Posts Tagged ‘single pole double throw’

Switch and Relay

 

Spa Switches and Relays

The wonderful thing about switches and relays is they really aren’t that hard. Believe me, if the Fabulous Spa Babe, in her bold beginning could somehow figure them out then it can be done! Everything you need to troubleshoot your hot tub switches and relaysis right here. You may want to print this page for a reference tool.  Most of the information on this page will refer to the switches and relays in mechanical hot tub controls.  While dgital systems with printed circuit boards also use switches and relays, they sometimes are not as easy to trouble shoot because the paths are enclosed on the circuit board. For the many hot tub operatos with mechanical systems, you will find a lot of good basic info here!  We start at the beginning.

Common Spa Switches

Inside a spa control,  electricity follows a path provided by wires and switches. A switch is simply a device that provides a bridge for electricity to cross (or not) between two contact points or poles.  When the switch is closed it allows the electricity to follow the path through it.  When "open"  there isn’t a bridge, therefore, no path. Digital spa controls utilize switches and relays mounted on a printed circuit board and these can be difficult if not impossible to troubleshoot.  Mechanical spa controls have physical swithces and relays attatched by visible wiring that can be traced.  Much of the efforts here, will concern this type switch.  The wiring logic however is similar, so even if you are troubleshooting a digital control you can use the information here to try and eliminate possible problems. A simple "single pole" switch when closed (on) allows power to go through and light a light bulb for example.  When open (off) there isn’t a path and no light.  These switches are also known as single pole single throw switches, one way in for electricity one way out. There are many single pole switches to be found in any spa system.  Testing them, to be sure they are working requires being able to activate the various switch activation mechanisms found and testing for continuity through the contact points, i.e. where the wires connect.  Removal of the wires from these "contact" poles is necessary so that you aren’t getting feedback from up or downstream.  These are power off tests with your multimeter set on ohms.  Since knowing how to activate the switch is part of the battle, we’ll go through all the single pole switches found in spa systems.

standardtstatThermostats (electromechanical) can be activated by turning them up with the power off.  If you listen carefully you will hear a faint click as you turn the temperature knob up.  That is the sound of the switch closing.  You’ll also hear it as you turn it down.  If you remove the wires from each side of the T-stat and place your meter probes across the poles you should have continuity (almost zero resistance) when you close the switch.  When you turn it down you shouldn’t have continuity after the switch "breaks."

High limit switches have a reset button that pops out when tripped.  This opens the switch allowing no path.  If the button is not popped out you should  have continuity through the poles of the high limit. this can be tested with the power off with your ohm meter.

pressureswitchPressure Switches exist to prove water flow before activating the heater relay. They operate by water pressure to a bellows that pushes up a rod  pressing on the switch activator. To test without power, they must be manually activated which can be a little tricky because the activating button is underneath the micro switch.  You have to stick a little flathead screwdriver in there to activate the switch because with power off you won’t have  pressure.  Be sure to remove the wires from it to test.  

Time clocks have switches too.  If you are troubleshooting a time clock on a portable spa control, first determine which wires are the time clock motor wires.  These are not the poles you want to check.  You want the time clock switch wires.  If you look you’ll see a diagram that shows the switch symbol something like this:  –/ — Those are the poles to remove the wires from and check.  Activate the switch by turning the timeclock knob clockwise until it clicks. Note: An important fact that may help is that usually only hot legs are switched.  You’ll notice that most neutrals (whites) are tied together and only serve to "complete the circuit."  Neutrals will be found on coils of contactors and relays but are rarely "switched."  That will become more clear to you as you delve into your system. Now that you’ve learned about single pole single throw switches it’s time to move on to another common switch type found in spa systems.

Single pole double throw switch

The spdt switch allows for two separate paths for the electricity to follow.  Power enters this switch via a "common" pole.  When the switch is not active the bridge to the "normally closed" or NC pole is closed.  When the switch activator is engaged the bridge to the "normally open" or NO pole is closed.  It is the spdt switch that provides the basis for the relay logic necessary to run spa systems.  Air activated relays often use spdt switches. For instance, almost all portable spas utilize a two speed pump motor.  This motor can run on high speed or low speed but not both.  Feeding power to both the low speed and high speed windings at the same time causes a frightful noise with an overload lock out in less than a minute.  This is prevented by the use of single pole double throw switches.  The common pole of the switch carries the power that will be used to run both high and low.  With the switch at "rest" the low speed runs.  When the switch is activated the high speed runs but never both together.  Cool, huh? Now, consider the fact that in a 120 volt spa you have a heater that can only run with the low speed pump.  The heater can’t run with the blower, only because there is no pump running and it will burn up.  High pump and heater can’t run together, there isn’t enough current at 120 volts/20 amp circuit.  Obviously there would be an overload with high pump and blower together.  Now you get a sense of why there are banks of relays to handle this logic. The Common Micro switch is found on many different relays in an electromechanical system.  Your Pressure switch is likely to have one.  Flow switches use them, relay banks use them. Air receiving relays have them as well. Sometimes, even thought the the switch may be a spdt switch only one "throw" pole is used.

Spa Relays

Now that you’re feeling more comfortable with switches lets move on to relays.  A relay is a switch with an activating mechanism attached, Some relays get a little more complicated in that they usually serve as a mount for several switches and can be powered by air (air receiving relays) or a magnetic coil like a contactor

tbs301Air receiving relays receive the air that is passed through the tube connected to your button  at spa side.  They are of two types: latching and non-latching (or momentary). They look identical.  Latching air receiving relays may actually run the equipment.  They will directly feed pumps, blowers, lights and even heaters. They can come with one, two or three micro switches. A single pole will have only one microswitch, a double pole will have 2, etc. There are four function "cam" action air receiving relays that can run every piece of equipment in a 120 volt portable spa.  Pump, pump and blower… blower only…. and low speed/heat with T-stat demand.  When you  press your button on the spa the force of the air moves an arm that comes up and turns a cam that activates the micro switches in sequence. Momentary air receiving relays generally send a pulse of electricity to the coil of a coil activated relay.  This causes a rod or plunger to move and in various ways activate a switch or switches on the relay.  When you push your button again – it again sends a pulse which will cause the relay to move to another position or move back to the original position. A word about coil voltages, while 240 volt coils and 12 volt coils are not unheard of most likely your coil voltage will be 120 volts.  Be sure of it though. It should say on the coil what the rating is.  It will also say what the switch rating is, study it to be sure you know which is which.  On Potter Brumfield coils the number at the top is the coil rating.

contactorContactors are a heavy duty relay that allow for heavier current flow, like to a heater.  Supply wires to a heater are large wires.  Contactors have the capacity to handle the wire size and the current flow and are activated by coils.  This allows for smaller wires to be used through the "control loop:" T-stat, high limit, pressure switch to the coil of the contactor. Many spa systems utilize cube relays which are type of coil activated relay that does not use a micro switch.  They are sometimes a little difficult to troubleshoot because you often can’t see what they are doing.  The coil poles are at the very bottom.  Common poles in the middle and normally open on top of that.  Often, the normally closed poles are snipped off, but sometimes present they are located at the top. USUALLY, but not always left and right is electrically isolated.  

Basic troubleshooting of spa switches and relays requires understanding the above and knowing how your spa works.  If your complaint is no heat, for instance, and you have established that you have flow and know your high limit isn’t tripped you must isolate the circuit and backtrack through it.  Knowing that your heater and low pump will work together helps.  If turning up your T-stat activates your low pump but not your heater contactor then start at the coil of the contactor.  With the power on, and a call for heat, (thermostat up) Set your  meter on volts:  Measure voltage across the coil of the contactor. This is the activating part of the contactor. If you have 120 volts there then your contactor should be activating.  If it’s not, it’s bad.  If you measure no voltage at the contactor then your problem is upstream of it.  Look for where it stops.  Do you have power to the T-stat? Out of it? To the high limit?  Out of it? To the pressure switch? Out of it?  Just trace the path.  If you have power in, but not out, that will be your problem component.

Obviously power on tests require great care for your personal safety and some measure of experience with an electrical meter.  Don’t attempt these tests if you are beyond your comfort level. Call a qualified technician.

The big thing to remember when you open up your box and the words "Oh God" come unbidden to your lips, you will be tracing individual problem circuits.  Sometimes, I do sit for awhile and contemplate the why did they do it like that concept, but if I’ve got a heater not working I’m only working with the spa heater circuit and maybe the low pump circuit.  You can easily isolate each component by following its power cord into the box.  Two speed pumps have 4 wires: red, black, white and green.  Red is usually low.  Blowers have 3 wires.  Lights have 2.  Heaters may have two or more see heater help for clarification.  Spa side controls with thermostats and air buttons have 6 wires. The ones you are concerned about are the red and the black.  Black is power to the thermostat, red returns it to the contactor or heater relay perhaps via the high limit and pressure switch.  Just FYI, the other wires of the 6 are white which is neutral, green is ground, yellow indicator light is for jets, orange indicator light is for blower. NOTE on the newer spasides that have an led temperature display the orange is used to power the display and the thermostat. The orange wire for these spa sides must be attatched to a terminal that is hot all the time and LINE 1 Only!

There are some manufacturers out there that really do like to confuse us.  Systems that have a lot of cube relays jumping from one to another can be difficult to troubleshoot, even for me!  This relay activates another relay and you can’t visibly see the action of the darn thing.  That’s why  with older controllers with multiple problems you may want to consider a new control system.  We have many starting at under 300 dollars. They also include heaters too so if you need to cut your losses and start fresh, we can help!  if you have one of those cube relay nightmares or if your spa control has seen better days check out the  spa control selection we have at spapartsnet.com    If you have questions on troubleshooting your relays just call us… tech support is always free and we are glad to help!   813 235 4574   All Techs will be able to help you!

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