Incorrect voltage reading from bench supply

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windmill john
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Incorrect voltage reading from bench supply

Postby windmill john » Mon Nov 13, 2017 7:08 pm

I have just picked up an Irwin EJ1001 bench top power supply.

I have had Schorsch’s old battery under my bench for 5 years; took it to the tip yesterday.
I occasionally used it to test bulbs, wires etc.

This Irwin was free, something I’ve wanted for years but couldn’t justify buying one, as it is only for very occasional testing.

Anyhow, it may be faulty!

Assuming my multimeter battery is good, the Irwin is giving me a reading tenth of what it should be; yes I’m in the right scale you cheeky buggers :grin:

So with the Irwin set to 12V, my meter shows 1.2V
With my meter set to 2V and the Irwin on 2V, I get out of range.

Anything simple I can check? Be gentle, my circuit board testing is, erm.... limited.

Thanks

John
http://www.kittos.co.uk
Best roads: 623 Burgos to Santander. A back road to Metz; can't remember which!
Schorsch 1978-80 R65 - bit of a Shetland pony; frisky and naughty.
Too many bikes have come and gone, trying to be sensible now!

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bwprice100
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Re: Incorrect voltage reading from bench supply

Postby bwprice100 » Mon Nov 13, 2017 7:19 pm

Check you multi meter against a new PP9 battery as a starting point.

I hope this helps

Brian

Sent by me using tapety talky

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1981 R80, (was a TIC)
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Re: Incorrect voltage reading from bench supply

Postby windmill john » Mon Nov 13, 2017 8:16 pm

i had just got from work and banged the meter on. I’ll try another meter tomorrow, Irwin now in the shed, cat on lap, can’t move!
http://www.kittos.co.uk
Best roads: 623 Burgos to Santander. A back road to Metz; can't remember which!
Schorsch 1978-80 R65 - bit of a Shetland pony; frisky and naughty.
Too many bikes have come and gone, trying to be sensible now!

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Re: Incorrect voltage reading from bench supply

Postby Galactic Greyhound » Mon Nov 13, 2017 9:21 pm

Hi John,

Voltmeters are very high resistance devices.

If you just switched the bench power supply to 12v output and clipped your Voltmeter across the output terminals then, depending on how the power unit is designed, it may not switch on because it will see the very high resistance i.e. almost an open circuit, and there will be negligible current flow.

Try connecting a 12v filament bulb (your Test Lamp? 12W = 1 Amp draw) across the power supply output and see if it lights up.
You can then connect your Voltmeter across the bulb/output terminals to see what the voltage is.

I know the problem with the cat on lap as well! :grin:
Ced.

R1100RT 1996.
Sent by Boson Quantum Transmission from the Starship 'Galahad'.
http://www.researchgate.net/publication ... ing_bosons" - It works!

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Re: Incorrect voltage reading from bench supply

Postby windmill john » Mon Nov 13, 2017 10:41 pm

Thanks Ced, I’ll see if I can get in the shed tomorrow night and check.

The other cat is on my lap now! I’m trying to get to bed! #-o :grin:


0CB26F39-681E-4335-AF5B-038AA5723CF8.jpeg
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http://www.kittos.co.uk
Best roads: 623 Burgos to Santander. A back road to Metz; can't remember which!
Schorsch 1978-80 R65 - bit of a Shetland pony; frisky and naughty.
Too many bikes have come and gone, trying to be sensible now!

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Re: Incorrect voltage reading from bench supply

Postby george baker » Tue Nov 14, 2017 11:24 am

Hi
Yep, some psu's only stabilize under load, some pc psu's wont give good 12v unless their 5v output is being loaded

Cats, bah!

George
Member 21, R100R, K75 and a Hyosung 250 FOR SALE

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Re: Incorrect voltage reading from bench supply

Postby P-K » Tue Nov 14, 2017 5:02 pm

george baker said :-
Hi
Yep, some psu's only stabilize under load, some pc psu's wont give good 12v unless their 5v output is being loaded
Indeed George. Dead right.
That's because a PC uses a switch mode power supply (no transformer).
A swine to fault find.

I'd guess the one in question is a linear power supply.
But you're right again George in that some require a few milliamps current flow before the voltage control circuit operates.
Phil,
''93 R100GSPD : '17 R9T Urban G/S : '12 R1200R
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Re: Incorrect voltage reading from bench supply

Postby windmill john » Tue Nov 14, 2017 6:32 pm

Well thanks all.

Okay, here we go. The 12 volt position does not work; that’s handy!

Bulb lit at the 2, 4, 6 and 8 Volt settings with obvious brightness increases; just not the 12V setting.

My lamp was actually a panel bulb of 2 watt rating.

Readings:

At 8 V, 7.4V
At 6 V, 5.99V

Great, so all I need to do now is buy an old bike with 6 volt electrics and I’m laughing :roll: :grin:

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http://www.kittos.co.uk
Best roads: 623 Burgos to Santander. A back road to Metz; can't remember which!
Schorsch 1978-80 R65 - bit of a Shetland pony; frisky and naughty.
Too many bikes have come and gone, trying to be sensible now!

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Galactic Greyhound
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Re: Incorrect voltage reading from bench supply

Postby Galactic Greyhound » Tue Nov 14, 2017 7:08 pm

Maybe that's why it was free! :lol:

Might be worth opening up and checking that the switch is not faulty. :-k
Ced.

R1100RT 1996.
Sent by Boson Quantum Transmission from the Starship 'Galahad'.
http://www.researchgate.net/publication ... ing_bosons" - It works!

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windmill john
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Re: Incorrect voltage reading from bench supply

Postby windmill john » Tue Nov 14, 2017 7:38 pm

As it was free, I have no qualms of popping inside and checking all.

Thanks Ced.

John
http://www.kittos.co.uk
Best roads: 623 Burgos to Santander. A back road to Metz; can't remember which!
Schorsch 1978-80 R65 - bit of a Shetland pony; frisky and naughty.
Too many bikes have come and gone, trying to be sensible now!

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windmill john
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Re: Incorrect voltage reading from bench supply

Postby windmill john » Sun Nov 19, 2017 4:42 pm

Yes P-K it is a linear power supply, just looked inside. Big transformer and the rest was a very simple circuit board.

I thought I’d have to order a rotary potentiometer, but it turned out simple and not needed.

It looks like it has been used on 6 volt for so long, the rotor was a bit gungy.
A bit of constant twiddling brought 12 volts back on line, all good.

Thank guys

BTW, I only know it is a linear power supply as I had recently done a bit of reading about the difference between switch mode and linear power supplies. I’d like to get more into the understanding of circuits.
http://www.kittos.co.uk
Best roads: 623 Burgos to Santander. A back road to Metz; can't remember which!
Schorsch 1978-80 R65 - bit of a Shetland pony; frisky and naughty.
Too many bikes have come and gone, trying to be sensible now!

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Galactic Greyhound
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Re: Incorrect voltage reading from bench supply

Postby Galactic Greyhound » Sun Nov 19, 2017 5:20 pm

Hi John,

See the following - lots more on YouTube!

Linear Mode Power Supplies:
https://youtu.be/brB1sZyJPls


Switched Mode Power Supplies:
https://youtu.be/nbKwUSH9NiY
Ced.

R1100RT 1996.
Sent by Boson Quantum Transmission from the Starship 'Galahad'.
http://www.researchgate.net/publication ... ing_bosons" - It works!

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windmill john
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Re: Incorrect voltage reading from bench supply

Postby windmill john » Sun Nov 19, 2017 6:02 pm

I did watch the video by the post apocalyptic inventor a while back...... well, he is German and so are my bikes :smile:
http://www.kittos.co.uk
Best roads: 623 Burgos to Santander. A back road to Metz; can't remember which!
Schorsch 1978-80 R65 - bit of a Shetland pony; frisky and naughty.
Too many bikes have come and gone, trying to be sensible now!

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P-K
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Re: Incorrect voltage reading from bench supply

Postby P-K » Sun Nov 19, 2017 6:57 pm

I used to teach some of this electronics stuff (and Computer Science) which is why / how I know.
I'm not into running an on-line tutorial, but for the odd one off answer, ask away.
Phil,
''93 R100GSPD : '17 R9T Urban G/S : '12 R1200R
Site Administrator, Assistant Webmaster and Official Club Tweeter @BMRidersClub

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windmill john
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Re: Incorrect voltage reading from bench supply

Postby windmill john » Sun Nov 19, 2017 8:58 pm

I think the hardest thing about learning electronics is why?

Like most things, you need a project.

So let’s say it suggest making a door buzzer, a moisture sensor etc. As you can buy one very cheaply, or more importantly you don’t need to make one, this is where I struggle.

Thinking of a useful reason to learn is the hardest.

Or, doing it in reverse. I once bought an old radio to repair. This was silly the other way because I didn’t know how to circuit test.
If I tested a resistance in part of the circuit for example, I didn’t know if the resistance showing was from the part I was testing or some other part of the circuit!
http://www.kittos.co.uk
Best roads: 623 Burgos to Santander. A back road to Metz; can't remember which!
Schorsch 1978-80 R65 - bit of a Shetland pony; frisky and naughty.
Too many bikes have come and gone, trying to be sensible now!

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george baker
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Re: Incorrect voltage reading from bench supply

Postby george baker » Mon Nov 20, 2017 1:30 pm

Hi John,
WHY? Is true about all learning unless you are on a course, Then the poor teacher has to "make you have it"



George
Member 21, R100R, K75 and a Hyosung 250 FOR SALE


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