# How to Charge Battery via Solar panel to power a push action solenoid

#### M3D0

Joined Oct 8, 2020
49
This is my first project ever, I'm running into some problems with the power supply stage, I hope you could help! I want to power a solenoid (12v/2A), which will get its voltage from a battery (12V/3000mAh) connected to a Solar Panel (12V/430mA – 5.2Watt). I would really appreciate it if you could show me a schematic design to this simple circuit. To sum my idea up [solar panel >> battery>> solenoid]. Thanks in advance!

Components used:
Solar panel: Mini Solar Panel 12V/430mA – 5.2Watt
Solenoid: JF-0826B Push Action Type Electric Linear Solenoid 12Vdc
Battery: Lithium-ion Super Rechargeable Battery Pack (12V, 3000mAh)

#### Tonyr1084

Joined Sep 24, 2015
5,239
Welcome to AAC.

First, 12 volt batteries (Li-ion batteries must be maintained at proper voltages) it's important to know how many batteries are in your 3000mAh battery. A Lion battery should be charged to 3.8 to 4.2 volts for a full charge (per single cell). And the way they're charged will require a battery management circuit board. If your battery has three cells, at 4.2V that's 12.6V when fully charged and should not be allowed to drop below 8.4 volts. Going below that voltage can, and may likely, damage the batteries. If your battery has four cells, the numbers need to be adjusted accordingly.

Since the solar battery doesn't produce steady output it's important to have good regulation. A Buck/Boost converter should be able to maintain 13.8 volts much of the daylight hours but I'd start with a higher voltage solar panel. But using a converter, you're going to lose some power. Since you're already starting with only 430mA, that's not going to be enough to keep your battery charged. Not unless the operation of this solenoid is going to happen only once in a while; like once or twice a week. And Lion batteries need specific current levels at specific times in their charging cycle.

Out of curiosity, what are you controlling? I mean, the solenoid is controlling? How often will this solenoid be actuated? And how many cells are in your battery pack?

They DO sell hobby battery chargers for those types of batteries. However, they run on 120VAC. Making one work from a solar cell will be difficult and wasteful.

Joined Jan 15, 2015
5,667
You do not mention the battery type?

Just looking at your numbers you have a solenoid which draws 12 volts at 2 amps. You have a 12 volt battery rated at 3,000 mA/Hr or 3.0 amp hours. On a good day under ideal conditions your battery will be run down in about 1.5 hours. Your charge method, under ideal conditions (bright sunlight) outputs 12 volts at 430 mA or 0.430 amp. Without doing the math and using real world numbers it would take over 6 hours of ideal sunlight to charge your battery.

This begins with knowing the battery type? Just as an example a 12 volt 2.0 AH SLA (Sealed Lead Acid) battery, in healthy condition is about 12.6 volts or 2.1 volts per cell. It would be charged at a higher voltage to a point. Matter of fact just read this.

When considering a battery for an application we consider the load and charge method. There are solar chargers available and also modules for managing battery charging. Just remember when looking at solar panel ratings they are given under ideal conditions, not cloudy days or in shadows.

Ron

#### Tonyr1084

Joined Sep 24, 2015
5,239

Joined Jan 15, 2015
5,667
Well duh. Thanks a bunch for pointing out what was clearly in front of me.

With that I would be looking at a battery suitable to sustain the forecasted On time of your solenoid when daylight is not available or solar panel output is low. A two amp load on a 3 AH battery gets you about 1.5 hours on a good day. That assumes the solenoid is constant on.

Thanks again Tony for pointing that out as I apparently read right over it.

Here are some Lithium Battery Charge Controllers designed around solar panel use.

Ron

#### MrSoftware

Joined Oct 29, 2013
1,936
Check a place like SparkFun.com, look for a solar battery charger module that is compatible with your solar panel and your battery chemistry. A 12v lithium battery will have multiple cells so keep that in mind. If you want to get fancy, you can get one that supports MPPT (maximum power point tracking) which is a fancy way of saying that it makes the most efficient use of your solar panel.

#### Tonyr1084

Joined Sep 24, 2015
5,239
I apparently read right over it.
Heck, I do that all the time too. In fact, my first imagination was a 12V SLA battery, just like you. Only after authoring my comment I looked back to see if there were any specifics - and there it was "Li-Ion" battery. Hence, I had to completely edit my comment.

#### dl324

Joined Mar 30, 2015
11,897
Welcome to AAC!
Components used:
Solar panel: Mini Solar Panel 12V/430mA – 5.2Watt
Solenoid: JF-0826B Push Action Type Electric Linear Solenoid 12Vdc
Battery: Lithium-ion Super Rechargeable Battery Pack (12V, 3000mAh)
You haven't given us sufficient details.
1. A 12V solar panel can't charge a 12V battery. What is the panel's open circuit voltage?
2. A lithium ion battery isn't going to be 12V. What is the voltage required for charging? The cells I use are 3.6-3.7V and require around 4.2V to charge.
3. You really should use a proper charger.
4. How long do you expect the solenoid to be activated and what is the coil current?

#### M3D0

Joined Oct 8, 2020
49
Welcome to AAC!

You haven't given us sufficient details.
1. A 12V solar panel can't charge a 12V battery. What is the panel's open circuit voltage?
2. A lithium ion battery isn't going to be 12V. What is the voltage required for charging? The cells I use are 3.6-3.7V and require around 4.2V to charge.
3. You really should use a proper charger.
4. How long do you expect the solenoid to be activated and what is the coil current?
1- Can I know the reason why I can't charge a 12V battery with 12V solar panel ?
2-I bought a solar panel charger (CMP12 BSV20A)
3-for the solenoid, I expect it to be activated for a second at max
4- the coil current is 2A

#### M3D0

Joined Oct 8, 2020
49
Welcome to AAC.

First, 12 volt batteries (Li-ion batteries must be maintained at proper voltages) it's important to know how many batteries are in your 3000mAh battery. A Lion battery should be charged to 3.8 to 4.2 volts for a full charge (per single cell). And the way they're charged will require a battery management circuit board. If your battery has three cells, at 4.2V that's 12.6V when fully charged and should not be allowed to drop below 8.4 volts. Going below that voltage can, and may likely, damage the batteries. If your battery has four cells, the numbers need to be adjusted accordingly.

Since the solar battery doesn't produce steady output it's important to have good regulation. A Buck/Boost converter should be able to maintain 13.8 volts much of the daylight hours but I'd start with a higher voltage solar panel. But using a converter, you're going to lose some power. Since you're already starting with only 430mA, that's not going to be enough to keep your battery charged. Not unless the operation of this solenoid is going to happen only once in a while; like once or twice a week. And Lion batteries need specific current levels at specific times in their charging cycle.

Out of curiosity, what are you controlling? I mean, the solenoid is controlling? How often will this solenoid be actuated? And how many cells are in your battery pack?

They DO sell hobby battery chargers for those types of batteries. However, they run on 120VAC. Making one work from a solar cell will be difficult and wasteful.
My application is simple, there is a proximity sensor which will sense an object ( a box in this case), and if a box is sensed near the proximity sensor the solenoid will push the box with a 20N force, and all of that will be powered by the solar energy. I bought a solar panel charger(CMP12 BSV20A) to regulate all that you mentioned earlier. Thank you for the information you provided. Is there any further advice other than using solar panel charger ?

#### Tonyr1084

Joined Sep 24, 2015
5,239
I bought a 12V solar charger(panel) meant to keep the battery topped off in the sunny afternoons. It's unloaded voltage with full sunlight is 19V. A 12 volt wet cell (car battery) has a nominal voltage of 12.6V. The float charge (level of charge the battery is normally maintained at when the engine is running) is 13.6 to 13.8V. After starting the car the battery charge may go up to 14.4V (from my experience) (It's said it can go up to 15 volts). The reason fro charging a car battery to those levels is to clean the plates of sulfates that may develop on the battery internal plates. Leaving an SLA (Sealed Lead Acid) battery on the shelf uncharged for long periods of time will result in a failed battery due to the sulfating of the plates. It's happened to me. Those batteries need to be charged regularly. Typically, I recharge mine every 3 months just to keep them healthy.

So to charge a 12 volt battery you have to supply it with more than its nominal voltage. Lithium Ion batteries are hugely different. The way they are charged is completely different. They're controlled by current as well as voltage. Hence, the reason for asking what the unloaded voltage of your solar cell is because if it is only 12 volts and three Lion batteries in series will equal a full charge of 12.6 volts, if you don't give it the full charge at the proper current then the batteries will degrade. Degraded Lion batteries can become dangerous. I've scavenged several of these batteries and have sorted out the ones that don't hold a charge. They don't hold charge because their internal structure has become either shorted or a resistive short has occurred and will drain them. It's when they go short that they become highly dangerous. They can explode. Proper handling, charging and maintenance of these batteries is not to be left up to chance. You can't just put them on a charger; it has to be the RIGHT kind of charger for the particular battery.

Also harmful to Lion batteries is under voltage. When their voltage drops too low that's when they start developing internal shorts.

#### Tonyr1084

Joined Sep 24, 2015
5,239
The purpose of the solar panel I bought was to power during the daytime a bark deterrent device. I have neighbors with barking dogs. Calling the police doesn't make for good neighbors, and often does nothing to stop the barking. My rig consisted of the solar panel, a buck converter (to 10V {a new 9V battery is typically 9.6V}) and the sonic bark deterrent device. During the day it provides enough power to interfere with dog barking. But when the sun goes down if there's a reason for the dogs to bark I don't want to deter them. It has been effective in controlling one of my neighbors dogs. Another neighbor's dog has learned not to bark by the side of my house. If only I could get my neighbors to put these deterrent devices up in their own yards their dogs would stop barking at every little stupid thing that occurs.

#### MrSoftware

Joined Oct 29, 2013
1,936
1- Can I know the reason why I can't charge a 12V battery with 12V solar panel ?
2-I bought a solar panel charger (CMP12 BSV20A)
3-for the solenoid, I expect it to be activated for a second at max
4- the coil current is 2A
Generally speaking; if the battery is supplying 12v, and your charging device is supplying 12v, no current will move and nothing will happen. As mentioned above a 12v battery will actually be above 12v when it is charged, so your charger has to be capable of delivering even more voltage than the battery can supply at peak charge, so that it can make current move in the battery and charge it. All of that said; if you bought a charger that matches your battery, then problem solved. Just be sure your solar panel matches the input requirements for the charger and you're set.

#### M3D0

Joined Oct 8, 2020
49
I bought a 12V solar charger(panel) meant to keep the battery topped off in the sunny afternoons. It's unloaded voltage with full sunlight is 19V. A 12 volt wet cell (car battery) has a nominal voltage of 12.6V. The float charge (level of charge the battery is normally maintained at when the engine is running) is 13.6 to 13.8V. After starting the car the battery charge may go up to 14.4V (from my experience) (It's said it can go up to 15 volts). The reason fro charging a car battery to those levels is to clean the plates of sulfates that may develop on the battery internal plates. Leaving an SLA (Sealed Lead Acid) battery on the shelf uncharged for long periods of time will result in a failed battery due to the sulfating of the plates. It's happened to me. Those batteries need to be charged regularly. Typically, I recharge mine every 3 months just to keep them healthy.

So to charge a 12 volt battery you have to supply it with more than its nominal voltage. Lithium Ion batteries are hugely different. The way they are charged is completely different. They're controlled by current as well as voltage. Hence, the reason for asking what the unloaded voltage of your solar cell is because if it is only 12 volts and three Lion batteries in series will equal a full charge of 12.6 volts, if you don't give it the full charge at the proper current then the batteries will degrade. Degraded Lion batteries can become dangerous. I've scavenged several of these batteries and have sorted out the ones that don't hold a charge. They don't hold charge because their internal structure has become either shorted or a resistive short has occurred and will drain them. It's when they go short that they become highly dangerous. They can explode. Proper handling, charging and maintenance of these batteries is not to be left up to chance. You can't just put them on a charger; it has to be the RIGHT kind of charger for the particular battery.

Also harmful to Lion batteries is under voltage. When their voltage drops too low that's when they start developing internal shorts.
So basically if I want to be on the safe side and avoiding battery explosions and damaging any components, I have to use a solar charger controller?

#### MrSoftware

Joined Oct 29, 2013
1,936
So basically if I want to be on the safe side and avoiding battery explosions and damaging any components, I have to use a solar charger controller?
A proper charger is the safest way, especially with lithium.

#### dl324

Joined Mar 30, 2015
11,897
1- Can I know the reason why I can't charge a 12V battery with 12V solar panel ?
There is no lithium ion battery that is 12V. The 18650 cells I use are nominally 3.6V. 3 in series would give 10.8V, 4 would give 14.4V. They require 4.2V/cell to charge.

2-I bought a solar panel charger (CMP12 BSV20A)
In general, the open circuit voltage for 12V solar panels would be higher than 12V. Research the specs for the panel to see what the open circuit voltage is.

To minimize issues with batteries exploding or catching on fire, you should use a proper charger.
3-for the solenoid, I expect it to be activated for a second at max
4- the coil current is 2A
One second at a time, but how many times an hour or day?

#### Tonyr1084

Joined Sep 24, 2015
5,239
So basically if I want to be on the safe side and avoiding battery explosions and damaging any components, I have to use a solar charger controller?
You need a solar panel capable of supplying the required amperage at a higher voltage than the battery at full charge. Then you need a Li-ion charger for the batteries.

#### M3D0

Joined Oct 8, 2020
49
One second at a time, but how many times an hour or day?
I'm making this project as a demonstration, so it won't be used daily

#### M3D0

Joined Oct 8, 2020
49
You need a solar panel capable of supplying the required amperage at a higher voltage than the battery at full charge. Then you need a Li-ion charger for the batteries.
How do I know the required amperage needed to be supplied to the battery, in this case I'm using: [Mini Solar Panel 12V/430mA – 5.2Watt] connected to [CMP12 Solar Charge Controller ] which will feed [Lithium-ion Super Rechargeable Battery Pack (12V, 3000mAh)] then it will power the solenoid mentioned above, could this connection result in any failure by any means? sorry if I'm asking dumb questions, I'm learning.

#### MrSoftware

Joined Oct 29, 2013
1,936
Read the instructions on the charger to see what it requires for input voltage and current. Some will take very little, others require more. There's nothing wrong with slow charging a battery, actually it will last longer, so as long as you can supply enough voltage and current to make the charger happy, you should be good.