Voltage drops when SOC pulls, need to upgrade cable?

kaizday

New Member
Joined
May 27, 2021
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74
Hello,

Another newbie question. So, my DC monitor reads 35v open circuit at the Mppt terminal when amperage is zero, but as soon as it starts to 'pull', amperage starts to rise, the voltage then drops to as low as 20ish.

is this a normal behavior or do i need to upgrade my cable? i am currently using awg 10 30ft or so since it's a small less than 20am at most. i do have about 3-4 mc4 connections and a couple of xt90 connecting different sections, not sure if it affects anything.

thanks
 

Rich585

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Ontario Canada 🇨🇦, somewhere near Ottawa
The 30 volts is the open circuit voltage of the panels. Once current is drawn, the mppt controller adjusts to find the optimal power point ( volts x amps). Yes it is normal. Mppt typically need 5v+ Above battery voltage to start.

Cloudy days you will get low volts and 1w charging rate when mppt solar panels is struggling to get enough sunlight.

I run 12 volt system. Batteries are fully charged I get 20v, but drops 13-18 v when charging depending on how bright the sun is. Direct sunlight is needed. Cloudy day, even though it looks bright is not sunny enough to produce anywhere near full out put. My panels struggle to hit 50% on overcast days.

Normal it is.
 

kaizday

New Member
Joined
May 27, 2021
Messages
74
The 30 volts is the open circuit voltage of the panels. Once current is drawn, the mppt controller adjusts to find the optimal power point ( volts x amps). Yes it is normal. Mppt typically need 5v+ Above battery voltage to start.

Cloudy days you will get low volts and 1w charging rate when mppt solar panels is struggling to get enough sunlight.

I run 12 volt system. Batteries are fully charged I get 20v, but drops 13-18 v when charging depending on how bright the sun is. Direct sunlight is needed. Cloudy day, even though it looks bright is not sunny enough to produce anywhere near full out put. My panels struggle to hit 50% on overcast days.

Normal it is.
thanks for a detailed explanation!!!
 

12VoltInstalls

…myself everything do I…
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run 12 volt system. Batteries are fully charged I get 20v, but drops 13-18 v when charging depending on how bright the sun is
This does. Not. Seem. Right. 18V is a crazy high for 12V batteries; it only takes 14.5 to 15.5 of 16V tops to equalize- higher than 15.7 I’d think you’d lose a ton of electrolyte water
 

Rich585

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Ontario Canada 🇨🇦, somewhere near Ottawa
Yes I was referring to PV. The mppt controller will drop the panel open voltage to the peak voltage/current which on my panels is 21Voc to 17-18 volts in bright sun but I have seen the volts drop to 14 v PV when clouds block the sun.

The battery voltage depends on profile set on the mppt charge controller that the OP indicated he was using.
 
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12VoltInstalls

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^^^ right
It is normal to have max volts on the input side. I got confused at the description
it’s not a concern
 
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