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48vdc conversion to 24vdc is there a simple way


im trying to make a replacement homemade POE for a microwave. i need to convert 48-54vdc from a rectifier down to 24VDC as easily and simple as possible. is there an easy circuit?  ive thought of using a dc/dc converter but it cost about $150. can i build it for less?

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karnuvap6 years ago
Find out how much power the microwave takes (it cannot be that much if it is currently getting its power over an ethernet cable). Then work out what current that equates to at 24 volts. Then stick a suitable resistor in series with the 48v line so that, at the appropriate current, it drops half the volts. E.g. if the microwave draws 480mW then this is equal to 0.02 amps at 24vdc. To drop 24volts across a resistor when 0.02 amps is flowing you will need a resistor of 12 ohms. It will need to be a hi Wattage resistor because it will get hot, and it is a waste of battery power but it does the job most simply. A better option would be to use a (well heatsinked) voltage regulator - the LM317 is your friend here.
A resistive dropper is a VERY bad idea to drive an electronic load, because it causes a lot of noise injection.

Steve
Re-design6 years ago
Take off the rect. Install a 2:1 transformer then the rect and that should be close. I don't think I make one for a microwave though.
iclymd2hi (author)  Re-design6 years ago
the rectifier is part of a dc power backup system for the equipment cabinet. it powers several other 48vdc pieces of equipment, the microwave is a ubiquity rocket m5. it uses 24 vdc over ethernet cable to power a radio at the dish. right now the power supply is factory made and converts 120vac to 24vdc. i want to get this unit on the battery backup in the cabinet.
Usually when one speaks of a microwave they are referring to the cooking kind.

Is the battery pack a single battery or several 12 volt.  If several then you can tap 24 volts off them.