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DC Power Supplies in Series?

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skywalker898

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Hi, I would like to connect two DC power supplies in series, and I am wondering what is the proper way to do this. Some websites recommend a reverse biased diode across the output of each power supply, but I do not understand the reasoning for this. In case you want to know the actual model numbers of the power supplies, I am using an 18V HY1803D, and a 24V SDN 2.5-24-100p. Any suggestions about DC supplies in series?

Here is info about each supply: View attachment SDN-P.pdfView attachment Mastech-HY1803D-DC-Regulated-Power-Supply-Users-Manual1.pdf

Thanks,
Brandon
 
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This thread explains the reasoning why ordinarily you can't parallel supplies, and about the reason for diodes:
 

Hi sky_123, that post is about power supplies in parallel and doesn't answer my question. I would like to connect two power supplies in series.
 

ah! so sorry. I misread. For series, in theory there could be issues, and primarily these stem from the fact that the circuitry is an unknown factor in the power supplies, and if (say) one power supply is switched on but the other isn't, then a voltage across the 'off' power supply (since now the 'off' power supply is essentially a 'load' to the 'on' power supply in series with the actual load) may cause it damage. For example, the supply may have internal polarized capacitors across the supply rails, and diodes that may not withstand the voltage that they are being subjected to. So, ideally you'd want to step-up a supply, rather than put them in series.
 
That's a good point with the possible problems when one power supply is turned off. I've drawn up a schematic with diodes that I believe protects each power supply from any reverse voltages when any power supply is turned off. Do you think this would fix the problems you speak of?



Thanks,
Brandon
 

Hi,

I think so, I think that might work. However, I really don't want to risk your power supplies! Hopefully someone else on the forums can concur or suggest an alternative.
 

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