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How to create 120 VAC to 90 VDC Power Supply? Answered

I need to create a 90 Volt DC Power Supply using a capacity, toroid and bridge rectifier. I know that with a toroid you have a primary (input) voltage and then you'll conserve power but have a different secondary (output) voltage. I know that if you put say 120 VAC in the primary, the outputs might be, for example, 50 Volts out, which are also AC. I want the voltage to be DC, so I know that I need a bridge rectifier that will boost the voltage by 1.41 because of the AC to DC conversion. However, you also need a big fat capacitor, and I have no idea how to size and select this. Help?



1 year ago

I just ordered a 1000v, 50amp bridge and a 6v to 90v 15a dc pulse with modulator off ebay.. got bout $6.00 invested.. I have a B&D electric mower with a ac to dc motor in it.. Oh yea-- FREE SHIPPING .. Going to use to resurrect an old treadmill. Maybe???? PWM are made to control DC Motors. All shapes, sizes, and H.P. Just though I might help someone doing the same...

Full wave rectifier

Vripple = I load / 2 * f * C

Half wave rectifier

Vripple = I load / f *C


Just about any home treadmill motor controller has close to what you are looking for - 10-15amp, with the bonus of variable speed (voltage) up to around 90-100 volts (most of the treadmill motors are around the 90-120 vdc range max). If you have the skillz you could hack it a bit to suit your needs.

You'd possibly be better with a boring-old-fashioned transformer. How much current do you need out of the 90V? L

I want roughly 10 Amps at 90 VDC. I can't seem to find anything at this power level of 1 kW. I'd be happy to take a commercially available solution, but I can't seem to find it.

If you want a high-ish current (above about 15 amps) and we bear in mind that the 90v AC is RMS, then the peak will be about 127V (voltage drop across rectifier is sufficiently small for my explanation), so, we need a capacitor able to withstand 127V and high current. You almost certainly won't be able to find this in a single component, so I'd suggest looking into series-parallel capacitor banks. Also, even with a capacitor, the output will have a bit of ripple.
To put it bluntly, it's going to be a bit of a pain =]

I think I want to make sure that you understand my question. I want to have 90 VDC out. Hence, that means the toroid I should find should give about 65 VAC rms from the secondaries. In industrial automation world, I've seen this before. I do want to find roughly 18 Amps out. I understand this is more than a $3.25 DIY project, this is something that will require a few hundred dollars. All okay by me.

The capacitor size is dependent on: Amount of current the device you are powering can pull and how much current the transformer is capable of.