[SOLVED] HV - LV Common Ground Problem

Hi All,

I try to build an electric car. Here is the basic shematic of my system. The scenario is below for the car's off position.

There is red a circle after DC/DC converter which indicates control circuits for 12V auxiliary battery. I intend to control output of DC/DC converter's output via this control circuit (when the vehicle is off). When 12V battery's voltage drops below specified value control circuit makes on the switch and main battery supplies 12V aux battery until its voltage level increases specified value.

I would like to know your thoughts, advices and experiments about this control circuit.

Another thing is about DC/DC converter's isolation. I purchased Delphi's 2.2kW universal DC/DC converter.

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I intend to make it always on for supplying aux. battery when it's voltage level is drop. As I mentioned above, I only contol its output via control circuit. But converter does not have galvanic isolation. It means that high voltage is not separated from low voltage equipments with transformer. Does this situation contain risk?

Note:

LOAD1 indicates devices which should be always on.

LOAD2 indicates devices which should work after ignition on.

Best regards.

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It sounds somehow arbitrary that the HV bus is grounded at the DC/DC converter, if grounded at all. Are you sure about it? Can you post the manual or a block diagram of the converter? According to my knowledge, the HV bus would usually implement isolation and an earth-leakage monitor for safety reasons.

@FvM thanks for reply. There is no clear statement in its manuel. And there is nothing about isolation without the statements which are in the attachment picture.

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Clear enough, though.

FvM said:

Clear enough, though.

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Do you think it is enough to see this statement about isolation. Unfortunately there is no any technical info about isolation.

What are you missing? Isolation can be expected according to applicable safety standards for 400V working voltage.

The link that you have provided gives the following error message:

Unfortunately the page you are looking for is not a part of Delphi

Yes, you get this invalid links by copying a link shortcut as text

I am sorry for delay to answer.

The link that you have provided gives the following error message:

Unfortunately the page you are looking for is not a part of Delphi

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@schmitt trigger, DC/DC converter is produced by Delphi. And the links are alive.

What are you missing? Isolation can be expected according to applicable safety standards for 400V working voltage.

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@FvM, you are right. Isolation is expected for safety but I couldn't see any clear expression in their manual. I sent mail about isolation question. And they answered :

"The grounds are isolated internally in the DC-DC converter, and should never be connected together. "

Thanks for your interest.

And the links are alive.

Click to expand...

They are. But you never tried what you copied as "link" in post #1.

@FvM, yes as you mentioned above it doesn't work. Here is the link for pdf :

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