Electric Vehicle Isometer

[sanwal209]

Hi Folks,

We are currently using isometer from Bender which is as follow:
https://www.bender.org/documents/IR155-03-04_datasheet_NAE1012830.pdf

I want to develop our own Isolation meter but i couldn't find any reference or documents for initial guidance. If anybody worked on such kind of project then please share some documents or at least basic working principle of isolation meter.

PS: We are using isometer to measure the isolation between high voltage battery pack terminal and chassis ground.

Any help would be greatly appreciated

Thanks

[capt bullshot]

The basic working priciple can be guessed from that datasheet:

The isometer applies a testing voltage (+40V / -40V alternatively) to the isolated circuit and measures the current (or vice versa). The test voltage is applied through a rather high impedance. So in case of a full earth fault the current is limited to a safe (a few mA) level.

All the rest is more or less sophisticated software that does some correlation and averaging of the results to handle the apacitance (the data sheet states 1uF is allowed, this must be charged / discharged while measuring) and filter high frequency components caused by the inverters.

The Bender PCB looks quite complex, I guess that is caused by all the real world problems that your device must handle then. The basic priciple is rather simple I guess.

[oldway]

Unless you are in the field, I advise you to not develop your own isometer because it is a device that can affect safety and therefore engage your responsibility or that of your firm in case of accident.

In addition, one must know the standards and regulations that apply if any.

For industrial battery chargers with ungrounded batteries, an insulation ground fault signaling (considered as non-essential, for information only) was made in a very simple way with some resistors, a 24V reed relay and a zener diode .
The reed relay contact was controlling an insulating ground fault signal lamp.

[sanwal209]

So i have two choices either to build the isometer based on discrete components or based on COTS SoC i.e http://www.sendyne.com/Datasheets/Sendyne%20SIM100%20IC%20Datasheet%20V0.4.pdf

As oldway said it will be too risky to build our own Isometer due to its impact on safety. I would choose SIM100 SoC instead of discrete components.

PS: I found three methods which are as follow:
1. BUS end voltage
2. AC Signal Injection
3. DC Voltage insulation measurement

@Capt bullshot the method you are talking about is AC signal injection.

These are actually quite interesting theories.