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Sorry for the crude drawing I hope it explains the situation.

Basically I have 12 pieces of 24v panels connected in 3 strings of 4 serial connected panels. My Open Circuit Voltage is 150V and I can have 3x10=30A of closed circuit current. I have a charge controller which can accept 150V and charge a 48v battery bank. So far so good. But now I need to connect a pump driver (a frequency control inverter) which needs at least 340V. I was wondering is it possible to use diodes as shown in the drawing to get both 150V and 450V from the PV arrays without damaging anything ?

enter image description here

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  • \$\begingroup\$ There will be no current flow if the diodes are reverse-biased. \$\endgroup\$ – Long Pham Jun 5 '18 at 13:40
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No, you cannot do that. Nothing will go bang, but you'll only get 450v from it.

It's rather difficult to show why with the circuit as you've drawn it there. It becomes a little clearer when redrawn using a more conventional 'more positive, higher up the page' convention.

schematic

simulate this circuit – Schematic created using CircuitLab

You can see that D2 conducts, and that all other diodes are reverse biassed. I think you may have intended D6 to go from the top of the battery to the output. It would then conduct, but not improve the 'two voltage' scheme. You could also note that D2 is superfluous. Actually, all the diodes are superfluous, as the situation is static, all the conducting ones could be replaced with links, and all the blocking ones replaced with open circuits.

Each diode position could have a changeover relay, this would allow you to switch the array between 150v and 450v configurations. Make sure that the relays are break before make (most are). Make sure you cannot connect your charge controller when the panels are in 450v configuration, use another relay, switched with the voltage selectors, to disconnect it.

Or you could find a charge controller that accepts 450v, or a 150v motor controller. Or buck or boost between the two supply levels.

[EDIT] As the OP himself pointed out, high voltage DC relays are not easily obtainable, and FETs would be rather better switches. The following would make a suitable arrangement.

schematic

simulate this circuit

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  • \$\begingroup\$ Thanks for the quick answer, and sorry for the drawing. I am guessing there is no way to get more than one voltage using diodes or any other component in any way ? \$\endgroup\$ – Samet Sevilen Jun 5 '18 at 13:46
  • \$\begingroup\$ Thanks. I see a lot better as you draw it. I already have the charge controller and happy with it. Also I could not find a motor controller with low input voltages. I think about a boost controller from 150V to 300V but I cannot find a ready solution and I don't think I can build one myself (the current and voltage is out of my league). Seems like using relays is the cheapest and easiest option. I will not be able to use charge controller while driving motors, but it is OK. Thanks a lot ! \$\endgroup\$ – Samet Sevilen Jun 5 '18 at 13:59
  • \$\begingroup\$ For that voltage levels finding a mechanical relay can be expensive or impossible. I am thinking of using solid state relays or build a type of combiner box with high voltage MOSFETS. I can use 2 mosfets which will make the system 450V when in closed position. And another mosfet which disconnects/connects the charge controller. I can make sure that both cannot be open or close at the same time. \$\endgroup\$ – Samet Sevilen Jun 5 '18 at 14:16
  • \$\begingroup\$ @OytunYılmaz Yes, given that it's DC, which relays really don't like, and FETs do, that's a sensible choice. \$\endgroup\$ – Neil_UK Jun 5 '18 at 16:45
  • \$\begingroup\$ Thanks for the schematics, @Neil_UK. Are those MOSFETS considered high side ? Do I have to use high-side MOSFETS drivers with n channel MOSFETS, a P-Channel mosfet ? Or can I use N-Channel mosfets directly ? \$\endgroup\$ – Samet Sevilen Jun 5 '18 at 17:21

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