Remote observatory power... amperage reading is not what I expected

[jujumaster89]

I am setting up a remote observatory and I'm building a data and power station for it. I am not an electrical engineer, so I've been learning a lot as I've progressed. Here's my current conundrum...

I have a remote DC Power Switch that uses two 12V DC power supplies for input power. Each one powers 4 channels (8 total) that I can turn on/off via an internet connection. There is a common ground (- wire) for all the channels and the two power supplies.

I put a multimeter on each DC power supply. Power Supply 1 = 14V, Power Supply 2 = 14.3V. If I have power supply 1 on only, I see a 2 amp reading with a few items loaded on the circuit. If I turn on the 2nd power supply, even with a very small load (0.1A), on its channels, things get weird. The 1st meter amperage drops to 1.8A and the 2nd one increases to about 1.4A. But, I only have 2 amps from my original reading and I now am showing 1.8A+1.4A=3.2A by turning on the 2nd power supply.

These are cheap meters, so there is a calibration risk that I have not tested.

These meters are effectively in parallel between the load and the negative terminal on each power supply. I am sure there is a formula that tells me what a parallel reading should be. If they are additive, then I would expect them to be 1/2 the total amperage or approximately 1A each.

What's going on here? How many amps should I be reading?

Thanks,
Ian

 

[davenn]

I have a remote DC Power Switch that uses two 12V DC power supplies for input power. Each one powers 4 channels (8 total) that I can turn on/off via an internet connection. There is a common ground (- wire) for all the channels and the two power supplies.

show us some photos/diagrams of the setup so we can better understand your setup

I put a multimeter on each DC power supply. Power Supply 1 = 14V, Power Supply 2 = 14.3V. If I have power supply 1 on only, I see a 2 amp reading with a few items loaded on the circuit. If I turn on the 2nd power supply, even with a very small load (0.1A), on its channels, things get weird. The 1st meter amperage drops to 1.8A and the 2nd one increases to about 1.4A. But, I only have 2 amps from my original reading and I now am showing 1.8A+1.4A=3.2A by turning on the 2nd power supply.

These are cheap meters, so there is a calibration risk that I have not tested.

show us exactly where you are doing the measurements

without seeing what you are doing it's very difficult to visualise the situation


Dave

 

[jujumaster89]

OK, here's my attempt at showing what I'm doing. For more information on the DC power supply and the meter, see these url links:

https://www.amazon.com/gp/product/B078LWJZ1P/ref=oh_aui_detailpage_o00_s01?ie=UTF8&psc=1

http://www.digital-loggers.com/dc3faqs.html#Whats new

The FAQs are the only place I could find a wiring diagram of the DC power controller.

Goal: Monitor the Amperage from each DC power supply.
Situation: My meter readings don't seem to be independent of each other. Therefore, I don't know how to read the amperage results. It seems A+B Not = C

Thanks,
Ian

 

[Alec_t]

Why do you have your DC-DC converter getting its power from both bus A and bus B? That may account for the odd current readings. Is it a supply back-up arrangement? Why the bridges?

 

[kellys_eye]

Bridges are unnecessary. Simple blocking diodes from supply positive (A+B) to the DC-DC converter input will do - and 'common' the negatives.

 

[jujumaster89]

The DC switch uses two separate power sources in case the user needs two different voltages. in my case, I only need 12 volts. I could just bridge the buses, but I'm still not sure why my amperage readings changed when I turned on the 2nd power supply.

Thanks,
Ian

 

[jujumaster89]

By the way, unless I don't understand the point made earlier, I do not have a DC to DC converter. I have an AC/DC converter that produces 12V. This is routed to my DC switch which splits it into 4 controllable channels per input line. At least, that is my naive understanding as a non-electrical engineer.

Thanks,
Ian

 

[Alec_t]

If one of the diodes in the two bridges were leaky and if the two power supplies were of different voltage then the higher voltage supply might be driving reverse current through the other, affecting the current readings.
Depending where your current probes are located, if bus currents share a common path the readings may interact.

 

[jujumaster89]

Thanks for the input. I may just use 1 power supply and bridge the bus A/B to keep things clean.

 

[davenn]

By the way, unless I don't understand the point made earlier, I do not have a DC to DC converter.

you have a DC-DC converter ... your diagram states that

your volt/amp meter also looks weird



I don't see how you are measuring amps in that configuration

You do understand that an ammeter needs to be in series with the supply line ... usually the positive rail ??


Dave