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

Sorry, been busy, didn't get by yesterday -

#1 hippie 20 cells
#2 brian g 30 cells
#3 JERRY 30 CELLS
#4 Duster_360 - 30cells


Thanks Sean!

[skellyo]

Originally Posted by Duster_360

#1 hippie 20 cells
#2 brian g 30 cells
#3 JERRY 30 CELLS
#4 Duster_360 - 30cells

10 cells still available. I can let an additional 2 cells go from my allocation if someone needs 12 though. Just let me know.

[simplechamp]

I'll take the other 10

[BrianG]

Cool, hopefully everyone is happy with these cells. The 5 I got are still working well for me. Just remember: charge at ~0.3A for best results. 0.5A would be the very max I'd charge at if you're in a hurry.

[BrianG]

The next thing I am going to do is make a charger for these. Yeah, you can use your R/C charger, but I am also going to want something smaller for trips and such. I've already drawn up a circuit which uses a constant current charge (0.3A) with temperature peak detection. It will charge two cells at a time, but the circuit is simple enough that making banks of two to get 4, 6, 8, etc will be easy enough. Power requirements will be ~6vdc and ~0.35A for each bank of two cells. So, charging 4 cells at once will require 6v @ 0.7A, which cheap "wall warts" can supply.

[suicideneil]

Dammit man, you said you were working on my Delorean....

Would it be okay to charge these kinda things ( I bought some Energizer AAs only a month ago, shame.. ) in a little rx pack-type cell holder, then connect it to an r/c charger? I have a couple old normal wall chargers, but I dont know the current output as the labels are long worn off- a low current in the sub 0.5amp range wouldnt melt the contacts or wires I imagine...?

[BrianG]

I accidentally sent the Delorean into the future without a passenger so I have no way to get it back. Sorry.

Anything 1A or less is fine in a holder like that. Just be aware that the higher current you charge, the higher the charger voltage will read because it has to overcome some voltage drop across the small wires and not-so-good contacts.

[Metallover]

I figure I am ordering too small a number of batteries to get in on this. Count me out of the group buy.. I will definately get some with me next order tho!

I charged the batts today and they got very hot. They melted the 1st 4 cell holder. I changed the holder to a new one. Hopefully it doens't melt this one as well. I set my charger to 0.3A. Should I set the final voltage to read 4.8v? Or let it charge to over 5v? I'm using it for DX3S on 4 AAs.

[BrianG]

What did you have your delta peak set to? I set mine to the lowest value on my charger (3mV per cell IIRC) and it works fine.

The charger I am designing uses thermal peak detection so once the cell gets to X*F, it shuts off. I feel this is a better method to detect when full charge is reached without relying on an unknown delta peak value that works well with these cells.

The Delta Peak is set on 3mV.

[BrianG]

OK, I hunted around the net a little bit for a simple proper 2-cell NiMH charger for these cells, and the best I could find was some USB-powered charger. It should work, but didn't like the fact that the reset function was not the best. So, I created my own circuit. I just breadboarded it and it looks like it works very well. Here's the schematic:



Although a bit unusual at first glance, it's pretty simple really, and was done from parts I had in my bins. The basic charge circuit consists of:
- R1: 6 ohm resistor rated for 1W or more
- Q1: TIP127 darlington PNP transistor. Should be on a small heatsink.
- R4: 100 ohm 1/4w resistor
- D1-D4: 1N4001 diodes

The diodes and R4 set up the biasing for the transistor in constant-current mode. R1 sets the charge current. With a R1 value of 6 ohms, the charge current is ~280mA. Two series NiMH cells are connected where stated.

The thermal peak detection portion of the circuit consists of:
- U1: Any general purpose SCR (or triac or thyristor).
- R3: Resistor to limit gate current
- R2: Resistor that along with the thermistor, provides a voltage divider.
- R5: Thermistor

Operation is pretty simple. The thermistor is physically placed in contact with the batteries. As the batteries heat up (signaling the end of their charge), the thermistor resistance drops. This causes more voltage to appear at the SCR gate until it turns on. When this happens, it essentially "shorts out" the biasing diodes D1-D4, and shuts off the charging transistor. The neat thing about SCRs is that once they are activated, they latch that way. So, even when the thermistor (batteries) cools off, the charger will not reactivate. You reset the circuit simply by removing power via a switch.

The thermistor is the one for my Eagletree logger, and the SCR used was not "ideal" (rated for 600v and something like 500A , but it's all I had). So I didn't list the actual values for R2, R3, and R5 since the real values would be quite different.

A regulated 6v, 0.5A power supply was used because a non-regulated supply would effect the voltage divider (R2 & R5). At that voltage, two NiMH cells can be charged at once. If you want to charge more cells, simply use two circuits at the same time in one enclosure. You can design it so that the supply is higher (like 12v) for charging 4 cells at once, but then you have to charge 4 cells at once all the time. Many devices use 2 cells, so I figured this would be more useful. Besides, 6v is a good value to use to keep power dissipation on the CC transistor low (~0.4w worst case).

In a few days, I'm gonna place an order for the proper components (SCR and thermistor mostly) so I can make an actual unit I can use on trips.

Can I use the Sanyo Eneloop charger to charge my Turnigy?

[BrianG]

Depends on how it works. If it's a true delta-peak or thermal-controlled charger, then yes. If it's just a timed charger, or simply charges on a power supply via a resistor, then those aren't the best because you can overcharge or undercharge.

The Eneloop charger for the Eneloop batteries shuts down and stops charging once the batteries are fully charged, presumably.