DX7 - Lowest safe voltage?

[HiltonSteve]

What is the safest lowest battery voltage on your'e DX7 that you can still fly with?

Does the range drop off with the voltage or with it being digital does that mean it either works or it does'nt??

[elektromodely.com]

Never checked, but for sure it does not cause the range drop - dx7 uses LMxxxx voltage stabilizer to get the 3.3V or 5V (I do not remember) to supply the transmitetr circuits so any higher voltage is enought to power it on. It is a good idea to use it fully charged only - you will never hear the accu warning beeps. I ignored it maybe three years ago and believe it will not be enough for the whole flight...

[robgt]

Mine tends to sit at 9.2 volts for quite a while before dropping below 9 and rapidly draining.
I generally don't let it go down to the low 9 volt range - prefering to keep it above 10 volts

Cheers,
Rob

[cjcj1949]

Mine tends to sit at 9.2 volts for quite a while before dropping below 9 and rapidly draining.
I generally don't let it go down to the low 9 volt range - prefering to keep it above 10 volts

Cheers,
Rob

Mine starts dropping quickly at 9.6v. It's down to how balanced your cells are.
Seriously though 10volts is a good figure to useas someone else said 'after the flight'.

[machasm]

Stuck an outrage XP lipo in it and never looked back.
Lasts for ages.

[Tim Procter]

Stuck an outrage XP lipo in it and never looked back.
Lasts for ages.

Ditto, Got the same Adrian.

[Kwickkwack]

I have a lipo in mine and have not re-charged it yet, Ok I dont fly as often as a lot of other guys, but it just goes on and on. a definite upgrade

[adeytecnic]

Stuck an outrage XP lipo in it and never looked back.
Lasts for ages.

Just a concideration if your going to use aftermarket lipos here is an extract from my club websit:

With the growing number of Spektrum transmitters in the club the following was found on the Spektrum Web site. Thanks to Darren for passing on.

Warning concerning use of non-standard transmitter batteries

Spektrum transmitters are designed to be operated on 9.6 or 4.8 volt Ni-cad or NiMh batteries only. Use of Li-Po or other power devices operating at higher voltage can add heat to the system, possibly overloading the power regulating transistor for reduced output. Despite what aftermarket battery manufacturers might suggest, use of non-standard batteries offers decreased reliability of your Spektrum. Our service department has received failures associated with Li-Po packs.

For increased flight time, please use increased capacity NiMh cells, like the JRPB5011 2500 Sanyo pack. Charge these packs with the JRPC223 9.6 volt 270mAh output charger.

Note from Chairman.

Having just installed Zippy 2500 mAh 3 cell packs in my DX7 I have noticed the rear of the transmitter getting quite warm.

The problem is as Spektrum state that 3 LiPo's give an extra volt over 8 NiCds or NiMhs. I recently converted my trusty old Multiplex Twinstar from 8 NiCds to 3 LiPo's and very quickly burnt out both motors.


Hope this helps.

[Si Goodchild]

I'm not sure that my standard 9.6v DX7 battery is performing correctly. It's brand new and the most voltage I get out of it is 10.0v for a few minutes after charging. It then seems to settle down to 9.6v after an hour or so even when the tx is left switched off. I really don't seem to get very much flight time out of it before it drops to 9.0v and I'm pretty sure that the voltage ebbs away when it's left on the shelf for a day or two.

Has anyone else expereinced this? What sort of battery life are you getting? Should I be sending it back to the manufacturer?

Any advice would be much apprecited.

Si

[cjcj1949]

You're 1.2 volts out. Could be duff cell. You can bodge it by putting about an amp through it. Horizon are very good though. They'll probably put a new pack in the post.

[Si Goodchild]

Many thanks for that: so what should be the voltage after charging? Pics in the manual have the voltmeter at 10.6v but like I said I only ever see 10.0v for a few minutes. The rating of the pack is 9.6v at 1500mAH.

If it is a duff cell as you suggest I'll go back to the retailer first (pity he's 35 miles away!) and take it from there.

[mark Taylor]

Warning concerning use of non-standard transmitter batteries

Spektrum transmitters are designed to be operated on 9.6 or 4.8 volt Ni-cad or NiMh batteries only. Use of Li-Po or other power devices operating at higher voltage can add heat to the system, possibly overloading the power regulating transistor for reduced output. Despite what aftermarket battery manufacturers might suggest, use of non-standard batteries offers decreased reliability of your Spektrum. Our service department has received failures associated with Li-Po packs.

For increased flight time, please use increased capacity NiMh cells, like the JRPB5011 2500 Sanyo pack. Charge these packs with the JRPC223 9.6 volt 270mAh output charger.

This is why i sold my fp lipo to james ( moonmanflyer )
as i wasn't prepared to take the chance on my dsx9

cheers

mark

[machasm]

I haven't had any issues so far but I also only charge the Lipo to around 90-95% just in case.

[cjcj1949]

DX7 battery volts.

Many thanks for that: so what should be the voltage after charging? Pics in the manual have the voltmeter at 10.6v but like I said I only ever see 10.0v for a few minutes. The rating of the pack is 9.6v at 1500mAH.


If it is a duff cell as you suggest I'll go back to the retailer first (pity he's 35 miles away!) and take it from there.

Sorry. My DX7 says 11.2 after charge. Anything below 11.0 volts is likely to be a fault with either the charger, the built in voltmeter or the NiMh pack. The individual cells have little charge left after 1.2 volts and are usually about 1.3v on a tx. They quickly drop to about 10.6v total and then fall slowly to about 9.6v. The tx current is probably about 300ma and so the battery should last about 5 hours. I can measure mine if you want.

If you fast charge your pack at 1.5 to 3.0 amps for a few seconds, by taking it out of the tx and charging as a NimH you should get the duff cell back to life. Then it'l need to be slow charged at 150ma or so for 15 hours. This is ok for testing the tx and it will probably be ok, but I wouldn't rely on it.

[cjcj1949]

Lipo voltage.

I haven't had any issues so far but I also only charge the Lipo to around 90-95% just in case.

Their regulator must be lower than 8.0v to work at the lower voltage level, so worse case you could be increasing the power dissipation in the reg by 50% by increasing the voltage drop across the reg from 3.0v to 4.5v. It should be ok to use the normal battery at 35 deg C so if a normal battery heats the reg up to 50 deg C then a fully charged lipo would heat it up 50% more or say 10 deg C more. So if you only go out on days when it's cooler than 25 deg C you should be ok. Looks good for a few months then. Voltage could be an issue but an increase from a fully charged 8 cell NiMh (Effectively open circuit if you switch on staright after charge) of about 12.0 volts to 12.6v for a lipo isn't very great. With measurements of the regulator temperature rise we can produce a derating graph so you can limit the lipo voltage against ambient temperature. About 12.6 volts at 25C to 11.0 at 35C. Or then again Horizon could publish the real figures.

You'll have to keep the volts down to 12.0 in the winter cause its a lipo.

On a more positive mode the rise in temperature in the tx case will keep the lipos out of the cold so long as they are kept in the warm car when switched off. It should be possible to drop the extra lipo volts to about 10v using a regulator. It would reduce the voltage across the DX7 reg and keep their reg cooler. A switching reg would be even better.