MPPT 75/10 Solar Controller settings for Marine Dual Purpose battery

LonesomeRoad

We purchased a new 2021 T@B 320 recently and I finally started trying to understand a little bit about the solar controller. As expected, the dealer put in a cheap Interstate Group 24 Marine Dual Purpose battery but did nothing to set the solar controller up for that (it was set for a default Victron AGM battery). I contacted Interstate this morning and they sent me the attached PDF to help me setup the controller. I defined a preset in the Victron app with the following: Absorption voltage: 15.9, Float: 13.15, Equalize: 16.15 and setup up automatic equalization every 30 days. I see no place to set the Bulk voltage of 14.4. I've also attached a screen shot of the settings in the app. Any opinions from the solar experts out here on my settings? 

On a related note, if I sit and watch the app, I can see the solar output moving up and down on a regular basis (unrelated to cloud cover) as illustrated in the attached screen shot (VaryMPPT). Seems like odd behavior, but I'm a solar newbie! Any thoughts? 

Unfortunately, I am guessing that most dealers just toss a battery in before delivery and never setup the solar controller properly. Eventually, we'll probably upgrade the battery, but no use trashing the existing battery with bad settings.

Thanks in advance for any help/comments.

pthomas745

What is running in your trailer?  Or is there a stray tree branch swinging back and forth across the panel?

LonesomeRoad

Nothing was running on the trailer at the time I did that screen shot outside of the parasitic drain of the Jensen. Fan was off, television unplugged, no lights, fridge off. No branch swinging. I had seen this behavior before as well, just never captured a screen shot. Seems like the controller was intentionally cycling but doing so rapidly.

ColoradoJon

Wow... that absorption charge voltage value seems really high.  15.9V is quite a bit.  That's even higher than the recommended equalization voltage of my 6V deep cycle batteries.  Are you sure that 15.9 is their recommendation for absorption voltage?  Also, you don't really need to equalize once per month.  Once per season on a seasonal camper is probably good enough.

Regarding the varying voltage - solar output can fluctuate quite a bit even when it looks like climate conditions have not changed.

LonesomeRoad

I attached the wrong file above. Attached here is what they sent this morning which has: 15.8 - 16.0 for Absorb. I know almost nothing about battery chemistry and hoped that Interstate would!

Grumpy_G

If you're referring to the left side of the graph, MPPT is constantly optimizing voltage x current = power from the solar panels. Remember voltage generally drops with increasing current, so these variations are caused by the controller, not the panels. As a side note it looks like the charge controller goes into float when the graphs smooth out. 

ColoradoJon

@LonesomeRoad well, it is an Interstate battery and if that is the information that they sent then it must be accurate!  Seems super high to me, though.  Keep an eye on the water levels and check for overheating.  If you lose lots of water you might want to contact Interstate again and ask them to verify those charge values.