# DC-DC boost converter design process, build, and testing



## bjfreeman (Dec 7, 2011)

reality check is most inverters have a dc-dc component that is then turned into 120AC.
they max at 10KW which is about 13HP.
those powered by 12v use dual 00 cables.
have fun.


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## DDDvvv (Apr 2, 2012)

its interesting that you should start this thread. i've been running simulations for the last three weeks, for a hv dc converter. im designing a converter with input of 250v dc, to output 650v dc.

im simulating with proteus and everything looks good on simulation. i noticed you use ltspice for your simulations. i have the full version of orcad pspice version 16.5, and its just too complicated ffor me. i just got done figuring out proteus.

for those questioning this direction, (converter design) we need this higher voltages to power ac industrial controllers, which feed on 320v dc and 640vdc (240v or 480v ac depending on drive).

getting ready to buy control parts. glad you have a working version, and keep us updated with the developments.


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## bjfreeman (Dec 7, 2011)

dc-dc I built is 390v to 765v at 330 amps based on 765v.
the 765V was derived from the output of the 150KW fuel cells from Ballard. The 390v was my orginal Battery bank when working with 96 kw 3 phase.
I did not want to invest more into batteries at the time, waiting for better price and specs.


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## PStechPaul (May 1, 2012)

I won't go into the mechanical design very much as it is posted elsewhere. I just mounted the motor (which happened to be a C-face) on a plate where the ICE had been, and I attached a small pulley which connected with a V-belt to the large horizontal pulley on the existing 5 speed tranny. It used a sprocket and chain drive to the differential.

I tested it using an extension cord and 240 VAC. Fortunately the VFD could be powered with single pahse, and most of the default motor settings wotked so I could run it from the front panel pushbuttons.

So, on to the design of the DC-DC. I started with a small 175 watt inverter I had, and I was able to make about 320 VDC by using a FWB doubler circuit with two large capacitors I had from surplus. The inverter provided a +/-160 V peak at 30% duty cycle as a stepped sine wave approximation. Here is the circuit:










In the simulation it provides about 720 watts with 760 watts input, and this was for a larger inverter I planned to buy. I was able to get the motor to spin, but any load tripped the VFD on undervoltage. With a 300 watt inverter I was just barely able to move. Obviously I needed more power. My first two videos show the progress up to this point, although they do not show my more successful ride on 220VAC, and I did not film the first attempts with the inverters:
http://youtu.be/SGd8i6dp4SY
http://youtu.be/DdvscTp3thw

I determined that the automotive inverters have an internal DC bus of about 160 VDC but I need twice that, and it is inefficient to use the 30% switched outputs. I also thought about using two in series with two batteries, but these inverters are not isolated, and so there would be high voltage on the batteries. I was going to purchase a 220 VAC unit but the 1000 to 3000 watt units were a couple hundred bucks, and still might not be what I really want.

So, I decided that I needed to build my own DC-DC converter. My next post will get into that design...


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