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Solar panel readings


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Ok, battery charging basics. When the batts are full, a good regulator will drop to "float" - the storage state for batts. Typically for a LA 12v battery, this will be circa 13.5-13.8v. The current (AMPS) going in to the batts is "decided" by the battery resistance - basic V=IR. When the battery is full, it should accept somewhere around 1% or less of bank capacity - so <1a for a 100a/h battery. 

If you want to test the solar panel, then discharge the battery to <70%(so the battery will accept a decent charge rate)  and then see what the solar produces in direct sunlight, panel set at 90 deg to the sun angle. Measure amps, check the voltage when the amps is read. AmpsXvolts=watts. A 160A panel should produce around 13a at 12v in perfect conditions.

What amps the panel puts into the batts at or near full charge is not really an indicator of anything. Check the voltage, and make sure it's the right voltage for your batteries. 

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2 hours ago, BOIGuy said:

IT, my Solar seems to end, after a day or two of no load/use, on float at 0.3A at 13.5v for a 130ah house + start setup, always thought it was a bit much but you think this is fine?

The fact that the system has charged the battery to 13.5 volts is the guide here to be confident that everything is working fine.

Depending on the charge controller type(MPT or PWM) make and model ( may or maynot give you user controllable paramters) determines just how exactly the controller will actualy work. But as IT said, 13.5 to 13.8V is float voltage.

If a battery never reaches that float stage, then there is something wrong. If the charge voltage is always above 14.4V or maybe higher (providing it is not in equalization charge) and never drops. then something is wrong. If the voltage is always in the 12's, then something is wrong.

And because we are measuring points of a Volt eg, (12.5/12.6) measuring the voltage requires a good digital meter and measurements need to be taken at the battery terminals and you MUST have a good clean connection.

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5 hours ago, BOIGuy said:

IT, my Solar seems to end, after a day or two of no load/use, on float at 0.3A at 13.5v for a 130ah house + start setup, always thought it was a bit much but you think this is fine?

Short answer - Yes.

All I can say is check the battery PDS (Product data sheet) to ensure that that is the correct voltage for your specific batts for float. While you are at it, check the bulk/absorbtion voltage requirements for the batts, and make certain that the solar is doing that as well. 

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Just to add to this conversation... 13.8 v as a 'float voltage' is quite a bit too high for a pure DC float voltage (as opposed to an AC battery charge sourced charge). Unless it is very cold out you would never want to see 13.8 as a float voltage on most Lead Acid (LA) batteries. The target for Float voltage would be much better at 13.6 volts.

I think his question about what readings to expect on his "BMS" have been well answered for LA,  except I'm curious because when someone says BMS (Battery Management System) they are customarily referring to a BMS on a Lithium Bank;  what chemistry are these batteries?

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