fish2005

Thanks for your repply. You say to run simple 2 wires for 5V and ground to the pot, and 1 shielded wire for the low voltage return? Something like this

Frequently a potentiometer is front panel mounted, far away from PCB. If this pot is used as a potential divider to form a voltage reference (let say 5V input from motherboard and milivolts range output back to motherboard ), the wiring problem becomes important. So what is the ideal wiring schematic? simple 3 wire twisted cable. 2 wire (in+out) whith 1 shield (ground) cable 3 wire (in+out+ground) whith 1 shield unconnected at one end Or maybe a complete separate ground like 2 simple wire for +5V - 0V input whith a 2 wire shielded cable for output? Brrrrrr... Adrian

Thanks for your answer, Kain. You are wright. Those PSU have a optional earth ground. On the front panel have 4 connectors for two positive PSU and one separate connector for earth ground. You can conect it in series and you have a double voltage PSU or a floating ground positive/negative supply (+ 0 -). This ground may be unconnected (floating), or conected to earth connector. You can also connect it in parallel for double amperage. This kind of design is verry flexible. In my searches I found many opinions about this subject. In my knowlege is OK to connect two transformers in series (or one transformer whith two independent secondary), but I hear people that say this is imposible after rectification (some kind of short thru diodes), so is imposible to conect two regulated supply. GRRRRR... I'm verry confuse... I whil try to find some service manuals whith schematics for original lab PSU. Adrian

I have a stupid question. 90% of profesional lab power supply is dual (floating). What is that? Is like two 1,5V batteries? If I want, can I conect it in series and make a 3V supply or positive/negative supply +1,5V/-1,5V whith a virtual gound. Supose I have 2 independent supply like "0-30 Vdc Stabilized Power Supply" wich are conected on two independent secondaries (double wound transformer), two independent bridge rectifier, and so on. Can I conect it in series whithout a big explosion? Sorry for my ignorance, but I googling about a week for a good answer. Adrian

This is easy. The transformer have 2 separate windings for 29V (is a 2x29V). So I can make 2 taps in windings and conect them in paralel. But I can't do this for primary. In my knowlege there is some losses in core, too. I dont know. Maybe I need some kind of experimental consumer, something at 24V 48W, I don't know what.

Thank's for your answer. You say: "So just remove turns until the loaded voltage is correct." There is the problem. It's verry simple to remove turns, check whith multimeter and have desired NO LOAD voltage. But can I calculate the NO LOAD voltage for a given FULL LOAD voltage. I need 24VAC at 48W - what is the no load voltage? My application (24V 48W) is sensible to voltage variations so I can't make an experiment whith it. There is a formula or solution for this problem ?

I have a big transformer: 170VA, 120V/240V primary and 2x29V secondary. This is all ratting information that I have. I need a 24V (at full load - 48W) secondary and is possible to remove some windings for this. My problem: I don't know the transformer regulation, so I don't know what is the no load voltage that I need. If I remove wire until the no load voltage is 24V, when I hook up the consumer, the voltage will be smaller. Once we connect a load across this winding, current will flow, and there will be a voltage drop across the winding. Hence, the voltage measured On-Load will be smaller than the voltage measure at No-Load. My application (24V 48W) is very sensible so I cant make an experiment whith it. Some ideas or formula for this?

I have allready the UAA2016, but is logic to try the simple solution first. I dont know...

Sorry! I double post because the subject was changed.

Thank you guys for your answers. From youre debate I understand some important things. 1. A DC power supply is fine for this job. This is verry good because I can use my 12VAC transformer whith a voltage regulator and a NPN current booster. If i use a ajustable voltage regulator, the problem of dimming is resolved. Please corect me if I am wrong. Question: In my knowlege, 24VDC is not equivalent whith 24VAC. What is the equivalent DC power for my iron specification. 2. This thread is a backup solution because I dont know if my project for a temperature controller will be a succes. This is my first major project. I orderred (today or tomorrow is delivery)this iron. This tipe of iron (24VAC, 48W, 2A) is sell as a spare part for a astronomical priced soldering station and have an integrated thermocouple. I intend to make a controller whith UAA1016 and a triac for this iron and save money. In UAA2016 datasheet is a simple circuit for this, but this circuit is designed for NTC tipe sensor. http://www.onsemi.com/pub/Collateral/UAA2016-D.PDF I find on net this circuits related to a homemade soldering station: This is the tested schematic for a NTC tipe sensor: http://tinypic.com/view/?pic=ekm6mv And this is the adaptation for a K thermocouple tipe iron made by same person and tested whith succes by others: http://tinypic.com/view/?pic=ekm6o4 My schematic is the combination of these ...but I'm not sure if everything is correct conected. If you guys wiew any errors please corect me. I repeat: this is my first major electronic project. I dont know the wattage for resistors. This iron comes in 2 diferent models, whith 2 specification for K thermocouple (7-8 mV at soldering themperature and 20-25 mV) , so require an adaptation of opamp resistors. So guys, if enybody is interested or want to help a novice....

Thank you guys for your answers. From youre debate I understand some important things. 1. A DC power supply is fine for this job. This is verry good because I can use my 12VAC transformer whith a voltage regulator and a NPN current booster. If i use a ajustable voltage regulator, the problem of dimming is resolved. Please corect me if I am wrong. Question: In my knowlege, 24VDC is not equivalent whith 24VAC. What is the equivalent DC power for my iron specification. 2. This thread is a backup solution because I dont know if my project for a temperature controller will be a succes. This is my first major project. I orderred (today or tomorrow is delivery)this iron. This tipe of iron (24VAC, 48W, 2A) is sell as a spare part for a astronomical priced soldering station and have an integrated thermocouple. I intend to make a controller whith UAA1016 and a triac for this iron and save money. In UAA2016 datasheet is a simple circuit for this, but this circuit is designed for NTC tipe sensor. http://www.onsemi.com/pub/Collateral/UAA2016-D.PDF I find on net this circuits related to a homemade soldering station: This is the tested schematic for a NTC tipe sensor: http://tinypic.com/view/?pic=ekm6mv And this is the adaptation for a K thermocouple tipe iron made by same person and tested whith succes by others: http://tinypic.com/view/?pic=ekm6o4 My schematic is the combination of these ...but I'm not sure if everything is correct conected. If you guys wiew any errors please corect me. I repeat: this is my first major electronic project. I dont know the wattage for resistors. This iron comes in 2 diferent models, whith 2 specification for K thermocouple (7-8 mV at soldering themperature and 20-25 mV) , so require an adaptation of opamp resistors. So guys, if enybody is interested or want to help a novice.... I post new thread for this subject: TEMPERATURE CONTROLLER

All dimmer is designed to use on main power {eg 220VAC} and is imposible to control a 24VAC load. I found on net manny DC dimmers for low power but no for AC. I need a schematic for a simple 24VAC dimmer. I mention that i intend to use this for a 24VAC 48W 2Aheater element. Please help.