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Old 22nd February 2002, 09:09 AM   #1
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Question PSU Capasitors for Aleph 2

I am sorry if this has been answered before, but I could not find anything so here goes.

Aleph 2 needs approx 35volt secondaries to produce 45 voltage rails. I presume 50 volt capasitors in the PSU should be sufficient, but I just want to be sure.

So, would 4 x 31000uF / 50volt be ok?

I`ve got a good deal on some Rifa PEH169 31000uf / 50volt caps and just wanted to check before i place my order.

Thank you in advance.
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Old 22nd February 2002, 09:53 AM   #2
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Default PSU Capacitors for Aleph

Salmacis,

This issue was covering in a previous thread.

However to answer your question yes the rifa are a very nice capacitors but you need to assess the maximum surge voltage and working voltage. (check the tech sheets on your caps)

For example you need to factor in the maxium mains voltage variations.

If the normal voltage under load is 45+- DC, then if the maximum peak increase on the mains was say say 10% then the dc voltage could be approaching the max operating voltage of your capacitors. (50 Volts)

You also need to add this the ripple voltage on top of the nominal dc voltage. I do not have the formulae handy for this.

The DC voltages need also to be calculated for the regulation of the transformer (no load vs full load) and allow for rectifier losses.

Typicially diode loss are 1.5 volts and assuming 3-4% regulation then this would give say 45 + 1.5 (for rectifier losses) =46.5 volts/1.414 =32.88 vac for the under load voltage of the transformer.

Yet another issue is the rating of the transformer, as a rule go for 2.7 times the maximum load, so for the Aleph use a 750 VA or preferable 900 va transformer.

So 35 volt AC secondaries may be a bit high for your 50 volt dc capacitors (ie 49 - 1.5 = 47.50 ) if we were to allow for 10% mains variations.

In my Aleph 2 project I am using plenty 15,000 uf 63 volt capacitors for safety and 900 va toroidals (33 + 33 volt ac secondaries)

Please do not however take my word for this and I suggest you check some good sites like Rod Elliotts DIY pages for a thorough analysis of power supply design.

best regards

macka
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Old 22nd February 2002, 10:38 AM   #3
hifi is offline hifi  Sweden
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one 900VA for one channel or both?

/micke
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Old 22nd February 2002, 11:07 AM   #4
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Thumbs up Rifa

The Rifa are exellent caps and I don't think you should have any problems. Check out aps notes at:

http://www.evox-rifa.com/n_america/e...ic_cap_cat.htm

H.H.
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Old 22nd February 2002, 02:24 PM   #5
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Micke,
At 300W of power consumption a 900W transformer only get you a channel...
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Old 22nd February 2002, 05:13 PM   #6
hifi is offline hifi  Sweden
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ok..nice....i got 2pcs of 900VA Audio rated custom torids from TOROID ;-)

and a couple of PEH169/47mF/63V and some 1.1mH coils for my aleph 2.60 ;-)

i just hope i got enugh cooling 2pcs of 30x30x4cm alu with 1x6x30cm solid copper bars for heat distribution from the mosfets... (the cooling is per channel)


/micke
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Old 22nd February 2002, 06:15 PM   #7
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Default Power supplies

Supply for preamp I am building. Piltron 225VA (2x18V secondary) transformer, 10,000uF Rifa PE169, Harris FRED soft recovery diodes, and 4 mH aircore choke. I am using two secondary winding with two diodes for full wave rectification. Most parts are surplus and I have about $50 of parts in it. It pays to shop around surplus. This would have cost twice this for new parts at retail outlets. There are more of the tranformers availible in anyone is interested.

H.H.
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