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Stepdown transformer problem

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ohionet1

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My scenario is to create a dc power supply circuit(Vout 3-15vdc) capable of 40A peak load. MUST use the below described TOROIDAL power xfrmer:





Input Voltage: Series: 230VAC, 50/60Hz
Parallel: 115VAC, 50/60Hz
Output Voltage: Series: 100VAC CT@ 10.0A
Parallel: 50VAC@ 20.0A

I need to stepdown to 30vac or less to allow for options in regards to regulation, protection, linearity, etc...

Can I use only 1 side of primary @115 and put both secondarys in series to get 25vac???
 

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tpetar

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My opinion for this job, that is best to decrese voltage on primary side, and adjust with this voltage on secundar to requirements. Other solutions will have huge amount of heat and dissipation, in other words waste of power, and unsafe device.

Search circuits on net for drill speed control with triacs, or motor speed controls.

Paralleling windings is possible if windings have the same voltage. Small difference in voltage can cause problems and waste of current, trafo can get very hot, and output current can be reduced by that loss of current in two windings. Both windings must be in phase. Trafo windings should be bifilar for this scenario.

Even we have parallel windings, we have 20A, You say You need 40A in pulse, but You didnt specify duty cycle (utilization).
 
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ohionet1

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I agree that would seem the most logical, but in this case the only available primary source is 115vac, the solution must be within the xfrmr or after.
 

tpetar

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You can regulate primary voltage of 115V like as 220V. Procedure is the same. Regulation after trafo is very difficult, of course is possible but with what cost? You should step down voltage from 50V to 20-30V its huge dissipattion for that high current. One possible solution is using switching DC-DC step down circuit.
 

tpetar

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sorry.. 50% duty

You should check whether you trafo support 100% over current for 50% dutty cycle.

What temp will be? Trafo is designed for what working temp? Core is predimensioned, what core square is, or core is smaller?
Wires are good protected with protective lacquer?


Some things can be seen only if you do experiment. Start from trafo idle, then, small current, then higher, then higher,...


If trafo not with bifilar windings and have voltage difference in windings, this will be bad idea.
 
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ohionet1

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class b (130 deg cel) size 175mm OD x 68mm h

---------- Post added at 08:24 ---------- Previous post was at 08:21 ----------

also rated @ 1000va / hipot test 4000va
 

tpetar

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What is working temp of that trafo for normal load ? (130C) What will happen when we overload it for 100% load 50% duty cycle? What temp will be (if we forget bifilar windings and voltage difference) ? What is max allowed temp of trafo core and windings temp ? Is there additional active cooling?


Hipot (high potential) test is insulation breakdown test. The Hipot test is used to ensure that an insulation can withstand a high potential without risk of failure.



First check :
- Windings are bifilar or not ?
- Windings voltage difference ?
- Windings resistance ?
- Max allowed temp of trafo core and windings ?


I understand your setting of problems, but sometimes its cheaper and easier to use appropriate trafo for job needs.
 
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