charging D NiMH at <.33C, & on C9000

[Rexlion]

Here's something I've been wondering. I saw my issue raised in some old threads, but saw no answers to it.

What about charging hi-capacity D cells? I have some 12,000 mAH ones. Fastest charge rate on most chargers is 2000 mA (many are less than that). That's .17C. Isn't this less than ideal for a NiMH? Won't it be somewhat harmful to the cell in the long run? Why don't the charger mfrs make universal chargers that put out 4000 mA or more? Doesn't the slow charge rate make end-of-charge detection problematic on these big cells?

Which leads me to my next thought. I just ordered a c9000 and was thinking I'd rig some leads so I can charge a few D cells with it. I figured I'd set it for 2000 mA. But I read one thread where someone was concerned about excessive heat with this setup and was keeping their c9000 set to 1500 mA. Would it be problematic if I use this unit with D cells at 2000 mA? Since the c9000 was not designed for C or D cells, will its termination algorithm do a decent job with them considering the .17C (or lower) charge rate?

 

[SilverFox]

Hello Rexlion,

Many D cells have been damaged by missed terminations. D cells actually have lower internal resistance than AA cells, so they are capable of being charged at higher rates.

If you look through some data sheets for high capacity D cells (those with more than 2500 mAh of capacity... ) you will find that the manufacturers recommend charging at 0.1C for 16 hours, or a fast charge that is very close to 2 amps, or higher. The higher quality chargers (like the C-808M) charge D cells at 2 amps, so there shouldn't be a problem. However, it is always best to keep an eye on things because "things can happen..."

The C-9000 is capable of doing a Break-In charge on D cells, provided you figure out a way to connect the D cell to the charger. This will charge the cells at 0.1C. You can also charge at 2 amps, but the C-9000 has a time limit that is set to around 4500 mAh. With a true 12000 mAh cell, you would have to reset the charger by unplugging it and plugging it back in a few times to get a full charge.

The electronics of the C-9000 do warm up while charging at 2000 mA, but since the D cells are removed from the charger, this heat will not be transferred to the cells, so there is no problem as long as you provide free airflow to the charger. Charging AA cells at 2 amps can cause the heat from the charger to heat the cells, and this can be an issue with AA cells that have higher internal resistance.

The comforting thought is that the C-9000 uses components that are capable of charging all day at 2000 mA without melting down...

Tom

 

[Black Rose]

Rexlion,

This is how I charge C & D cells with my C9000:

Those cells are 3000 mAh capacity cells. I charge them at 1500 mA.
The charger behind the C9000 is a C800S (AA & AAA only).

 

[rmteo]

Here's how I charge my 10000mAH cells:

The reason I use a 3.6A charge current is twofold. One is that it equates to 1mAH per second and the second reason is that any higher and the springs/contacts on these cheap battery holders get melty hot. It takes about 3 hours to charge from empty. BTW, all 8 Powerizer cells I have are just above 10000mAH in capacity.

 

[Rexlion]

Here's how I charge my 10000mAH cells:

The reason I use a 3.6A charge current is twofold. One is that it equates to 1mAH per second and the second reason is that any higher and the springs/contacts on these cheap battery holders get melty hot. It takes about 3 hours to charge from empty. BTW, all 8 Powerizer cells I have are just above 10000mAH in capacity.

You would have to show me that, wouldn't you!? Great, just what I need, another charger to drool over. :laughing: And it does 'em all, too! Gee, bet I could even charge the 12v battery in the trailer with that thing!

But hey... you're charging NiMH cells at 3.03V. Is that because you have them in series?

3.5A seems pretty good. I still am wondering if anyone knows why the makers of NiMH chargers don't jack up the amps for the C and D cells.

 

[rmteo]

Yes, it will charge just about any type of battery (LiIon, LiPo, LiFePO4, NiCD, NiMH) as well as Lead Acid types from 4-40V. At $34, you won't beat it for value.

These battery holders take 2 D cells in series. The only D cell devices I have all take 2 cells so I use (and charge) the cells in series pairs.

Most consumer chargers have built-in DC supplies and higher currents would mean larger and more expensive chargers. The charger shown needs an external 10-18V DC supply (with appropriate current capacity) - they are great for operating from 12V vehicle supplies. I have a 110/220 AC power supply that outputs 12V at up to 35A and is what I use to power these chargers.

 

[Black Rose]

I still am wondering if anyone knows why the makers of NiMH chargers don't jack up the amps for the C and D cells.

I would guess the main reason is that the ultra high capacity cells are more specialty cells as opposed to the 2500 - 3000 mAh ones you can get at B&M stores.

For example, putting 3.6A into the 3000 mAh C & D cells I have is more than 1C and would be too much for them.
But for rmteo's Powerizer cells, that's around that magical .33C charge rate for NiMh.

 

[45/70]

I still am wondering if anyone knows why the makers of NiMH chargers don't jack up the amps for the C and D cells.

I think it probably has to do with cost. I'd rather imagine that a charger that output 10-12 Amps per channel, and was big enough to avoid heat problems, would carry a pretty hefty price tag that most consumers wouldn't want to pay. Now that I think about it though, a lot of D NiMH cells are limited to about a 0.3C max charge rate, my Powerizer D's are anyway. Still, it'd have to cost quite a bit more.

Dave

 

[Rexlion]

I think it probably has to do with cost. I'd rather imagine that a charger that output 10-12 Amps per channel, and was big enough to avoid heat problems, would carry a pretty hefty price tag that most consumers wouldn't want to pay. Now that I think about it though, a lot of D NiMH cells are limited to about a 0.3C max charge rate, my Powerizer D's are anyway. Still, it'd have to cost quite a bit more.

Dave

I just read that Powerizer data sheet you linked to. Wow. A 10 AH cell, and they call for standard charge .1C and quick charge .3C. I'm surprised at how low that is. But hey, they make the cells.

 

[Rexlion]

... but the C-9000 has a time limit that is set to around 4500 mAh. With a true 12000 mAh cell, you would have to reset the charger by unplugging it and plugging it back in a few times to get a full charge...
Tom

Tom, thanks for chiming in. Where did you find this info? I've read as much as I could find on the C9000 and all I saw about timed charging was the topoff charge at the end. I was thinking it would keep going until it detected signs of a full cell.

 

[T0RN4D0]

Low charging current isn't really a problem for the cells, it only becomes a problem when the charger fails to terminate charging.

 

[SilverFox]

Hello Rexlion,

There is a thread in this section on the improved C-9000, and a review in the reviews thread. I believe you can find a lot of information on just how that charger works by reading both of those threads.

Tom