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I need to power a 300 W class D amplifier with positive and negative 65 V.

As I'm a do-it-yourself guy, I didn't know about positive and negative voltage and ordered a bunch of these normal step-up converters which were fine for my last projects, where I didn't require + & - voltages:

https://www.ebay.de/i/232461793739

I did some research and found that it is quite easy to get +/- voltage out of two batteries, but I read also that cheap bucket step-ups don't isolate the ground so it can create short-circuits - this was mentioned in posts using ONE battery. As I'm using TWO, is that case not relevant for me?

Here is how I would wire it:

/-------------\ + ---------- + /-----------------------\ + ------ +65V
| 12V Battery |             in | 20a Step-Up Converter |out
\-------------/ - ---\  /--- - \-----------------------/ - ------ GND
                  | ----- |                                                 300W Amplifier
/-------------\ + ---/  \--- - /-----------------------\ - ------ GND
| 12V Battery |             in | 20a Step-Up Converter |out
\-------------/ - ---------- + \-----------------------/ + ------ -65V

I'm especially unsure if wiring the lower batteries - to the + of the step-up converter is correct? Also I'm unsure if it will work this way, as I experienced these converters have incorrect polarity protection built-in, to prevent damaging it if you accidentally connect it the wrong way around.

I'm happy if someone can give me a hint how I can get my amplifier to work, without buying other stuff.

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  • \$\begingroup\$ Are these car batteries? Or else what in particular makes you choose 12 V, per se? \$\endgroup\$ – jonk Jul 1 '20 at 19:36
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    \$\begingroup\$ Okay. I'll just assume, for now, that they are. Back in the day (long, long before you were born, I'm sure) we used to use a technique I discuss here. An adaptation of that idea would work here. And you'd only need the one car battery. \$\endgroup\$ – jonk Jul 1 '20 at 19:43
  • \$\begingroup\$ Yeah, they are 12v car batterys. I also got a 22V 10AH LiPo, but prefer 12v Car Batterys in that project as they are more eco friendly in recycling. The option you mentioned looks interesting, i didn't knew about that, maybe i'll look into it with an old-electronics-enthusiastic friend at some point, but for now i try to get things work for a session in two days so i guess that is not a quick option. And still i ask myself if i can make use of the 4 big dc converters i already got here. \$\endgroup\$ – HimG Jul 2 '20 at 9:45
  • \$\begingroup\$ A modern version isn't difficult to create. So just keep it in mind, for now. \$\endgroup\$ – jonk Jul 2 '20 at 10:01
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i got the solution for my problem:

Bat1 + -> + converter 1 +65 -> amp +
Bat1 - -> - converter 1 0   -> amp GND
Bat2 + -> + converter 2 +65 -> amp GND
Bat2 - -> - converter 2 0   -> amp -

So don't cross the battery output before it goes into the converters - For everyone who has the same question ;)

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  • \$\begingroup\$ Be careful how you mount these. The picture shows the mounting screws are on plated holes. These could be connected to VIN- or to VOUT-, or may not be connected to anything. If they are electrically connected, then mounting both boards on a metal plate could short your -65V to GND \$\endgroup\$ – Yellow Yeti Jul 6 '20 at 14:54

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