Transformer Rewind for 3-phase.

[3Phase]

I am atempting to rewinde 3 small transformers to use in converting a portion of 48-volt 3-phase ac source to 12-volt 3-phase ac.  Most of my wind genny power needs to be 48 volt for my 4.3 kva inverter, but I would like to transform a portion of it to 12-volt for several smaller ups inverters that I have.

Transformer Technical info:

Original Specs.

10 to 1 ratio

Primary    410 windings of #25

Secondary   41 windings of ? (don't know the awg.)

Rating      80 watts continous

Rewound Specs. (Yet to be done.)

4 to 1 ratio

Primary    164 windings of #21

Seconday    41 windings of ? (Not rewound)

Rating       ? Hopefuly aprox. the same?

All three will be rewound with these specs.

Do I do a delta-delta connection of the transformers to get the voltage that I am after?

Dose the number of windings sound corect for a 1to4 ratio transformer set?

# 21 wire is the largest wire I think can fit with 164 windings on the primary. (Acording to my my math skills, 1+1=3)

With decreasing the primary windidng from 410 to 164 and increasing the awg from 25 to 21 do you think that each transformer will have similar power handling capability in watts as when it was originaly manufactured?

And finialy how do I relate the capasity of each transformer to the capasity of the transformer bank for use in 3-phase?

I do plan on using fuse protection on the primary of each transformer

Thanks for any help or sugestions

3Phase

[Electric Ed]

1. "Do I do a delta-delta connection of the transformers to get the voltage that I am after?"

Answer - Yes. A wye connection would produce 20.8 volts.

2. "Dose the number of windings sound corect for a 1to4 ratio transformer set?"

Answer - Yes.

3. "do you think that each transformer will have similar power handling capability in watts as when it was originaly manufactured?"

Answer - Power handling capacity depends on temperature rise, which depends on wire resistance and heat disipation (cooling). Use the largest wire size that you have room for.

4. "how do I relate the capasity of each transformer to the capasity of the transformer bank for use in 3-phase?"

Answer - If each transformer can handle 80 watts, the total three phase power will be 240 watts.

EE

[drdongle]

Just to ad my .02, power handling capacity is primarily dependent on the core size of your current transformer, if it is rated for 80 watts then that is the maximum you can expect with any winding combination. cooling is an issue but the amount of Iron set the the limits.

Carpa Vigor

Dr.D

[Flux]

I see problems with this idea.

Your transformers are rated for 60? Hz. It is likely that your wind generator runs at a lower frequency at cut in.

If it is half frequency you will have to double the turns so you will have a considerable reduction in power handling if this is the case.

I also see a problem of making the load share between the 48v and 12v.  If the ratio is too great you will not charge at 12v. if it is too small you will overload the transformers as it tries to hog more than its share of the output.

I think you will have to make the ratio low so that you get perhaps 16v and use a regulator to reduce this down to say 13.8v with perhaps a current limit to prevent overload.

I think it would be worth thinking about a dc/dc converter from 48 to 12v.

Flux

[Ungrounded Lightning Rod]

I see problems with this idea. Your transformers are rated for 60? Hz. It is likely that your wind generator runs at a lower frequency at cut in.

The way to handle that is to imagine your genny spinning fast enough to get 60 Hz and figure out what the voltage would be - and use a transformer rated for THAT voltage, along with the max current you want to pull from the genny.  When the genny slows down the voltage will drop in proportion but the peak current in the transformer windings and the peak magnetization of the core will remain the same.

[3Phase]

Thank you all for the help, and advice. I am thinking that I will limit the curent drawn through the transformers by suplying the recified 12-volt power the the circuits of a 10-amp automatic battary charger (Car battery charger).  I may also keep the ratio low and regulate the voltage a littelbit.

With the frequency at aprox. half of the rated of the transformer does this afect the voltage of the output or just the ampacity due the slower core magnatization cycles?  If the hz. of the system afects the ampacity of the system of transformers directly I think that it will still work for my use.

3. transformers rated 88 watts 60 hz wired in delta-delta, total capacity aprox. 260 watts.
   
3. transformers used at 30 hz, now 44 watt. wired in delta-delta, total capacity aprox. 130 watts.  Posibly enough to run my 10 amp automatic charger circuit.
   
   

Is my thoretical thinking incorrect about the direct relation between hz and ampacity?

I intend to build the transformers, rectifiers, firtration/regulation circuit, ampmeter, and charger curcit into the large case of an old computer powersuply with cooling fans ( they already are made to run off of 12-v dc).

Thanks for the advice and sugestions/technical education.  :-)

3Phase

[ElectricJim]

Hi there,

I have been taking a look through this section and noticed your porblem with your concerns of overheating the metal core and windings of the transformer.

If you get it right, the windings will run happily with little stress, however, nothing in this world goes according to plan, so build in a safegard to cool your transformer.

I suggest you take apart the charger and mount a cooling fan (use a computer fan)facing the core windings, so it is blowing right at them.

they draw very little current at 12V DC, you can also control the speed if required.

I have a backup DC power supply in my house, consisting of two medium size 12V vehicle batterys, I have them on a constant trickle charger modified cooling with a PC fan.

It has been working without fault in up to 40 degrees celcius without problems.

I also did the same with an old UPS, I put a LAPTOP fan in it, reducing the voltage with a LM7805 regulator. Before the windings werte to hot to touch, now it runs cool.

Again, when delving into the insides of high voltage, take care with what you are doing, if you dont know how to modify properly, then stop right there and get someone you know who knows what he is doing. TThis is for those who might happen to read this, you know the type, over confident persons with no knowledge of electric power and wouldnt know what the active and nuteral was about.

Good luck with your transformer conversion