High amp Charge Controller: Bulk-Absorb-Float

Thread Starter

jim0000

Joined Oct 28, 2020
120
Output: Lead Acid Battery: 12V 200Ah
Input: Solar panels in parallel to produce enough current
12v, 100w panels
Cycle use: disconnected at some point after full charge is reached. Can assume high irradiance during charge times.

Without using MPPT algorithm but perhaps a microcontroller for processing or sensing and data collection, what is a common way to automatically have the charge controller enter the necessary 3 stages of charging for lead acid? I am struggling since there is a high charging current of around 30A. I haven't seen any high amp designs?
 
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Ian0

Joined Aug 7, 2020
6,321
Probably you DO need to have an MPPT algorithm. The level of sunshine has much more control over charging current than you do!
What is the output voltage from your panel?
As there is no possibility of a continuous float charge between sunset and sunrise, it may just be easier to switch the solar off when the battery if it has spent long enough in absorption.
 

Thread Starter

jim0000

Joined Oct 28, 2020
120
Probably you DO need to have an MPPT algorithm. The level of sunshine has much more control over charging current than you do!
What is the output voltage from your panel?
As there is no possibility of a continuous float charge between sunset and sunrise, it may just be easier to switch the solar off when the battery if it has spent long enough in absorption.
Input voltage is 12V and the battery load can of course draw high amps especially for an initial inrush current which I believe is 30A or more. Yeah for sure this will be cycle use so it will be disconnected at some point when full charge is indicated. Even though it will be disconnected of course I want to use good practice and protect the battery, but also learn how to properly do the charge.
 

Ian0

Joined Aug 7, 2020
6,321
Is the input voltage really 12V? You need 14.7V to fully charge a lead acid battery. Or does the input voltage get up to about 20V with no load?
There will be no inrush current unless the sun puts out an extra burst of bright light!
 

LowQCab

Joined Nov 6, 2012
2,512
You may be over-thinking this too much.
Do You really need that last ~5% of Battery capacity ?,
or are You simply worried about the overall Life-Expectancy of the Battery ?
What does the Battery Power ?, ( average Amp-Load, and length of Time ).
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Thread Starter

jim0000

Joined Oct 28, 2020
120
Is the input voltage really 12V? You need 14.7V to fully charge a lead acid battery. Or does the input voltage get up to about 20V with no load?
There will be no inrush current unless the sun puts out an extra burst of bright light!
Yeah it will really be outputting up to 18v or 20v they just list the panel type as 12v. The battery gave an initial inrush current rating so I figured the circuit better be able to handle at least that
 

LowQCab

Joined Nov 6, 2012
2,512
Do You "need" to limit the Current delivered by the Panel for some reason ?
An Automotive-sized Battery would scoff at such a low Charge-Current,
but You haven't given us much information to work with.
But a small Gel-Cell Battery could easily be damaged by a ~30-Amp Charge-Rate.

Does the Panel need to Power anything else while Charging the Battery ?

Is the Battery only for use during limited, or no, Sunlight conditions ?

Does the Battery have enough Capacity to easily cover
nighttime, or limited Sunlight, requirements ?

What is the rated-Output of your Panel(s) ?
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Thread Starter

jim0000

Joined Oct 28, 2020
120
What's going to cause this alleged inrush?
The inrush I wanted to be prepared for was just listed on the battery as 'initial current', after looking it up it was saying that there could be an initial 30A, but then go to a lower value
 

Ian0

Joined Aug 7, 2020
6,321
The inrush I wanted to be prepared for was just listed on the battery as 'initial current', after looking it up it was saying that there could be an initial 30A, but then go to a lower value
30A into a 12V battery is 360W. And you have a 100W solar panel. The only way you will get 360W is if the sun shines 3.6 times as brightly as it usually does.
 

Irving

Joined Jan 30, 2016
3,131
A 200Ah battery won't be worried by a 30A charge current - You can fast charge a 60Ah battery at 30A if you monitor battery temperature! A rule of thumb is 25% C-rate which is 50A for your battery. But do you really need to? The actual charge rate will be limited by the solar panel(s) - a 100W panel will give a maximum of around 5A at full irradiance. But you can control the charge current if you so desire; more importantly you need the voltage to be 0.5-1v above the battery open circuit voltage.

A simple algorithm would be to measure battery o/c volts, then connect the panel, adjusting the operating point to keep the panel output above the o/c voltage. One way to do this is a boost converter between panel and battery. The MCU increases the boost converter output voltage until the battery charge current reaches a set value, or the maximum the panel can provide, sampling the o/c voltage every 500mS or so. Once it reaches a specific value, typically 14.4 - 14.8v depending on the battery, the charger switches to constant voltage and monitors the charge current until it drops below, typically, 0.1C or 2A, then adjust volts to maintenance volts, typically 13.8v.

It goes, I hope, without saying that the above assumes the battery isn't powering anything while charging.
 
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