Discussion in 'Power Electronics' started by vincecam, Dec 30, 2019.

1. vincecam

9
1
Dec 30, 2019
I have a 600 wat 240 Volt AC input to 12 Volt DC power output bench power supply capable of delivering 30 Amps, or so the makers advertise. When tested it was only delivering 7.5 volts and adjsutable pot is faulty and will not let me adjust the output. I would like to achieve an output varying between 6 volts and 14 Volts. I will replace the adjustable pot with a better and more efficient pot and I hop[e this helps.
However, I want to put a voltometer in the circuit to readily observer the wanted output and I would like to vary the amperage delivered with the desired voltage. This also will require an additional pot and I dont know what else I will require and at where in the circuit to wire them in. Is there anyone out there, that, by observing the picture of the unit (I dont have a circuit diagram) can tell me what I need and where in the circuit to place such. I would need some detail as I am only an ameture enthuseist.
I would be very greatful for qnyone's assistance.
The depicted pot is what I have purchased to adjust the output DC voltage.
The digital meter is what I would like to wire in to observe the desired output.
I will need to purchase one more pot to adjust the desired amperage. (Can the pot for the amperage adjustment be similar to the pot depicted?).

Last edited by a moderator: Dec 31, 2019
2. Bluejets

5,247
1,099
Oct 5, 2014
A lot more to an adjustable current supply than just adding a pot.
Best approach would be to go out and buy a new unit that will do what you want.
At 30 amp be prepared to dig deep.

3. Martaine2005

3,653
994
May 12, 2015
The math doesn’t add up either.
600W @ 240V is 2.5A and 600W @ 2.5A = 240V.
Where does 30A come from?

Martin

4. bertusModerator

2,252
840
Nov 8, 2019
Hello,

When you say that it is 600 Watts @ 240 Volts, and 12 Volts @ 30 Amp, there is a great loss (360 out @ 600 in).
For such a powersupply I would expext more in the direction of 40 Amp @ 12 Volts.

Bertus

5. Tha fios agaibh

2,215
738
Aug 11, 2014
Without more details its hard to say.
The 30a rating may be its peak rating.

If you had a heavy resistance across it, perhaps voltage dropped because it was overloaded.
Cheaper switch mode power supplies don't like to start under heavy loads.
I recommend buying a Linear type power supply with constant current mode and meters built in.

6. vincecam

9
1
Dec 30, 2019

As I did say in my first post I am an ametuer in the the raw meaning of the word. I am an engineer but electronics is my weakness. I will take the advice given and look for a unit that delivers whay I am looking for. In this respect does anyone have any suggestions.

Here is the email I received from the supplier prior to purchasing the unit. Does anuone have comment on what the email states.

From: xxxxxxxxxxx
Subject: Re: 600 Watt 12 Volt 50 Amp Power Supply Item #HF600W-SMF-12 \$148.73 \$103.46
Date:
23 July 2019 at 2:27:13 am AEST

Hi Vince Cam,
That HF600W-SMF-12 is designed for an AC input voltage range of 90~132 & 180~264VAC at 47~63Hz. Your 240 V 50Hz AC should be fine. I would NOT reccomend a continous 50 AMP load for this unit. It is rated at 50 AMPS maximum load, so I would advise that your load sould not draw more thanabout 30 to 35 Amps maximum to allow for an adequate safety buffer for a continous load.

XXXXXXXXXXX
Circuit Specialists
819 W Fairmont Dr Suite 2
Tempe, AZ 85282 USA

[mod edited - remove sales site addy]

Last edited by a moderator: Dec 31, 2019
7. vincecam

9
1
Dec 30, 2019
Hi, Regarding the voltage drop.... I did not have any resistance/load on the unit at the time it showed 7.5 volts. I simply tested the output via a multimeter.

8. Bluejets

5,247
1,099
Oct 5, 2014
600w/12v =50A but with efficiency maybe 30A....maybe typo also.

9. vincecam

9
1
Dec 30, 2019
Be it what it is you said that to achieve my objective I would require more that a couple of pots. Let’s assume I was adventurous walk me through the process.

10. Bluejets

5,247
1,099
Oct 5, 2014
Not worth the effort.
It's a completely different designed power unit.
If you want to build one, I'm sure there are plenty of circuits out there in the internet.
Some with the ability might see it as a challenge but I doubt from what you've indicated so far that you would fall into that category.

11. (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,501
2,841
Jan 21, 2010
I would try putting a small load on the power supply. A small vehicle lamp would suffice.

If you get a higher output voltage then the adjustment pot will probably work to adjust it.

12. vincecam

9
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Dec 30, 2019
Many thaks Steve

13. vincecam

9
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Dec 30, 2019
What you say is very accurate, however, thats the point of ametuer electronics is'nt it. When, and if I have done it I will message you.

14. 73's de Edd

3,253
1,364
Aug 21, 2015

Martaine2005 likes this.
15. BobK

7,682
1,688
Jan 5, 2010
You cannot. It is not possible to set both the voltage and current to a load. At any voltage it will draw a specific amount of current, To change the current, you must change the voltage.

Bob

16. Martaine2005

3,653
994
May 12, 2015
Ooops, forgot the 12v output!.

Martin

17. Tha fios agaibh

2,215
738
Aug 11, 2014
On some power supplies.
You can limit the current at a specific voltage, but you can't exceed what current the load normally draws.
For instance, you could set the voltage at 12v and hook-up a 12w light bulb that draws 1 amp. Then you can vary the current from 0-1A but can't exceed 1A.

Is this is what you want?

18. vincecam

9
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Dec 30, 2019
That is interesting Bob. So, if I am understanding you correctly, a load at a specific voltage will only draw the amperage specific to that load. Is this correct?

19. vincecam

9
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Dec 30, 2019
That sound right on the money

20. davennModerator

13,929
1,980
Sep 5, 2009

Yes, Ohms law .... I = V / R

So for a load with a specific resistance and a specific voltage across it, there will be a specific current through the load