Power Supply Soft Start Board

[RCruz]

Come on guys..... 12v or not 12v that is the question

PS: Like your new avatar Merlin QIU

[merlin el mago]

Thanks RCruz, what's QIU?

[RCruz]

Sorry... bad spelling... I meant KIU Keep It Up

[Tony]

Originally Posted by AndrewT

Two transformers equals two relays to bypass the two sets of soft start resistors/thermistors.

Another unhelpful post?

indeed, why complicate matters when simply paralleling two transformer primaries will work?

[JojoD818]

Originally Posted by RCruz

I need to build this softstart circuit for my new amplifier psu that uses two 250VA TX in parallel.

I will buy the boards but want to keep other expenses to a minimum so I would like to avoid buying the 24v relay as I allready have some 12V ones in my stock. Can I replace the 24v zener (D13) by a 12v one and use my existing 12v relay ?

Hi,

Unfortunately, the circuit calls for the use of a 24V coil relay.

[AndrewT]

Originally Posted by AndrewT View Post
Two transformers equals two relays to bypass the two sets of soft start resistors/thermistors.

Another unhelpful post?

and two 12V relays will operate from the same 24V circuit supplied by DIYaudio

Tony sees my posts as unhelpful.

indeed, why complicate matters when simply paralleling two transformer primaries will work?

Why?
because each transformer sees it's own current limiter. and each is unaffected by what the other transformer is doing/loaded.

[Tony]

Originally Posted by AndrewT

and two 12V relays will operate from the same 24V circuit supplied by DIYaudio

Tony sees my posts as unhelpful.Why?
because each transformer sees it's own current limiter. and each is unaffected by what the other transformer is doing/loaded.

if you are doing mono blocks, i agree, but if the amps are going to be built on a single chassis, i do not see any need for separate soft starters.....

remember that the series current limiters will be shorted out after a few secs delay so that Andrew's concerns are unfounded.....Have a very merry Christmas AndrewT.....


@ RCruz
if you want to use 12 volt relays and change the zeners to 12 volts, i'd say go ahead, after you have purchased the boards, it becomes your property and you are free to modify it to suit your needs....

[RCruz]

Originally Posted by Tony

@ RCruz
if you want to use 12 volt relays and change the zeners to 12 volts, i'd say go ahead, after you have purchased the boards, it becomes your property and you are free to modify it to suit your needs....

Judging by your comments, I would say it is feasible.....

I used spice to sim the circuit and in reality the zener seems to clamp the voltage at 12V.

The wattless dropper is used to set the time delay and I believe we can "play" with the cap value without fear of "overdriving" the relay.

I will build it p2p just to be sure....

Now regarding safety... what if the relay stops woking.... During power up, with a large amp TX with some 40000uF smoothing, there will be around 5.5amps on the 180r resistors, but after the 40000uf powerbank is charged, the current should go down, so even if the relay does not start, maybe the current on the 180r resistors is not so high ?!

[Tony]

45 ohms in series with your power traffo is significant if your relay stops working...

[tsip]

would there be an issue if C11 is 22n? X2 of course.

Thanks