Maximum charging voltage

[axis11]

Hi all,

How high would be the maximum charging voltage for 12v lead-acid batteries without causing damage to the battery?

I am currently using a 50amp PWM controller. Often times when Im home, I connect the panels directly to the batteries thinking it would charge faster. It is showing a faster increase in voltage on the battery.I do this only when I can keep an eye on the voltmeter.Once it reached 14V, I reconnect it again to the controller. Up to how high voltage can I let the panel directly charge the battery?

[Sunking]

Often times when Im home, I connect the panels directly to the batteries thinking it would charge faster.

No in reality no difference with PWM because both methods are the most inefficient methods. Typically if you are using a panel made for 12 volts, the efficiency is only about 65 to 70%. So in other words you change you 100 watt panel into 65 to 70 watts. Reason being is you are not operating the panel at maximum power point. Solar panels are current sources, not voltage.

But to answer your question it depends on the battery chemistry and construction and that voltage is anywhere between 2.25 to 2.45 volts per cell.

[Mike90250]

The problem is not so much "voltage" but the increased amps, as voltage rises. Amps cause heat, heat causes early battery failure. More heat, earlier failure

[axis11]

The problem is not so much "voltage" but the increased amps, as voltage rises. Amps cause heat, heat causes early battery failure. More heat, earlier failure

I have not seen the battery suffer from increase heating,only slight bubbles coming up even when the voltage reaches 14v during direct charging. I have read in some threads it is good to slightly overcharge the battery once a month and let it heat up a little bit. Using my PWM, it doesnt happen. Voltage goes up very very slowly after reaching 12.4V. After 3 hours of charging with the controller under a sunny day and no load in use, voltage increased from 12.4 to 12.45. Is my controller damaged or my battery is dying?
Is it ok if I let the voltage rise up to 16 volts as long as the battery doesnt heat up?

[axis11]

[QUOTE=Sunking;25690]No in reality no difference with PWM because both methods are the most inefficient methods. Typically if you are using a panel made for 12 volts, the efficiency is only about 65 to 70%. So in other words you change you 100 watt panel into 65 to 70 watts. Reason being is you are not operating the panel at maximum power point. Solar panels are current sources, not voltage.

QUOTE]

The MPPT is next on my list. Probably my PWM is damaged anyway. I was never happy with the PWM controller.

[Sunking]

Axis what size battery and what wattage are your panels?

Unless your panel wattage is grossly over sized for your batteries, it is almost impossible to heat them up and boil over. If all you are seeing is something less that 13 volts while charging means one of a couple of things.

Either your battery is toast, charge controller is toast, or your panel wattage is way to low for the batteries.

[axis11]

900watts panel,around 46 amps.200amp.hr 12v battery. I know that my batteries are way too low for the size of my panels,(budget constrainsts).Thats why imprepared to face the consequences of my defficiency. Ill just try to keep my set-up running at least another 11 months. Even during daytime only. Im 10,000 kms away from my solar installation and about 11 months remaining b4 I can do the fixing myself.

[Sunking]

900watts panel,around 46 amps.200amp.hr 12v battery.

Lets get you straightened up because what you think is not the way things work

Reality is you have way too much panel wattage for your batteries. Panel and battery size depends on two main factors, charge controller type, and panel configuration in relation to battery size

Ideally for Flooded Lead Acid wet battery you want to supply your battery with a C/8 to C/10 charge rate where C = Battery Amp Hour rating. So if you have 200 Amp Hours ideally you want to charge at around 20 to 25 amps. Gel cells limit is C/20, and AGM can be as high as C/4. So unless your batteries are AGM, you are way over the limit on paper.

OK next in line is the panel spec and charge controller type. I am going to assume you are using a PWM charge controller and using standard 12 volt panels with them all configured in parallel. So a typical panel Vmp voltage is 18 volts. so if you have 900 watts means the Imp total for all the panels should be around 900 watts / 18 volts = 50 amps and that is roughly what you said right @ 46 amps? With a PWM controller the Input Current = Output Current. So if you have a 200 AH battery charging at 46 amps, you are way over the max limit of 25 amps for a FLA product, but OK if AGM. If they are Gel, they are toast.

Now here is something that will make you mad as hell. If my assumption is correct that you have 900 watt panels using a PWM controller, that controller turned you 900 watt panels into about 500 to 600 watts. It is just the nature of the beast.

Now if you had a MPPT controller you are really cooking the batteries because a 900 watt array will deliver right around 75 amps to a 12 volt battery. Think about that. With a 900 watt array if you use PWM you only get 50 amps out to the batteries, but 75 if using MPPT. At 75 amps on a 200 AH battery you would be cooking them

If I were you and your controller is shot I would replace it with a 80 Amp MPPT controller, and reduce the panel wattage to 300 to 350 watts to maintain a 12 volt 200 AH battery. By doing that it will allow you to grow the battery capacity up to 750 AH using your full 900 watt panel wattage. But for now you are running way too much panel wattage unless you have AGM batteries.

[Mike90250]

My diagnosis:
Bad controller. or mis-configured charge settings.
So there is a lot of panel for the size of battery, It will charge hard and fast, heat a bit more than optimal, but the charger should sense the stages, and transition from bulk to absorb, and after the 90 min in absorb, (where the water bubbling happens) should switch to float. just add more water every week.

unless it's configured as a diversion controller for wind That will cook/buble your batteries dry with high voltage.

So the battery should last a year, but someone's got to water it weekly/monthly with distilled water. Once it dries out, the acid becomes too concetrated and eats the bottom of the plates off.

[axis11]

You're right, i've learned from my mistakes. But the soldier that has been wounded will not surrender, rather become more aggresive and regain the lost dignity. Im expecting that my controller and battery will not last so im preparing my next list. Mppt 24v @50 amps.400amp battery @24V and need to add 24-220v inverters. IT wont happen tomorrow,but perhaps within this year.

[Mike90250]

if you are going to be buying new gear, I'd suggest making the move up to 48V. You can put all 4 batteries in series - avoiding parallel strings, have same storage wattage, less total system losses, and capacity for growth (50A is close to the limit for the comon 60A controller, @ 48V, you would be at 25A charging, room to grow up to the 60A limit).

[axis11]

My diagnosis:
Bad controller. or mis-configured charge settings.
So there is a lot of panel for the size of battery, It will charge hard and fast, heat a bit more than optimal, but the charger should sense the stages, and transition from bulk to absorb, and after the 90 min in absorb, (where the water bubbling happens) should switch to float. just add more water every week.

unless it's configured as a diversion controller for wind That will cook/buble your batteries dry with high voltage.

So the battery should last a year, but someone's got to water it weekly/monthly with distilled water. Once it dries out, the acid becomes too concetrated and eats the bottom of the plates off.

I agree with you Mike. My first Assumption on this controller was not good at all. I maybe away from my panels but I see to it that my wife at home takes care of it. Shes doing the watering.

Tnx for the advice. Ill start searching again for 48 v components for my set-up.

[stevega]

Hi i'm new here.i have a solar system 12v with 6x150w panel and 4x140ah flooded batteries.my panel give me 400-450watt only.why?

[sensij]

Hi i'm new here.i have a solar system 12v with 6x150w panel and 4x140ah flooded batteries.my panel give me 400-450watt only.why?

Lots of possibilities... summertime heat makes panels less efficient, that could knock you down to 600 W or so even if you've got great orientation on the panels. A PWM controller could be responsible for the rest of the under-performance to your expectations. Maybe start your own thread, post more about the equipment you are using (charge controller? how are the panels wired?)

[Sunking]

Hi i'm new here.i have a solar system 12v with 6x150w panel and 4x140ah flooded batteries.my panel give me 400-450watt only.why?

It is a 6-year old thread. Start your own.