PH smoothing unit BNIB

[Nick Mitchener]

These are absolutely brilliant. They turn our half wave rectified mains supplies into dead flat lines on a CRO.
I have bought two, there are two left £10 each plus £6 carriage

UNILAB Power Smoothing Unit... Final Reduction. | eBay UK

Final Reduction to £13.

www.ebay.co.uk

 

[Zoology Dragon]

half wave rectified mains supplies

Given how cheap diodes are to make a full wave rectifier, I wonder why these are even made?

 

[Alman]

Given how cheap diodes are to make a full wave rectifier, I wonder why these are even made?

Full bridge rectifiers are for AC -> DC typically, this was intended for unsmooth DC supplies.

 

[Andrew Symonds]

I have some of those, very useful if you use unregulated power supplies with some data logging equipment and as you say great with a CRO, always worth using them to do the SHC experiment to see what happens to the results too.

 

[Zoology Dragon]

Full bridge rectifiers are for AC -> DC typically, this was intended for unsmooth DC supplies.

A full bridge rectifier will give unsmoothed DC from both halves of the cycle, a half wave only gives you a single side of the cycle:

 

[Wobbly John]

I already have one of those, and the older Unilab one. We used to use it for lots of things like the Helmholtz coils, etc, but the current teachers don't think it's necessary.

Most of our power supplies (such as the Unilab J link ones) are full wave rectified, but my workbench J link one has a smoothing capacitor (which looks factory fitted) - this can make it confusing when you switch off low current devices such as LEDs...

 

[Nick Mitchener]

I already have one of those, and the older Unilab one. We used to use it for lots of things like the Helmholtz coils, etc, but the current teachers don't think it's necessary.

Most of our power supplies (such as the Unilab J link ones) are full wave rectified, but my workbench J link one has a smoothing capacitor (which looks factory fitted) - this can make it confusing when you switch off low current devices such as LEDs...

We have just ordered a second one. We use batteries a lot for both KS4 & KS5 but particularly KS5. We mainly use power supplies when we want AC or higher currents. this will give me a nice smooth DC output for those higher current applications like the Leybold tube and some of the KS5 demos. Up till now I have used a rechargeable 12V battery.

 

[Alman]

A full bridge rectifier will give unsmoothed DC from both halves of the cycle, a half wave only gives you a single side of the cycle:
View attachment 21674

Yes I understand, but the image you provided isn't 'smooth' DC though; just rectified. If you were to pass an unsmoothed DC voltage through a FBR it will produce the same output. A LC circuit smooths it out, therefore a FBR is unsuitable for DC -> DC.

 

[Zoology Dragon]

Yes I understand, but the image you provided isn't 'smooth' DC though; just rectified. If you were to pass an unsmoothed DC voltage through a FBR it will produce the same output. A LC circuit smooths it out, therefore a FBR is unsuitable for DC -> DC.

View attachment 21675

The OP (Nick M) mentioned that he has half-wave rectified supplies. I was simply wondering why the power supplies weren't FBR given how cheap diodes are.

 

[Nick Mitchener]

The OP (Nick M) mentioned that he has half-wave rectified supplies. I was simply wondering why the power supplies weren't FBR given how cheap diodes are.

The OP is an OAP with few grey cells left. I should have said FBR, they all use the potted block one you see everywhere. No smoothing on our supplies but the smoothing unit plus an unsmoothed supply is an improvement on most smoothed supplies anyway.

 

[Alman]

The OP (Nick M) mentioned that he has half-wave rectified supplies.

I totally missed that, I understand the confusion now.

 

[Wobbly John]

BTW, when I gave the new grey PH spacesaver smoothing unit to a physics teacher who used to use the black Unilab smoothing unit, he asked where the power lead was...

 

[HatMan]

I always use one on the dc when using a deflection tube and helmhotz - the beam is "focussed" instead of turning into a smear at the end ...

 

[Zoology Dragon]

I always use one on the dc when using a deflection tube and helmhotz - the beam is "focussed" instead of turning into a smear at the end ...

On the heater voltage?

 

[Nick Mitchener]

On the heater voltage?

I think the Helmholtz. I saw this on the Leybold which needs rather more than the batteries I have so I used a mains supply. I think the smoothing unit will make a big difference there.

 

[Zoology Dragon]

Ah, that makes sense.

 

[Phystech]

These are absolutely brilliant. They turn our half wave rectified mains supplies into dead flat lines on a CRO.
I have bought two, there are two left £10 each plus £6 carriage

UNILAB Power Smoothing Unit... Final Reduction. | eBay UK

Final Reduction to £13.

www.ebay.co.uk

I use a big capacitor, to demonstrate smoothing. Other than that, we use regulated PSU's. Does anyone want some Philip Harris bench PSU's? We're getting rid of ours.

 

[Nick Mitchener]

I use a big capacitor, to demonstrate smoothing. Other than that, we use regulated PSU's. Does anyone want some Philip Harris bench PSU's? We're getting rid of ours.

freebies always accepted

 

[Technician Q]

I think the Helmholtz. I saw this on the Leybold which needs rather more than the batteries I have so I used a mains supply. I think the smoothing unit will make a big difference there.

We use a smoothing unit on our Helmholtz with our narrow beam tube.

 

[Technician Q]

I use a big capacitor, to demonstrate smoothing. Other than that, we use regulated PSU's. Does anyone want some Philip Harris bench PSU's? We're getting rid of ours.

The spacesaver ones?