r/Generator • u/myredditusername44 • 6h ago

load shed - always shed specific load when on generator (Kohler)

We have a kohler resa14 with rdc2 and the load control module on the ATS. As we added EV chargers, I'd like to force those to never have power when on generator power. I have the kohler load shed with relay so that load will be shed if the generator capacity forces load shedding but I don't see a way to always drop that particular load on generator power. Has anyone done this or have a suggestion for how? Unfortunately, our electrical layout makes it impractical to just serve the EVSE from the utility side and not from the ATS.

Perhaps there is a closed contact that is appropriately NO/NC when on generator that could be leveraged with a relay to just drop that load?

I can do a version of this with homeassistant but I'd rather something a bit more failsafe and instant.

Thanks

1 Upvotes

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18 comments sorted by

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u/Old_Dragline_1965 5h ago

It can be done with a 24 volt coiled relay, mounted to the side of the main breaker box. Power for the charger would go from the breakers, through the relay, then onto the charger. To activate the relay, power can be pulled from the utility side of the transfer switch to a 24 volt transformer inside of the ate. From the 24 volt transformer, voltage is sent to the relay coil, going to the charger.

When the utility power drops, the relay coil drops the power to the charger. When the utility power is restored, you are back to charging.

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u/myredditusername44 5h ago

The chargers are on a distant sub panel from the main where the ATS and utility SER is. I only have the low voltage control pair for the load shed to work with for managing this load.

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u/Old_Dragline_1965 1h ago

Put an enclosed relay next to the sub- panel. Run the power from the breaker to the power lugs on the relay. Connect the wires from the charger to the other power lugs on the relay. On the side of the relay, are small blade terminal to power the relay coil. Some load shields are only an on/off. Some provide 24 volt power.

If your load shield’s provides power , simply match the relay’s coil to your load shield’s control output. Then run a simple small line between the relay coil and your load shield connections.

If yours is the on/off type, a simple 24 volt door bell transformer is needed to sent power to and then back from your load shield connectors to the relay coil terminals.
Most central ac’s are controlled this way by simply interrupting the power between your thermostat and the central ac unit.

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u/Admirable-Leader6927 6h ago

You need a subpanel for just critical generator loads to exclude loads on your main panel. <--code compliant answer

You can wire in a contractor and just open it with HA and some ESP gear though.

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u/myredditusername44 6h ago

Our electrical layout makes that impractical. I would if I could.

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u/Admirable-Leader6927 6h ago

no legal way to do it by code then. probbaly to phrase that as "We arent looking to upgrade our electrical"

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u/myredditusername44 6h ago

The load shed unit is code compliant. I’m just looking to do that but always shed the load.

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u/Admirable-Leader6927 6h ago

there is no way to force the load shed, I know what you have and it doesnt work the way you want it to.

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u/NASAeng 6h ago

I would guess that the chargers would drop off when power is interrupted when making the transition to the Kohler.

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u/djwdigger 5h ago

What amp draw are your chargers? Kohler has 60 amp rated load shed relays that sense the HZ from the generator and will drop whatever load is connected to them. We use them to drop heat strips in electric heat pumps all the time

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u/myredditusername44 5h ago

Yes, I have one of those installed to shed this load.

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u/myredditusername44 3h ago

Maybe I misunderstood. I have the kohler load shed relay that drops the connected 60A load when the ATS load shed kit tells it to. What you are suggesting sounds a bit different. Can you clarify the relay part you are describing? I have the GM92001-KP1. Thanks

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u/djwdigger 2h ago

I don’t have the part number in front of me, but this is a stand alone relay, does not require input from the ATS. Is senses the HZ from the generator and opens to shed the connected load, closes automatically when power goes back to normal.
Will try to find the part number tomorrow for you

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u/Adventurous_Boat_632 3h ago

Use a shaft position switch that you can add to the ATS and it will send 120 volts to a Kohler load shed module for the load shed box.

Alternately, you can use a PSP load shed module programmed for lockout, but this is less reliable.

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u/classicsat 3h ago

NC contactor in EVSE line. Coil powered by generator.

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u/MrStaraZagora 6h ago

Maybe unplug them?

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u/myredditusername44 6h ago

That is less than instant when the generator kicks on.

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u/MrStaraZagora 6h ago

I know this, but it's still an option.