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Need help for 220 V to 120 V PS conversion

L

Lorne

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Jul 27, 2008
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Location
Chandler, AZ, USA
I just obtained an Altos 8000-1 from Australia.
It works on 220 V, 50 Hz.
And of course, I need it to work on 120 V, 60 Hz.

I've opened up the case and I think the power supply (transformer) might work on both voltages (although not via a switch).

I've attached a copy of the power supply schematic diagram, and a photo of the power supply wiring connections.

View attachment 1162

View attachment 1163

I think what I need to do is remove the connector that is between pins 2 and 3, and then take one of the white wires that is presently connected to pin 1 and connect it to pin 2.

Am I on the right track?

I'm no elecrician, so I want to make sure I've interpreted the schematic correctly before I screw it all up (which would be the usual course of events).

Is there anyone out there who can confirm my thinking, or point me in the right direction, if I've got it all wrong?

Thanks in advance.
 
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The markings on the transformer and the schematic are telling us this:

Line in *always* on pins 1 and 4

Link pins 2 and 3 for 230v operation.

Link pins 1,2 and separately 3,4 for 115v operation. Remove link from 2,3.


I will confirm this tomorrow (Sunday) by checking a few industrial dual-voltage control transformers where I work. The vast majority of dual-voltage transformers work in this manner.

Kent
 
Kent:

Thank you very much!
I'm glad I asked for assistance.
I now see what you were reading in the schematic.
The same jumper I see on the actual transformer for the 220V setup, is shown in two different locations on the diagram for the 120V setup.

The jumper for the 220V looks like steel or aluminum.
It should be OK to use copper shouldn't it?
And something like the same gauge as house wiring to a power receptacle?

Thanks again.
 
Transformer

Transformer

The idea is to get the series connected windings into a parallel configuration.
I can't tell from the schematic, the numbers are too small for me to make out.
The winding resistance in parallel should be double of the series configuration.

patscc
 
Windings

Windings

Much better, thanks. I agree, it looks like 1 & 2 , 3 & 4.
Lorne said...doesn't matter if the line voltage goes to 1 or 2, or 3 or 4 does it?
Click to expand...
No, since 1 & 2 are connected together (or will be ), anything going to 1 will go to 2 as well.
If possible, I'd disconnect the power supply from the rest of the computer, just in case, this way you can double-check the voltages.

patscc
 
That black wire on 3 goes to a fan, right?

If so, then:

  • Leave the white wires where they are.
  • Leave the black wires were they are.
  • Remove the jumper between 2 and 3
  • Connect 1 and 2
  • Connect 3 and 4

So, at the conclusion, you'll have:
  • Terminal 1: both white wires and a jumper to terminal 2
  • Terminal 2: A jumper to terminal 1.
  • Terminal 3: A black wire and a jumper to terminal 4
  • Terminal 4: A black wire and a jumper to terminal 3

I've got a couple of open-frame PSUs that have the same markings.
 
Chuck(G) said:
That black wire on 3 goes to a fan, right?
Click to expand...

Probably, but I really have no idea where the wires go ! I had a tough enough time taking it apart to even see the transformer. These things are built tough. It's a pain in the butt to get into them. I want to get it back together asap, before I forget where everything goes.

I've got it now - I know what I've got to solder.
Thanks for your help guys - it's much appreciated.
 
Fan

Fan

Lorne said:
And yes, I'm happy to reply that it does go to a fan.
Click to expand...
You will have a 240 Vac fan running at 115 Vac. Maybe in that situation, the fan will not blow enough air to do the job it's meant to do. Probably prudent to replace the fan with a 115 Vac version.
 
patscc said:
If possible, I'd disconnect the power supply from the rest of the computer, just in case, this way you can double-check the voltages.

patscc
Click to expand...

Yes, I was going to suggest this myself. Better to be safe than sorry.

Tez
 
The black wire going to the fan is connected to 2-3 when running at 220vac; the other wire is connected to 1. Since, on 220vac operation 2-3 represents the center tap of two series-connected primaries, a 120vac fan is used (you can check the nameplate on the fan, but I'm certain).

No fan replacement needed. This was a nice "trick" that was used in the days before SMPSUs. After that, manufacturers started using DC fans. The 5150 PSU is a notable exception--AC fan attached to the SMPSU.

That came as a surprise when we ordered a bunch of 5150s to send overseas (before the 5150 had made its debut on the Continent). The IBM sales office swore that the US systems couldn't be used on 220 vac--and they were right. But it wasn't because the SMPSU couldn't be jumpered for 220 volts--it was the fan! We bought them anyway and swapped the fans in the PSUs. They worked fine, as far as I know, even with the red "warranty" stickers broken.
 
I removed the one jumper, and added the other two.
It worked fine (and the fan blows loads of air too).

Thanks guys - I'm going to add some of you to my elec troubleshooting Rolodex !
 
Follow up question:

I just noticed the following inside the Altos:
View attachment 1171
View attachment 1172

I've got the disk drives spinning and the fan working, but will the other pieces work correctly? IE: did changing the voltage at the transformer allow everything to work as 115 V, or do I now have a parts machine? (And one that I can't even use all the parts from).
 
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Lorne said:
Follow up question:
I've got the disk drives spinning and the fan working, but will the other pieces work correctly? IE: did changing the voltage at the transformer allow everything to work as 115 V, or do I now have a parts machine? (And one that I can't even use all the parts from).
Click to expand...

I was going to ask about disk drives.

Short answer: No, the drives won't work, even if they do spin. Not only is the voltage wrong on the drive motors, but the pulley-and-belt setup is spec-ed for 50 Hz. Even if you put 240vac 60Hz power on these motors, the floppy would spin at the wrong speed.

The simplest thing is to replace the drives. The next simplest thing is to replace the drive motors and the drive pulley. The least simple thing is to run the motors off of 240vac (via a step-up transformer) and replace the drive pulley.
 
For my donated American IBM-PC (115v) I bought an inexpensive step-down transformer so I could run it off the 240v mains.

Is there such a thing as a step-up transformer which will boost 115v to 240v? If so, the simplist thing might be to just leave things as they are and buy one of those?

Tez
 
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