Dummy load

Doctore · Aug 24, 2013

First I want put 12vps into case but I decided to only add plug and don't put this into case.
So I get this 12V/1A like in your link, this will be the best choice.
Next question, I can put into PCB only M9 and M10 itp., for testing?
And in this situation ampmeter will show 5x too big value yes?
Thanks!

Doctore · Aug 24, 2013

In my circuit, max amps are 50A and volts 50V yes?

ronv · Aug 24, 2013

It is designed for 50 amps at 25 volts with some safety margin. It might run 50 A at 50 volts but it would be dangerous.

Doctore · Aug 24, 2013

So, what is safe value for max. voltage?

ronv · Aug 24, 2013

I would say about 30, but it all depends on the heatsink.

Doctore · Aug 24, 2013

Unanswered question.

Next question, I can put into PCB only M9 and M10 itp., for testing?
And in this situation ampmeter will show 5x too big value yes?

EDIT: wich resistors must be 1%?
Here is actual PCB:

ronv · Aug 24, 2013

Unknown heat sink, unknown answer.

The meter reads only the current thru M10, so if you use 2 (M9 & M10) the current will be 2X the meter reading. So if it reads 5.0 the actual current will be 10 amps total.

Sorry I can't better answer your question, I just have no good data on the heat sink and the loss between the FET and the cooling pipe, so I will be careful so you don't pop them like popcorn.

Doctore · Aug 24, 2013

Heat sink?
Copper pipe+water, fets soldered to pipe, like in oryginal dl1
So, If I solder only M10 and see on display(w/o dot) 05(0,5V) the true amperage is 10A?
And If I solder all fets, And I get 50 the true amperage is 50A, yes?

ronv · Aug 24, 2013

Doctore said:
Heat sink?
Copper pipe+water, fets soldered to pipe, like in oryginal dl1

Click to expand...

If you read thru Dummy load 1 and 2 you will find a long discussion on how much power was possible with this method. I was one who thought we were about right with 125 watts per FET even though the crude measurements we made said we might be able to do more. In the end the conservatives won out and we decided on more like 100 watts per FET for Dummy load 2.

So, If I solder only M10 and see on display(w/o dot) 05(0,5V) the true amperage is 10A?

Click to expand...

The circuit measures only the current thru M10 and converts it to a voltage - 1 volt = 1 amp. So with the dot the meter would read 1.0 for a current of 1 amp, w/o the dot 10. Since there are 10 FETs when the whole board is done if you left the setting the same the total current would be 10 times as high even though the meter w/o the dot would still read 10 because it only measures M10.

And If I solder all fets, And I get 50 the true amperage is 50A, yes?

Click to expand...

If you solder all 10 and the meter reads 50 (w/o the dot) the true current is 50 amps.

Doctore · Aug 28, 2013

Ok, what resistors must be 1% tolerance?
Here is list of resistors:

Part Value Package Library Position (mil) Orientation

R11 1,1k 0207/7 rcl (3950 1050) R270
R12 10k 0207/7 rcl (3600 1100) R180
R13 1,5k 0207/7 rcl (3600 1200) R0
R14 10k 0207/7 rcl (3600 525) R180
R15 1,1k 0207/7 rcl (3600 425) R0
R16 10k 0207/7 rcl (2900 425) R180
R17 390k 0207/7 rcl (2700 575) R0
R19 62k 0207/7 rcl (3250 800) R90
R20 4,3k 0207/7 rcl (3350 500) R90
R25 5,1k 0207/7 rcl (2050 300) R0
R26 68k 0207/7 rcl (2275 200) R270
R28 2,7k 0207/7 rcl (2500 300) R180
R29 5k 3RP/1610N pot (3800 150) R0
R30 75R 0207/7 rcl (275 2475) R180
R31 75R 0207/7 rcl (550 2250) R90
R32 75R 0207/7 rcl (1125 2475) R180
R33 75R 0207/7 rcl (1400 2250) R90
R34 75R 0207/7 rcl (1975 2475) R180
R35 75R 0207/7 rcl (2250 2250) R90
R36 75R 0207/7 rcl (2825 2475) R180
R37 75R 0207/7 rcl (3100 2250) R90
R38 75R 0207/7 rcl (3675 2475) R180
R39 75R 0207/7 rcl (3950 2250) R90

ronv · Aug 28, 2013

If 5% are cheaper they can all be 5%. The pot will be ok at 10 to 20%.
Are you able to find the .13 ohm resistors?

Doctore · Aug 28, 2013

Here is partlist from eagle with links to all parts:

Code:

Part     Value          Package      Library          Position (mil)        Orientation     TME/LISPOL

C1       100nF          C025-025X050 rcl              (500 1900)            R0              http://lispol.pl/product,365,kon_ceramiczny_100nf50v_r254.html
C2       100nF          C025-025X050 rcl              (1350 1900)           R0              =
C3       100nF          C025-025X050 rcl              (2200 1900)           R0              =
C4       100nF          C025-025X050 rcl              (3050 1900)           R0              =
C5       100nF          C025-025X050 rcl              (3900 1900)           R0              =
C6       100nF          C025-025X050 rcl              (3400 950)            R270            =
C7       100nF          C025-025X050 rcl              (2300 700)            R90             =
IC1      LM358N         DIL08        linear           (275 2175)            R180            http://lispol.pl/product,1243,wzmacniacz_operacyjny_lm358.html
IC2      LM358N         DIL08        linear           (1125 2175)           R180            = 
IC3      LM358N         DIL08        linear           (1975 2175)           R180            =
IC4      LM358N         DIL08        linear           (2825 2175)           R180            =
IC5      LM358N         DIL08        linear           (3675 2175)           R180            =
IC6      LM358N         DIL08        linear           (3700 800)            R0              =
IC7      LM35CZ         TO92         lm35             (3150 300)            R0              http://lispol.pl/product,1252,analogowy_czujnik_temperatury_to92.html
IC8      LM339N         DIL14        linear           (2750 850)            R0
M1       IRF520         TO220BV      transistor-power (100 3150)            R0              http://www.tme.eu/pl/details/sup57n20-33/tranzystory-z-kanalem-n-tht/vishay/sup57n20-33-e3/#
M2       IRF520         TO220BV      transistor-power (525 3150)            R0              =
M3       IRF520         TO220BV      transistor-power (950 3150)            R0              =
M4       IRF520         TO220BV      transistor-power (1375 3150)           R0              =
M5       IRF520         TO220BV      transistor-power (1800 3150)           R0              =
M6       IRF520         TO220BV      transistor-power (2225 3150)           R0              =
M7       IRF520         TO220BV      transistor-power (2650 3150)           R0              =
M8       IRF520         TO220BV      transistor-power (3075 3150)           R0              =
M9       IRF520         TO220BV      transistor-power (3500 3150)           R0              =
M10      IRF520         TO220BV      transistor-power (3900 3150)           R0              =
Q1       2N3906         TO92         transistor-pnp   (2100 500)            R90             http://lispol.pl/product,2584,tranzystor_pnp_150v300ma.html
R1       0,13R          VTA56        rcl              (200 1700)            MR90            http://www.tme.eu/pl/details/crl7w-r13/rezystory-drutowe-7w/sr-passives/#
R2       0,13R          VTA56        rcl              (625 1700)            MR90            =
R3       0,13R          VTA56        rcl              (1050 1700)           MR90            =
R4       0,13R          VTA56        rcl              (1475 1700)           MR90            =
R5       0,13R          VTA56        rcl              (1900 1700)           MR90            =
R6       0,13R          VTA56        rcl              (2325 1700)           MR90            =
R7       0,13R          VTA56        rcl              (2750 1700)           MR90            =
R8       0,13R          VTA56        rcl              (3175 1700)           MR90            =
R9       0,13R          VTA56        rcl              (3600 1700)           MR90            =
R10      0,13R          VTA56        rcl              (4000 1700)           MR90            =
R11      1,1k           0207/7       rcl              (3950 1050)           R270            http://lispol.pl/product,954,rezystor_11k_5_025w.html
R12      10k            0207/7       rcl              (3600 1100)           R180            http://lispol.pl/product,975,rezystor_10k_5_025w.html
R13      1,5k           0207/7       rcl              (3600 1200)           R0              http://lispol.pl/product,957,rezystor_15k_5_025w.html
R14      10k            0207/7       rcl              (3600 525)            R180            =
R15      1,1k           0207/7       rcl              (3600 425)            R0              =
R16      10k            0207/7       rcl              (2900 425)            R180            =
R17      390k           0207/7       rcl              (2700 575)            R0              http://lispol.pl/product,1006,rezystor_390k_5_025w.html
R19      62k            0207/7       rcl              (3250 800)            R90             http://lispol.pl/product,991,rezystor_62k_5_025w.html
R20      4,3k           0207/7       rcl              (3350 500)            R90             http://lispol.pl/product,967,rezystor_43k_5_025w.html
R25      5,1k           0207/7       rcl              (2050 300)            R0              http://lispol.pl/product,969,rezystor_51k_5_025w.html
R26      68k            0207/7       rcl              (2275 200)            R270            http://lispol.pl/product,992,rezystor_68k_5_025w.html
R28      2,7k           0207/7       rcl              (2500 300)            R180            http://lispol.pl/product,962,rezystor_27k_5_025w.html
R29      5k             3RP/1610N    pot              (3800 150)            R0              http://lispol.pl/product,1110,potencjometr_obrotowy_b_5k_l15mm.html
R30      75R            0207/7       rcl              (275 2475)            R180            http://lispol.pl/product,929,rezystor_75r_5_025w.html
R31      75R            0207/7       rcl              (550 2250)            R90             =
R32      75R            0207/7       rcl              (1125 2475)           R180            =
R33      75R            0207/7       rcl              (1400 2250)           R90             =
R34      75R            0207/7       rcl              (1975 2475)           R180            =
R35      75R            0207/7       rcl              (2250 2250)           R90             =
R36      75R            0207/7       rcl              (2825 2475)           R180            =
R37      75R            0207/7       rcl              (3100 2250)           R90             =
R38      75R            0207/7       rcl              (3675 2475)           R180            =
R39      75R            0207/7       rcl              (3950 2250)           R90             =
SG1      F/CM12P        F/CM12P      buzzer           (2050 1000)           R90             http://lispol.pl/product,1366,buzzer_z_generatorem_na_12v.html

If you can't find here is link for .13 https://www.tme.eu/pl/details/crl7w-r13/rezystory-drutowe-7w/sr-passives/#

ronv · Aug 28, 2013

Looks ok.

Doctore · Sep 1, 2013

So, parts ordered, some from tme, some from lispol and ebay.
Voltmeters/displays **broken link removed**
and cooling for resistors(I will add alloy heatsink offcourse) 3x **broken link removed**
Actual costs - 235PLN(about 75$).
I hope this circuit will work.
Thanks so much guys!

Doctore · Sep 15, 2013

Ok, PCB is complete and fets soldered to copper pipe, I must only solder fets to the PCB.
I test PCB and lm35, I heat lm35 and beeper starts at 100C, why?
How to get starting this at 70C?
I will show pictures soon.
Thanks

ronv · Sep 15, 2013

check the voltage at both input pins of IC8A. At room temperature the one from the LM35 should be about .25 volts and the other one .7 volts.

Doctore · Sep 16, 2013

Ok, thanks, I check this later.
Now I connect all and get tests with CH5, results?
I have short circuit between LOAD+ and LOAD- when I have power up board, when off I don't have short circuit between load wires, rotating POT does not matter, where is problem?

ronv · Sep 16, 2013

I'm not sure where load+ and load- is.
With no power supply hooked up to test and power on you should measure .13 ohms from the input to ground. With no current flowing the pot will not adjust because it will try to make current flow.

Doctore · Sep 17, 2013

LOOOOOOOOOOOOOOOOOOOOOL
It turned out that the pot was not a minimum but the max ...
Almost everything works, regulating the load work and load shutdown after exceeding the operating temperature.
The only thing that does not work, it is that pins for AMP/TEMP. metering shows 10x too small voltage, this doesynt show 1v/2A(two fets) but 0,1V/2A.
I checked voltages on pins of IC8:
1=0v
2=11,65v
3=12,16v
4=0,197v
5=0,393v
6=2,52v
7=2,05v
8=2,41v
9=2,52v
10=2,31v
11=2,05v
12=0v
12=0v
And IC6:
1=0,22v
2=0,2v
3=0,24v
4=0v
5=0v
6=0v
7=0v
8=12,15v

Doctore · Sep 17, 2013

Polish boys find mistake, descriptions of resistors R15 and R14 are swapped on the pcb...

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