Can someone please explain in solar battery : what's a cycle

offgridcabin2015

Solar experts , what im trying to understand is. How is this cycle registered, or measured.

For ei. Let say i use battery during float stage only. and if clouds hit and if i'm needing more juice , the batts are used. The day ends. Say i used 10% juice / 90 left in batts. Next day batts are again fully charged goes into float. 

is that one cycle being used . do i have a correct idea of what contitues a cycle.

Thank you experts.

706jim

Yes that would be a cycle. More important is the DOD or depth of discharge. AS DOD increases, battery life decreases at least with lead acid.

Photowhit

offgridcabin2015 said:

is that one cycle being used . do i have a correct idea of what contitues a cycle.

Sort of need to understand solar without putting labels on things.

A cycle for a battery is generally a nights use, though you can skip charging with a couple charge controllers. Even then cycles for battery consideration usually has to do with the the amount of discharge. Often batteries will come with charts on the amount of discharge cycles based on the amount of discharge. So a battery may do 500 discharges to 20% State of Charge but 6000 discharges to 90% SoC.

A charge controller might start over after a few hours of discharge, not sensing any charging. 

offgridcabin2015

so....how can i track ONE CYCLE.  / FROM what i'm reading these seem COMPLICATED 

Photowhit

What do you want to track, a 24 hour period?, a days charging? Some charge controllers will do this for you. What are your goals in tracking a 'cycle'?

Please understand that off grid solar MUST be very wasteful. It's the nature is that a system must be over built to reliably charge the batteries to 100% in ugly weather conditions.

Basically how battery charging works;

The voltage you are seeing is the system voltage and not the battery voltage. If you are connected to charging or a load it will effect the system voltage.

During charging, there are basically 3 stages of charging, Bulk, Absorb, and Float.

BULK;

First thing when charging starts you will be in bulk, the voltage rises from what ever the system voltage was to a set point, around 14.5 volts. At that point the Charge controller stops the voltage from rising. Higher voltage can damage sealed batteries.

ABSORB;

Once the battery hits the preset point the charge controller keeps it at that point. Your batteries are roughly 80% full. Flooded batteries will start accepting less current at 80-85% full AGM/Sealed may go a little longer before accepting less current.

On many controllers you can set this point, Some will have different presets for Flooded, and sealed batteries, or flooded, AGM, and sealed batteries. 

The charge controller has a couple ways to know when to switch to float, Most inexpensive Charge controller are just timed for 1.5-2 hours. Some will also see less current flowing through the charge controller and shut it down when minimal current is flowing through the controller. On more expensive charge controller. You can set battery capacity to give the Controller a better idea of when to stop. you can also set a longer Absorb time. Or set 'end amps' a amount of amps flowing through the charge controller to stop Absorb and switch to the final stage.

FLOAT;

Once the Controller has determined the battery is fully charged it reduces the voltage to a point where very little current is flowing to the battery. This will prevent the battery from over charging and heating up.

While in 'Float' the charge controller watch for voltage drop, which would indicate a load. If the voltage begins to drop the charge controller will allow as much current to flow from the panels/array to compensate and maintain the voltage. If the voltage can be maintained, the load will in essence be running directly off the array/solar. If the voltage drops below the preset float voltage, the controller may start a whole new cycle if it stays there for a period of time.

The system voltage drop you see at night when the sun goes down is the charge controller moving into a resting mode with no energy to contribute to the system.

The morning voltage may reflect a load present that is effecting the voltage level. With sealed batteries, you would want to disconnect the battery from the system and allow it to 'rest' for a while to get an accurate idea of it's SOC (State Of Charge) from the voltage

RCinFLA

You should avoid a charge control settng that often retriggers a full absorb voltage cycle.  Settings depend on charge controler design.

Some retrigger a full absorb whenever battery falls below float voltage.  Just a momentary heavy inverter load can do this.
The degradation this does to batteries depends on how charge absorb is terminated.  Two most common methods is just timed period in absorb and charge current taper off level exit.  Current taper off triggered absorb exit is better.  Timer is still used as safety backup if battery is gettng bad to avoid spending a long time in absorb and not achieving current taper off exit of absorb cycle.

Marc Kurth

RCinFLA said:

You should avoid a charge control settng that often retriggers a full absorb voltage cycle.  Settings depend on charge controler design.

Some retrigger a full absorb whenever battery falls below float voltage.  Just a momentary heavy inverter load can do this.
The degradation this does to batteries depends on how charge absorb is terminated.  Two most common methods is just timed period in absorb and charge current taper off level exit.  Current taper off triggered absorb exit is better.  Timer is still used as safety backup if battery is gettng bad to avoid spending a long time in absorb and not achieving current taper off exit of absorb cycle.

I wholeheartedly agree!

Time delays on "retrigger" are important and knowing your "end current" charging numbers are critical to maximizing battery bank life.