Settings for Victron's Smart 100/20 Solar Charge Controller On An RV

[busterbrown]

I've installed my first set of 100 watt polycrystalline solar panels on my RV and now am setting up my Victron Smart 100/20 MPPT solar charge controller. I currently have a 300 AH 12 volt AGM battery bank and have installed Victron's BT battery temp sensor.

I need help with the charge controller settings as this is my first solar installation.

Based on advice received from others, I have set the absorption and float voltages to the battery manufacturer recommendations (14.7V and 13.7 respectively). What is the preferred "maximum absorption time"?

I was also told to disable auto equalization of batteries and only perform a manual equalization when the batteries dip below their rated (or expected) capacity. How often would (should) that occur? And, what would be the ideal equalization voltage when the time comes?

Also, is there a recommended temperature compensation value for these AGM's? The disparity is quite big when I look at examples online. The manufacturer doesn't provide this in their specifications.

Finally, tail current setting. I've read 0.5 Amps for every 100 Amp Hours in the battery bank. Is this correct?

Any help is appreciated.

 

[gnubie]

The controller can use battery current to determine end of absorption charge but it has to either go through the load output terminals, which are good for 20 amps max, or via an external shunt. If you can't do either of those it will fall back to time based charging. Depending on your solar array vs battery vs DOD it may be good enough to leave the defaults or even to have to stay in absorption for as long as the sun is out. It all hinges around how many watts you need to put back into the battery, daily.

Victron also has a smart mode where the controller looks at the voltage on the battery at sun up and uses that to automatically scale the amount of time it has the battery in absorption charging.

I'd be happy with 500mA as the end point for absorption charging. Remember unless you have the load on the controller's load output terminals or use a shunt the controller will not be able to separate load and battery current so it can't determine when the battery is fully charged by checking the current.

The equalisation bit comes down to the quality of the batteries, so it's a bit of a how long is a piece of string question. Most people don't do any sort of capacity testing on their batteries, ever, so are blissfully unaware of what is going on. If your batteries do what you need, then all is good. If it gets to the point where they don't, and not because your draw has increased but because they have aged, then you'd do the equalisation charge cycle. Your batteries seem to have pretty standard charging voltages so personally I'd be happy with Victron's default equalisation charging votlage, but IMO in the range 15.5 - 16.5V.

Over time without proper charging the cells will drift away from each other in state of charge. For an AGM proper charging means being put through a full absorption stage charge regularly, if not daily. There is normally no need to put an AGM through an equalisation charge for the entire service life of the battery. Equalisation brings all cells up to fully charged by overcharging some of the cells while low cells are bought up to full charge. This is fine for an open flooded battery where you can replace any lost water, but for an AGM where you can't get access to the cells (normally) and where there isn't a lot of free water sloshing around in the first place, it's only something that should be done as a last resort, ie, "I'm going to throw them out anyway, so let's see if this does anything useful before I do that". At least that's my opinion, others may have their own.