Solar cell outputting 18V overloads 12V controller charging a 12V battery

[deanpk]

I have a solar cell that outputs 18V. My charge controller SS1203 registers anything above 14V as an overload and will not charge my 12V battery.

Is there something simple I can do to get my charge controller working with this 18V solar cell to charge my 12V battery?
Can I connect my 18V solar directly to my 12V battery and monitor the charge and disconnect the battery when fully charged?
Is charging the 12V battery with 18V supply bad idea?
The solar cell is 18V and 20 watt output.

My lead acid battery is a sealed small battery from a uninterrupted power supply - actually 2 of them in parallel.

[Sunking]

All 12 volt solar panels are 18 volts. Problem is not the panel.

[deanpk]

Good to know.

I have about 40 feet of light gauge solid core wire (telephone style solid core wire) connecting my solar cell to controller - could that be the problem?

[russ]

Good to know.

I have about 40 feet of light gauge solid core wire (telephone style solid core wire) connecting my solar cell to controller - could that be the problem?

You are dangerous!

[Sunking]

I have about 40 feet of light gauge solid core wire (telephone style solid core wire) connecting my solar cell to controller - could that be the problem?

Very much so. The voltage loss is way too high. What size panel do you have?

[deanpk]

20 watt solar panel. When I read the voltage it measures 18V after the 40 feet of wire. (UPG 87501 20-Watt Mono-Crystalline Solar Panel.) Thanks for your help. I thought the light gauge wire would not matter on such low current.

[Vern Faulkner]

20 watt solar panel. When I read the voltage it measures 18V after the 40 feet of wire. (UPG 87501 20-Watt Mono-Crystalline Solar Panel.) Thanks for your help. I thought the light gauge wire would not matter on such low current.

Couple of points: the panel is likely not generating 20 watts. On a good day, you may be generating, say, 15 watts of power.
Further, you are not using 40 feet of wire, but 80: the current has to go both ways.
Assuming you're using 22-gauge wire, you are ensured a voltage drop of at least 1.3 volts, by my rough calculations; 24 gauge wire? Two volts, certain.

[deanpk]

I replaced the thin wire with some heavy gauge wire between the solar cell and the voltage controller. The charge controller unit seems to be working correctly. The charge light flashed until I connected the batteries. Now the voltage reads 11.7V and the green light has come on the load LED I suppose suggesting that the battery are charged enough ready for a load. (This cheap voltage controller SS1203 has no useful user manual.)

The charge controller came with thin wired alligator clips to connect to the battery. I suppose they figure this wire is adequate.

[Sunking]

Word of caution here. Always connect the battery to the controller before connecting the panels. 11.7 volts while charging at the battery indicates a heavily discharged battery. Well actually a very DEAD battery that may be beyond repair.

[deanpk]

Thanks again. It is quite possible these battery are dead as they came out of an uninterruptible power supply that is a few years old. Can you recommend a 6 volt battery manufacturer that has modest amp hours such I can run two in series to get 12 volt. I am only powering cell phones and a laptop during power outages.

[Sunking]

With a 20 watt panel? Just buy 4 rechargeable AA batteries you use in a flashlight.

[deanpk]

I thought a 20 watt panel would charge a 12 volt lead acid battery even if it took a week. I will only draw on the battery once a month for a few hours. Is this an unreasonable expectation?

[Kebast]

Upg ub645

I thought a 20 watt panel would charge a 12 volt lead acid battery even if it took a week. I will only draw on the battery once a month for a few hours. Is this an unreasonable expectation?

I'm using a couple of these for similar purpose. Here's the first link that popped up on amazon, but you can probably find them a bit cheaper if you look around.

UB 645

UPG D5744
D5744

[PNjunction]

I thought a 20 watt panel would charge a 12 volt lead acid battery even if it took a week. I will only draw on the battery once a month for a few hours. Is this an unreasonable expectation?

Maybe - but where are you located since you'll want to calculate your hours of insolation, which differs from visible daylight - basically strong enough sun to actually do anything more than trickle even with the largest of panels. The hours are typically between 10a and 2p, but that is generous for much of the world and not counting days of purely bad weather. There are some online solar-insolation charts you can look up to get this info on how many hours you get per day - use the winter hours if listed for worst-case.

In the UK, you may be lucky to get one good solar insolation hour in the winter. Where I'm at, I get about 4 hours - and that's with the sun at a low angle going through a lot of morning haze and long shadows, so those 4 hours aren't as good as in the summer. In a week in the UK, all your panel will be able to produce is about 6.5 amps, whereas here, I could return about 25 amps in a week. So knowing your insolation is one of the big variables when deciding upon a panel / battery capacity, otherwise you end up in a "deficit charge" situation - kind of like never being able to pay off a credit card, and in this case, your battery sulfates and reduces the capacity you paid for pretty quickly.

You'll be able to charge cell-phones in a deficit-charge scenario for a long time wasting the battery, but if you want to do it right, you'll want to know your hours of insolation as one of the big variables when planning a system.

You mentioned a laptop - how much power does it draw per hour and how many hours are you going to use it? Unless you want to wing it, or deficit-charge the system, this is also crucial to know.

[deanpk]

Thanks for your thorough consideration. I am obviously a novice but I do work in a somewhat related field. I will make a better assessment of my loads and solar-insolation and probably be able to figure out what I need to do.