# Power Supplies in Parallel

#### mihaist

Joined Oct 25, 2021
3
Hi,

I have a power supply (PS1) of steady 400V, and a second power supply (PS2) that can offer 0-400V. How it is possible to connect the two power supplies in parallel to a load so that:
1. Only PS2 is used if its output voltage is higher then 350V
2. If PS2 output voltage drops below 350V, PS1 is only used

#### MrChips

Joined Oct 2, 2009
24,611
Two diodes.

Welcome to AAC!

#### mihaist

Joined Oct 25, 2021
3
Two diodes.

Welcome to AAC!
But, two diodes will work fine if you want to pull the current from the power supply with the highest voltage. I am interested in using just the PS2 up until its voltage drops to 350V, while the voltage of PS1 stays 400V. And when the PS2 voltage drops below 350V, switch to PS1.

#### ElectricSpidey

Joined Dec 2, 2017
1,962
It's possible, do you need complete circuits or just ideas?

Is it the load that is pulling PS2 down?

The basic concept could be to monitor the voltage on PS2 then use a relay or other device to switch the supplies.

You would need a divider, comparator etc, but the issue is if it's the load pulling down PS2 then how would you avoid oscillations.

Last edited:

#### mihaist

Joined Oct 25, 2021
3
It's possible, do you need complete circuits or just ideas?

Is it the load that is pulling PS2 down?

The basic concept could be to monitor the voltage on PS2 then use a relay or other device to switch the supplies.

You would need a divider, comparator etc, but the issue is if it's the load pulling down PS2 then how would you avoid oscillations.
Hi,
It would be nice if you could reference a circuit.
PS2 is represented by solar panels. PS1 is a battery pack.
It may also work in this way: if PS2 falls below 350V, PS1 is used in parallel with PS2.

During day the solar panels can provide the necessary power. When there is no sun, just a small load will make PS2 voltage drop a lot.

#### ElectricSpidey

Joined Dec 2, 2017
1,962
Simply switching between power supplies is a simple concept, but it sounds like you need a solar power system, and that is not my wheelhouse, but there are other people on this board who can help you with that.