voltage versus specific gravity

[Propwash]

 I have read the many posts on battery use and care but still am confused by my battery readings. I am running a 12' mill rigged for 12volt output. I have a bank of four 6volt golf cart batteries that were purchased two months ago. My mill has been happily running for the past 24 hours in a brisk NW breeze with no draw on it,putting out anywhere from 20 to 90amps depending on wind gusts. I currently have voltage readings between 13 and 15 volts. My specific gravity readings are 1.22 which according to the chart on the Otherpower home page is a 75% charge. This does not make sense to me. Can anyone help me get a grasp on whats going on here? At these voltage readings the high voltage limit in my inverter kicks out and if I had a charge controller it would be diverting the amps , Yet according to the specific gravity I am still no where near a full charge. Have I cooked my batteries?

                                          Kevin

[Flux]

Did you have specific gravity readings for the batteries when new and fully charged.

The s.g. may never have been adjusted correctly when new. 15v with a charge of 90A doesn't suggest that you are fully charged. The voltage on charge does change a lot with current. When fully charged and no charge control I would have expected 20A to push them up to 16v and they would gass violently.

It is rather unfortunate that batteries will not accept high rates of charge when they come towards the end of the bulk charge phase, much of the last part of the charge cycle is mostly wasted in dump loads under normal conditions.

If you have means to charge them at a fixed current ( say 10A) you should continue until the volts come well up and they start to gas significantly and then check the s.g. When it ceases to rise after another hour of charge you can take the reading as your full charge figure and use that for future reference.

It is a bit more difficult to do it with wind alone without a charge controller as the high currents are more than the battery can absorb in the final stages. You may be able to do it in light winds if you can wait that long without needing loads.

You ought to have some sort of charge control with those sort of currents and fully charged batteries.

Specific gravity is one of the better methods of determining state of charge but is no use without a new full charge reference figure. It is also not very reliable unless you can equalise the batteries to gassing point at intervals to stir up the electrolyte.

Flux

[Propwash]

Thanks Flux. I did get much higher sg readings when I first purchased these batteries. The winds have dropped out here this evening and I am not going to draw anything from the batteries tonight. They should get a gentle charge untill morning. I will check the sg in the morning and see what I get. I just got off the phone with a local guy that has been using an old Jacobs mill for about ten years. He asked me if when I was checking my sg if I ever noticed cloudy acid. Long story short I did notice cloudy acid quite some time ago so according to his thoughts I overcharged these batteries and cooked them.

  I understand what you are saying about the charge controller. I think if my batteries are functioning the way they should I will have a higher sg and more usable power before my voltages reach thier diversion point. I guess my lesson learned here is a little overcharging has the same effect as a lot of overcharging.Thanks again for your help.

                              Kevin

[SamoaPower]

I agree with a lot of what Flux has to say. Your four golf cart batteries should have had a capacity of about 450 Ah in a 12 V system when new. A rule of thumb is that the charging source should be limited to about 10% (in amps) of the actual capacity of the bank, which means about 45 amps in your case when new. The absorption phase of a charge cycle requires that the voltage be held at the bulk voltage (14.4 - 14. for a period to allow it to top off without severe overcharge. It can't be rushed.

If you frequently see those winds that produce up to 90 amps or so, I'm afraid that you have a mismatched system. A controller, as inaccurate as they are, will help and you might even find a good use for the excess energy through a diversion controller.

[Propwash]

I live on a coastal island where we get lots of wind. I saw 150 amp readings last week. 90amp readings are quite common. I assume a larger battery bank will help absorb this charge. There is no doubt I need a charge controller. I have been running a 1500 watt heater during heavy wind to use up the charge and in the lighter winds I run the heater on the 850watt setting. I have been shutting down the mill in heavy wind when I am not around to monitor it. I just got a leed on a bank of 2volt storage batteries. They have been described to me as Meynkee 560ah. Has anyone ever heard of these? I will be going to get more info on them tomorrow. I assume I will need a very large and expensive controller. When I first built this mill I had intentions of running 12volt heating elements in a hot water storage tank that could be tied into my baseboard heating system. I got off course and set up the inverter/battery system.  Considering the cost and fickle nature of inverters, controllers and batteries I am beginning to think that managing and storing hot water maybe  a better use of amps produced for the purpose of producing heat in my home. I am sure there are hills to climb with this process as well, but I think it will get some research time at a mimimun. I would like to hear from anyone that is currently  doing this or has tried it. Thanks again for all the help and input from you all.

                                 Kevin

[Nando]

KEVIN:

Using a wind mill for heating purposes, I recommend a high voltage wind mill feeding heating elements controlled by a MPPT controller with a "late-come-in" ELC controller SECTION to limit the upper generated voltage for protecting the wind mill from over RPM rotation.

I have been assisting a fellow in UK, 2 miles from the coast, with his 5 KW (7 KW Peak) Chinese Wind mill set as a heating energy producer.

He uses a PLC ( Programmable Logic Controller) to PWM ( Pulse Width Modulation) one of the heaters ( from 0 to 100 % insertion) and 4 additional loads ( heaters) to ON/OFF as needed that the PLC control to harvest the energy available at any moment.

From thinking that the system was not working to see that the wind mill can produce good power if the proper steps are taken.

IN your case, since the mill can produce high current at lower voltage, my suggestion is to use some of those heavy DC/AC inverters (MSW) to drive high voltage heating loads ( like 120 or 230 Volts AC) with a simple controller that switches the DC/AC inverter or the loads.

Battery charging that produce electrolyte clouding is an indication of plate peeling that in a short time may destroy the battery.

Can you inform what about the voltage Versus RPM @ open circuit of the mill ?

What about the power curve Versus RPM ?>

Regards

Nando

[Propwash]

Hi Nando,

  I had similar thoughts about voltage output. If I built a 48volt stator it would reduce the cost of wire required to make the runs and probably work much better for powering the heating elements. Three months ago I hardly knew the difference between ac and dc current so I have to do a lot of studying to keep up with my ideas. If I follow your post what you are saying is that I would have a series of heating elements which would be switched on and or off  as the supply of amps increased or decreased.

  I don't understand your question about voltage versus rpm's. Do you mean ac voltage readings prior to the rectifiers or dc at the batteries? As far as power curve goes, I get 50amps at 200rpms. Because my mill is on a 20' tower I get very turbulent wind and my readings above 200rpms are very fluttery but I would say I am getting 100amps or more at 250rpms. Once I go above 200rpms it is amazing how much more power is made. I know I will get scolded for this but all three of my 50amp guages are hard over between300 and 400rpms. I can only imagine what the actual readings are at those speeds. My mill does not show any signs of blade stall which may be because I still need to run some heavier wire in some areas. I have taken some of the wieghts off from my tail so that it furls sooner and I don't get those 400rpm readings any more. I am now furling in the range of 250rpms.

   As for my batteries I would say they are toast. In the last 24 hours running with no draw the sg has not come above 1.22 with a moderate charge going into them.

   Do you have this system up and running that you are working on?

                           Kevin

[Nando]

KEVIN:

The Chinese 5 KW wind mill is operating, the system is not mine, it belongs to fellow in UK, two miles from the south-west coast of England.

Still needs some adjustments but the fellow travels sometimes and he is adjusting the MPPT parameters when he is around it.

The Mills is now producing averages close to the wind velocities reported by a site some 30 miles away, he needs to optimize the PLC CONTROLLER to have the best MPPT curve possible, one of the parameters is time constant of the wind mill that is not yet well defined.

I see that you new to electricity.

The wind mill generates a voltage that is proportional to the RPM or volts/rpm.

I see that you have not characterized your wind mill to find how it behaves with the wind velocities, just some power points you have noted.

Since your wind mill produces good currents then it may be best to have a controller that limits the charge current to the battery by sidelining some of the current to the heater ballasts.

If you think that the batteries are toasted, then discharge them to 1.75 volts/cell then carefully measure SG, charge them again trying to be below the 10 % of amp/hour rating of the bank, measure the SG again and see if you have some improvement, If you can equalize, DO IT, note the time needed to charge it, if it fails, do the cycle again up to 3 times, with good data taken.

You may save them if the plates are not damaged, are they in warranty ?.

Nando

[Propwash]

Hi Nando,

  Yes new to electricity is an understatement.LOL I do have a wind guage set up next to my mill. It is one that I made from a bicyle speedo, a cd drive motor and a cd disc with easter eggs hot glued onto the disc. It works quite well. I will record some accurate readings for you but as I recall I am getting 2amps for every mph of wind up to 30mph winds. Winds above 30mph seem to have a much higher power ratio.

   I will give the battery salvage operation a try. I will charge them with my small ac charger so as not to overcharge them. And yes my golf cart batteries are  still under warranty but if I was at fault for ruining them I will eat them. Thanks so much for your help.

                              Kevin