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Charging the Leaf using a step-down transformer

Posted: Mon Oct 19, 2020 1:29 pm
by dmacarthur
Hi all- I am sure this is covered somewhere herein, but I can not find it and am hoping that you will take pity on me. I have been charging L1 at my garage, a long way from the house, it has worked fine for a couple of years but the voltage while charging (at the garage ) is about 100 volts and I know this is terrible for efficiency and speed. So today I dragged out an old 240V-120V transformer, swapped out the breakers at the house, ran 240 to the garage and plugged the Nissan factory EVSE in. Voltage reads 120 exactly, herz is 60 exactly, but the EVSE just blinks and does not power up. Plugging it back into a regular 120V outlet it all works fine. Some sort of workaround is needed clearly..... Similar to charging with a generator? Thanks all,... Dan

Re: Charging the Leaf using a step-down transformer

Posted: Mon Oct 19, 2020 1:43 pm
by LeftieBiker
Did you ground the new circuit? Most EVSEs won't work on ungrounded circuits. If you did ground it, check the solidity of the ground anyway.

Re: Charging the Leaf using a step-down transformer

Posted: Mon Oct 19, 2020 6:05 pm
by dmacarthur
I will double check- ground wire is continuous at least back thru the transformer......

Re: Charging the Leaf using a step-down transformer

Posted: Tue Oct 20, 2020 11:17 am
by dmacarthur
Ground is good, I have tried adding a separate ground along the way and the EVSE still blinks green, never starts charging OR shows Fault.... and the EVSE still works on the other older smaller circuit..... Something about transformed AC and the ground being separate? do I need to ground the body of the transformer? will try that.....

Re: Charging the Leaf using a step-down transformer

Posted: Tue Oct 20, 2020 11:43 am
by dmacarthur
PS- the Duosida EVSE works just fine, only the OEM Nissan seems to balk..... guess I am using the Duo!

Re: Charging the Leaf using a step-down transformer

Posted: Tue Oct 20, 2020 1:12 pm
by LeftieBiker
I believe the ground has to originate at the same panel as the circuit.

Re: Charging the Leaf using a step-down transformer

Posted: Tue Oct 20, 2020 3:50 pm
by dmacarthur
Even with that ground all the way back uninterrupted, the Nissan EVSE would not work. (although the Duosida does).... the transformer is ancient and I have a newer one with a grounding wire attached, which MAY solve the issue..... But thanks Leftie for your thoughts I will keep plugging away!

Re: Charging the Leaf using a step-down transformer

Posted: Wed Oct 21, 2020 5:25 am
by nlspace
The OEM EVVSE has an internal circuit which does a ground check before it will turn ON. It intentionally shorts out the input leads to ground to measure a current and verify that a path to safety ground exists.

Ground in your Mains panel is the mid-point of the transformer secondary on the pole at the street and the metal rod driven into the earth, which is also connected to the Neutral of the Line-Neutral pair of wires that provides 120vac. So both the 120 Line-Neutral and the 240 Line-Line have a path back to the earth thru the green ground wire in the connector plug.

But your step-down transformer is an isolation transformer--the secondary is totally isolated from the primary. So neither leg of your secondary has any connection path to ground or protective earth even if you run a wire from the panel or right at the transformer. So the ground test fails in the EVVSE and it won't turn ON.

You would need to connect the "Neutral" (wide blade of the 120vac plug, white wire) side of your isolated secondary to the green ground wire in order to pass the check.

This same issue can occur when trying to use a portable generator to supply AC for the EVVSE--unless the Neutral is tied to Ground it will fail the internal check.

Re: Charging the Leaf using a step-down transformer

Posted: Wed Oct 21, 2020 5:56 am
by jjeff
nlspace wrote:
Wed Oct 21, 2020 5:25 am


You would need to connect the "Neutral" (wide blade of the 120vac plug, white wire) side of your isolated secondary to the green ground wire in order to pass the check.
Agree but not sure if it's safer but don't some people use a plug with a resistor(not sure of value but for sure in K-ohms) to bond the neutral to ground? I believe this fools the check but still has some degree of isolation between ground and neutral.....

Re: Charging the Leaf using a step-down transformer

Posted: Wed Oct 21, 2020 8:07 am
by dmacarthur
nlspace wrote:
Wed Oct 21, 2020 5:25 am
The OEM EVVSE has an internal circuit which does a ground check before it will turn ON. It intentionally shorts out the input leads to ground to measure a current and verify that a path to safety ground exists.

Ground in your Mains panel is the mid-point of the transformer secondary on the pole at the street and the metal rod driven into the earth, which is also connected to the Neutral of the Line-Neutral pair of wires that provides 120vac. So both the 120 Line-Neutral and the 240 Line-Line have a path back to the earth thru the green ground wire in the connector plug.

But your step-down transformer is an isolation transformer--the secondary is totally isolated from the primary. So neither leg of your secondary has any connection path to ground or protective earth even if you run a wire from the panel or right at the transformer. So the ground test fails in the EVVSE and it won't turn ON.

You would need to connect the "Neutral" (wide blade of the 120vac plug, white wire) side of your isolated secondary to the green ground wire in order to pass the check.

This same issue can occur when trying to use a portable generator to supply AC for the EVVSE--unless the Neutral is tied to Ground it will fail the internal check.
Thanks, it makes sense explained that way- Duosida must not have the ground check circuit.....