Good afternoon everyone,

I am trying to design an AC Power Supply at my job. The purpose of the power supply is to perform an abnormal overvoltage test on a TMOV (Thermally Protected Metal Oxide Varistor) with 2 terminals to see if it will disconnect before burning up. I will have to test each TMOV at 240 Volts at a current level of 0.125, 0.5, 2.5, 5, and 10 amps. I will also be testing at 480 Volts AC at these same current levels. This is my 1st Design project which is why I am asking for some assistance. We are trying to make the power supply in spec according to UL standards. I am aware that I will need a load for each current level which consists of a voltage source, a series resistor, and a Variable resistor in some of them. A Transformer, heaters, fuse, etc.

Now that I've explained what I am trying to do I guess my question is has anyone ever built an AC Power Supply in a professional setting and knows first hand what exactly I need to order in order to get this experiment going ? My deadline will be arriving within a few days in order to present this to my managers. Also below is a link to a book on the UL certifications that are expected of us to have completed for the AC power supply. This is the email that my boss had sent me in regards to what we are trying to achieve:

Per our discussion I have attached a copy of the UL1449 standard. The TMOV and SPD devices that we are interested in are considered Type 4 Component Assemblies. As I explained we need to build a new piece of equipment to perform the Limited Current Abnormal Overvoltage Test (Section 44.4, page 95). Table 44.6 lists the required short circuit currents that we must meet. This section references back to Table 44.1, page 89, which specifies the minimum test voltages that must be applied for a rated nominal AC voltage. We are only concerned with the single phase voltage ratings.
I need you to start designing a tester that can apply the minimum test voltages and the selected short circuit currents. Remember that the standard requires short circuit currents at the minimum voltages listed. We will need to apply up to 1000VAC.

Attached to this email besides the PDF file of the UL standards is a picture of what our current AC Power supply looks like now.

Pretty much the summary of all of this would be what are all the components that I need to build this AC power supply ?, what capacity would I need for each item such as the uF for the capacitors, and the Ohms for the resistors etc, and how would this look in a schematic ? Like I said earlier I know that this is a lot I understand but I haven't been getting much help with it at work or from other sites. I appreciate anyone with the knowledge willing to share.

Moderator's note: The UL standard was deleted because it is copyrighted material assigned for the use of one specific individual.

 

I know how to do it.
A custom transformer would simplify the task considerably. Would there be money in the budget for this?

 

I know how to do it.

That's great, I have been struggling with this for a few weeks. I know what all of the components do but I have never done it in a design setting before at work. Would you be willing to help me ?

 

That's great, I have been struggling with this for a few weeks. I know what all of the components do but I have never done it in a design setting before at work. Would you be willing to help me ?

Sure. What is currently your biggest challenge?

 

Sure. What is currently your biggest challenge?

Finding the parts and as to what their capacities should be. I should be able to put the schematic together myself but that may take awhile. Be definitely all of the parts and their capacities. My manager said that I should find a 480 VAC Multitap Transformer. But so far I didn't know where to go from there with the other pieces. Do you think that transformer would work ?

The link below is the transformer that I have found:

http://www.lcmagnetics.com/transfor...rmer/multi-tap-transformer-6-65-kva-pn-17928/

 

I know how to do it.
A custom transformer would simplify the task considerably. Would there be money in the budget for this?

Would this Transformer work :

http://www.lcmagnetics.com/transfor...rmer/multi-tap-transformer-6-65-kva-pn-17928/

 

Right away I fail to see how you will get a 240 VAC output for your test. With 480 VAC on the primary, you can wire the secondaries in series and get 124 VAC. That is why I suggest you find a vendor that can give you the precise combinations you require.

 

I am posting because I want to follow this thread (does anyone know how to follow a thread with out posting to it? I would love to have that info)
AIDayley

 

Right away I fail to see how you will get a 240 VAC output for your test. With 480 VAC on the primary, you can wire the secondaries in series and get 124 VAC. That is why I suggest you find a vendor that can give you the precise combinations you require.

Okay I understand what you're saying. I found a company who makes custom made Transformers their name is Huntington. Should I just simply explain that I would like a transformer that will give me outputs of 240 VAC and 480VAC and can also reach up to 1,000 VAC ?

 

Okay I understand what you're saying. I found a company who makes custom made Transformers their name is Huntington. Should I just simply explain that I would like a transformer that will give me outputs of 240 VAC and 480VAC and can also reach up to 1,000 VAC ?

Yes. Write up your requirements and ask for a quote. If they ask you how many you plan to order, say that it will depend on the results of your testing.

 

For some initial testing I would recommend a 1:1 isolation transformer. That will give you 240 to 240 or 480 to 480. That way you can work with your TMOV devices and potential loads.

 

For some initial testing I would recommend a 1:1 isolation transformer. That will give you 240 to 240 or 480 to 480. That way you can work with your TMOV devices and potential loads.

Okay I just looked it up and that looks like it will work just fine. I know the transformer is a big thing but can I begin to design my loads for each current level if I haven't ordered that yet ?

 

I am posting because I want to follow this thread (does anyone know how to follow a thread with out posting to it? I would love to have that info)
AIDayley

You want to "watch" the thread. In the blue schema, there is a link to do so just above the first post on the page toward the right hand side. I think it is in a similar location in the orange schema.

 

Okay I just looked it up and that looks like it will work just fine. I know the transformer is a big thing but can I begin to design my loads for each current level if I haven't ordered that yet ?

Yes that should be eminently doable. Are you familiar with the free simulation program called LTSpice from Linear Technology? Besides simulating a design they have an intuitive schematic capture interface which is excellent for exchanging schematics

 

You want to "watch" the thread. In the blue schema, there is a link to do so just above the first post on the page toward the right hand side. I think it is in a similar location in the orange schema.

Thanks it is there
AIDayley

 

Yes that should be eminently doable. Are you familiar with the free simulation program called LTSpice from Linear Technology? Besides simulating a design they have an intuitive schematic capture interface which is excellent for exchanging schematics

I have heard of LTSpice but we weren't required to use it when I was in school they had us use LabVIEW. Do I type LTSpice into google and find the appropriate link ?

 

Yup. Here is the top hit
http://www.linear.com/designtools/software/

 

Yup. Here is the top hit
http://www.linear.com/designtools/software/

That sounds great can I exchange information/schematics on there with you ? I get off work in 40 min so I will probably download the software on my laptop at home. But as far as my loads, capacitors, fuses, and resistors, how do I determine which value to place on each of these devices ? I know I need Variable and series resistors for the loads as well.

 

I would start with a single case. Once you ave that nailed down you can consider how you might want to implement variable loads and test fixtures.