are these readings correct? - Page 1
Forum section: electronics / beginners

author: p.larner
author_rank: Frequent Contributor
timestamp: April 11, 2024, 10:54:38 am
content: I am building a hyland 030v 2ma-3a psu,i amusing a transfo from an old ham radio psu,ps-30m if i remember,the raw voltage into the bridge is 19v unloaded,but on the filter cap after a bridge rectifier i measure 44v,is that normal,seems high to me.

author: Zero999
author_rank: Super Contributor
timestamp: April 11, 2024, 10:58:27 am
content: wotz da AC volz on de trafo

author: xvr
author_rank: Frequent Contributor
timestamp: April 11, 2024, 11:07:34 am
content: > if i remember,the raw voltage into the bridge is 19v unloaded,but on the filter cap after a bridge rectifier i measure 44v,is that normal,seems high to me.Definitely high. Should be 19*sqrt(2) ~ 27V

author: coppercone2
author_rank: Super Contributor
timestamp: April 11, 2024, 11:23:07 am
content: level : dublin shipyard, 1951?I want this reply #1 dated more accurately by a expert . Paging Dr. Jackson. I want to learn this speak to help communicate with reply #0 better but it needs to be rightshit its like jamacian isent it? this thread sounds like its purpose is to rob a lorry?

author: p.larner
author_rank: Frequent Contributor
timestamp: April 11, 2024, 12:06:45 pm
content: the ac input to the transformer is uk mains circa 230vac,its odd to me having 44+v on the filter cap after the bridge,how can this be?,i am meashuring using a fluke83,using my avo8 ac into the bridge is 18v dc from the bridge is about 42v.,the transformer is running quiet and cool,this is all unloaded.

author: Zero999
author_rank: Super Contributor
timestamp: April 11, 2024, 12:23:06 pm
content: 2ndry winding volz?do u hav a voltage dubler?

author: tggzzz
author_rank: Super Contributor
timestamp: April 11, 2024, 12:35:52 pm
content: wozza vees whn lded?unlded vees wll be bigr

author: CaptDon
author_rank: Super Contributor
timestamp: April 11, 2024, 12:36:35 pm
content: It would appear to me the transformer is 19vac on EACH SIDE of center tap and he has a 4 diode bridge instead of 2 diodes with center tap return.

author: CaptDon
author_rank: Super Contributor
timestamp: April 11, 2024, 12:38:41 pm
content: Need some spaces after the commas?

author: tggzzz
author_rank: Super Contributor
timestamp: April 11, 2024, 12:43:18 pm
content: Quote from: CaptDon on April 11, 2024, 12:38:41 pmNeeds more than that.I consider it polite to respond to this OP in the manner in which he communicates (in a loose sense of the word) with us in his many many first posts

author: themadhippy
author_rank: Super Contributor
timestamp: April 11, 2024, 02:00:18 pm
content: QuoteCareful, that could be classed as illegal in some jurisdictions.

author: p.larner
author_rank: Frequent Contributor
timestamp: April 11, 2024, 02:40:35 pm
content: how about you guys stop being pedantic prats and answer the questions if you are able!?.

author: wasedadoc
author_rank: Super Contributor
timestamp: April 11, 2024, 03:30:00 pm
content: If you have supplied that 44 Volts to the board, the three opamps are now fried. Don't ask me how I know.Look at the maximun ratings for them on a data sheet. It isn't easy to find a transformer that will permit the board to give 30 Volts at 3 Amps but not blow the opamps when the load current is low.

author: CaptDon
author_rank: Super Contributor
timestamp: April 11, 2024, 03:53:45 pm
content: If the transformer is 19vac each side of C.T. that gives 38vac all the way across. The average rectified and filtered voltage would be around 48 to 50vdc. Not sure how you are getting 44 volts from a transformer marked as 19 unless the primaries are wired wrong although in that case the transformer would also self destruct with 240 on a 120 winding. If that were a ham radio supply it would have been designed for around 13.2vdc output so a 19vac winding would make sense. I don't have a clue how you will get 0-30vdc using that transformer unless it really is 38vac across the full winding. I have no other ideas or comments.

author: 807
author_rank: Frequent Contributor
timestamp: April 11, 2024, 04:12:30 pm
content: Quote from: p.larner on April 11, 2024, 12:06:45 pmI'm a bit confused about what meter you are using to check your voltages, as you mention a Fluke and an Avo8.Are you saying that (usingjustthe Fluke), that you get 18v ac from the secondary to the input of the bridge, and 42-44v dc (using the Fluke) on the smoothing capacitor?I assume this is just a basic, mains transformer/bridge/smoothing capacitor arrangement?

author: wasedadoc
author_rank: Super Contributor
timestamp: April 11, 2024, 04:36:13 pm
content: Schematic available in Aliexpress listinghttps://www.aliexpress.com/item/32686218522.html. Not the zippyshare link. Click the "View more" to see the lower half of the board layout and schematic.Or see the schematic in the OP's other thread.https://www.eevblog.com/forum/beginners/hyland-psu-questions/

author: p.larner
author_rank: Frequent Contributor
timestamp: April 11, 2024, 05:37:53 pm
content: just re meashured this with my fluke 83v ac input to the bridge is 18.9v dc across the cap is 40.73v,does that look about right?, the tranfomer has 2 secondary windings,one main winding and one aux winding,the bridge is connected to the main secondary winding.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 11, 2024, 05:42:24 pm
content: Doesn't seem right. The DV voltage should be 26.7VDC. Not 40. May be you can try to disconnect the down stream circuit. The Fluke 83 isn't a true RMS meter but then it shouldn't make a difference.

author: xvr
author_rank: Frequent Contributor
timestamp: April 11, 2024, 05:45:19 pm
content: > dc across the cap is 40.73vWhat cap? There are 3 power caps in schematic.

author: p.larner
author_rank: Frequent Contributor
timestamp: April 11, 2024, 05:47:15 pm
content: there is nothing downstream yet its just the transformer going into a bridge rectifier with a 22000ufcap hanging on the rectifier+ and minus outputs.,the rectifier has what looks like mall disc ceramics between all legs tho but i cant see that altering the readings?

author: p.larner
author_rank: Frequent Contributor
timestamp: April 11, 2024, 05:49:56 pm
content: i have done away wth the onboard rectifier diodes and filter cap and am usng an offboard cap+rectifier instead ok.

author: bdunham7
author_rank: Super Contributor
timestamp: April 11, 2024, 05:55:46 pm
content: Can you measure the AC voltage output of the transfomer when it is completely disconnected from your circuit? Those readings don't add up and the only two explanations I can think of are that either you have somehow set up a full-wave voltage doubler instead of a full wave bridge or you have a shorted diode and that is causing your input AC voltage to be read incorrectly by your meter. Or something else very strange is going on.

author: wasedadoc
author_rank: Super Contributor
timestamp: April 11, 2024, 06:10:52 pm
content: Quote from: p.larner on April 11, 2024, 05:49:56 pmThat may not explain the voltage readings anomaly but for the board to work you must supply AC. In addition to the board having four diodes forming the bridge rectifier to give the positive voltage there are two more generating a negative voltage.

author: Zero999
author_rank: Super Contributor
timestamp: April 11, 2024, 06:50:53 pm
content: Quote from: p.larner on April 11, 2024, 02:40:35 pmThen put some effort into writing your questions. You sound like a total pillock, which is why everyone is taking the micky. At least use a spell check for crying out loud.Quote from: p.larner on April 11, 2024, 05:37:53 pmThat makes no sense. You talk about AC input to the bridge being 18.9VDC, but I might have misinterpreted it, no thanks to the lack of commas.

author: p.larner
author_rank: Frequent Contributor
timestamp: April 11, 2024, 08:17:51 pm
content: sorry the ac input to the bridge is just about 19vac , The dc voltage when the bridge dc output is connected to a filter cap is 40.5v,seems too high?.

author: tggzzz
author_rank: Super Contributor
timestamp: April 11, 2024, 08:29:24 pm
content: Quote from: Zero999 on April 11, 2024, 06:50:53 pmJust so.I have a lot of time for beginners who make mistakes, listen, think, and makenewmistakes.People thatrepeatedlydon't listen (and usually don't think) are time wasters, a.k.a. time vampires.

author: 807
author_rank: Frequent Contributor
timestamp: April 12, 2024, 10:31:31 am
content: Quote from: p.larner on April 11, 2024, 08:17:51 pmYes. It is too high. I would expect a DC voltage in the region of 25-27v DC.Do you have a scope or another multimeter to verify the Fluke readings? You said you have an AVO8. Does that agree with the AC & DC readings of the Fluke?Edit...as mentioned above, the Fluke 83V is an average reading meter, not true RMS. But even taking that into account, I would still only expect around 28-30v DC across the capacitor.

author: Zero999
author_rank: Super Contributor
timestamp: April 12, 2024, 10:52:48 am
content: Could the primary be configured for 120V operation and it's run on 230V?#EDIT:I forgot the original poster said he measured the secondary voltage.I suspect it's a measurement error, either due to the equipment or user.Was the meter set to AC?It should be tested on a known voltage first, to eliminate that possibility.

author: xvr
author_rank: Frequent Contributor
timestamp: April 12, 2024, 11:04:16 am
content: > sorry the ac input to the bridge is just about 19vac , The dc voltage when the bridge dc output is connected to a filter cap is 40.5v,One possible reason for such high voltage could be non-sinusoidal AC output from transformer. May be a lot of high voltage peaks. Can you check transformer output with oscilloscope?