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OpenEVSE Current Throttling

I recently got a new car and my OpenEVSE seems to be throttling when charging at 40amps. It takes about 30 minutes to get up to 65c before throttling current down to 18amps (I think). It stays there until it cools to 55c and current ramps back up to 40amps. From there it curves up and down.

Any tips on how I can fix this issue?

I think my OpenEVSE is a v4 Advanced build from early 2017 (EVSE firmware version was originally 3.10 I think). It is plugged into a 14-50 outlet. I replaced the Struthers contactor early last year (stuck contactor errors became more frequent) and upgraded the ESP8266 to an ESP32 about a year ago now (WIFI stopped working on the ESP8266). 

Before this, I have been charging at around 24-30amps no problem for years. Other that the higher than expected idle temps, it has been working fine (5c over ambient is what I see when idle) without overheating.

Current firmware:

EVSE: 4.8.0 (anything higher and it seems to freeze with the ESP unable to communicate with it within a day of powering up)

WIFI: 4.2.2 (v2 GUI)


Hi Mark,

With WiFi 4.2.2 v2, you should be running firmware 8.2.2. 4.8.0 has a ton of missing RAPI commands. Lots of WiFi features will not work correctly. We are not aware of any freezing issues with OpenEVSE 8.2.2 and WiFi 4.2.2 v2.

Idle at 5C over Ambient seems about right. Is your station outdoors in the sun or inside? What is the temperature in the environment where your station is located. How long does the station stay at reduced current?

Here is an article on the throttling feature.

OpenEVSE support

Hi! Thanks for the quick response.

I will try updating the firmware to the latest version sometime today and report back any issues. When the OpenEVSE freezes, I can connect to the ESP fine and see the commands it sends to the OpenEVSE. The OpenEVSE does not respond back though.

The unit is inside the garage, mounted on a wall against the house (attached garage) and 5ft off the ground, and hidden from the sun.

I saw throttling last Saturday and the ambient temp was around 85* when charging the car. Image of session attached. The 30amp was one car and the 40amp was another. Sorry the graphs are not time-aligned as I wanted to show how the temperature stabilized over time.


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Quick update on firmware: OpenEVSE was updated to the 8.2.3 firmware and has been working without issues the past few days. My issues might have been caused by the use of RAPI to limit max current.

I will try and use my temperature gun over the weekend to see what is getting hot.

I was able to get some temps after 30 minutes of charging at 30amps. The hottest part was in between the 2 output terminals on the contactor. Left side and both contacts were at ~72c (160f). The right side was 82c (180f). The black plastic in between the 2 terminals measured at 93c (200f).

Terminals are secured so I'm not sure why its getting so hot.

Do you think a higher capacity contactor help?


The Struthers Dunn contactor is rated to 50A and the insulation on all AC lines are 105C.

Yes, higher capacity contactors and thicker wires have less resistance and less resistance means less heat.

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