Maybe this has been asked before...
I have a double mono power supply with two 625 toroids in one enclosure (so one IEC inlet) for my Aleph5. Is it sufficient to use one pair of CL60 thermistors. Or should I apply them after spliting the AC inlet, thus having one pair of CL60s for each toroid?
I prefer to use one pair for both toroids, because of the heat build up (working temp 60 is degrees C I believe) and extra space they will require. But is it sufficient?
I do want one to use one fuse for each toroid.
I have a double mono power supply with two 625 toroids in one enclosure (so one IEC inlet) for my Aleph5. Is it sufficient to use one pair of CL60 thermistors. Or should I apply them after spliting the AC inlet, thus having one pair of CL60s for each toroid?
I prefer to use one pair for both toroids, because of the heat build up (working temp 60 is degrees C I believe) and extra space they will require. But is it sufficient?
I do want one to use one fuse for each toroid.
Use one thermistor per toroidal transformer. The only reason you need a thermistor is to limit the current surge on turn on. Once the thermistor gets hot, it's resistance approached zero ohms and is virtually out of the picture. So you see, there is really no reason to use multiples unless parameters require it. For the steady state current required for an Aleph 5, again, only one per toroidal.
kilowattski said:
not quite right -- the "on" resistance is given in the Thermometrics or GE datasheets (or can be calculated if you have a programmable calculator) --- it can be significant enough that there will be an IR voltage drop
you can use one thermistor for the positive and one for the negative rail of a bridged power supply, or you can use on one the primary side of the trannie alone -- it just has to fit the design parameters.
Jack,
Not quite Jack, but a nice try. If he uses a CL-60 on the primary the "hot" resistance is 0.18 ohms. His Aleph 5 according to Pass Labs will draw 2.5 amps. If he does use two transformers, each will draw 1.25 amps. That will lead to a voltage drop across the thermistor of 0.225 volts. I would hardly say that is a significant voltage drop when the power company has difficulties maintaining even 5% regulation on the power coming into your home. Of course if his primary is 240 volts the drop will be even less. Putting thermistors after the rectifier on the secondary is not much help in supressing inrush current since most of the inrush is caused by the toroidal transformer itself.
kilowattski said:
here's the problem in your analysis -- these current limiters have higher resistance when operated below their maximum rated capacity, so the resistance for the CL60 at 1.25 amps is closer to an ohm, and at 5 amps it is 0.18 ohms. furthermore, the device doesn't respond instantaneously to a change in demand -- unless you are using a regulated power supply you will see the effects -- at least in an amplifier within poor PSRR.
i had experienced the problem of blowing MUR860's and MBR20100's -- putting the inrush limiter in the diodes in the circuit as described cured the problem -- but one was needed on each rail -- this was for a 2 x 120 watt amplifier. when i found that i could cut the size of the filter caps and not hurt its performance i was able to put the limiter ahead of the transformer.
jacco vermeulen said:
the inrush limiter is commonly used for "off line" switch mode power supplies, and as its name implies it limits the current into the filter/reservoir capacitor -- which in this case is on the primary side of the transformer --
for our linear supplies using a torroid there is a wallop of current into the transformer when the supply is turned on, and the filter caps also look like a dead short -- the limiter can protect "both" or "either".
Thanks for your all your replies. I was planning to use 2 in the primairy side. If I understand it correctly with one Alpeh5 channel (1.25 A) the thermistors won't get hot enough to reach the 0.18 ohm, but will settle around 1 ohm. When I use 2 of them per side the voltage drop becomes twice as large: 2 * 1 * 1.25 = 2.5V. Still not that much of a problem. Especially since my secondairy AC is 30V, which is a bit above normal Aleph5 specs.
On the other hand if one is enough... (I have 10 lying around btw)
Do I understand it correctly that with one 10 Ohm Thermistor (cold) per toroid the maximal inrush current wil be 24A (with 240 V AC). Still seems rather high to me, but it is only for a short period of time of course.
(BTW there will be 220 mF caps per channel, with CLC)
Second question. How long do these Thermistors last and what happens when they break down?
On the other hand if one is enough... (I have 10 lying around btw)
Do I understand it correctly that with one 10 Ohm Thermistor (cold) per toroid the maximal inrush current wil be 24A (with 240 V AC). Still seems rather high to me, but it is only for a short period of time of course.
(BTW there will be 220 mF caps per channel, with CLC)
Second question. How long do these Thermistors last and what happens when they break down?
Ducky,
your switchbox circuitmaker fuse is 16 amps, 10 amps inrush current does not blow the fuse.
With such a current main voltage may drop for a fraction but that would happen too when you switch on common household equipment, think of a high power vacuum cleaner, or a dryer in your washroom.
I had a 5-zone ceramic cooking stove, with a 7000 watt total rating.
2 zones switched on simultaneously made the lights flicker.
Anyone with a washer/dryer combo is familiar with the hassle if both are switched on the same single fuse.
I use a 230/380v arc welding device that i have to run on 230volts for the moment. Five minutes of welding and the fuse blows like clockwork.
It may be a problem if you switch on both amps simultaneously from your preamp.
Then inrush should equal 2*10= 20 amps, and the fuse will blow unless you have them on 1 fuse per amp.
I use 4 separation toroids (1600VA each) for my audio equipment.
With a timer ic these are relay bypass switched, one after another, 2 toroids on a 16 amp fuse.
After that juice goes to the amplifier toroids, those can not harm the main fuse with the separation toroids in between.
I think 16 amp relays on the primary transformer side work great, are longlasting, 16 amp Schrack/Omron/Siemens/Matsushita relays can be bought on the net for 1 Euro.
In my experience, thermistors are quite rugged devices and last a very long time. Because of that thermistors are built-in in a number of applications, like motors.
If one should break down your amp will not switch on, and the first thing to check would be the NTC.
I doubt that there is a chance that it leads to a shortcut because of the basics of thermistor behavior.
(maybe JackinNuevaJersey can confirm the latter or tell you that i am a BS artist).
JaccoinR.
your switchbox circuitmaker fuse is 16 amps, 10 amps inrush current does not blow the fuse.
With such a current main voltage may drop for a fraction but that would happen too when you switch on common household equipment, think of a high power vacuum cleaner, or a dryer in your washroom.
I had a 5-zone ceramic cooking stove, with a 7000 watt total rating.
2 zones switched on simultaneously made the lights flicker.
Anyone with a washer/dryer combo is familiar with the hassle if both are switched on the same single fuse.
I use a 230/380v arc welding device that i have to run on 230volts for the moment. Five minutes of welding and the fuse blows like clockwork.
It may be a problem if you switch on both amps simultaneously from your preamp.
Then inrush should equal 2*10= 20 amps, and the fuse will blow unless you have them on 1 fuse per amp.
I use 4 separation toroids (1600VA each) for my audio equipment.
With a timer ic these are relay bypass switched, one after another, 2 toroids on a 16 amp fuse.
After that juice goes to the amplifier toroids, those can not harm the main fuse with the separation toroids in between.
I think 16 amp relays on the primary transformer side work great, are longlasting, 16 amp Schrack/Omron/Siemens/Matsushita relays can be bought on the net for 1 Euro.
In my experience, thermistors are quite rugged devices and last a very long time. Because of that thermistors are built-in in a number of applications, like motors.
If one should break down your amp will not switch on, and the first thing to check would be the NTC.
I doubt that there is a chance that it leads to a shortcut because of the basics of thermistor behavior.
(maybe JackinNuevaJersey can confirm the latter or tell you that i am a BS artist).
JaccoinR.
jacco vermeulen said:
by the way, it's the People's Republic of New Jersey, but
what is it you want me to confirm? -- i only learned this the hardway -- using a thermistor with too high an "on" value -- this did cause one amp I worked on to momentarily distort when the input signal was quickly changed -- i guess that what I should do is trigger my spectrum analyzer with the pulse generator so you can see what I mean --
those square wave tests everyone likes to talk about -- it's really a test of bandwidth AND PSRR.
I don't fully understand the function of the thermistor.
The thermistor arranged at the primary side is considered mainly to suppress the surge/inrush current at turn-on. After that, the thermistor would heat up till it meets an equilibrium i.e. on the condition of a constant thermistor body temperature or the rate of heat lose equal to the power supplied to the thermistor. At this equilibrium condition, the thermistor resistance would remain constant with small voltage drop across it, where the voltage drop could be negligible figure to 240 Vrms of supply voltage. Is my understanding reasonable?
Meanwhile, since the environment temperature around the thermistor could be variable according to the amp operation condition, the equilibrium status could dance too. If so, the voltage drop values across the thermistor could also dance. Is this kind of possible dancing voltage drop still acceptable?
Thanks for your reply.
The thermistor arranged at the primary side is considered mainly to suppress the surge/inrush current at turn-on. After that, the thermistor would heat up till it meets an equilibrium i.e. on the condition of a constant thermistor body temperature or the rate of heat lose equal to the power supplied to the thermistor. At this equilibrium condition, the thermistor resistance would remain constant with small voltage drop across it, where the voltage drop could be negligible figure to 240 Vrms of supply voltage. Is my understanding reasonable?
Meanwhile, since the environment temperature around the thermistor could be variable according to the amp operation condition, the equilibrium status could dance too. If so, the voltage drop values across the thermistor could also dance. Is this kind of possible dancing voltage drop still acceptable?
Thanks for your reply.
Overhere that is: +10 %, -10 %.
At 230V target : from 207 to 253 volts.
Good side: voltage change is not that instant, and i have yet to see it reach those peaks.
Neither will thermistor voltagedrop, is my guess.
Yet another reason for using Shaffner filters, separation transformers, and high voltage caps in series, in my book !
At 230V target : from 207 to 253 volts.
Good side: voltage change is not that instant, and i have yet to see it reach those peaks.
Neither will thermistor voltagedrop, is my guess.
Yet another reason for using Shaffner filters, separation transformers, and high voltage caps in series, in my book !
Just been reading Elliots article on a softstart circuit ( http://sound.westhost.com/project39.htm ). In there he suggests much higher resistor values. In the 18 Aug 2000 update it settles on 33 ohm for 240 V areas. His argument is that he wants to protect the components (toroids, caps, rectifier bridge) agianst too high inrush current.
For these you would need at least 3 thermistors in series. Of course voltage drop will become a bit more then.
Maybe its not such a bad idea to include a softstart cuircit with a relay??
There seems to be one danger with too high resistor values:
Shoud I worry about this effect with an Aleph5 and say 33 ohm resistance (in a sofstart circuit)?
For these you would need at least 3 thermistors in series. Of course voltage drop will become a bit more then.
Maybe its not such a bad idea to include a softstart cuircit with a relay??
There seems to be one danger with too high resistor values:
Shoud I worry about this effect with an Aleph5 and say 33 ohm resistance (in a sofstart circuit)?
Mlaen,
Just download the application note from
http://www.rhopointcomponents.com/application/ap_surgegards.asp
See my answer on the other thread you posted.
Patrick
Just download the application note from
http://www.rhopointcomponents.com/application/ap_surgegards.asp
See my answer on the other thread you posted.
Patrick
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.