Turnigy Low Self-Discharge (LSD) NiMH AA's

[BrianG]

A couple weeks ago, I picked up 5 of the Turnigy low self-discharge 2200mAh AA cells from my LHS. I really couldn't come up with an ideal LVC solution to use lipo in my DX3r radio, and didn't want to deal with balancing a lipo inside a radio anyway, so I figured I'd give these LSD AA cells a try.

Fresh out of the package, they read ~1.25v each. I used them for about 3 hours total and the total voltage fell only 0.1v over that whole time, which included actual runtime and storage. Normally, after a couple weeks, regular NiMHs would drop down around 0.5v just sitting on my shelf, let alone actually using them.

So, tonight, I decided to discharge them all the way and recharge them to see how much charge they take. Discharging took 470mAh out of the cells before they hit 0.9v/cell on my discharger at 0.5A. From previous experimenting, the DX3r pulls 127mA, so if I ran for 3 hours plus the amount taken out via the discharger, means they came out of the package at ~40% charge. A full charge at 0.3A (3mv delta peak) brought them up to 1.46v/cell, taking a total charge of 2323mAh.

I felt that 5 cells at 1.46v/cell is a tad high (7.3v total) to use in the DX3r, so I bled 100mAh out of them, which brought the voltage down to 6.9v (1.38v/cell), which is what my regular NiMHs came out of the charger at. Instead of doing this rather tedious charge-and-bleed process to keep them at a decent voltage, I think I'm going to go back to using 4 AA cells in the DX3r again. These cells hold more than their rated 1.2v/cell until near the end of their cycle, so I'll set the radio voltage alarm for 4.7v.

In short, these cells do what they say; they exhibit VERY little self-discharge, and charge up to more than their rated capacity. For people not wanting to deal with lipo in their radios, yet still want a fairly flat discharge curve and low self-discharge, these cells fit the bill nicely. Only time will tell about their longevity, but their cost is comparable to regular NiMh AAs, so even if they do have a short cycle life (no data to support this anywhere I've seen), it's no big loss.

[marzac2]

I got them for my DX3R when they came out and I also have had very good results so far.

[nitrostarter]

I use them in my Tactic 2.4ghz radios. The work excellent and are suprising how long they last without much drain!

I suppose the only way to charge them is to leave them in the TX and charge thru the TX port?

[nitrostarter]

I use a one of these. I put a Rx connector on this and then just charged them at 1 amp.

[BrianG]

I rewired the stock radio jack and charge through that. These cells don't seem to like much more than 0.5A charge rate though; the voltage jumps too high for my liking. I figure 0.3A (~0.1C) is a good rate even though it does take around 7.5 hours. But these shouldn't need to be charged as often. The Spektrum draws 127mA, which means these 2200mAh cells should run it for around 17 hours.

[wallot]

Been using 2700mah Sanyos in my dx3r for 2 years now. they last forever with minimum self discharge. when they die will try turnigys

[Lauri]

Sorry to go a bit offtopic but why were you trying 5-cell NiMH for DX3R?

[BrianG]

Because 4 cell Alkalines is 6v, the same as 5 NiMH AA's...

[Lauri]

Do you know if the DX3R has regulatad voltage for the RF part? Do you get more transmitting power if you have higher supply voltage, like the case is with "old" MHz frequency transmitters?

[BrianG]

From another thread:

A little bored and no projects I can work on (or should I say, have no money to work on), I started thinking of the "ideal" lipo solution for the DX3r. But before I can do anything, I need to get some data first. So, I hooked up my home-made adjustable power supply to the DX3r's battery terminals and fired her up.

I found that the radio will power up at 2.6v, but does not transmit. Current draw during this time is ~70mA. Once the voltage gets to 3.1v, current jumps to 127mA and starts transmitting. What I thought was interesting is that the current stays at 127mA all the way up to 6.5v, at which time I did not want to go any higher.

What does this mean? Well, I suspect any voltage above 3.1v does not increase transmitter range. You may say "But as the voltage goes up, the power goes up even though current stays the same, so the range has to be better with higher voltage". The first part is correct, but not so sure about the range assumption. Why? Because I highly doubt there is circuitry in there that is designed to draw X current no matter the voltage. Just doesn't make sense.

There isn't a switching regulator because as voltage goes up, current would go down.

The only logical explanation (to me) is that there is a linear voltage regulator inside set to around 3v. So no matter how high the voltage gets, the extra is being burned off as heat, but since current is only 127mA, that heat is minimal. So, I really think anything above 4 AA cells is just a waste. Kinda makes my 5-cell mod a little pointless. Unfortunately, testing the range is a bit cumbersome since I'd have to have someone hold a vehicle at various distances to test. Maybe someday.

Another interesting thing I found is that the volt meter on the radio isn't accurate. The display read a constant 3.3v when I applied 2.6v up to 3.4v. After that, the display reads 0.2v lower than reality. Hmm, I wonder if that's the v drop of a germanium diode?

Anyway, just thought I'd share my findings...

Anybody using Energizer lithium AAs? I've measured voltage as high as 1.82v on those?? I was surprised - I bought a bunch of them, they seem to last forever in txs and lots seem to be using them for rtr radios instead of fooling with rechargeables.

They're advertised as a 1.5v AA but the 100 I bought have all been much higher than that.

[marzac2]

Those energizers are sooo expensive retail.

And with the LSD's, there isn't much "fooling around" anymore.

Guy on RCTechwas selling them brand new for 50cents/ea - all you wanted. Reason I bought 100.

Can I check if using the 4 x AA cells holder and charging it, how do I set the charger to charge them?