Quote:
Originally Posted by Ether
2) The 3-prong wall plug (hot, neutral, ground) of Charger B has no connectivity between either output and the hot or neutral inputs, but it does have connectivity between either output and the ground input
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Am I correct in thinking you checked for connectivity with a meter set to measure Ohms? If so, what was the resistance measured? If the resistance is lower than say 100 Ohms, it is Ground referenced.
Quote:
Originally Posted by Ether
Chose either output wire (plus or minus) from Charger A, and chose either output wire (plus or minus) from Charger B. Then measure the voltage between the two chosen outputs. The voltage reading is zero regardless of choice.
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Quote:
Originally Posted by Kevin Sevcik
Sounds like the outputs are floating/isolated relative to each other, so you should be fine connecting them in series to get your 38VDC that you're looking for.
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It is possible that the three-pronged charger may be referenced to ground. If the charger contains a regular 60 Hz transformer, it may be a type that provides no input-to-output isolation. If it contains a switched mode power supply, it is much more likely to provide isolation from the input ground.
Obtain a resistor, anything from 10 kOhm to 47 kOhm, 1/4 W or higher. Connect one end of the resistor to the positive of one of the chargers and the other end to a known Ground point (third prong on outlet). Use your meter to measure the voltage of the negative output relative to Ground. Then connect one end of the resistor to the negative of one of the chargers and the other end to a known Ground point (third prong on outlet). Measure the voltage of the positive output relative to Ground. if you get about 19 V in both cases, the output is one that floats relative to ground.
If just one of them is floating, it should be Okay to connect them in series. If one of them is Ground referenced, you may have to consider the effect on the equipment that you are powering with this supply. If both are floating, then you can treat them like a battery.
Quote:
Originally Posted by Daniel_LaFleur
Jason,
While this is true, a simple fix for parallel switchers is 'OR'ing diodes. This will cause the 2 supplies to droop share.
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Paralleling diodes only prevent one supply with lower output voltage from dragging down the other. The supply with the lower output voltage will not be able to push out much output current since it's paralleling diode will not be forward-biased as much or may be reverse-biased in the extreme.
True parallel systems typically have an isolating impedance (resistor or inductor) to allow each supply to put out slightly different voltages. Otherwise, they would all need to be controlled from a single controller that forces the paralleled supplies to all have the same output current. The inverters I work on at my day-job uses sharing inductors for all the higher powered models (518 to 1500 kVA).