Car SMPS Project

Hey Guys

I'm working on a 800W Smps to drive my Amps in my car but I'd like to test it out fully before I use it in my car
So I'm looking for a power supply to simulate car voltage to test and use the audio system at home (13.5 to 14.7V @ about 80A)

Which solution do you guys recommend:

1- Wind a 50Hz transformer
2- Build a regulated SMPS
 
Use a car battery and a charger

I have the car battery but about the charger, doesn't those only deliver about a couple of amps to charge the battery ?????
I talking about 30 to maybe 80A here the doen't need the battery to deliver much of the current

Maybe you mean different charger than what I have in mind.

I honestly tempted to buy a 90A car alternator and a 1ph ElectroMotor Rated at 4HP @ 3000RPM but the only problem I have is with the size of this things.
 

noonehere

New member
If its only short term then the small charger will be fine.. even a small lead acid battery will put out some serious amps short term
 
If its only short term then the small charger will be fine.. even a small lead acid battery will put out some serious amps short term

actually no as I said I may wanna use this at home so it should be something to dilever 60A for an hour or 2 without any problem
I can test the smps with the car battery that I have but without the altenator the voltage will drops and it will not be the case where I want this circuit to work(about 14V)
so i'm looking for some method to keep the voltage on the battery around 14v when I drawing that many current (basically like what an altenator in a car does)
I think a 50Hz transformer would be a good choice here but I don't know what output voltage and current my transformer should have? because after converting it to dc the level of voltage and current is different
does anyone know a good and valid reference to calculate the ratings of the transformer
 

Silvio

Active member
I see if I understand well that you want a mains driven smps that can deliver 13v at 60 amps well that is a little less than 800w. If the load is going to continuous that is one thing but if the load is intermittent say 50% than that will be another.

You can build an smps with half bridge like the 1000w smps and use thick secondary so that it can deliver current. You also need high current output diodes which have to be fast switching. feedback perhaps as well. You can use copper sheet for your secondary winding. If it is going to be for audio purpose then a current density of 5 amps per mm² will be ok.

Taking some assumptions 60amps at 5amps per mm² = 60 / 5 = 12mm²

ETD 49 bobbin is around 30mm long so a 0.2mm thick copper sheet will be 30X0.2 = 6mm² this is only half so you need to parallel 2 sheets together. One other option is to make a center tap winding and use 0.2 sheet for each winding then use a common anode diode on the output.

Regarding the size of an iron core transformer it should be the size of a microwave oven transformer more or less. The filtered secondary voltage will have to be larger so that it can be regulated to the desired output voltage. This will bring more complications to your setup and I think you should avoid it.

I hope that helps Silvio
 
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have you tried using a 2000va found in UPS

Actually as I haven't find the high speed & high current output diodes for the Smps in my area that my friend Silvio here suggested, I go for a powerful 2KW 50Hz transformer at it will be ready in a day or two
I also bought car battery and a 3 Farad cap to minimize its ripple and 4*100A diodes so can handle this much current
it cost about 300$ to gather this stuff but I think it will worth it
 

Silvio

Active member
Hi bad boy, I think you made a good choice as that kind of setup is more robust and more forgiving. What I am aware of is the 3 farad capacitor. This can easily destroy you rectifier diodes during start up. The transformer itself will also give surge in the mains and may blow your fuse during switch on.

If you want an easy soft start to build you can find one in my blog posts. I made this for my isolation transformer which was around 1500w.

One other option is to connect the battery first before switching on the supply so that the battery will charge the capacitor instead.
Please also note that the battery itself will act as a capacitor and smoothing down the ripple.

I would include the soft start as this will help things to tame down a little bit at start up.

Regards Silvio
 
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kegs

New member
Actually as I haven't find the high speed & high current output diodes for the Smps in my area that my friend Silvio here suggested, I go for a powerful 2KW 50Hz transformer at it will be ready in a day or two
I also bought car battery and a 3 Farad cap to minimize its ripple and 4*100A diodes so can handle this much current
it cost about 300$ to gather this stuff but I think it will worth it

For rectifier the best place is from a PC POWER supply as they are high speed and paralleling several is a good bargain
 
Hi bad boy, I think you made a good choice as that kind of setup is more robust and more forgiving. What I am aware of is the 3 farad capacitor. This can easily destroy you rectifier diodes during start up. The transformer itself will also give surge in the mains and may blow your fuse during switch on.

If you want an easy soft start to build you can find one in my blog posts. I made this for my isolation transformer which was around 1500w.

One other option is to connect the battery first before switching on the supply so that the battery will charge the capacitor instead.
Please also note that the battery itself will act as a capacitor and smoothing down the ripple.

I would include the soft start as this will help things to tame down a little bit at start up.

Regards Silvio

Thank you dear Silvio for your through explaination
The diodes I'm using are capable of withstanding 2000A surge current for an half cycle of 50Hz but always it's a good idea to have a protection board

Thanks again:w)
 
For rectifier the best place is from a PC POWER supply as they are high speed and paralleling several is a good bargain
that was the first place I look but those diodes can only withstand 30 to 40A current and I know that paralleling diodes is not a good idea unless they are exactly the same
 
I test my inverter with my car battery and here's the result :

Without load : 172V in output << 12.9V input
23W load : 152V in output << 12.9V input
65W load : 147V in output << 12.87V input
100W load : 145V in output << 12.75V input
230W load : 132V in output << 12.56V input
370W load : 118V in output << 12.38V input
450W load : 110V in output << 12.13V input


Here's my inverter's Schematic :
new.jpg

inverter frequency : 30 KHZ
Transformer windings :
Primary : 2+2 turns of 300 strands of 0.25mm wires ))
Secondary : 12+12 turns (( 70 Strans of 0.22mm wires ))

Is there something wrong with the schematic??? why the voltage drops is so high ???
I even test it with higher input (15V) and at 600W the output voltage reach 136V
???
 
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Silvio

Active member
Quote

Is there something wrong with the schematic??? why the voltage drops is so high ???
I even test it with higher input (15V) and at 600W the output voltage reach 136V
???


Let us consider things a little bit
According to the windings we have 2 turns Pri 12 turns sec So the ration is 12 /2 =6 The ratio is 1:6 This means that for 12v input the output voltage is 6 times higher so 12v X 6 = 72

We have a double secondary so the output suppose to be 72 X 2 = 144v Now you have to consider that if the battery voltage is say 13v then the output be 13 X 6 = 78 78 X 2 = 156v
Taking all this strait forward as shown above will indicate a specified voltage which is not true in reality. As you can see from every 1 volt lost in the input you are loosing 12v on the double output winding.

This voltage drop is unavoidable because loses exist everywhere 1) in the winding itself 2) leakage inductance in the transformer 3) the switching transistors 4) the output diodes 5) The internal resistance of the battery, 6) the traces on the pcb and also the wiring from the battery to the inverter.

The first light load as you saw lost a lot of voltage and it seems that that extra voltage without load is due to some spikes that generated this voltage are stored in the output capacitor. This extra voltage is dumped very quickly when loading the smps due to that this extra voltage has a very short pulse and not strong to sustain any load.

To overcome this problem you need to compensate either from the input which is rather hard in a way as a lot of current is involved and traces must be kept short and wide as possible. You should also enhance them by putting a few 0.8mm bare copper wire and soldering them directly on the traces of the pcb to minimize resistance. I chose 0.8mm because of skin effect at 30 Khz.

The other option is to make another turn or two on the secondary to get a higher voltage and add feedback to your circuit. If you intend to add feedback you must also include an output inductor. This will store voltage during short pulse on light load. Be careful as this has to be tailored for the best compromise between low and high loads.

One last thing I like to mention if you are loading a continuous load things seem a bit harsh on the smps and the 3 farad capacitor will not work here. When loading with an amplifier this becomes a different story as the load is not continuous and now the 3 farad capacitor will come into play and will sustain the voltage much better as it will have time to charge up again between each interval of the varying load.
The output capacitor has the same effect as the input. If you try to measure the output voltage with a working amplifier you will note that the output does not change that much.

I hope this helps you understand much better

Regards Silvio
 
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thank you dear Silvio

I increase each side of the secondary windings by 2 turns and the voltage drops seems to be normal now
but I have a problem now and that's when I connect 15V at the input and I get only 110V at output
and in this situation only three of the mosfets ( parallel) that are handling half of the cycle will get hot (under load) and the other side stay cool
I think it's a problem with 500 Pot that handle dead time as when I set it to different value it changes the hot and cool side

any idea?
 

Silvio

Active member
thank you dear Silvio

I increase each side of the secondary windings by 2 turns and the voltage drops seems to be normal now
but I have a problem now and that's when I connect 15V at the input and I get only 110V at output
and in this situation only three of the mosfets ( parallel) that are handling half of the cycle will get hot (under load) and the other side stay cool
I think it's a problem with 500 Pot that handle dead time as when I set it to different value it changes the hot and cool side

any idea?

Look closely what is happening. Check the gate drive on the mosfets and see that enough voltage is arriving at the gates >10v.
If for any reason this voltage is lower than it can be the case that the mosfets are not getting fully switched on as they should and tend to heat up. Hook up the scope for this test.

It could also be that the primary winding is not symmetrical and is causing this problem. Snubbers must be fitted here across each pair. See the wave form across the primary and search for any spikes on the waveform. These may prolong the switch off of the fets or may be disturbing the wave form at the gates. The dead time can be set for 2uS and left as it is. This should be enough for the time being. The larger the dead time the more power is lost.

Regarding the 15v input it is a bit too much and it could be that the core will tend to saturate.
Are you hearing some kind of clicking or whistling noises during high power output at 15v input?
You can increase the frequency to overcome the saturation problem, try at 40Khz instead. The reason for this is that at a higher frequency less turns are needed for a given voltage. With the copper wire used in your setup skin effect is not an issue as this being only 0.25mm which can go to 100khz or more.

Regards Silvio
 
Look closely what is happening. Check the gate drive on the mosfets and see that enough voltage is arriving at the gates >10v.
If for any reason this voltage is lower than it can be the case that the mosfets are not getting fully switched on as they should and tend to heat up. Hook up the scope for this test.

It could also be that the primary winding is not symmetrical and is causing this problem. Snubbers must be fitted here across each pair. See the wave form across the primary and search for any spikes on the waveform. These may prolong the switch off of the fets or may be disturbing the wave form at the gates. The dead time can be set for 2uS and left as it is. This should be enough for the time being. The larger the dead time the more power is lost.

Regarding the 15v input it is a bit too much and it could be that the core will tend to saturate.
Are you hearing some kind of clicking or whistling noises during high power output at 15v input?
You can increase the frequency to overcome the saturation problem, try at 40Khz instead. The reason for this is that at a higher frequency less turns are needed for a given voltage. With the copper wire used in your setup skin effect is not an issue as this being only 0.25mm which can go to 100khz or more.

Regards Silvio

It turns out that the problem was from saturated transformer (as you mentioned) but I am getting 1500W without any problem with ETD59 in my half bridge smps with 1600 gauss
and as I calculated I'm running the smps with 1600W at 15V in input
(15*10^8)/(4*32000*2*3.68)

am I missing something here? because I can't get more that 800W from the transformer without going into saturation
 

kegs

New member
Look closely what is happening. Check the gate drive on the mosfets and see that enough voltage is arriving at the gates >10v.
If for any reason this voltage is lower than it can be the case that the mosfets are not getting fully switched on as they should and tend to heat up. Hook up the scope for this test.

It could also be that the primary winding is not symmetrical and is causing this problem. Snubbers must be fitted here across each pair. See the wave form across the primary and search for any spikes on the waveform. These may prolong the switch off of the fets or may be disturbing the wave form at the gates. The dead time can be set for 2uS and left as it is. This should be enough for the time being. The larger the dead time the more power is lost.

Regarding the 15v input it is a bit too much and it could be that the core will tend to saturate.
Are you hearing some kind of clicking or whistling noises during high power output at 15v input?
You can increase the frequency to overcome the saturation problem, try at 40Khz instead. The reason for this is that at a higher frequency less turns are needed for a given voltage. With the copper wire used in your setup skin effect is not an issue as this being only 0.25mm which can go to 100khz or more.

Regards Silvio[/QUOT

The original diagram can be found @ http://sound.whsites.net/ Project 69
 

Silvio

Active member
Hi bad boy well saturation will only occur if there is not sufficient number of turns,

What is keeping you to try the inverter at a higher frequency? Try that and see if there is the same effect.

If you have the same result I am afraid you have to add another turn to the primary winding

Silvio
 
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