DC power chaining - how much is too much?

[Zack]

I've never really understood 100% about the science of how electricity works when it comes to resistance and loads, so maybe one of you could help me determine how to be efficient with my NP1 power chain?

I'm currently using two NP style NiMH batteries with these specs:

Capacity: 50wh (13.2v, 3.8Ah)Size: 7.28 " x 2.83" x .98"

Weight: 1.5 lbs.

Nominal Runtime (25w load): 2hrs.

I power x2 UCR-411's, SD-702T, PSC ProMix 6, distributed via Battery Bud.  So far, this set-up works great and stable for a good 4-5 hours.  I'm looking to now add in a Lectro SR receiver to the mix and would like to power it off of the same battery if possible, but I'm not sure how to determine if there's too much voltage draw to where I'm damaging anything or probably draining my battery faster than I can recharge them for alternating throughout the day?

[Ralf Hamann]

Hi Zack

it should be no problem to put another wireless in your system. but i think you should change your akkus. In my bag i use 4 Audio RMS 2020-2040, one 744T HD and one 442T mixer with only one IDX L7S for min. 4 hrs. I´ve got a single NP box with two AD-5X regulated powerswitchers http://www.hawkwoods.com ( one is one the pix). It will work perfect since years. I use 3 L7S for a day. Two are in use and one is backup. Charging this Lithiums take may be 3-5 hrs.(i never take the time. sorry ). The normal equipment is working between 7 an 18V so there is no conflict with max power of the akkus.

But never work with them without a NPF akku in your HD. The Lithium´s interrupt the power if they will get empty. Without warning.

But if you know the time how long you are working with one you can change to a full NP short before.

Here is my bag without wireless.

Greeting  Ralf

[Ralf Hamann]

sorry

i can`t sen pictures to the blog.

[JackHenry]

but i think you should change your akkus.

What is akkus?

[Ralf Hamann]

Sorry i mean: Rechargeable Batterie

[Derek H]

Akkus = Rechargeable batteries??  Just out of curiosity ralf, where does that term come from?

I'm also using older (bought used 3 years ago) IDX NiMH 50Whr and 1 of them will power my smaller rig all day on average.  That being a 302, 2xwireless and a Zax stereo Tx..

I'm still waiting for them to become unreliable..

[Ralf Hamann]

The word akku is the short form and came from the Akkumulator (from lat. accumulator „collector“). Latin was spoken in italy at the time were julius Caesar was the man in charge. 

We use it in Germany.

For a long working day 10_12 hrs i need 2 of the L7S. The 744 needs more power even when the NPF charging is on.

The 442 is all so more hungry.

Greets Ralf

[Zack]

The word akku is the short form and came from the Akkumulator (from lat. accumulator „collector“). Latin was spoken in italy at the time were julius Caesar was the man in charge. 

We use it in Germany.

For a long working day 10_12 hrs i need 2 of the L7S. The 744 needs more power even when the NPF charging is on.

The 442 is all so more hungry.

Greets Ralf

Interesting, thanks for sharing

[John Blankenship]

I'm currently using two NP style NiMH batteries with these specs:

Capacity: 50wh (13.2v, 3.8Ah)Size: 7.28 " x 2.83" x .98"

Weight: 1.5 lbs.

Nominal Runtime (25w load): 2hrs.

Think of a water hose...  Voltage is the water pressure; current is the amount of water that flows.

So how much current do you need to "water your garden"?

At its nominal voltage, your battery puts out 3.8Ah.  In simple terms, that means that if your equipment pulls 1A. (one amp), then you'll get 3.8 hours at the nominal rated voltage.  If your equipment pulls half that, or 500ma (.5A.), you'll get 7.6 hours at the nominal rated voltage and if your equipment pulls 250ma (.25A.), you'll get 15.2 hours at the nominal rated voltage.  If your equipment pulls 2A, you'll get 1.9 hours.  See how the numbers work?

Of course, the battery voltage will vary during its discharge cycle, and that will affect these numbers, but let's keep it simple for now.

Add up the current draw of all the equipment you'll be powering, then divide 3.8 by that number.

Lectrosonics lists the current draw of all their gear in each users manual.  If a manufacturer doesn't list the information, you can email them, or measure the device yourself with a current meter.

Be aware that equipment will pull differing amounts of current based upon how it's being used.  Things like the use of phantom power, how hard you're driving headphones, etc. will affect the amount of current a device draws.  A recorder many pull less when sitting idle and pull a good deal more when actually recording.

Sound devices claims that a 1500ma battery will run the 702T for about two hours, so that means, based on that figure, the 702T is pulling about 750ma (.75A.) but that would be rated at the 7.4 volts of the on-board battery so, if all the circuits are well designed, it would probably pull a good deal less at the 13.2 nominal voltage of your batteries -- say, maybe 35%-40% less.  The Lectro 411s are rated at about 180ma (.18A.) at 12v. and the SR receiver is rated at about 115ma (.15A.) at 12v.  I don't know what the ProMix 6 is rated at.  However, based on your figure of 4-5 hours per battery, it would appear that you're pulling a total of about 850ma (.85A.) (3.8Ah divided by 4.5 hours is (rounded up) about 850ma (.85A.).

So, based on these figures, if you're now getting about 4.5 hours, with the addition of the SR you should get about 4 hours (if all other factors are equal -- big IF).

Here are the secret formulas (the first is called "Ohm's Law"): 

    I=E/R  (Current = Voltage divided by the resistance)

    P=IxE  (Power = Current times the voltage)

From there you can run the numbers any way needed.

Geek joke:  "Remember, Ohm's law is for your protection -- Support your local electromotive force."

(Simply put, "Electromotive Force" is another way to say voltage -- hence the "E" in the above equations.)

I hope this helps more than confuses.

Oh, I must add:  YMMV!

John B.

[studiomprd]

" Lectrosonics lists the current draw of all their gear in each users manual.  If a manufacturer doesn't list the information, you can email them, "

[John Blankenship]

" Lectrosonics lists the current draw of all their gear in each users manual.  If a manufacturer doesn't list the information, you can email them, "

Hey Senator,

Is it your goal to be annoying, or is that just a byproduct of an obsessive personality?

When you actually contribute something to a discussion, it's usually worthwhile.  Crap like this, whose sole purpose is to draw attention to yourself and away from the subject being discussed, is not appreciated.

Please, start your own thread.  Your obsession is not what this topic is supposed to be about.

John B.

[Zack]

John, that's probably the best/easiest explanation I've heard so far...huge help tyvm.