Looking for a good +/-15v diff power supply

[stanwax]

Cheers Dave

I thought that would be the case.

Rob

[buffo]

To expand on this idea...

If you have a pair of power supplies you want to tie together and you notice that there is a potential difference between the two respective grounds, there is a quick and easy way to test if the difference is just due to "float", or if it's a genuine voltage difference that you need to be mindful of.

Simply connect the two points in the circuit with an insanely large resistor. (10 meg ohm ought to do it!) Now power the circuit up and measure the potential between the two power supplies (across the resistor). If one of the circuits was floating, it should drift down to end up at the exact same potential as the other. (Despite the fact that 10 meg ohms is a *shitload* of resistance, any connection between the two circuits, even a high resistance one, is enough to bring the voltages back together.)

On the other hand, if there really was a valid potential difference between those two power supplies (and not just a phantom floating voltage), then you will continue to measure the same potential across the resistor. But since the resistance is so high, there isn't going to be any appreciable current flowing between the two circuits, so there's no danger of frying anything. (On the other hand, conencting the two points with a jumper wire would create a dead short in this case, which might be the end of one or both of the power supplies.)

If you don't have a 10 meg resistor, you can probably get away with a 1 meg, or even a 100Kohm resistor. You just want some resistance in the jumper between the two points so that in the unlikely event that you've really goofed, you still won't blow anything up.

Remember that for the most part, ground is what you call it - so long as the circuit is *isolated*.

Adam

[SpyroS]

Hey hey hey i'm no spammer! People chill! Thanks for the insult lol

[stanwax]

Hey hey hey i'm no spammer! People chill! Thanks for the insult lol

You are welcome - and you should here some of the things I say about myself!!!

Rob

[shobley]

Buffo - that's good to know.

On the advice of Dave I just connected the grounds

- and made sure I was about 5' away before switching on


- it seemed to be OK.

[greenalien]

A few comments on the circuit shown at http://www.generalguitargadgets.com/...bipolar_ps.pdf

1) For a few pence extra cost, the 2 diodes could be replaced by a bridge rectifier for smoother full-wave rectification
2) I'd make C1 and C2 a bit bigger - 2200uF each
3) I'd definitely put fuses in the transformer primary circuit and the ac feed to the rectifier
4) I'd also change the capacitors around the voltage regulators - I'd use 0.33uF for C3, 2.2uF for C4 and 1uF for C5 and C6, based on the values shown in the data sheets for the Voltage Regulators - that's assuming that the voltage regs are 7815/7915 for a +/-15v supply.

(as it happens, I just ordered the parts to build one of these, to power a couple of GM20s)

The parts for this come to under £20, the cheapest Switch Mode supply that I could find was twice as much...)

[stanwax]

For cheap SMPS I use laptop supplies. Expensive if new but I bought 2 pairs of matched laptop supplies from my local computer fair - each one was £8 and they looked brand new. I opened up the cases hard wired the mains and low volts - inc joining the +ve to earth on one of them (after removing it from the 0v ) and now have 2 pairs of +/- 19v supplies at 4A. They are light compact and power my G120s a bloody treat!

Rob

[legato]

Does anyone have for sale a differential power supply capable of putting out a good clean +/-15v (100mA min) with a central ground not too far away from 'earth'.?

I have one but the ground is shifted by about 10v and it's creating problems when connecting it to my data acq box.

Hi,

I have one and it's a kit you build yourself. Easy to do. It can go up to 1.5A depending on the transformer you use. Let me know what you need exactly in terms of current and I'll write you quote.

Send email to legato@videotron.ca

To get an idea of what it looks like go see eBay, seller ID eKitForAll. I usually have it there for sale. The listing may say 100mA max, but I can provide you higher current without problem.

Cheers,
Norm

[edison]

Need a good supply? try this i think this is pretty good i think.

http://www.elecfree.com/circuit/powe...-ic-7815-7915/

Maybe something for the FTP server?

[allthatwhichis]

That was a big ass shovel you must have used to dig this old ass thread up with. Must be browsing the archives; interesting Saturday night activity... I know you got better things to do; maybe a pimp ass projector to work on...