#### Budda

Joined Sep 9, 2022
1
Ok so I have a 30 volt at 3amps power supply and I need a power supply at 18volts at 30amps. So I was wondering if I took the the 30 volt power supply and combine the ampage from a 12volt 100ah battery with the 18volts after the voltage regulator.
Because I've already know and tested the regulator with current booster circuit section and it works but thats from the same power supply with a voltage higher then the output voltage. So I was wondering if the same circuit would work but using a different power source for the current booster section of the circuit and then have it go into a audio power amplifier output section.

#### Papabravo

Joined Feb 24, 2006
21,013
Have you done your power out versus power in calculation?
Input power
30V x 3A = 90W​
12V x 10A for 10 Hours = 120W​
Output power
18V x 30A = 540W

You might be off by a little bit. You can't get something from nothing. That's called overunity and it is a banned topic here. So, your idea is, shall we say, stillborn. Actually, can I get some of what you've been smoking?

Last edited:

#### WBahn

Joined Mar 31, 2012
29,867
Have you done your power out versus power in calculation?
Input power
30V x 3A = 90W​
12V x 10A for 10 Hours = 120W​
Output power
18V x 30A = 540W

You might be off by a little bit. You can't get something from nothing. That's called overunity and it is a banned topic here. So, your idea is, shall we say, stillborn. Actually, can I get some of what you've been smoking?
What is the basis by which you are assuming that the 100 Ah, 12 V battery can only supply 10 A?

A typical car battery has about 40 Ah to 50 Ah, yet can deliver hundreds of amperes, in many cases over a thousand. There's no one-size-fits-all way to go from a battery's charge capacity to it's current capacity.

But even if the battery could produce the 40+ A of current needed to make the power balance numbers work out, the circuit has zero change of doing anything useful. If nothing else, the base of the pass transistor will be much higher than the emitter voltage forcing them into cutoff. Even if that weren't the case, the collector voltage would be 18 V while the emitter voltage is only 12 V. Not gonna work.

#### Papabravo

Joined Feb 24, 2006
21,013
What is the basis by which you are assuming that the 100 Ah, 12 V battery can only supply 10 A?

A typical car battery has about 40 Ah to 50 Ah, yet can deliver hundreds of amperes, in many cases over a thousand. There's no one-size-fits-all way to go from a battery's charge capacity to it's current capacity.

But even if the battery could produce the 40+ A of current needed to make the power balance numbers work out, the circuit has zero change of doing anything useful. If nothing else, the base of the pass transistor will be much higher than the emitter voltage forcing them into cutoff. Even if that weren't the case, the collector voltage would be 18 V while the emitter voltage is only 12 V. Not gonna work.
What does "zero change of doing anything useful." mean precisely? I'm not familiar with that particular terminology.

#### WBahn

Joined Mar 31, 2012
29,867
Typo. Consider it a puzzle.

#### AnalogKid

Joined Aug 1, 2013
10,944
In order for a 12 V battery to "combine the amperage" with an 18 V circuit, its output voltage must be boosted. At 100% efficiency (?!?), this increases the battery's output current by 50%. That is, for the battery to contribute 27 A to the circuit output, it must supply 40.5 A of battery output current to the boost converter.

That is at 100% converter efficiency. At a far more reasonable 80% efficiency, the battery has to supply over 50 A. Note that a 50 A boost converter is not an easy circuit to design.

ak