SOLAR MELTDOWN......almost a FIRE!!!

mbohuntr · Mar 18, 2018

Some people are scared of math, but this stuff isn't too bad. Let's see how bad a teacher I am... Watts = Volts X Amps. AC, or DC voltage. So, your 1200W microwave at 120v uses 10 amps... 1200/120=10 That easy...

Now lets go a little deeper.. I(amps)=V/R, Current = volts /resistance Most simple chargers use a constant voltage to avoid overcharging the batteries, and the voltage is actually the difference between the panel voltage, and the batteries. The resistance is in the batteries, and is very small, almost non-existent.

Think of a teeter totter with a bucket of water in the center, the steeper the angle, the faster water flows. The greater the voltage difference between the panel and your batteries, the more current flows. As the battery voltage increases, the current drops off until it reaches "float" If the sun goes behind the clouds, the voltage of the panel drops, and the current drops as well. Your 12 volt battery needs 13.6 volts to be fully charged at 12.4 volts that little difference in voltage allows little current to still flow.

Does that make sense? or did I mess that up...

Glad to help, I would want someone to treat me the same if I had questions.

BHD · Mar 18, 2018

if the controller fryed, you could have been reading battery voltage flowing back through the panels,

MossRoad · Mar 18, 2018

Here's an illustration I found that explains series connections, parallel connections, and series/parallel connections. It's pretty helpful...

Boeing · Mar 19, 2018

[quote from mbowhunter] "Now lets go a little deeper.. I(amps)=V/R, Current = volts /resistance Most simple chargers use a constant voltage to avoid overcharging the batteries, and the voltage is actually the difference between the panel voltage, and the batteries. The resistance is in the batteries, and is very small, almost non-existent."

Thank you,Bohunter. Can we go one step further.....do SOLAR controllers allow more current to pass if the batteries are low? That would be nice if they COULD. The solar panels produce X amount of current at 18 or so volts. The controller drops that to 14 +/- volts so as not to harm the batteries. So how would the amperage vary if the voltage is limited to 14V. Does a "low" battery add to the resistance? I'm sorta lost..... Sorry.

mbohuntr · Mar 19, 2018

Boeing said:
[quote from mbowhunter] "Now lets go a little deeper.. I(amps)=V/R, Current = volts /resistance Most simple chargers use a constant voltage to avoid overcharging the batteries, and the voltage is actually the difference between the panel voltage, and the batteries. The resistance is in the batteries, and is very small, almost non-existent."Thank you,Bohunter. Can we go one step further.....do SOLAR controllers allow more current to pass if the batteries are low? That would be nice if they COULD. The solar panels produce X amount of current at 18 or so volts. The controller drops that to 14 +/- volts so as not to harm the batteries. So how would the amperage vary if the voltage is limited to 14V. Does a "low" battery add to the resistance? I'm sorta lost..... Sorry.

There are many different types of chargers out there. The current is limited first, by the watts of your panel(s), and second, by the charge controller. Lead acid batteries are recommended to charge at a certain rate maximum, to prevent boiling, and a minimum to limit sulfation.

What most people don't realize is that a battery that is low, is essentially a short circuit in that the internal resistance is measured in milli ohms. If you did the math, the amps that it COULD draw is very high However... in the real world, the charger won't let that happen because the panels and the charger would be damaged. The circuit internals are sized to only handle less than 20 amps.
It is the voltage difference that allows current... no voltage difference, no current.. current flow is limited by resistance. More resistance means less current.

your panels are 4(100watt) panels, and in a perfect world will produce 22 amps. 400/18 volts=22 amps. A pulse charger, if I understand them correctly use a square wave higher voltage pulse to protect against sulfation even during long periods of being on float.

Here is a link that you might like... BatteryStuff | Knowledge Base

If you take your 12v battery and put a 10 watt incandescent battery on it... 10watts/12volts = .83 amps, or nearly an amp per hour.. A incandescent light is nothing but a resistor, so take your battery internals.. say .020ohms, or 20 milli ohms...

now your potential difference is say 3 volts because you have 11 volts on your battery,14 volts on your unlimited power super whamadyne charger, and an UNLIMITED current supply, not your panels... 3volts/ .02 ohms = 150 amps!

Theoretically, your battery is a short... but only in the theoretical world, you should understand this before you charge.. always protect battery chargers and loads with fuses..

Keep asking any questions, We are all here to learn, and i'm certainly no expert....

chim · Mar 19, 2018

Looks like a loose connection at the voltmeter was the culprit. The "before" diagram shows the load being connected to run through the Stakons on the ends of the wires. Loose connection for a load = heat. What I don't understand is how that ammeter worked if it was connected as in the "before" diagram. It appears to have been connected in parallel with the batteries.

A voltmeter won't be damaged by connecting it in series with a voltage within its range. However, voltmeters are designed with a very high internal resistance, so the load won't get sufficient voltage to operate. An easy way to find a bad fuse is to connect a voltmeter across the fuse in a circuit that should be operating. If the meter reads source voltage, the fuse is blown.

Boeing · Mar 20, 2018

chim said:
Looks like a loose connection at the voltmeter was the culprit. The "before" diagram shows the load being connected to run through the Stakons on the ends of the wires. Loose connection for a load = heat.
What I don't understand is how that ammeter worked if it was connected as in the "before" diagram. It appears to have been connected in parallel with the batteries.

Thank you, Chim. The AMPMETER did NOT work....my bad, I guess I had it wired wrong. I had never installed a shunt and had it wired incorrectly. Bowhunter sent a you tube link to correct that mistake.
I am concerned about those "loose" connections on the Voltmeter though. I wired that up 5 years ago and it has been fine. The little posts on the cheap V-meter are just that....small...a small post with a small nut. I torqued them down as much as I dared and was worried that I would twist the post out of the plastic meter. What would you do....maybe "recheck" them every 6 months or so?

GLyford · Mar 20, 2018

Make the connections on a terminal strip near by that is rated for the size of the wires, and run a pair of smaller jumper wires from there over to the meter, so that its connections are only for sensing the voltage.

Boeing · Mar 20, 2018

GLyford said:
Make the connections on a terminal strip near by that is rated for the size of the wires, and run a pair of smaller jumper wires from there over to the meter, so that its connections are only for sensing the voltage.

Mr. Lyford, that is a great idea. Now, I'm always thinking of the "easiest" or least risk way of doing something sooo..... Instead of cutting the 10 GA red wire and putting it on a terminal strip with lugs etc.....What if I just ran a smaller 16GA wire back up to the fuse box where the HOT wire originates? Wouldn't that be the same result? If it's a bad idea please tell me, thanks