Custom Li-Ion External Battery Pack for Digicams

[etman]

I own this camera which uses AA batteries and want to use for AP.
http://www.dpreview.com/news/0708/07083006nikonp50.asp

Problem is the battery life is very poor and Nimh cells are very heavy compared to Li-Ion. And so I want to convert it to a Li-Ion battery pack.
i.e. Buy a standard 3.7V Li-Ion cell phone battery + its specialized charger.
Adapt it with a custom made holder and cable and connect it to the battery compartment.

Anyone can help me with this? Anyone tried to do this?
Thanks!

[Andy W]

It uses either the internal LiIo battery or an external AC adapter - at least according to the link you provided. What is the output voltage of the AC adapter? Simplest solution is to make a lead that plugs into the AC adapter socket, powered by some external battery source..
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[etman]

Hi Andy,

Thanks for replying.
There is an AA x 2 battery compartment for this camera. The spec has listed wrongly. And I should think there is a DC power socket somewhere, I have to check again.

How about the 3.7V cell phone Li-Ion battery, it has three leads, + T -, which do I wire up? T is a temperature sensor right? If I just plug in the + and - and ignore the T, would there be any safety concerns? And how do I make a connection to the leads, solder them?

[etman]

Ok I think I'll forget about this idea, not cost effective and too cumbersome.

I'll use Sanyo Eneloop NiMH AAs. :D
According to reviews it has better charge retention apparently higher capacity than the normal NiMHs.

Review here (http://www.stefanv.com/electronics/sanyo_eneloop.html)

[jeffs555]

No, those have lower capacity than the best NIMH AA cells. Those are only 2000mah while 2700mah NIMH AA's are readily available and there is talk of 3200mah.

The only advantage of those Sanyo cells is the low self discharge rate. You can charge those cells and let them sit for a year and still have 85% of the charge left. A normal NIMH cell would be totally flat in that time.

[jeffs555]

The problem with a "3.7V Li-Ion" is that it charges up to 4.2 volts. Two fresh alkaline AA cells will be around 3.2 volts, so using 4.2 volts would be gambling with your camera. You would have to add a regulator to be safe and would need a switching regulator to use the battery efficiently.

[etman]

Hi Jeff,

Have you tried Eneloops and compared them with the other brands? Is the voltage drop less than the normal Nimh's?

It seems part of the apparent long life is the voltage does not drop as quick as the normal Nimh and so the battery gives more shots until the camera circuitry cuts-off at say 0.9 V per cell.

But that's all according to the review. Anyone has verified it?

[etman]

The problem with a "3.7V Li-Ion" is that it charges up to 4.2 volts. Two fresh alkaline AA cells will be around 3.2 volts, so using 4.2 volts would be gambling with your camera. You would have to add a regulator to be safe and would need a switching regulator to use the battery efficiently.

Yes you are right. A 3.7V Li-Ion would have 4.2 V at full charge and if I use that I have to check if the camera can take that high a voltage.

[Andy W]

I would still use the external source thru the socket..
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[jeffs555]

I would still use the external source thru the socket..
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Don't know about his camera, but on my canon that uses 2 AA's the DC input socket is labeled 3.15 volts so would still be taking a chance plugging a lipo charged to 4.2 volts into there without a regulator.


As for the Eneloops, I don't have any experience with them but I did just order some. It seems they do have a lower internal resistance than other NIMH but whether they would power a camera longer would depend on the current drain and the voltage cutoff level of the camera. I believe that some 2700mah cells have internal resistance as low as 30mOhm. Even if the Eneloops had zero internal resistance that would only be a difference of 0.03 volts per amp.

PS found this 1 amp discharge curve showing Sanyo Eneloop vs Sanyo High Capacity(2700mah?) cells. If your camera draws 1 amp and work down to 1volt per cell then the High capacity Sanyos would have 20% more run time than the Eneloops. http://www.eneloop.info/index.php?eID=tx_cms_showpic&file=uploads%2Fpics%2F1000mA_Discharge_25degC.gif&width=800m&height=600m&bodyTag=%3Cbody%20style%3D%22margin%3A0%3B%20backg round%3A%23fff%3B%22%3E&wrap=%3Ca%20href%3D%22javascript%3Aclose%28%29%3B% 22%3E%20%7C%20%3C%2Fa%3E&md5=f3d6ed33b429775af5f8cae298b84e0b

[Andy W]

Sorry, "I would still use the external source thru the socket.." with a regulator..
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