P.S.U “POWER UNIT EST20” from Power electronics (London) LTD 15 volt to 13.6 conversi - UK Vintage Radio Repair and Restoration Discussion Forum

short wave · 15th Oct 2013, 2:59 pm

I have one of these units (15 Volt says the dyno tape sticker) .The unit I assume is capable of supplying 20 Amps , 2X small mcb on front of unit . The unit measures 6.5” x 8.5” x 16.5”. It has a crowbar fitted . Main O/P tx are 2N3055s and main pcb/driver pcb has six 2N3053 on it . An interesting thing is all the O/P txs are in pairs and each pair is on a removable card , ideal if one goes S/C for fault finding. The unit is nicely laid out for servicing /access to components but suffers from dry joints (2 so far on rect stack.... actual lack of solder, havn`t looked as yet under
pcbs for others!)
The company “Power electronics (London)LTD “ now no longer trade.

Question is has any one a schematic or manual? as I wish to wind it down to 13.6 Volts (the preset wont quite do it).

Regards S-W (Andrew)

Herald1360 · 15th Oct 2013, 10:05 pm

Are there any helpful fixed resistors either side of the preset one's track? If so, making one higher and the other lower by the same amount will shift the control range either up or down a bit which may sort it.

Bear in mind that if it's linear, the output devices will now dissipate more at a given output current than before- it would be worth a check to see what their Vce is at the nominal 15V output and full current. Add 1.4V to that figure to see how much to derate max current by to get the same dissipation. In a typical scenario there may be say xV Vce- increasing this to yV means you need to derate current by x/y.

Or blow a fan over the heatsink!

Humber888 · 16th Oct 2013, 3:39 pm

Andrew, I have an EST20 which will go down to 13.5V on its front panel preset. On the front is written 13.8V @ 35A so your initial guess at current may be wrong. Having said that, I don't think I've ever had a big enough load to prove it!

I have some sheets of circuits and components for the EST20A. There may be slight differences but probably not many. It looks like these were copied from a full handbook as the page numbering goes 3, 4, 5, 19, 20. Hand written on one sheet are notes that say RV1 sets coarse voltage, RV2 sets f.s. current (up to 40A) and RV3 sets the foldback current. Someone here may have the full handbook which would be very useful; failing that I can scan what I've got and email it to you.

How do the big Daly 5000uF electrolytics look on your unit? One of mine has a small bulge on the rubber vent, although the unit was working fine when last used. Still, I'd check them for capacitance and ESR if you plan the really thrash the unit.

Mike

short wave · 16th Oct 2013, 6:05 pm

Thankyou "Herald1360" Chris and "Humber888" Mike.
The idea of modding the resistors on either side of the pot was an idea (will most likley get it to increase first rarther than reduce!!.. S**`s law) Info on dissipation useful ,2N3055 should be ok from memory about 45-50 volts and 125 watts dissipation -subject to temp. As i have a quantity of old ATX fans they may get used! Its O/P could power them!!
Mike, your sheets will be useful. I will send you a PM.
The capacitor "bank" takes up about 1/3 of the space total of 9 cans in a 3x3 block. I put the unit on a "variac" to power up as precaution,as its history was not known.
Regards S-W Andrew

Herald1360 · 17th Oct 2013, 12:50 pm

Quote:

Originally Posted by short wave

Info on dissipation useful ,2N3055 should be ok from memory about 45-50 volts and 125 watts dissipation -subject to temp.

Err, no chance. On a fan cooled heatsink, you might squeeze about 30W into a 3055. On a water cooled plate maybe twice as much. My forgettory says 115W Ptot @ 25C case temperature. Add a few C/W between case and ambient and the rating comes well down.

We used hundreds of MJ15024 and 2N6259 "250W" TO3s in days of yore and about 40W aircooled and 90W water cooled was as far as we were happy!

Humber888 · 17th Oct 2013, 2:12 pm

Looks like the pdf file of EST20 information is not too big to upload, so here is what I have. If anybody has the full handbook, this might give information on setting the unit up for different output voltages.

Mike

short wave · 17th Oct 2013, 5:16 pm

Thankyou for your info about max dissipation.
Mike it looks like the "bizz".I thaught the M.C.B. were to fully protect the O/P, seems to be used to protect the dual secondarys. I will start with the "voltage question " first as origionaly posted, then I will have to try and load the PSU up and see what the max current might be.The big Daly 5000uF electrolytics (70 working volt on my unit) don`t seem to have any vents.The bases are flat card/plastic and appear in as new condition . Regards S-W Andrew

15th Oct 2013, 2:59 pm	#1
short wave Pentode Join Date: Mar 2013 Location: Leeds, West Yorkshire, UK. Posts: 246	P.S.U “POWER UNIT EST20” from Power electronics (London) LTD 15 volt to 13.6 conversi I have one of these units (15 Volt says the dyno tape sticker) .The unit I assume is capable of supplying 20 Amps , 2X small mcb on front of unit . The unit measures 6.5” x 8.5” x 16.5”. It has a crowbar fitted . Main O/P tx are 2N3055s and main pcb/driver pcb has six 2N3053 on it . An interesting thing is all the O/P txs are in pairs and each pair is on a removable card , ideal if one goes S/C for fault finding. The unit is nicely laid out for servicing /access to components but suffers from dry joints (2 so far on rect stack.... actual lack of solder, havn`t looked as yet under pcbs for others!) The company “Power electronics (London)LTD “ now no longer trade. Question is has any one a schematic or manual? as I wish to wind it down to 13.6 Volts (the preset wont quite do it). Regards S-W (Andrew)

15th Oct 2013, 10:05 pm	#2
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: P.S.U “POWER UNIT EST20” from Power electronics (London) LTD 15 volt to 13.6 conv Are there any helpful fixed resistors either side of the preset one's track? If so, making one higher and the other lower by the same amount will shift the control range either up or down a bit which may sort it. Bear in mind that if it's linear, the output devices will now dissipate more at a given output current than before- it would be worth a check to see what their Vce is at the nominal 15V output and full current. Add 1.4V to that figure to see how much to derate max current by to get the same dissipation. In a typical scenario there may be say xV Vce- increasing this to yV means you need to derate current by x/y. Or blow a fan over the heatsink! __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

16th Oct 2013, 3:39 pm	#3
Humber888 Heptode Join Date: Jul 2012 Location: Bromley, London, UK. Posts: 702	Re: P.S.U “POWER UNIT EST20” from Power electronics (London) LTD 15 volt to 13.6 conv Andrew, I have an EST20 which will go down to 13.5V on its front panel preset. On the front is written 13.8V @ 35A so your initial guess at current may be wrong. Having said that, I don't think I've ever had a big enough load to prove it! I have some sheets of circuits and components for the EST20A. There may be slight differences but probably not many. It looks like these were copied from a full handbook as the page numbering goes 3, 4, 5, 19, 20. Hand written on one sheet are notes that say RV1 sets coarse voltage, RV2 sets f.s. current (up to 40A) and RV3 sets the foldback current. Someone here may have the full handbook which would be very useful; failing that I can scan what I've got and email it to you. How do the big Daly 5000uF electrolytics look on your unit? One of mine has a small bulge on the rubber vent, although the unit was working fine when last used. Still, I'd check them for capacitance and ESR if you plan the really thrash the unit. Mike

16th Oct 2013, 6:05 pm	#4
short wave Pentode Join Date: Mar 2013 Location: Leeds, West Yorkshire, UK. Posts: 246	Re: P.S.U “POWER UNIT EST20” from Power electronics (London) LTD 15 volt to 13.6 conv Thankyou "Herald1360" Chris and "Humber888" Mike. The idea of modding the resistors on either side of the pot was an idea (will most likley get it to increase first rarther than reduce!!.. S**`s law) Info on dissipation useful ,2N3055 should be ok from memory about 45-50 volts and 125 watts dissipation -subject to temp. As i have a quantity of old ATX fans they may get used! Its O/P could power them!! Mike, your sheets will be useful. I will send you a PM. The capacitor "bank" takes up about 1/3 of the space total of 9 cans in a 3x3 block. I put the unit on a "variac" to power up as precaution,as its history was not known. Regards S-W Andrew

17th Oct 2013, 5:16 pm	#7
short wave Pentode Join Date: Mar 2013 Location: Leeds, West Yorkshire, UK. Posts: 246	Re: P.S.U “POWER UNIT EST20” from Power electronics (London) LTD 15 volt to 13.6 conv Thankyou for your info about max dissipation. Mike it looks like the "bizz".I thaught the M.C.B. were to fully protect the O/P, seems to be used to protect the dual secondarys. I will start with the "voltage question " first as origionaly posted, then I will have to try and load the PSU up and see what the max current might be.The big Daly 5000uF electrolytics (70 working volt on my unit) don`t seem to have any vents.The bases are flat card/plastic and appear in as new condition . Regards S-W Andrew