48 VAC - 24 VDC Power Supply
48 VAC - 24 VDC Power Supply
(OP)
Hi,
I am trying to convert the 48VAC I have from a transformer into 24V DC for running a PCB. The current requirement would be 200mA max.
I cant seem to find any off the shelf power supplies or transformers so I attempted to build a circuit by rectifing the 48V and then using the zener diode method to give 28V DC (the PCB can accept 28V max)
I used a 6w 120R resistor and a 5W 28V zener but the circuit ran so hot that It burnt my finger! So I assumed this was not the right solution.
Is it possible for me to use a 240/110 transformer except put 48VAC into the primary and get 24VAC out at the secondary. I know I can build a circut to get rectify the 24AC.
Any thoughts any one?
I am trying to convert the 48VAC I have from a transformer into 24V DC for running a PCB. The current requirement would be 200mA max.
I cant seem to find any off the shelf power supplies or transformers so I attempted to build a circuit by rectifing the 48V and then using the zener diode method to give 28V DC (the PCB can accept 28V max)
I used a 6w 120R resistor and a 5W 28V zener but the circuit ran so hot that It burnt my finger! So I assumed this was not the right solution.
Is it possible for me to use a 240/110 transformer except put 48VAC into the primary and get 24VAC out at the secondary. I know I can build a circut to get rectify the 24AC.
Any thoughts any one?





RE: 48 VAC - 24 VDC Power Supply
And Yes "that" transformer would probably work fine as long as it's rated for 200mA.
RE: 48 VAC - 24 VDC Power Supply
The reg can give you up to an amp. Suitable choice of the other components, and 200 ma is easy.
BK
RE: 48 VAC - 24 VDC Power Supply
Anytime a zener is used as a regulator, count on a lot of heat and not a very stable supply.
RE: 48 VAC - 24 VDC Power Supply
I there is only one transformer in the panel (its a lifting winch) which is 3-Phase 415V to 48VAC. There is no neutral in the panel. There is no room in the panel for anything but the smallest transformer.
I think I might use a transformer intended change 240 - 110 to change 48 - 24 instead.
RE: 48 VAC - 24 VDC Power Supply
RE: 48 VAC - 24 VDC Power Supply
Use that transformer BACKWARDS! Use it to jump the 48Vac to 96Vac. Then use any of the many outstanding off-the-shelf power supplies available to efficiently create your 24VDC, filtered and without a bunch of heat u will be then forced to deal with, *after* it has caused other problems.
Example:
http://datasheet.astrodyne.com/MCA-10.pdf
You want the Chassis Mount Version.(last page of PDF) This puppy puts out 400mA with any input between 85Vac-265Vac, 47Hz-440Hz.
This will save you DAYS of screwing around. They cost about $80 bucks... This is a CHEAP solution. This will be far more reliable than your presently contemplated solution.
RE: 48 VAC - 24 VDC Power Supply
Thats a few ideas to get me started. Looks like the zener method is unsuitable for most projects.
A transmformer of some kind is in order.
Regards
Paddy
RE: 48 VAC - 24 VDC Power Supply
RE: 48 VAC - 24 VDC Power Supply
I DO NOT THINK YOU CAN GET A 48 TO 24 VOLT,
IF YOU CAN IT SHOULD BE 1/2 THE SIZE.
ANY 1 TO TWO IN REVERSE OR TWO TO 1
WILL WORK (BEST BET). ANY OTHER OPTION
WILL USE .2*24= 4.8 WATTS.
CALL IT 5 WATTS.
50 DEG C RISE = 75 DEG C.
5WATTS *132 PER WATT = 660.
IT SHOULD HAVE BURNT YOUR FINGER AND DIED.
50 /660 = .075 DEG C PER WATT NEEDED.
IF YOU ARE SO TIGHT ON SPACE
TRY USING A 100 OHM DROPPING RESISTOR
IN SERIES WITH THE REGULATOR (5WATT).
IF A LOT OF FREE AIR FLOW A 10 WATT
(RS10100) SHOULD GET TO ABOUT 112.5 C.
OR A RH10 SERIES WITH ENOUGH CHASSIS
MOUNTING WILL WORK (ABOUT 4 IN SQ).
THESE ARE GENERAL BALLPARK NUMBERS.