Can battery SOC affect stalling?

[Beaufort]

OK, I've been doing a bunch of testing using a small 100 ah, 12VDC deep cycle battery with a small wind turbine and the charge level of the battery is driving me nuts.  The simple question is this…can a discharged battery bring a turbine into stall at the top end, where a “more charged” battery would allow it to power through?  I seem to be getting very different peak power results if the battery was 11.3VDC at rest versus 12.5VDC, however there are other variables that I'm also playing with that may affect top-end so I wanted to eliminate this one.

It sort of makes sense that allowing the voltage to rise can keep a turbine on peak longer (isn't this how MPPT works?), so if the battery voltage is lower due to charge level it could cause the turbine to stall.  Keep in mind that this is a small battery and the turbine could be on the edge of stalling anyway at the top end, so could the battery push it into stall?

[Volvo farmer]

Others will know more about the top end, but I have definitely experienced stalling on the "bottom" end with a discharged battery, that seemed to go away when the battery was a few volts higher.  This was with an axial flux machine, you didn't mention the design of your wind turbine.

In my particular case, it seemed like my turbine was in too high of a gear, and the wind just couldn't push it well enough to get and good power out of it. I only observed this at lower RPMs and it definitely improved when the battery volts were higher.

[Flux]

Yes it could be a factor. Most forms of loading involve a certain degree of stall but blades will tolerate a fair bit. There comes a time when it suddenly goes into hard stall and then the performance falls off very badly.

If you are in the critical region then a small change in battery volts may tip you over the edge but I doubt that you are getting the best performance even when it is better, more of a case of being worse when it's dreadful.

High voltage machines tend to stall worse as the effects of rectifier drop and line resistance are usually less but even at 12v you can hit stall bad enough to kill the performance.

Flux

[Beaufort]

Thanks for the replies...good to know I'm not out in the weeds on this one.  This is an overwound axial machine, mostly playing with controlling stall performance at the top end but I think it has too many turns to make it this sensitive.  The tip-off was tracking TSR as a function of windspeed; with a fully charged battery it was doing TSR 4.5 up around 20 mph and pulling nice power (in Delta).  Running with a discharged battery did TSR 4.5 around 15 mph and then fell down to 4.1 around 20 mph, with a huge difference in power of course.  I've read Flux's advice on TSR's in the low 4's and he's right again...that's stall country.  At least now I can go back and back-solve the optimum AOA range for this blade, and then use it for the stall limiting setup. 

I'm guessing most aren't using such a small battery and testing a wide range of voltages like this, since I haven't read much here about battery condition affecting performance. 

[ghurd]

"Delta",  as in regular electric motor wiring Delta?

I have a feeling the circulating currents could have a fairly substantial impact, especially at the lower RPM.
Maybe not as much as you are seeing, but some.
Might be worth a try in IRP (Jerry Rigged).

G-

[Beaufort]

"Delta",  as in regular electric motor wiring Delta?
I have a feeling the circulating currents could have a fairly substantial impact, especially at the lower RPM.
Maybe not as much as you are seeing, but some.
Might be worth a try in IRP (Jerry Rigged).

This one starts in Star and switches to Delta.  I've tested IRP, parallel star, etc. and found that Delta gives the best overall performance at higher speeds for this particular machine.  I like the way a Star-Delta combination machine can follow the cube law of the wind by using the higher slope of the Delta, without massive resistance losses at the top end.

[boB]

It occurs to me that, depending on how the turbine is wound, if you had high wind speeds where the
turbine would be pretty much stalled, and your batteries really needed charging, you could temporarily
wire them in series to take advantage of the higher voltage capability of the turbine at those speeds.
Sort of a poor man's MPPT for wind.  You'd have to disconnect your nominal battery system voltage
loads and inverter at that time of course.

Just a weird thought.
boB

[tecker]

 I would say the battery being closed to full charge should push the wind generator Rpm up due to voltage increase . You may have really small wire internal to the Stator that is capable of higher voltage on the order ofdouble the battery voltage . It sounds like your charging a Marine 12 . I little more info about the genset will put the data in perspective ,