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Old 11-08-2018, 07:57 AM   #1
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Question Solar Battery Monitoring- % Full?

Just installed 6 solar panels on roof of skoolie (100W 18v 5.56A - 3 pairs wired in series and then the three pairs wired in parallel). I have (4) SLR155 lead acid sealed batteries wired in parallel (balanced charging configuration) each is 12V. I assume the configuration is 4x155=620 Amp Hours of capacity at full charge.

Connected to one of the positive battery terminals is first an inline 200A fuse then connected to the other end of the fuse are all of the following: + lead to 2000W inverter, + lead to Charge converter (shore power or generator charging), + lead to 50 amp inline breaker that then goes to my 40 amp MPPT Solar Charge Controller, + lead to DC Fuse Block, + lead to shunt monitor.

Connected to one of the negative battery terminal (not on the same battery as the positives are connected) are the following: knob type cut off, then on the other side of the cut-off is my shunt and then on the other side of the shunt are all of my negative leads for all of the items listed above.

With everything connected and on, I am confused by the output info from the charge controller monitor and the shunt monitor. At first everything seemed ok (Volts started out around 12.7 - it was night time and no charging from solar or generator) I was able to run a few LED lights. The charge control monitor has a battery level indicator and it looked to be about half full graphically. After a few minutes is went to 1/4. The next day was cloudy but the panels began to charge the batteries and by the end of the day the monitor showed the battery 7/8th full and the volts were around 14.

The big question or concern is that when i power on the inverter and run a small 600 watt microwave, within seconds the volts drop to under 11 and the battery level on the monitor goes down to 1/4 full within 15 seconds. When I turn off the inverter, to volts almost immediately return to the high 12/13 range but the battery level stays around the 1/4 full level until the solar has time to recharge. [I have not tested the generator charging yet]

I am really concerned whether I am getting accurate battery levels because I know how important it is not to discharge the Lead Acid batteries beyond 50%. Does anyone know what the best most accurate way is to know what the actual level of the batteries are? (Sorry for such a lengthy question)
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Old 11-08-2018, 08:18 AM   #2
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The only two points of SoC% that are easily and accurately determined are 100% and 0%.

Voltage does not correspond to SoC% without a long isolated resting period, 24-72 hours. Especially after big currents like that. No such thing as small microwave off batteries, 600W is huge.

IOW your current monitor is only marginally useful, basically just for show.

A combination of SmartGauge and Victron 712-BMV is the best you can do for guesstimating in between 0-100%.

There is no hard B&W magic number about average DoD vs lifetime cycles, your call how much you want to sacrifice to get a higher usable vs rated AH ratio.

LFP has basically the same curve BTW.

VMAX does not make great batteries for demanding deep-cycle usage.

Have a pro check out your install, maybe bad crimps, connections?

Meantime run the genny when you want to use the microwave.
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Old 11-08-2018, 08:21 AM   #3
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Note that each of the above points could get its own thread, dozens of disputed details, many hours of research for you to learn the truth.

Ideally stick to one aspect at a time to avoid overwhelm
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Old 11-08-2018, 09:47 AM   #4
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Heleads,

Not sure what kind of battery monitor you are using but, in spite of the shunt, it sounds like it is using voltage. As John said, that's no good.

A monitor that is actually using the shunt either needs to be told when SoC is 100% or has a detection mechanism. To begin, make sure you do what needs done to get it to that point. Since it is measuring the flow of electrons in and out - it needs to know the starting point.

Hmm... that's a fairly lame description but better words fail me at the moment...
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Old 11-08-2018, 10:38 AM   #5
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Lightbulb

Based on the help above, I ended up at the following site with a very in depth article that may be helpful to others who come across this thread: http://www.marinehowto.com/programmi...ttery-monitor/

I had no idea how complicated lead acid battery monitoring was. Wish now we had gone with Lithium batteries!
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Old 11-08-2018, 01:07 PM   #6
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LFP batteries need monitoring just as much in fact more being so expensive, and are less well understood.
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Old 11-08-2018, 09:57 PM   #7
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Buy a hydrometer, now, before you bugger up all your batteries*. Even a cheapo one will do the job, but Northern Arizona Wind & Power sells a bonzer Swiss one that's easier to use and probably more accurate. A fully-charged FLA battery has a specific gravity of 1.265 or thereabouts, not less than 1.260 and hopefully not more than 1.270. A hydrometer is the only truly reliable way to know your SoC.

If you want to get a battery SoC meter, be very cautious of all the aH counters such as the Trimetric and many others. They can give very inaccurate readings over time, thanks to Mr.Peukert. SmartGauge seems to have a viable alternative - if nothing else, read their article about SoC meters: SmartGauge Electronics - SmartGauge compared to Amp Hours Counters

I'm thinking that you simply don't have enough PV power. 600W of panels won't do much to keep 620aH of batteries happy, especially if they're mounted flat. FLA batteries should be charged at between 5 and 13% of their 20-hour rate - you're not even close to the top of that range which is where you need to be for a mobile PV system. FYI, I have just over 2kW of tiltable panels to charge about 850aH of golfcart batteries, and this will give me about a 13% charge rate. You need to buy more (lots more) PV! Also, I hope your battery cables are heavy enough; if they're not, nothing will work well. You should be aiming for a <1% voltage drop under load.

Here's a few websites to point you in the right direction:
http://www.solarelectricityhandbook....rradiance.html
http://www.solarpaneltilt.com/
https://rredc.nrel.gov/solar/pubs/redbook/
You should know the insolation rate for wherever you are, then you can design an effective PV system. Otherwise you're just guessing, and that will end up costing you more in the long run. Read all you can, especially the NAWS forum that has a wealth of good information.

John

* That's an English technical term, not an unnatural act.
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Old 11-09-2018, 07:16 AM   #8
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Hmm... I think the OP has sealed batteries so a hydrometer is going to be difficult to use. I've never dealt with SLA batteries in this context so I'm not sure of the right answer to your question. I'm probably wrong (happens often... ) but would think that individually charging each battery, letting it rest 24 hours, and then confirm it is 100% with a voltage check may be the easiest option. ????

Just spotted this thread where they are talking about this very topic:
http://www.skoolie.net/forums/f49/op...ged-24744.html

With respect, I disagree about the Trimetric and feel that it is a very good product. The problem is that most users don't take the time to tune it correctly (it is VERY configurable and this takes time and understanding). I know some will argue that this is a product flaw, others argue that it is a user flaw.
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Old 11-09-2018, 09:27 AM   #9
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Yes many AH counters are great, including Bogart's models and valuable even if you use the easier and more accurate SmartGauge for SoC.

Yes hydrometers are irrelevant here, and also completely optional for normal usage, once you have good monitoring gear.

Go to http://marinehowto.com and CTRL-F search for the other two "battery monitor" articles there, besides the one OP linked to.

Everything there at Maine Sail's site is gold!

Quote:
Originally Posted by Iceni John View Post
I'm thinking that you simply don't have enough PV power. 600W of panels won't do much to keep 620aH of batteries happy, especially if they're mounted flat.
Not true. If you have a decent BM, just make sure your consumption is less than what you put in each day.

Of course getting more solar is always good, but in a mobile context you often run out of mounting space.

Also, develop other charge source types, an ICE charge run before the solar day starts can be used to ensure getting back to 100% Full most cycles.

> FLA batteries should be charged at between 5 and 13% of their 20-hour rate

No harm if not, beyond longer charge time needed.
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