also if this is a problem is there a way to wire this up so they share the same 3S Battery supply but can split the voltage to the TX from the EzUHF. I want the Tx battery to remain removable so I can swap it out.
I currently have the EzUHF hard wired to the trainer port so it gets power via that which obviously passes through 8fg first.
Ice
Does this effect the 9c as well?
The 9C has the same schokkty diodes as well s its possible to smoke that as well.
You can not split the voltage and then drop it to the trainer port because the battery pins go straight into the PCB and then distributed across the board, You would have to break the PCB track and fit a few diodes to drop the voltage down to 9 - 10v to keep the tx safe. Then break the unswitched +ve futaba trainerport track on the RF board and put a link in straight to the +ve input pins from the lipo. If you could do that you could run it all day long with never any issues at all.
Most people elect to put the diodes inline with the lipo wire and drop the voltage down to 9 - 10v and then there is no need to modify the tx itself.
I've had this problem and got sorted out by good advice on this Forum -
Have the normal battery in the Futaba tx.
Connect EzUHF to Tx as usual - via trainer socket or wireless module pins
Connect 3S Lipo through dropper diodes OR an adjustable voltage regulator, set to say 10 volts to the EzUHF DC power jack socket.
Even though this means the EzUHF is getting 2 seperate DC supplies - one from tx and one from 3S - that's OK - EzUHF is designed to cope with this situation.
Word of warning: the 3S will last a 'long' time powering the EzUHF - your tx will run out of power way before the Ez does - with this setup.
wgt40w, not sure what your point is as I thought it was safe to run the EzUHF tx straight from the 3S without the need to drop down the voltage therefore getting full power out from the tx ,I think Iceman's idea is to do away with the need for 2 batteries and run everything from 1 3S.
A 3S Lipo, when fully charged can be approx. 12.6 volt - 0.6 volts above specification.
OK, I am being rather nerdish - you should be OK without the volts being dropped - but don't make a warranty claim if anything goes wrong. But, if you have a voltage limited supply, then you could also pop in a 4S with no problems !
Hi wgt40w If you read the first post we are talking about driving both the 8fg/EzUHF from the same 3S battery which is what sander/Immersion have been doing for a while
BTW cars use 12v but in reality its actually 13.8v.
14.4v with most when alternators running ;)
Might get 14.4v from the alternator on my old wreck but probably closer to 10v from the battery LOL
Lol