DX7 Lipo Battery field conversion

[richieclarkie]

So picture the moment..... I pack up the car with everything I need for few hours flying: 4 helis, flight box, TX, Starter stuff, fuel, flask of coffee, sandwiches....... yep I'm fully prepared

Takes me longer than normal to get to the field 45 mins - traffic is terrible!

Open the boot and start getting stuff out, helis, flightbox, starter, TX..... take a look........ NOOOOOOO!!! the TX has been left on overnight and it's dead . No field charger, just lipo charger and my TX pack is a sanyo 2700 ni-mh

So what do I do? Then I remember I have my soldering stuff with me - So I phone Jason Larkin up and ask if he's been getting on OK with the Lipo conversion in his 9x. He says yes, so far all OK.

So I try one of my 6 revvo 2100 Lipo for size and it JUST fits. Perfect I think and solder the solder the connector for the TX to the Lipo. Problem solved - I can fly for the rest of the day

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I'm going to keep using this set up for now. The advantage of being able to charge in 30 mins and the extra battery life you get with Lipos is too much of an advatage to want to go back. If I have any problems I'll let everyone know.

This is not a new concept but I thought someone might find this useful/interesting

A word of caution, Spektrum has officially said not to do this, so if you are thinking of doing it,on your head be it.

[Smoothound]

The problem is that the voltage is a bit too high at the start.

My Lipo in my PCM9X2 has a note on it about not installing it into the Tx within 5 mins of coming off charge. It appears to have some sort of electrickery inside the pack that drops the pack voltage a bit in this 5 mins.

I could be wrong though as I've chucked all the blurb that came with it away

[moyesboy]

That 5 mins is probably just for the natural voltage sag you get with a lipo.
Surely there is a device similar to the tail step down that could drop the voltage a little bit and keep things safe?
Richie, why not make a little loom with the tx plug at one end and the revo balance socket at the other. I have a few of the bits - maybe I will make some if there is room inside the tx for it.
Also with the cellpro10 you could charge the lipo in storage mode and thus avoid the maximum voltage (or swap it for one you did a flight on the 450 with).

A 1C charge with a field charger (if you had one) into the normal Tx battery might have taken less time and got you flying too

[raptorheli2]

i've had a revo 2100 3s lipo in my dx7 since june i think. still not charged it either. magic.

cheers

[Sesame]

I was using a lipoo in my DX7, but after hearing or the DSX9's having trouble and then reading the warning not to use lipos on the horizon site I went back to NiMH which are far more of a pain to charge the lipo lasts for weeks.

The only questionmark ive got, is if the Tx packs up during a flight and this causes an accident due to a lipo that the manufacturers have advised you not to use, how does your insurance stand? knowing insurance companies use any excuse not to pay out, well its just a thought.

[moyesboy]

I'm sure the BMFA insurance doesn't work like that.
does changing the tx battery effect the type approval of the tx? I think not.
Does your insurance still cover you if the battery falls out of your tx and your model causes an accident?
If the insurance only applied if all the manufacturers recommendations are followed then most of us would be excluded.
Obviously a careful attitiude is to be encouraged but there does seem to be an attitude among model fliers that the slightest thing might invalidate their insurance and BMFA seldom pipes up with any reassurance about it. For example a club banning DX6i txs for fear they wont be insured becuase the separate batteries in them do not follow BMFA recommendations.

[richieclarkie]

A 1C charge with a field charger (if you had one) into the normal Tx battery might have taken less time and got you flying too

As I said in my original post I only had a lipo charger so that wasn't an option. A voltage step down is a great idea in theory, but these can fail so that could be a worse scenario.

I had thought about making up a charge connection, but it's no real hassle to remove the battery tray and charge directly, plus I will feel happier removing the whole pack when I do this anyway.

I am concerned a little about the voltage issues. What I may do is finish the charge slightly short of full charge for now.

[raptorheli2]

tony has a very valid point. will remain unanswered i'm sure.

cheers

[Sesame]

There are a few guys at our club still using lipos and thats the answer they use, just dont fully charge the lipo, personnally I always took it out of the radio, knowing that lipos can be quite volatile I felt better doing that.

Paul, I think I may well give the bmfa a ring and just ask the question.

[Nutz]

The problem with using 3S lipos in your TX is that the voltage is a little bit higher than what the TX was designed for which in turns strains the components of the TX and leads to the TX prematurely failing.

[MrKev]

I'm sure the BMFA insurance doesn't work like that.
does changing the tx battery effect the type approval of the tx?

Yes, actually. Type approval is only valid if used in accordance with the manufacturers recomendations.

For example: Increasing the battery voltage on some transmitters may increase the power output.

[richieclarkie]

Very interested in what you find out Tony.

[Sesame]

The problem with using 3S lipos in your TX is that the voltage is a little bit higher than what the TX was designed for which in turns strains the components of the TX and leads to the TX prematurely failing.

Yes this is the same senario as people are always discussing re: servos and running them at 6 and 8v they will work but the question is for how long

by the way great to see you on here again Leon, its been awhile.

[robgt]

by the way great to see you on here again Leon, its been awhile.

I was thinking the same thing!!!
Nutz is back!!
Cheers,
Rob

[SRH990]

There's a conversion available in the US which involves replacing the existing voltage regulator in the DX7, a linear regulator, with a more efficient switching regulator. The linear regulator works by dumping the additional voltage through a resistance, a bit simplistic but it means that the increase in input voltage over an 8 cell Nicad/Nimh causes more heat and higher risk of failure. When the switching regulator is installed it works more efficiently and is similar to using an SBEC on a heli, less heat and even longer times between charges.

Unfortunately the JR PCM9X/DSX9 doesn't seem to have a recognisable voltage regulator in its circuitry so a conversion isn't possible AFAIK.