I was thinking of going to LIPO instead of NIMH to get longer xmtr battery time but the cost of a LIPO is huge compared to NIMH's so I though I would just build a 5 cell NIMH 2200mah NIMH pack to replace my 4.8 in my DX7S. Since the DX7S can run on either 4.8 or 7.4 is there a problem adding one more NIMH battery to my 4.8 pack or just bite the bullet and by a LIPO 7.4. Any advice greatly appreciated. Thanks

If you plan on keeping you DX7S for a while, I'd go with Eneloops. Most people in this section of the forum will likely recommend Eneloops over LiPos for use in TXs that are designed to take loose AA cells or packs made of AA cells.

I'm not familiar enough with the DX7S to advise you on the specifics.

@Wrend - Thanks. Since my DX7S can take more than 4.8v can I run 5 cells instead of 4?

You can try something like this.

http://www.hobbyking.com/hobbyking/s...dproduct=17955

The voltage seems a little high, being a 3S LiFePO4. 2S would probably be better, if you go with a LiFePO4 pack. 5S NiMH (such as Eneloops) would probably work as long as they fit.

But again, I'm not sure of the specifics of the DX7s.

@tenspeed - HK makes a lipo for my DX7S but on backorder.

Here's a 2S Lipo that is specific to the DX8 and DX7s.
http://www.valuehobby.com/power-syst.../dx8-lipo.html
One thing to keep in mind with using a generic Lipo such as this one, is that there is no balance circuit built into the battery. While you certainly could use the built in charging system with the radio set to Lipo, the battery won't be balance charged. If you have a good lipo balance charger and have an adapter board for the JST-HX balance tap, you're good to go.
Also, the generic battery does not have a low voltage cutoff, so if you leave the radio on in your carrying case and don't hear the inactivity alarm and low voltage warning, you could kill the lipo, but at 13 bucks, that's not a biggie. And no, running a lipo flat under low current draw is not a safety hazard. That's how we safely dispose of damaged ones. The Spektrum lipo battery does have a low voltage cutoff in the pack, I guess with a pack that goes for 70 bucks you would want that. Somehow having a cheap circuit in the battery that cuts the power to the radio when it thinks the voltage is too low, does not give me a warm fuzzy feeling
I use the 2500mAh Gforce for the Futaba 8FG, at 1/3rd the price of a replacement Nimh pack it's hard to beat. I just open the battery compartment to access the balance tap to charge with an FMA Cellpro charger. The 8FG has user settable low voltage warning, so you can set a warning level for Nimh, Life and Lipo, also the radio does have an auto shutdown at 5.5V that will keep the lipo from being damaged if you do leave it on unattended for too long.
Pete

Thanks Pete. How much longer xmtr time have you experienced

I get about 10 hours with the 2500mAh battery leaving about 20% capacity. Not too shabby.
Pete

Originally Posted by bimmerland

@tenspeed - HK makes a lipo for my DX7S but on backorder.

I thought you were talking about the DX7, not 7S. When I see the "S" after the DX7 I think plural. I probably will adjust my thinking sooner or later. The more I learn about the 7S the more I learn the differences, rather then the similarites to the DX7.

So can I get the same run time with 5 1.2 nimh 2500mah batteries?

OK... Need to start over...

check this http://www.spektrumrc.com/Products/D...D=SPMB4000LPTX

Please check my new post.

http://www.rcgroups.com/forums/showthread.php?t=1639234

thanks