When I search this forum I find 2 solutions:
- Using a thermistor like the CL60
- A timing circuit with a relay
Is there a limitation to the VA rating for which a thermistor can be used?
What is the effect of the capacitors in the power supply?
I'm planning to use a 1KVA transformer.
I like the thermistor solution because it's simple.
- Using a thermistor like the CL60
- A timing circuit with a relay
Is there a limitation to the VA rating for which a thermistor can be used?
What is the effect of the capacitors in the power supply?
I'm planning to use a 1KVA transformer.
I like the thermistor solution because it's simple.
A timing circuit with relay can be set up much more precisely.
Are you joking about capacitors? They must be used as a filter behind rectifier diodes, otherwise you will obtain pulsed voltage with 100 Hz repetition frequency resulting in very loud hum (in fact you will not listen to the music, but to the hum - without capacitors in the power supply).
Are you joking about capacitors? They must be used as a filter behind rectifier diodes, otherwise you will obtain pulsed voltage with 100 Hz repetition frequency resulting in very loud hum (in fact you will not listen to the music, but to the hum - without capacitors in the power supply).
Thanks for the reply.
I'm not joking. I just mean the the capcitors that are used after the rectifiers.
At startup they are act like a short circuit, so I imagine they will have an effect on the inrush current.
I'm not joking. I just mean the the capcitors that are used after the rectifiers.
At startup they are act like a short circuit, so I imagine they will have an effect on the inrush current.
Yes, partly. But inrush current is mostly caused by magnetizing currents in the core of large toroidal transformers (rated at 300VA and more). This inrush current will occur even with no load.
Anyway you need filter capacitors to change rectified sinus halfwaves into DC voltage. This DC voltage will have some ripple, depending on filter capacitor value and current supplied to the amplifier.
Anyway you need filter capacitors to change rectified sinus halfwaves into DC voltage. This DC voltage will have some ripple, depending on filter capacitor value and current supplied to the amplifier.
My company makes power amplifiers for professional use. The ones with a linear power supply and toroids use NTC inrush current limiters. The biggest is 400W output with a 800VA power supply. You can use NTC's for that VA-rating. I see no problem for 1000VA.
During operation they are a little above 100°C so be careful with your wiring insulation and mount them high above the PCB, or use ceramic terminal blocks ("kroonsteentjes") with screws.
Steven
During operation they are a little above 100°C so be careful with your wiring insulation and mount them high above the PCB, or use ceramic terminal blocks ("kroonsteentjes") with screws.
Steven
In my 500 W sub I use a 100 ohm resistor + relay with integrated time module ELESTA SKR135. In my QRO amp I have a solution on pcb.
The disadvantage of NTC is very long "reset time". If the voltage drops a short time this kind of circuit won't work.
It's more expensive to use a time relay but the function is 100% allways.
The disadvantage of NTC is very long "reset time". If the voltage drops a short time this kind of circuit won't work.
It's more expensive to use a time relay but the function is 100% allways.
McIntosh uses a 4 ohm inrush current limiter in their 120W amplfier with 40,000µF of filter C with an E&I type transformer.
Their larger models short out this 4 ohms with a relay with an RC constant of about 1 second.
BGW does about the same thing.
A Hafler DH500 comes with a 0.5 ohm inrush current limiter. The power switch and over-temp thermo-stats still fail.
I change mine to 2.5 ohms and go to a 3PDT speaker relay with the third pole shorting out the inrush current limiter.
Their larger models short out this 4 ohms with a relay with an RC constant of about 1 second.
BGW does about the same thing.
A Hafler DH500 comes with a 0.5 ohm inrush current limiter. The power switch and over-temp thermo-stats still fail.
I change mine to 2.5 ohms and go to a 3PDT speaker relay with the third pole shorting out the inrush current limiter.
Found this on ebay...GREAT DEAL!!
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=3856218825&ssPageName=STRK:MEWA:IT
Marc
edit:
Woops..I guess it's not so great. mouser.com has 10 for 12.40usd.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=3856218825&ssPageName=STRK:MEWA:IT
Marc
edit:
Woops..I guess it's not so great. mouser.com has 10 for 12.40usd.
specs
I'm interested in this discussion as well. Did you see this data sheet:
http://www.thermometrics.com/assets/images/cl.pdf
Looks like for a thermister (NTC) there is a maximum recommended capacitance (after the device) for maximum life, AND its way less than 10,000 uF. Jeez, havn't seen a DIY amp with that low amount of capacitance in a long time!
I didn't think you were joking about capacitance by the way, you mentioned it and it was very insightful. So, I'm wondering what you do with a NTC and 60,000 uF as we are prone to see around here.
I'm interested in this discussion as well. Did you see this data sheet:
http://www.thermometrics.com/assets/images/cl.pdf
Looks like for a thermister (NTC) there is a maximum recommended capacitance (after the device) for maximum life, AND its way less than 10,000 uF. Jeez, havn't seen a DIY amp with that low amount of capacitance in a long time!
I didn't think you were joking about capacitance by the way, you mentioned it and it was very insightful. So, I'm wondering what you do with a NTC and 60,000 uF as we are prone to see around here.
Hello,
I use a 1 ohm thermistor for my 950.000 uF Hiraga Monstre. Haven't had any problems with it so far (almost 1 year).
Cheers,
Johan
I use a 1 ohm thermistor for my 950.000 uF Hiraga Monstre. Haven't had any problems with it so far (almost 1 year).
Cheers,
Johan
Re: specs
The maximum capacitance after the thermistor is voltage dependent. The given values are for direct mains connection at 120 or 240Vac. After a transformer, going down in voltage, the allowed capacitance is much bigger. Suppose a type that can charge 1000u at 240V, then it can charge 4 times as much (4000u) at 120V, 16000u at 60V and 64000u at 30Vac secondary. These values are closer to how they are used in amplifiers. This is all true for an ideal transformer without additional losses. In practice these losses will be present, certainly at inrush. So even more capacitance is allowed then.
Steven
lgreen said:
The maximum capacitance after the thermistor is voltage dependent. The given values are for direct mains connection at 120 or 240Vac. After a transformer, going down in voltage, the allowed capacitance is much bigger. Suppose a type that can charge 1000u at 240V, then it can charge 4 times as much (4000u) at 120V, 16000u at 60V and 64000u at 30Vac secondary. These values are closer to how they are used in amplifiers. This is all true for an ideal transformer without additional losses. In practice these losses will be present, certainly at inrush. So even more capacitance is allowed then.
Steven
Re: specs
Hello all,
I can say that the Thermometrics datasheet is talking about a rectifier just behind the net voltage (no transformer). This means they talk about a high voltage capacitor bank.
The energy in the NTC to be dissipated related to the energy stored in the cap-bank which is CV²/2.
We DIY audio people are using for example :40V
The datasheet is talking about 240 or 120 V which is AC and which is to be multiplied even with sqrt(2).
as E ~ with V² -> energy to be dissipated with our 40V capacitor bank is much lower.
My conclusion is that often NTC is a suitable, easy and low ost inrush current solution. I only have troubles finding them in the electronica stores here in Belgium.
Disantvantages are already mentioned: part gets hot in normal operation, reset time exists.
Greetings!
lgreen said:
Hello all,
I can say that the Thermometrics datasheet is talking about a rectifier just behind the net voltage (no transformer). This means they talk about a high voltage capacitor bank.
The energy in the NTC to be dissipated related to the energy stored in the cap-bank which is CV²/2.
We DIY audio people are using for example :40V
The datasheet is talking about 240 or 120 V which is AC and which is to be multiplied even with sqrt(2).
as E ~ with V² -> energy to be dissipated with our 40V capacitor bank is much lower.
My conclusion is that often NTC is a suitable, easy and low ost inrush current solution. I only have troubles finding them in the electronica stores here in Belgium.
Disantvantages are already mentioned: part gets hot in normal operation, reset time exists.
Greetings!
Re: Re: specs
Won't get hot provided the relay switches on in several seconds. No reset time problem because the thermistor will be cold during normal operation because the relay contacts short it out. You could use perhaps a higher resistance thermistor than normal for an even softer startup but without any long term temperature problems that you would normally have by doing this.
Use a relay *and* a thermistor. Easy!AFKC said:
Won't get hot provided the relay switches on in several seconds. No reset time problem because the thermistor will be cold during normal operation because the relay contacts short it out. You could use perhaps a higher resistance thermistor than normal for an even softer startup but without any long term temperature problems that you would normally have by doing this.
JohanH said:
And Pass used them in the Aleph series production run. Reliability didn't seem to be an issue. I don't know what he uses now, but I wouldn't be surprised to see NTCs.
It is crazy thinking here - to get 950 000 micro capacitor to the amp in one side ( for ultralow internal impedance of PS ) and on other side kill it by serial resistor 
. What for hell do you realy need ?
. What for hell do you realy need ?
100 ohms?
Not likely to start.
BGW used a 5 ohm 50W part and a relay before they went to the thermistor.
Not likely to start.
BGW used a 5 ohm 50W part and a relay before they went to the thermistor.
I was flirting with the idea of a thermistor inrush current limiter for my power amp aswell - i've never tried it before, so somene enlighten me:
- Can you use thermistors in parallel (or series better), or is it not a wise idea? I have quite a bunch from recycled parts, mainly from old PC PSUs, but they seem rather small (2A @ 240VAC, if i recall correctly). Not that these thermistors are very expensive, but still..
My idea is to wire it ("them") in series between the line and the main transformer.
- How hot can i expect them to get?
- Can you use thermistors in parallel (or series better), or is it not a wise idea? I have quite a bunch from recycled parts, mainly from old PC PSUs, but they seem rather small (2A @ 240VAC, if i recall correctly). Not that these thermistors are very expensive, but still..
My idea is to wire it ("them") in series between the line and the main transformer.
- How hot can i expect them to get?
- Status
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