Help Me !

[FRIDGE]

I'M DOING A COLLEGE ASSIGNMENT, AND I NEED TO KNOW REASONS WHY YOU WOULD REPLACE A CURRENT RELAY WITH A PTC TYPE. I ALSO NEED HELP WITH WIRING UP 2 CAPACITORS, ONE 50Mf 230VOLTS AND ONE 100Mf 230VOLTS WHEN REPLACING A FAULTY 150Mf 230VOLTS START CAPACITOR. :

[shogun7]

Oh Marc must mean me
A PTCR is wired in series with the starting winding ( the same as a current type relay) in a single phase electric motor. The low initial resistance (about 3-12 ohms) of the PTC allows sufficient current to flow through the starting winding until the motor starts. The PTC then switches to its high impedance state reducing current flow through the starting winding to near zero. These usually are used with 1/12 to 1/3 HP motors. It also has a thermally operated overload protector and a capacitor. In a time constant the resistance will get to about 10 to 20 k ohms where it switches off the start winding

[FRIDGE]

Thanks for that useful info on the PTCR, but i still need to know the reasons why you would use it.

[FRIDGE]

Thanks Marc, thats really helpful info.

[Argus]

I think the question was "Reasons why you would replace a current relay with a PTC type relay".

Production cost.

They both perform thier purpose equally well.
________
vapolution vaporizer

[FRIDGE]

thanks for that info

[shogun7]

I think the question was "Reasons why you would replace a current relay with a PTC type relay".

Sorry old bean I thought the reason was implied in my answer...Like because you can! duh they work equally well

[Coolie]

there are no moving parts in the ptc, therefore less chance of failure due to wear and tear.

I did the nvq2 course a while ago and remember the specific assignment you are reffering to. Let me guess, you are at the college of north west london and you have a chap named John Morgan as you lecturer for electrics and the specific assignment you are reffering to is number two????

This is the answer I gave and it was accepted. Fortunately I still have the nvq files on my pc. If you are going to use this answer, just change the wording.

"It was discovered that the klixon was faulty, so I decided to replace it with a P.T.C. The advantages of this part make it a superior part to the klixon. It has no moving parts, so failure due to corrosion or wear is reduced. The arcing over switch contacts is not present. It also protects the compressor more effectively because it is specific to the compressor."

Not much detail, but then again you are only doing an nvq which does not require an indepth explanation!!!

Good luck with the course.

[rbartlett]

I did the nvq2 course a while ago and remember the specific assignment you are reffering to. Let me guess, you are at the college of north west london and you have a chap named John Morgan as you lecturer for electrics and the specific assignment you are reffering to is number two????

.

which is a shame as there used to be a good college doing fridge at SELTEC lewisham -which is far handier for a peckham dweller..

cheers

richard

ex nunhead..ex seltec

[frank]

"It was discovered that the klixon was faulty, so I decided to replace it with a P.T.C.

Now there's a thing!

I never knew that a klixon was a starting device!

[chemi-cool]

As I've said earlier,
every day you learn thomething new!

Chemi

[Coolie]

Well beleive it or not the question was posed along the lines of:
"you arrive on site to find the klixon to be faulty, write a report to eplain why a ptc is better than a klixon.

The ptc works as a starting device, true.
But what is a ptc? It is nothing more than a variable resistor that reacts to heat. Now if you choose one that was rated to increase it's resistance at the point at which the amps being pulled increases into danger levels, then you have effectively replace the klixon. Now, if you mount this ptc ontop of the comp then it is also sensing the temp of the comp. The ptc will react to the heat from the comp and the heat from the amount of amps being pulled and should cut the power to the compressor when this gets too high.
Using a klixon as a starting device will not work.

[Coolie]

Now there's a thing!

I never knew that a klixon was a starting device!

Sarcasm is the funniest form of wit, however it is also the lowest!
Maybe you should think outside of the box before you post something that, in my opinion, could easily have been avoided if you had only thought about the possibility, however strange it might seem!

[FRIDGE]

Thanks coolie, that info is well appreciated. Thanks for the luck, because i need it.

[Peter Mitchell]

Hi
no moving parts so there is less chance of failure,also the ptc relay also has a built in "anti-cycle" due to the fact that the realy has to cool down before the compressor can start unlike a standard current relay.
How long the delay is I have no idea but it never causes any problems.

Regards
P. Mitchell

[coolkev]

Generally its because one relay fits many comps and its impossible to carry all the different brands and types of mech relays , saves cost to customer with job complete in one call esp. in rural area like myself wher travel to job often 20+ km and odering parts can take several days. could be other reasons but thats mine simple economics

[coolkev]

small note klixon is a brand name they make both O/L's and relays think the orig. question was on replacing a current relay. I have found that recycle time can somtimes cause comp failure. If power off for short time comp trys to start it then sits in locked rotor situation witout additional current draw of start winding it takes longer for O/L to operate and can cook the dome . pros and cons for both

[RIZZLA]

Hi All

Just really echoing what has already been said.The P.T.C. has no moving parts and at a ambient temperature will have a low resistance.The P.T.C. is made of barium Dipped Titanite and will o/c at approx 72 c.

Thanks

Riz