SMPS for Lead Acid Battery Charger Design Help

Hi

I am designing a SMPS 500W for Lead Acid Battery Charging.

I am referring Figure 16 here.

**broken link removed**

I want to build this circuit (Figure 16 above link).

Battery will be 12V 100Ah to 200Ah and so the charging currents will be 10A to 20A and hence the SMPS should be able to provide 30A.

P = VI = 500W

V = 14V (Charging Voltage)

I = P/V = 500W / 14V = 35.7A

and So, 500W SMPS is enough for my work.

I will be using PIC18F46K22 with P1A and P1B signals (Half_Bridge) for the SMPS. I want to maintain constant output voltage.

How to choose value for C1, C2, C3, C4, C5, L1, L2, C6 ?


For filter at the input that is after bridge rectifier (230V AC to 325V DC) should I use the formula Xc = 1/2pifC where mains AC frequency is 50 Hz ?

If yes, What should be Xc ?

If I choose 330uF 450V then

Xc = 1/2*3.1415*50*330*10^(-6) = 9.64 Ohms

Is this Ok for smoothning capacitor ?

For transformer calculation I am referring this.

http://tahmidmc.blogspot.in/2013/02/ferrite-transformer-turns-calculation_22.html

How to implement constant output voltage ? Should I vary the Half_Bridge PWM duty based on output voltage ? Instead of optocoupler can I use adc to measure the output voltage and adjust the PWM duty ?

- - - Updated - - -

SMPS power is 500W

I = 500W/14.7 = 34A

Output voltage is 14.7V (0.7V drop across diode)

Constant Output Voltage required is 14V

Vp/Vs = Is/Ip

325V/14.7V = 35A/Ip

Ip = (IsVs/Vp)

Ip = 35/325 * 14.7 = 1.5 A

Primary winding AWG is 17

Secondary winding guage is AWG 6

http://www.powerstream.com/Wire_Size.htm


Transformer Calculations referring

http://tahmidmc.blogspot.in/2013/02/ferrite-transformer-turns-calculation_22.html

ETD44 Core

Vin(min) = 180V AC = 255V DC
Vin(max) = 250V AC = 254V DC
Vin(nom) = 230V AC = 325V DC

PWM frequency = 50 KHz

Npri = (Vin(nom) * 10^8) / (8 * f * Bmax * Ac)

Npri = (325 * 10^8) / 8 * 50000 * 1500 * 1.75)

Npri = 30.95 ~31 turns


Average voltage to transformer = 0.98 * 0.5 * 255V = 124.95 ~ 125V DC

Voltage ratio (primary : secondary) = 125V : 16V = 7.8125

N = 7.8125

Nsec = Npri/N = 30/7.8125 = 3.84 ~ 4 turns

If I use copper wire or copper foil does the number of turns remain the same ?

- - - Updated - - -

I want to implement this circuit for input side of SMPS

**broken link removed**

Figure 17

I will replace fuse and thermistor with resettable fuse

MOV will be used

What should be the value of C1, C2, C3, C4 and C5 ? AC mains frequency will be 50 Hz

What choke I have to use that is L1 value.

All capacitors will be 400V or above rated.

Bridge rectifier will be GBPC3510

C1 and C2 are Box Capacitors ?

I found the value of Choke and Capacitors from here.

http://www.poweresim.com/index2.jsp?LoadRecommendSystem=0


How to implement Active Power Factor Correction ? I know I have to use an additional mosfet and use an additional PWM but how to get the feedback voltage and input voltage for the power factor correction circuit (adc) ?

I didn't get answer to my questions. i made some changes to the circuit. I am now using GBPC3510 for the bridge rectifier to convert 230V 50 Hz AC to 325V DC for the switching transformer.

These are my calculations. Are they correct ? Can I proceed further with circuit designing ? Is GBPC3510 Bridge rectifier ok for the design ?

Vsec/Vpri = Nsec/Npri = Ipri/Isec

14.4/325 = 0.044307

Isec required is 24A (12V 240 Ah battery)

Design should be for 20% more of this rating. Am I right ?

So, 20% of 24A = 4.8

So, transformer secondary should be able to handle

24 + 4.8 = 28.8A current.

Ipri = N * I sec = 0.044307 * 28.8A = 1.276A

Referring below link for switching transformer calculation

https://tahmidmc.blogspot.in/2012/12/ferrite-transformer-turns-calculation.html

Npri = 50 choosen

PWM f = (325 * 10^8) / (4 * 50 * 1500 * 1.25)

PWM f = 86.67 KHz

Npri = 50

98% of 325 = 318.5

Vsec/Vpri = nsec/Npri = N = 14.4/318.5 = 0.0452

Nsec = N * Npri = 0.0452 * 50 = 2.3 = ~ 2 turns

Not going through your other calculations ,
the fig 16 you have referred does not have a smooth DC . it have only pulsating type in input.

Please discard the calculations in post #1 of this thread. Only consider post #2 and further posts regarding the project. Here is the new circuit. This is the final circuit. I still have to calculate the values of C14 and C15.

The main thing I want to know is whether the transformer primary current calculation is correct or not in post #2.

Only consider the circuit in this post for future reference.

Edit?: Sorry, The mosfet mentioned in the circuit is wrong. I will post new circuit after making corrections.

Here is the fixed circuit. Please have a look at it and tell me if there is any changes I have to make.

In the circuit of post #5 there will be

Pd = V * I = 1.0 * 25.0 = 25W power dissipated in the output side rectifier diode.. To reduce this can I use a mosfet as a high-side switch without PWM drive ? Then only

25A * 25A * 0.012 = 7.5W is dissipated.

Your voltage assumptions when calculating the core are incorrect.

A PFC controller is a boost controller which will maintain a fairly well regulated DC voltage, regardless of your AC input voltage.

Since it is a boost circuit, the voltage has to be higher than the peak of your maximum input voltage. This means that the controller will regulate between 360 and 400 volts, depending on how much margin you would like to provide.

It appears that you have a strong and sincere desire to learn. I congratulate you on that.
But instead of going to web pages and blogs which one never knows about their reliability, please go to the websites of Texas Instruments, OnSemi, STMicro and others. Those sites will have excellent, very detailed and for the vast majority, reliable documentation.
They already have app notes explaining every conceivable issue. And they offer full fledged IC solutions, along with all the detailed calculations for the design.

I must add that a PFC controller design is not simple or trivial. Go to trusted sources to learn.

Good advice from schmitt trigger, also you transformer calculations have a problem. A half bridge transformer only see's 1/2 of the DC input voltage so your 325 vdc in the formula should be is 1/2 of that. Also the constant in the formula should be 4 not 8.

Npri = (162 * 10^8) / 4 * 50000 * 1500 * 1.75) = 30.9 turns

By dumb luck your two mistakes cancelled out and you did get the correct answer. However as Schmitt trigger said with pfc you will be around 400 vdc. Do you really need pfc? This is not a beginner project, the possibility of success becomes more remote as complexity increases.

@schmitt trigger

Yes, I have only worked on embedded projects mostly but never had to work with Power electronics systems. No, I need to design a SMPS Battery Charger for a Inverter that I am designing. I think it is good to design a 30A max SMPS Battery Charger because it can charge almost all Ah rated 12V batteries from 40Ah to 240Ah.

I am currently working on a 12V Battery Charger based on Buck Converter. Once I finish that project I will continue with this project and thread.

@FlapJack

Thank you for pointing out the mistakes.