Solar Charger & Truck Power Question

Sam Spade wrote:

And a voltage source is quite different than a voltage drop.

We don't seem to be getting anywhere. Voltage is a potential, it is the same whether measured on an open source or a resistive drop. A voltage source is an object, a voltage drop is a measurement.

You said:

You can't have current without voltage.....and saying things like that just confuses people.

Saying that is confusing people, first and foremost because it is not true.

Charge regulators make assumptions about their energy source, in particular the I-V characteristic which can be drawn in a graph plotting I against V. Here is the graph for a current source, a horizontal line, same current regardless of voltage:


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Here is the same graph for a voltage source, a vertical line, same voltage regardless of current:


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They are orthogonal - could not be more different. But you knew that already if you are an EE.

Getting back to the original question: If a solar array is operated at just below its open circuit output, it will produce near its max rated current. If operated at zero volts (output short circuited - *zero volts*!) it will STILL produce near its rated current. It acts like a current source.

On the other hand if an alternator output is operated at is set point of 14.7 volts, it will produce zero current. If operated just below its set point it will product its maximum current. It acts like a voltage source. (For completeness I will add that if operated at well below its setpoint, it looks like a resistive source until it heats up and fries).

Yes you can design a solar controller to handle both input characteristics, but typically you would not design it that way, because it is not sold or intended to be used with an alternator as input, and doing so costs extra money. If connected that way it is likely to burn itself to a crisp, trying to make the alternator look like a current source.