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How to figure out positive negative dc to dc converter

Last response: in Components
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May 22, 2011 5:38:33 PM

Hello,
I have a dc to dc converter for a computer. the unit uses 12VDC and put out 12/5 VDC. the coverter has no markings and none of the pins have continuity with the metal chasis.

can i determine the pos neg inputs using a digital multimeter?
a b ) Power supply
May 22, 2011 6:44:26 PM

most decent multimeters will let you know if the polarity is reversed

you do need a ground to check against the hots

usually a black wire is a negative
you should have a black on each output

does is have white molex plastic 4 pin or black sata connectors?

if it 4 pin molex that is easy

(warning-disclaimer- I have 3 years of high school vocational AC/DC classes
and trained at Lincoln Technical for HVAC- I AM NOT an electrical engineer :)  )
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May 22, 2011 6:59:45 PM

unfortunately this is a propiatary PSU. It is from a company called DATA911. the model is 7647 and it has a sigle molex connector with 16 pins. out of all the connectors three of them show zero ohms(I assume those are grounds). I have a Fluke 77/bn and it does show positive and neg resistance. Without a diagram can I find out which are the pos neg 12v input?

Thanks for the help
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a b ) Power supply
May 22, 2011 8:02:42 PM

chiefaponte said:
unfortunately this is a propiatary PSU. It is from a company called DATA911. the model is 7647 and it has a sigle molex connector with 16 pins. out of all the connectors three of them show zero ohms(I assume those are grounds). I have a Fluke 77/bn and it does show positive and neg resistance. Without a diagram can I find out which are the pos neg 12v input?

Thanks for the help



a ground to chassis would have minimal resistance
measure voltage across the other wires to the ones that are thought to be grounds
you want to set meter to VDC and range to 20v
use black probe to ground
red probe to possible hots
usually the worst that can happen is you pop fuse on meter


if you can open it up
you can look where the connector joins the PCB board and sometimes they have very tiny markings
of what the pin outs are
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a b ) Power supply
May 23, 2011 2:54:18 AM

Couple of points.
(1) quote ...show positive and neg resistance.... End quote. No meter will measure negative resistance. If your meter shows a negative resistance then the line has a voltage on it and the reading is invalid.

(2) the term ground, negative, and rtn get used alot. (a) the term negative and positive are relative terms meaning that one point (wire) is at a higher or lower potential than the other wire. Ground and negative - If the wire with the low potential is tied to ground then it becomes ground. Ground is more a reference point UNLESS it is tied to earth ground (Note Earth ground, chassie Ground, and referance point all have a different circuit sysmbol). If you have two wires, a return and a positive, if you want a positive out then the return is tied to ground, if you want a negative, you simply tie the positive to ground. Russian Satellites (and real old english cars) tie the positive of the battery to Ground and have a negative Vout, Just the opposite of the norm.

The pins that show the highest number of wires "shorted" together (zero ohms) should be the return side, also refered to as common. Simply connect black DVM lead to one, then measure all the rest with the Red lead, then label your drawing showing the pin-out.

Fuse in Meter is only inline when measuring current. And does not matter what range you are on, if the meter is set to current and you put it across the voltage lines, you will blow the fuse, I know - I've done that a couple of times.

Fluke makes some very good DVM, I have the 85-III @ home and use the 87-V at work.
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a b ) Power supply
May 23, 2011 3:29:10 AM

a "negative" to chassis would have minimal resistance
measure voltage across the other wires to the ones that are thought to be grounds
you want to set meter to VDC and range to 20v
use black probe to ground
red probe to possible hots
usually the worst that can happen is you pop fuse on meter


if you can open it up
you can look where the connector joins the PCB board and sometimes they have very tiny markings
of what the pin outs are


@ Retired Chief

I think I said the same thing you did LOL
to quote
The pins that show the highest number of wires "shorted" together (zero ohms) should be the return side, also refered to as common. Simply connect black DVM lead to one, then measure all the rest with the Red lead, then label your drawing showing the pin-out.

so set meter to VDC at a range of 20VDC
then use black probe on the pins though to be ground (or common)(the ones with no resistance to chassis since most devices use negative for a common excluding Russian satellites and old Jaguars)
then use red probe to measure hopefully voltage from the other "hot" or "positive"
pins

should be either + 5v or + 12v on those pins

though me personally I would contact manafacurer and have them
fax or email me pin-out of the 16 pin connector
Pretend to be a contractor who needs schematics for state contract or something
like that
government agencies always want schematics for installs
the Data911 MDS 2000 was used in many police vehicles from which
that power supply was used for
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