Charging with solar

[NYSail]

Hello all.... so I am new to solar as of last year. Bought a single flex panel
And 40 amp mppt charger..... Both from Renogy. For winter I bought a rigid 50 watt panel and plugged it in. Brought my batteries to full charge after a few days. However I was at boat the other day..... battery monitor said 100% but was reading 14.volts. Seems high? Or is it the amps that I should be paying attention to?

thanks
Greg

 

[Davidasailor26]

14.1 is higher than you’d want for a float voltage. Does the MPPT have adjustments for battery type or float voltage? Does it stay at 14.1 throughout the day, or was it just up there shortly after finishing a morning charge?

 

[jssailem]

Greg was the sun shining?
With out more data it appears your gauge is reporting there is a charging in progress.

 

[dlochner]

At 14.9v and 2.4 amps the 50 watt panel appears to be operating at about ½ of its rated level. Assuming the sun is our and it is mid day, then the controller seems to be a the Constant Voltage stage of charging.

The other side of the equation is the current draw on the DC system. If there are loads, such as lights, monitoring gauges, stereo memory, etc, etc, the panels are putting 2.4 amps into the system which is being consumed by those electrical devices.

Any charging device sees the load on the total DC system and not just the condition of the battery. The current from the charging source goes where it is needed, the battery, the refrigerator, lights etc. If the battery is fully charged or close to it, such that it can only accept say 2 amps and you turn on a high current device the charge source will increase its out put to match the demand. Assuming of course the charge source has some kind of controller to recognize the demand.

 

[JohnShannon]

14.9 seems V is what I read, not 14.1. 14.1 might be OK on a cool day 14.9 seems high. What charger do you have?

Since this is the internet I will speculate.

The standard sort of sophisticated charge method is CC, CV and float. What that looks like is constant current into a discharged battery, if you believe the battery specs at a bout C/5 rate so 20A or so into a 100AHR battery. Your puny solar panel won't be able to manage that you might get 4A on a good day.

Eventually the battery voltage builds to enough voltage that you enter the CV ( constant voltage) area. Now the charger holds the voltage constant and the charge current will decline over time. This voltage should be temperature dependent a good charger will come with a temperature sensor to mount to the battery to adjust the CV onset based on battery temperature. If it is cool 14.9 is conceivably OK.

Eventually the current falls enough, the charger deems the battery "fully charged" and switches to float mode. This is really just CV mode with a different and lower CV number typically 13.6V or thereabouts.

So how is this decision made? I am guessing in this case your massive 40A charger is looking for the charge current to fall beneath say 10A or so to make the determination that the battery is fully charged. The problem is your puny 50W panel can't ever trip this circuit because it never achieves enough current to "arm" this circuit.


Bottom line your charger is massively too big for your panel and this is messing up how it makes its decision to transition from CV to float. We need more details on the charger but this kind of pathology might not be actually in the specification, their tech support might be helpful.

 

[NYSail]

Sunny day, panel tilted south..... 4- 6v Trojan t125, no load, Renogy rover 40 amp mppt charger. I turned the solar charger off for a week and today the batteries are 100% with 12.8v. I turned on the panel and these are the readings

 

[Tom J]

That 14.4 volts at rest seems very high. My 320 watts of solar will show 14.2 volts at max output in bulk mode with Mppt charger, and then 13.1 volts in float. Did you program your mppt for 12v input to the batteries, and not 24v?

 

[NYSail]

Yes it’s set for 12v also the picture is after I turned the solar back on..... 10 minutes. Light on only

 

[JohnShannon]

14.4 doesn't seem too high for the CV portion specially considering the temp at 7C (about 45F). The question is how is decision to made by the charger to move from CV to float? Is it time based, Is it current based?

 

[JohnShannon]

Well if you read the manual, I know desperate times call for desperate measures, you will see there is a little status bar on the left of the Renogy display. It looks like you are in bulk charging mode still so 14.4 hasn't yet tripped into the CV portion of the charge. Again the manual seems to indicate CV ( they call it Boost) is 14.6V but this is temperature compensated so will be higher in the cold. It looks like the Boost phase is limited to 2 hours so the exit from boost to Float is timer based.

So it seems this may be operating normally. What I would expect every day is the sun comes up and you start charging eventually you get to the boost voltage 14.6V plus some extra for the cold. You will sit there for 2 hours and then drop to the float voltage till the sun goes down. The next day probably this repeats.

If you are in a hurry to see the thing transition from CC to Boost what you can to is find the temp sensor and warm it up. This will have the effect of lowering the CV transition temperature. So you should see the charger transition from MPPT/CC to Boost on the little status bar. If it is warm enough 14.4V should do it.

 

[Captain Larry-DH]

If the temps are in the 30's or low 40's (as has been the case around here lately) then 14.9v is OK, assuming the controller compensates for temps. I think you got some good input above, and I don't think you should be too concerned about it. Can that app show you a 24-hour cycle of voltage in a chart or graph?