aleph power questions

[AndrewT]

Originally Posted by slr 5000

.......to be able to get some 25/0/25 in 1kva

then buy 50-0, 50-0 1kVA.
take each output winding and half it to get four secondaries of 25-0.
Now you can parallel pairs of windings to get 1kVA 25-0, 25-0 with a rating of 5Adc continuous after applying the <=50&#37; de-rating for cool running duty.

Even better, rectify each winding and then parallel them to keep the heat dissipation in the rectifiers lower.

[Bill Fuss]

Originally Posted by slr 5000

hi guys
great so i understand (i think)

now re the capacitance ,so are you saying that the 108,000mf per rail i have is not enough ? i thought it would be fine
jeez looks like im going to need a chassis just for the caps themselves

re the toroid i cant find 30,0,30vac toroids in over 500va so im stuck there
i do have 2x 1kva 40/0/40 toroids but the voltage is too high too use unless i could cut it down to 30/0/30 somehow

hi bill so all i have too do to increase the bias is leave r13 out ?

regards sheafer

I never considered trying that, it will probably change the % of current contribution from the current source. Try replacing with a 500K trimmer set at 220K then slowly increase it watching the source R voltage drop. Alternatively you could lower all the source Rs. Just be aware you are deviating from the design parameters.

[Melon Head]

Originally Posted by slr 5000

id love to be able to get some 25/0/25 in 1kva for the project but there is just nothinbg available in that voltage over 500va in australia

your oppinions are aleays appreciated
regards sheafer

You can get any voltage and any va rating from this guy Manufacturer of toroidal TRANSFORMERS-Home page
And they are of top quality, and excellent price. I highly recommend them.

[slr 5000]

hi all
sorry andrew
i re read your post and you did make it clear

instead of buying more toroids what can i do to make my 1kva 40/0/40 toroids work ?

how can i drop the voltage down to 30/0/30
is there a reg i can make or buy that could handle the current or perhaps unwind some of the secondry,s (not my prefered option if possible)to get the voltage i want

ive got enough heatsink to just run the 40/0/40 voltage but this would mean running less bias
from what i understand it would sound better if i run a lower voltage and bias the hell out of it or am i way off here

regards sheafer

[MEGA-amp]

Originally Posted by slr 5000

how can i drop the voltage down to 30/0/30

You've been asking the same question for some time now; are you expecting a different answer? The simplest i.e. cheapest way to do this is via CRCRC type PSU. Just use big resistors. Or, in lieu of all that, you can use a variac.

[AndrewT]

Hi Slr,
open up the insulation around the secondary output leads.
Find out how many wires are used to obtain the 12.5A current rating.
Are they a bi-fillar 1.6mm diameter pair?

If so, then you have options that can retain the 1kVA rating AND get 30,0, 30-0 windings.

[slr 5000]

hi all
thanks andrewt
i will open her up and check it out tonight
it would be great if i could use them as the were very expensive

hi megaamp
i realise the simplest way may be the psu you suggested but i already have 2x aussie amps psu with 108,000mf each and they are very good
so i would be wasting money not using them

regards sheafer

[slr 5000]

hi guys
heres some pics of one of the toroids with its wrapping removed
i presume to lower the voltage from 40/0/40 to 30/0/30 i just have to unwind each secondary wire the same amount of turns untill i get the required voltage correct?

regards sheafer
oops forgot
the secondarys are single wire looks to be 2mm or more each

[AndrewT]

2mm diameter wire is unusually thick for toroid windings.
It is just 3.1sq mm. That has a current density of ~4A/sq mm.
This density is a bit high.
What is the regulation of this 1kVA? 4&#37; or 4.5%.

At a current density of ~3A/sq mm you would expect ~3.5% regulation for 1kVA.

If you remove turns from this transformer you will reduce the VA rating, making the regulation even worse.

[slr 5000]

hi andrew
the secondarys are made up of 2x 500va each
regulation is 5%
12.5 amp
wire dia is at least 2mm but that is going by eye the data sheet does not specify
brand is nuvotem talema 1kva 40/0/40 from rs components

regards sheafer