Inrush current circuit

mlucitt

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#2
This is what I use for my P.L.
I like the circuit but I might use a 20mm sized 10 Ohm NTC thermistor instead of the 25 Ohm 25 Watt resistor. Because you are bypassing the current-limiting device with the relay after a few cycles, the resistor is protected after about 100 mS (six cycles at 60 Hz).
If you select a minimum 10 Joule thermistor, that means it can withstand 100 Watts for 100 mS.
 

grapplesaw

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#4
I have two soft starts to try soon
One is with thermistors and has two high heat sensors so I can get the ac off the back plate. The other also has built in remote on/off. That one is going in a 700b. I got it in 110volt configuration

I also want to add one to the D500 just because of the large inrush current using 33,000uf caps
 

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Wayne

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#6
I like the circuit but I might use a 20mm sized 10 Ohm NTC thermistor instead of the 25 Ohm 25 Watt resistor. Because you are bypassing the current-limiting device with the relay after a few cycles, the resistor is protected after about 100 mS (six cycles at 60 Hz).
If you select a minimum 10 Joule thermistor, that means it can withstand 100 Watts for 100 mS.
I have an inquiry going on with Littlefuse on what of power thermometer to use in the Pal.
Let's see what they say.
Could put these in secondary winding. I read they get hot when in normal run time. So they have to be away from other components.
If installed outside amplifier in series with primary this would not be a problem.
 

grapplesaw

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#7
I have an inquiry going on with Littlefuse on what of power thermometer to use in the Pal.
Let's see what they say.
Could put these in secondary winding. I read they get hot when in normal run time. So they have to be away from other components.
If installed outside amplifier in series with primary this would not be a problem.

If you look at the pdf I posted it shows best for difference capacitor sizes. I think the heat factor will not be of concern due to only cycling at turn on. I will use 4 of the 6 ohm part # 6D2-22

Here is all you wanted to know about thermistors
http://www.resistorguide.com/ntc-thermistor/
https://www.engr.usask.ca/classes/EE/392/2011/DataSheets/ntcnotes.pdf
 
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#10
You would still need to bypass whatever device is in series with the primary. As power draw increases, so does the voltage drop across the device. You need to install some sort of fuse resistor in series with the diode for safety.
 
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#11
What problem is the soft start solving? I've captured a number of current and voltage waveforms with a scope on 400's and 700's and the inrush current does not exceed the maximum surge current of the rectifier. Yes I've used a total of 40,000uf on 400's and 30,000uf on 700's. In addition, the curves for the standard 10 amp fuse will allow it to open before any inrush current could hurt the bridge rectifier.

If it is felt that a soft start is needed I would suggest using a phase angle control circuit as opposed to resistors/thermistors and relays. Phase angle control is the principle of operation behind the old style incandescent light bulb dimmers and uses a triac for the control. 9 out of 10 people believe that a dimmer is just a rheostat. Actually, a rheostat is used, but it controls the firing (turn on) of a triac.

There is a phase angle controller IC, TDA1085, that incorporates all of the functions needed to make a softstart. The datasheet has a PCB layout. Although I didn't check them out there are listings on ebay for the 1085.

I used the TDA chip to make an automatic softstart on an outdoor garage light. It phased on at dusk and off at night and the bulb lasted for years.
 

grapplesaw

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#15
What problem is the soft start solving? I've captured a number of current and voltage waveforms with a scope on 400's and 700's and the inrush current does not exceed the maximum surge current of the rectifier. Yes I've used a total of 40,000uf on 400's and 30,000uf on 700's. In addition, the curves for the standard 10 amp fuse will allow it to open before any inrush current could hurt the bridge rectifier.

If it is felt that a soft start is needed I would suggest using a phase angle control circuit as opposed to resistors/thermistors and relays. Phase angle control is the principle of operation behind the old style incandescent light bulb dimmers and uses a triac for the control. 9 out of 10 people believe that a dimmer is just a rheostat. Actually, a rheostat is used, but it controls the firing (turn on) of a triac.

There is a phase angle controller IC, TDA1085, that incorporates all of the functions needed to make a softstart. The datasheet has a PCB layout. Although I didn't check them out there are listings on ebay for the 1085.

I used the TDA chip to make an automatic softstart on an outdoor garage light. It phased on at dusk and off at night and the bulb lasted for years.
Good info here Don

As you and I have talked about this in the past my real interest for soft starts is three fold

First one is for start up of the multiple toroidal transformers of a high rail amp I am building. For this I have purchased some dual relay sets with terminators. I think these will work fine.

Second is I have a remote start setup with dual relays and thermistors for a 700b I am building( just for the hell of it). This also has the fiction to replace the stack ac therm switch’s to low voltage DC control. I really do not need the soft start function but it is there.

The third is to add a single replay setup for the dual500 Itpimaey on/off relay built in the amp will supply the soft start which has a resistor or thermistors at start to limit current and the the relay will connect ac direct through a 30 amp rated relay. The reason for this is the thing almost jumps when you press the on button. I had to use a slow blow fuse to keep it alive on startup.


So that’s my plans. Any comments or objections will be well received

I am attaching the different soft starts please no heckling form the peanut gallery
Glen
 

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