A challenging project....1500va toroidal power

[Alexontherocks]

Hello everyone. I have posted in the past regarding some new parts to use in a build. Things however changed in my professional life so I set the project aside for some time.

In the last 2 weeks I have however got back to it and here is the basic characteristics of it all:

3x500va toroids 36 -18 -0 -18 -36v

900 000uf cpacitors in series (small/medium and huge 40000uf caps).

secondary transformer for Softstart (QUASI design).

2 searate containers. In th first the power system, in the second the 6 nmos200 channels each with a DC protect circuit.

For now I have built only 2 channels and the common cd protect circuit.

Here are the pics



and



problems so far:

I keep blowing fuses. Th softstart works apparently but obviously the capacitors are a huge load on the transformers.

I would like to ask a couple of questions:

a) is there a a ready to print pcb, layout and all to get a slow start in order to avoid the problem I mentioned?

b) Are thermistors good enough? If yes, given my current setup, how would you guys go about installing them?

The resistor of quasi's softstart is hidden because it is bolted on the frame to guarantee best thermal contact and dissipation.

Please help. I Believe the project can work quite well but I have to resolve this mess with the transformers...

Thanks
Alessandro

[AndrewT]

three 500VA transformers.
Fuse each one separately. With a master fuse at the mains input (IEC) socket.

Soft start with delayed bypass.
A single Power Thermistor soft start can be used to start up all three transformers.
A CL60 is OK for a single 110/120V primary. Two primaries in parallel require a CL60 in each primary circuit. Do not parallel the CL60s.
A CL60 for a 240Vac primary does not provide sufficient resistance to significantly reduce the start up current. Use two CL60 in series for 220/240Vac supplies.

Disconnect all three transformers from the mains. Check with a bulb tester to help find wiring errors before direct powering from the mains. Then test each one in turn after you have proved the wiring is OK.
Next try two transformers on your two CL60 current limiters. Finally try three transformers on your two CL60 current limiters.

[Alexontherocks]

Thanks Andrew. Wiring should be okay but I will check.

The cpacitors act as a true shortcircuit. I was unfamiliar with this sort of behaviour. I have never used so many and witch such high values.

Stupid question. The thermistors should be positioned in series after the sofstart?

Thanks!

[tinitus]

ehhh, no outer isolation on supply caps, it appears
and looks like some are touching each other
if so, that might be a major problem

anyway, you amp boards looks like relative small output power, thus doesnt need a 1500watt supply
unless you want to use for low impedance load
but with highish 36Vac, they are probably not fit for anything lower than 4ohm
so, you have no use of that much power
I would rather consider double mono, each channel with one of those trafos
and use the third for something else

some times(often) simplification is the winner

[vijay_meyou]

Hi ,
if you connect the capacitors with different voltage range and different values in series it will blow the fuse as huge current will flow and act as short circuit.

i one experienced this issue in one PC smps one of the 2 220 mfd 250v capacitor was bulged and leak i replaced with 150 mfd 220v volt and powered on imedieately it busted with huge flash

vijay

[Alexontherocks]

I have drilled holes and connections and have space for 8 modules for a 7.1 system. Each can drive 200w in 4 ohm speakers (theroretically)

Anyway I will insulate the cans. I purchased them used but were in working order.

Is the solution described by Andrew good enough to avoid any caps bursting?


Cheers

[smartx21]

Originally Posted by Alexontherocks

I purchased them used but were in working order.

Well, the question is: how old are they? You should do intensive testings for each one, separetely. Every time I try to reuse old electrolytics I find lots of unusable ones, for small or large defects.
All the best.
Max.

[Alexontherocks]

not sure but they charge and discharge correctly and each passes (by not showing) the continuity test. I am unable to test for capacitance.


I really hope I can get this power unit working because the rest is fairly straight forward.

All the bodywork and cabling has been done and looks very very neat.

So far I understand the only viable solution is to insert 2 Cl-60 in series after the sofstart circuit.

Basically a slow start after the softstart. Correct?

[Bonsai]

Alex, why do you need all this filter capacitance?

[Alexontherocks]

Well several reasons

1) I got all those caps for very little over several months (100 euros max for all)

2) I would like to power 6 to 8 nmos200 modules in order to have a definitive system for a 5.1 to 7.1 system

3) I like the challenge.

Pure class A amplifiers do have a lot of capacitance ....I would think more than I have. I have a thing for huge/inefficient machines...this seemed a good way to go around building one.