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Newbie’s first embarrassingly stupid question — Parallax Forums

Newbie’s first embarrassingly stupid question

stevelsstevels Posts: 19
edited 2006-11-30 12:01 in BASIC Stamp
Hi Guys, although I am a seasoned computer guy and programmer geek, but completely new to the Microcontroller world.··I am DIGGING IT!!!

I want to use some logic to control some HVAC systems I am experimenting with. ·Clearly, I need to get some thermocouplers to provide my temerature inputs, but that is not the questin...

My question is this:
·
How do I control high amperage items like 12VDC 100 watt heater elements, or 120VAC 500 watt heater elements from the Basic2?· I want to turn them on and off based on logic from the STAMP2
·
Obviously, I need a relay of some sort, but I have not seen any examples of this in my very limited experience. ·Any advice would be respected, oh, elders.· Answer this one for me, and I will reward you with a flurry of other stupid questions [noparse];)[/noparse]
·
Thanks,
·
Stevels

Comments

  • bcw1011bcw1011 Posts: 8
    edited 2006-11-17 06:24
    easy way is to use TTL compatable solid state relays, theres all sorts of types out there. most are also isolated from the mains voltage as well which is a added plus
  • stevelsstevels Posts: 19
    edited 2006-11-17 14:00
    Thanks bcw1011,

    Being as green as grass on a rainy, summer's morning, I have no clue where to find these TTL solid state relays.· Is this something that is sold on the Parallax site, or is there a whole world of compatible components out there that I don't know about?· Wow, that would be cool if I could look over a catalog of components that would work with the BASIC2

    Please do tell where I can find these relays, and what I would need to know to see if they are compatible.· I promise I am studying hard and every day, to not be so clueless, but until then, your help is respectfully appreciated.

    Regards,

    Stevels
  • allanlane5allanlane5 Posts: 3,815
    edited 2006-11-17 14:05
    Try www.digikey.com. They tend to sell in "hobbiest" or "prototyping" quanties (1 or 2 at a time).
  • stevelsstevels Posts: 19
    edited 2006-11-17 14:15
    Thanks allanlane5,

    I am lookng at the site now, and downloading their 2K page catalog!!

    I must admit, it is a bit overwhelming to me at this point.· Forgive my ignorance, but what I envision is a device that looks like a typical relay, that I would typicaly use to switch high amprage AC by way of 1 amp of 12VDC control·voltage·-- except instead of 12VDC, I would trigger it from the BASIC 20mA high pin.· Am I on Crack?· Does this exist?·

    Stevels so confused!

    [noparse]:)[/noparse]


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    Expert in many fields, dumb as a stump with STAMP
  • aquasapienaquasapien Posts: 25
    edited 2006-11-17 14:15
    yes, relay's are a solution but they have two disadvantages I think. The reeds inside relays have been know to become "welded" together under fast flux of states, and the reed mechanisims being mechanical will wear out after a few thousand of switches.

    I used to use relays for everything instead of transistor as transistor used to scare me.

    As a side note:I used to control my ROV's thrusters with a "relay h-bridge"·Turns out that when relays flood they fail, yet transistor do not, well not at 12 volts anyhow. I have been a big fan over since



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  • Roger PiersonRoger Pierson Posts: 62
    edited 2006-11-17 15:16
    Check out this product I've been looking at:

    www.controlanything.com/Merchant2/merchant.mvc?Screen=CTGY&Store_Code=NCD&Category_Code=HYBRID

    The hybrid controller with the onboard relays really interests me. It just so happens that I have an application where I need multiple 10A realys AND multiple high-res ADC inputs AND numerous digital IO channels. This thing looks perfect.

    Anyway, the 5A relay board might work for your HVAC appliation. The board also accepts transducer inputs, per the documentation. Also the documentation specifically mentions compatability with BASIC Stamps. Best of all the whole thing is a serial device, so you can control it all with just a few IO pins.

    -Roger

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    Roger Pierson
    Senior Electronics Technicain
    DTI Assoicates
  • matthelmmatthelm Posts: 19
    edited 2006-11-17 15:20
    Let me try to explain what a (AC only) SSR (Solid State Relay) is. A SSR is a TRIAC that almost always includes (haven't seen one in ages that didn't) an opto isolator circuit.

    The opto circuit keeps then nice simple DC control circuit away from the 120 AC cirrcuit. It uses light to run the TRIAC so the high voltage and current can not get back to the low voltage and current DC part.

    A TRIAC is a AC switch. If the TRIAC is turned "on", it becomes a .7 volt drop in the AC currect, and when turned "off" becomes an Open, turning the load on and then off.

    The advantage of a TRIAC is mainly no mechanical movement.

    Main problem is surges will fry them easily!


    You can also look here:
    http://en.wikipedia.org/wiki/Solid_state_relay

    Oh great, this link says it uses a MOSFET. I'm 99% sure most high current AC SSR's use a TRIAC, and only DC SSR's use a MOSFET. Anyone want to tell me I'm out of my mind, it's OK. wink.gif Either way, it's a solid state switch.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-11-17 15:30
    Stevels,
    ·
    ·· Attached is a schematic for a BASIC Stamp to control a Relay.· A simple common NPN transistor is used to switch the Relay, which in turn switches the higher voltage/current load.· Since HVAC systems aren’t subject to high-speed on/off switching of the equipment (for obvious reasons), it is fine to use mechanical relays for this type of equipment.· I hope this helps.· Take care.


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    Chris Savage
    Parallax Tech Support


    Post Edited (Chris Savage (Parallax)) : 11/17/2006 4:53:48 PM GMT
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  • Vern GranerVern Graner Posts: 337
    edited 2006-11-17 17:39
    stevels said...
    How do I control high amperage items like 12VDC 100 watt heater elements, or 120VAC 500 watt heater elements from the Basic2?

    I'm surprised no one else has mentioned it, but a perfect solution to this is a former Parallax offering, now available from EFX-TEK called the RC-4 and four Crydon solid state relays.

    It is a small board that can host four solid state relays. It can control external high voltage loads. I use these to control lights and motors and such. Its pretty low cost as well with the board only about $25 and the relays for each channel are $10.00. I attached a closeup of my Haunt COntrol board with an RC-4. smile.gif

    Vern

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    Vern Graner CNE/CNA/SSE    | "If the network is down, then you're
Senior Systems Engineer    | obviously incompetent so why are we
Texas Information Services | paying you? Of course,if the network
http://www.txis.com        | is up, then we obviously don't need
Austin Office 512 328-8947 | you, so why are we paying you?" ©VLG

    Post Edited (Vern) : 11/17/2006 5:47:58 PM GMT
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  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-11-17 17:46
    Vern,
    ·
    ·· The reason I didn’t mention this is because the heater would draw over 4A.· The Relays on those boards were less than 4A as I recall.· And while there are higher capacity SSR modules that may fit that, the ones I am most familiar with do not fit the RC-4.· These units actually handle 50A @ up to 240VAC.· We used one in the Solder Pot Controller listed at the following link.

    http://www.parallax.com/html_pages/resources/catapps/cat_solderpot.asp

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    Chris Savage
    Parallax Tech Support
  • Vern GranerVern Graner Posts: 337
    edited 2006-11-17 17:58
    Chris Savage (Parallax) said...
    The reason I didn’t mention this is because the heater would draw over 4A. The Relays on those boards were less than 4A as I recall.

    Ah.. you're right, they are 3 amp according to their spec sheet. Hmm though it says 3.0 amps at 240v, does this mean it can handle more current at a lower volatge (i.e. 120vac?) I don't have much experience with these as all I've done with them is switch some halloween efx.

    smile.gif

    Vern

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Vern Graner CNE/CNA/SSE    | "If the network is down, then you're
Senior Systems Engineer    | obviously incompetent so why are we
Texas Information Services | paying you? Of course,if the network
http://www.txis.com        | is up, then we obviously don't need
Austin Office 512 328-8947 | you, so why are we paying you?" ©VLG
  • allanlane5allanlane5 Posts: 3,815
    edited 2006-11-17 19:01
    Nope. When a relay switches, the thing it switches is current. If it tries to pass too much current for it's rating (no matter WHAT the voltage is) it will pit and/or weld the contacts.

    You're correct, in some devices (resistors, linear regulators, transformers, AC motors) it's the POWER that's being disappated that is the critical value. Then, both voltage AND current come into the picture.
  • TechnoRobboTechnoRobbo Posts: 323
    edited 2006-11-19 18:48
    RIB Relays are the·device of choice·in the HVAC controls industry for retrofits.

    You can drive them through·switching transistor like Chris Savage explained.

    They fit into the knockout on a 1900 box.


    http://www.functionaldevices.com/

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    Have Fun


    TR
  • RottenJalapenoRottenJalapeno Posts: 27
    edited 2006-11-19 23:20
    now all you need to do is hook a PWM up to those heaters with·PID control...

    that would be fun...· Probably would t be too hard with the electric heating elements and I believe the basic stamp has a pwm command, now that would surely impress the ladies!

    just a thought
  • sam_sam_samsam_sam_sam Posts: 2,286
    edited 2006-11-20 00:19
    stevels

    How do I control high amperage items like 12VDC 100 watt heater elements, or 120VAC 500 watt heater elements from the Basic2?· I want to turn them on and off based on logic from the STAMP2

    These heater run on 220 Vols @ 15 amps for a 5 KV

    I am an A/C tech

    There is a very easy·way to do this First use a UNL2803 that Parallax sell···
    Just·tie all inputs together·with a·220 Ohm resters on·each input

    This is how i have done this before

    UNL2803......Stamp Pin P0···· UNL2803
    ···································· ·^········ ······ ·^>>>>>>>>>>>>>Relay Coil
    Input 1>>>>>>220>>>>^····· OutPut 1^
    Input 2>>>>>>220>>>>^······OutPut·2^
    Input 3>>>>>>220>>>>^····· OutPut·3^
    Input 4>>>>>>220>>>>^······OutPut 4^·
    Input 5>>>>>>220>>>>^····· OutPut 5^
    ·
    I·have done this before when i need to use a relay that has·more than 20 milamp

    The reason for this is that 5 KV heater coil draws 10 to 15 Amps and unless you have a relay that can handle this current will·then
    ruin the relay

    ·Now a·contactor can handle 30 amp·the coils draw about 150 milamps
    I can built this and tell you if·this will·work or not Please PM if you want me to do this for you

    Now you could use two relay one to use on·the UNL2803 then relay control the contactor
    Now this may not be the way you want

    Be careful about relay that you buy at Radio Shack these Relay Coils
    draw any where from 30 to 100 milamps there Relay Contacts·can only handle 10 AMPs

    Jamco and Digikey and Marlen P Jones ·sell some relays that have lower milamp relay but these Relay Contacts can only handle 10 AMPS

    I hope this helps you in what you want to do

    Sam

    Post Edited (sam_sam_sam) : 11/20/2006 12:49:24 AM GMT
  • sam_sam_samsam_sam_sam Posts: 2,286
    edited 2006-11-20 01:32
    TechnoRobbo said...
    RIB Relays are the·device of choice·in the HVAC controls industry for retrofits.

    You are right that these RIB Relays· are used in HVAC controls

    You can drive them through·switching transistor like Chris Savage explained.

    They fit into the knockout on a 1900 box.


    http://www.functionaldevices.com/

    I have used these RIB Relays·before and this will drive the contactor that controls the heater coil

    I have used these RIB Relays·before on a Basic·Stamp Pin before·and they will work But...............

    These RIB Relays·CAN NOT·be used as they come out of the box

    The reason is that they are setup to use 10 to 30 Volts AC current
    If you bypass the AC part of it still will not work because the switching transistor that used on the board·will not turn·ON the relay it·CAN·NOT·PUSH·THE·CURRENT with the·Basic·Stamp Pin·

    But the relay it self will work with a UNL2803 to a··Basic·Stamp Pin·as i talk about in the POST above the current is about 50 milamps
    you should use 3 inputs and·3 output tie together the UNL2803 dose not even get warm but if you try to drive the relay with
    ·one·input and one output the chip will run VERY WARM

    I hope this helps you with what you want to do

    Sam


  • sam_sam_samsam_sam_sam Posts: 2,286
    edited 2006-11-20 01:48
    Chris Savage (Parallax) said...
    Stevels,
    ·
    ·· Attached is a schematic for a BASIC Stamp to control a Relay.· A simple common NPN transistor is used to switch the Relay, which in turn switches the higher voltage/current load.· Since HVAC systems aren’t subject to high-speed on/off switching of the equipment (for obvious reasons), it is fine to use mechanical relays for this type of equipment.· I hope this helps.· Take care.


    ········································································· · smile.gif
    Chris

    Can you tell me·why when i use·12 volts relay i can not get this to work it try to turn ON but dose not pull the relay all the way ON
    How much current will this set up will handle At 12 volts and this will no resister on Basic Stamps Pin

    I·have to use this before and can get this to work

    Now if I·use· 5 volt relays this works very well

    Can you tell me why one set up works but not the other way

    Thanks for any light that you can shine on this matter·········· idea.gif

    Sam
  • TechnoRobboTechnoRobbo Posts: 323
    edited 2006-11-20 02:48
    We use RIB all the time (hundreds of them on our campus for HVAC and chemical feed purposes) but always optoisolated and via a pilot relay but I'm paranoid that way.

    Chris·Savages·circuit should work just fine.·The RIBU1C is the basic model and it can be driven AC/DC, as most of them can be.

    The RIBs often drive a 208V control circuit not the 480V·contactor itself because there are Thermal overloads ,pressureswitches,sail switches and klixons that we don't want to bypass.· . If your fan motor fails and you loose the 45 degree DeltaT your wires will consume themselves.

    For continous heater control we use SCR's·for critical rooms. 4-20ma control, it also works with 0 to 10V & 0 to 135ohms.·Manufacturer is Viconics

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    Have Fun


    TR

    Post Edited (TechnoRobbo) : 11/30/2006 3:34:58 AM GMT
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  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-11-20 05:14
    Sam,
    ·
    ·· What resistor value are you using?· If you’re using a transistor you must have a resistor in there or you will damage the Stamp I/O pin.· The resistor needs to be set to draw the minimum current required to provide the proper current across the Emitter-Collector junction, based on the HFE of the transistor, as well as a few other factors.· Basically whatever the Relay requires (How much is that?).· A minimum recommended resistor should be around 470 ohms for a 2N3904 and a typical 12V Relay.

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    Chris Savage
    Parallax Tech Support
  • TechnoRobboTechnoRobbo Posts: 323
    edited 2006-11-30 03:39
    The transistor is isolated from the stamp via an LED in the 4N35. only pins 1 & 2 of the optocoupler·are connected to the stamp.·The 5V is connected to the stamp in any way shape or form.

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    Have Fun


    TR
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-11-30 05:10
    TR,
    ·
    ·· Since Sam directed the question to me, I assumed, perhaps incorrectly, that he was using the circuit I posted, which is not optically isolated and does require a resistor.· Perhaps he should let us know exactly what he has connected so we can help.

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    Chris Savage
    Parallax Tech Support
  • TechnoRobboTechnoRobbo Posts: 323
    edited 2006-11-30 12:01
    Didn't catch his name at the start of the post. I see it now. Sorry

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    Have Fun


    TR

    Post Edited (TechnoRobbo) : 12/1/2006 11:57:37 PM GMT
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