Difference between controller readings and actual battery readings.

troyer · October 2018

The charger indicates 12.9 volts from the panels and on the charge controller the batteries indicate a 57% charge.

Checking each of the 4 batteries in the bank, they show 13.65 volts for each one.

Why the discrepancy between the controller indications and the actual battery readings.

Thanks,
Al

BB. · October 2018

Welcome to the forum Al,

What brand/model of charge controller do you have?

Do you a digital multi-meter (volt/current meter)?

It is always nice to have a second "opinion" when you are debugging.

A DC Current Clamp DMM is really nice for debugging:

https://www.amazon.com/gp/product/B07546L9RT (inexpensive "good enough" DC/AC current clamp DMM)
https://www.amazon.com/gp/product/B019CY4FB4 (medium quality meter)

And for flooded cell batteries, some sort of hydrometer is good to have:

https://www.solar-electric.com/search/?q=hydromter (our host Northern Arizona Wind and Sun)

If you get a glass hydrometer--Be very careful... The roll of the bench and break quite often.

And with a hydrometer, rinse it before you put it away with a couple of draws of distilled water (otherwise they get sticky inside and the floats get stuck).

-Bill

troyer · October 2018

What brand/model of charge controller do you have?

Do you a digital multi-meter (volt/current meter)?
-------------------------------------------

The brand is -"T" Series MPPT-M30 Solar Charge Controller [China]

Yes I do use a digital multi-meter.

Another issue is during the day the batts may show a 70% charge and the next morning the batts will show only a 40% charge without any load. The batts will not hold their charge.

[4-batts 120 amps each marine type.]

BB. · October 2018

I did not find the controller/manual with a quick search... Details matter here.

In general, a MPPT charge controller needs >~20 volts Vmp from the solar array to properly charge a 12 volt battery bank. Typically, if you have "12 volt panels" (which are Vmp~18 volts), you put two in series for Vmp~array ~ 36 volts for a good quality MPPT charge controller.

If you are getting 12.9 volts from the solar array, the MPPT controller cannot function correctly (or something else is wrong if Vmp-array is >> 20 volts).

If you have a link for the controller, or can tell us with the Vpanel input voltage range is (like 20 to 50 volts Vmp-array or whatever), that would be a good start.

So, tell us about your solar panels, how they are wired (Vmp/Imp, series/parallel wiring, how many of them) and something about your battery bank (type of battery, flooded cell/AGM/etc., voltage, how many batteries, size of batteries, etc... like 12 volts @ 200 AH battery bank).

The one warning here is that Lead Acid batteries do not like to sit around (storage) at less than ~75% state of charge or they begin to sulfate very quickly (permanently lose capacity and quickly become useless). So, if you have an alternate means of charging your battery bank, you probably should do that for now.

-Bill

troyer · October 2018

I get as much as 13.7 volts from the solar panels when the sun is right.

I have 5-15 watt panels in parallel.

If you can, look this up on youtube-

Ebay 30 amp MPPT solar charge controller regulator with LCD screen

This is the type I have.

littleharbor2 · October 2018

The only match on youtube I find has the word, "Fake" before the exact other words you've given. These controllers ARE fake as far as MPPT goes. Is this picture what you have?

Image: https://us.v-cdn.net/6024911/uploads/editor/9m/xn0u7fjd76zl.jpg

5, 15 watt panels Sounds like Harbor freight thin film panels. These panels typically last only a few years before they begin to fail. How old are they? Can you test each panel, individually? Test for voltage and amperage in full sun. Their open circuit voltage is supposed to be around 22 volts. Amperage , just shy of one amp.

mcgivor · October 2018

Is this the fake video? There are imposters sold to unwary customers, mutton dressed as lamb if you like, if this is the case consider it a PWM controller. The voltage seen would be dependent on the battery state of charge, 13.7V would be lower than fully charged, a value of ~14.4V would indicate fully charged. Always check with a multimeter of known reliability, the LCD display may well be eronious which would reflect the low cost.

troyer · November 2018

This is the controller I am using, there are other posts of others using the same one and not complaining.

[ebay]-10/20/30/40 Amp Solar Charge Controller MPPT 12/24V Three-time Timer with USB UP

I have 5 HF panels about 8 yrs old they are individually charging ok.

Ex. yesterday charging was 13.9 bringing the batts to an 83%charge. I plugged a grinder into the inverter and the batts immediately lost about 1/2 their charge.

I always ck with a multimeter and the readings will correctly correlate with the charge controller.

Thank you for the help here.

mcgivor · November 2018

The best way to see if the controller is actually a true MPPT is to open it up and see if there is a transformer, if there is not it would not be a true MPPT, there are ways to disguise the functionality by reducing input voltage then converting to PWM. Bottom line is you get what you pay for, it may function as a controller, appearing normal to most inexperienced users, but in reality name brand MPPT controllers are far superior but come at a price, the nature of the game.

The indicated state of charge is based solely on voltage, introduce a load, the grinder for example will immediately sag the voltage, this is normal , if it is quick to recover, the battery is probably in good condition, the indicated voltage of 13.9V would be around 80%, have you left it alone to see if it reaches ~14.4V, which would be close to100% on the display,, but in reality it would be in the PWM stage, arguably the most important stage where the final charging takes place.

Not to discredit your purchase, it may well satisfy your needs, careful attention is important to maintain a healthy battery, be patient, don't be anxious to explore the boundaries, see what it is capable of with regards to basic charging, before pushing the envelope.

littleharbor2 · November 2018

So you have a 480 Ah. battery bank and a solar array that at best, (when new), will only put out 5 amps. This may be your main problem. You should be pushing about 50 amps into your batteries to properly charge them.

My guess is your batteries are shot, your 8 year old HF panels are shot and even if all was in good shape your system wouldn't last long, as configured. How about some good pictures showing us your system. especially the battery and controller wiring?

BB. · November 2018

Just to give you an idea--Nominally 10% rate of charge into a 480 AH @ 12 volt battery bank would require:

480 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 904 Watt array nominal
904 Watt array / 15 watt solar panels = 60 solar panels

That would be the 10% rate of charge from 60x Harbor Freight solar panels--If they worked well--Which they have a history of not doing.

And you would need a minimum of a ~50 Amp MPPT solar charge controller to do this. As LittleHarbor2 said...

Solar power systems should be designed to support your loads/energy needs. We can start from a fixed point (like the size of your battery bank), and design a "balanced system" around the core of your system.

Generally, we suggest a 5% to 13%+ rate of charge for your battery bank from solar. 5% is OK for a weekend/backup system... 10%+ is really needed for a full time off grid power system.

Marine type batteries are "so so" for off grid power systems. Next set, you should get some true deep cycle batteries (for a starter system, 2x 6 volt @ ~200 AH "golf cart" batteries in series, and 2x parallel strings for a 12 volt @ ~400 AH battery bank).

But, again, it really depends on your energy needs.

-Bill

Photowhit · November 2018

troyer said:

This is the controller I am using, there are other posts of others using the same one and not complaining.

They will work, they just aren't MPPT, they are PWM which will deliver just a little less current so long as the panels are all within the guild lines. In fact for MPPT type controllers, you would want the panels to be at least 2 in series for a bit higher voltage.

troyer said:
I have 5 HF panels about 8 yrs old they are individually charging ok.

The old Harbor freight panels were 15 watts (if that) amorphous panels which have a bit shorter life perhaps 10-15 years.
So you have a 75 watt array.

troyer said:
[4-batts 120 amps each marine type.]

So 4x120 amps = 480 Amphour 12 volt bank.

Might note that battery manufacturers recommend a 5-13% charge rate in general. Your array produces high enough voltage to charge 12 volts so the VMP is likely around 18 volts, 75 watts ÷ 18 volts = about 4 amps or less than 1% of your battery capacity.

The good news is your marine batteries are likely not true deep cycle batteries, they are more likely lead calcium, so they don't lose much charge on their own so these panels may be able to maintain the batteries, but not really charge them.

troyer said:

Ex. yesterday charging was 13.9 bringing the batts to an 83%charge. I plugged a grinder into the inverter and the batts immediately lost about 1/2 their charge.

The charge controller really doesn't have a good way to monitor the state of charge of the battery. The fact that it's only indicating 83% at 13.9 volts, would indicate to me that they haven't reached absorb state of charging yet (but close!)

What the charge controller does is restrict the system/charging voltage so it doesn't 'run away' once the battery is about 80% full the voltage will continue to rise and create heat in the batteries and you will lose electrolyte and quickly destroy your battery. Once the battery reaches this stage of charging, the battery will reduce how much current it will accept.

troyer · November 2018

Yesterday the battery readings on all 4 were at 13.7 however the percent charge on the controller is reading 12.3 v. and showing a 3 amp charge.

Does mean that at some point the MPPT kicked in and did work. i mean why do the batts for the first time indicate 13.7 charge, apparently the charge held.

I manually set the charging to stop at 13.7 on the controller when I set the unit up.

However I am a bit confused at this point.

Again let thank all you guys for the help here.

littleharbor2 · November 2018

Clarify "I manually set the charging to stop at 13.7 on the controller when I set the unit up." Your typical settings would be something like Bulk/Absorb = 14.8 volts, Float = 13,6 volts. So what setting do you have set at 13.7 ?

BB. · November 2018

What kind of batteries do you have (flooded cell, AGM, GEL, VRLA, etc.)?

You do not have enough solar panels to properly charge the battery bank (need at least 5x more solar power)
You do not have high enough setpoint for charging voltage (should be 14.4 volts for AGM/Sealed, or 14.8 for flooded crell)
Looking for specifications, not enough "online" to figure out the proper solar array configuration (series, series/parallel, parallel, what voltage array, etc.). As near as I can tell, your controller would support a total of ~390 Watts of Vmp ~17.5-18.0 volt or so array (approximately 22 amps maximum in PWM mode from array).
Charge controller is probably PWM (Not MPPT). Certainly OK for smaller system. 5% of 480 AH = 24 amps minimum suggested rate of charge (at least it is a start).
Get your batteries properly charged. The longer they sit without getting a full charge, the sooner they are going to die (storing batteries below 75% state of charge, the quicker they sulfate. Running Lead Acid batteries below 50% state of charge often, they have less cycle life. Running lead acid batteries below ~20% state of charge, the more likely they are to die in weeks).
If these are flooded cell batteries, get a hydrometer to measure the specific gravity and their true state of charge (not estimates from meters/controller).

A 1% rate of charge is, at best, good enough to keep a fully charged battery bank charged (float charging). Not enough energy to actually support cycling of the battery bank without other charging source(s).

-Bill

Difference between controller readings and actual battery readings.

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Ebay 30 amp MPPT solar charge controller regulator with LCD screen

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