Black box DC current source into practical voltage source?

Thread Starter

Leo50

Joined Dec 12, 2020
5
There are several articles about how to turn a DC voltage source into a DC current source but what about the opposite?

The real situation is a "black box" current source capable of supplying 0.5 A DC current when connected to a 1K Ohm external power resistance.
Connecting two black boxes in parallel results in a doubling of the current value.
The open-circuit DC voltage is practically zero.
What is the best principal/practical way to convert this current source into a practical voltage supply ( high voltage DC or rather ultimately 110/220V AC ) without any modification of the black box?
What is then the best possible conversion efficiency?
 

ericgibbs

Joined Jan 29, 2010
11,630
hi,
Buy a 12V 120AHr lead acid battery , put it in a black box and connect the battery output to a commercially available 12Vdc to 230V AC inverter.

E
 

LesJones

Joined Jan 8, 2017
2,840
Leo50,
Your statement "The open-circuit DC voltage is practically zero. " is not consistent with the term constant current source. A theoretically perfect constant current source would need to provide an infinite output voltage to pass it's rated output current through an open circuit. You will find constant current LED drivers have a limited output voltage range. For example a constant current power supply that I removed from a 50 watt LED floodlight is rated at 1.5 amps output current but it can only maintain that current for output voltages between 27 an 38 volts.

Les.
 

Thread Starter

Leo50

Joined Dec 12, 2020
5
Leo50,
Your statement "The open-circuit DC voltage is practically zero. " is not consistent with the term constant current source. A theoretically perfect constant current source would need to provide an infinite output voltage to pass it's rated output current through an open circuit. You will find constant current LED drivers have a limited output voltage range. For example a constant current power supply that I removed from a 50 watt LED floodlight is rated at 1.5 amps output current but it can only maintain that current for output voltages between 27 an 38 volts.

Les.
I agree that the behavior of the black box is not like the ideal current source as it only works within a limited impedance range. Also, its maximum current ( 0.5 A) only occurs at 1K load impedance.
The question remains, is there a way ( eg by simulating the 1 K impedance) to convert as much as possible of the output current power into a practical fixed voltage output power?
Note also that I have presently no access to this black box for any additional measurements.
 

Thread Starter

Leo50

Joined Dec 12, 2020
5
Yes, as I already replied to LesJones above, the black box is not an ideal current source.
In the same reply, I also tried to reformulate my original question to:
"How can you convert as much as possible of the black box output current power into a practical fixed voltage output power? "
Some further info that hopefully could make things clearer: The black box is a new energy generating device that like a solar panel generates an electric current during certain conditions. Several boxes can be connected in parallel while adding the generated currents. The point of this exercise is to find out a way to practically convert the currents into practical use, similarily as is done from solar cells.
 

ericgibbs

Joined Jan 29, 2010
11,630
The black box is a new energy generating device that like a solar panel generates an electric current during certain conditions.
hi Leo.
Is this Black Box in any way linked to a Free Energy project.?
E
 

WBahn

Joined Mar 31, 2012
26,398
There are several articles about how to turn a DC voltage source into a DC current source but what about the opposite?

The real situation is a "black box" current source capable of supplying 0.5 A DC current when connected to a 1K Ohm external power resistance.
Connecting two black boxes in parallel results in a doubling of the current value.
The open-circuit DC voltage is practically zero.
What is the best principal/practical way to convert this current source into a practical voltage supply ( high voltage DC or rather ultimately 110/220V AC ) without any modification of the black box?
What is then the best possible conversion efficiency?
Your "black box" current source does not behave like a current source. If you open circuit a current source the output voltage will climb as high as possible in an effort to maintain the current at the programmed output.

If you have a practical DC current source, which means that it has a finite output resistance and a maximum output voltage, then to turn that into a DC voltage source that respects those limits and can deliver at most the programmed current, you can use a high-value load voltage sensing element (say that draws about 1% to 10 % of the total current at the desired voltage) a 10 kΩ resistor and then use a bypass transistor to shunt whatever current is not needed to maintain the desired load voltage into a current sink resistor.
 

WBahn

Joined Mar 31, 2012
26,398
Yes, as I already replied to LesJones above, the black box is not an ideal current source.
In the same reply, I also tried to reformulate my original question to:
"How can you convert as much as possible of the black box output current power into a practical fixed voltage output power? "
Some further info that hopefully could make things clearer: The black box is a new energy generating device that like a solar panel generates an electric current during certain conditions. Several boxes can be connected in parallel while adding the generated currents. The point of this exercise is to find out a way to practically convert the currents into practical use, similarily as is done from solar cells.
Why can't you just do it the same way that solar cells do?

No one can tell you how to do something with a black box unless you provide all of the details of how this black box behaves. We don't need to know how it does what it does within the box, but we do need to know precisely how it behaves at the connections to the box.
 

crutschow

Joined Mar 14, 2008
26,044
How can you convert as much as possible of the black box output current power into a practical fixed voltage output power?
The maximum power theorem states that, to get the maximum power out of your black box, the load impedance should match the source impedance.
For a constant source impedance that will occur when the output voltage is 1/2 the open-circuit voltage.
 

WBahn

Joined Mar 31, 2012
26,398
The maximum power theorem states that, to get the maximum power out of your black box, the load impedance should match the source impedance.
For a constant source impedance that will occur when the output voltage is 1/2 the open-circuit voltage.
But, according to his first post, his open-circuit voltage is zero.

If this is true, then what is in the black box is not a constant current source, so analyzing the problem as if it were may lead down a rabbit hole.
 

MisterBill2

Joined Jan 23, 2018
7,732
An easy start will be to try one of the wide-input-voltage-range switching power supply circuits. I am guessing that said black box has a "normal operating range", and feeding such a circuit could be a good start. For the claimed maximum output condition, " its maximum current ( 0.5 A) only occurs at 1K load impedance." That appears to be 500 volts out (E=I x R), and that input can be handled by a fairly standard input circuit switcher.

What is not mentioned is the output at other load resistances. What does the current do as the load resistance is varied from 400 ohms to 600 ohms, for instance.
 

DickCappels

Joined Aug 21, 2008
6,806
We are not allowed to discuss over-unity on this site, therefore the discussion here can only related to the electronics you need. You used contradictory statements to describe your constant current source. Can you explain in simple terms what the circuit or device you seek does?
 

MisterBill2

Joined Jan 23, 2018
7,732
We are not allowed to discuss over-unity on this site, therefore the discussion here can only related to the electronics you need. You used contradictory statements to describe your constant current source. Can you explain in simple terms what the circuit or device you seek does?
Given that there is no mention of any level of power input to the black box there is no way to consider this an "over unity" situation. The fact that we do not understand the specific conditions leading to this mode does not mean that it is impossible. There are chemical reactions that only happen under specific conditions, and likewise biological things. My suggestion of a variable input switchmode supply with a range centered around the claimed max power point is certainly a reasonable start.
 

DickCappels

Joined Aug 21, 2008
6,806
The point is that the discussion of efficiency and similar stops now. We can try to help you with electronic issues if you can articulate your needs.
 

MisterBill2

Joined Jan 23, 2018
7,732
My suggestion works for any device that will push 500mA through a 1000 ohm resistor. There are a few non-linear devices around and this might be a new one. It might even be a funny wind turbine. It may also be that some of the TS data is not right. That happens also.
 
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