Hi,
I've purchased a generic NTC-based soft start board from local store. It seems to work. Just wanna make sure that it behave correctly.
At cold stage, there are three NTC adds about 30 ohms to the load. When I put power in (220v AC), the output also reach 220v immediately. Then, NTC resistance decrease and then the relay kicks in to bypass the NTCs (resistance drops to zero) within 3 seconds of power on.
So, I tried connecting power amp to the board. Amplifier's VU meter still kicks hard when turning on. I use clamp meter to measure current, there is not difference between with and without soft start circuit. I don't have oscilloscope to see the wave form and I think my meter is not fast enough?
I thought that the voltage should slowly and reach full voltage. The local shop said that it is normal behavior since it is for amplifier not for AC motor which use reduced voltage method. They said that its limit the current not voltage... Is that right??
Please share your thoughts.
Thanks,
AP
I've purchased a generic NTC-based soft start board from local store. It seems to work. Just wanna make sure that it behave correctly.
At cold stage, there are three NTC adds about 30 ohms to the load. When I put power in (220v AC), the output also reach 220v immediately. Then, NTC resistance decrease and then the relay kicks in to bypass the NTCs (resistance drops to zero) within 3 seconds of power on.
So, I tried connecting power amp to the board. Amplifier's VU meter still kicks hard when turning on. I use clamp meter to measure current, there is not difference between with and without soft start circuit. I don't have oscilloscope to see the wave form and I think my meter is not fast enough?
I thought that the voltage should slowly and reach full voltage. The local shop said that it is normal behavior since it is for amplifier not for AC motor which use reduced voltage method. They said that its limit the current not voltage... Is that right??
Please share your thoughts.
Thanks,
AP
we use a "softstart" to limit the very high initial turn-on current from a large torodial transformer.
NTC's warm up pretty fast. When I added an NTC I could not tell much difference in the amp, but I knew something changed because the lights did not dim when powering on with the NTC. Did you notice any difference in lights on the same circuit? IE did they stop flickering on power on.
Today, in 2022?? Where are you? Show us a picture! And draw a schematic....
If you can measure some drop in resistance from the 30 ohms (cold), then it's probably working right. So maybe you just didn't need one, yet...?
that 30 ohms is about right when cold, and is effective in killing heavy transient currents, then the relay kicked in after about 5 periods, so you may even think it does not work, but sure it does....
The fact you said this suggests you were measuring the output of the board without a load. That is a non valid state. You will always see full mains in this situation.
The protection a soft start gives is often all over after just a few hundred milliseconds. It limits that initial surge over the first few cycles of the applied AC input.
Don't even think about using a scope on the AC input side of an amp unless you are fully conversant with safe operating procedures. A meter is nowhere near fast enough to show any of this.
Yes. although the two related. The voltage falls in response to the lower current but as mentioned, it all happens in a fraction of a second.
A soft start is not intended to fix 'bad behaviour' of an amplifier such as things thumping or meters kicking hard over at power on. Those are design faults with the amp.
Thanks all. I think I have verified that it works as it suppose to now, particularly on NTC and relay behavior.
Its just the initial current surge into transformer and caps you are trying to limit.
Once caps have charged a bit they become less current hungry.
I have done a bit of work with DCC model railway controllers.
They hate shorts. So I have to add 10R in series with cap on decoder pcb.
With this I can use 4700uf on decoder pcb.
Without the resistor max cap I can use is 47uf !
Its surprising what difference a few ohms can make.
Once caps have charged a bit they become less current hungry.
I have done a bit of work with DCC model railway controllers.
They hate shorts. So I have to add 10R in series with cap on decoder pcb.
With this I can use 4700uf on decoder pcb.
Without the resistor max cap I can use is 47uf !
Its surprising what difference a few ohms can make.