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Old 12-07-2021, 16:27   #16
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Re: Voltage drop solar controller to batteries

Most of the time the oontroller is pulse width modulating (PWM) the current. That is, the controller is turning the solar panels on and off such that, in effect, the average voltage is higher than the battery voltage.
Consider a 12V nominal system. When the controller senses the set charging voltage (say 14.4V) it turns off the solar panels. Then their voltage jumps to say 18.5V. The panels themselves have some capacitance (storage capacity). Next the battery voltage drops to below the point where the controller decides to turn the solar panels on. The solar panels discharge to near the new battery voltage. Then the solar panels raise the battery voltage to the set charging voltage. The controller turns the solar panel off. One pulse cycle occurred. Off, then ON, then Off.
As the batteries increase in charge, the amount of current needed to raise their voltage to the set point of the controller decreases. The pulses occur faster.
Modulation means ON-Off. Pulse width is the time that the controller keeps the panels connected to the battery.
The point to remember is this. When batteries are discharged, the current from the panels to the battery is the highest. Large gage wires are needed. But when the batteries are decently charged, the controller is pulse width modulating anyway. The solar panel is off more and more as the batteries develop more charge. The wire gage does not matter much.
If you are in the habit of discharging your batteries significantly, you need large gage wire.The battery will accept any current your panels can produce when heavily discharged. If you only discharge your batteries say 50% anyway, you can probably get by with smaller gage wires. Your batteries are somewhat charged and have lower capability to accept gobs of solar energy. The controller is operating PWM anyway.
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Old 12-07-2021, 17:42   #17
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Re: Voltage drop solar controller to batteries

Quote:
Originally Posted by Locquatious View Post
Most of the time the oontroller is pulse width modulating (PWM) the current. That is, the controller is turning the solar panels on and off such that, in effect, the average voltage is higher than the battery voltage.
Consider a 12V nominal system. When the controller senses the set charging voltage (say 14.4V) it turns off the solar panels. Then their voltage jumps to say 18.5V. The panels themselves have some capacitance (storage capacity). Next the battery voltage drops to below the point where the controller decides to turn the solar panels on. The solar panels discharge to near the new battery voltage. Then the solar panels raise the battery voltage to the set charging voltage. The controller turns the solar panel off. One pulse cycle occurred. Off, then ON, then Off.
As the batteries increase in charge, the amount of current needed to raise their voltage to the set point of the controller decreases. The pulses occur faster.
Modulation means ON-Off. Pulse width is the time that the controller keeps the panels connected to the battery.
The point to remember is this. When batteries are discharged, the current from the panels to the battery is the highest. Large gage wires are needed. But when the batteries are decently charged, the controller is pulse width modulating anyway. The solar panel is off more and more as the batteries develop more charge. The wire gage does not matter much.
If you are in the habit of discharging your batteries significantly, you need large gage wire.The battery will accept any current your panels can produce when heavily discharged. If you only discharge your batteries say 50% anyway, you can probably get by with smaller gage wires. Your batteries are somewhat charged and have lower capability to accept gobs of solar energy. The controller is operating PWM anyway.
The controller (MPPT) will be in PWM mode once absorption is reached, but not in bulk. With a typical charger of much size absorption is usually reached at about 80% SOC or so. With solar max current typically being a smaller percentage of bank size absorption is often not reached until the bank is at 90 to 95% SOC. The smaller the charge current the higher the SOC at which absorption voltage is reached.

Wire size does matter. I try for minimal voltage drop in all charging systems. 3% voltage drop takes a starting voltage of 14.4 and reduces it to under 14 volts. Aim for less than 3% drop.
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Old 14-07-2021, 07:53   #18
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Re: Voltage drop solar controller to batteries

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Originally Posted by stevo_002 View Post
The first sentence leaves me unsure if your intent. Good idea if I understood better.

Isnít the sensor wire connected to the sensor? And the other end of that node is the controller.

Apart from any consequence . . . Where else does the battery voltage sensor go ??
I believe he was saying that if the controller has voltage sense capability, the controller will make up for voltage loss by increasing the charge voltage, reducing motivation to move controller closer to battery bank.

Of course, not all controllers have battery voltage sensing capability, and in most conditions the net effect is that charging time will be increased.
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