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I have two 52 VDC voltage sources, each an equidistant of 200 m from my load. For this purpose, take it as one voltage source is coming from the east and the other from the west.

Along the 200 m path on each side (east and west) I want to power some small loads (30-80 W max). I realize when I eventually reach the end of my 200 m line I will have quite a voltage drop and so be wasting quite a bit of energy in transmission.

I was wondering if there is any way to combine both sources together at the middle - in a way which would somehow increase the overall efficiency of the system.

Voltage Spike
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Brandon Kellett
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2 Answers2

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schematic

simulate this circuit – Schematic created using CircuitLab

No, this would not help. On each 200 m line the voltage will drop a bit at every small load. At the meeting point both lines have roughly the same voltage drop and combining them there would not rise the available voltage at this point. So nothing would change.

Edit:

Running the simulator shows, that there is no voltage difference between U_LEFT and U_RIGHT and the current trough R13 (optional combinding point) is zero.

Jens
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  • Voltage drop would be half with two sources and two lines for a given load. – winny Aug 08 '22 at 14:53
  • @winny Yes for one load, but this is not the case here. I added a schematic for clarification. – Jens Aug 08 '22 at 15:26
  • Oh, I missed that part. Thanks. – winny Aug 08 '22 at 15:29
  • I understand the voltage levels will be the same, I was more so wondering if I combined sources at the central load - would I then draw half the current/power from each source? If so this would increase my efficiency in comparison to drawing the current/power from a single source only – Brandon Kellett Aug 08 '22 at 16:26
  • @BrandonKellett No, the only little improvement I see, is feeding each 200 m line in the center (at 100 m) with one supply each. This reduces the wire losses, but then you have additional wires to feed the 52V sources somehow. It would need a while to compensate the eco impact of this additional material by the slightly better efficiency. – Jens Aug 08 '22 at 16:42
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Yes, but you will need to use ORing diodes. You need to put a diode in series with one of the wires from each voltage source. You will lose ~1V per leg this way, and burn about 1W per amp through each diode, but this would effectively make a center connected load be powered by both voltage sources in parallel, halving the transmission line resistance and reducing the power lost by a factor of 4.

However, don't be tempted to use schottky diodes for their low voltage drop. 200m of cabling has potential (pun!) to see all sorts of weird voltage potentials appear on them due to things like weather or ground potential variations. So you want diodes with very high breakdown voltages. Also, this assumes that both voltage sources are isolated. If they aren't, then you may find that they are at very different potentials from each other at the 200m ends.

metacollin
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  • Would it be sufficient to place the ORing diode at each voltage source before the 200m run of cable? This way if one voltage supply fails, the other one can still power the other side (less efficiently of course) – Brandon Kellett Aug 08 '22 at 12:48
  • @BrandonKellett That should do the job. As your voltage is so low, you can use Schottky diodes to save a little bit of losses. – winny Aug 08 '22 at 13:48
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    @winny the OP wants to power his load from both of the sources at the same time. Diode ORing will not help on this matter. – Rohat Kılıç Aug 08 '22 at 15:07
  • @RohatKılıç It would prevent one power supply from back feeding the other at No or light load. – winny Aug 08 '22 at 16:15
  • @winny true, but the power drawn by the load will not be shared between the sources. The OP wants to share i.e. paralleling the sources. If there's no chance to adjust the output voltages (i.e. making them exactly equal) then neither diode ORing nor direct paralleling will work correctly. – Rohat Kılıç Aug 10 '22 at 07:31
  • I see your point but the level of sharing depends on the voltage drop of the lines and the missmatch of source voltage. There won’t be 50/50 sharing, that’s for sure. – winny Aug 10 '22 at 07:34
  • @winny That's what I described in my answer. If the output resistance is negligibly lower than the cable resistance, and if the voltages are close enough to each other then they can be safely paralleled. – Rohat Kılıç Aug 10 '22 at 12:50
  • @RohatKılıç Sorry, didn’t read it until now. But I still don’t see your objection to the diodes. It won’t do balancing but it would improve the performance of OP’s present system. – winny Aug 10 '22 at 13:47