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Author Topic: need advice, comments or someone to tell me to stop :)  (Read 1466 times)

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Offline phatdats

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need advice, comments or someone to tell me to stop :)
« on: July 02, 2009, 03:24:08 AM »
sorry if this is a late night ramble, been toying with this idea for a few weeks now...


so after almost 14 years of carrying around both 12v and 6v sla's, I finally have a bag full of gear that all has the ability to run off the same (more or less) voltage.

I am currently carrying:
grace V2 (6v)
apogee minime (rev. c)
edirol r44

I just bought a bunch of wally world batteries off ebay (9v, 5400mah).

my approx. current draws (according to manufacturers):
v2: 1.1ah (powering gefell m300)
mme: <1ah (just as an a/d - no preamp or phantom)
r44: .75ah (just as a 2ch recorder, no phantom or preamp)

first off, I know none of my low battery indicators will work on the v2 and mme by running 9volts...

so, worst case, not taking into account the steep drop off of li-on batteries, I get just over 1.5 hrs running my whole rig off one battery - but i am not gonna do this....

I was going to build a cable to allow 2 batteries wired in parallel, giving me 9v/10+ah, and the ability to swap batteries out as they get low without powering down anything...

first question:  with such a heavy draw on the batteries (just under 3ah) would I experience any sag when i changed a battery that would cause any of my gear to loose power? (simular to the lights flickering when the air conditioner comes on in my crappy house?)

now the real reason for the post.  I am looking at a big mess of cables.  I am thinking of building a little power distro box to use. simular to the VRboxes people were using with jb3s.  a small box that had 2 battery inputs and 3 outputs.  everything fused, and on locking connectors like minixlr, TA4M or something to keep size small...

second question: am i gonna loose too much power to heat or anything by running everything thru this box, or mini xlr connectors?

third question: is this just a waste of time?

fire away!

thanks!!!!!!
steve
mg300>v2>minime>r4

steve@phatdats.com
www.phatdats.com

Offline notlance

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Re: need advice, comments or someone to tell me to stop :)
« Reply #1 on: July 02, 2009, 09:23:46 AM »
I think what you propose will work just fine, depending on how well it's built.

"first question:  with such a heavy draw on the batteries (just under 3ah) would I experience any sag when i changed a battery that would cause any of my gear to loose power?"
Batteries can supply large amounts of current for a short time, so I don't think you will have a problem running off one battery for a while.  Just don't let the batteries run down too far before you swap them out because most Li-ion chemistries have a steep voltage drop when they are close to being discharged.

"second question: am i gonna loose too much power to heat or anything by running everything thru this box, or mini xlr connectors?"
In general I think you'll be just fine, especially if you use a separate power cord for each box.  One amp through a TA series connector is not a big deal.  Try to use as big a wire as you can get through the TA's strain relief, and keep the cable lengths reasonable.  The TA strain relief comes in two hole sizes with the larger hole size being less common.  However, it's not too hard to drill out the smaller strain relief to accommodate a larger cable.  If I were building this power distribution box, I'd skip the fuses since I don't see why you need them from a safety standpoint.

"third question: is this just a waste of time?"
Not a waste of time at all; sounds like a fun project to me.  Then again, I'm a nerd.

Offline Walstib62

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Re: need advice, comments or someone to tell me to stop :)
« Reply #2 on: July 02, 2009, 09:21:37 PM »
I am a firm believer in carrying more batt. capacity just for safety. I calculate how much power I will need for (X) hrs. continuous use. I then add 50% more capacity to my pack. That way, I can build in a safety margin for variables(temp, charge states, battery cell capacity loss) And yes, be careful about running the pack down too far before swapping. There can be enough of a drop that many units will automatically shut down below a certain threshold voltage, even for a very short time.

Offline page

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Re: need advice, comments or someone to tell me to stop :)
« Reply #3 on: July 06, 2009, 11:16:20 AM »
I am a firm believer in carrying more batt. capacity just for safety. I calculate how much power I will need for (X) hrs. continuous use. I then add 50% more capacity to my pack. That way, I can build in a safety margin for variables(temp, charge states, battery cell capacity loss) And yes, be careful about running the pack down too far before swapping. There can be enough of a drop that many units will automatically shut down below a certain threshold voltage, even for a very short time.

I'm in a similar boat in that I'd rather carry the extra capacity then get screwed.

With the proper process this can also have the tertiary effect of battery longevity. You get to charge the battery the night before you use it, run it down to around half charge during the show, take it home, and store it properly (as espoused by battery experts/people). Most batteries if they are going to sit, like to sit at half-charge or there abouts in a cool place. Over time, you'll get more "bang for buck" out of them this way before you have to chuck them.
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