DX7 Lipo Battery field conversion

[jiberjaber]

It's only 1.5V more than actually off a fully charged standard pack though.

Without looking at the actual regulator it is still hard to say, but most linear regulators will take quite an input range, up to 16V or more.

It comes down to the amount of power actually required by the radio to operate.

If you get say 5 hours of continuous operation out of a 1500mAh battery, then that's about 300mA, which equates to about 3.3W of total power dissipation at 11.1V. At 12.6V (3x4.2v/cell) that power dissipation is 3.7W. So not a huge difference.

But it depends on the circuit design etc. even a humble 7805 regulator can come in flavours ranging from 100mA upwards in the same package, so If I can be bothered whilst down teh shed tonght I might take a look and advise further.

I personally see no reason why not to use a LiPo other than the usualy fire risks.

[jiberjaber]

So I could find a low voltage drop out regulator on the spectrum TX board for 3.3V (500mA LM2937) and there is 5V kicking around on the LCD / computer board. I didn't want to disturb my CD in the DX7, so I didn't go taking that board out to have a look.

The 3.3V regulator has battery voltage on it's input. I also was able to find battery voltage on the computer board, so there must be some regulator on there, maybe on the LCD side of the board.

[machasm]

One thing to bear in mind here is that you found that your Tx was left on and drained your NimH battery.
If you leave your Tx on with the Lipo in you might find you wont have a Tx left!
Adrian.

[Tim Procter]

One thing to bear in mind here is that you found that your Tx was left on and drained your NimH battery.
If you leave your Tx on with the Lipo in you might find you wont have a Tx left!
Adrian.

Can you expand on that Adrian please..

[machasm]

Can you expand on that Adrian please..

Well if you over discharge a Lipo it can catch fire.
Expanded enough?
Adrian.

[Tim Procter]

Well if you over discharge a Lipo it can catch fire.
Expanded enough?
Adrian.

Well thats another lesson learnt today..

Didnt know that Adrian.. Thanks..

[funfreex]

After purchasing a new DX7 yesterday I now have a spare Tx battery from my now redundant X2720 that will stay charged and in the flight box for such occasions that I leave my Tx turned on without knowing it. (did it the other day actually)

[machasm]

After purchasing a new DX7 yesterday I now have a spare Tx battery from my now redundant X2720 that will stay charged and in the flight box for such occasions that I leave my Tx turned on without knowing it. (did it the other day actually)

Trouble is, unlike Lipos NiMh batteries voltages decay over time.
So unless you re-charge it regularly you might find that your fully charged backup battery is dead as well.
Adrian.

[funfreex]

Trouble is, unlike Lipos NiMh batteries voltages decay over time.
So unless you re-charge it regularly you might find that your fully charged backup battery is dead as well.
Adrian.

I intend to top up the battery now and then, but if I get to the field and find both Tx batteries are flat I will take it as an omen and drive back home!!

[guest222]

I thought lipos only expand when delivering very high currents? surely the power usage of a TX is not enough to cause a lipo to expand?

what the deal with with the Flight power lipo that is marked up for use with the DX7? is this killing my tx? Ive had it in there since july and still not charged it , its only 1500 mah 3 s

andy

[SRH990]

I'm using the same Flightpower lipo in my JR PCM9XII with a Spektrum module fitted. I was under the impression that the transmitter shuts itself down at a certain voltage (around 9V?) so wouldn't this make over-discharging unlikely? Certainly at the very low current in this application even if it totally discharged the lipo it wouldn't catch fire, lipo fires are caused by overcharging and shorting out. The advice when disposing a lipo pack is to discharge it at a very low rate.

[barney]

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.

Not a problem if your using a well known brand of Lipo, as the damn things never reach maximium voltage after a few cycles

[Ashley Davis]

Well if you over discharge a Lipo it can catch fire.
Expanded enough?

a slowly discharged lipo (such as one in a tx that has been left on) will not puff or catch fire if it is left to fully discharge, this info is not correct. Only a lipo overdischarged at high current will catch fire. The reason is that as you try to draw high current and there is no charge left in the elctrolyte it generates heat as the resistance has gone up due to lack of charged ions. In a situation where you are discharging slowly a lack of charged ions in the elctrolyte will not create heat as the amp draw is not high enough to do so.

[Smoothound]

I have a 3s TP1320 that spent a couple of months up a tree which was slowly discharged by the Rx to 0v. It is now not puffed, recharged and has been flying in my Lil Banchee for about a year since it happened

[machasm]

a slowly discharged lipo (such as one in a tx that has been left on) will not puff or catch fire if it is left to fully discharge, this info is not correct. Only a lipo overdischarged at high current will catch fire. The reason is that as you try to draw high current and there is no charge left in the elctrolyte it generates heat as the resistance has gone up due to lack of charged ions. In a situation where you are discharging slowly a lack of charged ions in the elctrolyte will not create heat as the amp draw is not high enough to do so.

I stand corrected.
Thanks for the info.
Adrian.