https://www.amazon.com/Step-Down-Converter-Regulator-Reducer/dp/B09ZP5W3P6/ref=sr_1_1_sspa?gclid=Cj0KCQjwk5ibBhDqARIsACzmgLQ39sI7OsePmtn2q-I5oBmLsjT9UhYxH2CIwkYFafdsHDo7F1jsH6EaAmPAEALw_wcB&hvadid=174260626222&hvdev=c&hvlocphy=9029733&hvnetw=g&hvqmt=e&hvrand=6514872896895464001&hvtargid=kwd-23673653981&hydadcr=19131_9441221&keywords=48v%2Bto%2B12v%2Bconverter&qid=1667681223&sr=8-1-spons&th=1
I would bet this is non isolated. It does not say isolated. It has the two negative wires next to each other coming out of the case, and they are probably tied to each other inside. This is the kind of product that can cause you major problems if trying to connect to –48. Some similar devices actually say “buck converter”. Again, cheap circuit but not friendly when connected to –48. When searching for isolated converter, some of them do you the kindness of actually saying “non isolated”. I had to go to suppliers like Mouser to find truly isolated converters. https://www.mouser.com/c/power/dc-dc-converters/isolated-dc-dc-converters/?q=48V%2012V Vicor, PICO and other companies make nice bricks for this. But everything on Amazon that I looked at was a buck type converter. From: Chuck McCown via AF Sent: Saturday, November 5, 2022 1:46 PM To: AnimalFarm Microwave Users Group Cc: ch...@go-mtc.com Subject: Re: [AFMUG] -48v to 12v 1A There really is no mystery. First, 48V is just 48V, like 12V or 5V. The fact that a minus sign is appended to the front tells the reader that it is a system where the chassis is tied to the positive terminal. If it said +48 it would say that the chassis is connected to the negative power input/out. If it just says 48V then you can guess that it is a floating input or output, chassis is not tied to either conductor. However that is dangerous to assume with 48 because the reason it is 48 is probably because it is related to telecom equipment and all of the old ilec carrier stuff was –48 with the positive terminals all tied to chassis/frame/earth ground. The first thing to check is whether it is truly –48 or just simple floating 48. Measure the voltage from the negative side to chassis. If you see 48 volts there then you truly have a –48 and the positive wires are connected to the chassis. DC-DC converters can be isolated or they can be non isolated. For example, you can get a buck converter, that just takes 48 volts, chops it into a very high frequency square wave, feeds it into a capacitor and inductor and the circuit controls the chopping frequency and the duty cycle of the square wave so that the capacitor sits at a lower DC output voltage. Like 12 volts. Very simple and cheap way to lower the voltage. However, many of those devices will chop the positive side and just pass the negative side straight through. On a –48 system, they would still work, but you would have to make sure that the negative side of the circuit board was isolated from any ground and on the output you would have a circuit that is –12 volts and the negative side would still be –48 V to ground. If you load was totally isolated and floating this would still work but this is a very ugly solution. I have done this kind of thing before, mounting stuff on plywood with large warning signs “WARNING, CHASSIS IS HOT 48 vdc WITH RESPECT TO BUILDING GROUND”. So a better solution is an isolated DC-DC converter. It take the input, chops it but runs it through either a transformer, or a set of capacitors to provide a true galvanic isolation between the input and the output. With these you can connect any type of 48 volt circuit to the input and you can connect any type of 12 volt to the output (or just the revers in the even you are boosting 12 to 48). Just look for isolated converters. 100% safe. The cheap buck converters can be used but you gotta know what you are doing. From: Sterling Jacobson Sent: Saturday, November 5, 2022 12:55 PM To: AnimalFarm Microwave Users Group Subject: [AFMUG] -48v to 12v 1A I’m not familiar with -48v power plant. What would it take to “convert” from a -48v wire pair to a 12v 1A wire pair? I’m converting a Mikrotik CCR 2004 to -48v plant in my cabinets. The 2004 doesn’t have replaceable power supplies so I was just going to cut and wire the 12v headers on the motherboard to a DC barrel installed on the back of the unit alongside the AC Input… Not sure if that would be best, easiest? It’s easy to find 48v to 12v downconverters, but -48v is a mystery to me. Help me demystify it? -------------------------------------------------------------------------------- -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com -------------------------------------------------------------------------------- -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com
-- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com
