Home Brew Duraloop Tx Battery

[gareth.ky]

I just had my day of flying wrecked for the last time by my Tx battery. I went out to the garage and found the Tx was at 6.0v and would shut off instantly. It was fully charged about a month ago (I had the flu and haven't felt like flying) and self discharged over that time. I was pissed and determined to make this the last time. Lipos or A123's were gonna go in this thing. So I started surfing around.

I ran across this thread that talked about the Sanyo Eneloop cells. Its a new type of Low Self Discharge (LSD) NiMh. For the particular task of powering existing transmitters these cells have a bunch of advantages.

• They have a dramatically lower self discharge rate that regualr NiMh cells. This is the big one for me.
• They don't go dead at low temperatures like Lipos and lions can.
• They come in a higher capacity (2000mah) than the stock 9303 Tx battery.
• The voltage is the same as standard NiMh. No diodes needed. No warranties voided.
• There is no danger of them exploding if you leave your Tx on buy accident like a lipo might.
• They are standard AA size so they fit in the Tx case unlike most lipos and all current A123 cells.

And now the disclaimer: I'm not going to put on a a battery building clinic. If you can't competently assemble these cells into a pack you put yourself and others at risk. One bad solder joint and the Tx could shut down in flight. Buy a pre-assembled pack instead. There I said it.

Now I'm curious by nature, I void warranties for breakfast and I have made hundreds of good solder joints and a few bad ones. So I set out to fix the problem and build a pack...

A search for Eneloop cells turned up Amazon. Only the now defunct Circuit City was mentioned as a major common retail source. Now Sanyo ships a LOT of batteries, they are in everything, so they must be selling them at retail somehow. Sure enough, a very helpful hobbyist has attached this pic and a note to the Eneloop 4 pack on Amazon:

"There are two versions of Duracell Pre Charged AA/AAA cells. The made-in-Japan version is identical to the Sanyo eneloop. The made-in-China one is identical to the Rayovac Hybrid. The Kodak Pre-Charged is different from the others."

Ya Rly! It looks like Duracell is having Sanyo manufacture the cells for them. The trouble is they are also having a Chinese company make similar but inferior cells, the one in the pic with the black top. There are also some 2650mah cells that are "Duracell Pre Charged" that are cheaper than these. Don't get fooled. Only the white top, made in Japan cells are real Sanyo Eneloops. I'm basing this on numerous discussions over on Candle Power Forums. They refer to them as "Duraloops".

So if you can pop in to your local Duracell retailer you should be in business. A few miles and 3 stores later I had the batteries in hand. Walmart only had the Chinese version with the black top, go figure . Walgreens had both kinds, but only one of each . Target had a whole bunch so check them first.

Here is the pack I made:

It's assembled in the same manner as the stock JR pack. All cells have a solder joint between them. I used solder wick/copper braid for the joints where the cells but up against each other and some scrap servo wire for the ends. I included dual leads, one has the tiny JR plug that connects to the radio. The other is a mini Deans to allow for fast charging at the field. The cables are CA glued to the heat shrink for strain relief. I estimate you could do a DIY pack like this for about $30 (+ tax or shipping) including the heat shrink and deans connector.

The stock pack include this mysterious device connected in series with the batteries:

I cant find any of those numbers on the web so I don't know its specs. I do think I know what it is. It's glued to the cells in the original pack. When you blast it with a heat gun it breaks the circuit. A thermal cutoff device. I assume its there to stop bad chargers from frying the pack. Since I will be using my Hyperion to charge this pack now I left the cutoff out.

Right now its in my Tx showing 10.5v and holding steady.

[DyrtyByrd]

thanks for the info i did find some duraloops at walmart @ 12.99 for a four pack and have intalled them in my Dx 6i so no need to assemble a pack as these only take four cells havnt got a chance to test them yet but well see also i was wonderin if it would be ok to charge them with the tx charger or would it be better to take them out and charge?

[gareth.ky]

The Spektrum/JR wall wart chargers that i have seen don't shut off automatically when the pack is charged. Over charging is one of the things that shortens the life of NiMh batteries. Over the long run you would be better to use a charger that does shut off.

I got an Aurora 9 and it's charger shuts off when the pack is charged. If your charger works like that then I would just use that to charge them.

[Hinckley Bill]

I use the Duracell charger for NiMh batteries to charge my rechargeables....................shut off is automatic so no worries.

[Boogie]

I've been using those eneloops for about 1,5 years and will never think about coming back to other producers- self discharge nearly doesn't exist!!

[Jezmo]

I've also been using the Sanyo Eneloops for about a year and a half. Great cells.