A solar/battery powered circuit that is running 24 hours a day has a battery that is normally is charge deficit, so float is not absolutely necessary.

A solar/battery powered circuit that is only intermittently used (eg a gate opener) has a battery normally held at full charge, so a float stage is recommended.

 

What is the amp hour rating of the battery?
Is there a load connected to battery while it's being charged?

Currently 5Ah battery but I would like to go bigger. There won't be a load while charging, only after its fully charged and disconnected

 

One Meter for Voltage, and one Meter for Current.

If the "Medium-Load" Voltage will remain above ~13.8-Volts,
then placing as many Panels as You want, in Parallel,
will create more Charging-Current.

If the Voltage sags below ~13.8-Volts, You may need to have 4-Panels, ( 2-pairs of 2-in series ),
this will give You way more Voltage than You really need, plus twice the Current-Capacity.

You don't need much Current to Charge the Battery at exactly 13.8-Volts,
( unless it's heavily discharged ), maybe only 2 or 3-Amps.

Are You trying to Power a Load and Charge the Battery at the same time ?
What is the Load the Battery is supplying ?
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Okay thank you, the battery will be disconnected while it has a load. To start only a DC load of up to around 500W, but I would like to eventually add an inverter for an AC load of 500W or more as well.

 

Your battery is very small for your load and panel.

A 5Ah 12V battery has a practical capacity of less than 50W. It will run a 500W load for six minutes or considerably less at that rate of discharge.

The recommended charge rate for a battery is about C/10 which is 0.5 Amp for yours 5Ah unit. Your panel supplies 10 times that, which means it will charge in poor daylight, but will require current limiting to stay within parameters in good light.

 

You're really pushing that Battery hard ...........

Does the Battery always get put on Charge Every Night ?,
it should be on Charge anytime it's not actively being used.

All You need is a 1 or 2-Amp "Automatic-Battery-Maintainer".

If You want to build one yourself here's a good way to do it ...............
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Does the Battery always get put on Charge Every Night ?

It's not going to be on charge at night from a solar panel!

 

You have not told us the amp-hour of your battery or battery bank, nor really explained the purpose of the system. So the size of componentry is undefined (number of panels, capacity of regulator, etc) as is the type and pattern of use of the batteries.

There are three steps to charging a lead-acid battery - bulk, absorb, float. Float voltage is the voltage a battery can be held at to keep it inert at maximum charge. A simple charger using a LM317 will bulk charge to 14.4V (the end of bulk stage ) and reduce the current through the absorb stage, but it is not going to then drop to float voltage (the maintenance voltage for leaving a battery stored on charge - about 13.2 volts). Leaving a battery on 14.4V for long storage is not good, which is why the lower 'float' voltage is switched in at the end. But if you are using this system so that it is mostly charging and spends only a little time charged, then you could just make the absorb voltage a bit lower to compensate for not having a float stage. If your system is used such that the battery will spend a lot of time idle at full charge, then a disconnect is not ideal as the self-discharge of lead-acid cells is surprisingly high and the battery will go flat by itself eventually - a float stage is needed.

You could consider a PWM charge control design, which is a common design for panel/battery charge regulation. By switching the panel to the battery at a high frequency with a mosfet (similar to your disconnection intention) problems with heat in the linear regulator are sidestepped, and the control is simply a voltage regulated PWM duty cycle.



No.

Ah I see thank you, I've read about the different stages, but I didn't realize how important it was for lead acid I should've considered that. I also had no idea how to implement the stages without a pwm signal or an mcu. So if I am understanding what you're saying correctly, do away with the automatic disconnect and use the absorb stage which should automatically happen with the lm317 so that the battery isn't at a voltage high enough to degrade it? Does that mean the absorb stage allows voltage to drop slightly due to current decrease (if using regulator method)? Does that mean it should stay connected to the panels until it is time to use it since I am disconnecting it before attaching a load?

 

A solar/battery powered circuit that is running 24 hours a day has a battery that is normally is charge deficit, so float is not absolutely necessary.

A solar/battery powered circuit that is only intermittently used (eg a gate opener) has a battery normally held at full charge, so a float stage is recommended.

Ahh, I see so maybe this answers my other question I asked on your previous post. It seems like absorb/float charge doesn't actually allow the battery to go to a lower voltage, but rather it provides less power due to less current (since I am using a regulator) and thus keeping it at full charge so it is ready for use? Thanks for your responses btw, I am learning a lot. I have read a lot on this, but it is hard to put it all together.

 

That's the idea. Your battery is VERY SMALL for the associated componentry, but if it was used regularly (daily or so) and not unused for extended periods then setting the regulator to say 14 volts or a bit less, and ensuring the current is limited to a maximum of well under an amp, means you could leave it on the solar charger until required. The voltage limiter means the current would taper off during absorb to a minimum necessary to maintain 14 volts, which is close to full charge.

The absorb stage does not drop the voltage to reduce the current - as the battery undergoes chemical change with absorbed charge it's internal resistance rises and that reduces the current.

 

Your battery is very small for your load and panel.

A 5Ah 12V battery has a practical capacity of less than 50W. It will run a 500W load for six minutes or considerably less at that rate of discharge.

The recommended charge rate for a battery is about C/10 which is 0.5 Amp for yours 5Ah unit. Your panel supplies 10 times that, which means it will charge in poor daylight, but will require current limiting to stay within parameters in good light.

Yeah, I think I need a much bigger battery, due to cost I am trying to stay with a lead acid type. You're right I would ruin my battery without a limiting feature in it. I wonder if I could include the limiting portion if using a small battery (specifically the 12V 5Ah), but have a mechanical switch so as to not include a current limiting portion when charging a bigger battery?

 

You're really pushing that Battery hard ...........

Does the Battery always get put on Charge Every Night ?,
it should be on Charge anytime it's not actively being used.

All You need is a 1 or 2-Amp "Automatic-Battery-Maintainer".

If You want to build one yourself here's a good way to do it ...............
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View attachment 259502

Nice I like that thank you, initially although not set in stone I was thinking I could just store it in a ventilated container. However, would that ruin the battery? Is that the reason you're saying it should be on charge every night? I know certain batteries like lipos can be stored off charge as long as voltage per cell is lowered a certain percentage, would I be safe doing something like that with lead acid?

 

That's the idea. Your battery is VERY SMALL for the associated componentry, but if it was used regularly (daily or so) and not unused for extended periods then setting the regulator to say 14 volts or a bit less, and ensuring the current is limited to a maximum of well under an amp, means you could leave it on the solar charger until required. The voltage limiter means the current would taper off during absorb to a minimum necessary to maintain 14 volts, which is close to full charge.

The absorb stage does not drop the voltage to reduce the current - as the battery undergoes chemical change with absorbed charge it's internal resistance rises and that reduces the current.

Oh, okay yeah that makes sense

 

You can simply switch between two sense resistors in the current limit portion of the circuit. The circuit you are trying to design is conceptually a simple linear regulator with a maximum current limiter.

With regard to storage, lead-acid cells have a high internal self-discharge, so long term storage on charge is advised. As long as it is charged after use and charged more often than every few days then all is ok.

 

You can simply switch between two sense resistors in the current limit portion of the circuit. The circuit you are trying to design is conceptually a simple linear regulator with a maximum current limiter.

With regard to storage, lead-acid cells have a high internal self-discharge, so long term storage on charge is advised. As long as it is charged after use and charged more often than every few days then all is ok.

Okay that's good to know I will have to come up with a storage plan. I think I will go with a mechanical switch so it can be used with my small battery as well as a larger one with a different spec (still 12V perhaps). I suppose that's the only switching mechanism I would need as long as the bigger battery is still at 12V right? Just a switch on the sense resistor in the current limiting portion?

 

The Battery-Maintainer that I provided a Schematic for
will completely Charge a 5-Amp-Hour Battery in about ~6-hours or less,
and does not require any special "Stages",
and may be left connected to the Battery indefinitely with zero harm to the Battery.

The Circuit will work with a Solar-Panel with no modifications.
But, will the Solar-Panel reliably provide at least ~18-Volts at 2-Amps
for a long enough period, to Charge the Battery ?

Are You trying to go completely "Off-Grid" ?
If not, put the Battery on Charge all night.

Now, if You want to "push" things, and Charge the Battery in the shortest period of time possible,
then the situation is different, and requires a sophisticated, and expensive, Automatic-Charger.
That is, only if it is to be left unattended for more than an hour or so.
A ~30-Minute-Timer for a 5-Amp-Limited Charge-Rate would be easy to implement,
which would then revert to a 13.8-Volt Maintenance-Charge after the ~30-Minutes has expired,
at approximately triple the cost.
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The Battery-Maintainer that I provided a Schematic for
will completely Charge a 5-Amp-Hour Battery in about ~6-hours or less,
and does not require any special "Stages",
and may be left connected to the Battery indefinitely with zero harm to the Battery.

Your Battery-Maintainer as a current-limited constant-voltage charger does follow a two-stage charging profile.

The PowerSonic document you attach also suggests a two-stage charge process (bulk, then absorb). It recommends several charge regimes depending on battery usage, each of which has an end-stage constant voltage higher than the 13.7 final stage of your Battery-Maintainer, which in use will cause greater long-term sulphation of the battery as it fails to reach adequate full-charge voltage as (an issue described on page 16 of your document).

 

The Battery-Maintainer that I provided a Schematic for
will completely Charge a 5-Amp-Hour Battery in about ~6-hours or less,
and does not require any special "Stages",
and may be left connected to the Battery indefinitely with zero harm to the Battery.

The Circuit will work with a Solar-Panel with no modifications.
But, will the Solar-Panel reliably provide at least ~18-Volts at 2-Amps
for a long enough period, to Charge the Battery ?

Are You trying to go completely "Off-Grid" ?
If not, put the Battery on Charge all night.

Now, if You want to "push" things, and Charge the Battery in the shortest period of time possible,
then the situation is different, and requires a sophisticated, and expensive, Automatic-Charger.
That is, only if it is to be left unattended for more than an hour or so.
A ~30-Minute-Timer for a 5-Amp-Limited Charge-Rate would be easy to implement,
which would then revert to a 13.8-Volt Maintenance-Charge after the ~30-Minutes has expired,
at approximately triple the cost.
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Interesting thank you for the info there's a lot of good stuff on that pdf. Page 17 has a similar charger using a 317 regulator as well I believe

 

It's a good document and worth a read. And it's worth noting that a standard lead-acid battery is intended to be charged at a RATE of 1/10 of its amp-hour CAPACITY. This means that a battery can be filled from empty in TEN hours and shortening this by increasing charge currentwill be detrimental to its life.

 

It's also important to note that battery charge voltages are given at a temperature of 20C or 25C. If the temperature goes a lot above this then the charge profile needs to be derated to cater for that.

 

It's also important to note that battery charge voltages are given at a temperature of 20C or 25C. If the temperature goes a lot above this then the charge profile needs to be derated to cater for that.

Geeze I will absolutely be above that. 100 degrees Fahrenheit is common. When you say de-rated, does that mean that charging a larger battery under high temps would be similar to charging a smaller battery under normal 20C or 25C conditions?