Battery problem

[Danny_DK]

Hi all,

Hope someone can give a small input to this.
I have also come across a slight problem and cant get my head around so I hope you can help.

I have built a small solar power unit that should constant power a GPRS connection module 24/7.

My calculations suggests a 20W panel should be enough to keep the battery charged (when there is sun light). The battery selected was a 12V 10AH AGM battery - which appeared to be pretty good for small projects from what i have seen. The Dc module operates between a 9-12V Dc supply with average current of 50mA.

I also included a charge controller to prevent over charging of the battery, as the battery specifications state 'charge current max of 4A' I used a 12V 4AH C/C. As the module operates between 9V-12V supply I basically had this connected through a voltage regulator to the battery. I used a voltage regulator to keep the output fixed to the module to 12V as a precaution.

This should be a very basic system to operate however on test I found the battery died after about two months of operation.

It was on test over Christmas (possible the worst time of year to complete initial testing) and the location where the test was carried out was in a remote location where the PV panel was only subject to sun in the afternoon.

The battery was charging as I measured the voltage in the battery every couple of days and kept a eye on the system.

Anyone else experience problem like I have? Could there be a temp problem or location test problem?

[SunEagle]

Danny

My guess is that you are using more watt hours than can safely be pulled from that 10Ah battery (which is ~ 120 watt hour total). And that 20 watt panel is not enough to put back what you take out on a daily basis.

You should size your battery to be discharged no more than 20% - 25%. Then due to bad weather you should also size your battery to last 4 to 5 days without sun. Then you need to put back more watt hours then you take out which will help size your solar panel wattage using your worst solar insulation hours in the Winter time.

Finally your CC needs to be sized to handle the total amp output of your panel wattage.

So first determine your true daily watt hour usage because just multiplying the average current of the load times the voltage times the hours used may get you a lower total "watt hour" number then you actually use because of efficiency losses.

[Danny_DK]

Hi SunEagle,

Thank you for your input.

I have followed your recommendations to what i have already calculated and they worked out the same. Going by the calculations a 10AH battery may have being to large to use but it was all I had available at the time (thinking bigger was better). I believe a 7AH battery should be suffice to provide the necessary power to load. Now with this change going by what you have said and my calculations the 20W panel should be suffice to charge a 7Ah battery.
Maybe this is incorrect in saying?

Yes the Charge controller was the part I was iffy in sizing, going by the battery spec the charge current max for 4A so I used a 4H C/C. Have you any insight to what sort of C/C should be using are the best to look for?

[Logan005]

Bigger battery is always better for anatomy, however a bigger battery requires a bigger solar array as well. You need a watt meter on the GPRS unit, get usage readings both when idle and more important readings wile under load. You can not rely on product specs as they are usually wrong.

[SunEagle]

Hi SunEagle,

Thank you for your input.

I have followed your recommendations to what i have already calculated and they worked out the same. Going by the calculations a 10AH battery may have being to large to use but it was all I had available at the time (thinking bigger was better). I believe a 7AH battery should be suffice to provide the necessary power to load. Now with this change going by what you have said and my calculations the 20W panel should be suffice to charge a 7Ah battery.
Maybe this is incorrect in saying?

Yes the Charge controller was the part I was iffy in sizing, going by the battery spec the charge current max for 4A so I used a 4H C/C. Have you any insight to what sort of C/C should be using are the best to look for?

It sounds like you sized your system properly but I would imagine there are losses due to wire runs, little sunlight and poor efficiency that is adding to your true watt hour load causing the battery to drain faster.

A quick rule of thumb would be to size the panel wattage / CC / battery so that you have a charge rate between C/8 & C/12 where C = Ah rating of the battery. So for a 10Ah battery you need between 1.25 and 0.84 amps from the CC & panel. A 20 watt panel should be able to deliver Vmp ~ 1.2 amps during peak sunlight but between the losses during charging and minimal sunlight during the winter you may not be charging that battery enough.

Because you have such a little system a good PWM CC is all you would need but I would get at least a 10 amp one just in case you want to enlarge the system some time down the road.

But to get more than you need you might be able to increase that wattage to 30 without over charging that 10Ah battery.

[inetdog]

Bigger battery is always better for anatomy, ....

Autonomy????
Autocorrect?

[Barek]

Any recommendations for a reliable renewable energy battery company?

What have you found to be reliable?

Thanks

[SunEagle]

Any recommendations for a reliable renewable energy battery company?

What have you found to be reliable?

Thanks

Depends on the application, size of the system and battery chemistry. Way too many options to only point to one as being the best

[sensij]

Hi all,

My calculations suggests a 20W panel should be enough to keep the battery charged (when there is sun light). The battery selected was a 12V 10AH AGM battery - which appeared to be pretty good for small projects from what i have seen. The Dc module operates between a 9-12V Dc supply with average current of 50mA.

I also included a charge controller to prevent over charging of the battery, as the battery specifications state 'charge current max of 4A' I used a 12V 4AH C/C. As the module operates between 9V-12V supply I basically had this connected through a voltage regulator to the battery. I used a voltage regulator to keep the output fixed to the module to 12V as a precaution.

Some of what you've written here is hard to follow. It sounds like you've got two components between the solar panels and the battery... a charge controller and a voltage regulator. If so, the voltage regulator may be screwing up the charging process.

What specific panel did you buy? Where are you located (roughly), and how do you have it oriented (direction and tilt)?

[Sunking]

OK first thing is get rid of the Voltage Regulator. All that is required is the charge controller. A 12 volt regulator is just wasting power and takes at least 13 volts input to get 12 volts out on the VR. At night your battery voltage drops to maximum of 12.6 volts when the sun sets and goes down from that point on to morning. So get rid of the VR.

Second point you have a PWM controller. With any PWM controller INPUT CURRENT = OUTPUT CURRENT. A 20 watt 12 volt battery panel maximum output current at noon is only around 1.2 amps or less. A 4 amp controller only means it can pass a mximum of 4 amps from the panel. To get 4 amps charge current would require a 70 watt panel. So 4 amps charge current is fantasy form a 20 watt panel . Panel determines current, not the controller.

[Danny_DK]

It sounds like you sized your system properly but I would imagine there are losses due to wire runs, little sunlight and poor efficiency that is adding to your true watt hour load causing the battery to drain faster.

A quick rule of thumb would be to size the panel wattage / CC / battery so that you have a charge rate between C/8 & C/12 where C = Ah rating of the battery. So for a 10Ah battery you need between 1.25 and 0.84 amps from the CC & panel. A 20 watt panel should be able to deliver Vmp ~ 1.2 amps during peak sunlight but between the losses during charging and minimal sunlight during the winter you may not be charging that battery enough.

Because you have such a little system a good PWM CC is all you would need but I would get at least a 10 amp one just in case you want to enlarge the system some time down the road.

But to get more than you need you might be able to increase that wattage to 30 without over charging that 10Ah battery.

Hi SunEagle,

During my calculations I did account for charge and wire losses but you may be onto something regarding the little sunlight. During testing it was installed along a build which is blocking the sun light hitting the PV panel until the afternoon. This would have an effect on the charging of the battery.

With the 20W panel I currently the VMP is 17.5VDC and IMP is 1.15A. This is within what you say about the charge rate. I though the battery and PV panel was sized ok for such a small system and with the components available at the time.

The Charge Controller was something I was unsure about. I will look into a PWM C/C and see what I can find. So sourcing a 10AH C/C should be ok for charging the 10AH battery or should I go for smaller battery? I don't really like to increase the size of the solar array itself.

[Danny_DK]

Some of what you've written here is hard to follow. It sounds like you've got two components between the solar panels and the battery... a charge controller and a voltage regulator. If so, the voltage regulator may be screwing up the charging process.

What specific panel did you buy? Where are you located (roughly), and how do you have it oriented (direction and tilt)?

Hi sensij,

The Pv panel is connected to the C/C which is then connected to the Battery, the only component between the Pv panel and Battery is the C/C. A supply from the battery is then taking to the Voltage regulator. This provide the 12V supply then to the voltage reg and onto the Gprs module.

The PV module is facing south and an angle of approx 35 degrees, however it located near a building which is blocking some sunlight until the afternoon. This will be having an effect on the charging process I will have to change the location for next testing phase.

[Danny_DK]

OK first thing is get rid of the Voltage Regulator. All that is required is the charge controller. A 12 volt regulator is just wasting power and takes at least 13 volts input to get 12 volts out on the VR. At night your battery voltage drops to maximum of 12.6 volts when the sun sets and goes down from that point on to morning. So get rid of the VR.

Second point you have a PWM controller. With any PWM controller INPUT CURRENT = OUTPUT CURRENT. A 20 watt 12 volt battery panel maximum output current at noon is only around 1.2 amps or less. A 4 amp controller only means it can pass a mximum of 4 amps from the panel. To get 4 amps charge current would require a 70 watt panel. So 4 amps charge current is fantasy form a 20 watt panel . Panel determines current, not the controller.

Hi SunKing,

The voltage reg is not connected between the C/C and the Battery, this should not have an effect of the charging process. The module which I am using operates between 9-12V as a safety precaution i decided to use a 12V voltage reg as protection so 12V is only going to the module.

[sensij]

The PV module is facing south and an angle of approx 35 degrees, however it located near a building which is blocking some sunlight until the afternoon. This will be having an effect on the charging process I will have to change the location for next testing phase.

Yes, it sounds like this is the root of your problem. It is possible to model the output of the panel in unshaded conditions to see if a new location away from the building will be enough of an improvement. If you look at PVWatts, and read through the documentation, you can see how to apply it to your situation. Keep in mind as others pointed out that with a PWM controller you will not be operating at the maximum power point of the panel, so in the model output, POA irradiance and PV current are more applicable than the modeled power output.

[Sunking]

Hi SunKing,

The voltage reg is not connected between the C/C and the Battery, this should not have an effect of the charging process. The module which I am using operates between 9-12V as a safety precaution i decided to use a 12V voltage reg as protection so 12V is only going to the module.

Huh?

Who said anything about between the CC and Batteries? That would not even allow the batteries to charge if you did that.

I mean between the Battery and Device as you have it connected. . Get rid of it. It is wasting power and will shut down your device after dark when the battery voltage drops below 13 volts. A VR has a forward voltage drop of 0.6 to 1.5 volts. That means for it to output 12 volts requires 13 volt or more on the input.

You may indeed have other problems, but you also have a VR issue you are over looking. Get rid of the VR, your device will be fine if it is made to operate on 12 volts.