When rechargeable batteries lose charge fast (like a few weeks) it means the internal insulating layers are degraded and allowing leakage current which discharges the batteries. Very common problem with NI-CD or NI-MH cells.

 

Old Ni-cad and Ni-MH cells were discharged when purchased. They self-discharged very quickly. New ones are pre-charged because they are made differently with a much longer shelf life for each charge. Their capacity is a little less than the old ones.

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Uncle $crooge

 

Must have been before my time, and I am a dinosaur. I heard tales of REALLY old NI-CADs shipped with shorting bars across them to keep them fully discharged. With no potential difference between the cathode and anode, they can't grow those internal crystal structures some of them do when the separators are not sealed well enough. Every NI-CD I have seen in the last 40 years shipped with a partial charge... and when started self dying quickly, it meant the separator was hosed. And they had to be ZAPPED with a capacitor to blow out the internal short to get it to take a charge again.

 

Audioguru, how does the AC adapter magically route power away from the batteries? If I wire the adapter parallel to the batteries, won't some current be routed through the batteries, dangerously? I will remind you that I have not constructed this yet. It is not a prebuilt stereo that automatically switches between batteries and adapter. I need help making a circuit that will switch between batteries and a DC adapter. Or, I suppose, I could just make a manual switch so I can use either. But automatic would be much neater.

Also, I have no idea what you guys are talking about fake "D" cells for... I buy Duracell D's and they are extremely heavy for their size. They are no doubt different from C cells. I have measured the cells with a multimeter and they do output at different current levels. I do not know about other brands, however. Can anyone help me make this thing?

 

It will be automatic if you use a standard 1/8" jack connector and matching plug. The jack has a normally closed set of contacts you route the battery power through (these kind of jacks are often used for the speaker of a portable device, which is disconnected when the headphone plug is inserted). In your case, the power from the AC adapter goes to the plug. When the power plug is inserted into the jack, it breaks the line to the batteries and provides power directly to the radio from the AC adapter. Very easy to wire up.

 

Like I said earlier in this thread, "Most products that are powered from a battery and an AC adapter use a jack with a built-in switch to disconnect the battery when the adapter is plugged in." The switched jack makes it automatic. You can make the AC adapter a battery charger if you want.

We were talking about Energizer Ni-MH rechargeable D zize cells that have a little AA cell inside. I don't think Duracell sells C and D Ni-MH cells.

For your little amplifier you need six AA Ni-MH rechargeable cells and a charger for them.

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Uncle $crooge

 

Radio Shack and many others sold fake D and C cells with smaller batteries inside them. The clue is to look at the mA-hr capacity printed on them and notice they are the same: they used to have sub-C cells in there that were only good for about 1500 mA-Hrs. I believe a full D cell in Ni-CD is more like 4000 - 5000 mA-hrs, and a full C cell NI-CD is about 2000 - 2500 mA-hr.

 

Energizer and other battery manufacturers do not sell Ni-Cad cells anymore. They sell Ni-MH cells now that have a capacity that is 5 times more than Ni-Cads.

An AA size Ni-MH cell is 2450 to 2800mAh.

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Uncle $crooge

 

Those must be new technology, the AA NI-MH that came with my camera (and the replacements I bought when they pooped out) were all rated 2000 mA-hr.

 

Then who is making all the NI-CDs? Everybody still sells them and I even see them in packs at FRY's. Somebody is making them, maybe not in the USA because of environmental laws, but they are cranking them out someplace. This place sells a lot of ni-cads:

http://www.harborfreight.com/cpi/cta...emnumber=47440

Here are some typical AA NI-MH, notice they are rated 2000 mA-hr:

http://www.harborfreight.com/cpi/cta...emnumber=90148

There are probably better ones available, these are generic.


This plac has tons of new NI-CADs:

http://shopbatteryhouse.com/nickelcadmium-2.aspx

 

Sanyo still makes old Ni-cad cells.
Harbour freight sell stuff that they guess on their ratings.

My cheapest Chinese solar garden light has a Ni-Cad cell that is only 380mAh. I have never seen one rated so low.

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Uncle $crooge