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

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.

[suicideneil]

If it says 'intellegent charger' anywhere, then it should shut down once the batts are fully charged, or switch to trickle charging mode- I might find a speky wallwart charger that just plugs into the socket on the side of my speky radio, so I can charge them in-situe.

[skellyo]

FYI to the folks who got in on the group buy...I just got an e-mail that the order has shipped to me. I expect it to be at my house by Thursday or Friday this week.

[skellyo]

All of the AA's were sent out today except hippie's. His package is going out tomorrow as his box was the only one too big to fit in my mailbox!

BTW Jerry, got the MO today, thanks!

[JERRY2KONE]

Originally Posted by skellyo

All of the AA's were sent out today except hippie's. His package is going out tomorrow as his box was the only one too big to fit in my mailbox!

BTW Jerry, got the MO today, thanks!

No problem Kelly. I am just happy that you were willing to get this order going so we can all have a shot at using these cells for our needs. Thank you very much for your support and efforts in making this happen. Nice to know that there are still some guys out here who have integrity and are willing to do the right thing for fellow hobbiests. Nice doing business with you Sir.

[rchippie]

Originally Posted by JERRY2KONE

No problem Kelly. I am just happy that you were willing to get this order going so we can all have a shot at using these cells for our needs. Thank you very much for your support and efforts in making this happen. Nice to know that there are still some guys out here who have integrity and are willing to do the right thing for fellow hobbiests. Nice doing business with you Sir.

Kelly is his last name . His first name is SEAN.

[JERRY2KONE]

Originally Posted by rchippie

Kelly is his last name . His first name is SEAN.

And your point is? Reitired US Navy and after 20+ years of using only last names I am too old to start changing my ways now. I'm sure he knew it was meant for him. You do some time serving our Country and then come talk to me about something so trivial. I doubt that he was offended. I know I know I should learn that I am a civilian now. BUT actually now I am a Federal Agent and the same protocal still applies to my every day life.

[rchippie]

Originally Posted by JERRY2KONE

And your point is? Reitired US Navy and after 20+ years of using only last names I am too old to start changing my ways now. I'm sure he knew it was meant for him. You do some time serving our Country and then come talk to me about something so trivial. I doubt that he was offended. I know I know I should learn that I am a civilian now. BUT actually now I am a Federal Agent and the same protocal still applies to my every day life.

BLAH BLAH BLAH Sean is not smart enough to be offended .

[skellyo]

Originally Posted by JERRY2KONE

And your point is? Reitired US Navy and after 20+ years of using only last names I am too old to start changing my ways now. I'm sure he knew it was meant for him. You do some time serving our Country and then come talk to me about something so trivial. I doubt that he was offended. I know I know I should learn that I am a civilian now. BUT actually now I am a Federal Agent and the same protocal still applies to my every day life.

Not offended by it at all. There's actually a lot of us that call each other by our last names at work and refer to a lot of others that way as well. We have a lot of ex-military where I work and deal with the military quite often...especially since they're our customer.

[skellyo]

Originally Posted by rchippie

Kelly is his last name . His first name is SEAN.

Originally Posted by rchippie

BLAH BLAH BLAH

I'm cool with him calling me by my first or last name, but my middle name is off limits. That's reserved solely for use in my whole name when I'm in trouble with the wife.

[BrianG]

Cool! They're on their way. I guess I'm gonna have to finish my homemade charger then. Did some tweaks to the schematic posted a while back, and ordered the necessary components. The biggest problem is finding the proper enclosure. Unfortunately, finding one that is the perfect size seems to be impossible; they are either too big, or too small, or the wrong dimensions (wasted space).