Author Topic: Batteries self regulate? (Read 1928 times)

bigkahoonaa · « **on:** July 06, 2007, 03:37:05 PM »

I was scanning this board, trying to figure out how to regulate voltage for a wind mill, and found this story:

Is it true that batteries can self regulate? If so, then why do we need something like an MPPT? Am I missing something?

Mau (a.k.a BigKahoonaa)

Confused again ...

Don't be too confused. We have a user who tends to push MPPT as the answer to everything. You do need a controller tho. I will let the users explain.

bigkahoonaa · « **Reply #1 on:** July 06, 2007, 09:44:44 AM »

Ooppss! I screwed up the link. This is the story:

Need help on how to regulate voltage

whatsnext · « **Reply #2 on:** July 06, 2007, 10:14:02 AM »

Batteries "self regulate" by boiling themselves dry. Not really useful unless you can babysit them full time and even then not really useful.

kurt · « **Reply #3 on:** July 06, 2007, 10:16:20 AM »

http://www.fieldlines.com/story/2003/11/4/124345/260

here is an artical from the FAQ that may help it is a little out of date and a couple of the links are dead but still good info.

bigkahoonaa · « **Reply #4 on:** July 06, 2007, 12:40:10 PM »

Kurt:

The FAQ page is where I got the story. I can see that batteries self regulate a little. If you look at the voltage from an AC charger, it could read 6 to 9 VDC open voltage, but plug in 3 AAA bateries in series and the volts drop to 4.5 V. There must be a limit to this self regulating abbility, even when the batteries are NOT fully charged.

Confused again ...

Bruce S · « **Reply #5 on:** July 06, 2007, 12:57:53 PM »

You are correct in thinking that batteries themselves do not actually self-regulate.

When you connect a charger the voltage drop is due not to the battery regulating the charge but a voltage drop while the charger uses the voltage and current to recharge the battery. Normally an un-loaded charger will read slighty higher that what the battery's usage voltage is. This is normal.

Hope this helps

Bruce S

Gary D · « **Reply #6 on:** July 06, 2007, 01:15:03 PM »

The battery bank capacity is the key. If you have too large of a generator with a small battery bank, the voltage will rise, giving a surface charge but not fully charging the bank...

Dump loads keep overcharging (overvoltage) from boiling the water out. This is a very simplistic explanation. hope it helps....

wpowokal · « **Reply #7 on:** July 06, 2007, 10:32:57 PM »

Some links..

http://www.sandia.gov/pv/docs/BattIntro.htm

h http://www.oasismontana.com/batteries.html

http://www.trojan-battery.com/Tech-Support/BatteryMaintenance.aspx

allan

bigkahoonaa · « **Reply #8 on:** July 06, 2007, 10:45:45 PM »

Bruce & Gary :

Batteries can self-regulate but only within limits? A charger should dump excess load if batteries are at capacity, to keep them from "boiling".

What's the voltage limit? How much open voltage can a battery take? Is 30 to 50 volts a good ball park figure?

wpowokal · « **Reply #9 on:** July 07, 2007, 08:55:38 AM »

There are several factors here..

Type of battery, most common for serious Re systems is still flooded lead acid, other types have different charge requirements.

The open voltage of your wind turbine is not all that relevent, those are design paramiters for turbines, bateries are the discussion here, I think. The batteries will hold the turbine voltage down, rising slowly until they are fully charged. This is the point at witch a charge regulator will start dumping.

The rate of charge should be around 10% of total battery amphour capacity. More than that and they will be unable to convert the charge (amps) chemically at suficient rate, this will give a false high battery voltage. This may/will cause a charge controller to dump valuable Re.

Flooded lead acid batteries will be damaged if the rate of charge(amps) is excessive, and they get too hot. They need a good equalising charge at regular intervals, this will cause bubbling but is normal, a 24v bank can be floated at 30V for equalising, with out harm for several hours.

Flooded lead acid batteries will boil away the water from the electrolite(acid/water mix) if charged at a high(relative) current for an excessive period. If the plates are exposed they will be damaged.

I get the feeling you are confusing turbine design with battery charging, which is fine but I have not grasped what you are actually wanting. Maybe some of this general imfo will hit the general spot for you.

regards

Allan down under

(unknown) · « **Reply #10 on:** July 14, 2007, 12:47:31 AM »

hi everyone. i have constructed a 24 foot turbine. i have the generator coupled to a honda 6 horse for testing. tonight i see 50 volts at 70 rpm which is good but at high rpm i see 120 volts. my question is what would happen if the 100+ voltage is going to my 48v bank. could you explain the best way to control the voltage. thankyou

(unknown) · « **Reply #11 on:** July 14, 2007, 12:59:26 AM »

one more thing. i heard xantrex c40 can handle up to 125v even when set up for 48v. does it just dissipate the extra power to waste or would it still be efficient at 100+ in and 48 out. thankyou again

TomW · « **Reply #12 on:** July 14, 2007, 06:31:20 AM »

ghopper;

Ever heard of thread jacking?

You just did it [twice], and it is not considered very friendly.

T

bigkahoonaa · « **Reply #13 on:** July 14, 2007, 11:39:08 PM »

gbopper

My best ball park figure is 30 V open voltage for a 12 V system. If you have a 48 V sytem, your max V should be about 120 from the genny, open voltage.

Do you have pics of your 24'?

bigkahoonaa · « **Reply #14 on:** July 15, 2007, 10:08:33 AM »

gbopper

On second thought, I don't think 120V is a good idea for a 48V system. That's the kind of logic you get after a night out! It's probably more like (system V + X), with X at 10 to 15 V. As to the best way of charging, I'm still trying to figure that one out.

(unknown) · « **Reply #15 on:** July 18, 2007, 07:58:14 PM »

i am sorry to threadjack? i think its relivant to your questions. i guess i dont know internet rules too good. i dont mean to be an ass i just thought answers to my questions might be usefull to you. if i may ask 1 more question... how do you guys regulate your voltage if cut in speed is about 60 rpm for rated voltage and at 180 rpm the voltage is 3 times as high as rated voltage. their is always going to be quite a large voltage span. i dont understand. sorry if i should not ask this i mean no dissrespect at all.

CmeBREW · « **Reply #16 on:** July 19, 2007, 06:12:31 PM »

I'm not sure, but you both seem to be asking the same basic question. Batteries "self-regulate" (so-called) by simply HOLDING DOWN the voltage to what ever the battery bank voltage is. (12v; 24v; 48v) The 'open voltage' that the generator makes is not that important. (within reason) 2-or 3 times the voltage of your batts is normal I think for an 'open voltage' test.

Hook the mill to the battery bank. When the mill reaches the 'cut-in' voltage, (12,24,48) then that is when the voltage HOLDS (or,so-called "regulates") at that voltage level, and then the AMPS keeps going up from that point as the mill turns even faster. This is normal.

It gets more complex though. If your 'open voltage' is TOO high-- like 50v+ for a 12 volt battery bank, then problems will probably happen. Namely, the blades will STALL (be held back from turning fast enough) ,,, or it could burn out your coils in a strong wind. Sorta like driving down the freeway in only 1st gear. If its pushed too hard (strong winds)it will over-heat and burn out--because you are in the wrong gear to be going fast. The coil arrangement (stator)in any generator represents the transmision in a car. You need to be in a reasonable gear for the speed (battery bank voltage) you need to go. For example, if your generator makes 35-50 open volts in a decent rpm, you should probably have a 24volt system.

I'm certainly no expert though. Thats the way I understand it at this time. Im sure there are better, more accurate explainations than mine.

Perhaps the word "regulate" could be confusing you since it is used in this instance and in other ways too.(like a 'voltage regulator',etc)

I'm not sure that answers your question.

(unknown) · « **Reply #17 on:** July 19, 2007, 06:32:11 PM »

i would like to thank you for your explanition. based on what you say i should be ok with 120 volts "open circuit" in severe winds for my 48 volt bank. i will post pictures next week. im going to my cottage this weekend to fabricate the tower and possibly raise the gen but only temporarily until i figure out what controller to get. thanks again. which controller would you reccomend?

CmeBREW · « **Reply #18 on:** July 19, 2007, 07:20:31 PM »

gdopper,

YOur question was related to the original post. I have done that myself instead of start a whole new thread just to ask a simple related question. I am still learning the best etiquite for this particalar discussion group myself! It is difficult.

However, That is a pretty serious system you are talking about. A 24 foot diameter windmill plus 48volt lead acid batteries. Wow. You really should post a new thread yourself about this serious system in the Wind section. No need to be shy friend! There are many experienced fellas here with better, more accurate experience with a serious Large system like that than myself. Personally, I only have experience with the 12volt system. (And I'm still making my first 8 footer) However, to the best of my knowledge I believe what I said to be in the right ball park estimate. But I really believe you need to start a new thread in the wind section because there are many other very important factors. For example: What amps will this mill make at 48volts? The C-40 does have the max 125volts, but the max amps is only upto 40 sustained. The C-60 only has a max of 55volts. Also proper furling is a must. You no doubt have a lot of money and time involved. I think you should post a new thread and get more advice. You need better advice than myself to get a safe and efficient set-up without burning out your stator and the blades fly away!

(unknown) · « **Reply #19 on:** July 19, 2007, 09:27:55 PM »

thankyou again for responding. i will post next week hopefully with pictures

CmeBREW · « **Reply #20 on:** July 20, 2007, 09:32:09 AM »

Gbopper;

Look forward to it. I've been using my 4 foot mill for many months in strong winds--and it's 'open voltage' is around 35volts into my 12volt batts. I did all kinds of heating experiments also letting it free spin. Everything is fine. This is a normal range. Batteries are tough. I suspect your in the normal range also. The c-40 will do upto 2000 watts at 48volts- but you may need something even bigger like a OUTBACK controller which is more expensive. The C-60 only does upto 24 volt systems. Looking forward to seeing that beast.

bigkahoonaa · « **Reply #21 on:** July 20, 2007, 09:52:19 PM »

Don't know anything about thread jacking, but I agree with CmeBREW. We both have high V mills, but need to control battery charging. I have a 12V system and you have 48V.

You have a beast. Don't know of many 24' on this site. Start a new post, with pics.

Mau

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Author Topic: Batteries self regulate? (Read 1928 times)

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