Trying to convert 28VAC input to 120/240VAC or 9/36VDC....

James9782 · Oct 31, 2014

I have a query from a customer who is looking to buy a 5W product from me which runs on 120/240VAC or 9/36VDC. The problem is, they are in an isolated location where they only have a 28VAC power supply. I have looked around the web and cannot find any obvious solutions, does anyone know of any solutions/products which will solve this issue?

Best regards,

James

Bobster · Oct 31, 2014

A couple of diodes.

LeeH · Oct 31, 2014

A bride rectifier the 28VAC TO DC.

That's a pretty odd supply voltage.

Knobhead · Oct 31, 2014

A bridge rectifier will give about 39VDC. If needs be use some form of voltage regulator.

tazz · Oct 31, 2014

If the 28vac is at 50hz then and bridge rectifier will output at 100hz .....As Tony stated will need regulating..
Suggest bridge rectifier first...output to LM7815 reg, this will give stable 15v dc out.
omit transformer from diagram

[ElectriciansForums.net] Trying to convert 28VAC input to 120/240VAC or 9/36VDC....

chlee-penang · Oct 31, 2014

If the 28VAC is from secondary of transformer with center tap, i.e. 14/0/14V, and ripple is not a problem to the lamp, I would suggest simpler solution by using 2 diodes to form a full wave rectifier, that will provide 0.9x RMS - 12.6 VDC.

Correct me if I am wrong.

Besoeker · Oct 31, 2014

James9782 said:
I have a query from a customer who is looking to buy a 5W product from me which runs on 120/240VAC or 9/36VDC. The problem is, they are in an isolated location where they only have a 28VAC power supply. I have looked around the web and cannot find any obvious solutions, does anyone know of any solutions/products which will solve this issue?

Best regards,

James

I'm surprised that no one has suggested a transformer.
Seems to me it would be simplest and most obvious solution to get from 28Vac to 240Vac. Or 120Vac.

tazz · Oct 31, 2014

Besoeker said:
I'm surprised that no one has suggested a transformer.
Seems to me it would be simplest and most obvious solution to get from 28Vac to 240Vac. Or 120Vac.

Spot on...being ac you can use a 28/240 transformer in reverse...giving 240ac out.

James9782 · Oct 31, 2014

Thank you gentlemen,

your replies have given me food for thought... Very grateful. For clarification, the appliance is going on-board a naval vessel.

Regards,

telectrix · Oct 31, 2014

but current would be high on the primary 28V side, approx. 4 x the 120V current.

tazz · Oct 31, 2014

Yes Tel......so if the unit is 5w at 28v then current is 0.18a .....@ 120v current will only be 0.04a.
everything equals out between primary & secondary (increase one...decreases the other)

Besoeker · Oct 31, 2014

telectrix said:
but current would be high on the primary 28V side, approx. 4 x the 120V current.

The current on the 28V side is always going to be higher than on the 120V side for the same power. Regardless of conversion method used.
That's kinda how electricity works...........

tazz · Oct 31, 2014

It will always be equal.....and wattage is the key....primary voltage is higher lower current......secondary voltage lover, higher current...put this in equation of total power for both and you can see current is proportional V/IR ...P/V

Besoeker · Nov 1, 2014

tazz said:
It will always be equal.....and wattage is the key....primary voltage is higher lower current......secondary voltage lover, higher current...put this in equation of total power for both and you can see current is proportional V/IR ...P/V

More correctly, it's VA.

Neglecting losses, you get

V[SUB]1[/SUB]I[SUB]1[/SUB] = V[SUB]2[/SUB]I[SUB]2[/SUB]