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Old Nov 19, 2004, 09:23 AM
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Miami, FL, USA
Joined Sep 2001
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Power Supply for Power System Bench Testing

Hi, Everyone!

This is just FYI.

Recently I purchased a Himax 2025-4266 motor/gearbox combo for my Yard Bee. The pack Iím using is a Kokam 2s1p 1500 lipo pack. My prop/gearing selections were based on a motor chart found on parkflyermotors.com, I found that the chartís numbers did not match reality. In some instances the amp draw differed enough that it exceed the rating of the pack. Needless to say that this proved to be a bit of a hazard for the lipo pack. This brought me to the conclusion that there has to be a better way to test known and unknown parameters without having to worry about the following:
∑ Amps exceeding pack rating.
∑ Having a consistent voltage throughout your testing.
∑ The right size pack at hand.

What I found was a regulated variable voltage (6 to 15 volts) power supply capable of 22 amps continual and 25 amps surge by Pyramid (I have their 12volt/14amp unit that Iíve used with no problems for over three years). Its has both (analog) volt and amp meters. I purchased the unit at etronics.com for 79.99 plus shipping. I received it last night and immediately gave a try. Let me tell you, this unit is AWESOME! You can easily control the voltage to tenth of a volt. Just plug your Watt Meter to it and you're ready to go.

http://www.etronics.com/product.asp?...re=&catid=4071

I just wanted to share this find with those who have similar situations/issues.

All the best and happy flying.

Angelo
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Old Nov 19, 2004, 02:37 PM
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Miami, FL, USA
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Here's a photo of the unit.
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Old Nov 19, 2004, 03:19 PM
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Chattanooga, Tennessee, United States
Joined May 2003
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Sounds like a good deal - I bought one of these and it seems pretty good - I guess it should be at the price!

http://www.allelectronics.com/cgi-bi...512&type=store

How does yours cope with voltage drop with increasing amp load? - I set mine at, say, 11v and it drops to 10.8v at ~5A, and as low as 10.3v at ~22A. Obviously one can adjust back up to the nominal 11v, but that's a pain in the a... while one is running a test! - how many hands does one have?

Cheers, Phil
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Old Nov 19, 2004, 03:45 PM
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Miami, FL, USA
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Phil,

My voltage drops is about .3 volts @ ~15 amps.

All the best.

Angelo
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Old Nov 20, 2004, 10:46 AM
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USA, IL, Barrington
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Phil, is that at the motor or the power supply? Power loss in smaller gauge wire can be substantial in a 5 to 6 foot run.

Pete
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Old Nov 20, 2004, 10:58 AM
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Chattanooga, Tennessee, United States
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That's at the Medusa Analyzer - two banana plugs, one foot of 16ga wire and a Deans Ultra connector away from the power supply. I naively thought that a Power Supply like this could be set on, say 11.0v at no-load, and maintain EXACTLY that no matter how many amps I pulled from it. Is this voltage drop an inevitable characteristic? or should the PS do better than this? An e-mail to the supplier asking this question ellicited no response.

Cheers, Phil
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Old Nov 20, 2004, 11:10 AM
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Colorado
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Phil,

All PS will sag under load. The parameter that matters is the load regulation. I use this PS:
http://www.xantrex.com/web/id/80/p/3...19/product.asp

It's load regulation is:
Load Regulation:
Voltage (0.02% of Vmax + 5 mV) 13 mV
Current (0.02% of Imax + 5 mA) 11 mA

In order words, the voltage will not deviate by more than 0.013V no matter how much current is drawn (up to a mx. of 30A). However, this PS sells for about $2,800. Less expensive hobbyist PS generally have much poorer performance in this regard (they will typically drop about 0.1V for each Amp).

As with everything in life, squeezing the last 5% of performance out of a product accounts for 95% of its cost (think LittleScreamers).

Quote:
Originally Posted by Dr Kiwi
That's at the Medusa Analyzer - two banana plugs, one foot of 16ga wire and a Deans Ultra connector away from the power supply. I naively thought that a Power Supply like this could be set on, say 11.0v at no-load, and maintain EXACTLY that no matter how many amps I pulled from it. Is this voltage drop an inevitable characteristic? or should the PS do better than this? An e-mail to the supplier asking this question ellicited no response.

Cheers, Phil
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Old Nov 20, 2004, 11:11 AM
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Edmonds Wa. (Seattle)
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Phil,
I am looking to buy a power supply too,
As I need to run to many tests to use the batts,
By the way, That was your motor that were trying to destroy
Just kidding
Scott
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Old Nov 20, 2004, 11:14 AM
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Edmonds Wa. (Seattle)
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Rene'
That's not a power supply that's a piece of art!
scott
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Old Nov 20, 2004, 12:20 PM
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I have a couple of HP Lab Grade PSs over 30 years old a 0-40v 10 Amp and a 0-20v 50 Amp rack mounts sim specs. Have many other DC supplies, some I built. Have found many of the adjustable high current bench supplies under $200 to be lucky to keep 5% acuracy under a 10 Amp load!

Pete
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Old Nov 20, 2004, 12:22 PM
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Edmonds Wa. (Seattle)
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I am trying to get a nice one with digital readout and 0-18v 29ampsmax
Will make my testing so much easier,
I should have bought one a long time ago
Scott
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Old Nov 20, 2004, 12:39 PM
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Miami, FL, USA
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Hey, Scott,

My Watt Meter is my digital display.


Angelo
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Old Nov 20, 2004, 12:59 PM
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Paducah Barkley, Kentucky, United States
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I'd search for further specs on that Pryramid PS before ordering it. Yesterday I checked Astron's variable voltage metered supply's specs and was supprised at how much they derated the current as you dropped the voltage (abt -50% of the 13.8v A rating at 10v and went down fast from there), and the Pyramids are a lower quality supply so... ?

Aparently they're limited to what power the heatsink and power transistors can dissapate, and the lower the volts the more that they have to.

In my experience with Astron's which use the LM723 voltage regulator with output voltage sensing at the output terminals (typical for this type supply, and the Pyramids I've seen use the same reg, IC), under heavy loads, 0.1v is a typical drop.

And like AstroNut says, a Whattmeter, or in my case a MR Power Analyzer Plus, is the digital readout.

mike
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Old Nov 20, 2004, 01:52 PM
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And as Mike and AstroNut say, in my case, too, a MR Power Analyzer Plus, is the digital readout. [I made extensive enquiries about digital read-out on a PS, and giant $$$ signs were flashed in front of me at every turn - it's actually not very useful since the Analyzer or Whattmeter is what one looks at, not the PS which could be hidden behind a wall for all I care]

My Zurich Power Supply is an excellent machine, don't get me wrong - it is obviously not Rene's "Rolls-Royce" though! Mine says "1% line load regulation" - what exactly should that translate to if I'm setting it at say 10v and 20A load???? Mine seems to drop perhaps 1-2% (0.1-0.2v) for the every 5 amps increase in load.

Cheers, Phil
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Old Nov 20, 2004, 02:50 PM
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Paducah Barkley, Kentucky, United States
Joined Sep 2003
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How important is tight V regulation?
I mean, the battery packs were going to use in flying sure aren't close to 5% from no load to max load?

With all the variables considered (batteries, props, motors, wires, ESCs... scales, meters, temp, humidity... not being exactly the same), is getting very tight voltage regulation really that important? Won't we still see variations as folks do their own testing, or even as we do our own repeats?

mike
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