I am presently trying to design a solar panel based system. I want to procure the evaluation board SM-3220-BATT-EV . While trying to procure that, the following questions cropped up.
1) nRF24LE1 micro controller has been used . Do you supply the programmer kit to program the controller ? Or else how do I program it ?
2) In the application note 2121. The controller is PIC rather than the nRF24LE1 . Do you have the same evaluation board using PIC controller. Actually we don't need the RF communication stuff.
3) If we use nRF24LE1 in the evaluation board, and I need to send some debug information to the PC via UART how should I do that. What receiver should I procure ?
4) In my application I need some 18A of load current, if I change the components like, inductor , Mosfet, will the PCB be able to support 18A of current. Or can you please kindly mention us the changes that we need to make.
Please kindly help us with your feedback
Please kindly provide your feedback
I found that SM3320 BATT-EV, uses a PIC , it would be helpful to me. But I have another doubt regarding "SM3320 BATT-EV CHARGE CONTROLLER REFERENCE DESIGN".
According to the above mentioned document, the inductance that has been used is 27uH. In our application we need to make some changes as this reference design has maximum output current of 9A, where as we need some what above 20A. So we need to calculate the Inductance. We referred the document SNOSB84B, but according the formula's provided over there we are not able to calculate how the 27uH got generated in the reference design.
Can any one help us with the reference design , mentioning what is the frequency at which the PWM is running in the circuit, what is the output voltage, what is the input power. As these are vital parameters to calculate the value of inductance.
According to to the document SNOSB84B, the value of L1 is calculated as
L1 = ( ( Vout_min * Vout_min ) / ( 0.6 * Pmax ) ) * ( ( 1 - Dbk_min ) / Fsw_min ); // L1 for buck modeL1 = ( ( Vmpp_min * Vmpp_min ) / ( 0.6 * Pmax ) ) * ( Dbst_max / Fsw_min ) ; // L1 for boost mode The greater of the two values is chosen as the value for inductance.
I have attached two files for your reference. Please give us your feedback.
8507.SM3320 reference design .pdf1731.SM72442.pdf
I had given the input values as
MINIMUM_OUT_VOLTAGE 13.5 MAXIMUM_OUT_VOLTAGE 14.5 MAXIMUM_POWER 495.0 MAXIMUM_FREQUENCY 200000.0 MINIMUM_FREQUENCY 180000.0 MINIMUM_V_MPP 15.0 MAXIMUM_V_MPP 40.0 MAXIMUM_OPEN_CKT_VOLTAGE 50.0 MAXIMUM_SHORT_CKT_CURRENT 11.0
With these input values and the above formula. I was able to get the value of the inductance as 2uH. Then was the value of 27uH chosen as a trade-off , is it necessary number or just a redundancy ?
1) The evaluation boardhas a PIC16F722. We currently do not support other microcontroller although there is a porting to MSP430 currently ongoing
2) See 1)
3With the PIC on the board, debugging can be achieved through the ICD programmer
The reference design SM3320-BATT-EV was based off the SM3320-A1 initial design. Board and general placement was left unchanged. The custom made inductor was also kept in the system as it was adequate to handle the current at the operating frequency.
Because the SM3320-A1 was designed to operate at wider current and output voltage settings, the inductor might be overdesigned for this application.
The formulas are correct but they are not perfectly adapted to this system. Because charging a battery means that the system can run at full power away from MPP (voltages closer to Voc), there is no direct correlation between the voltage at MPP and the power.
You should use this formula:
DeltaI = 0.3 x I_out_max
L> Vout_max x (1- Vout_max/Vin_max) / (Fmin x DeltaI)
Vin_max=Voc_max of the solar panel
Vout_min = min battery voltage
Note that this formula works only as long as Vin_max>>Vout. Because Vout_max x (1-Vout_max/Vin_max) is quadratic, there can be a peak between the extremes of Vin and Vout.
The total constraint on L for the Buck part is :
L> MAX[Vout x (1- Vout/Vin)] / (Fmin x DeltaI)
I am extremely grateful to you for your support. Can you please tell me what programmer had you used on your side for programming the PIC module. I ask you these as we tried to program this using PIClKit3 by soldering some wires beside the connector, but we are getting huge errors, the connector that is provided on the board does not match with the connector of the ICD provided by microchip . In case we are able to know what you had used on your side, we can procure the same.
The issue got solved. There had been some power problems.
I connected the SM3320 EV to the solar panel and battery. But when I connected a multimeter in series with the battery I found that the current is only 0.749 A. I have used a 280W solar panel, and there is a very good amount of sunlight. The input voltage is 39.5V . On reading the register 1 of SM72442 through I2C I receive the following values
Iin = 0x0016 Vin = 0x0196 Iout = 0x0042 Vout= 0x0194
Can you please help me on this. I expected the current to be 9A. I am attaching the datasheet of the solar panel.
We checked the short circuit current it was coming to be 5.5A , and open circuit voltage 39.5 V. Initially suddenly we might get a current of 3.3A but within few seconds it would gradually get down to 0.749 A and this value would remain constant. What can be the reason of this. I was experimenting with a 12V 65 AH battery. The output voltage would always remain 13.6V.
Another thing we noticed that as evening approached the input voltage became 30.5 and the output current increased to 1.190 A. Please help us a bit on this.
One more thing I would like to tell. I am glad to speak Mr. Florent Boico. Actually I heard your name from some journal before. Glad to meet you Florent.
I had used the firmware source from the CAD files. Is it a bit different from the code that was actually burned into the controller, while it was shipped ? I had re-flashed , using the code that I had got from the CAD folder. I have some more queries like :
1) By reading the reg 3 of SM72442 we get the value of the input current as 0x0016, how can it be so when the short circuit I tested was actually 5.5A.
2) The output current remains constant 0.764 A, I feel the MPPT controller is making that.
There was a time time when I had suddenly got a output 2.2A current . The corresponding reg3 values were Iin = 0x0051 Vin = 0x0192 Iout = 0x00F9 Vout= 0x0196. Here we find that the input current has increased. Is it possible for any reason the circuit is drawing less current from the solar panel.
Please help a bit. Till we finish experimenting with the eval board, we would not be able to begin the actual work. Waiting for reply.
Hi Subhajit, There might have been a small tuning of some of the constants in the code between the version programmed on your board and the version on the website
1) Was the current constantly 5.5A?
2) What is the output voltage when you have a locked 0.76A output? There is a protection in the code to reduce the charging current if the output is below 10-10.5V.
Thank you so much or your feedback. The problem got solved, by discharging the battery completely, by means of an UPS. I am getting some about 9.5 A output current. I expect then that the controller was charging at floating current previously. But I had actually given some debug prints, in the floating charge section in the code, but never would the control go to the floating charge section. Does that mean that the MPPT controller was handling floating charge control by itself, rather PIC module doing the same ?
The input voltage was 38.5 V. But one of the Mosfet was getting extremely heated , so much that I was unable to keep on my fingers.I can provide a heat sink and a heat sink paste. But would not the Mosfet be worn out due to much heat, that is generated now. Is it the same at your side ?
I am using the code that I got form the website. Is there a change between the code that was actually burnt into controller while it was shipped. Can please provide me the latest code.
I will experiment with this board for a couple of days. Will keep you updated. Thank you so much again for your continuous support.
With this input/output configuration, Q1 will take most of the losses of the converter. When running the eval. board at full current for a constant time, proper heatsinking must be applied.
I suspect that your FET is fine if it still switches properly. However, you should screw a heatsink to it.
The code should be essentially the same. I believe we offset the ADC result by one bit (1 LSB). I will have the website updated with the code that is currently flashed in the microcontroller.
Thank you for your help. Also while we were using the eval board , we found that as the battery gets charged and the voltage of the battery crosses 12V , the output current from the eval board starts decreasing, initially its 9.5A it goes down to 6.6 A and likes wise to 4 A, 3.5 A while voltage reaches 12.5V towards 13V . The firmware that we got form the website doesn't show such logic, nor do the software algorithm in the document. According to the document the current would be remaining constant till 13.6 V after which there would be trickle charging. Can you please help us on this.
Also can you please tell what are the components that we need to change if we want to make the maximum output current to about 20A. As we are using a 280W solar panel, we would like to make full use of it.
Waiting earnestly for your reply.
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