Extract 5W low voltage power from 3000W high voltage source

Question

I have a solarpanel array that generates 600V, 5A (3kW). I want to create a small electronic unit to measure the DC current and voltage and transmit this wireless. For this I have an electronic board with ADC's and transmitter. This board uses a maximum of 3.3V and 100mA. I want to use part of the power generated by the panels for this board.

I found some components like the LR8 from Supertex, but this is not supplying enough current and has a max of 400V. It seems like whatever I do to convert this voltage down to 3.3V, I loose a lot by heating of powertransistors or mosfets. As the board might be floating I wonder if there are more smart methods to power this board?

Any ideas would be very much appriciated!

Answer 1

Super wide-range buck converter based on the VIPer16
ST AN2872 - 500 VAC / 700 VDC input

Low−Cost 100 mA High−Voltage Buck and Buck−Boost Using NCP1052
ONSEMI NCP1052 - AN8098D
<= 700 V in

Pushing the limit - 600 V rated NXP AN11136 SSL2109T/AT/SSL2129AT controller for SSL applications

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Design Considerations for High Step-Down ratio Buck Regulators

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You will have some voltage drop between the panel low voltage end and the battery or load. An energy harvesting IC or a custom boost converter running from a fraction of a volt would be able to provide the energy you need.

To produce 3v3 @ 100 mW = 330 mW assume you need 500 mW in.
At 5A, to produce 500 mW you need a potential of 0.5 W/5A = 0.1 V. That would be with all the drop being used by the converter. If you had 0.5V drop available you need 1A. The first essentially requires interrupting the feed cable and the second is still a substantial proportion of the 5A load current.
If you introduced a point voltage drop across eg a MOSFET it would be more controllable.
Say 0.5V at up to 5A available = 2.5W.
Series MOSFET, regulate to 0.5V drop.
Efficiency loss = 0.5V/600V = 0.08%

BUT

You say

• ... I want to use part of the power generated by the panels for this board.

• ... but I do not have the option to use a single panel for this.

• ... As the board might be floating

but you do not say why these conditions apply.
Giving a fuller definition of your problem would help.

You say that your target load is 3V3 x 100 mA = 330 mW.

Adding a small PV panel to power your system would be trivial.
Presumably there is a converter supplying mains and or battery.
Presumably using these is not acceptable. Saying why may help.

Answer 2

There are parts that will easily withstand a 600VDC input. TI has a reference design of a converter that will handle 800V input and produce a 25V/0.25A (6W) output that could easily be used to create your 3.3V required power.

I do suggest that you consider shopping for such a converter on the market though- making the transformer will require some technique for safety as well as functionality and will not be very cost-effective for a one-off (sourcing custom magnetics in small quantity seldom is).

Note that the ratio of 600V:3.3V or even 24V is way beyond what you can reasonably expect to achieve without a transformer or tapped inductor (about 10:1 as a rule of thumb), and that probably means you need a custom magnetic component unless you want to do it in a bunch of stages.

Answer 3

I would use 2 power diodes in series , generating 1.2V, enough to run a small boost converter chip to say 3.3V to power the rest. max dissipation in the diodes is 5x1.2V=6W but that is nothing compared to the 3kW. this may work as soon as you draw more than 100mA off the solar array (60W)

Answer 4

What you want is a buck converter. That is a type of switching power supply that makes a lower voltage out than in.

Since you only want to drive a microcontroller and a little electronics around it, you don't need super high effeciency. 100 mA at 3.3 V (330 mW) would be a lot for your circuit. Even if this overall draws 1 W from the solar panel, that shouldn't cause any trouble.

I'd keep this power supply simple, probably a pule on demand system. The tricky part will be controlling the high side switch accross 600 V. The high voltage will also greatly restrict the parts available for that switch. Arranging for something that produces a 500 ns pulse, for example, whenever the low side power voltage is below a threshold would be good enough. I wouldn't try to regulat the 3.3 V directly. Make something like 4 V minimum, then have a linear regulator make 3.3 V. That 4 V minimum might go up to 6 V at its peak right after a pulse, but again, your power levels are so low that efficiency really isn't a big issue here.

A 100 mΩ sense resistor can be used to measure the current, and a voltage divider to measure the voltage. The output of these would be measured by the micro, which would send on the information digitally, perhaps over a opto-isolator.

Answer 5

For powering your circuit you may look into the possibility to tap into the series-connected array. Usually individual panels have voltages much below the final system voltage, e.g. 12 or 36V. If you connect your circuit to only one panel you may have the power supply problem solved:

^{simulate this circuit – Schematic created using CircuitLab}

Where "CIRCUIT" would be your circuit/power supply while the dashed box represents the whole array of panels (four in this case).

Measuring 5A should not be hard to do either, but someone else will have to hint you at viable solutions to safely measure those 600V.

Disclaimer: Your project is potentially dangerous to you or your environment. What I said above is my personal opinion and may be completely wrong. Proceed at your own risk, but do so very carefully.

Answer 6

Would it be possible to generate 5W through induction off the main feedline?

Otherwise, why not go the simpler approach and add a separate, smaller panel, to generate the 5W needed for the electronics?