cl60 equivalent

[AuroraB]

Thought I'd post this in the Pass section rather than under Parts, as it seems more appropriate here..and a search didn't reveal any answers....

Does anybody know of a european equivalent to the CL60 that NP uses in his designs, or any european supplier of the CL60?

TIA....

[Rodeodave]

The CL-60 is a thermistor that has 10 Ohm resistance at roomtemp (25°C) and has a maximum steady state current of 5A (RMS).

I buy mine at Farnell.

GE SENSING / THERMOMETRICS|CL-60|THERMISTOR, SERIES CL | Farnell Österreich

[Beftus]

Epcos. http://www.epcos.com/inf/50/ap/ntc.pdf

[AuroraB]

OK.. thanks, guys...
on another foot, for those of you who use this part.....
It is probably OK, and also since Nelson uses this in almost all of his designs..
110-150 deg operating temp----some of this heat will inevitably transfer through the leads, and then this sounds like old tube TVs; lots of heat and rotting solder joints???
What's your experiances????

[spzzzzkt]

The CL60's run cool - there should be very minimal current passing through the device unless there is a fault.

[Rodeodave]

There are basically to ways the CL-60 is being used.

As a ground loop-breaker: The thermistor is used to connect the circuit's ground to earth-ground. Ground-loops see the thermistor as a high resistance and thus can only develop a small current (low resistance ground-loops develop induced currents usually below 100mA, this is worst-case). So as long as nothing goes wrong the thermistor will stay at room temp. In case of some malfunction (wire coming loose, cap leaking, ...) a higher current will develop causing the resistance to drop very fast. At 1.25A the CL-60 will have a residual resistance of 1 Ohm and at 50% load (2.5A) it will only have 0.44 Ohm.
Using a thermistor to shield a circuit's ground from earth still requires to CONNECT THE CHASSIS TO EARTH DIRECTLY! Sorry for the emphasise but I think this is a very important point.

The second usage as a inrush-current limiter relies on the same principle (R drops as I increases). Usually (in Europe with 240VAC) the thermistor is used to connect the two primary windings of a transformer in series, causing the current through the primaries to rise more slowly. In a steady state the device will be at a certain temperature above room temp. The thermistors are designed to have a maximum (and seemingly still safe) temperature when the maximum steady state current is passed.

From the datasheet it can be seen that the CL-60 has R=0.18 Ohm @ I=5A.
I*R=5*.18=0.9V should be across it then. P=I*U=5*.9=4.5W are dissipated at the maximum current.
Now the part I'm not certain about: They give some sort of dissipation constant which is 25mW/°C. So 4.5W / (.025W/°C)=180°C is the temperature rise?! Is that correct? It seems way too high.

I use a CL-60 for that purpose in my Mini Aleph and the thermistor gets hot, but not too hot to touch it briefly.

[AuroraB]

Used as current inrush limiter was exactly what I was wondering about.. how hot does it get in practical use... it doesn't seem to be problem, though....

As I'm old enough to have repaired 60's and early 70's TV sets with lots of power resistors, and the usual rotting solder failure, it struck me that this could be a problem, but it obviously isn't.
Thanks guys

[MEGA-amp]

I've burned a few up, the casing will start to smoke/break apart and ultimately fail long before you start melting solder.

[Rodeodave]

My MiniA draws about 80W when powered on (+/-12V DC PSU). So the current through the primary side of the transformer shout be a 1/3 A (rms). I'm using an Epcos NTC 10 rated at 3.7A: EPCOS|B57237S100M|THERMISTOR, NTC | Farnell Österreich.

When the amp is on this NTC gets hot, but as I said, not too hot to touch. maybe 50-60 °C? I'm using a screw terminal to hook up the mains to the transformer (of course after fuses and switch), connect the primaries via the NTC and put a X2 cap across. See pic. No solder.

[giulia67]

The 5 amp rated CL60 is that for transformers with 5amp RMS output? Do you just solder one leg on each of the primary leads on the transformer on a 120 volt ac? Thanks