battery charging

jchamp

maybe i am expecting to much. i have 4/45 watt solar kits 180w 2 each tied in paralell to a 30 amp sunforce controller. i am using about 800 watts in about 4 1/2 hours. after that i get a warning of low battery. i have 6 - 115a/h d/c batterys. the thing is my batterys do not get a full charge according to my controller. i can never get a green lite for the full charge. am i expecting to much from my panels to charge this many batterys? thanks for your help.

BB.

Re: battery charging

First, fire up a generator and recharge those batteries... The longer they sit below ~75% state of charge--the quicker they are aging and approaching and early death.

Next, you said you are using "800 watts in 4 1/2 hours"...

Not sure what you intend to say...

800 watts * 4.5 hours = 3,600 watt*Hours (3.6 kWhrs) ???

Or:

800 Watt*Hours over ~4.5 hours

Or a load of:

800 Watt*Hours / 4.5 hours = ~178 Watt load running for 4.5 hours

In any case, where were you? Alabama somewhere?

Picking Montgomery Al, assuming 180 watts of panels, and you are using an AC inverter for an overall derating factor of 0.52 ... I would guess you should get about 0.36 kWhrs (or 360 Watt*Hours for an average February day.

Depending on what your total power use is--either is using way more electricity than I believe your system is capable of generating...

-Bill

jchamp

Re: battery charging

you are right i am using 800 w/h about 170 watts per hr. i do live in so. al. i guess i was using so many watts because my batterys were new. i am using more watts than my panels can produce and its slowly killing my batterys. thats why they never reach a full charge. i will try and not use more than 360 watt h. per day, untill i get more panels. also i have a 400w corba inverter. i just put my batterys on a charger. am i headed in the right direction this time?

BB.

Re: battery charging

jc,

Yep... Getting there... One thing, the Watt*Hours and Watts:

Watts is like a rate or a speed (miles per hour)
Watt*Hours is a distance (like miles)

I know it feels backwards--but it does work out.

So the rate is 170 Watts, the time is 4.5 hours... So the distance traveled is:

170 watt * 4.5 hours = 765 Watt*Hours

And, your panels are generating (roughly) 360 Watt*Hours this time of year.

So, you have to cut your usage by a bit over 1/2 or over 2x the number of panels to break even.

Do you have a kWhr meter (or a Kill-A-Watt meter) for your AC loads?

For smaller DC loads/systems, the Watts Up or Doc Wattson look interesting (one person here preferred the Watt's UP as more accurate. The Doc Wattson, I believe is a larger unit.

A battery monitor (see the kill-a-watt link), with the number of batteries you have--would be much better vs the Watt's Up and such.

Your other issue is you have some 690 AH of 12 volt batteries...

Your solar panels have (180 watts / 16 volts = Imp) 11 amps of current...

For your size battery bank, proper charging would be around 5%-13% of 690 A*H or 34.5 amps to 90 amps. You will probably need to put a larger AC charger on your batteries about once a month to fully charge them and properly equalize.

You should also get a hydrometer (and thermometer) to measure the specific gravity of the electrolyte and make sure they are not sitting below 75% charge for any length of time (recharge the next day with your AC Charger--if you have to).

-Bill

niel

Re: battery charging

you are also short on the charge current for all of those batteries to charge properly. it should roughly be within 5-13% of the ah of the batteries. 5%=34.5a. you're roughly about 1/3 of that minimum. i might suggest that when you want more pv that it is better to get larger capacity pvs than to handle and mount all of those little 15w pvs.

jchamp

panel hookup

I have 12 - 15w amorphous panels 180w. I want to go to larger panels. I know if I mix them the smaller panels will cut wattage of the larger ones. If I get 3or 4 65w amorphous panels can I run them to another controller then into the same battery bank of 6 115ah d/c batterys that I have hooked up? or do I have to start another battery bank? I have a 12volt system with a 30a controller. I've been told I need to get away from all the small panels because of all the tie ins I have to make. Thanks for all your help;

BB.

Re: battery charging

Jchamp,

I went ahead and merged your two threads... This is really one conversation about your system--and I think it would help if all of the information is in one thread.

You have several options you can follow. Basically, you can add multiple solar panels to one charge controller (as long as you follow some series/parallel connection rules appropriate for the PWM or MPPT controller). And, you can add several different charge controller (each with their own strings) to one battery bank.

Combining a number of small solar panels panels together is a pain... Multiple connections... 32x12=24 points of failure, having to mount 12 panels instead of a one or several larger panels, etc. Small wattage amorphous panels that (in general) do not last much beyond 10 years vs the 25+ years for a good quality, larger wattage, silicon panel...

But, if you already have the first 180 watts done--then you probably would be happier to simply leave the first panels+charge controller connected, and work on adding a second charge controller and string.

Choosing a controller type; PWM (less expensive, typically smaller systems/arrays) vs MPPT (larger systems and arrays, more expensive, solar panels can be mounted farther away from the battery shed); special needs (wide temperature ranges for panels and batteries, support of mulitple battery bank voltages), ability to tie controllers together with a digital bus, etc.--it all really depends on your specific needs.

In the end--define your loads (daily, seasonally).. Define where you array will be mounted relative to the battery "shed" (long distance, very close). Where the system will be (sunny/cloudy climate, etc.). Can you use a generator for backup power (i.e., sufficient power for 9 months of the year, need generator occasionally the other 3 months of the year)...

There is no one "right" answer... But if you try and design/cost out a couple solutions--you will find some that work better for you than others.

-Bill

jchamp

Re: battery charging

Thanks for all the help and advise and keeping me on the right track. jc

niel

Re: battery charging

until you get more pv going, you may wish to obtain a battery charger to prevent your batteries from discharging too far. it will need to be a large charger or you can individually charge the batteries up. you can bring them up to the absorb voltage point and just use solar to do the final charging. remember they are voltage sensitive and you do not want to exceed that voltage point and you will only be trying to take the strain off of the solar with the majority of the charging (bulk charge stage) being done by the battery charger.

jchamp

Re: battery charging

hey guys, I am still upgrading. I am going to 100 watt panels now. The trouble is the small panels have only two tray wires in the juction box + and -. The new 100w panels have three connectors on the panel. how do I hook these panels up? Thanks for talking me into getting bigger panels. I am hooking them to another controller. they are 100w solar cynergy polycrystalline. I am sure this will solve my battery chargeing problems.

jchamp

Re: battery charging

It was hard to find but it was black on black + & -.