# Which voltage spec matters?

My EB200 requires a minimum of 35V for solar input. I’ve seen panels are spec’d with max power voltage (Vmp), open circuit voltage (Voc), and nominal voltage. Which one(s) is/are relevant?

Hi @Joules22, When you charge with solar panels, you can refer to the open circuit voltage OCV range.

Thanks for the clarification.

Another question. I read somewhere that excess PV amp output doesn’t matter because the controller will only draw the amps required by the system. Is this true, and if so, is there a limit to how much “over amping” the input will tolerate?

Thanks.

I don’t think there’s any limit or danger with this set up because the device receiving the electricity is responsible for limiting how many amps it pulls during normal operation. it works the same way as an AC laptop charger; let’s assume a 100W AC charger can supply 20V at up to 5A but if your laptop is rated at a maximum charge current of 60W then the AC adapter will only supply 3A of the possible 5A @ 20V and the remaining 2A are not generated or used, but could be.

Thanks. This is all new to me so I appreciate the help.

Solar (photovoltaic) panels work as an energy pump. Voltage is the pressure while flow is the current (in amps). You can run a pump with no flow (maximum pressure) or at a maximum flow with a voltage drop. That is why each panel has two voltage ratings, The Voc is the voltage at no load (open circuit), while Vmp is at its maximum power output (with a load). The panels in series add the voltage (increasing pressure) while in parallel adds current (flow). Always check the Voc of any panel and compare to the maximum voltage your power station can accept. The total voltage in series must NEVER reach or pass the station input limit (too much pressure).

And you can short circuit the panel cables, since it is a pump. The voltage is zero but it will have a current rating (Isc) . That makes them safer than batteries which are energy storage.(tanks), If you short circuit a battery they can explode as a real energy tank can!