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SjoerdSmits 27th January 2013 10:26 AM

Huge voltage drop on PSU
Hi All,

I get a really large voltage drop when I connect the amps to the SPS01 power supply. NEG-Ground = -17VDC and POS-GROUND= 22VDC

Unloaded the voltages are 33VCD.

I have a toroid from Amplimo whitch provides 2 x 25VAC at 10 Amps.

I mounted rectifiers: 8x MOSPEC U30D20 rectifiers. The datasheet of these rectifiers state that the operating voltage should be between 50 and 200V. I supply 25VAC.

So I see 2 strange things:
1: It takes upto 3 minutes for the SPS01 to go from 0 to 33VDC.
2: When load is applied, the voltages drop dramaticly to 17 and 22 VDC.

Question: What could be the problem?

Kind regards,
Sjoerd Smits

wintermute 27th January 2013 10:46 AM

Have you got for smoothing capacitors? If so Are you using a CRC or just C Also how large are the capacitors? if you are using CRC, what is the value of the resistor and how much current is the amp drawing?

edit: the 50 - 200V rating is for the different models. the U30D05 model has a maximum of 50V, the U30D20 has a maximum of 200V.


SjoerdSmits 27th January 2013 10:56 AM

Capacitance: 22000
Lower Cap Tolerance: 20
Upper Cap Tolerance: 20
Working Voltage: 63
Surge Test Voltage: 72.5
Terminals 2 PIN SNAP-IN
Other Dimensions
Rated ripple current 10.5 A rms at 100 Hz and 85
Diameter (mm) 40 -0/+1
Length (mm) 80 +/-2
Temperature range -40 C to 85

There are 8 of these on the PSU...

SjoerdSmits 27th January 2013 10:58 AM

They are Slit Foil....

I mounted the U30D20

SjoerdSmits 27th January 2013 10:59 AM

I Measured the amp idle. Nothing connected to it... Do you think the slow power up is strange?

Mooly 27th January 2013 11:04 AM


Originally Posted by SjoerdSmits (
I Measured the amp idle. Nothing connected to it... Do you think the slow power up is strange?


Measure the AC voltage to the rectifiers during start up and maybe post some pics of the set up.

SjoerdSmits 27th January 2013 11:07 AM

Where do I post pictures?

AC Voltage is steady at 25VAC....

KatieandDad 27th January 2013 11:11 AM

Check wiring and orientation of components very carefully.

You have either (1) A Mistake, (2) A High Resistance or (3) A Short.

I've seen this when one cap is inserted Back to Front.

wintermute 27th January 2013 11:11 AM

88,000uF per rail is quite a bit and would take a while to stabalise but 3 minutes to reach 33V seems excessive.

I'd check that you don't have a high resistance joint on the secondaries, where they are connecting to the PS board. It seems like you have some significant resistance somewhere in the circuit. If you know what the resistance of your secondaries are, then try measuring it on the board at the rectifier AC pins (make sure it has properly discharged first though).

edit: Also as AndrewT always asks, are you using a light bulb tester?


SjoerdSmits 27th January 2013 11:14 AM

Resistance on both AC1 and AC2 is 3,92Mega OHM..... Both the same.. is that too much?

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