I was looking at buying a generator to run two 15 000 BTU air conditioners and a lot of articles I read talk about how they use more current at startup. My question is, when they are talking about more current at startup, is it only on initial start-up or it's every time the compressor kicks on in the AC unit? If so, then you would need a generator capable of supplying startup wattage at all times if you don't want the circuit breaker on the generator to trip? Am I understanding the electrical requirement correctly?
Applicane power consumption at start-up?
- Thread starter johnnyh55
- Start date
Bones
Well-known member
You should see generators give you a prime and surge number. Sometimes on the smaller generators they advertise surge not prime. Prime is the amount of power supplied constant. Surge is as it states the start up of any electrical device.
However surge is something that happens every time a device starts.
Does that help?
Well see that's thing, does Surge only happen only once? So If you start the AC and you have it running for 5 hours, surge only happens at he beginning of the first hour? Or every time the compressor in theA/C needs to start, it is going to Surge hence needing more energy than just running power.
Bones
Well-known member
Start/Surge amps is every time an electrical appliance starts no matter what the component is. Typically Start/surge is very quick. Since you are asking specifically about an AC and you state it is running constant, I'm assuming the fan is running, every-time the compressor starts it's cooling cycle you will have start/surge amp drawn higher than rated. It may not be high but you will have a surge. If your not careful and you get a generator that is inadequate and you have start/surge it creates a cascading affect on power. Meaning it can drop voltage and amps will climb until it can't handle it anymore.
If the AC is running and is cooling you will see the constant Amp draw which should be matched to 80% prime of the generator. If you are running 2 AC's units you can pull upwards of 29 to 35 amps constant. So lets assume 40 amps to call it safe at 120 volts you need 4800 watts of prime power with maybe a 6000 watt inrush/peak curve
Ah that's what I was missing in my calculation, everything is 120v inside the RV since the 240v 50A is two separate legs of 120v unlike a house. I kept calculating the amps x 240v, that's why it didn't add up, it makes a big difference when you calculate amps times 120v to find out the wattage. Thanks for this!
Bones
Well-known member
Your welcome.
dave10a
Well-known member
As a rule of thumb surge or start current is usually twice and sometime 3X the running current depending the winding inductance. Also it generally will last long enough to blow a circuit breaker of fuse that is not rated to handle it. Also if a generator is not rated to handle surge current they most likely not recover fast enough to run properly and will hunt(oscillate). A 4000/3500 watt generator will cope well with a 15,000 btu AC but a 3000/2700 watt gererator my have problems. A 5500 watt generator should handle two 15000 btu AC if they are not started simultaneously. There are after market hard start capacitors for ac's that are available to help minimize the surge current.
