9 Solar Panels in parallel ?

[gary350]

I bought 9 solar panels from Harbor Freight with NO DC to AC inverter. These come in a 3 panel kit with 1 inverter per kit but the inverters were all broken so I got a good deal on 9 panels. I am wonder if I can connect all 9 of these panels in parallel to charge a car battery.

3 solar panels are rated 45 watts.

Open circuit voltage per panel is 18.5 volts.

9 panels in parallels = 135 watts. I want to take the solar panels camping to charge a car battery during the day then use the battery for lights, cell phone charger, computer, etc. after dark. It the forest during the day often there is only a few hours of direct sunlight in the middle of the day. If I am lucky I hope to get 5 hours of direct sunlight each day to charge a 600 amp car battery.

The 600 amp car battery I have now with no way to charge it will last 6 days using lights only after dark. I have FOUR 15 watt and TWO 25 watt light bulbs inside the camper. I have light strings around the camp site. National Parks have NO electricity.

QUESTION. Should I put a safety fuse or diode in the circuit for each solar panel? I don't see a problem with solar panels shorting out and draining the battery but maybe it will. Is there any fire hazard problem with 9 solar panels being a dead short across a car battery after dark?

**broken link removed**

 

[nsaspook]

Diodes or fuses for your low power individual parallel panels are not needed (maybe one fuse per three panels group to a main combining point for all panels) if you have a charge controller that disconnects the panels from the battery at night but a fuse at the battery terminal for the charging connection is a must as the battery can deliver hundreds of amps into a short. Do you have a solar charge controller?

 

[NorthGuy]

What do you mean by 600 amp car battery? 600 CCA? The CCA rating doesn't mean anything for battery capacity. You need AH rating. 600AH battery will weight 400 pounds. Car batteries are perhaps 20-30AH. 100W load will drain it completely in 4 hours.

Car batteries are not designed to be cycled. They have thin plates. They are designed to provide huge current for a very short time. If you're going to drain it regularly to 50% or so, it'll die very soon. You need some sort of deep cycle battery (dual purpose marine batteries might be ok).

 

[KeepItSimpleStupid]

Car batteries have a small distance between the plates. Deep cycle batteries much larger distance. Smaller distance - more current, easy to short. Larger distance - less current, not so easy to short. Short means the stuff (sulferization) that grows and gets removed from the plates during charging/discharging shorts the plates.

 

[Nigel Goodwin]

Many solar panels already have diodes built-in, if not just add a diode in the feed from each panel - I wouldn't have thought you're going to need any kind of charge controller for your intended purpose, but you might like to test it at home first for a few days, with an ammeter measuring the charging current (take regular readings and plot a graph over a few days - including night time).

 

[gary350]

I have NOTHING but the 9 solar panels.

The 3 charge control units were all damaged that is why the 9 solar panels were sold for $20 each panel.

I have used a car battery for 12 years for camping in national parks. I take the battery from the extra vehicle with us camping and it provides lights for 6 to 7 days before it is almost dead. I have a 150 watt DC to AC inverter to run the 120 VAC lights. Sometimes if we travel and camp for a month I take a battery charger to charge up the car battery once a week. I am not putting a heavy load from the battery, 25 to 40 watts for about 60 to 90 minutes each evening.

I was hoping to use the 9 solar panels in place of the battery charger. The solar panels are larger and harder to deal with than a car battery charger but I don't have to look for a 120 AC outlet to us the battery charger. Sometime I leave the battery charger at home then I swap the vehicle battery with the camping battery every day to keep it charged when I drive the vehicle.

I am tired of swapping the vehicle battery every day and I am tired of the battery charger too. If we stay at the same camp site for a week I think the solar panels will be a lot less work. I am not sure I need all 9 solar panels that might be over kill but in a shady camp site it might not be over kill.

 

[NorthGuy]

Assuming you use 40W for an hour, you need 40WH put into the battery every day. With all the inefficiencies, you probably need 60WH produced by the panels. If you leave it on charge, to produce this in 3-4 hours, you'll need 20W of panels. You need much more if you want to get something on a cloudy day.

When battery is discharged it can take a lot of current, so you can just connect the panel directly to the battery. But when it gets charged it cannot take much. At this point it would be nice to limit voltage to 14.5-15V (14-14.5 if you have AGM). If it goes much higher than this, it'll boil out the electrolyte. You can manually disconnect at this point (the battery won't get fully charged, but you can top it up when you're back home), or you can get a charge controller that limits voltage automatically. There are plenty of cheap ones on e-bay.

 

[gary350]

What is AGW?

Open circuit voltage is 18.5 but when connected to the battery voltage is 15.

With misc clouds and trees it is hard to know if the battery will get a full charge in 1 hour or 10 hours each day. I am not sure there is a way to know when the battery is fully charged.

I was thinking about removing the transformer from a car battery charger and using the solar panels in place of the transformer. The solar battery charger could charge the battery. I am not sure what type circuit is inside the unit but I notice the meter reads different as the battery becomes charged. If a cloud blocks the sun every 15 minutes that would be like turning the battery charger OFF then ON again every 15 minutes all day. What kind of problems will take cause?

Slow charge on the battery charger is 15 amps. The 9 solar panels produce about 9 amps total in full sun. It should work fine to connect all 9 panels to the battery if there is some way to know the battery is fully charged so it will turn off automatically, some how.

 

[NorthGuy]

AGM is a sealed battery.

You can connect all the panels to the battery, but you don't need to. 20W (1.5 amp) panel will re-charge what you took in the evening (if your asessment is correct).

The only bad thing that may happen with direct charge is overcharge. It happens when there's too much current. The battery instead of charging starts to boil. Hydrogen is produced during the process, so there could be a fire or explosion. Therefore, it's a good idea to keep voltage below 15V. When the battery gets charged, the voltage go up. The standard practice is to limit the voltage.

The charger does exactly as you described - it switches it on and off trying to keep the desired voltage, except not every 15 minutes, but faster, usually in kHz.

 

[avrilcory]

The optimal voltage to be running from these panels is slightly over 12 volts. We recommend our customers to have the panels' voltage to be 1.5 times higher than the voltage of battery because it is also important to get a controller to sit in between your panel and the battery. If you are using a 12V system and want to add extra capacity to your system you will wire your batteries in parallel.


Thanks
Luminousrenewable