Topic: A question regarding watt hours

[pdxdanmusic]

I bought an external battery to use with a SD MixPre-D. The battery is rated at 98 watt hours (26400 mAh). I was told that the MixPre-D draws about .09mA (without P48) and my mics (Josephson C42mp) are rated 48mA (I would assume each) and the battery and MixPre-D are both 12 volt.

So my question is how long should I expect the battery to last?

[jefflester]

48mA would be a huge draw for a mic. This: http://www.josephson.com/pdf/srs4.pdf says 4.5 mA.

Is it this battery?
http://taperssection.com/index.php?topic=161651.0

I think it's going to last more hours than you can tape....

[pdxdanmusic]

48mA would be a huge draw for a mic. This: http://www.josephson.com/pdf/srs4.pdf says 4.5 mA.

Is it this battery?
http://taperssection.com/index.php?topic=161651.0

I think it's going to last more hours than you can tape....

My mistake on the mic I just looked again and it is 4.5 mA (I saw the 48v for phantom) and yes that is the battery I ordered. I might also use the battery to run my PMD661 since it puts out 5v and I already have the cable. If it works as a festie battery I will be very happy.

[pdxdanmusic]

I suspect the Mixpre uses more than 0.09mA, which is 90 *micro*amps.  Maybe 90mA, or 0.09A?  At 12V, that's 1W.

According to this spec:

http://www.sounddevices.com/products/mixpred/specs/

2x AA is about 5Wh, so that's around 1W without phantom.

With phantom, probably between 1.5W and 2W, depending on the mics.

You are correct the tech at Sound Devices said 0.09 A with no phantom but if I can get between 1.5W and 2.0 W with my mics I will be able to use it for festies. I have 3 ext. batteries for my PMD661 that give about 11 hours each so hopefully with what I have and rechargeable AA's I should be set.

[dnsacks]

i strongly suggest doing a series of "dry runs" with the setup recording ambient noise to see how much time you get out of the battery.  with a solid state recorder, it should be as simple as hitting record and seeing how long the saved recording is when the recorder shuts down.  Do a few tests to confirm consistency and you'll have a good yardstick for how long your specific gear combo can run on your specific battery

[pdxdanmusic]

i strongly suggest doing a series of "dry runs" with the setup recording ambient noise to see how much time you get out of the battery.  with a solid state recorder, it should be as simple as hitting record and seeing how long the saved recording is when the recorder shuts down.  Do a few tests to confirm consistency and you'll have a good yardstick for how long your specific gear combo can run on your specific battery

I plan to do that. That is how I measured one of my external batteries for my PMD661.

[twatts (pants are so over-rated...)]

I suspect the Mixpre uses more than 0.09mA, which is 90 *micro*amps.  Maybe 90mA, or 0.09A?  At 12V, that's 1W.

According to this spec:

http://www.sounddevices.com/products/mixpred/specs/

2x AA is about 5Wh, so that's around 1W without phantom.

With phantom, probably between 1.5W and 2W, depending on the mics.

You are correct the tech at Sound Devices said 0.09 A with no phantom but if I can get between 1.5W and 2.0 W with my mics I will be able to use it for festies. I have 3 ext. batteries for my PMD661 that give about 11 hours each so hopefully with what I have and rechargeable AA's I should be set.

You've answered your own question:  if you MixPre-D w/ 48vPP draws 2W of power, a 98WH battery will last (98/2) 49hours...

Terry

[pdxdanmusic]

I was looking for a simple formula so the way I figured it out is. 4.5ma x 2 for the mics=0.009A plus 0.09A for the MixPre-D = 0.099A x 12 volts for the battery = 1.188 W then I took the 98W and divided it by 1.188 and got 82.4915... I then figured about 80% efficiency  which means I should get about 66 hours. This is about what I was hoping for when I got it.
My mistake was plugging in the wrong values which threw my calculations way off.
I am going to have a cable made to go from the battery to the MixPre-D so I will have to wait until I get that to try the dry run. I will try a dry run with my Sanyo Eneloops and Energizer Lithium Ultimate (I know this will waste a set) to get an idea.
I will post my results when I get done.

[pdxdanmusic]

Thanks for the clarification.  Trying to come up with a simple formula does not seem that simple.

[dmonkey]

Bummer. Thought this was a thread about the number of hours Mike Watt has rocked so far. It's a big number.