Post by malewithatail on Mar 1, 2023 10:41:27 GMT 10
Using surplus home solar panels to charge a 12 v battery.
A quick primer on using surplus high voltage solar panels to charge battery's, without using an expensive MPPT regulator, but a standard PWM or even linear type.
Most solar panels coming onto the surplus market have a open circuit voltage of around 45 volts, although some are over 100 volts. The info below doesn't apply to these high voltage usually grid connect panels for safety reasons.
What if we want to charge a 12 volt battery from a surplus, say 200 watt solar panel ? Simple if using a MPPT type of regulator, but what if you haven't got one handy, or are too tight to buy one and have managed to scrounge a old PWM type from the tip ?
A 200 watt solar panel, can deliver around 4 amps at around a Maximum power point of 45 volts. Great, just connect it to the battery and we will get 4 amps into the 12 v battery, for a while anyway. 12 volts at 4 amps is 48 watts, what happens to the other 150 odd watts the panel is delivering ? You are effectively operating the panel at its short circuit current, and the power is being dissipated as heat in the panel, adding to the heat already due to the sun. This will cause a hot spot to appear on the inter-cell connectors, quite often visible, and will eventually result in the solder melting and the panel going open circuit. (These spots are fixable by cutting around the Kevlar backing and re-soldering the joint, then covering it with sikiflex or similar).
If we could dissipate that power, we could use the panel for our small 12 v system, say in a greenhouse etc.
So, we need to drop 45 - 12 = 33 volts, at 4 amps or about 130 watts. A 24 volt truck headlight usually has 2 filaments rated at about 60 watts each, so simply connecting them is series (48 volts) and putting the light in series with the solar panel output, will drop the excess voltage and power, and still allow about 3 or 4 amps into the battery via a linear or PWM regulator. Don't worry that the filaments may have different wattage's, say 50/60, the setup will still work but you may see the lower wattage filament glowing a bit brighter than the other one when its in operation. The panel will not be damaged, the lamp will glow showing that the battery is charging, and it will work for ever, or until the lamp blows, but as we are operating it at much reduced voltage, its life should be measured in years. Anyway, sealed beam 24 v headlights are available from a truck wreckers for almost nothing, everyone's going to leds now. Note, a led wont work the same a a bulb for various reasons that I could explain if there is demand.
A quick primer on using surplus high voltage solar panels to charge battery's, without using an expensive MPPT regulator, but a standard PWM or even linear type.
Most solar panels coming onto the surplus market have a open circuit voltage of around 45 volts, although some are over 100 volts. The info below doesn't apply to these high voltage usually grid connect panels for safety reasons.
What if we want to charge a 12 volt battery from a surplus, say 200 watt solar panel ? Simple if using a MPPT type of regulator, but what if you haven't got one handy, or are too tight to buy one and have managed to scrounge a old PWM type from the tip ?
A 200 watt solar panel, can deliver around 4 amps at around a Maximum power point of 45 volts. Great, just connect it to the battery and we will get 4 amps into the 12 v battery, for a while anyway. 12 volts at 4 amps is 48 watts, what happens to the other 150 odd watts the panel is delivering ? You are effectively operating the panel at its short circuit current, and the power is being dissipated as heat in the panel, adding to the heat already due to the sun. This will cause a hot spot to appear on the inter-cell connectors, quite often visible, and will eventually result in the solder melting and the panel going open circuit. (These spots are fixable by cutting around the Kevlar backing and re-soldering the joint, then covering it with sikiflex or similar).
If we could dissipate that power, we could use the panel for our small 12 v system, say in a greenhouse etc.
So, we need to drop 45 - 12 = 33 volts, at 4 amps or about 130 watts. A 24 volt truck headlight usually has 2 filaments rated at about 60 watts each, so simply connecting them is series (48 volts) and putting the light in series with the solar panel output, will drop the excess voltage and power, and still allow about 3 or 4 amps into the battery via a linear or PWM regulator. Don't worry that the filaments may have different wattage's, say 50/60, the setup will still work but you may see the lower wattage filament glowing a bit brighter than the other one when its in operation. The panel will not be damaged, the lamp will glow showing that the battery is charging, and it will work for ever, or until the lamp blows, but as we are operating it at much reduced voltage, its life should be measured in years. Anyway, sealed beam 24 v headlights are available from a truck wreckers for almost nothing, everyone's going to leds now. Note, a led wont work the same a a bulb for various reasons that I could explain if there is demand.
Simply connect the 45 volt solar panel positive lead in series with the filaments, and connect it to the positive input of the regulator. Connect the negative to the regulator solar input. The regulator output connects to the battery as normal. The light will initially be quite bright, but will dim as the regulator cuts back the charge rate as the battery comes up to full charge, probably going off when fully charged and at night.
What happens to that power when using a MPPT type of regulator ? Its converted to current and increases the output current, not power as that's fixed, into the battery. So, 200 watts at 45 volts as mentioned before is around 4 amps, but at 12 volts, its 16 amps, magic eh ? That power level changes with temperature as well, usually dropping the voltage and increasing the current with increasing temperature, and the MPPT regulator will 'track' the solar panels voltage and adjust itself to deliver the maximum power into a battery.
Rules that guys wish girls knew.
1) Learn to use the toilet seat. If its up, put it down.
1) Learn to use the toilet seat. If its up, put it down.