I have a solar panel with a built-in 6-18v auto adjusting output (based on draw) and a step up/down 1.5-24v DC-DC converter with an auto adjusting input. I was thinking of using them in conjunction with each other, but was afraid of the consequences of connecting two auto adjusting connections.

My question being, is it safe? And if so, what decides the voltage between the two if neither has a set amount?

Here's the converter
Here's the solar panel


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In fact, there is very little information about solar panel behavior, most likely, it decreases output voltage when it can not provide enough power for the load.

As for the DC-DC converter - it adjusts its current to get enough power for its load.

Therefore your connection (most likely) would be OK when "the sun is bright enough": solar panel makes enough power for your load.

It is difficult to predict what happens when it can not make enough power. The system can shut down or go into oscillations or just decrease the power supplied to DC-DC converter load. It depends on many factors that we can not control.

So, if you connect your system like you suggest - keep your eye on it and stop it when there is not enough power.

  • \$\begingroup\$ OK, based on your answer, I tried this yesterday evening. The solar panel was in full sun, and the DC-DC output was set at 24v. The solar panel output started at 12v, then jumped to 18, and then continually oscillated between 14 and 18 in 5 second intervals. I left it like that for 60 seconds, but disconnected because the converter was getting too hot under the stress. Surprisingly though, this whole time, the DC-DC output of the converter remained completely still! \$\endgroup\$ – john kieran May 5 '16 at 15:04
  • \$\begingroup\$ What was the load of your DC-DC converter? And I suggest setting DC output of the solar panel to 18 V or even 12 V. \$\endgroup\$ – Master May 6 '16 at 8:57
  • \$\begingroup\$ What voltage do you need for your final load? \$\endgroup\$ – Master May 6 '16 at 8:58
  • \$\begingroup\$ The output voltage from the solar panel is automatically adjusting, and my load on the converter was 1.4a. My goal voltage is 21.6v 2a from 18v 3a \$\endgroup\$ – john kieran May 6 '16 at 17:03
  • \$\begingroup\$ First, this behavior is not surprising, unfortunately. It goes like this: your DC DC converter sinks current roughly inversed proportional to its input voltage. So, lower voltage from the solar panel leads to larger input current. It means negative resistance and leads to oscillations, exactly as you see. \$\endgroup\$ – Master May 7 '16 at 14:03

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