# AC power source for lab

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1. Apr 7, 2015

### Jerry Friedman

Hi. I'm joining this forum to ask about some equipment I need. At the community college where I teach, we do a lab in freshman physics where students measure the input to and output from a transformer. My AC sources are reaching the end of their lives, so I'm looking for replacements. As far as I can tell, what I need is

110 V at 60 Hz input
0 to 15 or 20 V output in at least four steps (e.g., 4 V, 8 V, 12 V, 16 V)
Current up to at least 1.5 A
Reasonably sinusoidal output, not clipped or chopped, at all voltages
Output easily connected to banana plugs or alligator clips
Price no more than a few hundred U.S. dollars

What I'd like, more or less in decreasing order of importance, is

Output voltage limited or limitable to something definitely less than 100 V
Good quality--steady output voltage, long life even if bumped, easy fine adjustment, anything else that comes to mind
DC operation with an on-off switch (for another part of the lab)
Accurate digital meters of output V and I

Can anyone suggest anything?

2. Apr 8, 2015

### CalcNerd

Please provide some detail on the equipment you are replacing. It appears you want a signal generator with some ability to drive various types of loads and not a simple power supply.

Quality units are not going to be cheap, but you might find some reasonable units if you look and do some research. How many do you plan to buy?

3. Apr 8, 2015

### Jerry Friedman

These are replacing things like an Educational Equipment AC/DC power supply, or things that look like thishttps://www.amazon.com/Elenco-XP-62...428528785&sr=8-10&keywords=AC/DC+power+supply, but the results in this lab haven't been good, and I'm starting to wonder whether the problem was with the power supplies. I think a signal generator does sound better. I'm also thinking about settling for lower output voltages.

Amazon has some for under $100 that get reviews like "Great value for the money". The next cheapest one that I've found is$170 and will clearly do what I need and much more. I'm asking questions there, but are we allowed to discuss specific brands here?

If I can use a $50 one, I'll probably get 6. If I need the$170 one, I'll probably get 2 or 3, depending on what my boss says.

Last edited by a moderator: May 7, 2017
4. Apr 8, 2015

For the main lab -- do the students work with / measure the 110V side - or are all of their experiments at 20V and below? For example are they measuring the input out put of THIS transformer - or is this just the source to supply the experiment.

5. Apr 8, 2015

### Jerry Friedman

They don't work with 110 V. They measure the input and output of "dissectible" transformers and hope that V2 / N2 = V1 / N1. I'm just looking for a power source.

6. Apr 9, 2015

### CalcNerd

Does your school have an electrical lab too? If so, perhaps you can pool your \$. They may have a preferred unit that may meet your needs and then you have commonality between labs. May even be able to get a discount due to their previous purchases and obtain a better warranty and support as well.

7. Apr 9, 2015

### Jerry Friedman

Thanks, I don't know why I didn't think of that.

8. Apr 9, 2015

Also -- I for some reason missed your second post - looking at the amazon link that seems to meet your needs - what do you mean the results of the lab were not that good? -- Have you had the existing units looked at? Also - this unit ideas not seem to have any protection - so it may be getting damaged - kids winding transformers - I am sure they have exceeded the 5 A -- you could take one or two to a tech, or have an EE colleague check it out - a scope will say alot about this animal. I am sure this is very basic and can be repaired.

9. Apr 12, 2015

### Jerry Friedman

Sorry to take so long. The students aren't winding transformers, but it's quite possible they've made excessive currents.

I think looking into exactly what the the surviving AC sources are doing and why the broken ones are broken is a great idea, but I haven't been able to get in touch with the right guy in our tiny engineering department.

10. Apr 13, 2015

Where are you located?

11. Apr 13, 2015

### Jerry Friedman

Santa Fe. N. M. (I do not speak for Santa Fe Community College, my employer.)

12. Apr 13, 2015