MS4448PAE and electric motor

Wbuffetjr1

I have this electric motor.  
http://www.baldor.com/catalog/EL3510#tab="performance"
Starting current is 40A

Thoughts on whether or not the 4448PAE could run this motor???
Spec sheet says "100msec surge current (amps AC) Line-Line: 40".

I am not exactly sure what that means.....

Thanks!

mcgivor

The surge current is the inrush when the motor starts from stall which is generally around 10× the load current, the duration of the inrush is 100  milli seconds or 0.1seccond. The inverter specs claim an inrush capability of 40A for 100msec at 240Vac, the motor rating is calculated at 230V so at 240V the current would be slightly lower, so technically it should work as long as there are no other loads on the inverter at the same time.

Raj174

     It means 40 amps AC at 240 volts for 1 tenth of a second, or about 9600 watts. The inverter also has a surge capacity of 8500 watts for 5 seconds. So if 40 amps can get it turing, then I would think that the 5 second surge capacity would bring it up to speed. However, this is right on the line of max capacity, so not a sure thing IMO. My OB 4000 watt Radian inverter can handle a 36 amp AC surge. That sounds close to proportional to your inverter and load.
It's hard to say for sure. Maybe other members will have more experience with pumps.

Rick  

BB.

Part of it also depends on the load on the motor... A fan or compressor with an unloader--Shorter starting surge. A compressor with a large (heavy) flywheel and/or no unloader--May be more difficult to start.

-Bill

mcgivor

@Wbuffetjr1 Here is some information that relates to your question about starting current.
http://powertips-elec.blogspot.com/2010/11/motor-starting-and-running-currents-and.html

Wbuffetjr1

Thanks fellas!

The motor will be hooked up to a Gast 0740 rotary vane air compressor. The compressor will only be operating at ~70% of it's rated PSI.  I have no idea how to measure what kind of load that will put on the motor.

mcgivor

The Gast 0740 is rated at 1/3 hp, with a maximum pressure of 10 psi, so not much for the motor, in fact the motor seems to be on the large end of the scale. Is this the correct compressor? See attached link.
http://gastmfg.com/products/compressors-and-pumps/rotary-vanes-separate-drive/0740

jonr

Some general suggestions:

1) don't use a larger motor than needed (as mcgivor suggested)
2) reduce the starting capacitor size if you don't need all of the available starting torque
3) add a run capacitor to improve the power factor
4) consider reducing starting torque needed (as Bill suggested).  This reduces the time (not peak amps) to start.
5) consider a hard start add-on that will switch in extra capacitance while starting (ie, help with power factor during start)

Baldor motors are nicely documented.

Wbuffetjr1

Sorry guys, I mistyped.  I have a Gast 0740 on a 1/3hp motor (EL3501).  The EL3510 is hooked up to a Gast 1550. 

mcgivor

The 1550 is 3/4 hp, still low pressure at 15 psi max, a vane type compressor is probably not much of a load  at such low pressure and no large flywheels to get into motion so the start up current would probably be less than at 100% load.

Wbuffetjr1

That would be great! I won't even be running it at 15 PSI.  Probably 10-11 PSI maximum.

mcgivor

In that case you might want to consider using a smaller motor, perhaps 3/4 hp, but in the overall picture, probably won't make much difference. 

Wbuffetjr1

Unfortunately this 1HP motor is an extra I already have.  I would rather put it to use than keep it sitting around.

Thanks for all the good info!

mcgivor

If that's the case use it, no sense in letting it go to waste, in the automotive field the same pickup, one with a V6 and another with a V8, the V8 is more efficient, because it doesn't have to work as hard, FWIW.

Wbuffetjr1

10-4.

With that in mind it does concern me to possibly be bumping up against the limits of the surge current for the inverter.  Should I be worried? 

Estragon

If you already have the motor I would go ahead and just try it (assuming an inverter outage won't bring your life support system down).

If the surge is too long and/or too big, the inverter should just fault and likely need a manual reset. Further assuming wiring etc is properly sized for the inverter, the magic smoke should stay where it belongs.

Dave Angelini

The battery and its connection is almost as important as the ability for the inverter to surge. Too small in AH of battery, cable, and connection quality need to be considered.

Wbuffetjr1

3 strings of golf cart batteries (my sacrificial set) to start out.  I understand 3 strings isn't the greatest, but I want to start with a cheap set and want more AH than two strings provide. Hoping they last 2-3 years at least. 

Using 2/0 welding cable for all the battery cables. 

BB.

What is the battery bank voltage? (12/24/etc.).

-Bill

Wbuffetjr1

48v

BB.

Assuming 200 AH batteries (3x parallel strings) gives you 600 AH @ 48 volts... That is good for a ~6 kWatt inverter with 12 kW surge (assuming inverter handles that output).

• 6,000 Watt * 1/0.85 inverter eff * 1/48 volts * 1.25 NEC derating = 184 amp minimum (185/200 amp) recommended DC branch circuit+breaker rating.
• 4,400 Watt * 1/0.85 inverter eff * 1/48 volts * 1.25 NEC derating = 135 amp minimum recommended DC branch circuit+breaker rating.

Your battery bank should be fine (checking/logging specific gravity and voltage per battery?).

-Bill

Wbuffetjr1

Thank you BB!

I am going to be checking and logging as much as I can.  Unfortunately, this system will be at 10,000' at a remote cabin in CO.  I am only there ~7 weeks out of the year currently. In GA the rest of the time.  Will be moving out there to the base of the mountain the cabin is on in three years. In the meantime, I can get a buddy up there periodically to check on things or add water as needed. 

I will be using this system for very small, intermittent loads in the cabin while we are out there.  LED lights, ceiling fans, flat screen TV, cpap, etc. The rest of the year, the system will run aeration for an 8 acre lake. I will run the 1hp unit during the summers and as far into the fall as I can and then have a friend switch over to the 1/3hp unit during the winter to keep holes open in the ice.