Solar not Working Correctly?

[noelex 77]

Originally Posted by capt-couillon

Anyway, the short answer to your question is that your average "battery monitor" determines battery SOC via voltage. For a 12V LA battery average values are (about) 100% SOC = 12.7V, 50%SOC = 12.2V, 0%SOC = 11.8V )

Most battery monitors count AHrs in and out to determine SOC.
Smart guage is the exception using a voltage based algorithm.

Originally Posted by capt-couillon

Your "Solar Controller" on the other hand, being a fairly recent innovation, will probably contain some sort of micro-processor and base its transition points on the current acceptance curve of the battery rather than straight voltage measurement.

Most use a simple voltage terminating the absorption stage after a set time at fixed voltage.
Some use a variable time based on the total time in bulk.
Some will also terminate on a voltage/current formula, but this does not function if there is any load so very rarely comes into play when the boat is being used.
A very small number will use battery return amps, but this is very rare.

[monte]

I think Simons monitor uses ams in and out and peukerts to calculate SOC. Otherwise SOC would jump to 100% using the theory that it resets at 12.7v. I believe our mastervolt is the same, currently showing 13V but at 90%. Of course I could be wrong!

[Ex-Calif]

Originally Posted by monte

I think Simons monitor uses ams in and out and peukerts to calculate SOC. Otherwise SOC would jump to 100% using the theory that it resets at 12.7v. I believe our mastervolt is the same, currently showing 13V but at 90%. Of course I could be wrong!

Yes - and the auto reset is a big gotcha...

[simonpickard]

I'm going to keep looking at this and maybe post a few photos of the solar wiring.

With nothing on in midday sun the battery monitor was showing around 7amps + but I think the batteries were pretty full at that point.

I'll post back when I've tested more.



Please visit my blog:
www.sailing-interlude.com

[Maine Sail]

Originally Posted by monte

I think Simons monitor uses ams in and out and peukerts to calculate SOC. Otherwise SOC would jump to 100% using the theory that it resets at 12.7v. I believe our mastervolt is the same, currently showing 13V but at 90%. Of course I could be wrong!

Most battery monitors/ Ah counters /Coulomb counters do not use the amps in/out to calculate full... They rely on an accurate reset when full. If they do not reset accurately, when full, and most DO NOT, they will snow ball and counting errors can become huge...

Most Ah/Coulomb counters reset on:

Net current in % of "C" (usually 2% or less)
Voltage
Time at % "C" current
Time at voltage

It is very, very, very easy for solar, wind or hydro to replicate the above "re-set" parameters. When this happens the battery monitor will reset to 100% regardless of where -Ah's are.

I have been standing there at a nav desk when a battery monitor for a 460Ah bank suddenly went from 91% SOC to 100% SOC... That can't physically happen, but the solar system made it appear to happen to the Ah counting monitor..

These devices were designed around battery chargers and alternators that can provide a steady current and voltage in excess of the set parameters so when set parameters are attained it is usually a somewhat accurate representation of what is really happening (course far to many charge sources enter float prematurely so that involves another very long discussion on why your Ah counter may not be accurate..) .

Solar, wind and hydro can easily mimic "full" parameters unless the monitor is carefully calibrated and "known full" human powered resets are performed regularly. Ah coutners require human intervention to work the best they can.

At a bare minimum they also need to know:

Peukerts Constant (which is really never "constant" but the best we can do)
Battery Temperature (avg case temp or add a temp sensor if it allows)
Actual Ah Capacity (very rare that a bank is delivering at "rated capacity")
Charge Efficiency/Coulombic efficiency


As to solar not performing panel temps reduce efficiency. The fact that on most boats the panels are flat mounted can also affect performance. Long wire runs with small gauge wire can also eat into charging performance. For the best charging performance it becomes necessary to get the voltage to the battery terminals so the most current can flow into the bank..

I was on a boat earlier this year where the wire from the controller to the bank was sized for a 3% drop. Yep it had slightly more than 3% at 3.4% when I measured it.. What did that mean at the batts when the controller was pushing current? It meant that the bank was seeing 13.9V not the 14.4V the controller thought it was regulating/limiting voltage to. On top of that this was an MPPT controller and the wires going to the controller were also dropping precious voltage so his MPPT boost performance was also lacking. A few wiring tweaks and his solar performance was, and I quote, "stellar man".......

There is a lot at play here and many things that could be leading to the performance issues.. We really need more data... Nolex's test outlined above is the easiest to perform. Turn on a load larger than the solar and if solar performance does not change or improve the issue is not full batteries it is in the solar system. If the solar output goes up, you are dealing with Ah counter calibration issues.

[barnakiel]

Originally Posted by simonpickard

(...)

With nothing on in midday sun the battery monitor was showing around 7amps + but I think the batteries were pretty full at that point.

(...)

On our bank we near full when Amps are well below 1% of the bank. I often see figures of 0.2 A and below at midday with the boat in standby. Our bank is 110 Ah. Our charger is a PWM. The monitor is a Bogart.

Cheers,
b.

[simonpickard]

I'll run the tests given here tomorrow.
I think the thing that's throwing me is I'm trying to work stuff out when the batteries are 95% or more full. I stupidly thought that the solar would throw as much as it could in at all times and then just trickle charge to keep at 100% but that doesn't seem to be the case.

I'm not going to plug in tonight and then do a 300watt test tomorrow and see what I'm getting around midday.





Please visit my blog:
www.sailing-interlude.com

[UNCIVILIZED]

Simple question, but have you checked the voltage AND amperage coming out of each panel vs. what they are (ideally) rated to produce? If not, it'd likely pay to do so. That, & to see what kind of output you get with each panel when it's directly hooked up to a battery. It might be worth trying out for a week, & keeping a daily log, with readings a couple of times a day.

When I lived aboard, I took just 1 panel & a looong set of wires to it, with alligator clips on the ends for the battery. Then I'd find a totally non-shaded spot for the panel, & check it's output at the terminals with my multimeter (voltage & amperage).
Depending on how much both the boat & shadows danced around sometimes I'd have to move the panel a few times during the day in order to keep it completely clear.

Admittedly I had a simple system on the boat, but once I'd figured out how much battery juice I burned in a given day, I just mounted enough panels to keep up with the draw (with a disconnect switch that I'd flip @ sundown). Or rather enough to have say 80% of my bank charged by day's end. And then perhaps once a week, & a bit more often in the winter (less solar charging hours), I'd hoist up my trusty Redwing wind generator for part of the day to top things off.

Eventually I mounted a dedicated, fixed meter, so that I didn't have to pull up the floor boards, & dig out the multi-meter every other day. But the setup kept things properly charged, & was KISS.
It's just something to think on. How much fancy equipment do you really NEED in order to have enough power on tap? And what of that which you own is giving you headaches overly much?

Just playing Devil's Advocate. Especially when I see folks with 10k $ charging setups which own them.

[simonpickard]

Reason I'm getting into this more is that I'm doing the ARC rally soon.

Before I never bothered with my readings overly as every few days we'd head into a marina anyhow and fully charge up. But for the ARC crossing I wanted to know if I could have a net positive at the end of each day.

All I'll be using is autopilot, fridge, instruments and lights. I've measured the cost of each so know my net loss per day. Just need to know how much I can get in on an average day.

Will run some tests and get back to you all.



Please visit my blog:
www.sailing-interlude.com

[monte]

Thanks for the feedback Maine sail. I understand how the BM can be fooled into thinking the bank is 100%, but can you explain what happens after this when the bank continues to charge for let's say, 4 hrs off solar and becomes in fact fully charged. Does this then mean all is good, batteries charged, BM shows 100% and from there the BM SOC reading should be as close as possible, given the variables?

[Stu Jackson]

Originally Posted by simonpickard

Well how can my solar controller know when that battery is 'full' i.e. goes from bulk into float but my battery monitor can't?

Because going from absorption to float is NOT full.

Full is when the battery gets to 2% of its amp hour rating.

Read some more of Maine Sail's stuff.

Also learn more about Battery Acceptance.

[Maine Sail]

Originally Posted by Stu Jackson

Full is when the battery gets to 2% of its amp hour rating.

Actually 2% or less AT ABSORPTION VOLTAGE/14.4V +

AT ABSORPTION VOLTAGE is the part everyone tends to forget. Just because you are in float does not mean the battery actually got full. There are far too many dumb "smart" controllers, chargers, regulators that use simple egg timer programs that may NOT match your bank for the proper transition to float from absorption...

Less than 2% AT FLOAT voltage is not always full unless it previously attained less than 2% at 14.4V +........

It should also be noted that 2% is not technically full for many banks but is rather "cruiser full", which means close enough to deem it full.

[monte]

Thanks Maine sail, great info as always. My monitor is showing

So I guess it is close to full...? I'll keep an eye on the voltage in futures..

[monte]

Battery bank is 700Ah lead acid..so 2% is erm ???not sure what the 2% figure relates to?

[sailinglegend]

Originally Posted by monte

Battery bank is 700Ah lead acid..so 2% is erm ???not sure what the 2% figure relates to?

Full is when the battery gets to 2% of its amp hour rating.

This is clearly posted by Stu Jackson only three posts back.

I don't understand why good old Maine Sail and others waste their time posting on here when people just don't bother to read the posts properly.

I know "Electrickery" is complicated for some people but please don't expect to get ALL your answers here in one post - buy some books, several books, and if you still don't understand then come here with specific questions and you will always get very helpful answers!

There is a wealth of knowledge on this Forum if you use the search function and ask questions.

"When is full not full?" finds 469 threads. Please get reading!