Just wanted to chime in with my implementation of the soft start board. My new amp has 240kuf in the solid state power supply plus another 1.2k for the tube supply. I initially chose .33uf for c9. The relay would not latch. I added another .33uf for .66uf total and the board is working as it should. The boards I have gotten from DIYaudio are great, and the excellent build guides are appreciated.
Evan
Evan
Perhaps this could help...
G5LA-1E 24DC - OMRON ELECTRONIC COMPONENTS - RELAY, PCB, SPDT, 24VDC | element14 Philippines
G5LA-1E 24DC - OMRON ELECTRONIC COMPONENTS - RELAY, PCB, SPDT, 24VDC | element14 Philippines
Thanks jojo
Any recommendation for R, C9 and fuse value for a 300VA 230VAC traffo to works at ideal condition for the soft start ?
Be very careful changing C9.
This is a direct online mains powered project.
It is usually forbidden to discuss this on this Forum. But for some reason the usual LIFE SAFETY rule has been ignored.
As for mains fusing a close rated fuse for 300VA and 230Vac is 300/230 = 1.3A
Use a T1.25A
If this works reliably, then try reducing it to T1A and see if that works reliably.
It's OK , I have reported my own post for those that think commenting on other's decisions is inappropriate.
This is a direct online mains powered project.
It is usually forbidden to discuss this on this Forum. But for some reason the usual LIFE SAFETY rule has been ignored.
As for mains fusing a close rated fuse for 300VA and 230Vac is 300/230 = 1.3A
Use a T1.25A
If this works reliably, then try reducing it to T1A and see if that works reliably.
It's OK , I have reported my own post for those that think commenting on other's decisions is inappropriate.
Hmmmm
I'm using a Novutem 0300P1-2-025 Toroidal 300VA 2x25V o/p Nuvotem 0300P1-2-025 to be exact and recommended fuse is 6.3AT. So why there's so much different ???
IMHO his discussion & suggestion might save my life
An inductive load needs a very different start up fuse from a resistive load.
The "normal" fuse for an inductive load is:
fuse rating = VA / Vac * 3
300VA / 230Vac * 3 = 3.9A
Use a T4A. Most transformer will start with a T4A, some will need a higher fuse rating.
Some will start reliably with a lower fuse rating.
But this is not close rating of the fusing.
That T4A will pass 8A for many seconds and in extreme cases can exceed half an hour before rupturing.
How much heat will the faulty equipment generate if 7A or 7.5A or 7.9A is passing for 30minutes? What happens if the faulty equipment is unattended?
That's where close rated fusing offers a big safety advantage. But transformers need a soft start to allow close rated fusing to be adopted.
Yet another unhelpful post?
The "normal" fuse for an inductive load is:
fuse rating = VA / Vac * 3
300VA / 230Vac * 3 = 3.9A
Use a T4A. Most transformer will start with a T4A, some will need a higher fuse rating.
Some will start reliably with a lower fuse rating.
But this is not close rating of the fusing.
That T4A will pass 8A for many seconds and in extreme cases can exceed half an hour before rupturing.
How much heat will the faulty equipment generate if 7A or 7.5A or 7.9A is passing for 30minutes? What happens if the faulty equipment is unattended?
That's where close rated fusing offers a big safety advantage. But transformers need a soft start to allow close rated fusing to be adopted.
Yet another unhelpful post?
the reason for using a startup limiting resistor is to prevent your switch from being arc welded at turn-on, in my super leach amp build with a 2kva power traffo, i used a dale 10 ohm/50 watt aluminum clad power resistor, time delay of about 3 seconds....i used a power switch rated for 15amperes...and 20 years later, the amp and its switch is still good...
Tony and others who feel the need to read my unhelpful posts:
The 10r Tony has used for 20years is equivalent to four (4) 40r resistors in parallel (R15 to R18 inclusive). Looking at the table that I put up for discussion I see the progression from 270r down to 68r for the range of transformers from 100VA to 1.8kVA (on 110/120Vac).
Tony's 2kVA (is this on 220/240Vac?) is just beyond that range and 40r would seem to fit almost exactly into the extrapolated range of values.
Thanks Tony for that evidence.
Has anyone else got evidence (pro/con) to put up for discussion?
no need for additional power switch.....
how big is your power traffo and how many ufd is your psu caps?
up to about 400VA i wouldn't even bother with a soft start circuit...except maybe if you have about 100,000ufd of capacitor filtering....
Like Tony said, there is no need for a separate switch. However, you must put a jumper wire between pwr_sw1 and pwr_sw2 pads.
up to about 400VA power traffo i would not recommend the use of soft start circuit at all, unless you are using a torroid and have tons of filter caps, about 40,000 or more....
if you are using a power switch rated for 15A, then no soft start circuit is required, again the exception is if using a torroid and that you have lots of filter caps....
in all cases, a Dale 10ohm/50watt aluminum clad resistor in series with you power traffos will do.....in addition, having a power switch rated for 15 amps or more is even better...
i have no idea how AndrewT derived his table values, he does not explain so it is useless....
a delay of about 3 seconds is all that is needed, and no need to be even too precise, 3.1 or 2.8 seconds won't really matter...
even for speaker time delay, a timing period of 4 seconds and up is enough to kill the turn-on transients(prevent it from reaching the speakers), 3.8, 5.5, or even 6 seconds hardly matter, no need to be too precise, the 555 timer lowers the parts count if you wish.....
Great question. The reason for this is that we want to give you the best prices possible. We pay a per-item packing fee to our fulfillment center, which means we can't really sell small, low value items without either adding that fee to each item and significantly increasing the price, or losing most (or all) of our profit.
We currently absorb that packing fee (we don't charge you packing fee at all, we pay it ourselves) and we also don't make any money on your shipping rate - what you pay for the shipping is exactly what we pay to USPS/UPS/Fedex/etc, plus you get access to our merchant preferred rates which are in most cases even cheaper than the public gets from those shippers.
Since both those boards are "related", rather than sell them separately and have to charge a lot more for each one, we opted to bundle them together and sell the pair at a more much more reasonable price to offer the best value for money possible. This is the same reason we sell most of our boards as two-packs or sets, instead of individually.
So, thanks for letting us know you are interested in purchasing the speaker protection board separately. We're always really interested to hear what you want and how we can be doing things better. We'll definitely give some thought to offering it separately in the future, especially if we grow and economies of scale help with our pricing models.
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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 ?
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 Andrew
The two transformers have their primaries connected in parallel to the mains.
The secondries are in series so I can get out + - 26AC with a center tap.
PS: Allready told you I always find your posts to be VERY helpfull
Can I use a 12v zener to feed the 12v relay ?
The two transformers have their primaries connected in parallel to the mains.
The secondries are in series so I can get out + - 26AC with a center tap.
PS: Allready told you I always find your posts to be VERY helpfull
Can I use a 12v zener to feed the 12v relay ?
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