I'm looking at a Crydom HDC100D160. This picture is really all the detail the datasheet provides as far as usage.

Diagram from Datasheet

On the output side, does the polarity for my DC equipment or the direction of charge really matter? My application is to connect a solar system to a battery. At different times, I need to either charge the battery when the sun is out or to have the battery provide power for the system when the sun is not out.


2 Answers 2


The data sheet clearly indicates that the polarity is important.

+/L1 -/L2


On the output side does it really matter on the polarity for my DC equipment or of the direction of charge?

On this model yes, it does. Look at the MOSFET symbol in your diagram; it incorporates a diode and current will always flow in that direction irrespective of whether the relay is activated or not: -

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The clue is in the part number: HDC100 implies a DC output where polarity is important. If you look at a HAC model from Crydom, it can have an AC load current: -

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  • \$\begingroup\$ However, as the HAC model uses thyristors for its output, it can only have an AC load. It can't control a DC load that may need reverse charging current. \$\endgroup\$
    – Hearth
    Nov 25, 2022 at 21:32
  • \$\begingroup\$ Precisely, it is only suitable if the AC commutates the thyristors @Hearth. I'm not recommending this part; I'm just pointing out that the DC part in the device product name means it cannot be used to switch an AC voltage on and off effectively. \$\endgroup\$
    – Andy aka
    Nov 25, 2022 at 21:37

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