diy solar

diy solar

Powering a HUGE air compressor

time2roll said:
PF at 73% says you will need 30% additional apparent power from the inverter.
I assume the nameplate is the start surge maximum close to 30kW. Running should be less. I think I would want to plug it in and measure the actual start and run power draw. That is a monster.
Click to expand...
Yeah... I'm looking into a newer, more efficient air compressor to rethink this all with.
 
Hedges said:
208Y, 37A
That's 4440W (or VA) for each of three 120V phases.
I don't spot LRA locked rotor amps. Assume 5x nameplate, 185A

Running it is easy, with enough battery and/or PV.
3x Sunny Island 6048US and 3x Sunny Boy 7.7

The problem is starting. Rated surge power of Sunny Island is 11 kW for 3 seconds. Peak current is 180A for 60 ms, enough time to trip a breaker but probably not to start a motor.


A VFD that ramps the motor up to speed would help. Probably ramp fairly quick before pressure builds in the line.
I have had an issue with Sunny Boy giving a fault when trying to wake up while VFD is running. I think it is OK if VFD is off at the moment Sunny Boy wakes up from night or reconnects after generator/grid issues. DC coupling PV is another option, although I really like AC coupling.



Which equipment do you recommend? I just suggested about $16k to $20k (msrp) of inverters, although bargains can be had. We haven't even gotten into batteries and PV panels.

Silly thing is, VFD is an inverter that can run it just fine, and for cheap. If only we had a good MPPT SCC to take in PV and put out 350V or so.
Click to expand...
I'm going to change out my air compressor for something more efficient and will rethink this from that compressors need. Thanks for the input.

I already have 20+ 350w panels and 15+ 85ah Duralast batteries. It's a start. Not the greatest batteries, I know, but they will work for something right?
 
Hedges said:
208Y, 37A
That's 4440W (or VA) for each of three 120V phases.
I don't spot LRA locked rotor amps. Assume 5x nameplate, 185A

Running it is easy, with enough battery and/or PV.
3x Sunny Island 6048US and 3x Sunny Boy 7.7

The problem is starting. Rated surge power of Sunny Island is 11 kW for 3 seconds. Peak current is 180A for 60 ms, enough time to trip a breaker but probably not to start a motor.


A VFD that ramps the motor up to speed would help. Probably ramp fairly quick before pressure builds in the line.
I have had an issue with Sunny Boy giving a fault when trying to wake up while VFD is running. I think it is OK if VFD is off at the moment Sunny Boy wakes up from night or reconnects after generator/grid issues. DC coupling PV is another option, although I really like AC coupling.



Which equipment do you recommend? I just suggested about $16k to $20k (msrp) of inverters, although bargains can be had. We haven't even gotten into batteries and PV panels.

Silly thing is, VFD is an inverter that can run it just fine, and for cheap. If only we had a good MPPT SCC to take in PV and put out 350V or so.
Click to expand...
i always thought that 3 phase has much less inrush peak current ?
 
circus said:
FYI 10hp (35cfm) is puny for sandblasting. You'll spend most of your time waiting for the pressure to build.

Using a diesel screw compressor won't use any electricity and blasting will take 10 minutes instead of an hour. Buy one used, use it for five years then sell it for what you paid...... If your still alive.
Click to expand...
The compressor provides 200psi at 80cfm... I've had no issues. I'm trying to eliminate costs though and be fossil fuel free... switching to a gas powered machine doesn't fit those interests
 
Hedges said:
PV powering an air compressor could save on fuel costs and be a great convenience, if total consumption is large. Problem is how much needed at once. If 10kW to 15kW of PV provides what's needed for daily use, could be great. That's a big motor, so smaller motor and different pully size could scale it to different output.

For occasional use, burning fuel as suggested is easiest and cheapest.
Click to expand...
Yes. I can see I was overly optimistic. I'm looking into upgrading my compressor. I want to go off grid with this. If upgrading my equipment to more efficient machinery is needed then so be it.
 
Doug Wall said:
I'm curious to see how this turns out. My first thought is "How much real estate do you have to mount the panels?" We have 6kW mounted on our roof. That's 24 panels. 12kW would be 48 panels. 15 kW would be 60 panels. The problem is that they rarely put out the full power! If you wanted to run "off grid" you would probably need 30% over. With batteries to act as a buffer, you would need a monster bank to handle the amperage needed. The idea of a diesel compressor would be a better way to go.
Click to expand...
I do have twenty 350w panels and 15 85ah 12v batteries. None of it is connected yet. Not sure if the batteries can even be used for a decent solar system. Since I have them I'd like to use them. I want to move my sandblasting container away from my home and into a remote corner of my property that has no electricity to it. I have plenty of ground space so building a ground array in addition to having the solar mounted on the container is not an issue. I'm mounting to my container to provide the container with shade to help mitigate summer heat issues.
Biggest issues is my big motor. I've decided to switch out. I'm looking for a efficient replacement currently.
 
SolarShedTed said:
WTF is your problem? I had much more important business to attend to than replying to the thread I had started. Life occasionally takes turns. Covid fell upon me and my family. Sorry I didn't respond to your advice. But shaming someone because you felt ignored? Come on! Grow up.
Click to expand...

An unresponsive poster who then returns notably later, abandoning the original thread and starting a new one is at best poor etiquette. It completely goes against your "Knowledge is a gift. I respect your time and advice. Thank you in advance for helping me live through this adventure."

Now you have two threads going, splitting attention and wasting others' time.

I apologize for not including a smiley in the "join us" post. It would have better conveyed my overall disposition in this matter. No shame was intended, and I recommend you revoke any authority you have given me to shame you. I'm just a schlub on the Internet. I only have the power to shame if you allow it.

Again, hope everybody is better.
 
SolarShedTed said:
Yes. I can see I was overly optimistic. I'm looking into upgrading my compressor. I want to go off grid with this. If upgrading my equipment to more efficient machinery is needed then so be it.
Click to expand...
Have you considered a water cooled compressor and inter/after cooling to help reduce overall energy consumption?
 
houseofancients said:
i always thought that 3 phase has much less inrush peak current ?
Click to expand...

Much better torque because a good phase angle between windings (not just shifted by a capacitor.)
Inrush is still going to be stall current, from winding resistance and any inductance.

VFD pulses narrow spikes of voltage (from its capacitors) so can limit input to constant current. It should deliver constant torque at all speeds, rather than axle-breaking torque when drag racing (or spinning up a machine.)
 
sunshine_eggo said:
Single phase to 3phase VFD substantially increases the input current beyond the power requirement of the 3 phase motor - typically double.
Click to expand...

3rd scope image shows 28A current peaks feeding a VFD.
Split-phase 2 HP pump ran with 15A breaker, VFD feeding 2 HP 3-phase trips 20A breaker if turned up to 60 Hz.

diysolarforum.com

Battery ripple current

After reading of someone tripping battery breakers at well below rating, I realized that could be due to pulses of current drawn by the inverter. Ideally capacitors would smooth out current draw so high frequency switching pulses and 60 Hz draw all came from the caps, and current from batteries...
diysolarforum.com diysolarforum.com

PV to high-voltage battery to VFD would be ideal for OP's application.
3-phase battery inverter running motor will work if sized correctly.
3-phase inverter feeding VFD for ramp-up, then switch out VFD and give it straight 3-phase 60 Hz sine wave could be an improvement. Soft-start, and then eliminate that diode/capacitor VFD front end from the equation.
If you can get a VFD with near 1.0 PF (draws sine wave current), that would be great.

(with VFD, may be OK that compressor pressure builds during gradual spin-up. I think that could possibly be a problem for soft-start devices used on single-phase motors. Solenoid or other pressure relief that remains open until running full speed could help.)

With VFD, you could use an analog pressure sensor and regulate RPM. If an application cycles compressor and lets pressure ramp up and down in tank, while pressure regulator maintains desired air pressure for application, regulation wastes energy. Less consumed if tank pressure controlled to just above regulated output. But for sandblasting, you may use the variable higher pressure to get more work done.
 
Last edited:
sunshine_eggo said:
Huh?

Too rich for my blood.
Click to expand...

Slipped on a copy/paste, sorry.

Now has link to my post with AC (and battery) current measurements.
Compare resistive load, synchronous A/C compressor, VFD drive.
 
Get a scroll type compressor (no reciprocating losses) and use a DC motor wired directly to the batteries.

And also, don't do this. Just run grid power. You'll get the benefit of having the money go towards real-estate improvements your kids can sell and make money instead of having to spend their inheritance disposing of a bunch of solar panels and old batteries and shipping containers.
 
Hedges said:
208Y, 37A
That's 4440W (or VA) for each of three 120V phases.
I don't spot LRA locked rotor amps. Assume 5x nameplate, 185A

Running it is easy, with enough battery and/or PV.
3x Sunny Island 6048US and 3x Sunny Boy 7.7

The problem is starting. Rated surge power of Sunny Island is 11 kW for 3 seconds. Peak current is 180A for 60 ms, enough time to trip a breaker but probably not to start a motor.


A VFD that ramps the motor up to speed would help. Probably ramp fairly quick before pressure builds in the line.
I have had an issue with Sunny Boy giving a fault when trying to wake up while VFD is running. I think it is OK if VFD is off at the moment Sunny Boy wakes up from night or reconnects after generator/grid issues. DC coupling PV is another option, although I really like AC coupling.



Which equipment do you recommend? I just suggested about $16k to $20k (msrp) of inverters, although bargains can be had. We haven't even gotten into batteries and PV panels.

Silly thing is, VFD is an inverter that can run it just fine, and for cheap. If only we had a good MPPT SCC to take in PV and put out 350V or so.
Click to expand...
More straightforward approach would be 350v from mppt feeding VFD dc bus directly.
 
You might want to consider an unloader valve. The compressor motor starts but it doesn’t immediately start working against the air in the tank. Once the motor is up to full speed the unloader can be closed, and now you have some flywheel effect working for you. You could either buy a valve or make one.
 
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