Capacitor blast off!

xavierok

Hi
I have an invertor 4000 watts 23amp 220v soft start and variable frequency connected in paralell with 2 array of 9 300 watts pv connected in serie.

At the other end the single phase 3hp motor come from factory with 2 capacitors the blue one is a start capacitor and the white one is a run capacitors. Details on pictures.

There is 2 capacitors one for start and the other one for run.

I try start the motor aND the start capacitor blast off.

After I read that in that situation start capacitor is not needed. Can I remove it?

What about run capactor?

What should i do to have a correct installation running.

AC 220 volts is done at z2 and u2.

Thanks

mike95490

3 ph  motors don't have Start Capacitors.   They may have 3 Run caps to normalize phase shift

Check the Soft Start module settings, you may be spending too much time at too low of Fq for the caps to phase shift power to start the motor.  No More than 5 sec should be enough to spin up the motor.   Or your inverter cannot supply the Power Factor needed to run the motor properly.  I use a 6Kw inverter to start/run a 1/2 hp motor.

jonr

Single phase motors aren't well suited to soft start.  Being so close to the limit, I expect that you will need to use a 3 phase motor with a separate VFD.   Maybe with a line reactor on the input to the VFD.

xavierok

> @jonr said:
> Single phase motors aren't well suited to soft start.  Being so close to the limit, I expect that you will need to use a 3 phase motor with a separate VFD.   Maybe with a line reactor on the input to the VFD.

Thank you @mike95490 and @Jonr

Should I keep the start capacitor or remove it?

Do my inverter can perform also in 3 phase? It looks that it have 4 oit put. The user manual is very weak. I will open the case today to see if I find more adjustment or how to alterate the value @mike95490 gave me

I have 3 motors to run (not in the same time) 2 2hp and 1 3hp all single phase.

Inverter spec:
4000W 23A 1phase 220VAC solar pump inverter with IP65 full auto operation for 4HP 3KW water pump for solar pump system
Specifics
Output Type Single
Input Voltage 250-500 VDC
Weight 12.5KGS
Type DC/AC Inverters
Output Voltage 1phase 220V
Output Frequency 50/60HZ
Output Current 23A
is_customized Yes
Model Number PS4000S1
Output Power 1 - 200KW
Size 45X33X25CM
MPPT voltage 280-450V
Rated Input Current 23A
PV Power 5.04KW
Inverter Output Current 20A
Pump Rated Power(HP) 4
Pump Rated Power(KW) 3
Function Soft start and variable-frequency function
Water roof degree IP65
Operation Full automatic operation
Descriptions

jonr

Maybe the harmonics in the output are exceeding the voltage limit of the capacitor.  You could try a higher voltage one.

xavierok

@Jonr thanks for your input.

I still a have the same question.

Should I remove the start capacitor or not knowing that the inverter have a soft start.

Also you said the harmonics in the output are exceeding the voltage limit of the capacitor. You talk about which capacitor the start or the run? If I increase the voltage the inverter will not increase also it s output due to its "smart" reaction?

BB.

OK--Here is an explanation of a motor with both start and run capacitors:

http://c03.apogee.net/contentplayer/?coursetype=md&utilityid=elpaso&id=12646

So--You need both. if the motor does not need high starting torque, you could drop the size of the starting capacitor (blue 250uf cap in your picture--I think) (smaller uF rating). That would reduce the starting current load. In theory, a motor with a motor run capacitor should start turning on its own--So if low starting torque is OK, perhaps no starting cap is needed for your application (like running a fan). You can try it for a few seconds and see that happens (should not damage anything).

However, I do have some questions:

I try start the motor aND the start capacitor blast off.

Not sure what you mean by this statement? Did the starting capacitor self destruct? If it failed, did it "blow up"  the case (like an over voltage/spark) when you supplied power... Or did it overheat after running a while (if the centrifugal switch in the motor is stuck "on", the starting capacitor and/or starting windings can overheat).

And then this question:

I have an inverter 4000 watts 23amp 220v soft start and variable frequency connected in parallel with 2 array of 9x 300 watts pv connected in series.

In general, you would not run a single phase capacitor start AC induction motor with a VFD (Variable Frequency Drive), and even capacitor run/permanent split phase motors applications are not common (usually fractional Horse Power motors):

https://www.wolfautomation.com/blog/vfds-for-single-phase-motors/

Nominally, you would use a VFD (a variable frequency 3 phase inverter) to drive a 3 phase AC motor... That is common and very heavily used with water pumping applications (India, and I assume China where many of these VFD's are made). Just supply the VFD with DC power from the Solar array, then the VFD takes care of running the induction motor (is this what you are trying to do?).

I believe you can find/configure a VFD to run your capacitor start induction motor--By simply removing the capacitors and ignoring the centrifugal switch.

Basically then what you have is a "broken" three phase motor (only 2 or 4 active pole windings vs 3/6 for a typical 3 phase motor).

Using a VFD with 2 phase output put would then be programmed to supply both the primary (main) winding and the start winding. Supply both windings (with 2 phases) to start, and once up to speed, reduce the current (or turn off) the start winding power.

You should talk with your VFD (Inverter) supplier engineering about your specific application.

I believe you are better off starting with the correct motor... 3 phase induction motor. Do not try to do the single phase + VFD solution unless you can get single phase motors for less cost than 3 phase motors (in general, 3 phase motor would be the same price or less than same HP/KW rated single phase motor).

Also, make sure what ever motor you get is properly derated for use with VFD's... VFDs generally cannot output a "clean" AC sine wave--The harmonics can make the motor run hot--And needs to be rated for the extra heat because of VFD power.

-Bill

jonr

> You talk about which capacitor the start or the run?
Increasing the voltage rating of the start capacitor may make it more resistant to "blasting off" - with no other effects.

I agree with Bill - see if the VFD can be wired such that the VFD produces a different phase for the start winding.  If so, remove all capacitors.

While multiple sources say that single phase output VFDs only work with PSC motors, there is the Pentek Intellidrive which seems to work with a variety of well pumps (single phase, two and three wire).

xavierok

Again thanks @BB. And @jonr for your imput.
The invertor seller told me that I can't modify the value of the vfd as it have be tailored to my needs (aka the motor spec plate picture) and tell me to remove the run capacitor only.
When I will remove it should I let the circuit open or close it?

BB.

From what I can tell, just disconnect the motor run capacitor (and do not make any other electrical connection changes). The motor will have a bit worse power factor--But will probably run better from a VFD (which is typically a square wave type output--The sharp edges, i.e., the high frequency components, of square waves will not work well with capacitors in a typical motor, or other type, current limiting/phase shifting applications).

I don't think it will hurt anything. Just monitor the motor temperature to make sure it does not over heat. And also that it starts reliably with your load(s). If the motor does not get up to speed (for whatever reason), the start capacitor will stay connected (the cetrifugical switch will not reach disconnect RPM).

If you had a start capacitor failure--I am not sure that removing the run capacitor will do (the two capacitors are in parallel during the start cycle of your motor).

Capacitors+Inductors (motor windings) can get a bit strange when subjected to square wave-forms. Sort of like ringing a bell with a hammer--An "impulse wave form" has a very wide frequency content--If there are issues with LC resonance, a square wave can excite them (one of the frequency of the wide range of frequencies in the square wave).

http://www.ab.com/support/abdrives/documentation/techpapers/qanda01.htm


The square wave + oscillations create several problems--It can cause very high voltage spikes (damage insulation, "blow up" capacitors).

Also, the non-fundamental frequency current flow (i.e., not the 50/60 Hz used to "rotate the motor") does nothing but create heat.

Lastly, it is also possible for the high frequency magnetic fields to cause mechanical failures in the motors (windings come loose, metal pole plates and stators to come lose and vibrate, etc.).

And for these issues to cause the VFD to have stability issues with it control software/hardware. Imagine trying to tow a vehicle with a rubber cord vs a chain or rope--The vehicle could "bounce" forward and backwards as the towing vehicle moves forward. Could create an uncontrollable towing situation.

To talk about resonance with inductor/capacitor "tank" circuits--We speak of "Q" or quality of the circuit. The Q number is higher if there is not very much resistance in the circuit--And it is much more likely to oscillate because of low resistance (like a bell). And motor circuits generally have very little resistance (power systems, resistance is not good).

Again--This is a bit beyond my skill level. I would hope your VFD mfg. tech support/engineers can help you with this setup. What you are doing is a bit confusing to me. Normally, I would expect the start capacitor to be removed from the circuit (no motor run cap), and the VFD would supply the 2nd phase (offset from the main phase) to create a "rotating field" to start the motor. What they do once the motor is up to speed (continue with second phase, or shut down), I do not know.

Your motor is "tuned" to run as efficiently as possible as a multi-HP single phase motor. In most applications, a 3 phase motor would be used instead for these applications (better starting torque, more compatible with VFD technology). A VFD with with a single phase motor (and capacitor start) is not usually ideal.

Good Luck,
-Bill

jonr

Long wires (from inverter to motor) are also known to cause problems (voltage peaks).

Maybe use your 2HP motor until you get things figured out.

A start capacitor is an electrolytic that cannot be left connected for long - the motor must get up to speed so that it is switched out .  Maybe that's why it failed.

https://en.wikipedia.org/wiki/Motor_capacitor#Start_capacitors

xavierok

Thanks @BB. And @jonr for your reply. Actually we are using 40 meters wire from inverter to motor but we can start the 3hp with almost no problem after we removed the start capacitor and keep the run inside. (We try all kind of configuration including nothing with and without bridges closing and opening circuits).
Best configuration is run capacitor only and no bridge on start capacitor.
We notice that: when we position the motor the motor shaft in some well determinated position this one start and run with no problem. When it s bad positioned it doesn t start and make sone noise.
Also when we re-integrate the motor and attached it with the oil pump it worked almost ok until the oil pump need to give more pression to the press Brick machine (yes we are using in construction equipment and do compressed earth block ).
Then the motor stop and doesn't want to start again because of the hi torque necessary at that point.
Our inverter is a Pvingery PVPS4000S1 the last one on the list you can't see the 1.
http://www.pvinergy.com/content/?328.htm

Today we open the inverter and see that it s designed for 3 phase. We guess that it can be re programmed and wired for it.

So the plan it s to pass it to 3 phase and swap the 3 engines we have to run to 3 phase with the same brand. Also we can ask for some customizaton too.

Our aim here is to build house and school with machinery only powered by solar energy and not using any other energy.

Thanks for you input. We start to understand why 3 phase are more performant than 1.

jonr

We notice that: when we position the motor the motor shaft in some well determinated position this one start and run with no problem. When it s bad positioned it doesn t start and makes some noise.

Yes, removing the start capacitor can cause problems with lack of starting torque. .  Sounds like insufficient phase shift that could be addressed by putting back some start capacitance.  Ie, not as much as you originally had (this caused a problem), but some.

You might also address the issue by adding a clutch. Ie, start with no load and only apply load after it is spinning.

 Sounds like an interesting project.

BB.

The math behind induction motors is pretty complex--But to explain it simply... A three phase motor has three field windings (really 6 to run the motor at a more reasonable speed of ~1,800 RPM @ 60 Hz). A three phase motor has a "naturally rotating field" because of this (each phase is 120 degrees apart). The rotating field "drags the stator around". And, for an "induction motor", the rotating field generates current in the stator (there are no permanent magnets in the stator). The generated currents create a North/South field, and this is what the rotating field is "dragging" to create torque. Note, because the motor is "inducing" current in the stator, you have some losses because of this. And there is always "slip" between the 1,800 RPM rotating field (60 Hz) and the ~1,765 RPM under load of the stator (motor shaft). The "slip" is what creates the magnetic field in the stator.

A "simple" single phase motor has only two field windings. And the field does not "rotate", but just "flips" up and down (N/S to S/N). And there is no rotating field. So, you need something to get the motor turning. The short answer is if you attach a rope (starting cord) around the shaft and pull it (like starting a gasoline engine), once the motor begins spinning, it will continue up to speed (the math is complex but you can thing of the N-S alternating fields as if there are two rotating fields, one going clockwise and the other going counter clockwise--Adding up to an Up/Down alternating field. Once the motor is spinning, there is now the field of the rotating stator, And to the two "counter rotating fields", the the one in the direction of rotation sees the magnetic field and has low impedance (complex resistance) and continues "pumping" the rotation in the same direction (think of peddling on a bicycle--Your legs only go up and down, but if you aply force in the correct "phase" to the peddle position, you will go faster. The counter rotating field sees "high impedance" and the current is very low, and has very little practical effects in the motor).

Since there is no rotating field in a "simple" single phase induction motor, you need a second field rated off of the first field. This would be a start winding. Put a capacitor in series with the start wiinding, and the current flow through the windings is offset by something like 90 degrees (because of the capacitor in series--The start capacitor). Now you have a rotating field, and the motor can start and come up to speed. Once at speed, the capacitor is turned off (centrifugal switch) and the motor runs as a "simple" single phase motor. Or, you can use a "permanent" capacitor (smaller size, less starting torque) for this second winding. And there are other techniques too.

Now--Back to the induction motor--We are "wasting" generating this field. There are Permanent Magnet AC motors (synchronous) which are more efficient (10% +/-).

http://machinedesign.com/motorsdrives/whats-difference-between-ac-induction-permanent-magnet-and-servomotor-technologies
http://www.ashraeboston.org/resources/Documents/Presentations/January Main Presentation.pdf

However, PM type motors have "zero" starting torque if "turned on" with 50/60 Hz power... You need to start at near zero frequency to "pull" the magnets around and raise the frequency as the RPM rises until you hit full speed. This is what a VFD plus a synchronous motor system does.

You have to figure out if the increase efficiency of a PM drive is worth the cost vs a simplicity/lower cost of a standard 3 phase induction motor. In your case with single phase AC power source, you still have the VFD--So that part of the system design remains (mostly) the same (as always, the details of programming the VFD are different).

One of the problems with direct from solar power is that you either need an "oversized" solar array, or you need to figure out how to "throttle the power" to the load. I.e., you start in the morning, the energy from the sun is low--You want the motor to turn slower (i.e., classic example is a water pump--So you get 1/2 the capacity at 9 in the morning--It is still pumping and doing work. And at noon when you have more sun, you want the pump to move the maximum water flow--So higher RPM).

If your process can take variable motor speed--A VFD programmed with MPPT (maximum power point tracking of the operating curves of the solar array) will have the VFD run at a slower frequency in the morning, and then up to maximum speed at noon.

The variable frequency of the VFD+MPPT allows the motor to produce high torque at low RPM (power = RPM * Torque). This allows the hydraulic pump to still be turning (and doing work) even if you do not have full sun on the array. Sort of like the "electronic equivalent" of a a gear box or automatic transmission that matches available energy from solar array to the torque/RPM profile of your load.

Also--Do not get too wrapped up in Solar and "going green" vs practical issues. Once you have built the school--What next. Will the solar array be re-purposed to powering school lighting/fans or even pumping water for local farmers? Or will the whole system be bundled up and trucked to the next building site?

Solar power can make cost efficient and clean energy when used for applications that have years/decades of life. A 6 month building project then obsolete--Not so much.

Also need to look at available labor and costs... If your labor runs from 8:00 to 17:00, but your solar power (no batteries) only supports 9:00-15:00 "work"--Then your labor force (and building time frames) may be negatively impacted. Running a diesel or other fueled pump for a few months may be more "cost effective" and overall more efficient for a specific project.

Sounds very interesting. Good luck (and good skills)! Let us know how it all works out. And pictures!

By the way, are you located in Thailand?

-Bill

BB.

I should also emphasize what Jonr said... Put the VFD next to the motor (if it is not already there--protected from sun/weather).

Placing inductors and capacitors at the end of a long wire run with a VFD (generally some sort of pulsed/square wave output)--It is just asking for resonance problems with the the system (including blown caps).

-Bill

xavierok

@BB. Thanks for your generous input. Yes we are in Chiang Mai Thailand.
The project name is Permaculture Children's House encapsulated in The Permaculture House project. Size is 10 acres 20 minutes from Chiang Mai.
Solar cell and system will be used in different way including pumping so still a long term use.
@jonr thanks too. the vfd is IP65 so yes it can be shaded and set close to the motor.
I will keep you updated.