Power reduction across parellel circuits Help

Thread Starter


Joined Jul 21, 2014
I have an interesting problem.. I have an Engine/Generator that provides 28VDC... It powers all systems on a vehicle adequately. It then branches off into two step up power inverters, and one step down transformer (assuming I'm calling them the correct names). Two convert to 110VAC and the last one converts to12VDC.

Networking Equipment is powered by the 110VAC inverters. Split into two equipment racks. Total items on the racks are not equal. Rack 1 has about three times the load of rack 2.

The problem that I have is: When the equipment connected to the first racks 110VAC inverter is OFF, and everything on the second racks 110VAC is turned ON, everything from the second set works as expected. When equipment on the first inverter is powered on, one at a time, there in an incremental drop in power on everything connected to the second inverter. Eventually transmitting items become unusable. Equipment on the first rack seem to never lose any power.

Inverters have already been swapped.

Any hints as to what could cause this?

This setup is mirrored in three different locations, but only one location shows these symptoms.

Some of the things I am contemplating are; a bad splice at a junction somewhere, or something to do with the power distribution across a parallel circuit.

Any hints on where to start looking would be greatly appreciated.

Thread Starter


Joined Jul 21, 2014
Note: Rack one is all network equipment. Rack two is network and radio equipment.

As rack one is powered, we lose the ability to transmit from rack two.


Joined Jul 18, 2011
If I understand your problem, it sounds like the supply is dropping out on the one rack. Check to ensure you haven't exceeded any power ratings.

Do you have a diagram of the system?

Thread Starter


Joined Jul 21, 2014
I can't really provide a diagram... for reasons.
Two Equipment racks in a "vehicle". Is about as much as I can say on the topic.

Everything is powered by the engine. Two inverters are in parallel. .... At least I was told they were.
An engineer is working on the issue, but has had no luck for a few weeks now.

When only the second one (in the back) is on, everything attached to it works, there is no problem with anything in the rack. .. SatCom TX gear.

When the First one (front) is powered on everything still works as it should. As the routers and servers attached to it are powered, there is an incremental power loss on the equipment in the rear rack. When everything is powered on in the front, the gear in the rear no longer gets enough power to function correctly.

Both inverters have been swapped. All gear in the rear rack has been swapped.

I couldn't physically get to the input side to measure, only the output side. I can watch the power levels drop by about 1/8 of the "total loss" for each item that is powered. Ending in about 50% of the initial transmit power levels. No longer strong enough to use.

So, a rewording of my question would be:
Assuming all the equipment is in good working order, what could cause power to distribute to one rack more than the other.

Load levels, shorted wires, increased/decreased resistance across the power lines, Incorrect grounding, something else I'm missing?

I'm mostly looking for overall ideas that could cause this.


Joined Apr 24, 2011
Since you have other systems that work, and swapping equipment around does not move the problem, the problem would be in what has not moved.

I believe that is the wiring itself. Can you check all the terminations or connection are still tight? A loose wire nut or terminal screw can and will oxidize and make a drop in line with the power path.

Too bad you cannot access the inverter output just to rule it out, but it sounds like it is fine (you swapped units with no change). That all points to some wire fault, and given your high power levels a simple ohmmeter may not resolve it.


Joined Dec 13, 2013
either your inverter output is not rated high eenough, or your 28 volt supply is. it could also be the wires carrying the 28 vdc are too small, dropping voltage with increased amp draw.