Sensing current in high voltage DC system

Thread Starter

VTBalla34

Joined Aug 14, 2017
4
Hi all, thanks for this great resource and appreciate you taking a look at my problem.

I am trying to design a low profile test tool for work that will detect current flow in a high voltage DC system. Existing COTS solutions won't work as it will need to be ruggedized and miniaturized for final design.

The circuit to be sensed is a capacitor that discharges around 2,300 VDC and a 33 Ohm resistor. Our bench testing has shown current peaking at about 130 Amps before falling off.

I do not need to know actual current amount, just that it is present, so a binary solution (LED on/off) is fine. Thinking ~50A as the threshold but could be lower (a lot lower actually).

The alerting circuit I have envisioned is a simple 3 V battery into an LED and a 43 ohm resistor.

Is a reed relay a possible solution here? I'm not sure if there are any reed relays on the market that would work at these voltage/current levels as I don't really understand what the spec sheets/ratings are saying.

Failing that there is a RR capable of that capacity, would just a small Hall Effect Sensor into an op amp to switch the circuit be the only solution?

Thank you all for your help.
 

GopherT

Joined Nov 23, 2012
8,009
Hi all, thanks for this great resource and appreciate you taking a look at my problem.

I am trying to design a low profile test tool for work that will detect current flow in a high voltage DC system. Existing COTS solutions won't work as it will need to be ruggedized and miniaturized for final design.

The circuit to be sensed is a capacitor that discharges around 2,300 VDC and a 33 Ohm resistor. Our bench testing has shown current peaking at about 130 Amps before falling off.

I do not need to know actual current amount, just that it is present, so a binary solution (LED on/off) is fine. Thinking ~50A as the threshold but could be lower (a lot lower actually).

The alerting circuit I have envisioned is a simple 3 V battery into an LED and a 43 ohm resistor.

Is a reed relay a possible solution here? I'm not sure if there are any reed relays on the market that would work at these voltage/current levels as I don't really understand what the spec sheets/ratings are saying.

Failing that there is a RR capable of that capacity, would just a small Hall Effect Sensor into an op amp to switch the circuit be the only solution?

Thank you all for your help.

Put a couple of turns in your wire to make a magnet, then a reed relay switch that turns on a circuit with a 3 v battery, a small resistor and an LED will work.
 

Thread Starter

VTBalla34

Joined Aug 14, 2017
4
Put a couple of turns in your wire to make a magnet, then a reed relay switch that turns on a circuit with a 3 v battery, a small resistor and an LED will work.
Thanks, that's what I was thinking but wasn't sure if the 2200 Volts would be too much for the reed relay to handle?

So I would coil the wires around the relay to induce the magnetic field through it, right?

from our bench test graphing, the load is seeing the current peak at immediate discharge and return to zero in around 20 microseconds. Is this adequate time to switch the reed and light up the LED before current is no longer present?
 

GopherT

Joined Nov 23, 2012
8,009
Thanks, that's what I was thinking but wasn't sure if the 2200 Volts would be too much for the reed relay to handle?

So I would coil the wires around the relay to induce the magnetic field through it, right?

from our bench test graphing, the load is seeing the current peak at immediate discharge and return to zero in around 20 microseconds. Is this adequate time to switch the reed and light up the LED before current is no longer present?
No, the coil is only near the reed. Once the current starts flowing, the coil makes a magnetic field. The reed relay responds to the magnetic field and closes the switch inside the relay.

The two wires on this relay are connected to a 3v battery, an LED, and a resistor (all in series).

|-------------------------------------------|
|-- relay -- LED -- battery -- resistor --|
 

Thread Starter

VTBalla34

Joined Aug 14, 2017
4
No, the coil is only near the reed. Once the current starts flowing, the coil makes a magnetic field. The reed relay responds to the magnetic field and closes the switch inside the relay.

The two wires on this relay are connected to a 3v battery, an LED, and a resistor (all in series).

|-------------------------------------------|
|-- relay -- LED -- battery -- resistor --|
I'm tracking and that makes sense. But wouldn't I have a stronger magnetic field acting on the reed contacts if I just wrapped the coil around the reed? That would seem to make the equations a bit more straight forward, would it not? Just curious why you recommend placing beside of instead of inside.
 
Top