hard start kit

Paul S_3

i have a question on a hardstart kit. i know that it is a pot relay and a start cap. the qustion is on that relay is that a coil or a heater which opens the contacts on terminals 1 & 2.because on most schematics you will see that the coil [terminals 2 & 5] have a opposite potential, but if you hook up a hard start kit on terminals herm and com on the run cap there is no opposite potential to energize the coil  [terminals 2 & 5]. ?????????    how does that coil get energized?

Wayne_16

Potential relays

Potential relays receive there coil operating voltage from the back electromotive force (emf) off of the start winding.  Terminal 5 is wired to the common terminal of the compressor, terminal 2 is wired to the start winding, terminal 1 is wired to the start capacitor and the other side of the start capacitor is wired to L1 as well as the run capacitor and the run terminal



Here's what happens in a split second.  There is a inrush of electrical current through the run capacitor, to terminals 1, then 2 of the potential relay and then to the start winding.  At the same time the inrush of current is across the run capacitor as well as to the run terminal directly.  As the motor starts spinning and is about 75 % of operating speed there is enough back electromotive force (emf) to electrically charge the winding between terminals 2 and 5 to open the switch (1-2).  As long as there is electrical power applied to the motor, the back emf will keep the coil (2-5) energized, the switch (1-2) will remain open.  As soon as the power is removed from the motor, the back emf is lost, switch 1-2 closes, ready for the next cycle.



Minnesota Wayne

Techman

or

another way of saying what Wayne said is, the coil of the potential(voltage) relay operates at a higher  voltage  than the line voltage(110 or 220 vac) of the system. on a 220v system the coil of the pot relay will see up to 502vac , depending on the compressors back EMF or 420v or 395v or down to 253v .this higher than line voltage is generated or created in the comp due to the inherent charorictical  differences between the main winding (run) and the start winding. the main winding is shorter and fatter and, the start winding is longer and skinnier. i'm saying main and start windings  because the start and run capacitors are both in the start winding. start cap,run cap,start winding,run winding ?!  i have my copy of Modern refrigeration and air conditioning,copyright 1968, which states the run cap goes in the run winding and the start cap goes in the start winding.taking that for gosspil was confusing for several years. you can look at the mars potential relay cross reference or the copeland electrical handbook and see the "continous coil voltage" section  for the higher than line voltage voltages that the pot relay coil will see . Waynes version is shorter.the coil is across L1 and L2  on 220v  or, hot and neutral on 115 v but thru the start winding

Techman

see for yourself

on the next compressor you work on .check the voltage at the pot relay on term #2&5 . it will be higher than line voltage .

Paul S_3

thankx

thankx guys that really helped

Wayne_16

I beg to differ

The potential relay coil is across the start terminal and the common terminal, 2 or the start terminal and 5 the common compressor terminal.  Not across the hot and neutral or L1 & L2.  If you study the wiring diagrams correctly, you will find the run capacitor is wired across the S & R terminals as is the start capacitor for a very brief moment in time.

It is the counter emf voltage that creates the high voltage the potential relay sees and such is why the potential relays have different operating voltage ratings.

Thank you,

Minnesota Wayne

Techman

ok

but which winding are the caps operating in?it can't be both.!The common of the comp is connected to L1 and the run winding is connected to L2, and the start winding is also connected to the same L2 but thru the caps.Electricity does not flow THRU a capacitor like it does thru a motor winding,instead it builds up on one side(plate} and then the other side ,charging and discharging in tune with the sine wave or hertz.Where did the counter emf come from? It started out in the different magnetic fields{start and run windings} created by the different size and lengths of wire  in the two windings.And the two windings are out of phase with each other ,just a tiny bit ,making them additive ,giving you the higher than line voltage readings. L1 is 110vac and L2 is also 110vac but different 110's or out of phase 110's so they are additive making the 220vac.The cap's hold back the electricity for half a sine wave making the start winding even more out of phase with the run winding making the motor more energy efficient.L2 is connected to the run winding and L2 is also connected to the run cap,innie side, and L2 is also connected to the start cap innie side . The two caps are in parallel. And L1 and L2 can be interchanged ,which ever way you like!

Empire_2

Sorry to inturupt.........

We all agree that Potential relay's are used in high torque motors...:  As Techman Stated, it's operation is based on the increase in voltage as the load approaches and reaches it's rated speed.  The contacts in the off cycle remain closed,...ready to become a High torque relay..



Upon a call to start, and as the motor speed increases, Higher voltage, creates more magnetism in the coil pulling the contacts apart, opening the start winding.  Remember the coil in not only a magnet, but Weighted too.  Jokingly, it's a well oiled balancing act. 



Resistance of the contact points to voltage being applied must be high enough to prevent the points from opening before the load reaches 80 to 90% of its full speed.   excess resistance due to pitting or dirty environment can drastically throw off this relays ability to open and over heat the Load.  Remember the more voltage being applied through the relay  itself, but for only just a second will pull the armature apart, killing the start winding...................................BACK EMF this is the relation to voltage and the magnetic field it creates.......



My .02



See Attached..



Mike T.

jhatfield

back emf

so, what can cause the back emf voltage to  drop out, deenergize the potential relay coil, charge the start cap., causing the start cap to explode. all while the compressor is running a full stroke and the potential relay is energizing and deenergizing until the cap blows?

Techman

back emf

Is that "machine gunning"  you are talking about? Low voltage is one cause ,wrong pot relay or start cap or run cap is another.Or ,lets say you have a freezer comp that just came out of a defrost cycle.The low side press is  very high due to the electric defrost heaters, the "load" on the comp is very high, the running amps are very high,the "load"is so high that it over powers the strength of the comp motor causing the comp to slow down a little ,dropping  the pot relay coil voltage[back emf] and the pot relay re-energizes ,again and again until the cap or relay blows.Or a tight compressor,or slugging the comp w/ liquid refrigerant.

ddlong1286@yahoo.com

So what about KickStart

So how does the KickStart work with just two wires across the Run Cap??



don in MO

Techman

Same way

as far as back emf is concerned.There is line voltage,then there is the start winding back emf voltage [ pot relay coil voltage] between C & S and then there is a different back emf voltage [ Kickstart type ] between R & S .Measure it out on your next service call.

jhatfield

back emf

i found the problem where i was losing (as it appeared) my back emf causing the potential relay to de-energize and energize until the start cap blew up.....this was on 19 trane pkg. units on a school.....someone wired power to the potential relay thru the low ambient control relay....so when it is cool in the morning the low ambient control kept varying the condenser fan motor to maintain head pressure which also varied voltage to the relay until the cap blew.......