Can a solar panel and charge controller over-charge a battery?

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anm

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I'm getting my van setup for living in, and I'm going to have a single Renogy poly 100 watt solar panel, and their no-frills 30 amp charge controller connected to my AGM 400cca, 10hr - 35(A) battery. The solar panel's optimum current output is 5.62 amp at the charge controller's ~14.6 volts. The solar panel will be generating 50-60 ah per day, whether I use any electricity or not, and assuming our Texas sun doesn't go nova, or we have a cloudy day. Is the battery at risk of being overcharged? Or will the charge controller see that it isn't?

Edit: would it be worth going to their more expensive charge controller that allows setting of the charge parameters?
 

DC Fuse

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anm, I am going to use AGMs this time around myself so i've been researching them. I'm seeing that they want a heavier bulk rate charge voltage into the 15+ voltage area. Plus you will need that level of voltage or more for regular equalization charge.
So i would consider getting the better quality programable charge controler. 14.6 volts is too low for bulk charging especially on a agm.
You will learn as you go of your charging needs and those extra volts available are important.

Consider getting a tri-metric battery monitor. You'll be able to see volts/amps going out in use and going in at charge. You won't regret it.
Check your battery manufactuers recomendations too.
 

VanLifeCrisis

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The charge controller primary fuction is to prevent overcharging :)
You can in theory hook 12v solar panels straight to battery but it could dangerously overcharge hense using a controller between.
 

SternWake

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The AGM batteries you get will recommend anywhere from 14.2 to 14.7 volts as the absorption voltage limit. Regularly exceeding this ABSV is not good for an AGM, but brief bursts here and there are of little consequence. I've not seen any AGM recommending higher than 14.7absV in regular day to day use, though Lifeline AGM has a reconditioning procedure with similar voltages to a flooded batteries equalization charge, that is mid to high 15's.

The cheap controller, if it allows more voltage in the ABSorption stage than the particular AGMs want, especially on Hot AGMs, can indeed overcharge the AGM.

Hotter temps voltages should be adjusted down, colder temps adjusted upwards. the ABSV listed by manufacturers is for 77 to 80F.

I've no data on the cheap Renology controller or what the set ABSV voltage is, but that is the key figure with all batteries, and many controllers/ charging sources without adjustable absV will set them low as undercharging is safer than overcharging, at the expense of battery life

I think your 50 to 60AH harvest estimate is a bit generous unless you are moving the 100 watt panel to face directly into the sun several times a day.

A solar controller with a battery temp sensor and adjustable setpoints will eventually pay for itself in battery life, especially if one charges in areas with wild temperature extremes.

Even a small solar panel, hooked directly to a fully charged battery, can overcharge it.


 

DC Fuse

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SternWake, i'm getting conflicting info on this charge rate issue re:agms. Some say i can have a short time @ 14.7 - 15 volts before it going into bulk rate of 14.5. Especially at a 50% DoD. Others say 14.6 max.
I realize ambiant temp plays into this but for us neophytes it gets confusing on what to believe.
I trust your knowledge as much or more than anybodies so if i had a 300ah bank and used overnight 130ah would you set your controller to no more than 14.6 volts?
My 55 amp Iota charger showed 52 amps @15.2 volts going in on initial charge lasting about 20 - 30 minutes where it then dropped to 14.8 volts @ 48 amps slowly dropping to 28 amps @ 13.2 volts.
Was this in your opinion wrong all those years?
For the record, i did get 5 years out of each set of six GC batteries.
I thank you for your help.


One more thing. If those GC batteries were a car i beat them like i stole it. The second set i had @ year 3 i was pulling 23 amps from them for 4 hours a day when i "heard" a sudden drop and while they still worked they were no longer the same. Was this a short in a cell? Never was able to figure that out. Specific gravity was in range.
 

freenez2

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The Morningstar charge controller I use has dip switches for setting the correct battery absorption rate. Battery manufacturers should provide specifications for the recommended charge rate. In regards to temperature, often a temperature sensor probe can be attached from the charge controller to the battery so the controller can adjust charge rates accordingly. I use a 45 amp rated Morningstar charge controller with temperature sensor and sun extender AGM batteries.
 

SternWake

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Bulk rate is maximum amps the charging source can supply until the absorption voltage is reached, at that point the amps required to hold the ABSV will taper. The longer the battery is held at ABSV, the more the amps required to hold ABSV will taper. At some point, either time, or the amps required to hold ABSV fall below a threshold and triggers float mode.

This is how pretty much all 3 stage automatic chargers work, but they all have differences in how high the ABSV is set, and some of them cannot hold their bulk max amp rate on the way to ABSV.

And ultimately it is up to the battery how many amps are required to reach and hold ABSV. AGMs have much less internal resistance and can really suck up huge charging currents and tax the charging source.


Some AGM's state to feed them all the amps you possibly can, Some other AGMs say not to exceed a 30% rate, or 30 amps on a hundred amp hour battery. Most important thing one can do with any particular AGM is to find the manufacturer recommended ABSV, and find a charging source which allows one to set this figure, or one that comes the closest.

All charging sources are basically compromises, and with AGMs since there is no way to check Specific gravity readings, which is the Battery polygraph, one determines state of charge by when the battery can no longer accept a certain amount of amps at the recommended ABSV.

It really depends on the battery manufacturer specs on how much current the battery can accept, and the ABSV stated by the manufacturer, corrected for temperature.

I know a lot of info states to limit the charging amperage as it is safer and 'better' for the battery, but it really depends on when the next discharge cycle begins and hohw much time one has to get the battery as near to 100% as possible before that next discharge cycle begins.

Somebody who has days to allow a charging source to top off a battery, can go low and slow, but the guy on the generator who has limited hours when he can run the generator should force as much amperage into the batteries as possible, and not exceed the manufacturer bulk amp rating, if one is listed.

All the top quality AGM's like Lifeline, Odyssey, and Northstar basically state there is no easily attainable limit on Bulk current, where as lesser AGMs will state the 30% maximum. Lifeline says their 100 amp hour battery can accept 500 amps no issues, until 14.4 is reached and the battery will in fact enjoy this much current, but supplying that much current is nearly impossible with charging sources commonly available.

If your battery bank was still taking 28 amps at 13.2 volts after requiring 48 amps to hold at 14.8v, they needed much more time at 14.8. Float mode should only require a small percentage of amp hour capacity to hold the float voltage. Premature efloatulation is the demise of many a battery, and is the fault of the charging source reverting to float voltage way too early.

The charging source which lets one dictate how long ABSV is held is a rare creature. All the algorithms by the converter/charger makers are compromises which basically say we know what is best for your batteries and do not question us, when each battery has slightly different requirements so a one size fits all charging source is more like a one size fits none.

How widely the charging source misses the mark is directly proportional to battery lifespan and performance during that lifespan.

When any givern converter cannot hold ABSV long enough the battery is not being fully charged. Finding a charging source which can take over when the converter ends puts one into the power supply area.

a 30 amp power supply with adjustable voltage should have no problems taking over when a converter decides to drop to float.

I have been contemplating getting one of these to replace my Schumacher 2/12/25 amp "smart" charger which misses the mark each and every time.
http://www.amazon.com/MegaWatt-S-35...Supply/dp/B00JZBE97U/ref=cm_cr_pr_product_top

They offer larger amperage models. The voltage is adjustable to the mid 15's so it should be able to do a EQ cycle on flooded batteries, but these need to be monitored as they are not automatic.

I reprogram my solar controller to do 16v every 2 weeks or so. I found mid 15's doubled and tripled the time required to max out the specific gravity, so now I don't screw around, just push it to 16v after a normal charge cycle and hold it at 16v until the SG stops rising or reaches my max expected baseline.

AGMs in general, should not really be fed voltages above 15, with a few exceptions, but again the most important thing is the recommendations of the battery manufacturer, and few if any commonly available charging sources can fully charge a battery in the minimum possible time required to do so, and getting as close to 100% as possible daily, when cycling nightly, as is the common pattern in Van dwelling, is most important aspect of recharging to yield the best battery life.

But when the efforts required to reach 100% as often as possible cost more than a replacement battery, the battery depleter needs to draw a line of what they are willing to do to get every possible cycle out of the battery. When setting up a system it is highly desirable to have charging source come as close as possible to battery manufacturer specs. Those who already have batteries or charging sources should find one which meets the other, as close as possible.

Often when a charging source such as a converter is not behaving as expected, it is the cabling between the charging source and battery which is too long and too thin and the voltage at the converter output terminals is very different than the voltage read at the battery terminals. Always check for the difference and do not trust voltage readings taken in the middle of a circuit, or at just one end. The most accurate readings are taken right at the battery terminals, especially at higher charge rates, or discharge rates. Since most charging supplies do not have separate voltage sense wires, they are not accounting for voltage drop in the circuit and just assume battery terminal voltage is the same at converter output voltage, when this is basically an impossibility with a hungry battery, a high amp charging source, and anything less than a short length of 4/0 cable from one to the other.

So the short list, always set the ABSV limit according to battery manufacturer specs, and if possible hold it until specific gravity no longer rises.
With AGM's hold ABSV until amps required to hold ABSV drop to 0.5 amps for a hundred amp hour battery, dropping to float voltages.
Any time float voltage is triggered before this 0.5 amp per 100 A/h threshold with AGMs is reached, tha battery is less than fully charged and float voltages might take another 2 or 3 days to indeed fully charge the unused battery.

Check out this video about how voltage and amps work in relation to each other on a fully charged battery:

 

anm

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SternWake said:
The AGM batteries you get will recommend anywhere from 14.2 to 14.7 volts as the absorption voltage limit. Regularly exceeding this ABSV is not good for an AGM, but brief bursts here and there are of little consequence. I've not seen any AGM recommending higher than 14.7absV in regular day to day use, though Lifeline AGM has a reconditioning procedure with similar voltages to a flooded batteries equalization charge, that is mid to high 15's.

The cheap controller, if it allows more voltage in the ABSorption stage than the particular AGMs want, especially on Hot AGMs, can indeed overcharge the AGM.

Hotter temps voltages should be adjusted down, colder temps adjusted upwards. the ABSV listed by manufacturers is for 77 to 80F.

I've no data on the cheap Renology controller or what the set ABSV voltage is, but that is the key figure with all batteries, and many controllers/ charging sources without adjustable absV will set them low as undercharging is safer than overcharging, at the expense of battery life
These are taken directly from Renogy's manual on the cheap, 30a charge controller:
Battery Parameters
Description Parameter
Load Disconnect 11.1V (12V), 22.2V (24V)
Load Reconnect 12.6V (12V), 25.2V (24V)
Equalization Voltage (30 minutes) 14.6V (12V), 29.2V (24V)
Boost Voltage (30 minutes) 14.4V (12V), 28.8V (24V)
Float Voltage 13.6V (12V), 27.2V (24V)
Battery type
Sealed Lead Acid and Flooded
From what you said it looks like it will be safe (from over-charging).

Sternwake said:
I think your 50 to 60AH harvest estimate is a bit generous unless you are moving the 100 watt panel to face directly into the sun several times a day.
After I posted that message I found Renogy's sunny-day estimator, it says the same thing, 30-40 might be a better estimate.

Stermwake said:
A solar controller with a battery temp sensor and adjustable setpoints will eventually pay for itself in battery life, especially if one charges in areas with wild temperature extremes.
...
The more expensive Renogy charge controller has the temperature sensing and adjusting provision. Maybe it would be better to just buy a 100 watt panel and the better charge controller, rather than the basic kit (which includes the cheap charge controller).

But will excessive float time overcharge a battery? Suppose my van is parked in the AZ desert and I go on walkabout for a couple of weeks, is my battery going to be ok?
 

SternWake

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Batteries that are not being cycled each night do not need to spend hours at 14.x ABSV per day, but in general if it was not discharged the night before, 14.x will be reached very early in the morning and Should, Should, not last very long. It depends on the algorithm programmed into the controller. When Istop cycling my flooded battery, I lower ABSV voltage and duration and lower float from 15.3 to 13.1v. I use the float stage, as a finishing/top charging stage, the ABSV to get it to 95% and the finish at 15.3v to try and shoehorn that last 5%. US battery recommends this 15.3v finishing charge, and my observations and experiments have confirmed it is absolutely required.

13.6v is a high float voltage for flooded batteries, but most AGMs are in this range.

I'm not linking renology's boost for 30 minutes at 14.6.

Equalization is a term marketers love, I guess it sounds impressive and inspires confidence, but true equalization voltages are in the mid to high 15v range. This is a forced overcharge to max out the SG in a flooded battery. Marketers like to call destratification equalization. A lot of converters will claim another charging stage, and call it equalization, but all it really does is after 18 hours at float voltage, it will up the voltage to the mid 14's that causes bubbling and gassing and will stir the electrolyte as without the denser stronger acid will sink to the bottom of the cells and be more corrosive to the bottom of the plates.

I read that renology controllers have a positive ground, or some other requirement which makes using the alternator as a bulk charger and work in conjunction with the Solar all but impossible. I'm not into Solar Kits. The panel alone might be a fine product, but trusting the included controller to do what any given battery wants is a bit of a crapshoot.

I'd stick to better known controller brand names, and one which can handle the addition of another panel, as most people overestimate their harvest and use more than they think and need to upgrade and find themselves limited with the Kit provided controller and the thin cabling provided with it.
 

anm

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SternWake said:
Batteries that are not being cycled each night do not need to spend hours at 14.x ABSV per day, but in general if it was not discharged the night before, 14.x will be reached very early in the morning and Should, Should, not last very long. It depends on the algorithm programmed into the controller. When Istop cycling my flooded battery, I lower ABSV voltage and duration and lower float from 15.3 to 13.1v. I use the float stage, as a finishing/top charging stage, the ABSV to get it to 95% and the finish at 15.3v to try and shoehorn that last 5%. US battery recommends this 15.3v finishing charge, and my observations and experiments have confirmed it is absolutely required.

13.6v is a high float voltage for flooded batteries, but most AGMs are in this range.

I'm not linking renology's boost for 30 minutes at 14.6.

Equalization is a term marketers love, I guess it sounds impressive and inspires confidence, but true equalization voltages are in the mid to high 15v range. This is a forced overcharge to max out the SG in a flooded battery. Marketers like to call destratification equalization. A lot of converters will claim another charging stage, and call it equalization, but all it really does is after 18 hours at float voltage, it will up the voltage to the mid 14's that causes bubbling and gassing and will stir the electrolyte as without the denser stronger acid will sink to the bottom of the cells and be more corrosive to the bottom of the plates.

I read that renology controllers have a positive ground, or some other requirement which makes using the alternator as a bulk charger and work in conjunction with the Solar all but impossible. I'm not into Solar Kits. The panel alone might be a fine product, but trusting the included controller to do what any given battery wants is a bit of a crapshoot.

I'd stick to better known controller brand names, and one which can handle the addition of another panel, as most people overestimate their harvest and use more than they think and need to upgrade and find themselves limited with the Kit provided controller and the thin cabling provided with it.
Once again, thanks for your knowledge Sternwake.

The Renogy charge controller does state that it's positive ground, but the way I've wired the house system, neither side is grounded to the vehicle. There is no connection between my house wiring and the van chassis, both systems are totally independent. But my plan is to NOT use the van alternator as an alternate charging source. Experience may change that though...

I guess it's time to start researching charge controllers... inexpensive charge controllers...
 

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