Got Some Golf Cart Batteries

[valterra]

My Golf Cart batteries (2 of them) are 6 volt 220AH.  

That is the C20 rating, which I understand means they can supply 11 Amps for 22 hours.  I also take that to mean it's safe to charge them at up to 11 Amps.  I saw Flux post somewhere that as long as you're under the C20 rating, you don't have to worry much about controlling.

I have GHurd's dump load circuit all done, and it's set somewhere near 14v.  I'm not able just yet to determine exactly what it's set to (don't have a variable voltage power supply), but I know it's less than 15.5 and more than 13.7, so it's about right.

Anyhow, I'm concerned about the 11 Amp thing.  Right now, on the best windy and sunny day, the most I can put into them is about 9 amps.  But eventually I want to build a bigger generator.  I figure 11 Amps is only 132 watts at 12vdc (11x12=132).  Does that mean I can't use a generator that puts out over 132 watts?  That hardly sounds right.  It would mean I need a LOT more batteries ($$$$).

Or is that C20 rating a sort-of "net" rating?  If my loads are balanced with my generation, can all the numbers go up?  

For example, say I have 31 Amps of loads, and a solid 35Amps of generating going on.  That's a "net" charge of 4 Amps (35-31=4) which falls well within the C20 rating.

Does that sound right to anyone?  I don't want to burn out these batteries (although Sam's has a 12 month replacement warranty), but I also don't want to invest more money in batteries at this point.

[jzeveney]

That sounds right but I'm a newbie.  If you blast much more current into those you'll smoke the plates.  Others can eloborate on this however I think you need to measure the temprature of your batteries while charging to see what is the max current they can take in before you damage them.  Simple solution more batteries.

Z

[kurt]

golf cart batteries can handle a c10 charge rate easy so for your batteries that would be 22 amps you can go to a higher charge rate than that but you mite experience some boiling.

[zeusmorg]

 IF your load is balanced with the amount you generate, there will be no charging(or discharging for that matter). So you are right your charge is dependent on load on the system, also.

 Going over the C20 rating momentarily will not significantly shorten the battery life, however going over that constantly will burn them up!

 The idea behind creating a good RE system is balancing all the components, and having protection to take excess heavy loads if they exist.

 For example if you generated 35a constantly, and had a 35 A load constantly there would be no need for batteries at all. Batteries are storage for excess during light loads, and replacing generation capabilities during heavy ones.

 If you design your storage system to take care of ALL the possible loads at one time you could place on it, chances are that you've got too big a battery bank. You want to design to take care of above average situations. Some modification to lifestyle can save on resources also. Like don't run the A/C while washing clothes, etc.

 Right now, with a generation capacity of only 9 amps, you're safe from overcharging the batteries.  You're probably in more danger of draining the batteries too much. So just watch your low voltage conditions.

 I'd worry about re-sizing your battery bank when you get more generation input.

[scottsAI]

Valterra,

Great start!

I assume your question is based on that you can charge better than 11 amps?

The correct answer depends:

On the SOC.

Temperature of the battery.

Capacity of the battery.

Must be something else...

If the battery is 80% discharged then you can charge at 200amps even higher, battery voltage must be limited and battery monitored to insure its not gassing excessively. No definitive answer here, your idea of excessive and mine may not agree.

Limit Battery gassing until 90% charge level, going above is getting into finishing charging and gassing is required. Normally as the battery is charged gassing starts around 65% SOC more gassing as its charged to like boiling water at the end of finishing charging. (this should only be done 4 times a year) Get manufacture recommendations on charging for a guide.

When heaving charging very important to monitor battery temperature and Voltage.

You can charge the battery at the currents you discharged it at. You must be very careful!

To fully understand this will require further reading.

I bet you have seen wooferhound post:

http://www.fieldlines.com/story/2008/4/22/142649/842

Good luck. (I charge my golf cart battery at 75 amps, using a fork lift battery charger)

Have fun,

Scott.

[valterra]

Thanks, guys.  That information answered all of my questions!

My biggest problem isn't figuring my constant load amount - it's my generation ability.  When the wind is really kicking, I will get over 3A from the wind.  Then 1A, then nothing.  You guys know.... the wind don't blow all the time!

The solar component is more steady, but of course, the output depends on the time of day!

Switching gears here... about batteries not being necessary if loads are balanced.... I am building a large treehouse for the kids, and I want to put a small wind genny on it.  But I really don't think it is worty all the expense and effort of regulating, batteries, etc.

If I wanted to run, say, a small radio, how would I regulate the voltage without a battery?  Is that even possible (or 'reasonable)?

[ghurd]

No battery?  Not a good idea.  The voltage swings would be crazy.

Could use a stepper motor type windmill, a 6V (4 AAs) radio, and regulate the batteries with a zener diode.

Wouldn't get many hours of sound per day with a CD player.

Would be pretty decent with an MP3 player and small low power speakers.

G-

[valterra]

yeah, or a small fm radio.

I thought it through after I posted... a circuit to replace the battery's voltage regulation might work.  But any circuitry will be useless to replace the battery's supply during times of no wind.  duh.  

Could be done with solar though.    But I can't slap together available parts and make solar like I can with wind.