Yet another F5 building log

[buzzforb]

the "30" part defines its resistance, I believe and perhaps power rating. Good opportunity to look on digikey or mouser at the two and compare datasheets.

[dimkasta]

Yep. I was already on it.
Googled and mousered it fast.
http://www.ge-mcs.com/download/temperature/920_325a.pdf

CL-30 is rated at 2,5R at 25 degress celcius and 8A of constant current flow, while CL-60 is rated at 10R at 25 celcius and 5A current.

[AndrewT]

you would need 8 off CL30 to give you a total of 20r to limit the start up surge current.
you need 2 off CL60 for the same 20r.

BTW,
I consider 20r of limiter resistance to be far too low for all transformers under 1kVA and 220/240Vac.
They cannot use a close rated fuse, eg. 750VA would require a T3.1A and with only 20r for soft start, this fuse is likely to blow too frequently.

Another example. I am using 140r @ 240Vac for a 80VA transformer and it starts on a T500mA.

[dimkasta]

How much resistance would you use in such a case?
The store's board is using 4x180R @5W which means 45R @20W

[Zen Mod]

4 CL60 in series then instead crummy resistors

putting these (4x180R) in parallel in that gadget is sign of constructor's incompetence

[dimkasta]

The issue in that case is that since the F5 works at ~180W, the constant current expected to be run through the thermistor on the primary side is a bit less than 1A.

This means that the CL-60 thermistor will work on ~20% of its max current capacity (5A), meaning at full F5 operation, it will be around 1R .
And 4 in series give 4R

On the other hand, a CL-90 (120R @25 celcius and 2A max capacity) will give an even bigger initial current reduction and will eventually work at 50% giving ~3R resistance at full F5 operation.

Another issue that concerns me is that the recomended max capacitance rating for them is ~1500uF @240VAC. Aren t we pushing them way above their comfort limits? According to the datasheet, this is not their max safety threshold, but rather an indicator that their life might be shortened.

Maybe we should use 2-3 in parallel? (Which of course starts another round of discussion about what happens if one of them burns and/or shorts...)

[Zen Mod]

you said "store board" , meaning on usual gizmo soft sart circ - bunch of resistors shorted with relay after small delay ?

so - I said - just use NTC's instead of fixed resistors in same circ

if not - just use same as Nelson does , and stop trying reinventing the wheel

[AudioSan]

here is a nice softstart. hypex softstart.
i removed the 2x33ohm resistors and replaced them with 2xCL60 in series.

[dimkasta]

No offence meant. Just trying to learn and combine your's and Andrew's input into something useful and interesting.

Don t know yet what I am going to choose to use. Just trying to learn.

[Zen Mod]

I didn't saw/read any offense ;

just trying to give you practical solution and save you from loosing energy where it isn't needed