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Running A GE 2HP Motor on an inverter With Batteries, Starting Wattage Needed

CoveredInBees

Plastic
Joined
May 31, 2020
I'll make a longer story short:

I'm currently trying to size an inverter and batteries for an air compressor motor.

Here is the information from the Motor's Nameplate:

GE Motors
AIR COMPRESSOR MOTOR
MODEL: 5KCR48SR396U
PART NO.: 9035
VOLTS: 115/230
AMPS: 18.0/9.0
RPM: 3400
HP: 2.0
1 PHASE
PC: B1024
CODE: F
SERVICE FACTOR: 1
56-FRAME


GE 2HP MOTOR.jpg

So here is my question, the nameplate mentions that the motor's code is letter F, is that the NEMA nameplate rating?

Anyway here is my attempt at figuring this all out.

INRUSH = (5.59 'Code F' * 2HP * 1000) / 120 Volts = 93.2 Amps

93.2 AMPS * 120 Volts = 11,180 WATTS, but lets round that to 12,000 WATTS

Does that really mean I need a 12KVA Inverter just to get the motor started.

I do have a 1800 Running / 3600 Peak Dewalt Inverter, should I even bother trying it on that, or is that a little too under-powered?
 
Sparky here.

Code letter 'F' refers to the motor's maximum locked-rotor current.

Your math checks out for a 2HP, 115V, single phase, code letter 'F' motor. That motor will pass somewhere between 83.3 and 93.2 amps if you try to apply 120 volts at a standstill.

If you were trying to drive a variable-torque load (like a mill or a lathe, which both start unloaded) I would say the easiest solutions would be either a 'soft starter' or a 'starting torque limiter', followed by one of the old school reduced voltage starting techniques like a variable/fixed autotransformer or a series choke. If you're the creative type and have access to some contractors and switches you could even set up a circuit to switch the motor between 230V ("starting") and 115V ("running") configurations: 1/2 the voltage, 1/2 the current (torque) and 1/4 of the power (HP).

BUT an air compressor is largely a constant-torque load - meaning that the motor will be required to exert a lot of torque during startup to avoid stalling. With electric motors, torque is largely proportional to the amount of current passing through the windings. What this means for you is that you will most likely need to either:

- Furnish an inverter (and suitable batteries) with a starting rating of 12kVA, or:
- Install an unloader valve constructed and configured in such a manner as to allow the pump to run unloaded until the motor has been successfully started using one of the aforementioned methods. If you're okay with manual operation, this could be as simple as a ball valve and a 'tee' fitting inserted between the pump discharge and tank check valve. Otherwise a large orifice direct-acting solenoid valve and a timing relay would probably do nicely.

Failing that, you could always look into adapting one of those cheap 12 volt automotive air compressors and a portable receiver tank for your application. It would be slow and annoying, but relatively cheap and easy. Just be mindful that most of those portable pumps are intended for short-time operation and unloaded starts with a very finite service life. Three or four gallons at a time is about all they will handle before becoming dangerously hot.

Hope that helps.


EDIT:

Here's a visual in case my explanation of the unloader valve was a bit unclear.
YouTube
 
You can get 230v inverters, not sure what sizes. Running that motor on 115v line power will be iffy because of starting amps, especially on a compressor. Without running the numbers, a butt load of batteries will be required. I would be looking for a generator to run that.
 
Thanks Sparky,

I installed a 1/2" unloader ball valve between the compressor head and the tank check valve. That seemed to solve the issue I was having.

I had another question about something you had mentioned. When you mentioned a variable transformer can be used to lessen the startup load, will that work on an inductive motor with a start and run capacitor.

I was under the impression that was a no-go on certain motors. To make things even more tempting I do have a 30-amp 120 volt direct wire Variac (The type with 130v over-winding) I've used on resistive wire heaters. Could you advise if that would even be safe and where to wire it in if it is?

Regards,
Kyle
 
They make gasoline powered air compressors that will supply a decent amount of air.

They make air compressors that run off your truck motor that will fill a tank up while you drive to the site, and then the clutch kicks in again when the pressure drops.

Hell, renting a bunch of illegals at the local home depot, and paying them to pump a bunch of bicycle pumps is likely a better and more effective way to get an air supply, than trying to run a load like that off batteries.
 
They make gasoline powered air compressors that will supply a decent amount of air.

They make air compressors that run off your truck motor that will fill a tank up while you drive to the site, and then the clutch kicks in again when the pressure drops.

Hell, renting a bunch of illegals at the local home depot, and paying them to pump a bunch of bicycle pumps is likely a better and more effective way to get an air supply, than trying to run a load like that off batteries.


+ 1 on what he said

Air compressors are power hogs.
 
How long does this have to run off batteries?, is it for a stationary solar battery installation or for portable use?. Some large CO2 cylinders would provide a large quantity of compressed gas so long as the cooling off of the cylinders can be addressed by swapping to a warm cylinder as one in use cools off.
 
I notice that you have a single phase motor. Typical industrial inverters expect to run a 3 phase motor. Perhaps they would still work with only one motor phase connected, but I have my doubts. Of course you can probably buy an inverter specifically for single phase motors that accept a DC input, but you will have to make sure that this is what you have.
 
I notice that you have a single phase motor. Typical industrial inverters expect to run a 3 phase motor. Perhaps they would still work with only one motor phase connected, but I have my doubts. Of course you can probably buy an inverter specifically for single phase motors that accept a DC input, but you will have to make sure that this is what you have.

I thought the same thing but was 'hoping' he meant he had some sort of inverter like they use in my truck that allows a single phase 120v load to run off the truck battery. But, I am pretty sure my truck won't run a single phase inductive load like a motor would be, only resistive loads. I also thought this thread was yet another thread where someone has an idea that is very opposite of reality but who am I to bludgeon the dreamers of this world?
 
I thought the same thing but was 'hoping' he meant he had some sort of inverter like they use in my truck that allows a single phase 120v load to run off the truck battery. But, I am pretty sure my truck won't run a single phase inductive load like a motor would be, only resistive loads. I also thought this thread was yet another thread where someone has an idea that is very opposite of reality but who am I to bludgeon the dreamers of this world?

Meh. As the old saying goes, you may not be able to fix stupid, but sometimes you can hit it with sticks enough to head it off in some other direction!

Sometimes the real answer is to let the guy spend his money, and let him come to his own conclusions.
 
I really think that its pushing a rope. You do realize that 2 hp on the DC side is at best 125 amps if on a 12 volt battery? You might get a couple minutes of battery life unless you run it off a generator.

I tried to run my sump pump off of a 2000 watt inverter. Forget if it was a 1/2 or 1/3 hp motor. And granted, might not be same motor technology, but the inverter laughed at it. Ended up buying a 12 volt DC motor sump pump that drew a fraction of the amps and works great.
 
This used to be done all the time for backup air on marine vessels that had pneumatic propulsion control systems. We would use a Prestolite 12V motor and use that to run a ~2HP Quincy air head . . . if I recall, it would draw as much as 125 Amps and with the marine batteries and the mains running, it wasn't enough to dent the batteries at all. Some vessels had 24V battery banks which cut current in half and made for lighter wiring and the solenoid starter lasted longer.

We build systems now that can run a 480V motor from a 36V (or higher) battery using a DC : DC converter that takes the 36V and boosts it to 680V and from there to a standard VFD that creates the 480V 3phase.
 
If this is running off solar, they make some great VFDs where you wire the solar directly into the DC bus (open circuit voltage around 300-380V for a 230V motor), and the VFD uses whatever power is available, no batteries required. Mostly intended for water pumps on farms.

Needs a three phase motor, obviously.
 
This used to be done all the time for backup air on marine vessels that had pneumatic propulsion control systems. We would use a Prestolite 12V motor and use that to run a ~2HP Quincy air head . . . if I recall, it would draw as much as 125 Amps and with the marine batteries and the mains running, it wasn't enough to dent the batteries at all. Some vessels had 24V battery banks which cut current in half and made for lighter wiring and the solenoid starter lasted longer.

We build systems now that can run a 480V motor from a 36V (or higher) battery using a DC : DC converter that takes the 36V and boosts it to 680V and from there to a standard VFD that creates the 480V 3phase.

I should have mentioned this before I was trying to use the air compressor for boat maintenance at a service yard with no power hook up.
 








 
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