dead 24v series battery

Thomas

Hi, I have 2 35 Ah batteries connected in series and a 1200 watt 14v-28v grid tie inverter connected to it. The panels are 750 watts @ 24 volts, pairs of like panels, 40wx2,60wx2 210wx2.and a 140 watt 12v....
why did my battery die?
one battery is 12.5~good all night
the other[positive end,of seires]is dead as a doornail @ 1.6 volts at night.
when charging the dead battery only recovers to ~6v
the inverter has been running constantly with sun for about 400-800 watts 6 hours a day.
I just changed to 24v
Will I be able to keep the battery bank?
is there a way to prevent this?
my 12v system ran good for a long time.

BB.

Re: dead 24v series battery

Your battery bank AH capacity was probably too small... A 1,200 watt battery based GT inverter would need around 240 AH @ 24 volt battery bank to be able to properly absorb the 120 Hz ripple current.

Your 35 AH battery bank probably just "micro cycled" the battery until one (or more) of the cells has failed.

In terms of money spent--You would need a ~7x larger battery bank to meet our normal rules of thumbs for this application, and would a 7x larger battery bank last 7x longer? Not sure... You probably got good bank from the buck for your application.

-Bill

Photowhit

Re: dead 24v series battery

Thomas wrote: »

Hi, I have 2 35 Ah batteries connected in series and a 1200 watt 14v-28v grid tie inverter connected to it.

What is this? a hybrid inverter? a Grid tied inverter? Not familiar with any that small.

Thomas wrote: »

The panels are 750 watts @ 24 volts, pairs of like panels, 40wx2,60wx2 210wx2.and a 140 watt 12v.....

This looks wrong, You have pairs of panels that I hope are 12 Volt nominal panels? meaning a VMP of @17.5volts? are the 210Volt panels in this range? most of this wattage are higher so there may be waste there. Then you have in parallel a single 140 volt 12 volt nominal panel? That should bring the voltage down to the VMP of this single panel.

Thomas

Re: dead 24v series battery

Bill -thankyou, I ran across something about that when worrying, I will look into it[ min.size]
They were straight in line, if I put them off line attached they still may act as capacitance for clouds/anomolies.
[untill the system gets to a percent of my metered bill....a proper battery bank is not realistic.[I have learned]

Yeah, it is a hybrid from Asia. I had a 1000 grid tie before that ran at like 45'C I think that one was rated at 1000 surge...
this one is a lot larger, runs cooler and actually stops my meter hours on end daily with sun...cool This one is not MPPT though..so maybee a MPPt controller...

A Sunny Boy or Frontius 1500 or 2000 are way too expensive right now!

yes all my panels to date are 12v range, though none actually give over 20v OC!?
the 210 are Evergreen I think they were manufactured for people to add 12v to 24v panel systems for 36v...
Oddly I have found that hooking up the single 140 watt panel does decrease th voltage some, but the gti keeps it between 15 and 20 anyway.[besides it boosts the amps some.]
Bill my amp meter attached right before the inverter seems to read power 5 @X100 instaed of 5 Amps. P=A[V] is consistant to 75 watts/ 3 Amps 2 volts ranges...[error]

Thomas

Re: dead 24v series battery

would a 1200v 40A blocking diode stud anode to terminal between battery positive and inverter stop the back ripple? micro cycling? as a temporary preventative measure while I save money and add batteries at an affordable rate?

BB.

Re: dead 24v series battery

I have no idea--But you will probably find that the inverter will not work correctly, or at least have lower output.

-Bill

Thomas

Re: dead 24v series battery

You believe the inverter may not work properly with a diode? even if the little arrow is pointing downstream to the inverter?
I noticed reduced power trying my remaining 12v battery and charger, I ended up with 1/2 power output ant way I added the remaining good 12v battery.
the bad battery has been charging on a SCI shunt charger and 50 Watts all day and drops right off to like 2 volts. Dead right? sometimes you never know!
maybe I should just replace this one battery instead of doubling it with 2 more , and see if a diode between my wind generator and/or inverter make any difference. I replaced the stator, and a new rectifier.
I believe I will replace the entire thing in a few seasons.
this battery problem started when I bought a charger on e-bay for the wind generator, a special dc output one[fully encapsulated] that drained my batteries by morning.

BB.

Re: dead 24v series battery

Placing the diode between the Battery and the GTI--I cannot see anything that it would help... It will add 1-2 volts of drop, or it will stop current flow to the GTI. Neither seems to be a help.

If you put it on the battery, either the battery will only charge, or only discharge... Again, what does good would happen?

-Bill

Thomas

Re: dead 24v series battery

My thoughts after becoming aware of reverse ripple. Battery only charges/discharges?[I thought that was all a battery was supposed to do!]
1200 watt inverter.
1200v blocking diode[70A] the inverter stays at the inverter/ no visiting the battery, one way door. It may cause a volt or two loss...oh well, I am not that precise all round yet anyway.
seeing that the ampmeter is reading power or amps AC...[ full sunlight it reads 5-7 amps on a scale of 20A. Which divides/multiplies to be ~ power at my line voltage/panel amps.
what would the amp meter read[between the battery/ inverter} with diode?
or maybee I misunderstand ripple[back feed]?
insulate battery from inversion prosess.

BB.

Re: dead 24v series battery

The GT AC Inverter does not have large input DC Capacitors. It normally relies on the Battery Bank to "buffer" the current.

With a single phase inverter, each AC Sine Wave peak (when under load) is also a Current/Power Peak. So, the DC input to the Inverter looks like a 120 Hz sine wave train (technically, it is is a squared (Sine) wave).

In normal operation, the battery would be at ~27 volts, the the ripple voltage will always be above ~25.4 volts (aka 12.7 volts where a battery begins to discharge).

So--the battery behaves like a large electrolytic capacitor. If the battery capacity is too small, then the battery voltage drops below ~25.4 volts and actually starts "micro discharging" every 1/120th of a second, and recharges (from the solar panel/wind turbine) every 120th of a second... If you can keep the battery+ripple voltage over 25.4 volts minimum, then you should not have a micro cycle issue.

Of course, there is a lot of "ripple" current here too... More or less, if you have high ripple current it can cause the battery to overheat too (just like an electrolytic capacitor would with excess ripple current). If your batteries are not getting too warm--Then this may not be a problem for you. Without and oscilloscope to measure voltage/current, it is pretty hard to tell what is happening on your system (battery died early because of how you are using it, or it just died early because of other issues)...

-Bill

Thomas

Re: dead 24v series battery

Is there another dimension to the measure of cyclic discharge at 1/120 th? like a reference to volts/amps/time.
Because the battery did deplete daily however it started not rebounding back up to 24v levels.
There was a couple of things going on at this time .
I added the 12v panel to the line because the operating line voltage was 15v to 20v loaded.
My new stator and rectifier were starting to work for better than 12v finally for whole minutes during wind.[forget amps still] and I got the new controller/brake for it.
All is good. Morning. Dead Bank. Great. hmmph. Thats all. Neglect killed it I think.
All I was using it for was capacitance anyway, the notion of overnight with batteries....dreaming.
I had my system directly in-line. Panel-charger-battery-inverter.
would a change like this make a difference.
panel-charger- simultaneous output instead of sequential here
battery/inverter

I think my wind generator was spinning backwards with my meter!I had no blocking diode in for this while also.
Did reducing my 24v array with a 12v panel cause the ripple voltage differential to be significant[like decay to zero significant instead of replenishable?], even under load does the open circuit capacity make a difference? like spell check?

techntrek

Re: dead 24v series battery

"I just changed to 24v ... my 12v system ran good for a long time."

By any chance was your dead battery the only one you used on your 12 volt system before you converted to 24 volts? If yes, you combined a new battery with an old one which guarantees the old one will die - as yours did. You must start out with two new batteries.

Thomas

Re: dead 24v series battery

Boy this is costly...I could only afford one replacement, is there any way of preventing the death of the 'new old battery' now? Or at least prolonging life for another window in the solar/budget launch window?

Thomas

Re: dead 24v series battery

there is no way to tell if the dead battery is the one I was using for 12v GTI. The only way to tell the difference is with a volt meter. Interstate power patroll 35 Ah nut/bolt

Thomas

Dead Battery SOLVED,I found it...thanks

When I reinstalled a new relay I accidentally connected my shunt/ground to positive instead of negative for some reason. I read the amps and have a neg ground at gti neg...I guess I was in a hurry, it could have been worse I think, haste only makes waste...
thanks to you who answered, all answers turned out to be right , just not the right answer to my problem!
my 3 phase is finally:roll: working some.

techntrek

Re: Dead Battery SOLVED,I found it...thanks

If it hasn't been too long since you added your newer battery, I would replace the (presumably much older) dead battery with a new one and continue on.