Variable AC Dummy Load

[Xenobius1]

Hi guys, I am looking for a circuit so that I can build a variable dummy load AC not DC. Could anyone help out?

I am currently using rows and rows of 200W bulbs .. but they heat up too much. Any other IDEA apart from Resistors which are really really expensive?

thankyou

PS. I did find a DC dummy load here in the forums but as said.. its DC not AC

THANKS

 

[SM2GXN]

Hi Xenobius!

I'm real curious  ;D sounds like you are dealing with high power, what are you doing?
What is the frequency, mains or higher and what is the maximum power the dummy load have to withstand?

 

[ante1]

Yes, I am curious too! I got an AC dummyload for 0 to 120kW; it’s a very expensive tool!

 

[Xenobius1]

Nice to see you are interested. Well I am working with 230vac at 50hz.

I have some solidstate relays which I need to load to test them. I know its expensive but I still would like to give it a shot here

Thanks guys!! Looking forward to your help as I am lost hehe 

Will post some pictures of it when I finish it (if I start it) hehe 

 

[Xenobius1]

Yes, I am curious too! I got an AC dummyload for 0 to 120kW; it’s a very expensive tool!

Cool did you buy it or did you make it? Do you have any pictures or anything?

thanks

 

[Muhammad Abu Bakar]

Hello Xenobius!

I can remember something about the transformer properties.  IT says

To change the voltage level

v1= (n1 / n2 )*v2

v1=secondary volts
v2=primary volts
n1=secondary  turns
n2=primary turns

similarly it transfers impedence to the other side by!

Z1 = Z2 * (n1 / n2)^2
Z2 = actual impedence at one end
Z1 = Effective transffered resistence at other end.

and u can variation in Z1 with either changing (n1/n2) or Z2
For fixed Z2, using a transformer with taps can help change turn ratio.

An auto transformer can be used for the purpose. ( I have one in my REGULATOR with lot of taps and capable of voltage change upto 50%)

 

[Xenobius1]

hmm  thanks mate. Do you think you can explain this a little better as I coudn't imagine how to doit. Thankyou !!

 

[Ldanielrosa1]

I am currently using rows and rows of 200W bulbs .. but they heat up too much. Any other IDEA apart from Resistors which are really really expensive?

Well, with a dummy load you're facing a challenge turning the energy into anything besides heat.

I don't know if it would be worth your while, but you could build your own resistors from a heating element.  This would allow you to make whatever load you want.  It would also reduce the startup surge that bulbs have.

 

[SM2GXN]

I remeber those big resistor packs they used to load heavy diesel generators when I worked in SAF, they were air cooled but represented only fixed loads not variable.
I don't know if it is possible to wind own high power resistors with kanthal, alkrothal or nikrithal, honestly never tried with any of these but whatever dummy load you use you will have a lot of heat transfer.
How is that 0-120Kw ac dummy built Ante?
Have you checked inside this dummy load, don't say you haven't?  ;D

 

[SM2GXN]

Ldanielrosa that's an good idea cold resistance of the bulbs results in high inrush current but on the other hand these relays should manage to cope this surge otherwise they will be useless in some applications.

 

[Xenobius1]

Yes I agree about the heat in the dummy load. Well at least its only Heat and not BANG .. there goes the bulb ... hehe

Im still terribly interested in knowing more. For example about the DIY resistors .. using some special wire you said.. Any more information please?

thanks guys please keep it up  8)

 

[SM2GXN]

Hmmm third post in a row  ;D
Dummy loads I've built has been for RF and purely resistive, some of them has been air cooled or liquid cooled by oil and I have one which is made of two copper wires in salt/water solution (not for internal use  ;D) that give 50ohms.
Xenobius here is a link to something that might be of interest, this guy uses heating elements (same idea as Ldanielrosa had) that probably can be used from trashed washing machines for free:
http://www.homepower.com/files/shuntregulationhp72.pdf
what do you think?
I read your last post, I will have to check up on the wire cause I have never tried it myself someone might have more on this.

 

[Muhammad Abu Bakar]

Hello Xenobius!

Can you tell us please which kind of source u r using for load test?
A Generator, transformer or something elese..

 

[ante1]

Hi Guys,

Well I don’t own it, I just use it; I bought it for the company where I work for US$8000 including shipping. It’s the size of a suitcase, here it is:  http://www.cannonloadbanks.com/l120.htm
Works perfectly, outstanding quality!

 

[Xenobius1]

Well I am using either single phase current which is 230VAC at 50Hz or 3 phase supply which is 400VAC between phases at same frequency.

 

[Xenobius1]

Hi Guys,

Well I don’t own it, I just use it; I bought it for the company where I work for US$8000 including shipping. It’s the size of a suitcase, here it is:

 

[Xenobius1]

Ah no good for me because its only upto 200v and its for 400Hz

 

[ante1]

There are other models here : http://www.cannonloadbanks.com/PRICING.html
You have to ask, but I think the 60Hz versions will also work with 50Hz.

 

[SM2GXN]

Here is a schematic of a factory made dummy load from 1-32KW to much I guess  ;D ofcourse it can be scaled down but the problem is still there on how to make those power resistors to fit your needs :

http://babelfish.altavista.com/babelfish/tr