Convert ESP114A to floating ground

I did write a post on powering and using ESP114A power supply some time ago. To make the power supplies even more useful you can also convert one of them to a floating ground power supply. Floating ground power supplies can be connected in series to get higher voltage. Please note that converting the power supply may be dangerous (especially so if you don’t know exactly what you are doing) and if you attempt it you do so on your own risk. The power supply itself has quite some safety features inbulit but at 900W you can expect quite a lightshow if something goes really wrong 😉

According to some people writing online you can also use ESP114 power supplies in parallel (they will automatically share current when going above some treshold) to get “insane” 110A currents at 12V output voltage. At these currents you could probably use it for welding…

To make the power supply floating groud you have to break the connection between output ground and system ground. You can see from the following diagram that connecting two power supplies with grounded outputs in series will simply result in lower power supply being in short circuit while the upper power supply will work normally and output 12V at it’s output. The numbers in red show wanted voltages, while the actual voltages would be from up down 12V, GND, GND, GND.

One of the ways (the simplest way actually) to disconnect the ground connection that is sometimes used is to simply omit connecting the power (input) ground connection to one of the power supplies. This however means that the housing of the power supply is at an unknown potential. It is dangerous to handle it when the outputs are unconnected and if connected the housing will be at the potential which is connected to the output ground connection. To get away with this way of doing it one would usually isolate the housing of the power supply. If the housings of the two power supplies would accidentally get in contact it would mean short circuiting one of the power supplies.

Another way is to modify one of the power supplies and break connection between the input and output ground. This means that the ground is still connected to the power supply chasis while the output ground is floating. Please note that this probably can’t be done on all power supplies, but most of them can be modified this way. So here is how I did it on ESP114A.

First one needs to open the ESP114 power supply by removing the screws that hold the housing together. It’s actually quite crowded in the housing itself 🙂 To fully dismantle the power supply you have to disconnect the cables that connect the circuits from the lower and upper part of the power supply. You should take a photo of the cables, but I think that there are not two connectors of the same type, so you probably can’t really connect them wrong.

The connection between the input ground and output ground is made on the lower PCB, right next to the output/input connector of the power supply. You hawe to remove some more screws and to take out the PCB you will also have to disconnect the fan and front leds connectors.

To make the power supply floating ground you have to cut the tracks between input and output ground. Some types of ESP114 power supplies actually have a SMD resistor there so you just need to desolder them and there in no need for physically removing/cutting the track as with the power supplies I have.

I also added a large value / large power resistor between the input and output ground (this is not really necessary). It makes the output ground somewhat fixed – making it less likely to float to voltages that may be dangerous if it is left unconnected. The resistor value was also chosen so that at normal voltages there will be no significant current through it. At high voltages (eg. if somehow line voltage gets across to the output) there will be enough current to trip the FID protector (if you have one installed – if you don’t have FID the resistor will not do anything but heat itself). I fixed the resistor inside the power supply housing on the opposite side of the fan.

And just a few pictures of the two supplies wired in series. The lamps are 50W, so there is 2 x 250W connected across both power supplies. The big wire “holder” (the thing connected with red and green wires) next to the power supplies is meant to be populated with resistance wire to get the full 55A out of the supplies for testing purposes.

And a picture of the whole setup running 🙂

I left the thing run for a few hours and then shut it down. All seemed to work well, no magical white smoke coming from anywhere 🙂 I plan to do the whole 55A@24V ~1300W test after I get the resistance wire to wind that 1kW+ resistor 🙂