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Old 02-12-2020, 14:29   #1
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Solar panel voltage

I would like to know the Solar panel supply voltage voltage.
With the solar panel wires disconnected from the system I get 25v+/-
When I connect the wires to the system I get the battery voltage,
If I installed a diode in the + solar panel wire connecting the + VM wire here and then connected the Other end of the diode to the system would this solve the problem ?
There is a diode at the solar panel to prevent nighttime discharge.
Thanks. Nick
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Old 02-12-2020, 15:23   #2
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Re: Solar panel voltage

If you connect the solar panel to the battery without a solar controller, the solar panel voltage will always be the same as the battery voltage (ignoring voltage drop in the wiring). The same is true if your use a non MPPT (often called a PWM) controller.

If your open cell solar voltage is 25v you need a MPPT controller. You can then use a simple voltmeter to measure the solar panel voltage. Some controllers (such as the popular Victron Smartsolar) report the solar panel and battery voltage so no voltmeter is needed. With an MPPT the solar panel voltage and the battery voltage will be different.
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Old 02-12-2020, 15:24   #3
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Re: Solar panel voltage

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Originally Posted by Cat Nap3 View Post
I would like to know the Solar panel supply voltage voltage.
With the solar panel wires disconnected from the system I get 25v+/-
When I connect the wires to the system I get the battery voltage,
If I installed a diode in the + solar panel wire connecting the + VM wire here and then connected the Other end of the diode to the system would this solve the problem ?
There is a diode at the solar panel to prevent nighttime discharge.
Thanks. Nick
It's not a problem. It's called connecting to the load.

See the back of the panel for the voltage you should get without a load. (it will probably say 25 volts if you used a calibrated meter) It may be called Voltage Open Circuit (VOC) or some such.

Btw that is a good troubleshooting tool when troubleshooting any circuit if the voltage is at VCC or voltage supplied you have an open

Don't get caught up in the amateur wannabe techs that want to put diodes into places they aren't needed.
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Old 02-12-2020, 15:33   #4
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Re: Solar panel voltage

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Originally Posted by noelex 77 View Post
If you connect the solar panel to the battery without a solar controller, the solar panel voltage will always be the same as the battery voltage (ignoring voltage drop in the wiring). The same is true if your use a non MPPT (often called a PWM) controller.

If your open cell solar voltage is 25v you need a MPPT controller. You can then use a simple voltmeter to measure the solar panel voltage. Some controllers (such as the popular Victron Smartsolar) report the solar panel and battery voltage so no voltmeter is needed. With an MPPT the solar panel voltage and the battery voltage will be different.
What he said.

In the good old days a small panel might have an 18V or 19V nominal voltage, which means that with temperature they really operated at around 15V for maximum output. You could connect to the battery, and if the panel to battery size was reasonable there was little risk of over-charge.

With bigger panels have come higher voltages. If you connect direct to the battery you can still get some power, but you are wasting a lot, and your risk of over-charge goes way up. A PWM controller between panel and battery will prevent the over-charge but not the waste of energy. An MPPT controller will convert the higher panel voltage to be right for your batteries and deliver the most charging value from your solar panel.

[Edit] the solar panels on our boat are 46V open circuit.
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Old 03-12-2020, 16:48   #5
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Re: Solar panel voltage

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Originally Posted by thomm225 View Post
Don't get caught up in the amateur wannabe techs that want to put diodes into places they aren't needed.

Can you then explain where he needs them, and why?
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Old 03-12-2020, 16:52   #6
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Re: Solar panel voltage

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Can you then explain where he needs them, and why?

What?

I said he didn't need diodes....the load is bringing the voltage down, but if he leaves it hooked up long enough, the voltage will approach VOC if everything is turned off onboard

But again the open voltage number can be a good troubleshooting tool in any circuit
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Old 05-12-2020, 10:12   #7
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Re: Solar panel voltage

Years ago I purchased a 14 watt panel at Defender's sale and the vendor said no controller was needed! I found our 12vdc batteries at 22vdc and got a controller, but still had to replace the older batteries the next year.



I would suggest always having a controller.
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Old 06-12-2020, 17:54   #8
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Re: Solar panel voltage

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Originally Posted by thomm225 View Post
What?

I said he didn't need diodes....the load is bringing the voltage down, but if he leaves it hooked up long enough, the voltage will approach VOC if everything is turned off onboard

But again the open voltage number can be a good troubleshooting tool in any circuit

Sorry, I misunderstood "where they aren't needed" to imply there were other places where they are needed, like the bypass diodes in included in panels.
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