Hi all,

I’m new to this and would appreciate your feedback on the attached circuit. I’m trying to measure bidirectional current—mainly for a rough estimate, but most importantly to confirm the direction of current flow.

I’ve attempted to simulate it in eDSim, which has been a learning experience in itself. Any suggestions or corrections would be highly appreciated!

Thanks in advance, Morten

 

Does the simulation work?

What is the purpose of U1, U3, and R1?
The 10meg resistors seem to serve no useful purpose.

Exactly what output do you expect from this circuit?

 

I am not convinced that you can use the same supply to operate the op-amp that you are monitoring.
AND the whole scheme seems to have more resistors than it needs. What is the purpose of U4??

 

Does the simulation work?

What is the purpose of U1, U3, and R1?
The 10meg resistors seem to serve no useful purpose.

Exactly what output do you expect from this circuit?

It was a transient analysis and it kind of worked with a 50 times the current over the shunt + the 2.5V. But lots of *convergence errors* and unable to find dc operating point. Might have left some resistors on the circuit diagram that I thought would help the convergence, like the 10meg from the output.
R1 is standin for a 40A fuse. U1 and U3 is suppose to lift the reference so the voltage will swing around 2.5 to be able to measure negative current.

The 12.6 V source is a battery. More batteries is planed to go in parallel. So want to be able to measure if there is a mismatch, eg. one battery is only 12.1V and current will start to flow from the other batteries into that battery. Most important is to see the direction, less important is the precision of how many amps is flowing. But am testing with a proper currentsens amplifier TSC2011 which has internal ref of 2.5V and 60 times amplification. Its a bit pricy though.

 

I am not convinced that you can use the same supply to operate the op-amp that you are monitoring.
AND the whole scheme seems to have more resistors than it needs. What is the purpose of U4??

I should have pointed out that it is suppose to measure current from the 12.6V battery and more 12.6V batteries is suppose to go in parallel. Each with its own shunt and current sens circuit. The 5V regulator will supply them all. There is also some temp measurement included with a break function.

 

Not all op-amps "play well" when an input voltage equals or exceeds the supply voltage. THAT was the reason for my comment.

 

In addition to all the other comments, how do you expect the opamp’s output to provide a negative voltage without it being powered with a bipolar supply?
Of course, by biasing the opamps inputs mid supply.
But a far, far better solution would be a Hall effect based sensor. Not only it provides bipolar(*) current sensing capability when powered by a single logic level supply, it also provides isolation from the line being sensed.

(*) I know that there are devices that are designed for single polarity sensing, but the majority of available devices are bipolar.

 

But am testing with a proper currentsens amplifier TSC2011 which has internal ref of 2.5V and 60 times amplification. Its a bit pricy though.

U$3 is pricy?
How much do you think the devices in your circuit cost?

 

WHY the very large resistors around the amplifier IC?? AND, is it actually an IC, or is it a differential amplifier that has separate connections for setting the gain??

 

More batteries is planed to go in parallel. So want to be able to measure if there is a mismatch,

So you will have one circuit for each battery?

 

Often times battery matching is done at installation. Thus a quick and easy tester is wanted.

 

The two TL431s are going to cause trouble. In spice they will have the same voltage but in real life they will not.
Us a Rail to Rail input and output op-amp. There are many. There are some nice ones that work if the supply is under 6V. Use an op-amp that has a Comon Mode input voltage range that includes the negative supply. Or use a R-R amp. Put a cap on the OP-amp supplies.
I don't understand the many diodes. I removed most. I put a small diode so only plus voltage will go to the regulator. Revers battery protection.
Regulators need input and output caps.

 

Read TSC2011 datasheet:

 

CERTAINLY Danko, in post#13, has presented what I consider an effective circuit to provide the functionality described in post #1.
If very accurate current readings would be required then adding regulation to the supply for the op-amp and offset divider may be required.

 

WHY the very large resistors around the amplifier IC?? AND, is it actually an IC, or is it a differential amplifier that has separate connections for setting the gain??

The TSZ121 is an STM op amp with zero drift (chopper). The 10meg is a resistor I forgot to remove.

 

In addition to all the other comments, how do you expect the opamp’s output to provide a negative voltage without it being powered with a bipolar supply?
Of course, by biasing the opamps inputs mid supply.
But a far, far better solution would be a Hall effect based sensor. Not only it provides bipolar(*) current sensing capability when powered by a single logic level supply, it also provides isolation from the line being sensed.

(*) I know that there are devices that are designed for single polarity sensing, but the majority of available devices are bipolar.

The setup is suppose to be able to distinguish hopefully down to at least 10mA current flow in both directions. Dont think a hall can do that?

 

So you will have one circuit for each battery?

Maybe 3 $ is not that much. But it all add up. The shunt resistor is actually very expensive for a resistor. And yes one for each batteri. Up to 8. So everything is multiplied.

 

Often times battery matching is done at installation. Thus a quick and easy tester is wanted.

Yeaa this setup is a little experiment. So want to see current over each pack.

 

The two TL431s are going to cause trouble. In spice they will have the same voltage but in real life they will not.
Us a Rail to Rail input and output op-amp. There are many. There are some nice ones that work if the supply is under 6V. Use an op-amp that has a Comon Mode input voltage range that includes the negative supply. Or use a R-R amp. Put a cap on the OP-amp supplies.
I don't understand the many diodes. I removed most. I put a small diode so only plus voltage will go to the regulator. Revers battery protection.
Regulators need input and output caps.
View attachment 362524

Thank you very much. There is plenty of headroom for protections diodes. This is great.

 

Read TSC2011 datasheet:
View attachment 362537

Promise you - it has been studied. Actually think it will be its cousin, TSC240 though.