Isolation Requirements for Low Voltage DC Charging System

[sabu31]

Dear All,

I would like to know if there is a mandatory requirement for isolation when charging a 48V lead acid/lithium ion EV battery from a 120V DC source. Can non isolated chargers be used for the purpose. Are there any specific standard regarding same.

Thanks

 

[stenzer]

Hi,

if you are planing to design the charger by your own make a web-search for IPC-2221. There are clearance distances stated which are accepted by the electronic industry.

The clearance depends on the applied voltage and the kind of trace by means of coated or uncoated. Be aware there is also a larger clearance required if the circuitry is operated above 3050 meters.

Generally, for voltages larger than 60 V DC you have to take measures to avoid the touching of the circuitry. Of course you can use a 120 V DC non-isolated based charger as it is done for various SMPS. But you have to take care that no one is touching the 120 V DC part of your electronics e.g. by an appropriate housing.

BR

 

[KlausST]

Hi,

Of course you can use a 120 V DC non-isolated based charger as it is done for various SMPS. But you have to take care that no one is touching the 120 V DC part of your electronics e.g. by an appropriate housing.

Non isolated with 120V input .. means you need to treat the 48V like it was 120V.

A single failure may cause the high side of 120V short to earth ground making all the batteries potential lifted up by (-) 120V.

Now it depends on the regulations whether 120V DC needs to be protceted by isolation/housing or not.

Klaus

 

[stenzer]

Hi Klaus,

A single failure may cause the high side of 120V short to earth ground making all the batteries potential lifted up by (-) 120V.

thank you for pointing this out!

 

[sabu31]

Hi,

Non isolated with 120V input .. means you need to treat the 48V like it was 120V.

A single failure may cause the high side of 120V short to earth ground making all the batteries potential lifted up by (-) 120V.

Now it depends on the regulations whether 120V DC needs to be protceted by isolation/housing or not.

Klaus

Thanks KlausT for the reply. But is there any IEC standard that mandates isolation for 120V DC

--- Updated Sep 25, 2020 ---

Hi,

if you are planing to design the charger by your own make a web-search for IPC-2221. There are clearance distances stated which are accepted by the electronic industry.

The clearance depends on the applied voltage and the kind of trace by means of coated or uncoated. Be aware there is also a larger clearance required if the circuitry is operated above 3050 meters.

Generally, for voltages larger than 60 V DC you have to take measures to avoid the touching of the circuitry. Of course you can use a 120 V DC non-isolated based charger as it is done for various SMPS. But you have to take care that no one is touching the 120 V DC part of your electronics e.g. by an appropriate housing.

BR

Thanks Stenzer for the reply. So mainly Creepage and CLearance should be taken care of. But there is no specific standard as such which clarifies this issue of isolation ?

 

[KlausST]

Hi,

It depends on your country.
For me there are German regulations, European regulations....

It also depends on the expected use: Commercial, industrial, medical, military...
And usually within the regulations on: dirt, humidity, altitude....

Klaus

 

[FvM]

Protection of a 120V DC circuit against operator contact is required by all international standards, e.g. IEC 61010, IEC 61140. If the 48V circuit insulation (battery case, ables, connectors) is sufficient for 120V working voltage, the charger doesn't necessarily need galvanic isolation between 120V and 48V circuit.

Please notice that 48V is also considered as hazardous contact voltage under wet conditions.