# Does 21.5 volts Seem About Right?



## MoonRiver (Sep 2, 2007)

I have a 100 watt solar panel (RENOGY 100W Watts 100 Watt Polycrystalline Solar Panel) connected to a charge controller (Renogy 30 Amp PWM Charge Controller Regulator Off Grid for Battery Charging).

The output from the charge controller is connected to aux power and ground on a 7-way blade rv connector (vehicle side).

I checked the DC voltage and get 21.5 volts. Does this seem right?

The plan is to plug the 7 blade connector (tow) into the 7 blade connector (trailer) to charge the battery.


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## haley1 (Aug 15, 2012)

seems high for charge controller, I would think that might cook a 12 volt battery system?


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## MoonRiver (Sep 2, 2007)

I got an email from Renogy and they said it was because it was open voltage. Supposed to connect charge controller to battery before connecting solar panel.

This doesn't fit my situation.


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## wy_white_wolf (Oct 14, 2004)

No battery means you'd be checking the VOC (Voltage Open Circuit) 21.5 would be about right. VOC for the panel is listed at 22.4V. 

System may not work properly if you are planning on having the panel hooked to the charge controller before you hook it up to the battery. If it doesn't put an on/off switch on the panel side of charge controller. Leave it off until after you've plugged in and turn it off before unplugging from the battery.

WWW


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## MoonRiver (Sep 2, 2007)

wy_white_wolf said:


> No battery means you'd be checking the VOC (Voltage Open Circuit) 21.5 would be about right. VOC for the panel is listed at 22.4V.
> 
> System may not work properly if you are planning on having the panel hooked to the charge controller before you hook it up to the battery. If it doesn't put an on/off switch on the panel side of charge controller. Leave it off until after you've plugged in and turn it off before unplugging from the battery.
> 
> WWW


I'm planning on plugging into the 7 blade trailer connector. That should run it through the trailer's charge controller before it gets to the battery, similar to when the trailer is connected to the tow vehicle.

Does that sound OK?


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## wy_white_wolf (Oct 14, 2004)

All that you're pluggin in then is the solar panel? That should be OK if you are sure that runs through a charge controller setup for solar. If it's ment just to work from the tow vehicles alternater it could only be a battery isolator. Using that wouldn't work.

WWW


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## haley1 (Aug 15, 2012)

Won't that small wire cause you to loose some of your amps?


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## MoonRiver (Sep 2, 2007)

haley1 said:


> Won't that small wire cause you to loose some of your amps?


Somebody ran the numbers on a similar setup and figured it might take 1/2 hour longer to fully charge his battery.


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## 12vman (Feb 17, 2004)

The charge controller needs a battery (Load) on the output to be able to control voltage. It needs that reference voltage to adjust to. The controller also gets its power from the battery to operate, not the panels..

If you were to put a capacitor on the output of the controller, that would give the controller something to work from. (200-400 microfarad electrolytic) Any light would easily charge the capacitor and give the controller a reference to work from. The excess current would be dissipated by the controller as heat but the voltage would be regulated. No need for a battery..


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