Charging Lead Acids

[(unknown)]

I hope someone can clear my mind for me . . . I have a 230Vdc 2.25HP treadmill motor which generates 1 V per 50(ish) rpm input.  I wish to charge two 6 V 560 Ah batteries which I use, connected in series, to provide 240 V ac through a 1000 W inverter.

Each of the 6 V batteries provides access to three 2 V cells.  I can therefore charge a 12 V, 6 V, 4 V or 2 V battery bank with cut in speeds of 600 rpm, 300 rpm, 200 rpm and 100 rpm.  Most convenient would be to charge and discharge at 12 V - but that 600 rpm cutin is worrying.  I can buy two more similar batteries and have two feeding my inverter with 12 V while I connect the other two in any configuration on charge.

I think that charging the batteries connected as 2 V in parallel I an going to get the least power from the mill, but I will get power in the lowest winds.  My difficulty is that I do not understand the physics of this - can anybody please confirm this is true and guide me to understand the mechanism so I may make an informed trade off in charging configuration and blade sizes.

Many thanks,

Mal

[ghurd]

There is no power available to be harvested below 6MPH, so the blades should be turning the motor at slightly less than cut in voltage at 6MPH.

I try to make mine start charging at 7MPH, or even a bit faster, and when I stopped chasing getting power from 6MPH wind, my results improved.

That's awful fast for 12V charging, but not impossible.

It is more efficient to charge all the batteries at the same time, in the same bank.

And the changing the batteries around will become a chore.

Considering the total effort and cost expended, I would recommend looking for a more suitable motor.

G-

[Flux]

In theory you can charge 2 or 4 volts but in reality it will be so messy as to be impractical, the cells are linked within the 6v block and it will be near impossible to do as you wish and keep the batteries in step.

You can charge at 6v either individually or more sensibly with the cells linked in parallel. I have serious doubts whether you will get enough charging current to charge such large batteries from a tiny inefficient windmill but you could do it if your load is very small.

 To me it seems silly to buy expensive batteries to use one set and charge the other when the money could be better spent on a windmill that worked properly at 12v but that is not my decision.

Flux

[Mal Farrelle]

I understand, and I do intend to build a 10 footer.  I am building this mill to experiment with, and ideally provide power for my next trip to spain.

I don't think the battery cells are linked internally - there are three pairs of terminals presented and the connections are made externally with large steel bars.

Thanks,

Mal

[Flux]

If the links are as you say then you do have the other options. What you describe seem more like Nife cells or traction batteries but in that case the links wouldn't be steel.

I doubt that grouping less than 6v would be worthwhile as your motor would have a limited current output and would take forever to charge that bank in parallel at 2v.

Flux

[wpowokal]

Battery charging efficiencies dictate that it is much more efficient to have any incoming supply the inverter, with any surplus charging batteries.

Therefore using one bank while charging a second is inefficient.

allan