Adjustable Power Supply- amps or volts?

[ahazi]

I will answer both questions:

That's a good question, I don't know anything about anodizing but wouldn't mind to know the answer.

Theoretically you can use a variac followed by a rectifier (bridge) to supply DC current to a chemical process. But... be careful, a variac is an autotransformer which means the secondary is NOT isolated from the mains voltage 110 or 220 volt. Also the voltage range is rather high. You can use a variac followed by a step down transformer (lower voltage, higher current) followed by a bridge rectifier. By adjusting the variac output you can control the current into your process. Depends on how much current you want/need, you might be better off with just buying the variable power supply that I recommended as it comes with current limiting in addition to the variable voltage control which is something that you will not have with the variac.

I mainly want to use it for a 3 AMPS, 230 Watts ,brushed motor, I would consider the bigger variac if I could set the output not to go beyond 3 AMPS.

Is it a DC motor? 230 watt, 3 amp motor requires 230/3=76.6 volt nominal. For that the absolute minimum variac size is 3 amp x 115 volt ~= 350 watt. But... a smaller variac will not limit your current, it will just burn itself up. Use a bigger variac, add a current meter in series and monitor both voltage and current not to exceed whatever the maximum is.

I hope this helps.

Ariel

 

[Bi11Hudson]

There are several possibilities depending on what you are going to be doing. For low voltage work, 5 or 12 volts, nothing beats an old computer supply. Two connected in series will yield 10 or 24 volts. I use a couple of computer supplies on my bench. Not so much price as having test leads exactly +5 and +12 volts with a few amps capacity just by connecting. But my work is model building in the 12 volt range, using 5 volts as a test bed for motors.
Two on the bench in series would provide either 10 or 24 volts. Set up for an installation, especially in a metal enclosure would be a little more difficult. The low voltage ground is actually a "common" and must be isolated when doubled. The 5 and 12 volts share a common , care must be taken to use one or the other. They both are not accessable together.

A variac is a variable autotransformer, from naught to 130%(M/L). Actually a trademark by the primary manufacturer, it has become the general reference sort of like "Cresent wrench" for adjustable spanners. The key factor there is that a "variac" cannot be used with a switching supply. And neutral connection must be observed, the "120volt line" can be easily connected to the low voltage load. They are great for linear supplies if there is a transformer between the line and load. I have a couple on my bench, mostly used for homemade resistance soldering devices. A variac is a very useful device to have when you need it, but there are limitations on using one.

For more "Lab" quality output, a 30 volt variable supply will give good service. But most are quite touchy about adjusting to within less than half a volt. They can be modified to give more easily adjustable voltage ranges down to the m-volt range. I have used them in an industrial environment but for home shop use the computer supplys have what I need. On the rare occasion that I need some esoteric voltage, I do have a variable 20 volt linear supply, preset to 18 volts. But it sits on the shelf most of the time.

You are looking to build "C-NC" equipment. I have worked, in the distant past, with "NC" equipment. Resolvers instead of encoders, basically. For resolvers, 24 volts is a standard. With the added "C-NC" being for computer numerical control, a +5 volt supply becomes a standard for the computer equipment. I cannot advise on newer equipment, and don't use NC or C-NC for what I do. You're on your own there.

Bill Hudson​

 

[GunsOfNavarone]

I have a sneaking suspicion, if I faced more volts (DC) over amps, I will find it limiting. I THINK more amps, less volts is the way (for me) to go. 60v/10a will be my route unless there are good arguments for the other. I know the perfect world is more of both gives more options, but I don’t think I’ll be working on things regularly that require more than 60v but would need more than 5a.

 

[SLK001]

I have a sneaking suspicion, if I faced more volts (DC) over amps, I will find it limiting. I THINK more amps, less volts is the way (for me) to go. 60v/10a will be my route unless there are good arguments for the other. I know the perfect world is more of both gives more options, but I don’t think I’ll be working on things regularly that require more than 60v but would need more than 5a.

Let us know the prices you find on 600 watt power supplies. Let us "feel" the sticker shock that you experience.

 

[ahazi]

Let us know the prices you find on 600 watt power supplies. Let us "feel" the sticker shock that you experience.

I was about to write something similar... Buy the 30 volt, 5 amp variable bench power supply from Amazon for $80. It is a very good unit and you cannot go wrong with it.

I designed, built, bought and repaired power supplies from milliwatts to multiple kilowatts and just like the difference between a two seater roadster and a semi trailer the prices, sizes and weights are very different. A 30 volt/5 amp is your family sedan, can do a lot and priced very competitively.

Good luck!

 

[pontiac428]

In a proper bench supply, 5 amps is plenty for testing electronics. If you need to test motors and other big power consumers, you can hook up a switching power supply (if appropriate) or linear supply, or use whatever supply powers the appliance in service. Bench supplies don't need much amperage to be incredibly useful. Fine tuning volts and limiting amps is about all the functionality you would need. If you want to do electrolysis, plating, anodizing, and the like, get a car battery charger (do not use a bench supply for plating ever). There may be no one size fits here, so what kind of supply you get depends on how you plan to use it...

 

[GunsOfNavarone]

Aaannnd....I’m not sure now which way to go. You make some sane, rational arguments there Pontiac. Fine tuning adjustments are important you say? TBH, I was just going with course adjustment. Seems like you want 10, 11, 12v not so much x.17v
I might just flip a coin, but it’d probably land sitting straight up on its edge.

 

[AGCB97]

I never figured out what you want to use it for. Naming a few possibilities would help me understand and help others help you.
Aaron

 

[jlesser27]

Bench top Lab Power Supplies should allow you to set a desired voltage and limit the current. When developing a circuit or project you want to be able to limit the current on startup which keeps you from releasing the magic smoke. There are quite a few options on amazon for around $80 but I opted for a quality used one from Amazon. Here is a picture of the one I bought for $85 on eBay. This one allows you to have two separate outputs or put them in series for higher voltage. This one also allows you to source both a positive and negative voltage for using operational amplifiers. Most projects for CNC will use 24v and 5v so a 30v 5amp device will be fine.

Sent from my iPhone using Tapatalk

 

[GunsOfNavarone]

In the past 3 months, building the ELS for the lathe, building the VFD as well. The last week building a whole circuit for coolant controlled by CNC mill. I was always in situation needing juice to check the the whole circuit was wired correctly. Multimeters give me some affirmation, but sometimes I need DC running to confirm before I connect to a system that is sensitive to bungle headedness. My electrical skills are acceptable with anything to do with cars motorcycles, AC wiring is coming along but the wiring AC to DC of the mil was daunting. The coolant system works flawless and only ended up costing me about $80, but there was a lot of time drawing it out to help myself feel better about flipping the switch. I feel like a bench power supply would have allowed a lot of testing of single pieces as well as whole units before making the leap into the real deal.