LP 2 Lily,
Always around friends you shall never fear.
-Fumu / Esopus
1 Like
we all have our baggage , so no problems here . my 2 cents [ opinion ] is that if you have 1 big power supply [ 8 amps or more ] you are going to have to regulate it down [ heat / wasted energy ] because most modules run on mili amps . seems like it would work the same or more efficient to run 4 @ 2 amps .
my cases are pretty spread out so this works better in my case for sure . but what ever works for you. it seems like there is no absolute right way to do things in the diy synth world . just keep it safe , enclosed mains hook ups , fuses and remember the heat has to go somewhere .
1 Like
After reading over every ones responses I realize the teachers I had in the past were abusive in a way. Getting yelled at only because I was confused and slow was what my mother said. The last teacher I had was a jerk. All the other students told me he yells at you when your having trouble. Especially when it came to PLCâs in the shop. So, having the ability to see there are good people out there gives me a lot of hope. I had wonderful mentors in the past. However, college was inconsistent with this. In tech school its several times worse because of common core math that older people are forced to learn. Yea, they force it on the adult students as well.
.
More to the point though I always been familiar with DC. I only went from a wall wart to an actual bench top DC power supply in the past two years. I do understand there is a risk when there is more current. If there is no fuse then nothing is going to prevent things from overheating or worse cause a fire. I always use multiple fuses because the parts are expensive. I knew heat is a byproduct in converting electricity. This is why its so hard to power devices from a Li-po cell wall in off grid solar systems. A lot of energy is wasted over creating that 60 hz sign wave. I did not know this can be the case for AC transformers as well. Thanks for being kind and patient with me and my questions.
1 Like
Naah, I think I used all the shipping I paid for in the first four weeks of lockdownâŚ
1 Like
yeah I am going to have to work my ass off the rest of the summer to pay my cards down .
but its been worth it . learning new stuff , making new friends , making noise and having constructive fun .
2 Likes
oops , what was this thread about ? , oh yeah . LP2Lily thats B.S. that is no teacher . not that all of us can help " teach " very well , but we at least we can respect one another . and about the power supplies it would be cool to design our own thing but it is kinda like reinventing the wheel . there are many affordable options out there. it seems like doing that would take away from designing the fun stuff .
3 Likes
Makes you wonder what current a 1000 oscillator setup would draw.
2 Likes
Well, each has an LEDâŚ
2 Likes
The 3340 consumes ~5 mA, so 5 A for the oscillators. Double that for the rest of the circuitry, double again so you can add some shiny LEDs and have some margin, and youâre at 20 A total.
Which incidentally is what Samâs using for the not-3340 oscillators in the megadrone (2 A per row, 10 rows).
2 Likes
Yep 20 A sounds right to me. He better adapt his wiring to that current then.
2 Likes
Heâs using one 2A supply per row, which simplifies the wiring a bit (well, the supply part of it, at least).
2 Likes
At 2A per row he should use IR LEDâs and get a tan at the same time!
1 Like
Ok so I got the motivation to continue working with this schematic. I decided to bread board it and see if the diodes were the problem. To my surprise the diodes I circled in Rayâs schematic cause a short and burns the 2amp fuses I have protecting my transformer. Not sure I want to waste anymore now that I know that this will happen. Apparently these diodes are only there for protection. Unfortunately they cause further problems with my transformer. If I remove only the circled ones the circuit works flawlessly. I even had a perfect (-12v) read on my multi-meter. Does anyone know why Ray thinks they have to be there? On the page he says; âDiodes CR3, CR4 and CR5, CR6 are protection diodes recommended in National Semiconductor Application Note AN-182 for protecting three terminal regulators from unwanted current paths that the output capacitors can inadvertently cause under certain conditions.â I drew in a new diode that is rated 2amps for the ground connection. Would this prevent unwanted current paths? Thanks for the help!
Are you sure you mounted them the right way? Theyâre there to make sure capacitors in the downstream modules donât discharge through the regulators when the supply is turned off, and theyâre definitely the right way in the schematics (i.e. âbackwardsâ). If they turn on when the supply is powered on, odds are theyâre mounted the wrong way.
2 Likes
The only way I could get it to work is if the line on the diode was opposite of that of the schematic. Would this mean the schematic is wrong or am I missing something? Thanks for all your help by the way. The line means the negative side and we donât want current going through these safety diodes right?
.
.
Edit:
A big Teen Titans Boo Ya. I had a 7812 for a negative and I replaced it with 7912 and now it works! You would think I would notice that. SIGH
The schematic is correct â if you follow e.g. the upper positive rail from the wall wart end through the diodes, current goes through CR1 but not through CR3 and CR4, i.e. CR1 and CR3/CR4 should point towards each other.
Same for CR2 and CR5/CR6, but the other way around.
Note that the line on the diode marks the cathode, marked with âkâ in the schematics. Iâve stumbled upon EasyEDA PCB footprints that have it the wrong way, but you were breadboarding, right?
If you have a multimeter with a diode continuity function, you could check that your diodes donât have weird markings (LEDs mounted backwards isnât unheard of, at least if you get cheap no-brand ones, but I donât think Iâve seen that for diodes).
1 Like
Yet, I did not notice the obvious. Of course the 7812 will create a negative just like two nine volts in series. Unfortunately this regulator is not meant to work in this configuration. Better to pair it with a 7912 instead. MIDI in with the Opto isolator uses a diode backwards for the same reason. Only for a accidental reverse cable. I wonder how many times I got that backwards and not known it. Thanks again for the help
Ok I been weeding through the problems and I found that I had to subtract two caps and remove the final output diodes. No matter how I put them in and I did this several times over adding caps, subtracting caps, and changing the direction of the diodes multiple times. However, I was able to get the diodes onto the three pin voltage regulators. Assuming this is enough I think I burnt enough fuses for one day.
Fuse count thus far = 23 burnt 2amp fuses
All on this power supply. In conclusion I had the circuit correct. However; the transformer I have is high amperage in 8.5 amps at 12v ac. I think this might be part of the problem. Any ideas are welcome. For now I am just going to be grateful I got he two diodes protecting the voltage regulators. I will put a 2 amp diode on the ground wire just to prevent current going the wrong direction there. Final schematic for now.
23 burnt fuses, that is quite a lot.
That should make you wonder whether you are doing things right, doesnât it? I donât mean this in a negative way. Look at this logically. Could there not be another way of testing the circuit without risking to blow fuses?
Well, there are several. But not all of them may be available to you.
1: use a variac, this is a transformer the output voltage of which you can choose via a dial. You may have seen those in physics labs at school. In stead of connecting your circuit to the mains supply you could connect it to a variac and slowly crank up the voltage while keeping an eye on the current the circuit draws. If that is much more than you expect, there probably is a short somewhere. Getting diodes reversed in some places can lead to that easily as you have experienced.
Make use of Ohmâs law:
2: use a multi meter and measure whether what the resistance is between the + and - line of the circuit if it is not powered. If that is very low, like several ohms or less, you probably have a short somewhere.
3: if you have no variac, I guess most people wonât have one, then temporarily add a power resistor of say 1 Ohm and a high wattage between the transformer and the bridge rectifier and measure the AC-voltage across the resistor, from that you can calculate the current through the resistor. If the currentâs value is near the AC voltage divided by the resistorâs value, you know there is a short in the subsequent part of the circuit.
4: you can do the same with a resistor between the bridge rectifier and the rest of the circuit. Here you can measure the voltage across the resistor and calculate the DC current through the resistor. If that current is in excess of what you would expect the circuit to draw, that could be an indication of a short.
5: if you have a regulated DC power supply, you can use that to test the power supply you are building. Connect the regulated power supply to the bridge rectifier where you would normally connect the transformer. Then while measuring the current slowly turn up the voltage. Keep an eye on the current. If that gets too high, you know there is a problem in the circuit.
In all of these cases, no fuses will be blown, as long as you keep an eye on the current that is drawn, keep it low and stop the measurement as soon as the current gets too high.
I hope one of these methods is feasible for you.
1 Like
I started a thread on Soft-start circuitry because I figured that it was a different topic. The transformer is working beautifully. However, with the added capacitors it draws an enormous amount of current. Normally a transformer does not put out that much and the capacitors take a little while longer to load. Mine puts out 8.3 amps or 100 watts of power. My guess is the in-rush current is blowing my fuse. If I use a soft start I can limit the current draw until the caps are filled and then a relay can bypas the resistor you suggested in 3 and 4. Hopefully I did not cause a problem with the new thread on soft starts. I totally apologize if I did.