Seeing output results that look odd to me.

bigbillsd · September 2018

Hi, I am a solar newbie. I setup a victron 100/50 controller to my RV house battery bank, 6v batteries connected up to give 12v. Today I hooked up 4 160w flexible solar panels, each 2 serially, then paralleled to the controller. This was just a test senario prior to putting them on the roof, they were laying flat on the ground, very similar to their orientation for the roof.

At 11am today the Victron was seeing 425w from the panels up from about 375 watts at 10am, were charging the batteries in "Bulk" at around 30 amp. Around noon I went back out to check if the wattage was closer to 500w from the panels, but it said 102w and 7amps going into the Battery in "Float", not Bulk anymore. Not sure where absorb went, but thats not the question for this thread.

My question is, what happened to the incoming watts? Being a newbie, I think the watts from the panels should still be up near 500w, not at 102w. I would think that only the amps to the batteries would be throttled down due to Float mode but that the panels would still be producing 500 or so watts.

Did my panels go Kaput? Or is that normal?

What is happening to the other 400w if this is normal, are they becoming heat somewhere?

Thanks, Bill

Thom · September 2018

I think it’s working correctly. I’m in float mode panels output is 47.6v .7a 33w charge controller output to batteries 2.3a 13.4v

Thom

littleharbor2 · September 2018

If you connect some loads to the batteries you'll see some of that missing power . The batteries are near full and only accept minimal current in this state. Your controller is throttling back without any load.

bigbillsd · September 2018

Ok, I was hoping that was normal and the panels hadn't gone kaput in one day.

I thought the panels continued to push the full wattage they could gather from the sunlight available even though the battery side of the controller would be pushing in way less. So that means the only time I will see max watts from the panels will be during bulk charging which on my battery pack leaves approx 100 AH to get from 80% SOC to 100% SOC. That implies that adding more panels cannot help getting the array to 100% due to the low amperage the battery can accept.

My initial thoughts were to run the Genny mornings after pulling the batteries down to 50% SOC only during the Bulk charging phase, then let the panels do their thing the rest of the day to get them to 100%. But with this information that, rest of the day might not be long enough to get the batteries to 100%.

Implying that solar might not be able to get my batteries to 100% SOC even by adding more panels.

-Bill

BB. · September 2018

It also depends on where you live (equator=more hours of sun most of the time; Northern US & Canada, not much sun in winter).

With "typical" solar conditions, it is a bit difficult to recharge a 50% discharged lead acid bank in one day--It takes ~8-10+ hours of charging, and most of your charging current will come between ~9am and 3pm...

If you are full time off grid, planning on discharging 25% of your battery on a typical "day" (usually evening/night time), then you can get the battery bank >~90% state of charge with one day of charging.

You do not need to recharge your lead acid batteries to 100% every day--And it is kind of hard on the batteries to do that. This is basically "equalizing" your battery bank (lots of gassing, hard on plates). Getting to >~90% state of charge a couple of times every week is a common goal... And just getting >90% once a week is usually fine for a daily cycling battery bank. Cycling between 80% and 50% 6 days a week, and getting back >90% once a week is common scheme too.

What is also bad for a lead acid battery bank is to let the batteries set below ~75% state of charge (not cycling) for even 1 day, let alone days/weeks/months... That will cause your batteries to "sulfate" (the fluffy lead sulfate that forms during discharge and goes away during charging--Will turn to a hard black crystal if your batteries sit unused/under charged).

Using your genset to recharge from 50% to 80% (and 90% one day a week during winter) and letting solar finish the charging is a good way to use your genset optimally (least runtime, most fuel efficient).

Solar panels are historically cheap (for now--Later????), and if you have room on your RV, adding panels can be very nice way to save on fuel costs and genset runtime (may only make sense if you are using the RV a lot--A few weekends/weeks a year, the genset is probably not going to kill you with fuel costs).

-Bill

Seeing output results that look odd to me.

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