Solar charge current

[DarkSkySeeker]

I've read about solar charging systems, and am impressed when the owner boasts of the current generated. What I don't understand is how a system that generates 20-50+ amps doesn't fry the batteries. In these high current systems, is the charge being passed through a bank of batteries in parallel so each battery sees reasonable current?

[Almot]

DarkSkySeeker wrote:

If I had a big array and one battery, the charge controller would limit the 50+ amps to perhaps 4 amps to the one battery?

Max current accepted by battery depends on how deeply it is discharged. Could be a lot more than 4 amps for one 100AH battery - at the beginning. Then current drops as it's nearing the Full. Then it jumps up again when you turn some powerful device On - solar outputs the energy directly into the device.

Controller controls volts, differently on different stages of charging. When it controls volts, amps (= charge flowing into battery) are also affected.

As long as it doesn't interfere too much with RV aerodynamics, there is no penalty for having a bigger solar than you think you need, but there are often benefits.

[2oldman]

..

[ktmrfs]

under ideal conditions most flooded cell lead acid batteries will have maximum cycle life if the intial charging current is limited to about C/10 C=rated AH. However, you can still get very long life cycle even charging at an initial C/2 to C/4 rate. The charge rate will decrease as the battery bank gets near full charge, starting to taper at when the battery is about 70% charged.

So... a initial 50A charge rate isn't excessive for a couple of 12V or pair of 6V golf cart batteries.

what controls the current going into a battery is the source voltage, battery voltage, battery internal resistance, the current the source can supply and the charging algorithm.

On a deeply discharged battery on initial charge the charging current will be limited by either the source max current or the battery internal resistance. Generally the max source current is the limit.

[beemerphile1]

To visualize it, think of it this way; the current isn't pushed into the battery, the battery sucks it in. When the battery is full and stops sucking, the current stops.

[2oldman]

MrWizard wrote:
DOES your converter limit charge to 4 amps
DOES YOUR ALTERNATOR LIMIT CHARGE TO 4 AMPS

Obviously not. I assumed he meant 'during the course of charging' it would get to a point where the current was limited.

Not that he'd actually want to set something like that.

[pianotuna]

During the day time, if I want to harvest some free power, after the battery bank is full, I'll use the inverter to run the water heater.

[MrWizard]

DarkSkySeeker wrote:

2oldman wrote:
Yeah, that's why it's there.

So - here's a silly example.

If I had a big array and one battery, the charge controller would limit the 50+ amps to perhaps 4 amps to the one battery?

No..if it did, I would change controllers

DOES your converter limit charge to 4 amps
DOES YOUR ALTERNATOR LIMIT CHARGE TO 4 AMPS

It would take days to recharge the batteries

Charge rate is applied voltage versus battery resistance

My converter can do 75 amps

My previous RV I installed over 600+ ways of solar panels

[2oldman]

twodownzero wrote:
My controller knows how large my array is and what kind of batteries (conventional lead acid) are attached to it.

My Outback controller doesn't ask how big the array is, but it does ask for the battery bank size in ah.

[twodownzero]

My controller knows how large my array is and what kind of batteries (conventional lead acid) are attached to it. I can adjust the charge voltages as well. I expect my batteries will last many years since they are never dead or even close.

[BFL13]

2oldman wrote:
The controller handles the current that's needed.

No, the controller controls the battery voltage. The controller has an amps rating. Some controllers have a current limit so they don't over-heat by amps going above the controller's rating..

The battery itself controls the amps going into it by its "natural acceptance rate", which is higher at higher voltage. It accepts more amps at 14.4v than at 13.6v.

Current to the battery depends on whether it is an MPPT or PWM controller. With PWM you can get the panel's Isc rating worth of amps, but with MPPT you get the controller's output watts divided by the battery's voltage at the time. The battery doesn't care where its amps are coming from though.

[2oldman]

DarkSkySeeker wrote:
If I had a big array and one battery, the charge controller would limit the 50+ amps to perhaps 4 amps to the one battery?

That's what a decent controller is designed to do. As said above, they're just like any other charger.

[time2roll]

DarkSkySeeker wrote:
I've read about solar charging systems, and am impressed when the owner boasts of the current generated. What I don't understand is how a system that generates 20-50+ amps doesn't fry the batteries. In these high current systems, is the charge being passed through a bank of batteries in parallel so each battery sees reasonable current?

Same way your 55 amp converter does not damage the battery or your 130 amp alternator does not burn out your vehicle battery.

Just like any charger... the voltage is controlled and as the battery comes up to the same voltage the amps taper off to zero at full.

[red31]

Battery and/or bank of batteries will accept all they can until a voltage set pt is reached. Then the controller limits power to the battery to maintain the set pt voltage.

High current into a small bank will cause the bank's voltage to rise quicker and then be limited by the constant voltage set pt.

[DarkSkySeeker]

2oldman wrote:
Yeah, that's why it's there.

So - here's a silly example.

If I had a big array and one battery, the charge controller would limit the 50+ amps to perhaps 4 amps to the one battery?