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Author Topic: Battery monitor says 100% charged, SG says not  (Read 2339 times)
Pord
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« on: January 23, 2019, 01:25:53 PM »

We've been running the following 24v system for about 7 months:

4 x 250w 24v pv panels, each pair connected first in series then the pairs connected in parallel
Victron mppt 100/50 controller
Victron BMV700 monitor
Victron inverter
4 x 6v Crown CR220 FLAs

The controller settings include 29.6v absorption, 27.2v float, 31v equalisation.

I've recently compared the battery charge via the BMV700 and battery SG and while the monitor shows 100%, the SG is around 1255-1265 (that's without temp compensation for the current 4degC), so it appears the batteries aren't fully charging.

Last week I did an EQ charge and it only pushed the SG up a little. I tried another EQ today as there's plenty sun, but it kept switching EQ off and back to standard charge status, apparently whenever the input wattage hit around 300w with the panel voltage around 70v.

Do I need to change my controller settings?
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billi
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« Reply #1 on: January 23, 2019, 01:52:34 PM »

Quote
Do I need to change my controller settings?

No  Grin take a brake to the canary islands  and come back  and your batterymonitor ,will still tell you 100 % full  but actually  its 120% full ....

Not sure if the new versions of Victrons batterymonitors are  taking  that Peukert   thing ( never understood it completely)  more into account , but my basic  investigation was that my chargecontrollers kept on charging , while the monitor said 100%    and after i(we = sun and me) managed to  put much more AH into the batteries  than 100%   i told the batterymonitor that 120 % -is now for controllers limited brain - a full charged 100% battery


Hope that was not too confusing now  norfolk
« Last Edit: January 23, 2019, 01:54:09 PM by billi » Logged

1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
Pord
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« Reply #2 on: January 23, 2019, 04:28:34 PM »

Thanks Billi.

Yes, it does have a Peukert option but I don't use it. It's not so much the monitor reading I'm concerned about, more the fact that the batteries are apparently not being fully charged, even when there's plenty solar gain available (like this morning). I'm therefore wondering if my controller settings are somehow throttling power into the batteries and if so, how to safely adjust the settings to allow them to become fully charged.
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Scruff
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« Reply #3 on: January 24, 2019, 03:12:31 AM »

The monitor is not as accurate as the specific gravity.
I understand peukert's exponent and find with discharge levels under C10 not using it is most accurate.

You need to either change the charge controller settings or the charge controller.

My MorningStars charge to between 105% to 120% and specific gravity 1.275 per cell at  2.47V p/c plus remote temperature compensation depending on how hard I am on the battery.

I have found my Victron appliances to consider 1.265 to be fully charged.

« Last Edit: January 25, 2019, 02:27:46 AM by Scruff » Logged
Scruff
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« Reply #4 on: January 24, 2019, 03:19:54 AM »



If you look closely in this head to head you'll see Victron is pushing low float while MorningStar is in Bulk. Speaks Volumes.

Here's a close up what happens most days.



Victron has a lie in while MorningStar gets to work.

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Scruff
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« Reply #5 on: January 24, 2019, 03:24:49 AM »

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Nickel2
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« Reply #6 on: January 24, 2019, 08:39:22 AM »

Some home brewers have remote monitoring/blue-tooth digital hydrometers that measure 1.000 to 1.300. Would one of those be suitable?
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1.140kW mono south-facing at 49*
EpEver 4210A at 24v
24V 400 Ah battery. (4x200Ah FLA)
EpEver STI1000-24-230 pure sine inverter
Of course it'll work. (It hasn't caught fire yet).
oliver90owner
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« Reply #7 on: January 24, 2019, 08:49:48 AM »

Not sure that any home brewer would need an SG anywhere near as high as 1.3!  1.15 would make a high-ish alcohol wine - the brewers amongst us would settle for about 1.07 as a high norm, and 1.1 for the brewers of really strong beer.

But the analogy is close enough, I suppose. Smiley
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Pord
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« Reply #8 on: January 24, 2019, 10:10:12 AM »

Thanks Scruff. I was planning to add the facility to use our portable 1.9kw genny to top up the batteries, but if I can tweak the controller to increase the charge via the panels then it shouldn't be necessary (our useage is very low).

Am I worrying unnecessarily? Our fully charged Crowns should be at 1.275 at 25degC. At our current 4degC the 1.255-1.265 currently reading across the 12 cells would adjust to (I think) approx 1.240-1.250.

If we can work with the existing controller for now, which settings would you suggest changing?

Any idea why the controller wouldn't stay in EQ mode? And would an EQ charge actually help fully charge the entire bank?

Nickel2, just to be clear, it's not measuring the battery charge per se that I'm primarily struggling with, it's how to get the solar controller to increase the charge to the batteries.

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Scruff
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« Reply #9 on: January 24, 2019, 11:13:47 AM »

Hi Pord, you are working against two very difficult problems to overcome.
The first: Victron don't think external temp sensing is required on their small controllers.



This equates to 800mV too low from what it should do and what it does do.
They take a one time reading from the internal sensor and then it assumes it's unwaivering as the controller temp rises and makes it redundant.
It's included as a feature to place them beside their competitors however it does not work.

The second is Victron are AGM biased for mostly idle systems like posh boats and lawsuit mitigation. They spend more on marketing than product R&D.
I've given up trying to charge batteries with them. I just use mine to load compensate my manshed supply and use a MorningStar to actually charge them.

I think you'll find the absorption times too short (by several days at times) regardless. Victron EQ is another redundant feature that doesn't work. Too conservative for golf carts ie. AGM bias again. To compound this it's pulsed not consistent.

If you have a 30v constant voltage supply you can be the manual regulator...turn it off after a few days when you hit your SG target.

Digital hydrometers don't last long in acid bath.

If you want to stick a band aid on the situation you can raise the absorption to 2.62V p/c until April.
For now keep resetting EQ until SG stops improving. 6 hours at 32v and probably then some.
« Last Edit: January 24, 2019, 05:26:44 PM by Scruff » Logged
Scruff
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« Reply #10 on: January 24, 2019, 11:25:54 AM »

I don't think you're worrying unnecessarily. If you charge to 1.275 SG yer crowns will be immortal.

Charging to only 1.265 SG is degenerative cycling and makes a ground breaking case for smanchy expensive li-smions.

To be honest I bet 30 cell panels with an MS PWM controller will knock the socks off a Victron MPpT.

« Last Edit: January 24, 2019, 11:28:33 AM by Scruff » Logged
Pord
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« Reply #11 on: January 25, 2019, 03:48:13 PM »

Thanks Scruff, very much appreciated.

The current absorption value is set at 29.6v, so when you say raise it to 2.62v per cell, is that simply 12 (cells) x 2.62 = 31.44?

EQ currently set at 31v, so I'll give that a nudge up to 32v.
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Scruff
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« Reply #12 on: January 27, 2019, 10:43:10 PM »

Yes but set absorption to EQ threshold until it's fully charged.
As I say Victron EQ doesn't work.
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eabadger
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« Reply #13 on: January 29, 2019, 06:48:57 AM »

even the multiplus inverters have an odd way of eq.

i treated us to a victron bmv712 and a vrm box.
having fiddled with the peukert's settings and our bmv now matches sg pretty well.
we have a high load and charge regime on lead acid forklift cells.
i find the vrm app good for when i am away, it can send the wife emails to remind her to run the generator or errors.

steve
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1600w PV main array at 24v, excide 2v 1000a forklift cells now x 2, 320w PV secondary array at 12v. Enfield 1944 ex RAF 5.6kw diesel genset (now in pieces, big ends gone), Petter AC1 28v diesel charging set at 2.8kw.
1kw wind turbine.
26kw wood stove back boiler to underfloor heating and dhw
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« Reply #14 on: January 29, 2019, 08:10:23 AM »

As soon as I saw this thread I thought, Pord needs to bin the Victron and buy a Morningstar but had no data to back up my statement. You put it so eloquently Scruff  genuflect

The second is Victron are AGM biased for mostly idle systems like posh boats and lawsuit mitigation. They spend more on marketing than product R&D.
I've given up trying to charge batteries with them. I just use mine to load compensate my manshed supply and use a MorningStar to actually charge them.


 hysteria  hysteria

P
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