# This is how 40A @ 50V (2kW) looks like



## Norppu (Jul 23, 2018)

The thing is that this power supply would be far easier to do using switching PSU technique. However, there are these boat-anchors and as it happened those suit for the task. This power supply is going to be used to feed an induction heater. There is a project thread for that and I will give a more detailed description there ... later.

Auxiliary transformer, soft start relays (25A continuous, 100A rush), rectifier (90A continuous), FET array for power control (240A continuous). The wiring is NOT an overkill, I am actually a little bit worried about it. Time will tell.



Some smoothing capacitors are required. These are high current capacitors 30mF (aka 30000uF)  a pop. Although these are quite old they still exceed their specifications. They have very low ESR (Effective Series Resistance) and their capacitance is still 10% over what is on the label. The leakage current @50V was 4mA.



This is why a soft start is required. The toroid transformer is fully capable of frying the fuse if connected to mains without precautions. The soft start relays first connect a 100 ohm resistors and then after the voltage in the capacitors is at working level this resistor is bypassed by the other relay. This transformer can output 36V @ 50A. It is also quite heavy.


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## RJSakowski (Jul 23, 2018)

I share your your enthusiasm for high power power supplies.  

My first was  a linear supply with SCR switching in the bridge.  It had an OCV of 28 volts and would charge a 12 volt battery at up to 70 amps.  To take full advantage of the power cycle, I built a delay in the trigger circuit to fire the SCR at the start of the next half cycle.  I wound my shunt resistor on a ceramic core using 14 AWG copper.  

The second transformer based power supply was built for anodizing.  It is a constant current supply with an OCV of 25 volts and a maximum of 30 amps.  Current is regulated via an LM350 voltage regulator configured as a current regulator and controlling a bank of three bipolar power transistors.

I have also assembled a pair of 40 amp constant voltage power supplies for the purpose of charging deep cycle batteries. 

I say assembled because the basis for these supplies were  5 and 7 volt, 40 amp constant current supplies.  The power supplies were purchased at hamfests for $ 1 to $4 each.  

The first consisted of two 5 volt Power One supplies, modified to output 7 volts each, The supplies were wired in series and and a digital volt/amp panel meter added.  A .5 ohm current limiting resistor was added to the output to limit current in the event of a totally dead battery and welding cable was used for the leads.  The supply was housed in a metal tool box for portability.

After some thirty years, the supply finally failed and a second supply was built, this time based on three 5 volt 40 amp Meanwell supplies adjusted for an output of 14 volts..  Again, a volt/amp digital panel meter a current limiting resistor, welding cable leads and housed un a metal tool box.

Finally, a WIP restoring the failed first charger.  This time around, the basis is two 7.5 volt  40 amp Meanwell supplies.  The old tool box is being retrofitted for the new supplies and a new panel meter.  It will weigh in at around 14 lbs. This build will be documented in another post in the near future.  

I also have an induction heater to feed so there may be yet another supply in the future.


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