3 volt drop at outlet when charging

i don't think anyone has ever checked this before. is the car charging within time parameters?

 

There is a good chance your HVAC is 220 volts, so is not pulling as much current as you would suspect. (Mine is 3 phase, but that is unusual in residential and lowers current even more.)

Air conditioning and heat pump loads on a generator

Your Prime is a 110 volt load. (unless you have an aftermarket level 2 EVSE)

Plugging in your numbers, I keep getting about 9.2 to 9.7 ohms.

1500w @ 121vac is 12.4 Amps
1500w @ 118vac is 12.7 Amps

Ohm's Law calculator

It is almost undoubtedly on a 15 or 20 Amp breaker, so that is fine.

Wikipedia says "A distinction should be made between the voltage at the point of supply (nominal voltage at the point of interconnection between the electrical utility and the user) and the voltage rating of the equipment (utilization voltage). Typically the utilization voltage is 3% to 5% lower than the nominal system voltage; for example, a nominal 208 V supply system will be connected to motors with "200 V" on their nameplates. This allows for the voltage drop between equipment and supply. Voltages in this article are the nominal supply voltages and equipment used on these systems will carry slightly lower nameplate voltages." - Mains electricity - Wikipedia

The difference between 121 and 118 is 2.5% which seems to be 'normal'.

 

When I was using Clawson Manor's electricity (landlord charged me $15.00/mo for the use) the 120 VAC outlet on my Kill-A-Watt was 106 VAC on all three of my past and present Prius Plug Ins, so since 2012 I have not had any issues charging my car except that I thought $15.00/mo was too much

 

Check for heat at every device on that circuit. Safely touch the outside of every receptacle and other device. The drop is going into heat somewhere. If you feel any warmth, shut the circuit off and fix the problem. A loose wire connection might be the culprit. It gets hot, expands, loosens more, gets hotter, etc. 3 volts at 12 amps is 36 watts that's heat somewhere inside your walls.

Most receptacles on the usual 120 volt circuits have connections where a bare wire end is pushed into the device. A thin brass strip there holds the wire and transfers the electricity to the receptacle, and these can loosen over time--59¢ retail cost and worth every penny. The wires to the next receptacle are pushed into other holes in this receptacle...the whole thing is daisy chained along. If you find some that are warm to the touch, replace them with better units. You can get heavy duty 15 amp or 20 amp receptacles, as suitable for your circuit, for a small extra cost. These will have screw connection instead of the push in's.

 

The code advocates a maximum 5% voltage drop under full load at the end of a branch circuit. Five percent of 120 volts would be six volts. The lower the better, of course, but the charger is drawing pretty close to full load and a 2.5% voltage drop isn't anything to be ashamed of.


Mike Holt Voltage Drop Calculations

Your central air is surely fed on a different circuit from your panel, so that current doesn't even flow on the branch circuit feeding this outlet.

I recently played with one of these interesting testers:



You just plug it into an outlet and it shows you the voltage in real time (rather like a voltmeter, that). Then you push a button and it shows you the % voltage drop, and the voltage in real time, at 12, 15, or 20 amps.

You hold the thing in your hand and it doesn't sear you, so clearly it isn't just sitting there drawing 1440, 1800, or 2400 watts and showing you the voltage.

With a little bit of further investigation involving additional kinds of toys:



it turns out what the thing does is take one very short 15 amp sip the instant you push the button into voltage-drop mode, and it remembers what the voltage drop was during the sip, and calculates the percentage. Then, just to make everything that much more convincing, from then on it reads you the real-time voltage scaled down by that percentage. When you set it for 12 or 20 amps, it doesn't take another sip, it just assumes Ohm's law applies, and it shows you the numbers based on the 15 amp sip, scaled proportionally to 12 or 20.

Kind of entertaining....

-Chap

 

I would consider that drop normal, and I'm a power engineer.