I have 15A 240V variac, and I want to limit the inrush current. It seems an NTC thermistor is a simple way to do this. Unfortunately I am even simpler than the calculations needed!
At the moment there is nothing connected to it, but it could be used for powering a large Japanese 100V amp.
So, any help would be welcome.
At the moment there is nothing connected to it, but it could be used for powering a large Japanese 100V amp.
So, any help would be welcome.
This is a very interesting subject, and I look forward to the exchanges here.
I have a variable transformer, and whenever I turn it on for the first time (even with output knob all the way down), it always trips my 15A home breaker. Once I reset the breaker and turn on the transformer, it works as normal. I rarely use the transformer so months may pass between uses. I am speculating that the magnetic core of the transformer is unmagnetized after long periods of disuse, and turn-on causes a surge that trips the house breaker.
I have a variable transformer, and whenever I turn it on for the first time (even with output knob all the way down), it always trips my 15A home breaker. Once I reset the breaker and turn on the transformer, it works as normal. I rarely use the transformer so months may pass between uses. I am speculating that the magnetic core of the transformer is unmagnetized after long periods of disuse, and turn-on causes a surge that trips the house breaker.
well we don't know what the rating of Halauhula's transformer is, and not all breakers are created equal....
1500 VA variable transformer, bought new from Marlin P. Jones. Works well, no vibration or hum when in use. Just sets off the breaker, that is all.
Breaker is a GE, as I recall, but it could be another name brand breaker. Never had problem with the breaker (I run my soldering iron, lights, and Milwaukee battery charger on the same circuit (not all at once in fact nothing else is on the breaker when using the transformer) EXCEPT when for first turn-on of transformer. Hence, I think the breaker is not the problem.
Breaker is a GE, as I recall, but it could be another name brand breaker. Never had problem with the breaker (I run my soldering iron, lights, and Milwaukee battery charger on the same circuit (not all at once in fact nothing else is on the breaker when using the transformer) EXCEPT when for first turn-on of transformer. Hence, I think the breaker is not the problem.
that is a heavily inductive load to switch on!
i would use an inductive load breaker or a motor protection breaker as they are tolerant of the circuit conditions.
and all breaker manufacturers make different types in case you weren't aware...do your own research but if your lazy here's a little light reading for you https://www.icrfq.net/the-complete-guide-to-square-d-circuit-breakers/
i would use an inductive load breaker or a motor protection breaker as they are tolerant of the circuit conditions.
and all breaker manufacturers make different types in case you weren't aware...do your own research but if your lazy here's a little light reading for you https://www.icrfq.net/the-complete-guide-to-square-d-circuit-breakers/
for the current levels involved i don't think an NTC is the way to go a MOV would be more suitable.
https://www.sunrom.com/p/7d471k-varistor-mov-for-220v-ac
https://www.sunrom.com/p/7d471k-varistor-mov-for-220v-ac
@awkwardbydesign
When you say "Japanese 100V amp", do you mean it's a 120 VAC mains voltage version, Accuphase have a few mains voltage versions for different markets, the other two are 220 VAC and 230 VAC according to the PDF, link below.
https://www.accuphase.com/model/e-480.html
https://www.accuphase.com/cat/e-480_e.pdf
https://web.archive.org/web/20220000000000*/https://www.accuphase.com/cat/e-480_e.pdf
As for NTC's as inrush limiter for your variac, which can be treated as a transformer of the same kVA rating, you may have a look at the two article links below, the links takes you directly down to the relevant text discussing NTC's pertaining to your case.
In short it's not at all recommended to use an NTC and in particular when the load is not constant, such as a power amps like the Accuphase which datasheet says: "Power Consumption 93 watts idle, 425 watts in accordance with IEC 60065", (exceptions would in mostcases be for class-A amps).
https://sound-au.com/articles/soft-start.htm#s3
https://sound-au.com/articles/inrush.htm#s61
If you look around at that site you will find other types of inrush limiters, but a one single component solution there are not, if you need just a temporary solution it's best to add a suitable resistor in series with the variac and a switch to bypass the resistor, the inrush current spike is usually decaying away within the first couple of seconds.
When you say "Japanese 100V amp", do you mean it's a 120 VAC mains voltage version, Accuphase have a few mains voltage versions for different markets, the other two are 220 VAC and 230 VAC according to the PDF, link below.
https://www.accuphase.com/model/e-480.html
https://www.accuphase.com/cat/e-480_e.pdf
https://web.archive.org/web/20220000000000*/https://www.accuphase.com/cat/e-480_e.pdf
As for NTC's as inrush limiter for your variac, which can be treated as a transformer of the same kVA rating, you may have a look at the two article links below, the links takes you directly down to the relevant text discussing NTC's pertaining to your case.
In short it's not at all recommended to use an NTC and in particular when the load is not constant, such as a power amps like the Accuphase which datasheet says: "Power Consumption 93 watts idle, 425 watts in accordance with IEC 60065", (exceptions would in mostcases be for class-A amps).
https://sound-au.com/articles/soft-start.htm#s3
https://sound-au.com/articles/inrush.htm#s61
If you look around at that site you will find other types of inrush limiters, but a one single component solution there are not, if you need just a temporary solution it's best to add a suitable resistor in series with the variac and a switch to bypass the resistor, the inrush current spike is usually decaying away within the first couple of seconds.
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Thanks for the advice. I will look at those articles. And it would be a 100V version, which is the Japanese voltage.
Unfortunately I am still in the same position. My variac is 3600VA, and thermistors and relays would need to be specced for that, I assume. The ESP figures assume a max of 1000VA.
MOV is for over-Voltage.
https://www.sunrom.com/p/7d471k-varistor-mov-for-220v-ac
Protect electronics against high voltage spikes and surges
https://www.sunrom.com/p/power-ntc-10d-9
Thermistors typically used as Inrush current limiters in Switching Power Supplies
Your wall-outlet can surely support 16 Amps? In the listings and data linked just above, the maximum max current listed is 12 Amps.
Model Number - R25 - Max.Current (A) - Approx. Resistance in Max. Current at 25
NTC0R7D-20 ----0.7 --12 --------------- 0.018
Since your actual load "large amp" is under 3Amps @ 240V, you could even use NTC20D-15, 20r, 4A. The peak current is 240V/20r or 12 Amps.
Of course a fixed autotransformer is a better bet for steady use. The cat can't bump it from 100V to 189V. The EI core has less surge. It saves a lot of iron.
For laboratory use: connect a 150 watt incandescent light bulb in series between the mains and the variac. Connect a household SPDT light switch in parallel with the bulb.
Before turn-on: set the SPDT switch to its open circuit ("off") position
At turn-on: apply AC mains to the series assembly. The light bulb glows and limits the inrush current to a value less than or equal to (150W / MainsRMSvoltsge) amperes.
1 second after turn-on: the inrush event is over, the variac's sinusoidal voltage waveform and sinusoidal current waveform are now in their proper phase, so it is now time to close the SPDT switch ("on" position) and short out the light bulb. Now the variac is connected directly to the AC mains.
Before turn-on: set the SPDT switch to its open circuit ("off") position
At turn-on: apply AC mains to the series assembly. The light bulb glows and limits the inrush current to a value less than or equal to (150W / MainsRMSvoltsge) amperes.
1 second after turn-on: the inrush event is over, the variac's sinusoidal voltage waveform and sinusoidal current waveform are now in their proper phase, so it is now time to close the SPDT switch ("on" position) and short out the light bulb. Now the variac is connected directly to the AC mains.