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May I charge the battery directly?
By john2008, Section Newbies Posted on Thu May 8th, 2008 at 04:15:44 PM MST
hi

Most of the time, My wind turbinge's output is 5v to 30V AC,after bridge rectifier and filter, it goes to 8~50v dc.may I charge a 12v battery directly right after rectifier and filter?

May I charge the battery directly? | 14 comments (14 topical, 0 editorial)

Re: May I charge the battery directly? (3.00 / 0) (#1)
by Flux on Thu May 8th, 2008 at 10:53:10 AM MST
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It won't be ac after the rectifier. You don't need a filter but it wont hurt. Yes you can charge the battery direct, what else do you expect to do?

Flux

Re: May I charge the battery directly? (3.00 / 0) (#2)
by john2008 on Thu May 8th, 2008 at 11:29:40 AM MST
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thx! flux, I thought that I should at least Boost-Buck it to 14v first before I charge it. 50v might burn the battery. Am I right?

[ Parent ]

Re: May I charge the battery directly? (3.00 / 0) (#6)
by Flux on Thu May 8th, 2008 at 12:33:14 PM MST
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You will not charge if the dc volts are less than the battery volts. If there is energy there and just the volts are too low then you could boost the volts if you have the technology, If there is not enough energy from the wind source it may be pointless.

If it is a commercial device it will be chosen to cut in when there is useful power from the wind and below this point boosting the volts may get you nothing or stall the blades. If it is something you have built and you have got cut in speed wrong then boosting may get you somewhere.

Input volts above battery volts will be ok. Wind turbines have a high source impedance and the battery will determine the volts and the source impedance will determine current.

The source impedance is composed partly of the electrical impedance of the generator and partly by the limited power available from the blades. Battery resistance is too low to be worth bothering about.

This is not the same situation as the bit you mentioned later about paralleling a 12v battery with a 24v one. In this case the only limiting factor is the very low internal resistance of the batteries and connecting these in parallel will burn something, wires, battery lugs or explosive gas. All common charging systems have restricted current capability but using one battery to charge another will cause damage unless you include something to limit the current.

Flux

[ Parent ]

Re: May I charge the battery directly? (3.00 / 0) (#7)
by john2008 on Thu May 8th, 2008 at 12:39:47 PM MST
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thanks!

[ Parent ]

Re: May I charge the battery directly? (3.00 / 0) (#5)
by john2008 on Thu May 8th, 2008 at 12:02:32 PM MST
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what is the current when you charge a 12v battery by 50V?
(50-12)/R, what's the value of R. Is it the resistance of the battery?

[ Parent ]

Re: May I charge the battery directly? (3.00 / 0) (#8)
by mettleramiel on Thu May 8th, 2008 at 01:55:51 PM MST
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Yes, according to ohm's law V/R=I, but that won't help you here. The amount of current going in is completly dependant on the mill. A 10' turbine will put more amps in a battery at 12v than a 2' one so your question is impossible to answer with such limited information. If you want to know for sure how much current you are generating, get your multimeter out and measure it.

[ Parent ]

Re: May I charge the battery directly? (3.00 / 0) (#3)
by ZooT on Thu May 8th, 2008 at 11:48:36 AM MST
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The battery should hold the entire system down to it's current voltage.....
You hook up your 50 volt turbine to the battery and the voltage should drop to the current but slowly climbing battery voltage....

That's where the dump controller comes in, in that when the battery voltage gets too high, it's dumps the excess to keep it down to a safe level

Re: May I charge the battery directly? (3.00 / 0) (#4)
by john2008 on Thu May 8th, 2008 at 11:55:20 AM MST
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what happen to one battery(12v) that is charged by two batteries(24v)?does it show 12v or 24v when you measured it by a multimeter? it does not make a sense if it is 12v?(but you might right,just wondering.)

[ Parent ]

Re: May I charge the battery directly? (3.00 / 0) (#9)
by ghurd on Thu May 8th, 2008 at 06:02:57 PM MST
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He IS right.
One of the batteries might explode, if the wires or terminals didn't melt off first.

You need to read and understand some of this stuff before someone gets hurt.
Or worse.

Start with Ohm's Law. Then Watt's Law. Then Kirchoff's Law.

If this is some kind of a joke, it is not funny.

[ Parent ]

Re: May I charge the battery directly? (3.00 / 0) (#10)
by TomW on Thu May 8th, 2008 at 08:26:29 PM MST
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G-;

I think a lot of folks do not "get" the kind of instantaneous, violence a large [or even small] battery bank can deliver faster than you can even register anything happened.

In my misspent youth I was working on a forklift battery and accidentally shorted the bus bars and had the dubious honor of seeing lead terminals melt and flow away from the connections at light speed amid a thunderstorm of sparks and crackling noise. All took like a half a microsecond. Luckily I was wearing long sleeves a hat and sunglasses and no battery exploded just the sparks smoke and molten lead spewing around.

Oh, yeah the wrench was pretty much fused to the bus bars. Needless to say it destroyed the battery by melting or mostly melting off the terminals on all of them. Was not my finest moment but I learned to respect batteries from it.

Just something to think about before diving into the handling of batteries.

You Mileage May Vary.

Tom

"Education consists mainly of what we have unlearned."--Mark Twain
[ Parent ]

Re: May I charge the battery directly? (3.00 / 0) (#11)
by ZooT on Fri May 9th, 2008 at 12:22:31 AM MST
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John,

I don't know ohm's law or watts law......but I do know what I see here at my place...

My wind turbine will put out 50 or 60 volts unloaded......but a battery is a load.....and it'll hold the voltage of your system down to the current battery voltage......which will rise slowly or quickly depending on your turbine and the wind....

This I'm not real clear yet about this.....but I guess the volts rise because the turbine is forcing either amps or watts or maybe both into the battery....
I guess volts is like water pressure, and watts and amps is like the number of gallons of water being pushed through the pipe at the pressure(volts)

Maybe someone will explain that a bit here......or maybe they'll tell us both to use the nifty seach feature of this board and figure it out ourselves 8^P

Re: May I charge the battery directly? (3.00 / 0) (#12)
by Flux on Fri May 9th, 2008 at 03:39:15 AM MST
(User Info)

I thought I covered this above but perhaps it was too technical.

Wind turbines, solar panels and most charging devices including small engine driven generators have limited current producing capability. Batteries can be charged at reasonably high currents unless fully charged so you can safely connect a turbine or a solar panel to a modest size battery and as the source has restricted current capability the source voltage will be dragged down to that of the battery and all is well.

Solar panels have an inherent current limit based on the size and light level and you can short them and they just produce constant current.

A wind turbine can't supply more current than the wind speed and prop diameter allows so once again even if you short its output there will be only a limited current. If this limited current is within the capability of the battery to handle then you just connect the thing to the battery and let it get on with it.

For very tiny batteries you would exceed their safe charging current if you connect them to large panels or turbines but normally batteries sized for the system can just take it.

If the charging source is capable of very high short circuit currents ( monster engine driven generators or other batteries) then you need to add resistance to the circuit to limit the current.

For dealing with batteries and powerful generators you can use Ohm's law and the current will be the difference in voltage divided by the circuit resistance.

Doesn't work for solar as the panels are current sources. Works a bit for wind but again the resistance is not the only factor determining the current so it will always be less than the prediction from Ohm's law.

Flux

[ Parent ]

Re: May I charge the battery directly? (3.00 / 0) (#13)
by wooferhound (tim((NoSpamAt))wooferhound.com) on Fri May 9th, 2008 at 07:21:13 AM MST
(User Info) http://wooferhound.com

Electricity as water flow . . .

Volts = the pressure of the water
Amps = the size of the pipe
Watts = amps times volts = total flow or gallons per minute
W o o f -={(

[ Parent ]

Re: May I charge the battery directly? (3.00 / 0) (#14)
by finnsawyer on Fri May 9th, 2008 at 09:05:35 AM MST
(User Info)

The Poobahs closed out your other post, which I felt was rather harsh. Wind turbines are usually used to charge a battery, which I guess you know. The power provided by the turbine is the power into the battery, which is the product of the battery voltage times the current flowing into the battery. It's as simple as that. Measure the current and voltage simultaneously and multiply them together. This power will depend on the RPM of the turbine (alternator actually, but the two are connected). The power into the battery will increase with RPM or wind speed, and is supposed to reach 500 watts before the thing self destructs, which can happen because of heating of the alternator coils. Yep. That current is also flowing through the coils and causes heating in them. Too hot, and it's bye, bye.

I got the impression you were actually doing a "bench" test, which is fine. At 15 volts open circuit at 300 RPM you have a rather high cut-in RPM, which implies a small mill. Again, that's fine for experimentation. So, just redo your tests with a battery connected and also measure the current for different RPMs. Just be careful the alternator doesn't get too hot.

I would also like to suggest you get a book on basic circuit theory and study it. There is no easy path to knowledge. Good luck!
GeoM

May I charge the battery directly? | 14 comments (14 topical, 0 editorial)

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