MME keeps tripping breaker

jrstinkfish

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Starting about 2 months ago, my MME seems to trip the breaker for my charger seemingly every time I try to charge. I have to go outside and flip the breaker switch to get it to start charging again. My wife's Kia Niro EV charges without issue, so I am feeling confident the issue is with the MME, though I suppose it could be the charger, but just not sure why it would do it just for the MME.

I've had my Wallbox installed for about a year with no issues. Now, it is hot this time of year in Memphis, but again, it doesn't affect my wife's Niro when it's charging, just the MME.

Anyone else experience an issue like this?
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what type of box? what size breaker? what size line to the wall box?
 

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How big is the breaker? What is the max current setting of the EVSE? The MME can only draw whatever the max current is set to in the Wallbox. From the sound of it, the Kia EV draws less current.

In short, the problem is not with the car, its with the EVSE or breaker. Breakers do go bad over time and become more prone to tripping at a lower current.
 

Mach-Lee

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What size is the breaker and how is the Wallbox installed? Plug or hardwired?

A Kia Nero draws less power (30A max) than a Mach-E (48A max) while charging.
 


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jrstinkfish

jrstinkfish

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It was installed last August. A dedicated 240v 50 amp circuit was installed, as well as a new breaker for the charger (I am not sure the size of the breaker). It is a plug-in model. I guess I can call the electrician and see what he says, and dial down the amps in the Wallbox app until then.
 

Mach-Lee

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It was installed last August. A dedicated 240v 50 amp circuit was installed, as well as a new breaker for the charger (I am not sure the size of the breaker). It is a plug-in model. I guess I can call the electrician and see what he says, and dial down the amps in the Wallbox app until then.
OK, you need to go into your electrical panel and verify the charger breaker says "50" on it. You also need to verify the Wallbox is set to 40A (proper setting for a 50A breaker). I'm guessing the electrician didn't set the amperage correctly when it was installed (many don't). If you can set it to more than 40A in the app then he messed up and you need to call him back to set the amperage dial in the unit correctly.

The maximum rate you can charge the car on a 50A breaker is 40A. By default the car will try to charge at 48A which is too much. If you have a 40A breaker then it needs to be set to 32A.
 

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It could be "brown outs" in your local grid during hot summer peak hours ... an under voltage situation will cause your amp to spike up thus tripping the breaker which otherwise would not have done during winter or colder days. I did dialed my Tesla J1772 Wall charger from 40A down to 36A (50A circuit breaker)... and it did lower the cable temperature.
 

Mach-Lee

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It could be "brown outs" in your local grid during hot summer peak hours ... an under voltage situation will cause your amp to spike up thus tripping the breaker which otherwise would not have done during winter or colder days. I did dialed my Tesla J1772 Wall charger from 40A down to 36A (50A circuit breaker)... and it did lower the cable temperature.
The car will not up the amps if the voltage sags, it's locked to whatever current limit the EVSE is set to. So it will draw 40A regardless of whether it's getting 240V or 180V. Works differently than induction motors which do draw more current as voltage sags.
 

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The car will not up the amps if the voltage sags, it's locked to whatever current limit the EVSE is set to. So it will draw 40A regardless of whether it's getting 240V or 180V. Works differently than induction motors which do draw more current as voltage sags.
Good to know ... thanks for the info. But in my case, my garage was over 98ºF in the night and my wiring was at 110ºF, by dialing down to 36A I was able to lower the temp to about 99-100ºF.
 

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Good to know ... thanks for the info. But in my case, my garage was over 98ºF in the night and my wiring was at 110ºF, by dialing down to 36A I was able to lower the temp to about 99-100ºF.
110ºF wire temp is totally fine and normal/expected in a 98ºF garage. I would only get worried if you see temps more than 40ºF over ambient or about 140ºF or higher. No safety issue there, but I understand if you want to reduce heat output.
 

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110ºF wire temp is totally fine and normal/expected in a 98ºF garage. I would only get worried if you see temps more than 40ºF over ambient or about 140ºF or higher. No safety issue there, but I understand if you want to reduce heat output.
Yes ... the temp went down considerably and still be able to charge within the Duke Energy's OFF PEAK hours window. Didn't see any noticeable longer hours ... charging from 15% - 90% SOC from 10:00PM to 02:30AM and up 100% by 03:30AM.
 

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Do you have confidence in your electrician? If not get another. If so, send him back. You should not be tripping a 50A.
 

mikenindorf

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our house has breakers that would randomly trip. Was not a load issue, but a breaker issue. I replaced all that where built in between 2016 and 2018. Date is on the breaker. I was told by the electrican that installed them originally, that some of the breakers built then have bad software. Why did he install them orginally- builded gave him no choice. or he was looking for side work.
 

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OK, you need to go into your electrical panel and verify the charger breaker says "50" on it. You also need to verify the Wallbox is set to 40A (proper setting for a 50A breaker). I'm guessing the electrician didn't set the amperage correctly when it was installed (many don't). If you can set it to more than 40A in the app then he messed up and you need to call him back to set the amperage dial in the unit correctly.

The maximum rate you can charge the car on a 50A breaker is 40A. By default the car will try to charge at 48A which is too much. If you have a 40A breaker then it needs to be set to 32A.
What's the reasoning for this 40Amp max on a 50amp breaker? I'd like to read more about it. My car can pull 48amps continuously on a 50 amp breaker without tripping it.
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