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Will OpenEVSE work with LCD disconnected?

I just finished building my OpenEVSE v4 bought in May the other day. Everything worked on the first try :-).

I charged my car on Level2 at 30A for about 15 minutes. Then I ran down to the basement to see if the 50A breaker was OK. Neither the breaker or the #6 wire had any abnormal temperature. I went back outside to check the NEMA 14-50 outlet and the plug felt fine. However, I can feel the AC input cable towards the cable gland was lukewarm (ambient temperature was around 78F). The OpenEVSE box itself felt fine, though.

Is this normal? I did not expect a 15-minute charging session at 30A will cause the 14-50 cable to be lukewarm at all. The cable was rated to be safe at 40A. Also the plug to the outlet was not warm at all. Later I opened the box and verified the AC terminals were indeed tightened properly.

If I disconnect the LCD will the OpenEVSE still work? If so I can check the temperature of various parts the next time I charge my car.


Hello, Le! Yes, the LCD is not an obligatory part of the OpenEVSE system. It simply serves to visualize the system, convenience. Only the LCD screen has its own RTCs that are responsible for the time. If you do not need the delayed charging function, which takes the exact time from these hours, then you can turn off the screen and everything should work fine.

Yesterday I found time to disconnect the cover and charge at 30A for 15 minutes. After that, I unplugged the unit and used a probe connected to my multimeter to get temperature readings from various parts.

The ambient temperature was 77F before the charging started.

After 15 minutes below are the readings:

Input cable near OpenEVSE box: 84F

Ev cable near OpenEVSE box: 81F

Struthers & Dunn relay top left terminal: 97F

Struthers & Dunn relay bottom left terminal: 95F

Struthers & Dunn relay top right terminal: 105F

Struthers & Dunn relay bottom left terminal: 98F

OpenEVSE controller: 90F

Since I did the reading in sequence the temperatures may be higher due to the delay in reading.

My question is: do these readings look normal? I did not realize the relay generates so much heat. All the terminals were tightened properly so the heat can not be from bad connection.

An even more alarming finding was that I noticed one of the 120V pin of the NEMA 14-50 plug was warm and it measured at 98F after 15 minutes of charging.

The NEMA 14-50 outlet is a Midwest U054 I got from home-depot:

I thought maybe the terminal was not tightened properly when the electrician installed it a year ago. I pulled the receptacle out and found the terminals were indeed tightened. 6 AWG stranded wires were used for neural and hot lines and 10 AWG stranded wires was used for ground. I am really not sure why one pin on the plug can be at 98F after 15 minutes of charging. This happened twice so far so it is not random thing. Maybe the receptacle is defective?

I noticed the wires were secured directly to the terminal without using ferrules. Shall I re-do the wires with ferrules? The electrician said he has installed EVSEs for Teslas so I assumed he knew the stuff.

within the EVSE all wires must be terminated in ring terminals for the Struthers and Dunn Relay. For your socket the wire should not have ferrules, this is only for finely stranded wire not the stiff wire used in the electrical system.

The temperature rise looks normal. All input cables and EV cables from OpenEVSE are certified to 105°C (221°F) so you are nowhere near where you need to worry. 

It's good to know the temperature looks normal. All the wire connections within the OpenEVSE are ring terminals.  It is just the wiring of the NEMA outlet was not. I need to investigate this further to see if the outlet was defective.

Turns out the cheap 14-50 outlet from homedepot (Midwest U054) was the problem. I swapped it out with a Hubbell HBL9450A and the outlet is no longer warm after charging.

I'm not sure if the U054 was defective, though. I measured the resistance between pins and they are below the limit my multimeter can detect. I can only assume the cheap pints on the U054 outlet somehow has greater resistance when plugged in and caused the outlet to warm up during the brief 30A level 2 charging session. I would image the U054 will hold fine for other usage such as an electric range or dryer.

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