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Can we use constant voltage + constant current 24 VDC supplies in parallel as shown below (to meet higher current/power demand):

Product link

Datasheet

wiring diagram

I have two opposing thoughts and hence the confusion.

  1. Parallel connection should be avoided because it is very common to have some voltage mismatch between two PSUs. When that happens, one PSU will try to drive some current through the other PSU and that might end up badly.

  2. Parallel connection is fine because PSU with higher voltage will naturally provide power to the load. In case of higher demand, a voltage drop on supply line will occur, and when it goes below the output voltage of other PSU, it will automatically start supplying power to the load.

Which one is correct?

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    \$\begingroup\$ It may or may not be acceptable. I've used Omron 24 V, 1000 W PSUs which allows parallel connection of two but not three units. (They didn't explain why.) What does the datasheet say? \$\endgroup\$
    – Transistor
    Sep 6 at 12:26
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    \$\begingroup\$ Current sharing is something that is usually designed in. If the unit isn't built for it, I wouldn't parallel them. It would (or should) be mentioned in the datasheet. To answer your question "which is correct", the answer is both depending on the supply. Although in case 2 that doesn't necessarily mean that they will share current well. Post a datasheet for the power supply and you will get better answers. \$\endgroup\$
    – Stiddily
    Sep 6 at 12:40
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    \$\begingroup\$ Note that when paralleling switch-mode supplies, each addition places the output capacitors in parallel. This has the affect of adding the capacitance together, which will eventually upset the control loops and lead to instability and oscillation. If the datasheet claims a maximum output capacitance, do not exceed via parallelization. \$\endgroup\$
    – rdtsc
    Sep 6 at 12:50
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    \$\begingroup\$ @stiddily - apologies. I have added the datasheet. Also, the PSU says CV+CC. Sorry to miss out on this detail. The sample I had in hand didn't say so on it. \$\endgroup\$ Sep 6 at 13:34
  • \$\begingroup\$ @rdtsc - that's a valid point. However I couldn't find any spec related to max capacitance in the datasheet. \$\endgroup\$ Sep 6 at 13:36

2 Answers 2

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There is nothing in the datasheet explaining how parallel arrangements would work, so assume it is not supported. Furthermore that is actually a constant current power supply. According to the manual you can run it in constant voltage mode, but it might be cheaper to buy a regular 24V power supply rather than pay for two CC supplies you don't need.

If you want to use two separate power supplies (for example to power from opposite ends of a run of lights), cut the strip down the middle and use two different RGB controllers, one per end.

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Yes it is possible to adjust two of these supplies to share current with a stable load and stable conditions. It is also possible to adjust it, so that it oscillates and is unstable.

Let's consider the 300 W, 24 V supply is rated for a R=V^2/P = 2 Ohm resistive load (approx.) perhaps with forced air cooling)

Thus two supplies might be rated for a 1 Ohm load.

The 24V supply load regulation error is +/-1%. That means the voltage source resistance is <= 1% of rated load or 20 mohm per unit.

The DC unit will have some CC-CV error bandwidth which can regulate disturbances < less this BW. There is no Meanwell step-load regulation error spec. and phase margin + BW is unknown.

You will want some kind of filter to reduce the disturbance of current to the regulator such that the DCR and ESR of the L,C components are about equal or less to the supply step load resistance. With a low duty cycle load that raises the average impedance and a high DCR can add damping and isolation but also affect phase margin of supply.

here is an example of a single supply and filter with PWM in on and off state

enter image description here
enter image description here

When two voltage sources are balanced with no step load disturbances, you want the voltage regulated within 0.1% so that the current can be shared somewhat equally.

In some cases such as tandem power transistors with slightly different hFE's they will add 0.1 to 0.2 ohms with each emitter depending on max power for a 8 ohm speaker. Now imagine you have a 1 to 2 Ohm speaker. You may want to consider this and don't add any stored energy reactance filter to the PWM and just run it so that it is not harmonically related to the Meanwell switcher frequency in case of intermodulation or aliasing.

Anecdote.

I once fixed a production problem in a Unisys factory over 20 yrs ago with two redundant "Power One" rack-mount power supplies in current sharing mode that oscillated under light loads. The solution was to adjust voltages to match with no error (<0.1%) powering CPU MOBOs. These were already designed with current-sharing links.

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