Toroidal mains Tx inrush limiter - retrofit

"Grant"
They aren't designed for use at mains voltages/currents, though... at
least, I haven't seen any that are.

Me neither, other thing with polyfuses is that there's approx 2:1 current
difference between trigger point and hold point.
Click to expand...
** That is utterly misleading !!

There are no separate trigger and hold points with PolySwitches.

The makers specs allow for some device to device variation in the actual
current level that will trigger a RANGE of similar devices to change state
and go high resistance.

The max current that fails to trip all examples of a given type is called: "
I Hold ".

The minimum current that will trip all examples of a given type is called: "
I Trip".

" I Trip " is double " I Hold".

For any given device, the trip current is one number.

Once a device has tripped, the current needed to HOLD it in the new state is
a function of the applied voltage and is generally 5 to 20 times less than
the trip current.



..... Phil
 
This green thermistor limiter 10 deg C over ambient with no throughput and
20 deg C over with 0.4 amp mains with amp driving load.
 
In article <in4d0o$4dq$1@dont-email.me>, N_Cook <diverse@tcp.co.uk>
writes

This green thermistor limiter 10 deg C over ambient with no throughput and
20 deg C over with 0.4 amp mains with amp driving load.
Click to expand...
Bit warmer than I would be comfortable with.

--
Mike Tomlinson
 
"Mike Tomlinson"
Nutcase Kook"
This green thermistor limiter 10 deg C over ambient with no throughput and
20 deg C over with 0.4 amp mains with amp driving load.

Bit warmer than I would be comfortable with.
Click to expand...
** So neither of you has a clue how NTC surge limiters are meant to work ?



...... Phil
 
Mike Tomlinson <mike@jasper.org.uk> wrote in message
news:GZ$5xNEjVclNFwGu@jasper.org.uk...
In article <in4d0o$4dq$1@dont-email.me>, N_Cook <diverse@tcp.co.uk
writes

This green thermistor limiter 10 deg C over ambient with no throughput
and
20 deg C over with 0.4 amp mains with amp driving load.

Bit warmer than I would be comfortable with.

--
Mike Tomlinson
Click to expand...

Odd you say that. The next amp I looked at, this time mixer amp but also
300W and toroid Tx. Owner bought knowing 2 of the 8 channels were duff and
used as such for some years. He now needs all 8 ch .
Before he owned it , it must have been dropped and broke the awkward
size/shape mains switch. So someone spade jumpered the leads and covered
with heatshrink, leaving un-blanked off hole in chassis. Under his
heatshrink and touching the ordinary mains wire sleeving is an inrush
thermistor. Black , with 0.8mm leads, marked SG 130, 3.2R cold, 0.8R 20 sec
of soldering iron barrel. Presumably originally fixed to the sw and
unsupported other lead other than cable tie further down the cable loom.
Hopefully originally there was some woven glass sleeving over the thermistor

data for SG130 RTI Surge Guard, 0.07 ohms at 7 amps max , 2.5R at 25 deg C
27 joules rating for a 15 x 6.3 mm black (body radiator?) lump and .8mm
leads for anyone who can convert to temperature (not on the RTI datasheet)
 
It looks as though you use the de-rating curve
http://www.rtie.com/ntc/surggard.htm
So for 7 amp NTC running outside of short duration peaks say an average 1/3
of 7 amps of mains 240V for driven amp and less than rated mains fuse then
125 degrees would be the operational maximum of the thermistor.
Would be nice to know a rule of thumb formula for real life "black body"
radiator/convector temperature and power consumption whether disc
thermistors or rod
resistors
 
Testing this SG 130 on a 12V SLA and headlamp, stabilised at 2.8 amp, .91V
over it and 102 deg C (ambient 18 deg C), no woven glass sleeve covering
 
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