Something seems "off" (nominal voltage from F-313X)

[Paul-in-KC]

All,

I didn't have time last night to collect more information (which I will need to do). But, after installing my rectifier/voltage "doubler" module I am seeing almost 23 VDC at the outputs.

Maybe this correct, but I was expecting something closer to half of that. My wall voltage is a bit higher than 115 - but not like double.

Shouldn't the F-313X output something like 6.3 VAC and then come out of the rectifier/doubler at ~ 12 VDC (plus whatever for the higher "mains" voltage)?

Or, am I completely misunderstanding this circuit?

I'll investigate further - but wanted to verify that I had the concept right (or wrong).

Many thanks.
-Paul

[martin manning]

Unloaded, the transformer output may be quite high. Measure the AC and see what it is. If it were 6.3 VAC, I would expect to see close to 17 VDC out of a doubler.

[Paul-in-KC]

Unloaded, the transformer output may be quite high. Measure the AC and see what it is. If it were 6.3 VAC, I would expect to see close to 17 VDC out of a doubler.

Martin - thanks so much for posting.

I didn't realize that the transformer output could be quite a bit higher than spec when unloaded.

I would expect the AC output to be a little bit higher than the 6.3 VAC rated with 115 VAC input (since I know my mains-wall voltage is > 120 VAC).

So, if you would expect something like 17 VDC from the doubler - maybe my 23 isn't as crazy as I thought. But this is more than I would want to feed my 12VDC Relay. I guess I should (need to) add a 12V regulator as so many do (like 7812).

Seems like I could also insert a potentiometer used as a voltage divider to dump some of that voltage to ground (?) But simpler I suppose to add a fixed regulator.

Thanks!
-Paul

[martin manning]

Definitely go with a regulator. You need some current capability, and the load is variable. A fixed resistive divider would not maintain a constant voltage.

[Paul-in-KC]

Definitely go with a regulator. You need some current capability, and the load is variable. A fixed resistive divider would not maintain a constant voltage.

Roger that. Went ahead and ordered some 7812's after reading your first response.

I'll disconnect the (F-313X) secondaries from the rectifier/doubler board and post the VAC that I see. But sounds like what I was seeing wasn't as goofy as I thought.

Thank You!
-Paul

[Paul-in-KC]

Unloaded, the transformer output may be quite high. Measure the AC and see what it is. If it were 6.3 VAC, I would expect to see close to 17 VDC out of a doubler.

Martin, I have 8.6 VAC at the secondary with 117.8 VAC on the mains.
This accounts for my 23 volts after the doubler. Right in line with your 17 V figure with 6.3 on the secondary. So, I guess the only thing "off" is the output from the F-313X. But no harm there, I'll just add the 12 volt regulator and be done.

Thanks again.
-Paul

[Paul-in-KC]

Unloaded, the transformer output may be quite high. Measure the AC and see what it is. If it were 6.3 VAC, I would expect to see close to 17 VDC out of a doubler.

Martin, I have 8.6 VAC at the secondary with 117.8 VAC on the mains.
This accounts for my 23 volts after the doubler. Right in line with your 17 V figure with 6.3 on the secondary. So, I guess the only thing "off" is the output from the F-313X. But no harm there, I'll just add the 12 volt regulator and be done.

Thanks again.
-Paul

Just saw a voltage regulation spec (full load to no load) of 35% typical. Which is our 8.6 no load.