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Adjustable Power Supply- amps or volts?
- Thread starter GunsOfNavarone
- Start date
- Joined
- Feb 13, 2017
- Messages
- 2,138
Having read your responses to a number of posts, I just have to jump in here again. To say you are comparing Apples to Oranges is an understatement. You seem to be more comparing bricks to bananas. The question of "volts vs amps" is actually asking two entirely unrelated questions. It sounds like you need to learn a little more about electricity. I don't have room(books) here, or time(months) to teach electricity. A good(?) starting point is at:
Just an introduction though, even the listed books just give an overview. Electricity is a deep subject. I am (used to be) an electrical engineer. Yet I only have a passing knowledge of electronics. The freehanded availability of electronic components is a little misleading. Remember Robert Heinlein's books, TANSTAAFL, there ain't no such thing as a free lunch.
VOLTS: Think of pressure. In the old days, it actually was referred to as pressure. Compare a garden hose to a fire hose. they both have the same pressure, the city fire main. Excluding houses with a pressure regulator, of course.
AMPS: Think of those hoses again. The fire hose can deliver a hundred times more water in the same time as a garden hose. And is much more difficult to handle. Look at the size of the two relative to each other.
WATTS: The amount of work that can be done. A garden hose can spin up a small fan. A fire hose can push a car down the street. Same pressure, remember. . . Think about how difficult it is to handle a 3 inch hose compared to a 3/4 inch hose.
To consider volts, a microwave oven has a transformer that can deliver 3,500 volts for the Klystron. But only a few thousandths of an amp. A car battery, on the other hand, is limited by the number of cells in that battery. It can only deliver 13.2 volts from full charge. But it can deliver several hundred amps for a few seconds. The two, volts and amps, cannot be compared. But they work together to produce watts.
Watts only apply in small devices when comparing name plates. What matters is amps and volts. Watts only matter in large items like motors, comparing output like watts VS horsepower.
To say you are competant in automotive electrical systems is to say you know how to change the fuse or install a radio. What about using an automotive alternator to get 120 volts 3 phase power?
.
Just an introduction though, even the listed books just give an overview. Electricity is a deep subject. I am (used to be) an electrical engineer. Yet I only have a passing knowledge of electronics. The freehanded availability of electronic components is a little misleading. Remember Robert Heinlein's books, TANSTAAFL, there ain't no such thing as a free lunch.
VOLTS: Think of pressure. In the old days, it actually was referred to as pressure. Compare a garden hose to a fire hose. they both have the same pressure, the city fire main. Excluding houses with a pressure regulator, of course.
AMPS: Think of those hoses again. The fire hose can deliver a hundred times more water in the same time as a garden hose. And is much more difficult to handle. Look at the size of the two relative to each other.
WATTS: The amount of work that can be done. A garden hose can spin up a small fan. A fire hose can push a car down the street. Same pressure, remember. . . Think about how difficult it is to handle a 3 inch hose compared to a 3/4 inch hose.
To consider volts, a microwave oven has a transformer that can deliver 3,500 volts for the Klystron. But only a few thousandths of an amp. A car battery, on the other hand, is limited by the number of cells in that battery. It can only deliver 13.2 volts from full charge. But it can deliver several hundred amps for a few seconds. The two, volts and amps, cannot be compared. But they work together to produce watts.
Watts only apply in small devices when comparing name plates. What matters is amps and volts. Watts only matter in large items like motors, comparing output like watts VS horsepower.
To say you are competant in automotive electrical systems is to say you know how to change the fuse or install a radio. What about using an automotive alternator to get 120 volts 3 phase power?
.
For general bench use Astron and many others offer units that have optional interface.
From basic box with binding posts and power switch, then meters added to show volts or amps to the upper end with both being adjustable which is what we have used for 40 years in the trade.
When we worked on portable radios and pagers micro miniature stuff a probe can short out things and smoke things.
Being able to limit the current to just enough to operate but not enough to damage saves a great amount of repairs.
Sent from my SAMSUNG-SM-G930A using Tapatalk
From basic box with binding posts and power switch, then meters added to show volts or amps to the upper end with both being adjustable which is what we have used for 40 years in the trade.
When we worked on portable radios and pagers micro miniature stuff a probe can short out things and smoke things.
Being able to limit the current to just enough to operate but not enough to damage saves a great amount of repairs.
Sent from my SAMSUNG-SM-G930A using Tapatalk
Last edited:
- Joined
- Jun 26, 2018
- Messages
- 1,733
Bill, I wasn't comparing amps to volts. What I am getting at is (the original question) is there a good reason on a bench power supply to favor one over the other, that is, would I be in a situation where I'm working with a DC motor and it requires 60 volts at 1 amp or adversely, a circuit that need 12v but 6 amps?
As far as my hobbies and what I have wired, I have recently built a chopper and had to create the entire wiring harness from scratch...same with a '63 vw bus. This new direction I am seeing a little bit of everything and I'm a firm believer in having the correct tools for the job. If it's of no matter, I'll just buy he purdiest one I find. I'm not sure that the understanding of using an alternator to create 3 phase power is anything I am currently, or in the foreseeable future, needing to do. Now...fighting with a bad contactor and now having a convenient way to test it at my work bench? Yup.
I understand there are many around here with a very strong skill set in specific fields, that's the appeal for me, unfortunately I've got to take the bad with the good I suppose. Many here are learning as they go (I think Practical machinist web site would be the anti version of this website) and I can say in the last 3-4 years, I have expanded greatly in fields I barely dabbled in. I can take an idea, fully mock it up in CAD, then CAM and make working part. I moved from a manual lathe to a manual mill to a CNC mill and am now converting my lathe to CNC. I won't excel in the electrical field, it's not even in my sights, but I WILL competently acquire the skills I need to complete whatever tasks I set my sight to. Track me down in another 3 years and we can discuss all I have achieved....I'm guessing an alternator powered, 3 phase spaceship won't be one, but its good to dream.
As far as my hobbies and what I have wired, I have recently built a chopper and had to create the entire wiring harness from scratch...same with a '63 vw bus. This new direction I am seeing a little bit of everything and I'm a firm believer in having the correct tools for the job. If it's of no matter, I'll just buy he purdiest one I find. I'm not sure that the understanding of using an alternator to create 3 phase power is anything I am currently, or in the foreseeable future, needing to do. Now...fighting with a bad contactor and now having a convenient way to test it at my work bench? Yup.
I understand there are many around here with a very strong skill set in specific fields, that's the appeal for me, unfortunately I've got to take the bad with the good I suppose. Many here are learning as they go (I think Practical machinist web site would be the anti version of this website) and I can say in the last 3-4 years, I have expanded greatly in fields I barely dabbled in. I can take an idea, fully mock it up in CAD, then CAM and make working part. I moved from a manual lathe to a manual mill to a CNC mill and am now converting my lathe to CNC. I won't excel in the electrical field, it's not even in my sights, but I WILL competently acquire the skills I need to complete whatever tasks I set my sight to. Track me down in another 3 years and we can discuss all I have achieved....I'm guessing an alternator powered, 3 phase spaceship won't be one, but its good to dream.
- Joined
- Apr 23, 2018
- Messages
- 6,537
Oh, you can surely get to space on alternators. Look, there's room for four more on the other side!
- Joined
- Mar 3, 2017
- Messages
- 747
Would those VarI Acs be any good for anodizing? (Different subject)
[/QUOTE]
Yes, but that's not all. A variac will typically have a current limit (set by the contact resistance of the wiper) of a few amps,
and anodizing requires rather high DC currents at low voltages. You'd be best off with a fixed transformer to
step down the voltage (the high current output of such a transformer has no wiper problem), in conjunction
with a variac to adjust at the low-current-high-voltage input of the fixed transformer.
A hundred watts is under 1A at 120V, but is 50A at 2V. The variac won't like the 50A output condition,
even though the line cord won't be at risk of catching fire. So, you use a stepdown fixed transformer,
and the variac feeds 1A/120V or adjusts down to 3A/40V and neither element has a problem.
Anodizing and plating require DC, so a rectifier after both transformers is required. Electroplating and
anodizing can use very BIG rectifiers for those currents, with a variety of tricks to keep 'em happy.
[/QUOTE]
Yes, but that's not all. A variac will typically have a current limit (set by the contact resistance of the wiper) of a few amps,
and anodizing requires rather high DC currents at low voltages. You'd be best off with a fixed transformer to
step down the voltage (the high current output of such a transformer has no wiper problem), in conjunction
with a variac to adjust at the low-current-high-voltage input of the fixed transformer.
A hundred watts is under 1A at 120V, but is 50A at 2V. The variac won't like the 50A output condition,
even though the line cord won't be at risk of catching fire. So, you use a stepdown fixed transformer,
and the variac feeds 1A/120V or adjusts down to 3A/40V and neither element has a problem.
Anodizing and plating require DC, so a rectifier after both transformers is required. Electroplating and
anodizing can use very BIG rectifiers for those currents, with a variety of tricks to keep 'em happy.
- Joined
- Jun 12, 2014
- Messages
- 4,815
One of my power supplies is a BK Precision 1761 which has 3 separate DC supplies, two are 32V@3A, one is 2.6-5V@5A. I often need 2 or 3 power supplies when testing circuits, boards, electronics. Each power supply is isolated from the other (floating) so one can either put the two 32V supplies in parallel for 32V@6A or in series for 64V@3A, which is sufficient for most of my low voltage needs. Often when testing a circuit one wants to limit the amperage, so one sets the current limit and then raises the voltage. This can limit damage to the electronics and can also determine the operating current. In some of my control circuits I am current limited by the devices or power supply so it is important determining the actual operating limits of the design. In other cases if current is not an issue then you can set the current to maximum and then set your voltage. The BK power supply tells you when you are current or voltage limited. In addition, the 1760 series of BK are not a switching power supplies, so the supplies are isolate (use transformers and traditional regulation). This can be important for noise isolation and also can be an issue when using a positive and negative DC supply rail. This is also a common issue in volt/amp meters that the power supply shares a common negative to the voltmeter negative. I tinker with tube equipment and one of my other supplies go to 500VDC@200mA x2 (plate and screen), -100VDC@10mA for the grid, 0-40VDC@1A and fixed center tapped VAC 6.3/12.6 for filament supplies all in one unit. So the type of power supply depends on the type of circuits you are dealing with. I recommend getting a dual VDC supply similar to the BK if you can find one at a reasonable price and it meets your voltage and current requirements.
Overall if you can pick up a BK 1760, 1761 or 1762 used in working condition, they are great VDC power supplies for low voltage DC work (mostly solid state). Motors generally need much higher current and do not need the degree of regulation, so an adjustable high current switching power supply would be more desirable. They tend to be very reasonable. Variac is used for for adjustable AC and they are not isolated, which can be desirable for certain type of equipment. I have several, the larger unit uses an isolation transformer with a variac, it is useful for powering up older tube equipment and also can measure leakage to the chassis. My tube amps put 1100VDC on the plates, I do not like to play around when voltages get that high, it is the kiss of death if you screw up.
Overall if you can pick up a BK 1760, 1761 or 1762 used in working condition, they are great VDC power supplies for low voltage DC work (mostly solid state). Motors generally need much higher current and do not need the degree of regulation, so an adjustable high current switching power supply would be more desirable. They tend to be very reasonable. Variac is used for for adjustable AC and they are not isolated, which can be desirable for certain type of equipment. I have several, the larger unit uses an isolation transformer with a variac, it is useful for powering up older tube equipment and also can measure leakage to the chassis. My tube amps put 1100VDC on the plates, I do not like to play around when voltages get that high, it is the kiss of death if you screw up.
This thread is getting "interesting" with such relics as powering filament, plate, grid, screen grid etc... For me this is mostly the past during my younger years...
Mark just expanded the (wide) scope of what (bench) power supplies can be. I have designed, built, repaired, used, owned and still have many of the types mentioned throughout the thread and much more. It is a very wide field and my recommendation to anyone that wants to start and get a first bench power supply is to start simple and unless you have severe budgetary restriction and ability to repair eBay used power supplies - buy new.
Look at my earlier post for my recommendation that I stay firmly behind as this is one of my bench power supplies and it is my go-to one. I have others that are double and triple output, higher voltage and higher current and I keep going back to this one. The prices of good linear bench power supply with digital control and display is below the price of components that any of us can source and not much more than a used one.
Ariel
- Joined
- Feb 17, 2013
- Messages
- 4,406
I would sincerely appreciate such a rewind!