zeb59
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What resolution in reading you expect to achieve with current shunt 0,0004Ω (400µΩ) ?
My sense resistor in my amp-hour meter (mentioned in post #3), was a few inches of #12 copper wire.
I do not understand what you intend to do about how much current is drained from it. Do you plan to cause a relay to disconnect it if the load is greater than 100 A?
What will prevent the relay from closing again immediately after it opens?
Moreoever besides arranging to keep the relay open, how will you make the system detect whether someone has reduced the load sufficiently so that it is okay to let the relay close again?
In fact, the very lead used for connecting charger with battery can also play the role of sense resister. All you need is a seperate wire from battery clip to run along to go to current sense circuit inside the charger box. To detect current of load and to disable output in our ups, we use a tab 4 inches away from power module so that the joint stays in the box. This setup works very good upto 0.1A resolution, when checked with Amp-meter and works reliably. It is also used for controlling chaging current. LM324 operational amplifier is used in this circuit sensing voltage developed on -ve lead.
I would like to use a commercially available shunt. Ordinary Pakistanis are not likely to have the knowledge and skills required to homebrew a shunt. 60mv/100Amp shunts used with Analogue meters to display current are easily available in the local electrical goods supply markets. All these things should prompt someone to start manufacturing the management system.
Regards
Zeb
In fact, the very lead used for connecting charger with battery can also play the role of sense resister.... It is also used for controlling chaging current. LM324 operational amplifier is used in this circuit sensing voltage developed on -ve lead.
AlertLinks,
The method you are using is a cost effective replacement of a shunt. However it has the issue of variation with temp. etc, as described by Casemod. But I think for charging current measurement in the +/- 5-10% range it should be a good cost effective system. The only issue I have is that you have this connected to the -ive lead which means you are using low side sensing, while I want to take the high side route.
I have played with the circuit (in my first post) on PROTEUS. It however completely refuses to provide any gain to the differential voltage developed across the shunt resistor connected in series with the battery. My hunch is that the circuit reads the differential voltage AS THE COMMON MODE VOLTAGE.
Can someone knowledgeable about theory shed some light on my hunch. If I am correct what corrective modification should I make in the circuit.
TIA & Regards
Zeb
Why would you want to monitor the high side currents?
Regardless if you want to take the high side route, just put the shunt on the positive, cant see any issue with that.
In the circuit, voltage supply for IC is 10V. The iputs of the IC are working near 6V. That's what resistor divider network do, to pull down the input voltage within the safe limits. Here I put voltmeters to monitor voltages are within safe limits as proteus does not warn when safe limit is crossed. Mains AC voltage with peak of 315V can be monitored if divider resistors are set accordingly without dammaging the IC.
At 12A and 51A load, input pins never exceed 6V. Output stays within 5V in full range to be directly connected to the ADC in MCU. Batttery is of 24V
Yes, but in addition to adding more complexity to the circuit, the output may not be directy connected to 5V ADC.
Also on, say a 100mV/50A shunt (that would dissipate 5Watts at 50Amps), using a 1/4 voltage divider the precision will be 4 times less. Assuming say 100mV @ 50Amps, with the voltage divider of 1/4 thats would be 25mV per 50Amps or 0.5mV per A, In real world makes it quite hard to measure low currents and any magnetic field may cause a small voltage enough for an error. At such low voltage levels noise can be a real issue.
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