NiCD charging using a bench power supply...

Hi,

For single cells I can use some jumpers to connect them to the C9000, but I've got a couple of battery packs of multiple NiCD's and no charger for them. What I do have is a bench power supply with constant voltage/constant current limits that I can use to charge with and I'm often sitting right next to this so I can keep an eye on it.

Obviously I can set a charge limit of 0.1C per cell for NiCD and leave for the recommended 14-16 hours, but can I charge faster by doing something like this:

Decide what the max voltage per cell is fully charged (1.54V ?).
Set Voltage Limit to 1.54 * cells.
Set Current Limit to 1C.
Connect pack.

This should let it charge at up to 1C, but as it approaches the fully charged voltage per cell, the current should drop to 0.

Will this work? Is there a better way?

(Obviously this assumes that all cells are at the same state of charge)

Thanks,

Alan

Get a hobby charger and place between your bench supply and the batteries.
They are not that expensive and will reduce the risk of mishaps.

If you don't immediately have a hobby charger, temperature is a useful variable to control with. Insert a temperature probe inside the pack and monitor it carefully. Set the current limit to 1C, don't apply a voltage limit (use excess voltage), then charge until you notice a steep uptick in the pack temperature. As a backstop, cease charging after 110% of the calculated time in case you don't observe the temperature response by then.

Incidentally, many hobby chargers come with a temperature probe and make use of this automatically to control the charging.

The best way to charge packs of NiMH is to use a charger designed for them. Maha makes a nice one:

MH-C777PLUS-II Universal LCD Charger / Analyzer / Conditioner

While hobby chargers are popular, they aren't the cat's meow as far as I am concerned, and good ones are rather costly and really do require that you know what you are doing.

Otherwise, I would go with using the 1/10 C and a timer with your power supply. Your supply may have c and v limits, but it is NOT a charger and will not function correctly for such use. Don't forget that NiMH batteries drop slightly in voltage when they reach full charge, then they start to generate heat rather than charge further.

Regards

Christian

kaptain_zero said:

The best way to charge packs of NiMH is to use a charger designed for them.

Click to expand...

That is exactly what a hobby charger is and the above MAHA is what is usual called a hobby charger.

On a hobby charger you select chemistry (NiMH/LiIon), battery capacity/charge current and number of batteries in series. Then it will charge the pack. With LiIon packs you also has a balancing connection that secures that each battery get exactly fully charge.

I have used my bench supply as follows: I charge at a constant current high enough to generate a decent negative delta V, usually at least 0.5C. Then, since you are sitting there and observing the voltage, just stop when the voltage starts to go down. This occurs a little over 1.5V per cell for my NiCd packs.

Just to clarify, the Maha 777 is a universal NiMH pack charger (it will not charge a single cell alone). It does NOT charge liIon cells, nor balance them. It does however work in a similar fashion to the Maha 9000 charger, only it is meant for *packs* of MiMH, including hand held communication radio packs where the charger can be configured to connect to the contacts of a proprietary battery pack used on such radios. It can discharge, recharge and analyze such NiMH packs and generally bring such packs back into balance using a low rate trickle charge following a normal fast charge.

Hobby chargers are do everything chargers, designed primarily for electrically powered remote control planes, helicopters, cars etc. that use a variety of battery packs made from different chemistry's Lipo appears to be the most common in Hobby use as far as I know, but I am not an expert on such.

The 777 will read the pack voltage and adjust it's charging voltage to suit... you do not need to tell it if you have 3, 5 or 7 cells etc. in a pack. I have the older model C777 without the LCD display and it has been a solid performer. I frequently use it for maintaining my power tool battery packs, letting my cycle them to keep them in top shape. The original poster was looking for a suitable way of charging *packs* of NiMH cells.... I thought it only appropriate that I point out that a suitable charger exists for exactly that sort of thing and is readily available, and is simple to use.

Regards

Christian

alank2, you can do as Mr H suggested. The way I used to charge NiMH packs with a bench PS, was to charge them at about 0.5C and check the temperature with my hand, frequently. When the pack first started to get warm, I'd drop the current to 0.1C, or below, and top them off for an hour or so.

kaptain_zero said:

The best way to charge packs of NiMH is to use a charger designed for them. Maha makes a nice one

Click to expand...

Unfortunately the 777 series chargers (which as I recall, aren't even made by Maha) don't have a very good reputation. I burned up a good many camcorder and handheld transceiver packs with the non plus version, myself. You were never quite sure what was up with it. From what I've heard, the plus versions aren't any better. I'd take an inexpensive hobby charger over the 777's any day.

Dave

Hello Alan,

I would also recommend getting a hobby charger... but...

If I were going to use a bench power supply to charge a NiCd pack I would set the voltage to 1.5 volts per cell and limit the maximum current to 2C. Your cells may not end up fully charged, but they should be close.

Monitoring temperature can be informative, as others have mentioned.

After charging you can balance the pack by increasing the maximum voltage to 2 volts per cell, and limiting the current to 0.1C. The pack should only be balanced like this for a couple of hours, and only needs to be done every 10, or so, charge/discharge cycles.

This is not the best set up, but it will get you by, for awhile.

Tom

I have a 10 cell NiCd pack for my drill that I thought was dead. I brought it back with a few charge/discharge cycles, using my bench supply to charge and a 12V car tail light bulb to discharge. I used 0.1C to trickle charge after reaching negative delta V in order to balance the pack.

I consider my bench supply as a complement to a hobby charger. Buy a cheapo charger for your NiCd packs. They are worth not having to keep track of the voltages involved with the bench supply. Buy a charger without a dc source (it is cheaper), since you can use your bench supply to power the charger.

kaptain_zero said:

Just to clarify, the Maha 777 is a universal NiMH pack charger (it will not charge a single cell alone). It does NOT charge liIon cells

Click to expand...

Then these specification are wrong (The are from Maha's website)?

Supports Lithium Ion, Lithium Polymer, NiMH, and NiCD battery chemistries.

Supports a wide voltage range of 1.2V to 14.4V (1 to 12 cells) for NiMH & NiCD, and 3.6V to 14.4V (1 to 4 cells) for Lithium Ion.

Click to expand...

HKJ said:

Then these specification are wrong (The are from Maha's website)?

Click to expand...

The earlier 777 only charges NiCd/NiMH packs. The 777 Plus, has an LCD display, charges higher cell count NiCd.NiMH packs (higher voltage), and also charges Li-Ion packs. Other than that, they're pretty much the same.

Dave

45/70 said:

The earlier 777 only charges NiCd/NiMH packs. The 777 Plus, has an LCD display, charges higher cell count NiCd.NiMH packs (higher voltage), and also charges Li-Ion packs. Other than that, they're pretty much the same.

Dave

Click to expand...

Urghle...... I never noticed that. I have the original 777 and it does not do LiIon, then came the 777Plus and then the 777Plus-II. I'm wondering if the change was made with the Plus-II? No matter, I was wrong and I will beg forgiveness from the almighty lumen as well as those who read this thread....

Regards

Kaptain "Gotta remember to read the specs on gear newer than 20 years old before writing about them or I'll look like an old fool......" Zero

kaptain_zero said:

......I'm wondering if the change was made with the Plus-II?

Click to expand...

I'm not sure kap, I like you, have the original MH-C777 and haven't really kept close track of them. Mine sure didn't impress me very much, and I know some people personally, as well as reading about others experiences with the 777 series here and there, that weren't impressed with any of them. About the only good things you ever read about them are in reviews where everything the reviewer reviews sounds like it's the greatest thing since sliced bread.

Sounds like you're happy with yours. Maybe you lucked out and got a good one. There is a thread around here somewhere, I looked but to no avail, where it is mentioned that at least the first one wasn't really even a Maha, but simply relabeled. At the time the the thread was written, it sounded as if Maha wasn't all that happy with it either. Maybe things have changed with the plus II, not sure.

Dave