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Why won't my DC solar panel power a small DC motor when the output volts and amperes are higher than the battery that does power it?

Thankyou everyone..Alot to review Regards

Matthew Nisbett
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    You're probably looking at the wrong specs of both the solar panel and the battery. If guess that you're looking at the panel's short-circuit current and open-circuit voltage specs, but you can't get those both at the same time. For the battery, make sure you know the difference between current in amps (A) and capacity in amp-hours (Ah). – brhans Apr 19 '23 at 05:02
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    Which motor, battery, and solar panel? How do you know the solar panel puts out more volts and amps than the battery? – Bruce Abbott Apr 19 '23 at 09:04
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    Also, current out of a solar panel is relative to the amount of sunlight that's hitting the panel. They are usually specified for the best case, bright noon sunlight shining directly at the panel. If you have 1/3 of the light you only get 1/3 of the current. And if you try to take more current than whatever the panel "naturally" wants to produce, the voltage drops quite drastically. – user253751 Apr 19 '23 at 09:59

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You always need a Maximum Powerpoint (MPPT) Module to get the power out of the PV-module.

The problem is:

  • if you want the maximum current out of the PV-module, then you get no voltage and no energy
  • if you want the maximum voltage out of the PV-module, then you get no current and no energy

There is a sweetspot somewhere, there you get not the maximum current and not the maximum voltage, but the most energy out of your PV-system.

I had a little garden light (6x0.4V=2.4V) and could drive a 0.2 Watt motor with it, so I believed that a step-up voltage converter could create 13.8V and I can load my battery with this system slowly up. The output current was not regulated, because the energy at all was so small.

But here comes the problem, the stepup converter try to pull all the current what it can out of the PV-module and because of this the voltage drops to a level were it can not get a useful amount of energy out of the PV-module any more.

What a MPPT-module does is simply, measure the current of the input and the voltage of the input. If the energy (I*A=P) drops, then the output current will be reduced or increased till the controller found the point of the maximum energy output. The controller swings around a area to measure the energy and find the "max power point".

In your case, you apply the motor, it needs a much higher current for starting and because of this the voltage drops to nearly nothing. So you have a current flow, but no voltage.

https://en.wikipedia.org/wiki/Maximum_power_point_tracking

brhans
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MikroPower
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    just in case the reader is curious to know, an MPPT module is the same as a stepup converter except with a different controller chip. It tries to keep the input power maximum and let the output voltage and current wander, instead of keeping the output voltage constant and letting the input voltage and current wander. – user253751 Apr 19 '23 at 10:01
  • @user253751 - Oh, yes good description of what it does. There are several types available for consumers, stepup and stepdown. The most people have several PV-modules in line and create a higher voltage (30V x 6 = 180V) and want to load a LiFePO4 accu with normally 48V. But there are micro-MPPT modules for every single PV-module too, this have other advantages. They create from 30V of the PV-module the voltage for the 48V battery, but there the cable have to be thicker. – MikroPower Apr 20 '23 at 03:37