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# denci

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1. ## Current monitor/sensor

Yes, but what with 5V voltage drop on 0.5E dischatge resistor? Is this nedd to take into account, or? Now i tasted with 4A, so 2A only through each mosfet and i measured 75degree per C on heatsink so from calculation is junstion temperature is allowed range. Is that not truth?
2. ## Current monitor/sensor

Hello, ia have one question regarding heatsink temperature, so i have two IRFP460 mosfet on pretty big heatsink en testing on 4A current and i measured temperature on heatsink after one hour arround 80 degrees, so high. I made calculation and says: P_Dmax=5A*(12V-(5A*0.1Ω)-5V)=5A*6.5V=32.5W So max power dissipation is one transistor is 32.5W, thermal resistance THj-c is 0.45C/W. why then so high temperature, i select pretty bigger heatsink that it sould be regarding my calculations??
3. ## Current monitor/sensor

Maybe because missing capacitor on ADC pin to hold voltage??
4. ## Current monitor/sensor

If i burdened battery or. increase discharge current reading of voltage becomes smaller. I have 33kE and 11kE resistors serial from battery + pin to ground, so this is resistor divider, so if no current flows from battery there is normal reading, when current is higher reading is wrong or smaller as i said, for example battery voltage is 11.5V, adc reading is only 9.5V.
5. ## Current monitor/sensor

I finally figured out where has problem been all the time, ground noise because battery connector. PWM signal is on picture below and you can see oscilating on ground. I solved this by putting 0.47uF capacitor between battery connector and signal is smooth and now voltage on -pin is the same as on +pin (which is suprising me, so voltage inequality reflected by input noise of OP????) but i must perform test also with higher current but for now this is part of solution.
6. ## Current monitor/sensor

Thanks but i gave an example of measurements in previous posts, mosfets are IRFP460, so only problem is that voltage on - pin does not follows voltage on + pin, regarding mosfet transistor Vds should not be a problem for this case. I wondering why voltage on - pin is lower than voltage on + pin and ouput voltage of OP is lower as i exepected - in upper case only 5.5V.
7. ## Current monitor/sensor

I measured 5.5v on op output when input voltage is 1v, then voltage on r4 resistor is 0.75v, current is 1.6a, power supply voltage was set on arround 11.8v. So if increasing voltage of power supply (which represent battery) than current is increas to arround 1a and than stops increasing which is logically, so mosfet most probably not suitable for such a battery voltage.
8. ## Current monitor/sensor

I am using mosfets IRFP460, regarding datasheet these transistor are suitable for project, i will check LM324 output voltage and then report values. However problem is that battery voltage is reduce by high current so theoretically when 10A is flows out of battery, 5V is on R4, battery voltage could reach critical value arround only 9V (depends of battery healthy) and then source voltage of mosfet is only 4V, so mosfet can provide high current only on that condition, or not??
9. ## Current monitor/sensor

So i have changed filter and improve ground and provlem with currenr spikes is now solved. I was testing circuit with power supply instead of battery and i figured out that current decreasing with bat voltage decreasing which is not allowed, maybe because too small mosfet drain to source voltage, i must find 22e resistor and put it into circuit also but most probably this is not because of gate resistor missing?? Voltage on - pin is little bot lowe again that voltage of +pin of op i must solve this too.
10. ## Current monitor/sensor

Ok i sould adding resistor. So, do you still think that the signal spikes represented on picture above is reflected by poor ground, i must perform test once again i add some kind of "star" ground so all gnd is connected at one point with thicker wire.
11. ## Current monitor/sensor

This is schematic you suggested me, only different is that there is no 22E resistors to mosfet gates.
12. ## Current monitor/sensor

, So i forgot to tell you that i have separate PCB board, one is power board and one is control board and only thin wires (flat cable) connecting them together so this is the main problem i must provide low resistance ground. I have other question, why voltage on -op pin is not equal (aprox. 20% lower) then on +input pin (voltage follower orientation)??
13. ## Current monitor/sensor

I placed thicker wire in some ground places in order to avoid voltage drop as you said above and also put the thicker + and - connection wire for battery connection and problem solved when discharged current to above 2A is flowing, but when increasing current using PWM modulation as described above (increasing duty cycle) signal starts oscillating (picture from scope - some kind of charging capacitor). So do i have improve ground further to decrease voltage drop?? All works fine but only because of oscillating i have wrong adc reading and i need to use adc averaging but also using this result not precise as i wanted to be!
14. ## Current monitor/sensor

is this parasite capacitance? otherwise i solved problem with thicker positive and negative wire for battery connection but wires must be close together, if they aren't effect of capacitance appear again!
15. ## Current monitor/sensor

With spacing between battery wire (+ and - cable), signal is increasing it's shape like above, when wiring of battery so close together ther is just some little spikes appear on signal how can i avoid this problem, how can i get dc signal on discharging resistor while battery being discharged.
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