Cheap PWM Charge controller

[alex2017]

I got a 20 bucks charge controller from Amazon (https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1) I need to check that its properly working in PWM mode and not killing my batteries. How to do it? I checked that when the batteries are fully charged 13.4 volts, it still is sending like 0.5 amps to them,and sometimes the voltage goes up to 14.4-14.7 volts. Is it normal? My system is very simple 19AH 12 volt battery and 25Watt panel. Its my understanding that when batteries are charged it should go into float,and send very little current. (I am using a clamp meter to check the amps)

Thank you for your help, Alex.

[Sunking]

PWM controllers are pretty simple device. They are basically a switch that turns on/off real fast. They regulate voltage by modulating the on/off time. At 100% modulation is a fully closed switch which connects the panel directly to the battery. At 0% modulation completely disconnects the panel from the battery.

So th etrick to knwing what is going on is measuring the input voltage from the panels. When panel voltage roughly = battery voltage you know the controller is at full Bulk charging power. As the battery reaches full charge the input voltage will start to rise. When the battery is fully charged, the panel voltage will be 18 volts or higher, while the battery voltage is at 13.5 volts.

[alex2017]

what about the current,how much should PWM send when the bat voltage is >=13.5

[Sunking]

what about the current,how much should PWM send when the bat voltage is >=13.5

PWM does not regulate current. It controls the voltage. The battery voltage and solar panel regulates the current.

If the Controller set point voltage = the battery voltage, this is no current.

[PNjunction]

Alex - your controller is acting normally. Your battery is a sealed-agm. It is not a gel, nor a flooded. If you can cross reference the voltages in the controller to the settings, then the 14.4 to 14.7v "absorb" is what you want.

This is a "conventional agm" (not a pure-lead type), and as such has a maximum charge current of 0.25 to 0.3C, which means 19ah * 0.25 = 4.75A max bulk charge current.

While your 25 watt panel works (generically capable of 25w / 18v = 1.38A max current), you could upgrade to an 80-watt panel if you needed a faster charge, depending on your depth of discharge and solar insolation.

Just know that to TRULY fully recharge an agm battery, it takes an additional 8 hours *after absorb switches to reaching float* to do so! Nobody has that amount of time daily in the sun with any moderate discharge, so if you are cycling it often, give it a good day or more to just sit and float in the sun once in awhile. I suspect that this is a non-critical application, so you should probably be able to do this.

TIP: If a controller or other piece of critical gear, like a charge controller, offers convenient usb ports - don't use them! Far too often if you short or blow out the usb port, it takes down the main logic board with it, rendering the controller part useless. Far better to wire up some "mobile" cigarette lighter adapter ports to your 19ah battery directly.

And, do not use the "load" controls to attach to the battery.

[AzRoute66]

what about the current,how much should PWM send when the bat voltage is >=13.5

But I do like the question from the point of view that if the battery is in float, the current from the charge controller should equal the self discharge current in the battery (I think).

If so, are there any rules of thumb for how much that current is likely to be for different battery types? different battery bank capacities? Is this a number that can be found in the battery spec sheets, it's not one I've ever noticed. I would think it could be quite thermally sensitive. If the current goes to zero, or a abnormally high number, is that indicative of any particular type of battery fault? I understand that if the battery has just entered float from absorb it probably isn't near a steady state, so I think I'm talking about one that has been in float for 'quite some time'.

[Sunking]

But I do like the question from the point of view that if the battery is in float, the current from the charge controller should equal the self discharge current in the battery (I think).

If so, are there any rules of thumb for how much that current is likely to be for different battery types? different battery bank capacities?

I can tell with with a great deal of accuracy exactly how much charge current will be flowing at any given moment. In fact have done it many times. Even wrote a Sticky so anyone can do it.

So what do we have to know to determine Charge Current.

The Charge Source current and power limits. Example in a 12 volt AC charger will have a Limit Rating of say 10 amps. Or a Charge Controller Power Input
Charger Set Point Voltage
Battery Open Circuit Voltage (OCV)
Battery Internal Resistance.

So 2 examples. First example I have a Super Duper Infinite Current Battery Charger. 1-amp, 10-amp, 100-amp, 1000-amps or whatever to infinity unlimited power and current. I also have a 12 volt 100 AH battery with a OCV = 12.1 volts (50% SOC) and an Ri = .01 Ohms. I now take my Super Duper AC Turbomatic Battery Charger set to 14.8 volts. How much charge current is there?

Charge Current = [CV - BOCV] / Ri

Where

CV = Charger Voltage
BOCV = Battery Open Circuit Voltage
Ri = Battery Internal Resistance

So we have 14.8 volts - 12.1 volts] / .01 Ohms = 270 Amps or a C2.7 rate. We are gassing the hell out of the batteries for about 20 minutes, and it will take another 8 hours to fully charge until charge Current stops. .

Example 2 now I use a Normal 10 Amp Battery charger on the exact same battery and same exact conditions. We connect the Charger, set it to 14.8 volts and we notice two things. Charger Current = 10 amps, and voltage = 12.2 Volts. The formula for Charge Current does not change. So why do we not have 14.8 volts and 270 amps?

Real simple, the Charger is Limited to 10 Amps or 122 watts with 12.2 volts and 10 amps. So what is going on? Well the Charger Folded Back the Voltage to limit current to 10 amps.

Voltage = Current x Resistance

We have 10 amps flowing through the battery resistance of 0.01 Ohms or 0.1 Volts. The Voltage of any Charging Battery = Battery OCV + (Charge Current x Ri). Are battery has an OCV of 12.1 volts, 10 amps of charge current, and 0.01 Ohms. Do the math. 12.1 + (10-Amps x .01 Ohms) = 12.2 volts.

Now that 10 amps continues to charge the battery. As the battery charges up, its voltage begins to rise. After a few hours our battery reaches 14.7 volts. At 14.7 volts, are charge current starts to taper off toward 0 amps. When the battery voltage reaches 14.8 volts, all charge current stops. Why? Do the math of a charging battery.

14.8 volts - 14.8 volts / .01 Ohms = 0 Amps

Zero divided by anything = ZERO

Last question to test your knowledge. At what voltage did our Super Duper Turbomatic Charge current start to taper off at? Everything you need to know is in this reply.

[inetdog]

Sunking,

Can you provide a rough estimate of the self-discharge current for various battery types? As a function of C₂₀ AH, of course.

[Sunking]

Sunking,

Can you provide a rough estimate of the self-discharge current for various battery types? As a function of C₂₀ AH, of course.

NP. Although at C/20 is not doable because batteries like NiCd and all lithiums are rated at 1C. Age, temps, and cycling increases the self discharge rates. Typical rates, but not limited too are:

Lithium Ion Types 2 to 5% in first 24 hours, then 1 to 3% per month
FLA and AGM 10 to 15% per month
Nickel Based 10 to 15% in first 24 hours, then 10 to 20% per month.

Primaries include:

Lithium Metal 10% in 5 years
Alkaline 2 to 3% per year

As easy to notice Primary Cells have the least, and Secondary have the highest. Either category Lithium wins. Also evident Nickel based cells just suk because no tonly is charge efficiency piss poor of 60 to 80%, you also loose 10 to 15% over night just sitting there. With Nickel batteries means it takes 50% more energy to recharge them. A 100 AH 12 volt FLA might require a 200 watt panel. and on Nickel a 300 watt panel.

[Mike90250]

...... Also evident Nickel based cells just suk because no tonly is charge efficiency piss poor of 60 to 80%, you also loose 10 to 15% over night just sitting there. With Nickel batteries means it takes 50% more energy to recharge them. A 100 AH 12 volt FLA might require a 200 watt panel. and on Nickel a 300 watt panel.

Wow, in 60 years when I change these out, I'll have such a surplus of power......

[Sunking]

Wow, in 60 years when I change these out, I'll have such a surplus of power......

Tell you what, if you and your batteries live another 60 years, I will instruct my Grand Children to buy them for you with their inheritance.