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Old Sep 15, 2011, 08:31 PM
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TX battery voltage...how low do you go?

Just curious as to what's everyone's go/no-go point for recharging their TXs... 10.0 volts? Until the low batt alarm? I have a DX7 with the stock battery pack.
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Old Sep 15, 2011, 09:00 PM
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For 8-cell NiMh batteries (9.6 V nominal), I fly down to 9.5 Volts.
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Old Sep 15, 2011, 09:10 PM
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For 8-cell NiMh batteries (9.6 V nominal), I fly down to 9.5 Volts.
Does range fall off as the battery pack gets weaker? Or does it maintain "full link" until the nominal voltage/alarm? Come to think of it, I've never run my DX7 down and don't even know what the alarm voltage is.
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Old Sep 15, 2011, 09:50 PM
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Range does not fall off.
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Old Sep 15, 2011, 10:14 PM
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For many old 72Mhz radios, the output power actually does go down as the Tx battery
voltage falls. For 2.4Ghz radios and modules, they're all regulated down to 3.3V or 5V
internally so they'll handle any Tx battery voltage above that.

I am perfectly comfortable flying my Tx battery down to the alarm. On the 9C that's
about 8.8V, which is still 1.1V per cell, which is fine for a NiMH cell with a 1.2V nominal voltage.
I'm always mystified when people think that reaching the nominal voltage
(9.6V for Tx, or 4.8-6 for 4-5 cell Rx pack) is when they should recharge.
It's called the "nominal voltage" because it's the average for the entire
normal discharge curve. The flat part of the curve is nominal and most of
the juice is there.

ian
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Old Sep 15, 2011, 10:16 PM
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For many old 72Mhz radios, the output power actually does go down as the Tx battery
voltage falls. For 2.4Ghz radios and modules, they're all regulated down to 3.3V or 5V
internally so they'll handle any Tx battery voltage above that.

I am perfectly comfortable flying my Tx battery down to the alarm. On the 9C that's
about 8.8V, which is still 1.1V per cell, which is fine for a NiMH cell with a 1.2V nominal voltage.
I'm always mystified when people think that reaching the nominal voltage
(9.6V for Tx, or 4.8-6 for 4-5 cell Rx pack) is when they should recharge.
It's called the "nominal voltage" because it's the average for the entire
normal discharge curve. The flat part of the curve is nominal and most of
the juice is there.

ian
Good to know. What you said about the older 72Mhz stuff is what I experienced before. Didn't know if it was the same thing with Spektrum/2.4Ghz type stuff and that's why I asked. I also love the fact that the battery lasts so much longer than 72Mhz TX's. Flying down to the alarm would be a LONG time before having to recharge, in comparison. I had to charge my old equipment every time before I went flying...or at least every weekend.
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Old Sep 15, 2011, 10:21 PM
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I normally recharge at 10 volts or so (just so I know I have lots in the battery), but I would have no hesitation flying down to 9.6. After that I'd be a bit cautious, as by the time to alarm goes off, you may not have a lot more time to land.

But I use a 2000 mAh Eneloop pack and all of this is a bit academic as it runs forever. The only time I've seen it around 9.6 was when I left it on all night -- it was still going in the morning.

Just to confirm, the transmitter gives full range at any voltage down to the alarm (and below).
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Old Sep 15, 2011, 10:28 PM
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But I use a 2000 mAh Eneloop pack and all of this is a bit academic as it runs forever. The only time I've seen it around 9.6 was when I left it on all night -- it was still going in the morning.
I've been thinking HARD about this modification. I love Sanyo Eneloops and use them in everything that takes AAs, so I have plenty around. I also like the fact that you can charge them right in the TX, unlike a lipo TX battery.

Did you use the 8 cell battery holder from Radio Shack? Any problems with it or the cells not actually being "hard connected" to each other? I read some horror stories where the springs in a TX with removable/replaceable batteries weren't strong enough to push the batteries together and make a good contact, both with Eneloops and regular alkaline disposable AAs...
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Old Sep 16, 2011, 09:33 AM
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Originally Posted by mhunter View Post
I've been thinking HARD about this modification. I love Sanyo Eneloops and use them in everything that takes AAs, so I have plenty around. I also like the fact that you can charge them right in the TX, unlike a lipo TX battery.

Did you use the 8 cell battery holder from Radio Shack? Any problems with it or the cells not actually being "hard connected" to each other? I read some horror stories where the springs in a TX with removable/replaceable batteries weren't strong enough to push the batteries together and make a good contact, both with Eneloops and regular alkaline disposable AAs...
DO NOT use those battery holder deals with the spring wire contacts...

There are a number of vendors who'll sell you an Eneloop tx pack for whatever radio you have and most of those will have welded tabs and an appropriate connector.

That includes the little 4 cell pack for a DX8....

Been running Eneloops in my 12X basically since I've had it and the DX8 I bought for a backup/trainer got an Eneloop pack too....
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Old Sep 16, 2011, 10:02 AM
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Would you happen to have a link to a reliable vendor with a reasonable price?

Edited to add: Just ordered one for $50 with shipping and Spektrum connector installed. Hope that's a decent price.
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Old Sep 16, 2011, 10:50 AM
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Would you happen to have a link to a reliable vendor with a reasonable price?

Edited to add: Just ordered one for $50 with shipping and Spektrum connector installed. Hope that's a decent price.
I got mine from
http://www.hangtimes.com/nobsbatteries.html
It's very nicely put together.

The website shows $45. I think by the time I paid shipping it was close to $50.

I also have Eneloops in a holder in a transmitter I use on the bench, and a homemade soldered pack in a spare Tx. Finally, I made up a pack from RayoVac Hybrid cells for a Tx used as a buddy box. It's still going strong after 6 months of occasional use but no charging.
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Old Sep 16, 2011, 10:53 AM
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I got mine from
http://www.hangtimes.com/nobsbatteries.html
It's very nicely put together.

The website shows $45. I think by the time I paid shipping it was close to $50.
Good, so I didn't really overpay. Mine was $51.95 from Batteries America with shipping and connector, according to the confirmation email. $7.95 for regular mail was kind of steep, though. Oh well, at least I didn't have to pay the 9+% AZ sales tax.
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Old Sep 16, 2011, 12:06 PM
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2SLiPo $7

http://www.dealextreme.com/p/trustfi...s-2-pack-19770

Hey, you rich guys. Why spend $50 when $7 2SLiPo can do the job.

2SLiPo 7.4V is perfect substitution for the latest 2.4 TX which uses 6 AA cells 7.2V.

Some 2.4 TX which come with 9.6V battery also work fine with 2SLiPo. I experimented and confirmed success with Turnigy 9X, Airtronics RDS 2.4, Futaga 9C with 2.4 module. Other TX such as Futaba 8U, JR 8103, 2.4 RF module works but program window displays are disrupted by "LOW BATTERY" warning.

2.4 RF works on 3 - 5V regulated voltage. Any voltage above will work.
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Last edited by John Kim; Sep 16, 2011 at 12:17 PM.
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Old Sep 16, 2011, 12:35 PM
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I don't like lipos in my TX. 'Nuff said.
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