AC running on a generator

[henni]

We use a Honda Eu6500is to power four 12,000 BTU Mitsubishi heatpumps, that is 4 tons of cooling with a 5500 watt genset.

It works really well due to the Honda being an inverter as well as the Mitsus, all run fulltime in variable speed mode, compressors and blowers.

When the Mitsu's start up, they typically pull 200 watts of power and very slowly ramp up to around 650-750 watts each.

 

[JimPghPA]

Originally Posted By: GeneralEclectic
Originally Posted By: JimPghPA

The outside AC unit has the following specks:

Goodman Manufacturing Co.


Well, there's the first part of the problem. Goodman is (I don't mean to be insulting) the bottom of the line. Builder's specials made of generic components. That kind of thing. They're okay as long as they're installed competently, but you can rest assured that they contain the lowest of the low grade components.

Given that, you can probably assume that your compressor does not have a "hard start kit" installed. Because that costs about $100-$200 extra and Goodman would simply never include anything that's not absolutely necessary.

The hard start kit is basically one (or sometimes more) capacitors and a load/speed sensing relay that switches them into a phase-shifting circuit whose purpose is to generate more starting torque while pulling LESS starting current. The idea is that the hard start kit raises the probability of a successful start under marginal -- poor wiring, high source impedance, low line voltage, etc -- conditions. Well, that's basically what you're facing with a generator. The high source impedance part of it.

So, if you're experiencing a heavy load that bogs down the generator, you should probably ring up your HVAC guy and get him to install the kit for your compressor. Assuming that there is one, but there should be.

I can tell you that I have a similar situation. Honda ES6500. Trane 2.5T split high-efficiency heat pump RA ~7A depending. Hard start kit is standard equipment in this. The generator hardly burps when the system switches on.


A second contactor (start relay) for the outside fan with a time delay of a few seconds (probably 4 seconds would be best) would also significantly reduce the total start load. That would give it about 4 seconds for the compressor to start, followed by 4 seconds for the outside fan to start, followed by the existing house air blower motor that already has a delay of 8 seconds after the compressor.

 

[JimPghPA]

Truth be told, I am amazed that the current outside system and the inside section "A coil" have never leaked enough to require any additional refrigerant. The current unit is probably at least 12 years old.

I have talked with people who have put in more modern whole house AC units, and usually they are changing the house breaker from a 30 Amp 240 Volt, to a 20 Amp 240 Volt. That alone indicates that the most more modern units draw less at start up.

 

[JimPghPA]

I talked with the family friend who has the heating and ac business, and one thing he mentioned is that due to changes in what refrigerants are being used, and the improvements in efficiency, when a section of a whole house AC system goes such as the outside unit leaking or the inside A coil, it is too hard to find a existing proper size replacement, and he always does the entire system, instead of ever trying to do only one section.

 

[JimPghPA]

BTW, I totally follow the part about the additional package to reduce the compressor start current, but as for us and our system, the generator can handle the current system if it ever has to.

 

[tig1]

UPDATE:

Today at about 1:30PM we lost our power because of a construction accident that severed a large line. Several thousand are without power, and it's 98F this afternoon.

I fired up the Power Mate at 1:45 and all is well including the AC unit which I ask about. I heard power may be restored by 6PM but time will tell.

 

[tig1]

The power came back on at 5:30PM and my genny performed great with the 2 ton AC I have. This is the second power outage we have had this summer for a total of 15 hrs. and the Subaru engine hasn't used any Mobil 1 10w30 yet. As already mentioned, it was 98F here so that was a good test for my entire generator package in high heat conditions.

 

[JimPghPA]

I am glad it worked for you.

Here in Pittsburgh the electric power is arranged in rings and branches. The closer you live to the center of the city the more rings you have around you. There are also different high voltages that these rings are set up with. The way a ring works is when there is a fault the ring goes down, and then the ring is sectionalized so that the smallest section around the fault is left with no power and the rest of the ring still is powered. When you get far out from the city there are branches instead of rings. When a fault occurs with a branch circuit the sectonalizer can only cut loose the fault and also ALL of the customers further down the branch.

Because we are close enough to the city to be on a ring, when there is a fault usually only one or two blocks of houses are without power. Sometimes even less than a whole block is out, depending on where the fault is at. And the houses that are out are often out for less time compared to houses on branches where the repair crew may have to travel more to find and fix a fault.

 

[tig1]

Originally Posted By: JimPghPA
I am glad it worked for you.

Here in Pittsburgh the electric power is arranged in rings and branches. The closer you live to the center of the city the more rings you have around you. There are also different high voltages that these rings are set up with. The way a ring works is when there is a fault the ring goes down, and then the ring is sectionalized so that the smallest section around the fault is left with no power and the rest of the ring still is powered. When you get far out from the city there are branches instead of rings. When a fault occurs with a branch circuit the sectonalizer can only cut loose the fault and also ALL of the customers further down the branch.

Because we are close enough to the city to be on a ring, when there is a fault usually only one or two blocks of houses are without power. Sometimes even less than a whole block is out, depending on where the fault is at. And the houses that are out are often out for less time compared to houses on branches where the repair crew may have to travel more to find and fix a fault.


Makes since. Not sure if it'e due to the hot temps we are having now, but last night about 8:15 the power went off again(2nd time this week)and sparks flew just behind my house. Once again I powered up the genny and everything worked well(I back feed through my welder outlet) including the AC. The power was off for nearly 3 hours again. As it turned out a power line severed into and fell into my back yard. Live action all over the place.

 

[HangFire]

Originally Posted By: JimPghPA


I wonder if the connectors and wires from the generator to the fuse box, combined with wires from the fuse box to the compressor, help protect the generator by acting as a series resistance that drops enough voltage to limit the surge, or if the voltage drop from said wires and connectors hinders the generator by requiring the start current to be of a longer time duration due to the voltage being lower, compared to how long it would take to start with very thick wires over a very short distance with very heavy connections.


Not only does line resistance hurt the start time, it enhances the chances of motor burnout. Low voltage coupled with ample current and a slow starting electric motor is the recipe for coil burnout, as the motor stays in the high current draw phase longer. The same wattage with higher voltage will draw less amperage, start the motor sooner and be much safer.