EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: rthorntn on October 23, 2012, 08:35:50 am
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G'day,
I have two chinese ps305d bench supplies and I want to create +/-15v and gnd.
Am I right in thinking, I:
Connect negative on PSU one to ground on PSU one
Connect negative on PSU two to ground on PSU one
Connect positive on PSU one to positive on my item
Connect positive on PSU two to negative on my item
Can I connect ground on the psu to ground on my item?
Obviously I will measure it first.
Cheers
Richard
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fisrt things first, are the outputs isolated? if yes, then
yes you can link ones negative to the others positive and use the center junction as your circuits ground, with + and - around it,
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Thanks rerouter,
How do I confirm they are isolated?
If I can confirm isolation, can you break down the connection required to make +/-/ground
Psu1
+ connects to ?
- connects to + on psu2
Gnd connects to ?
Psu2
+ connects to - on psu1
- connects to ?
Gnd connects to ?
What is a centre junction, do I need extra cables/connectors?
A diagram would be amazing, if someone can chime in :)
Thanks.
Richard
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ok, if each supply has a ground terminal (probably green) seperate from negative then it is probably safe to assume its isolated,
you would leave those ground terminals disconnected on both,
PSU1:
+ goes to your circuit +
- goes to your circuit ground
PSU2:
+ ties to PSU1 -,
- goes to your circuits -
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To see if they're isolated, check resistance between the ground socket on the power supply and its earth pin on its wall plug, or just plug them both in and check between the grounds. If it is isolated there will be no connection between them, you may also want to check while they are on (between their grounds) just incase. If it has green earth terminals it is probably isolated also.
if they are isolated;
psu 1 psu2
(+)(-)---------(+)(-)
v+ 0v 0v v-
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Thanks boys, the psu has three terminals on the front, as a quick check can confirm continuity with my fluke between the gnd on the front and the earth pin on the IEC socket?
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he meant the negative, the green earth terminal should be tied to mains earth, but for an isolated supply the negative should not,
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Doing a continuity check between the earth pin on the power cable and negative on the front, no beep.
Doing a continuity check between the earth pin on the power cable and ground on the front, beep.
So it's floating.
Thanks guys.
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Thanks guys, so I cabled it up, if I measure the voltage by clipping the + terminal on PSU1 and the - terminal on PSU2, I get 30v is that correct, come to think of it I am basically measuring it in series that way :)?
Which terminals would I measure to see -15v, or is that not possible?
I just want to confirm it's ok before hooking it up to the board?
Thanks again.
Richard
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+ of your meter to where the 2 supplies are joined, and - to the negative of PSU2
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Thanks rerouter
So I cabled it like you said:
PSU1:
+ goes to your circuit +
- goes to your circuit ground
- goes to + on PSU2
PSU2:
+ ties to PSU1 -
- goes to your circuits -
So in the above config - on PSU2 to + on my fluke and - on PSU1 to - on my fluke gives me -15v
So to confirm, should I be good to go:
PSU1 + to circuit +15v
PSU1 - to circuit gnd
PSU2 - to circuit -15v
Richard
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Which terminals would I measure to see -15v, or is that not possible?
Any time you want to see -15 V instead of +15 V just swap over the positions of the red and black test probes when you are measuring. Which is another way of saying -15 V and +15 V is just what you make of it.
For your test setup you will put the two power supplies in series, so that the red terminal of #1 is connected to the black terminal of #2 (this connection is your common, or 0 V point in the circuit). To measure voltages, place the black meter probe at this middle point, then while leaving it there move the red probe from one side (black of #1) to the other (red of #2).