Author Topic: Electronic constant current DC load  (Read 92627 times)

MJLorton

  • Administrator
  • Hero Member
  • *****
  • Posts: 817
Re: Electronic constant current DC load
« Reply #15 on: October 01, 2012, 04:03:39 AM »
Hi Martin,

Just an update on my el-load project.  I have been working on the design (Dave's and yours)  for the last couple of days and it is nearing completion.  It is Friday night here in California and I think I will be able to post most of the design information this weekend.  I am waiting on the chassis and a digital meter which should be here in a few days.  Basic features (that might change) are:  0 to 5 amps at 12 volts, digital readout of current with set feature and on-off output control, heatsink tunnel with fan, two E-MOSTFETs (the ones you selected) for load control, only need one quad opamp, and some other goodies.  I plan to put the control circuits on a PC board and the basic design can support much higher voltages and currents... given a lot more E-MOSFETs.

John

Hi John,

Excellent, I look forward to seeing how it turns out. It's great seeing everyone's own tweaks and adaptations for their needs.

Thanks for the post.

Cheers,
Martin.
Play, discover, learn and enjoy! (and don't be scared to make mistakes along the way!)

MJLorton

  • Administrator
  • Hero Member
  • *****
  • Posts: 817
Re: Electronic constant current DC load
« Reply #16 on: October 01, 2012, 04:06:29 AM »
Hi Everyone, I am new to the forum and an amateur at electronics (but I am a very experienced software engineer). I watched Dave's and Martin's DC load videos and decided to build one as well. I have it working successfully on a breadboard, although I still need to do some more in depth measurements with the scope across a broader range of voltages and current. I built my load circuit using the same op amp, mosfet and power resistor as Martin. I also used a 10-turn pot that is nearly identical as well. My original attempt powered the op amp at 12V but I ran a voltage divider and another voltage follower to drop the voltage to the pot and comparator up to 11V. The circuit did work but I did not have much granularity in the pot - less than one turn and I was over 1 amp! Yikes! Today I tweaked the circuit to be more like Martin's last video on the subject by building up an LM317 with a couple of resistors to give me a 6V supply to the load circuit. I also added a pair of 10K resistors to form a fixed voltage divider just before the comparator op amp and another 10K resistor to ground just before the mosfet's gate. Under this config, the 10-turn pot has a lot of fine-grained control, which is nice. I am only using one 50K, 10-turn pot, not the coarse and fine controls. I do not believe I need a fine control. I have only tested it up to 1.5 amps for a very short time since I'm on a breadboard and I don't want a meltdown - the mosfet gets hot fast as I near one amp of constant current. My load is connected to a separate bench top power supply much like Martin does in his videos. Pretty cool project! Thanks for all of the great information!

Hi Wade and welcome to the forum.

Thanks very much for your post and the information on your project. I look forward to hearing how it progresses...do post some pictures if you have the time.

Cheers,
Martin.
Play, discover, learn and enjoy! (and don't be scared to make mistakes along the way!)

jwrelectro

  • Newbie
  • *
  • Posts: 36
Re: Electronic constant current DC load
« Reply #17 on: October 01, 2012, 05:03:57 PM »
The case and digital panel meter should be here today.
There will be several posts on the design and fabrication of the el-load.
 I thought I would start with the homemade heatsink tunnel.  It is composed of two 100mm x 100mm x 25mm aluminum heatsinks that are taped in their centers for a TO-220 mounting screw.  There is a ball bearing 80mm x 80mm fan for forced air-cooling and it operates on 12V DC at a rated 70 mA, ( I measured just 55 mA),  24.7 CFM, 22 dBa noise.  Part number is 3110GL-B4W-B19 and I got mine at Jameco Electronics for $5.95 USD.  I pounded into the heatsink fins eight threaded standoffs so I could attach the fan to the two heatsinks and then attach the whole module to the chassis.  I got a couple of small rectangular aluminum pieces for  the  top and bottom, which with the heatsinks form the air channel.  The fan is so quite I am going to let it run all the time while the unit is turned on.  Each of the two E-MOSFETs are attached to their respective heatsink and one of them has a thermistor to monitor the temperature.  The heatsink tunnel's performance is very nice.  With the fan turned off and an ambient temperature of 25 degrees C (from now on 25C) and a load current of 5.0A the temperature of the transistor cases where at 102C in 5 minutes.  Same measurements with the fan on the transistor case temperatures were 62.5C.  I am using the transistor Martin selected, BUZ31LH.  Maximum operating temperature for these devices is 150C but there total power dissipating at this high temperature drops to zero.  I decided to limit their temperature so I could easily get 5 amps load current at 12 VDC.  I also experimented with blowing air over just the channel and associated heatsink fins and then  the channel plus the exterior fins.  Using the fan and blowing air over all of the fins the temperature was 66.8C.  Blowing air only through the channel the temperature was 60C.  I think the reason for this is I didn't have a container around the external fins and so some of the air flow escaped.  Also directing all the air flow through the channel added additional cooling to the transistors which are the heat source.   My heatsink will be enclosed in a metal case and therefore no physical connection to the outside.  This is important because the metal tab on the TO-220 case is electrically connected to the drain and therefore high voltages could appear on the heatsink.  I did used an electrical insulator so no voltage is on the heatsink but the metal tab still presents a hazard.   As an example if you have a 30 to 40 volt solar cell panel connected to this device there may be a shock hazard.  These heatsink tunnels are basic modules and you could add more for higher load currents.  I have tested this one to 6 Amps and 12 volts with no problems and the total cost including transistors and thermistor was around $20.00 USD.  I will be adding more posts over the next few days and include a schematic diagram of el-load.  Hope you find this material helpful but I probably don't know what I am talking about but then again that never stopped me before.

Below are a few pictures of the heatsink tunnel...
« Last Edit: October 01, 2012, 10:43:45 PM by jwrelectro »

jwrelectro

  • Newbie
  • *
  • Posts: 36
Re: Electronic constant current DC load
« Reply #18 on: October 02, 2012, 02:28:25 PM »
This is the second post on my el-load.  In this post I will describe over temperature protection.  As mentioned in the previous post I installed a thermistor in the heatsink tunnel.  It is physically clamped to one of the E-MOSFETs.  The circuit could support monitoring both transistors but I decided to just monitor one.  A nice thing about evaluating the temperature of the device is that it is determined by both the current (IL) and VDS of the transistors.  Also it can detect if the fan fails.  A negative... there's always a negative is the thermal inertia of the system. The BUZ31LH E-MOSFET's can operate at a maximum temp of 150C.  At this high temp the devices dissipation rating drops to zero.  Looking at the devices de-rating curve I wanted to limit the temperature of the transistor's case to a maximum of 100C.
The thermistor is shown in one of the pictures below and I soldered a couple of blue wires with heat shrink to make the probe.  I purchased this part from Jameco, part number 207037 for $0.59 USD.  The thermistor can operate up to 150C, tolerance is +/- 10 % and nominal resistance is 10K-ohms at 25C and 637 ohms at 100C.
Please refer to the schematic section of the Over Temperature circuit, (OTC) shown in the picture below.  The entire design of the complete el-load uses one inexpensive Quad CMOS opamp, the MCP6004.  It works very well, is stable driving the E-MOSFETs and is a power supply rail-to-rail output device.  It also has the same pin out as the LM324 series devices.  I got my MCP6004 devices for about $0.50 USD each from Mouser.com
U1D is running on a regulated supply voltage of +5V.  The OTC circuit is a voltage comparator with hysteresis (meaning two trip/threshold points).  The opamp is running positive  feedback via R4 and is comparing one of the two reference voltages at pin 12.  The thermistor TH1 is bonded to the E-MOSFET in the heatsink tunnel.  R9 and TH1 form a voltage divider and send a voltage level related to the temperature of the transistor to pin 13.  You could use a potentiometer in place of R9 if you wanted to calibrate the temperature voltage.  R1, R2, and R4 set the two reference voltages that correspond to 90C and 100C.  These two temperatures could also be easily changed with different values of those three resistors.  D1 is a red led that indicates when over temperature has occurred.  R5 is just the current limiting resistor for the led and to not overload U1D.  R11 connects the U1D output voltage to the gate of a control E-MOSFET and the 270-ohm value was selected to minimize capacitive loading of the opamp and make sure it is stable (phase margin).
Ok so what is the basic operation of this circuit?  When the temperature of the E-MOSFETs is below 100C the led is off and the system operates normally.  If however you select a load current (IL) and the load voltage is too high the temperature of the E-MOSFETs will start rising.  At a 100% power overload of the system I noted a 1C increase per second.  When the temperature reaches 100C the led will light and a positive control voltage is feed from R11 to an overload E-MOSFET.  That FET, not shown in this section of the diagram will pull the control line of the system low and turn off the load E-MOSFETs.  The temperature will then start dropping but because of the two trip points it will not restore or turn off the led until the temperature drops to 90C.  This is important to prevent erratic operation of the OTC.  Just like your home heating system has two trip points so you are not cycling the furnace off and on rapidly.  When the 90C temp is reached the OTC will turn off the led and restore load current to the device under test (DUT) automatically.  Therefore you have some protection of the system if left unattended.  I am planning on putting the red led directly above the load current control so the user can easily see when over temp occurs.  Another option for this circuit is to have a buzzer installed so you have both visual and aural notification of a problem.  Total cost of this circuit is around $2.00 USD.  A much better but more costly option is to use a micro-controller.  A few more posts to come with a complete circuit diagram of the entire system.  Hope this is helpful.  John
« Last Edit: October 04, 2012, 12:51:28 AM by jwrelectro »

SeanB

  • Administrator
  • Hero Member
  • *****
  • Posts: 1008
Re: Electronic constant current DC load
« Reply #19 on: October 02, 2012, 03:32:58 PM »
Thermal paste between the mosfet and the sensor will make it respond faster, as it will have better heat transfer from the tab to it. A thin blob around it before clamping will do.

jwrelectro

  • Newbie
  • *
  • Posts: 36
Re: Electronic constant current DC load
« Reply #20 on: October 02, 2012, 04:15:33 PM »
SeanB,

Thanks for the suggestion and I will give it a try and see if it speeds up the reading.

MJLorton

  • Administrator
  • Hero Member
  • *****
  • Posts: 817
Re: Electronic constant current DC load
« Reply #21 on: October 03, 2012, 07:32:18 AM »
Hi John,

Thanks very much for the great posts and progress...I'm wiser after reading about your additions.

Cheers,
Martin.
Play, discover, learn and enjoy! (and don't be scared to make mistakes along the way!)

jwrelectro

  • Newbie
  • *
  • Posts: 36
Re: Electronic constant current DC load
« Reply #22 on: October 03, 2012, 06:19:25 PM »
Here is the third post on my el-load.  In this post I will discuss a simple section of the el-load.  This section is the control voltage stage which sets the load current (IL).  As mentioned earlier this is basically Dave Jones' circuit.  Please refer to the schematic diagram picture below.  RV1 is a 50 k-ohm, 10-turn potentiometer (pot) that I already had in my parts box.  The pot forms a simple voltage divider and it can output a voltage from 0 to 5 volts on its wiper (pin 2).  The voltage supplied to this pot is from a 5 volt regulated power supply.  The voltage to this pot needs to be regulated because if it changes so does the value of IL.  Most ohmic values for the pot, say from 5k-ohms to 100k-ohms should work in this circuit.  The selected voltage at the wiper of the pot is applied to pin 3 of U1A which is 1/4 of the MCP6004.  This stage is a voltage follower used as a buffer and its gain is set to unity by the wire connecting pin 2 to pin 1, (100% negative feedback).  The output of the opamp at pin 1 drives an adjustable voltage divider circuit of R3 and RV3.  This scales and limits the control voltage from 0 to 2.5 volts,  In my circuit the 2.5 volts equals 25 amp of IL.  Obviously my E-MOSFET transistor would not be happy and quickly die if I tried to get 12.5 amps from each of them.  That is why I have RV3 which can set the current limit on the system.  I have it currently set to 550 mV maximum which equals a maximum IL of 5.5 amps.  RV3 is also a 10-turn pot that will be located on the circuit board and should not be changed once an optimum/safe value is determined for the system.  R3 has a second function which is to protect the opamp when the crowbar E-MOSFET shuts down the IL, (discussed in a following post). The opamp's short circuit output current is typical +/- 23 mA but I don't like shorting opamp outputs to ground.  Therefore the U1A opamp will always see at least 10k-ohms at it output thanks to R3.

jwrelectro

  • Newbie
  • *
  • Posts: 36
Re: Electronic constant current DC load
« Reply #23 on: October 03, 2012, 07:37:17 PM »
Here is the fourth post on my el-load.  In this post I will go over the error opamp and output transistors.  Please refer to the schematic diagram shown below.  U1B is the error/driver opamp which is 1/4 of the MCP6004, (yea the 4 in that number stands for 4 opamps (quad).  Pin 5 of the opamp receives the control voltage from the previous stage and that voltage determines the load current (IL).  The opamp is wired to compare the control voltage to the voltage drop across the current sense resistor R8.  This opamp has a stated minimum Avol or Aol, (open loop voltage gain) of 88 dB or stated another way 25,000. Since this is a differential amplifier (pins 5 and 6) the difference signal between those two pins gets amplified by at least  a factor of 25,000.  So for finite output voltages from 0 to 5 volts the input differential voltage would be almost zero.  So as a first approximation just think that the opamp will try and output a voltage at pin 7 to make the voltage at pin  6 equal the voltage at pin 5.  Let's say we want an IL of 5 amps with a load voltage of 12 volts.  Note that R8 is in series with the load circuit so the load current passes through R8  and using Ohm's Law 5 amps flowing through R8 a 0.1 ohm resistor will give rise to a voltage drop of 500 mV (5 amps x 0.1 ohms = 500 mV).  Therefore we would set our control voltage to apply 500 mV to pin 5 of the error opamp.  This means at power up the opamp sees 500 mV on pin 5 and 0 volts on pin 6.  The opamp would then see this error and adjust its output voltage at pin 7 such that the voltage at R8 would equal 500 mV and thus pin 5 and pin 6 would have approximately equal voltages.  What is the output voltage at pin 7?  It has to be the 500 mVs across R8 but it must also add the threshold voltage of the transistors Q1 and Q2 plus a little more to get the 5 amps to flow through the output.  The BUZ 31LH E-MOSFETs have a typical threshold voltage of:  1.2 v min, 1.6 v typ, 2 v max.  I measured 4 of these fets and found them all very close to 1.555 volts, (great a good match).  So back to our example the voltage would need to be a little over 1.555v + 0.5 v.  So the voltage at pin 7 is a bit over 2 volts.  If you monitored the pin 7 voltage as you turned up your voltage control pot you would almost immediately see the voltage jump to a little over 1.5 volts and then adjust up more as you dialed in higher control voltages.
The two E-MOSFETs are in parallel and if they are well matched they should divide the IL equally with half of the 5 amps flowing through Q1 and the other half through Q2.  Let's assume that when we set the IL to 5 amps each transistor has 2.5 amps of drain current.  The power dissipation of one transistor is then VDS x ID.   VDS is the voltage drop across the transistor from Drain to Source.  We said we were doing 5 amps at 12 volts do the VDS is 12v  - .5v = 11.5 volts and then multiple by ID of 2.5 amps would  equal 28.8 watts.  The 0.5 volts in the previous equation was from the voltage drop across the sense resistor R8.  Each transistor is dissipating approximately 29 watts for a total of 58 watts.  My sense resistor R8 is a 5 watt 0.1 ohm.  The power the resistor must handle at 5 amps is the current squared 25 time the resistor's ohmic value of 0.1 ohm which equals 2.5 watts.
So what happens if the IL current tries to change?  If it tries to increase that will drop a larger voltage across R8 which will increase the voltage a pin 6 of the opamp.  The opamp sees that this voltage is greater than the control voltage at pin 5 and since the larger voltage is on the negative (inverting) input the opamp will reduce it output voltage which in turn will increase the channel resistance between Drain and Source of the fets.  This action will lower the current back to the set value.  If the IL tries to decrease the voltage on pin 6 will drop and the opamp will see that a larger voltage is on pin 5 the positive (non-inverting) terminal and will increase its output voltage and thus lower the channel resistance of the fets and this will increase IL back to the set value.  To recap the two transistors are acting as variable resistors in parallel and the opamp is varying the resistance from the Source to the Drain so that the current matches the value related to the  control voltage.
Not shown on this diagram is the thermistor which is monitoring the temperature of Q1.  The purpose of R6 and R7 is to make the circuit stable when the opamp is driving a capacitive load.  From the data sheet the input capacitance of the BUZ31LH worst case is 1600 pF.  Using the diagram and design formula from the MCP6004 I determined I needed 250 ohms of resistance.  I chose a standard value of 270 ohms for the build out resistors R6 and R7.  The circuit on a breadboard and with a rats nest of wires seems to be very stable... we shall see.  Check out the rats nest and breadboards for the completed circuit in the picture below.  As a side note I have not put in any discharge resistors from the gates of the fets to ground.  Initial tests seem to show they may not be need more on that topic later.  So far I am really liking this quad opamp (MCP6004).  Hope this helps and that I didn't make any major mistakes.  More to come,  John

« Last Edit: October 04, 2012, 10:14:36 PM by jwrelectro »

jwrelectro

  • Newbie
  • *
  • Posts: 36
Re: Electronic constant current DC load
« Reply #24 on: October 04, 2012, 06:12:00 PM »
Here is the fifth post on my el-load.  In this post I will discuss the complete el-load excluding the +12v and +5 volt power supply.  I will cover that dual voltage power supply and the case later.  Please refer to the schematic diagram in the picture below.  In previous posts I covered the Over Temp Stage (OTC) in the lower left-hand of the diagram. I also covered the voltage control and output stages that appear across the top of the diagram.  In this post I will cover the switching, crowbar, line driver, load on LED, and panel meter.  Sorry the switch symbol is so large but that's what was available.  I am just learning the open source KICAD program so there are a few things that I will need to change.  I hope to also use KICAD to make the circuit board artwork.

 OK let's talk about the switching.  It looks a bit involved but is actually pretty simple and inexpensive.  The four symbol circles represent actually just one rotary switch that cost $3.50 USD.  It is a three position, four pole, non-shorting switch.  This switching operation could be done with electronic switching or relays but this approach is simple and cheap.  One pole is section S1A at the top of the diagram and it has three positions; 1, 2, and 3.  A little confusing but starting from position 1 and going to position 3 is moving the panel knob clockwise on this diagram it is counter-clockwise.  The three positions of the switch are OFF - SET - ON.  In the OFF position the unit is turned off... duh.  In the SET position the unit is turned on but the load is disabled.  In this position you can set the current using the front panel LCD meter without the load being in operation or even connected.  This is helpful because it is hard to know initially where the 10-turn RV1 is set.  Moving to position 3 (ON) enables the load current and reads its value on the LCD meter.  At anytime you wish to disable the output without turning off the unit, you would just move the switch from ON to SET.  Then make any changes to the external circuit and then switch back to ON position to restore operation.  Also as a little safety feature you can never turn the unit completely on without going through the SET mode.  That way you can see the current you are about to allow before it actually happens.

  Looking at section S1A you can see that it connects the green Load On led to the output of U1D.  This means that the ON LED D2 will only turn on in this position and that the output of U1D must be in a low voltage state.  If however there is a fault with the temperature U1D's output will be high and not allow the Green diode D2 to be on while the Temp red LED D1 is on.  If the output of U1D is high, near the 5 volt rail it will bias Q3 the Crowbar E-MOSFET to saturate and pull the control line going to pin 5 of U1B near zero volts.  This will turn off  Q1 and Q2 and therefore IL will go to zero.  Why use such a large FET for Q3.  They are cheap and I had one.  It is also nice for repair to have to only deal with one type.  You could of course use a very low power device for Q3.

Switch section S1B grounds the input to pin 5 of U1B in the OFF and SET position so that IL is zero.  In position 3 the switch couples the control voltage to pin 5 of U1B for normal operation in the ON mode.

Switch section S1C in the OFF position grounds the input to both the panel meter and the line driver U1C.  I like grounding these input until the unit powers up.  In the SET position section S1C connects the control voltage from the wiper of RV3 to both the line driver and panel meter.  This allow you to view and set the IL current before enabling the output.  When section S1C is in the ON position the voltage (related to IL) across R8 the sense resistor is sent to the line driver and panel meter for monitoring.

Section S1D is the AC power section and connects to the power supply.  In the OFF position the AC line is broken and the unit is off.  In the other two positions the power supply is turned on.  This rotary switch control the 120 volts AC and this switch has that rating and is also fully enclosed and has a plastic shaft for safety.  If you decide to use a rotary switch make sure it can handle and is designed to operate AC line voltage.  For example the one I selected cannot handle the 220 V provided in other locations.

I have a close-up of this rotary switch in a picture below and it hasn't yet been wired for the AC line but all the other connection have been made for testing.  I like using ribbon cable to make the wire management neat.  So far I have been running test to see if when switching the system, it had transients or instability.  Below is a oscope picture showing the turn off and turn on of the system and this is at a low sweep speed and looks very clean with no overshoot.  I also used much faster sweep speeds and still looks good with a slight ramp up.
 
In this post a couple of comments on the line driver and panel meter.  The panel meter is under $20.00 USD and is 3 and 1/2 digital back light LCD.  It can be programmed with solder jumpers for AC/DC current and voltages.  It also includes several ranges and you can set the decimal point.  Right now I have it set to DC volts on the 2 V range with the decimal point 2-digits from the right.  Therefore it is reading out in amps with a resolution of 10 mA.  For example if the display is 12.50 that would represent 12.50 amps of IL.  I am not too happy with the back light, pretty dim but it does the job, I guess.  I was going to use the light from the panel meter to indicate when the unit was on but decided to add a red power on led in the power supply section.  The purpose for the line driver U1C is to provide either the SET voltage or the voltage related to IL to a remote voltmeter.  The back of the unit will have two banana jacks at 3/4-inch spacing so you could plug in a dual banana jack connected to a DMM.  This way you could read down to milli-amps or for easy monitoring.   For example have the unit under the bench and still easily view the IL value.  R12 is another 270 resistor and will limit the opamp current to a safe value so that if you accidentally short the remote wires together the opamp will not be harms and since U1C is a buffer you will not upset the operation of the el-load.  I plan to do a PC board, final case assembly, and  performance testing but this may take a week or two.  Hope this helps, John
« Last Edit: October 05, 2012, 08:19:32 PM by jwrelectro »

jwrelectro

  • Newbie
  • *
  • Posts: 36
Re: Electronic constant current DC load
« Reply #25 on: October 08, 2012, 12:20:25 AM »
Me again...  Here is the sixth post on the el-load.  In this post I will go over the power supply for the el-load, (not much here).  If you were not using a 12 v DC fan then the only power needed would be at 5-volt DC and very low current.  This power supply is not battery power and is designed to operate on 120 v AC 60 Hz.
Please refer to the schematic shown below and I have also included a picture of the physical circuit.  As you can see on the left side of the schematic are the 3 wires coming from an AC outlet, (a plug will be added).  Wiring here in California, USA is the hot line is usually colored black with the neutral being white and the ground is green.    There is a fuse yet to be determined, once I measure operating power requirements of the circuits.    There are two wires after the fuse that are labeled TO S1D.  This is the main power on switch located on the other schematic and it is the 4th pole of that rotary switch.
T1 has a secondary winding that is center tapped, (12.6 v CT).  I wanted a CT so that the differential voltage across the input and output of the 7805, 5-volt regulator would be reasonable and not generate unnecessary heat.  The four rectifier diodes are 1N4007's and are what I had in my parts box.  They are rated at 1000 v PIV and IDiode of 1 Amp.  The transformer is rated at 2 A so a bit of overkill.

The 4 diodes act like a full-wave bridge and deliver a peak voltage of around 18 volts to the main filter capacitor C3 for the 12 volt side.  This capacitor is for storing energy and filtering the ripple.  C5 is for high freq noise suppression and giving stability to the 3-port voltage regulator 7812.   The 7812 is a 12 v, 1A linear regulator and I only need a little current so again overkill.  C7 on the output is also noise suppression and for stability.  There are other capacitors in the system for filtering and decoupling close to the active devices.

Note that the supply for the 7805 is from the center tap and therefore improves efficiency because the voltage to the input of that regulator is only half of the 18 volts peak.  Added to the output of the 7805 is R13 and D7 for a power on indicator. . Oh I forgot there are two other resistor in the photo (not in the schematic) and were used for testing.  Again not much to this circuit.  Hope this helps, John.
« Last Edit: October 08, 2012, 12:26:46 AM by jwrelectro »

MJLorton

  • Administrator
  • Hero Member
  • *****
  • Posts: 817
Re: Electronic constant current DC load
« Reply #26 on: October 08, 2012, 03:19:27 AM »
Thanks very much John. Great posts.
Play, discover, learn and enjoy! (and don't be scared to make mistakes along the way!)

jwrelectro

  • Newbie
  • *
  • Posts: 36
Re: Electronic constant current DC load
« Reply #27 on: October 14, 2012, 12:29:24 PM »
Hi Martin,
Hope these post have some useful information on the el-load.  Just an update, I have been trying to learn KICAD so that I can layout a circuit board for this project.  Today I think I may know just enough to start the layout.  I hope to have a completed circuit board in about a week.  I will be doing my own PC board fabrication and since I do not have any experience in silk-screening , it will be just a plain circuit board.  I also think I have all the case and external parts to finish the build.  Hopefully more to follow.  John

MJLorton

  • Administrator
  • Hero Member
  • *****
  • Posts: 817
Re: Electronic constant current DC load
« Reply #28 on: October 15, 2012, 01:01:26 AM »
Hi Martin,
Hope these post have some useful information on the el-load.  Just an update, I have been trying to learn KICAD so that I can layout a circuit board for this project.  Today I think I may know just enough to start the layout.  I hope to have a completed circuit board in about a week.  I will be doing my own PC board fabrication and since I do not have any experience in silk-screening , it will be just a plain circuit board.  I also think I have all the case and external parts to finish the build.  Hopefully more to follow.  John

John...you are a good man, hats off for all the effort.

I was about to consider fabricating my own PCB too...but I might leave that for my second build. Look forward to seeing yours.

Cheers,
Martin.
Play, discover, learn and enjoy! (and don't be scared to make mistakes along the way!)

arekm

  • Newbie
  • *
  • Posts: 7
Re: Electronic constant current DC load
« Reply #29 on: October 15, 2012, 12:44:34 PM »
I do not have any experience in silk-screening , it will be just a plain circuit board.

I've just done my first PCB in house. Silkscreen with the same method as copper traces - thermotransfer. Not perfect but quite good IMO.