Dual Power Supply (+/-65V) from two 12V Car Batterys with two Dc Converters?

I need to power a 300 W class D amplifier with positive and negative 65 V from two 12v Car Batterys.

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:

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.

I’m especially unsure if wiring the lower batteries - to the + of the step-up converter is correct?

That will destroy the converter, if it does not have reverse polarity protection.

Just make the two battery/converter circuits identical and connect only the converter outputs in series, like you would two batteries. “GND” is the center connection to the amplifier.

converter 1 +65 → amp +
converter 1 0 → amp GND
converter 2 +65 → amp GND
converter 2 0 → amp -

Note: voltages are measured with respect the ground (GND), which can be freely chosen.

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?

That’s correct, but the batteries have to be isolated from each other. It looks like you have the + of one battery connected to the - of the other and that’s no good in this situation.

The inputs to both DC-DC converters should be connected “normally”… Positive battery to positive converter input. (You’ve got the bottom one reversed.) One of the DC-DC converter’s outputs is “positive ground”.

The negative/ground output of one DC-DC converter should be connected to the positive of the other. That’s your amplifier ground.

This isn’t actually in a car, right? In a car you could potentially get a short through the car ground through the signal connections or through the amplifier chassis, etc.

jremington:
Just make the two battery/converter circuits identical and connect only the converter outputs in series, like you would two batteries. "GND" is the center connection to the amplifier.

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

Note: voltages are measured with respect the ground (GND), which can be freely chosen.

Thanks for explaining things!
Still i'm a bit confused: So if + has 65, gnd has 0 and +65 and - has 0, where i get the 130Volt drop the Amp needs? Doesn't converter 1 would have to boost to +130V to achieve that?

DVDdoug:
This isn't actually in a car, right? In a car you could potentially get a short through the car ground through the signal connections or through the amplifier chassis, etc.

No, on a bicycle trailer/carrier :wink: I'll mount the amp and the converters in a wood box, so no worries about that.

where i get the 130Volt drop the Amp needs?

Voltages add in series.

65+65=130

What you decide is "0V" (GND) is arbitrary.

jremington:
Voltages add in series.

65+65=130

What you decide is "0V" (GND) is arbitrary.

Thanks a lot, so its just like putting two batteries in series, now i got it, worked great!

Just two last questions to wrap my head around the whole setup:

  1. The converters are rated max 20a each. This are 240w on 12v. But the amp could handle 300w (messured by people in the web). Is it right that with this serial setup the total amp flow is limited to the 20a of one converter and doesn't shares the load like it would be in paralell setup? So the whole 20a is going through all cabels and converters on full power? Or is it that the amp will drew its 300w for one half from the + to gnd end, and the other 300w from the gnd to - end, so each converter only has to bear 150w?

  2. I gues because the converters are boosting it to 65v anyway it doesn't matters wich type battery i connect, so i could also use one 12v Car battery and one 22V LiPo 6s battery as 1 and 2, right?

  1. Who knows? You posted no information about the amplifier.

  2. That should work for a while, but it won't be good for the batteries, the converters or the amplifier, if one battery goes dead before the other while the setup is operating.

It is best to have matched components, and you should have "battery low" detectors that shut the whole system down.

jremington:

  1. Who knows? You posted no information about the amplifier.

Ok, so it depends on the Amp, so i'll see if i can find infos in the data sheet. Its the IRS2092S btw.

jremington:
2. That should work for a while, but it won't be good for the batteries, the converters or the amplifier, if one battery goes dead before the other while the setup is operating.

It is best to have matched components, and you should have "battery low" detectors that shut the whole system down.

All right, i'll check the battery voltage for sure, won't be good if they run out on singel setup as well so i'm used to that. Some battery low beepers will be good help, for now i only got them for my lipo, so i'll look out to implement something like this for my 12v batteries as well. Other option would be to use the low voltage shut of adjustment of the step up converters.

Again, thanks a lot you took the time for giving the advises! Really appreciating this international forum culture!
Have a good time.

Unless you really need hundreds of watts, an amplifier based on the IRS2092S chip should run perfectly well on a pair of 12V batteries. No converter required.