[RE-wrenches] Autotransformer for Single Phase Motor Headache

Mon Jan 31 11:59:48 EST 2022

Hi Chris, 
I’m not enough of an EE to know that answer. 

But my guess is it isn’t going to be enough to make much of a difference, still a massive hit on the inverters 

Given the cost of the transformers with install vs the correct motor with VFD drive. 
I’d go with new motor/VFD and you know for sure it’s going to work. 

Jay

> On Jan 31, 2022, at 9:50 AM, Chris Sparadeo <sparadeo.chris at gmail.com> wrote:
> 
> 
> Thanks for offering Darryl, but I have pretty good data on the 120/240VAC single phase motor I am up against. NEC 430 suggests LRC is 188 A, but I am measuring more like 112A during start up. I am thinking that using the VFD for slower ramp up AND as a phase converter from single phase to three phase will help lower inrush significantly. 
> 
> Jay-  with the autotransformer option, I was hoping that the 240V input and 240V output capability of the Victron autotransformer would add some of the benefits of a transformer based inverter to the Sol Ark's transformer-less design. Less about balancing phases and more about adding some inductive kick when the load drops. Am I correct in thinking this is a possible use of this specific device? 
> 
>> On Mon, Jan 31, 2022 at 9:43 AM Darryl Thayer <darylsolar1 at gmail.com> wrote:
>> Hi i have a single phase motor at a old install that i replaced about 8 years ago.  Would it help if i made some starting load surge measurments?
>> 
>>> On Fri, Jan 28, 2022, 11:52 PM Darryl Thayer <darylsolar1 at gmail.com> wrote:
>>> Hi Chris, In the past, I was able to start a 5 hp pump motor using a VFD. , I can not remember the make, of the VFD but I think it was an ABB 7.5 or 10 HP connected to a single-phase motor.  I started it on two Outback 3548s (or maybe 3024s).  Now for the tricky part, I have done this several times over the years so I keep confusing the systems.  you must power the VFD before starting the motor to charge the capacitors as the VFD will also have a loading surge.( one time on maybe 10 HP I did a homemade resistor)  The VFD has a large capacitance and will have a surge.  Most water pumps do not have a high zero-speed torque requirement, meaning low inertia, so you can use a slower ramp to speed.  watch your speed as the VFD can Overspeed the motor increasing the load.  The advantage of the VFD is it can run at a lower speed reducing the load on the inverter.  I also think an Auto Transformer will balance the load between the inverters, but may not be necessary.
>>> Also be aware that starting surge is on the battery also,  If your motor has aGH motor it can have a 4 to7 times the running loads on starting.  NEC 430,7 I think.  This can be well over 100 amps.  The inverter will sag in voltage during startup but they may draw 400 or 500 amps from the battery.  If my memory is correct the 10 HP VFD has the possibility of adding an extra capacitor which reduces AC starting draw.
>>> Sorry, this was so long, it was more than 20 years ago for me.  
>>> 
>>> 
>>>> On Fri, Jan 28, 2022 at 10:46 AM Chris Sparadeo <sparadeo.chris at gmail.com> wrote:
>>>> Hi all,
>>>> 
>>>> I currently have an off-grid client that has a 120/240VAC  7.5 HP -  40A FLC single phase pool pump. Locked rotor current is around 110 A. I had initially (and naively) thought that two Sol Ark 12k units would be able to handle this load. Due to the lack of a transformer, the unit's just can't output the required inductive startup inrush. Now getting clarification from Sol Ark that max inductive HP output is 2.5 HP per unit. We had installed an amply sized SR35 soft starter, with no avail. The 20 kW generator can start the motor, but it is noticeably shaken with the intense load drop. 
>>>> 
>>>> I am toying with the idea of installing a VFD and upgrading the pool pump to a three phase motor. Would make for a much smoother ramp and self start. The client is a bit hesitant to upgrade and would like to continue using their clunky, non-self starting single phase motor.  
>>>> 
>>>> My other thought was to implement an autotransformer to add some copper to the equation and help the Sol Ark's get the job done. Has anyone had any experience with the Victron 100A autotransformer for both 120/240 input and output? 
>>>> 
>>>> Any suggestions or relative experience would be greatly appreciated!
>>>> 
>>>> -Kindly,
>>>> 
>>>> -Chris
>>>> 
>>>> --
>>>> Chris Sparadeo 
>>>> NABCEP Certified PV Installation Professional ® # 042919-015652
>>>> NABCEP Certified PV System Inspector ® # 052920-015652 
>>>> State of Vermont Journeyman Electrician # EJ-07619
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