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I've noticed that when charging my Tesla on my 40A OpenEVSE, after a while the EVSE limits the charge rate to 20A because it has gotten over 60C.  It stays at 20A for 5 minutes or so, then goes back to 40A for 10 minutes, then back to 20A. Up and down.

I don't think this is a problem, but it does mean that the car charges a little more slowly than it could, since it averages 33A while in this mode.

However, I notice that the OpenEVSE case is a sealed enclosure.  Given that my unit is mounted inside my garage, far from any door or window and not going to get wet, would it be useful to cut some ventilation holes in it for cooling?  I'd probably put them on the side, one near the bottom and one near the top.

Does anyone see any issues with this?

Oh, it's also worth mentioning that the 33A average is at current temperatures (springtime).  In the summer when the garage is hotter, I expect the reductions to be longer and more frequent, and the net charging rate slower.

Shawn we would recommend inspecting your station, you should only see throttling at 40A if ambient temperatures are above 110°F. Please look at the interface between your cables and contactor, this is the most common cause of excess heat. For the Packard contactor with screw terminals, sleeve ferrules must be installed on the cable ends.

Ventilation is not recommended and can be very unsafe. In a sealed enclosure a fire would almost instantly consume all the oxygen go out and the station would shutdown. With ventilation a fire can ignite, continue to burn and spread.

Hmm. My kit came without the lugs, so I cut the ferrules off, stripped the wires and wrapped the wires around the screws. Everything should have really good contact.

I'll let it warm up and then disconnect and open it up and see where the hot spots are.

The argument against ventilation makes sense.

It's the relay (Struthers & Dunn) that's getting hot. The hottest parts of it are the low-voltage screws, which seems odd.  My infrared thermometer measured them at about 160F right after I opened the cover. The input and output terminals were all about 145F.

The low voltage screws power the relay coil. The coil resistance is 70 Ohms so at 12v that is 2.05 watts, so the heat is not too odd.

We will send you heavy duty ring terminals and see if that helps.

Thanks!  Could you also send new wires?  I cut the ends off of mine.  Do you need an address?

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