First project - stumped

I'm using Slone's Tab book to learn the basics. It's pretty good so far although once in a while the book takes bigger leaps so I stumble a bit.

What I've got so far is the the two 24V transformers with the primaries in parallel, the secondaries in series. I've tested the outputs from each secondary (about 28V each) and the secondary circuit common reads 50V. I've added a 250V 6A bridge rectifier and attached the free secondary leads from each transformer to the AC inputs on the bridge. The bridge shows 50V DC out.

The book has me (temporarily) add two 10K resistors - one between the secondary circuit common and the bridge positive lead, and another from the secondary circuit common and the bridge negative lead.

Testing DC between secondary circuit common and the + bridge lead shows +24V. Testing DC between secondary circuit common and the - bridge lead shows -24V. This agrees with the book. His next two tests don't work for me.

Testing" AC" between secondary circuit common and the + bridge lead shows about 50V. Testing" AC" between secondary circuit common and the - bridge lead shows about 0V. His book indicates I should get about 12V for each. That I don't understand. Something just doesnt seem to read right here.

I've rechecked what I've done with the schematic and everything looks good. All tests have agreed with the book except for these last two.

Any advice much appreciated.

H. Dixon

Reply to
H. Dixon
Loading thread data ...

If you are using one of the el-cheapo $3 Harbor Freight type meters, be advised that they read AC simply by using a single diode to half-wave rectify the signal. For an ordinary sine wave, it works pretty well, but any DC component will throw off the readings "big-time". It is best to get a true-RMS meter, but at least get one that uses a precision full-wave rectifier circuit. Any meter that has low AC volts and AC millivolts should work OK. But there are decent true RMS meters available on eBay and discount places for as low as $60 or so.

formatting link

An acceptable meter (not true-RMS) can be had for about $15:

formatting link

Even for about $13 you can get a 4 digit meter that has autoranging, capacitance, frequency and duty cycle:

formatting link

I have ordered meters from Multimeter Depot before and have been quite satisfied.

Paul

Reply to
Paul E. Schoen

t

ld

Thanks - I hadnt thought it might be the DMM. Its an old one I cant even remember where/when I got it. I see the radio shack around the corner has an Extech True RMS DMM model 22-816. Brief googling seems to show Extech as acceptable in quality. It's 89$ but seems to have a lot of bells and whistles.

Maybe I'll pick that up tomorrow (unless someone screams NO).

Thanks

H. Dixon

Reply to
H. Dixon

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.