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Old 02-27-2017, 11:55 PM   #3031 (permalink)
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I used one of the AC control/driver boards to make a 240v/120v split phase inverter, so that there are 2 120v supplies, and a neutral. The 2 120v supplies are 180 degrees out of phase, so you can use the 2 hots to make the 240vAC. I finally got it working well with the newly configured MPPT just last night. So, now I have the solar panels putting out between 380v and 450vDC, and that goes to the MPPT, which charges 28 (just the number I had laying around!) 7amp*hr 12v batteries, which are all in series. Then, the 28 batteries feed the input of the split phase inverter, and now I'm using that to power my house! Finally I can run both 120v and 240v stuff from the same inverter. And it's 100amp 240v service! Well, I can do 200amp surges. The hardware overcurrent is set to 200amp.

Josiah is going to help me do a nice video of the whole setup. He's been practicing his lighting, and has been acting as my apprentice lately.

Oh, and you can just change one little setting, and boom, you have 3 phase power at your house! 208v 3 phase up to 480v 3 phase.

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Old 02-28-2017, 09:09 AM   #3032 (permalink)
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Originally Posted by MPaulHolmes View Post
I used one of the AC control/driver boards to make a 240v/120v split phase inverter, so that there are 2 120v supplies, and a neutral. The 2 120v supplies are 180 degrees out of phase, so you can use the 2 hots to make the 240vAC.
This is GREAT news! Looking forward to seeing that code!

Does the inverter deal with the current surge drawn by an induction motor starting up, like an air conditioner, or a water pump?

It may make sense to have an option for soft start, where the inverter ramps up from 0.5 Hz to 60 Hz in 2 - 5 seconds to avoid that 5 to 10 times rated current surge from a single connected motor.

Quote:
Oh, and you can just change one little setting, and boom, you have 3 phase power at your house! 208v 3 phase up to 480v 3 phase.
YET MORE AWESOME PROGRESS!

I just happen to have a 30 HP, 575V, 3 phase motor that I can use to stress the startup of a 3 phase 'supply'.

Sounds like I will have to start working on connecting the 2 AC Controller boards that I have. I really want to get the split phase output working at a 48V buss so that I can run a sump pump in the spring ... using a golf cart as the power supply. I will try running at 60 Hz, but I doubt that the motor on the sump pump will operate properly at the lower voltage ... I guess I'll see ...


Assuming that I get any of this done ..
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Old 03-01-2017, 12:24 AM   #3033 (permalink)
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The soft start is a good idea. Right now I was just ramping up voltage at startup, but I didn't ramp up frequency too.
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Old 03-01-2017, 02:05 AM   #3034 (permalink)
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I have been studying and testing soft starting single phase motors.
The only way to soft start a single phase motor with a load attached using constant frequency power is to reduce starting voltage down to around 220v with a transformer then quickly ramp up to full 240+ volts.
Using this sequence on an air compressor with an auto transformer I was able reduce starting amps by about 20%.
The only way to soft start a single phase motor on constant frequency is to completely unload it, resistor or transformer start with a clutch to engage the load after the motor is up to speed.

If you can reduce frequency and voltage you will likely have much better results starting the motor with load than I did.
But you have to get the motor up to speed quickly or the start circuit will burn up.
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Old 03-01-2017, 10:49 AM   #3035 (permalink)
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I have been studying and testing soft starting single phase motors.
Thanks for sharing - I am just making assumptions so far

Quote:
The only way to soft start a single phase motor with a load attached using constant frequency power is to reduce starting voltage down to around 220v with a transformer then quickly ramp up to full 240+ volts.
Using this sequence on an air compressor with an auto transformer I was able reduce starting amps by about 20%.
My load is a centrifugal pump, so it does not have a lot of load on start. There is not much water moving until you hit 30 - 35 Hz. I'm more concerned with the startup current that the motor wants, with a slip of 1800 rpm to begin with instead of maybe 60 rpm at running speed.

I am hoping that I can start at about 0.5 Hz .. since that seems to be where all of my VFDs start for some reason .. and ramp up to 60 Hz in the 2 - 5 second range. The capacitor start that is part of the sump pump will still shift the phase, I hope, and give some starting torque. But the speed switch (I think that is what deactivates the capacitor start) should switch the circuit to 'normal' single phase induction motor after maybe 20 Hz?

At a buss voltage of only 48V on a lead acid pack, I may not be able to run the sump pump at 60 Hz. But I need to get at least high enough to disengage the capacitor start, and to actually move some water. And of course I need to limit the current on the motor to the full load amps. It will be interesting, and I will no doubt learn (or perhaps re-learn) some stuff. And I will be using a sump pump that has bad seals and that overheats from previous abuse ... so if I mess it up, it's not much of a loss ....
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Old 03-01-2017, 10:51 AM   #3036 (permalink)
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The soft start is a good idea. Right now I was just ramping up voltage at startup, but I didn't ramp up frequency too.
Does that work to limit the current on startup? With less voltage applied, I would expect that the startup current would be lower than 10 times rated amps ... but my experience is with 3 phase motors. I'm a bit iffy on single phase motors

My single phase motors all have capacitor start. Does yours?
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Old 03-01-2017, 12:20 PM   #3037 (permalink)
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Is it really that difficult to soft start a single-phase motor?

I suppose it's having a full load already present that makes it a headache.

I have a good sized motor to test it on...I'll have to muck around with it. Just what I need, another project!

Thyristor control not work? You could literally dial-up the power...

oh, wait, this is derailing the topic. Back to whatever you guys were discussing.
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Old 03-01-2017, 03:23 PM   #3038 (permalink)
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Is it really that difficult to soft start a single-phase motor?
I'm not sure! I guess that's where the discussion starts - when no one actually knows ....

Quote:
I suppose it's having a full load already present that makes it a headache.
Plus, in my case, trying to use a lower voltage, like 48V, to run what should be fed from a buss that's about 150V .... wait - that would be for single phase 120V not 220V. Paul - what voltage are you running your Buss at to get 220V?

Quote:
Thyristor control not work? You could literally dial-up the power...
I think that's what my 3 phase soft starts do at work. That's a variation on what Paul does, reducing the voltage on start but not changing the frequency. We drop from about 10X rated current on a loaded start to around 3X rated current on a loaded start with the thyristor-based soft starts. With an AC controller, you should be able to stay under rated current the whole time and not heat the crap out of your motor .. in theory.
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Old 03-01-2017, 03:51 PM   #3039 (permalink)
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It's very difficult to start a single phase capacitor start motor with a load attached.
The start circuit doesn't kick off till the motor is at least 75% to as much as 85% of running speed.

It's bad enough that I am switching one air compressor over to an ABB drive and 3 phase motor.
I have the motor and drive l, just need to get it on the compressor.
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Old 03-02-2017, 05:50 AM   #3040 (permalink)
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It's very difficult to start a single phase capacitor start motor with a load attached.
The start circuit doesn't kick off till the motor is at least 75% to as much as 85% of running speed.

It's bad enough that I am switching one air compressor over to an ABB drive and 3 phase motor.
I have the motor and drive l, just need to get it on the compressor.
Put a CVT or at least a centrifugal clutch on it? Just gotta make sure it doesn't slip under full load...at least the CVT would just "gear down" instead.

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