Where’s the Watts?

I am doing some efficiency testing on a light fixture. It has 3 Meanwell HLG-240H-C2100 power supplies.

Testing the DC output of the PSs, they are running very close to spec:

#1 - 114v 2.077a = 236.77w
#2 - 113.5v 2.097a = 238w
#3 - 115v 2.1a = 241.5w
716.27w total

My working assumption (which is where I probably need enlightenment) is that the power output / efficiency (93.5%) = 766w - should more or less equal the AC watts at the wall. At the wall I get 813. 

Probability #1 - my assumption is wrong. The numbers are in line with expectations. These  watts = additional heat in/emanating from the fixture.

Possibility #2 - Your assumption is correct. Those $30 in line meters are garbage. Get a decent multimeter. 

Hi,

What is the question?

If the power supplies are outputting 716 watts and are 93.5% efficient, shouldn't
the input watts be 716/93.5=766w and not be 813w?

Hi,

If we would observe the power supplies, it is not working at the 93.5% efficiency. Generally, it is just 750/ 813 = 92.25% which is based at the datasheet. Looking at the datasheet, the power supply can only handle 250W. There are factors of heat dissipation that can actually affect the overall output.

Hi Edward Howard

When the input power feeder is loaded heavily it can reduce / limit your current consumption since the feeder is heavily loaded usually this happens in the night time . if it is an industrial area this can happen at any time .If the heavy loads in the in put of your feeder is switched off then your load current will automatically come up i think this makes that difference.

This happens when the feeder supplier has not designed and calculated the total power
requirements required for your area properly, or some party is over loading his circuit without the knowledge of the feeder supplier.

Drop in voltage.
Poor, quality of wires or non standard wirings ie wire standard not matching according to the
Power requirement, loose contacts in the wire joints loose contact in the plug , switch and socket
Will develop heat and can reduce the supply voltage. Even if your neutral wire is over loaded this
Can happen.