Undercharging batteries on solar with Victron MPPT

[john61ct]

Originally Posted by motion30

You could raise the float charge to 14.4 or so

As mentioned above, and can be 14.8V or whatever the Absorb spec is

> Set Float to Absorb V when cycling. Set it back when stored no loads pulling SoC down.

If you forget to reset when not cycling can lead to damage from overcharging, especially with sealed chemistries

[travellerw]

Originally Posted by noelex 77

I think the factory default is 6hrs.

This is not the real absorption time which can be anywhere from 0 to 6 hrs on this setting, but might typically be about 30mins to 1 hour of genuine absorption time, although the controller will always report this as between 1 and 6 hours.

Yes it very confusing

Changing the 6hr default setting to 8hrs is only a very slight difference. This will only typically give another 5-10mins of genuine absorption time, so work in larger steps at first, but look at large number if cycles as the genuine absorption time will be very different for each cycle.

Yup.. I just checked the settings we had for our lead acid. We actually had that value set at 11 hours.

However we found the biggest improvement was bumping the voltage slightly as I detailed in my last post.

[noelex 77]

Originally Posted by travellerw

However we found the biggest improvement was bumping the voltage slightly as I detailed in my last post.

Yes the voltage settings make a significant differnce. The correct setting will not only hit 100% more often but will get there quicker. Generally they are set too low and I think this is part of the reason people report the absorption time is too short.

The best thing most owners could do is to take the time to reaserch the ideal voltages and then correct these for controller error, voltage drop (this will vary unfortunately) and temperature (a small number of controllers will do some of these corrections automatically, so check first).

[admiralslater]

My battery geek supplier suggested that I equilize the battery every two days and monitor the water . This makes up for the bad days of sun . Depending on your sun this may or may not be a good idea . It works well in Toronto on a mooring with a fridge running 24/7. I am using victron mppt

[noelex 77]

Originally Posted by john61ct

As mentioned above, and can be 14.8V or whatever the Absorb spec is

> Set Float to Absorb V when cycling.

This has been discussed before but for the record I think disabling the float stage is bad advice.

In a few cases it can be fine, but these are very specific examples. To advocate this as a general guideline when cycling is not correct in my view.

[john61ct]

Yes no substitute for a better quality system adjusted properly, temporary kludge at best.

But for those making do on a very tight budget, better than nothing.

Long as you don't leave it set that way when sitting at Full already.

[macman4190]

I don’t see the benefit to increasing the time on solar. There is a only so much sun high enough to power the absorption stage. For example, changing the time from 18 hours to 20 hours does not help - just to make a point. In my case, I was done with bulk and into absorption by 10am. Absorption was a few hours. I had 425 watts of solar and only used 20-30 amp hours overnight. It is hard to overcome an under powered charger of any kind.

[john61ct]

Yes of course.

Running a high-amp dino juice source in the early morning until the bank is at 80+% SoC may only take an hour or two, and will help a lot

when the goal is to get back to 100%, at least a few days per week.

[Tessellate]

Thanks! Replies inline...

Originally Posted by john61ct

I presume only after many hours of Bulk, striving to reach Absorb V.

What is the pattern when on shore power, say 60+A available?

Yes, we're typically in bulk 6-10 hours per day. Morning bulk of course is only a few amps and we usually finish absorb around 3 or 4pm after 1-3 hours of peak sun.

On shore power (20amp Xantrex TrueCharge), for instance today we plugged in with -19 Ah showing on Link 10 and batteries at ~12.5 in the morning and the charger pushed 17A for a little while (10-20 min), dropping off quickly (10A, 5A) as batteries approached 0 Ah on Link 10 counter. Reached 14.7 after about 1.5-2 hours and went to float (13.8) shortly after that. The shore charger holds absorb voltage for 1 hour. This isn't configurable.

Originally Posted by john61ct

> I bumped up the absorb voltage to 14.8 and float to 13.7 after first suspecting undercharging

What was Absorb before?

It was at the default of 14.4/13.4 (14.3/13.3 at the batteries) prior to July of this year. Also our shore charger was on the "warm batteries" setting instead of "cold batteries" setting - 14.4/13.5 (14.3/13.4 at batts) instead of 14.8/13.9 (14.7/13.8 at batts). That's it's max voltage and what we're using now.

Originally Posted by john61ct

> At the end of absorption the batteries are typically accepting < 1.0A

With what instrumentation do you get that measurement?

The Link 10 (shunt monitor). It typically seems accurate, and we don't have any "sneaker wires" afaik.

Originally Posted by john61ct

> There's no way to force it to do longer absorption

Are you using the dongle / SmartSolar menu? I thought there was.

We have the Bluetooth dongle (VictronConnect). There's a "max absorption time" setting (default = 6 hours) but that notes "The actual duration is determined by the battery voltage when the solar charger starts up in the morning." I had a misunderstanding about their wording - I thought this was just a safety setting for max absorb hours in a day, but actually it's the scale factor that plugs into the table they use for their absorb algorithm.

They explain it better here: https://www.victronenergy.com/live/v...-solarchargers
(search for "absorption time limit")

So if I increase max absorb time by 50% (to 9 hours), I'll get 1.5 hours when the batteries start the day at >12.6 and 3 hours when they start between 12.2 and 12.6. That seems like what I should do. That's less hacky and safer than just setting float = absorb. I could still hit the tail cutoff of 1A, but so far that hasn't happened much.

"The Absorption stage ends before the Absorption time has expired. The Tail current is 1A for models 100/20 and smaller; and 2A for larger models."

The manual for the MPPT controller is here:
https://www.victronenergy.com/upload...E-ES-SE-ul.pdf

They have another VictronConnect page here:
https://www.victronenergy.com/live/victronconnect:start
Between this one and the other one, there's over 1500 user comments, some of them absorption related - I'm going to have to read through these!

Originally Posted by john61ct

> Perhaps I should use its auto equalization feature every 2 weeks?

Yes but not auto, do it manually, ideally on shore power.

Doing that is a lot of work though (taking SG measurements hourly). The Victron auto equalization algorithm sounds pretty decent actually.
But realistically if I can't keep the batteries healthy without doing bi-weekly shore power equalizations, I'm better off just buying AGMs (or other non-memory-effect batteries).

Originally Posted by john61ct

> If Victron MPPT set to 14.8/13.7 and reaching float on most days is still undercharging our batteries, what can I do to get it to stop doing that?

Set Float to Absorb V when cycling. Set it back when stored no loads pulling SoC down.

> Did I do equalization correctly? Is it common to not be able to get the batteries to 1.265 after 18 hours?

Interstate should provide the protocol.

The only Interstate related docs I could find with Google are here: INTERSTATE DEEP CYCLE BATTERIES CHARGING RECOMMENDATION

It says to equalize at 15.6 for 2 hours (seems short), every 4-8 weeks. Also says absorption voltage of 15.5 for 2-4 hours (high!) - this is higher than our shore charger supports, 15.5 is its equalization voltage. Not sure if I should trust that page or not.

[Tessellate]

Originally Posted by noelex 77

+1

The batteries will accept a small current even when they are fully charged and on float. The battery monitor is just counting the AHrs and assuming, incorrectly, the batteries are becoming more charged.

35.5 AHrs over 10 days means on float the batteries were accepting 0.15A (assuming no house loads and that the battery monitor did not reset itself while you were away) which is normal and does not indicate the batteries were not fully charged when you left. If you have any house loads, such as an occasional bilge pump, or even small indicator LEDs the batteries have accepted even less current.

Sorry I'm not sure I understand - when you say "the battery monitor is just counting the AHrs and assuming, incorrectly, the batteries are becoming more charged" are you saying that additional 30-35 AH was not additional charging? That the batteries were already 100% and 3.5Ah per day just dissipated into keeping the batteries on float?

We didn't have any house loads on. All breakers off and no bilge pumps (dry bilge). Only LEDs would be the shore charger status panel and the Victron Bluetooth dongle status light.

Others' explanation that the float + solar absorb slowly added 35 Ah to the bank is more consistent with my understanding. If that explanation is correct my problem is how to adjust so we don't need 10 days to do that.

[Stu Jackson]

Originally Posted by Tessellate

Sorry I'm not sure I understand - when you say "the battery monitor is just counting the AHrs and assuming, incorrectly, the batteries are becoming more charged" are you saying that additional 30-35 AH was not additional charging? That the batteries were already 100% and 3.5Ah per day just dissipated into keeping the batteries on float?

We didn't have any house loads on. All breakers off and no bilge pumps (dry bilge). Only LEDs would be the shore charger status panel and the Victron Bluetooth dongle status light.

Others' explanation that the float + solar absorb slowly added 35 Ah to the bank is more consistent with my understanding. If that explanation is correct my problem is how to adjust so we don't need 10 days to do that.

To answer this question, read the manual for the monitor. All manuals for these units, which almost all share the same algorithms, discuss how this works. In great detail. Happy reading.
Some of the manuals for the more basic monitors may not. In that case, get the Link 2000 manual which does explain it. Xantrex has a discontinued arhive section with those manuals.

[john61ct]

I would ignore the Link AH readings for now wrt charge control, just use it as an ammeter for now if it is accurate.

Keep adjusting the Victron AHT upwards until you verify endAmps is reached at Absorb most days.

If not reached at least a few days a week, burn dino juice early AM as above, or add more solar.

Until endAmps is reached, should not drop to Float.

Replace the shore charger, I like Sterling ProCharge Ultra or ProMariner Pronautic P, maybe Magnum with their fancy remote + BM.

You need 30A if sticking with FLA

Test the bank to see if EoL, buy better quality next time: Deka, Trojan, Crown, Superior.

Avoid AGM unless you need it.

Equalizing can use endAmps rather than SG, follow mfg specs.

[Tessellate]

Originally Posted by Stu Jackson

To answer this question, read the manual for the monitor. All manuals for these units, which almost all share the same algorithms, discuss how this works. In great detail. Happy reading.
Some of the manuals for the more basic monitors may not. In that case, get the Link 2000 manual which does explain it. Xantrex has a discontinued arhive section with those manuals.

I have read the manual for the Link 10, and reread it now, but I don't see something to explain how +Ah in to the battery would not correspond to charging of the battery.

This is the manual I have: http://www.xantrex.com/documents/Dis...-01_rev-A).pdf

I read a lot of discussion of the CEF (charge efficiency factors) and Peukert's exponent, but it appears to say these mainly pertain to determining whether the battery is fully charged (when the 4th bar starts blinking, indicating 100% charge attained).

I'm not using the monitor for that function (although I do pay attention to it), understanding that it's not perfectly accurate. And I could try modifying the CEF parameters, but Xantrex doesn't recommend that, suggesting setting battery capacity instead (which I've done, reducing about 20% recently with the presumption that our batteries likely have lower capacity now).

But I don't see how the Ah counter wouldn't represent amp hours that went into charging the battery. As I understand it a shunt monitor is basically an ammeter that measures amp flow by voltage differential. So I still don't understand noelex77's statement that the +35 Ah could've been on top of a 100% charged battery and that the 35 amp hours don't represent charged capacity.

[john61ct]

Originally Posted by Tessellate

I have read the manual for the Link 10, and reread it now, but I don't see something to explain how +Ah in to the battery would not correspond to charging of the battery.
…
So I still don't understand noelex77's statement that the +35 Ah could've been on top of a 100% charged battery and that the 35 amp hours don't represent charged capacity

At high SoC, only a tiny fraction of current accepted by the bank does anything to raise SoC.

The vast majority is just dissipated as heat.

> As I understand it a shunt monitor is basically an ammeter that measures amp flow by voltage differential.

Amps is instananeous, AH are accumulated, "integrated".

> I read a lot of discussion of the CEF (charge efficiency factors) and Peukert's exponent, but it appears to say these mainly pertain to determining whether the battery is fully charged (when the 4th bar starts blinking, indicating 100% charge attained).

Even the best SoC meters, and dozens are more accurate than the Link, are just guesstimating.

And **none** are suitable for determining 100% Full based on AH in/out. Certainly not for the purpose of transitioning from Absorb to Float.

It is usually the owner's job to manually reset the BM's 100% setting, based on endAmps.

Ctrl-F for "battery monitor" here at Maine Sail's HowTo site http://marinehowto.com and read closely those three articles

[Tessellate]

Thanks again for all your input. I do basically just use the Link as an ammeter - to know how many amps I'm pulling or pushing in, and how many I've used so far for the day.

How do I find endAmps for my batteries? I don't see anything published about that for Interstate batteries, I guess I could try contacting them? I know they're not the best, but it's the only FLA that was being sold by the marine store I went to 2 years ago when our prior set got to <50% rated capacity.

I notice you always write endAmps as one word, with end in lowercase and Amps capitalized (sentence case). Is that a standard symbol / acronym? I couldn't find much on it via google, but what I've read usually recommends from 1a to 2% of capacity (3a or so for us) as the typical end amps. You also mentioned Defa spec of holding till <0.1a, but I'm not sure if that's a general recommendation (every day) or a 1-time thing.

Originally Posted by john61ct

I would ignore the Link AH readings for now wrt charge control, just use it as an ammeter for now if it is accurate.

Keep adjusting the Victron AHT upwards until you verify endAmps is reached at Absorb most days.

If not reached at least a few days a week, burn dino juice early AM as above, or add more solar.

Until endAmps is reached, should not drop to Float.

Replace the shore charger, I like Sterling ProCharge Ultra or ProMariner Pronautic P, maybe Magnum with their fancy remote + BM.

You need 30A if sticking with FLA

Test the bank to see if EoL, buy better quality next time: Deka, Trojan, Crown, Superior.

Avoid AGM unless you need it.

Equalizing can use endAmps rather than SG, follow mfg specs.