air-x for 48 volt inverter

[(unknown)]

I am putting a system together from bargain/barter parts. The inverter I came up with is a pylon 5000 pure sine I got on e-bay for $250. so that pretty much set the tone for the dc voltage for my system. I have a couple of xentrex c-40 charge contollers that I can configure to 48 volts and solar pannels to drive them. I also traded a bike for 3 air-x 12 volt wind plants. Can I hook the air-x genny's to one of the c-40's and charge  a 48 volt battery? Can I modify the air-x output voltage?

[Countryboy]

Hi big,

  In order to charge a battery, the voltage from the generator must be higher than the voltage of the battery.

  In this case, you can not get 48+ volts from a 12 volt generator.

I would recommend selling the Air-X generators on eBay, and using the money to obtain a generator capable of putting out 48 volts.

I once heard a rule of thumb for system voltage.  If you are producing <1000 watts an hour, use 12 volt.  More than 1000 watts an hour go with 24 volt, and if over 1500-2000 watts hourly production go with a 48 volt system.

[richhagen]

The following options are among those available to you.  

I'm not a big fan of the Southwest Wind Power series of mills, but you can obtain parts for them.  There have been several posts indicating that they are pretty good about replacement parts, so you could contact them and probably obtain a 48V. stator for your mills, and the regulator as well and change them out. I have a 48V. mill, and the only differences to my non-expert eye are the stator windings and the regulator.  If I were going to do this I would talk to Southwest Wind Power as they designed and built it so as to do it right.

As I indicated, I am not a big fan of them so I would probably sell them and build or buy a 48V machine.  The Air403 does not start up as early as other mills I have up, so much of the time here, at least for mine, is idle.  

Lastly you could attempt to rewind the stators yourself and bypass the internal regulator, however, this I probably would not do myself, or recommend especially if they are reasonable about replacement parts.  Rich

[whatsnext]

"I once heard a rule of thumb for system voltage.  If you are producing <1000 watts an hour, use 12 volt.  More than 1000 watts an hour go with 24 volt, and if over 1500-2000 watts hourly production go with a 48 volt system."

Where did you hear this rule and what possible sense does it make? I'm just asking because it just seems illogical to not consider your uses first.

John..

[TomW]

John;

Not sure who or where the rule of thumb came from but I suspect the logic has to do with battery cable sizes. 1kw at 12 volts nominal is a bit over 80 amps  and only 40 or so at 24 volts nominal and at 48 volts nominal only around 20 amps. Each requiring progressively less cable size. Maybe I am missing something?

Just an opinion.

Cheers.

TomW

[dinges]

Yes, think so too. In fact I saw the same rule of thumb a couple of days ago. Had typed a response but can't remember whether I pressed delete or post. (I tend to delete a lot of my posts recently, before posting...)

There's a lot more to take into account than just cable size. Besides, this 'rule' only says NOT to use 12V for hi-power usage; nevertheless it can be 100% legitimate to have a 1000W 24V system. Or 500W, for that matter.

That's the problem with many rules (of thumb) and theories: they're taken as a fixed thing, without realizing for what specific application they were intended (wiring size being the limiting factor, nothing else) and the underlying assumptions. Given enough creativity, I could probably come up with a perfectly legitimate 10kW 12V system too.

Guess it's just a rule of thumb. No fixed law. Use common sense and judgement when applying. As when doing anything else, for that matter.

Peter.

[Ungrounded Lightning Rod]

Doubling the current when doubling the power quadruples the voltage drop and wire heating losses - and requires twice as much copper to maintain the same percentage loss (and wire heating), or four times as much to maintain the same absolute loss (and wire heating).

Doubling the voltage when doubling the power does nothing to the voltage drop and wire heating losses.  Without changing the wire size your losses and heating remain the same, and their percentage of your total power drops.

Copper is expensive.

A kilowatt at 12 volts is a tad under 100 amps, which is starting to push it for obtaining stuff like switches for mill-short shutdown, fusing for protective circuitry, and current out of ordinary batteries.

The rule of thumb seems to be intended to limit the current to 100 amps or so.