External Battery

Does anyone know the DC voltage output of the EH-5a external AC power adaptor for use with the D300, or why it has a 4-pin plug? I am wondering what voltage(s) would be needed to power the camera with a large external battery.

It amazes me that people go out and spend $450.00 on an external battery pack for their SB-800 flash units when they could build one with parts available at Radio Shack for under $40.00. A simple 6 VDC lead acid battery is all that is needed, along with cables and a bag to put them in (e.g. a small camera bag). Too bad Nikon did not have the insight to put a 6 VDC jack on the SB-800 instead of a 330 VAC jack. That would be better than having to fool with putting "dummy" batteries in the unit.

The expensive solution is to buy the power supply unit, an inverter and a 12V battery.

Be careful with the tensions and polarity. Maybe the tension is in the specs of the power supply unit.

If you manage to do it please post the schematic.

--
http://www.frikosal.blogspot.com

I am GUESSING (at this point) that the battery for the camera is "center tapped" since it has a third connection. In such a case it would output both 7.4 VDC and 3.7 VDC and the AC adapter has similar output voltages.

If such was the case, one could then use two of these batteries:

http://www.ragebattery.com/power-sonic/SLA-4_5-4.html

Wire them in series, and use the center tap to provide the 3.7 volts and the end tap to provide the 7.4 volts. The slightly higher voltages (4.0 and 8.0 volts) should not cause any problems, but I would put in-line fast-blow fuses on both taps of the circuit to prevent shorting the battery and pulling too much current into the camera. Also, one should probably remove the in-camera battery to prevent it from over-charging, or else put a resistor on both taps of the circuit to prevent the internal battery from pulling too much current.

The whole kitten kaboodle could be housed in a small camera bag. One would also need a battery recharger, of course, and the only difficult part of the project would be finding a plug that fits the DC input of the camera.

One could probably take 8,000 pictures with this setup before having to recharge the batteries.

I would try to measure the output of the EH-5a AC adapter, or look for it, it must be posted. Maybe it is only 1 tension. Take care, I don't think the fast fuse can protect the camera.

--
http://www.frikosal.blogspot.com

the en3 series of batteries appears to be a 2cell lithium. It'll have a fresh off the charger voltage of 8.4v and it'll be dead when it gets down to approx 7.1v.

The additional contacts must be either for per-cell tapping and/or serial I/O to the onboard battery management chip

The EH-5a is specified on the name plate as 9 volts. I haven't measured the actual voltage nor the impedance (which as you probably know determines the voltage under load).

John4 said:

The EH-5a is specified on the name plate as 9 volts. I haven't
measured the actual voltage nor the impedance (which as you probably
know determines the voltage under load).

Click to expand...

impedance = 0 most likely, they are electronic (as all power supplies nowadays) and manage to keep the same tension under different loads.

How is the connector to the camera ? Is it standard ? (I don't have the camera yet)

--
http://www.frikosal.blogspot.com

Thanks to those who replied. It seems to me that the need for an external battery for a camera such as the D300 is less of an issue as the need for an external battery for an SB-800 or SB-600 flash unit.

I have seen "external flash batteries" that supply 330 VAC directly to the flash bulb in the SB-800 that cost ca. $450.00. These units have a quick charge time. Unfortunately, the SB-800 really needs a several second cooling off period between multiple flashes anyway, so I really do not see the wisdom in buying one of these units (unless you want to burn out your flash bulb prematurely).

The other "external battery" I have seen is the Al Jacob's "Black Box." This product supplies DC to the SB-800 via a chord (purchased separately) that has an RCA phono plug on one end and "fake" batteries on the other end which you install in the SB-800 or SB-600. The unit is considerable cheaper and thus reasonable in cost and does not encourage burning out the bulb or flash circuitry of the flash unit. The trouble I have with this unit, however, is:

1. It is kind of "Rube Goldberg" in having to depend on inserting "fake" batteries in the SB-800 and not being able to close the battery door or having to drill a hole in the battery door for the cord. This is really Nikon's fault in that they don't include a 6 VDC input jack on the SB-800.

2. The "Black Box" uses the RCA phono jack--this jack was never intended for carrying power--it was designed for audio. It is easy to short out the plug/jack and thus short out the lead acid battery, and because:

3. There is (apparently) no fuse in the "Black Box" (someone correct me if I am wrong--it is hard for me to believe its designer could overlook such a necessity) a short in the connecting cord could cause the lead acid battery to explode. Not a pretty picture.

4. One could easily build their own "black box" with parts that are easily obtainable. This would be a better solution than continually replacing AA batteries in the SB-800 or the Nikon external battery (which contains 6 AA batteries).

Any comments from people with experience with any of these products are welcome.