MPPT Controller Explanation For Dummies

[T1 Terry]

I agree with you there, far more battery damage to lead acid batteries by under charging than over charging. A few people on another forum have been experimenting with adding small amounts of distilled water to the cells in poor performing AGM batteries, upped the solar float voltage to 14v and got quite a good result. The higher state of charge achieved and stirring of the acid brought them back from the grave. High battery temps when they are located in an engine room would cause a few loss of electrolyte problems as well.

If the MPPT controller has adjustable absorption and float voltages then I'd look at a more aggressive charging regime to achieve the same results as a good PWM controller can achieve, that pulsing of high solar voltage helps to break up the sulphation on the plates, MPPT controller don't seem to achieve the same high voltage hits on the battery when they switch to PWM voltage control.

T1 Terry

[Mystic38]

imo I don't see any need for a battery monitor to read past 100%, none at all..

What is needed is the battery monitor to look at battery voltage and charge current. Many battery monitors look for a predetermined (and adjustable) float voltage, and a predetermined (and adjustable) low current limit . When these two conditions are met, then the battery is deemed at full charge...and the charge % reading sync'd to 100%...to me, if the battery monitor cannot do that, its not really a battery monitor, simply a voltage and current meter and of little value to the non-technical cruiser.

I have the xantrx linklite and it has served me very well for the last 5 years.

Originally Posted by T1 Terry

The battery monitors that don't read past 100% can be very misleading as you have no idea if the monitor is still in sync with the batteries, a monitor that displays past 100% gives an instant signal that it’s accuracy has drifted and needs to be reset.
A true test for any battery monitor would be to check the current still flowing in when the monitor claims the batteries are at the displayed 100% SOC, it should be down around 1 to 2 amps, if it's still 10 amps or more the monitor is out of calibration compared to the actual condition of the battery bank. A battery bank has not reach a 100% SOC till no more Ah can be pumped in.
It requires a greater number of Ah in than Ah out to get a lead acid battery back to 100%, if this is not accounted for the error becomes accumulative and the battery monitor could be well off the mark after a mth or so of deep cycling.
An instrument is only a guide and that guide is only accurate if a program of verifying the displayed results is part of a regular routine.

T1 Terry

[noelex 77]

Originally Posted by Mystic38

imo I don't see any need for a battery monitor to read past 100%, none at all..

It does help show if the battery monitors setting are inappropriate.

Probably the most useful display will read + AHrs, and over 100%, but reset this to 0AHs and 100% at the start of a discharge cycle.

[goboatingnow]

Some systems do measure battery return amps independently of load ( like mine), but it is not common.

Interesting Noelex, what is your charging system.

What is needed is the battery monitor to look at battery voltage and charge current. Many battery monitors look for a predetermined (and adjustable) float voltage, and a predetermined (and adjustable) low current limit

In my experience, BMs either dont 'reset' or just reset by using a minimum current setting, thats easily confused by load sharing issues. I cant see using float voltage as any indication of anything.

The only way for BMs to do things properly is to seperate charge currents from load currents and therefore the current threshold begins to make sense.

Or switch to Lithium, where terminal voltage is more useful and accurate !!

dave

[noelex 77]

Originally Posted by goboatingnow

Interesting Noelex, what is your charging system.

It is an outback 60 with flexnet DC and mate.
The latter act as battery monitor with 3 shunts to give data on the various charging inputs.

It is overkill for most boats, but I live almost 365 days on board and solar provides 95% of my charging. It is a very good system that will terminate the absorption cycle correctly on battery return amps, as well as giving a wealth of information.

Notice on the display here
http://www.cruisersforum.com/forums/...-105162-2.html
(Post 28)

the absorption cycle was only 6 minutes before switching to float for yesterday.

[Mystic38]

I think we should accept that our experiences are different and let the thread go back to Solar/MPPT.

My post on the the use of the BM was in response to my (clearly unpopular to some) statement that the MPPT charger gave me a clear 25% improvement in charge current, and that I could achieve full charge by ~2pm.

With regard to your post, to me, the fall of the charging voltage to float level indicates that the charging algorithms of voltage, time and current have been met by the charging system(s) in use. ie.. the charging system considers the battery bank to be charged. I am comfortable with this as a prerequisite logic condition for a required indicator of full charge...whether you are or are not is your decision on your vessel...

I confirm, as stated fact, that my battery monitor will re-sync automatically to the conditions I described in my prior post :
a) Charge Voltage fall : ie full charge asserted by charging system
b) Charge current below preset limit : ie full charge confirmed by measurement.

Given that my charging systems (three, each with a 3 stage charger) all have greater current capability than my predominant load, there is zero issues with load sharing...as any load under use is being supplied by the charger and not flowing through the shunt, and therefore the BM solely measures charge current in such case.

regards

Originally Posted by goboatingnow

In my experience, BMs either dont 'reset' or just reset by using a minimum current setting, thats easily confused by load sharing issues. I cant see using float voltage as any indication of anything.

The only way for BMs to do things properly is to seperate charge currents from load currents and therefore the current threshold begins to make sense.

Or switch to Lithium, where terminal voltage is more useful and accurate !!

dave

[Maine Sail]

Originally Posted by Mystic38

I think we should accept that our experiences are different and let the thread go back to Solar/MPPT.

My post on the the use of the BM was in response to my (clearly unpopular to some) statement that the MPPT charger gave me a clear 25% improvement in charge current, and that I could achieve full charge by ~2pm.

With regard to your post, to me, the fall of the charging voltage to float level indicates that the charging algorithms of voltage, time and current have been met by the charging system(s) in use. ie.. the charging system considers the battery bank to be charged. I am comfortable with this as a prerequisite logic condition for a required indicator of full charge...whether you are or are not is your decision on your vessel...

I confirm, as stated fact, that my battery monitor will re-sync automatically to the conditions I described in my prior post :
a) Charge Voltage fall : ie full charge asserted by charging system
b) Charge current below preset limit : ie full charge confirmed by measurement.

Given that my charging systems (three, each with a 3 stage charger) all have greater current capability than my predominant load, there is zero issues with load sharing...as any load under use is being supplied by the charger and not flowing through the shunt, and therefore the BM solely measures charge current in such case.

regards

Mystic,

Just because a charge device, regulator, solar, wind or battery charger has gone into float it does not necessarily mean the bank is full. These systems really are a lot dumber than we often give them credit for.

Just because it says "smart" may not mean it is truly smart.. All it usually means is that the bank has hit absorption voltage and the algorithm, which often uses time and is programmed very conservatively, drops down to float voltage based upon time at absorption voltage not necessarily whether the bank actually got full at absorption voltage.

You should see less than 2% acceptance at 14.4V before a bank can realistically be deemed "full". If you drop to float too early based on time at voltage then getting that last bit into the bank can take multiples longer because the voltage is the pressure and a float voltage simply can't drive the current that an absorption voltage can.

In the world of solar, wind, chargers and alternator regulators I rarely see the transition from absorption to float occur when it should, at 98% SOC at 14.4+/- V. These devices are usually designed to be a one size fits all product and what may work on a 150Ah bank may not work so well on a 800Ah bank, but the same device often gets used on both and has no way of knowing..

As an example just Monday evening I had to replace a tachometer on a 40 footer with a small solar panel. When I got there the battery monitor was blinking "FULL". The controller was in "float"... To the owners eyes the batteries were fully charged.

When I fired up the engine to test the tachometer, and calibrate it, the bank was still taking 32A of charge current, after the brief in-rush settled down.

By the time I finished calibrating the tach it was still taking 28A of charge current this was with no loads on and the DC main breaker was off. The boat has a 400Ah bank so "cruiser full" of 2% acceptance for this bank is about 8A of accepted current at 14.4V.

Just because a battery monitor says full or the solar controller is in float mode this often may not mean the bank is actually full. It very often just means the battery monitor was tricked into resetting early by the solar or the controller went into float based on time at absorption voltage.

Unless you have a system that can independently monitor loads going out and charge sources going in (this requires multiple shunts) then it is very hard to keep an Ah counting battery monitor accurate especially when you add solar to the mix. Manual re-sets when known full are really the about only way to minimize counting errors other than drastically tweaking the "full parameters" of the batt mon to not get tricked by solar..

The easiest way to determine full is less than 2% acceptance at 14.2V - 14.4V with no loads on.... If your absorption voltage is 14.6V to 14.8V then you may want to consider "full" at about 2.5% acceptance... This means using an alt or charger at absorption voltage and usually not solar because solar may not have the oomph at the time of day you are testing unless the array is very large... This test takes but a few seconds and can be done before you leave the hook while the engine is warming up and the alt reg is still in absorption mode. If you see 2% or less flowing into the bank, with no loads on and at 14.4V, then simply hit the manual re-set.

Battery monitors are great tools but they really do need human intervention...

[Mystic38]

if you had read my post completely you will see that I clearly stated that for me, reducing to float is an necessary but insufficient indicator of full charge... I also discussed bank load while charging and clearly stated why this was a non-issue, as is my house bank size (programmed).

Please allow the thread to revert to topic, as I have no concerns, questions or issues with my charging system.

regards.

Originally Posted by Maine Sail

Mystic,

Just because a charge device, regulator, solar, wind or battery charger has gone into float it does not necessarily mean the bank is full. These systems really are a lot dumber than we often give them credit for.

Just because it says "smart" may not mean it is truly smart.. All it usually means is that the bank has hit absorption voltage and the algorithm, which often uses time and is programmed very conservatively, drops down to float voltage based upon time at absorption voltage not necessarily whether the bank actually got full at absorption voltage.

You should see less than 2% acceptance at 14.4V before a bank can realistically be deemed "full". If you drop to float too early based on time at voltage then getting that last bit into the bank can take multiples longer because the voltage is the pressure and a float voltage simply can't drive the current that an absorption voltage can.

In the world of solar, wind, chargers and alternator regulators I rarely see the transition from absorption to float occur when it should, at 98% SOC at 14.4+/- V. These devices are usually designed to be a one size fits all product and what may work on a 150Ah bank may not work so well on a 800Ah bank, but the same device often gets used on both and has no way of knowing..

As an example just Monday evening I had to replace a tachometer on a 40 footer with a small solar panel. When I got there the battery monitor was blinking "FULL". The controller was in "float"... To the owners eyes the batteries were fully charged.

When I fired up the engine to test the tachometer, and calibrate it, the bank was still taking 32A of charge current, after the brief in-rush settled down.

By the time I finished calibrating the tach it was still taking 28A of charge current this was with no loads on and the DC main breaker was off. The boat has a 400Ah bank so "cruiser full" of 2% acceptance for this bank is about 8A of accepted current at 14.4V.

Just because a battery monitor says full or the solar controller is in float mode this often may not mean the bank is actually full. It very often just means the battery monitor was tricked into resetting early by the solar or the controller went into float based on time at absorption voltage.

Unless you have a system that can independently monitor loads going out and charge sources going in (this requires multiple shunts) then it is very hard to keep an Ah counting battery monitor accurate especially when you add solar to the mix. Manual re-sets when known full are really the about only way to minimize counting errors other than drastically tweaking the "full parameters" of the batt mon to not get tricked by solar..

The easiest way to determine full is less than 2% acceptance at 14.2V - 14.4V with no loads on.... If your absorption voltage is 14.6V to 14.8V then you may want to consider "full" at about 2.5% acceptance... This means using an alt or charger at absorption voltage and usually not solar because solar may not have the oomph at the time of day you are testing unless the array is very large... This test takes but a few seconds and can be done before you leave the hook while the engine is warming up and the alt reg is still in absorption mode. If you see 2% or less flowing into the bank, with no loads on and at 14.4V, then simply hit the manual re-set.

Battery monitors are great tools but they really do need human intervention...

[colemj]

Originally Posted by Maine Sail

Unless you have a system that can independently monitor loads going out and charge sources going in (this requires multiple shunts) then it is very hard to keep an Ah counting battery monitor accurate especially when you add solar to the mix. Manual re-sets when known full are really the about only way to minimize counting errors other than drastically tweaking the "full parameters" of the batt mon to not get tricked by solar..

Can you explain this more - particularly the solar part? Lets say the batteries are under a 5A load and the solar panel is putting in 5A. Our battery monitor with a single shunt passing all in/out current will show "0" on the ammeter and the "amps from full" will decrease very slightly through time because it is programmed so that the charging source is less efficient than the load draw (puekert, charge efficiency, etc).

Over time, our "amps from full" counter keeps relatively accurate count regardless of the various charging sources used. For example, we just got shore power after a year on the hook and let the Victron charge the batteries to full - stopping only when it actually quit float mode after ~20 hours and turned itself off. Checking the "amps from full" on the BM showed +23A on the 675Ahr bank. That seems pretty accurate to me considering it has been counting for a year with alternator, solar and generator charging sources and many days below full charge. It is possible that I reset the counter once or twice throughout the year - I don't recall.

This behavior is the same regardless of the charging source - I don't know why you singled out solar as different. I'm pretty sure our BM doesn't count solar amps any different than alternator amps, or even knows what source is present at any time.

Mark

[Maine Sail]

Originally Posted by colemj

Can you explain this more - particularly the solar part? Lets say the batteries are under a 5A load and the solar panel is putting in 5A. Our battery monitor with a single shunt passing all in/out current will show "0" on the ammeter and the "amps from full" will decrease very slightly through time because it is programmed so that the charging source is less efficient than the load draw (puekert, charge efficiency, etc).

Over time, our "amps from full" counter keeps relatively accurate count regardless of the various charging sources used. For example, we just got shore power after a year on the hook and let the Victron charge the batteries to full - stopping only when it actually quit float mode after ~20 hours and turned itself off. Checking the "amps from full" on the BM showed +23A on the 675Ahr bank. That seems pretty accurate to me considering it has been counting for a year with alternator, solar and generator charging sources and many days below full charge. It is possible that I reset the counter once or twice throughout the year - I don't recall.

This behavior is the same regardless of the charging source - I don't know why you singled out solar as different. I'm pretty sure our BM doesn't count solar amps any different than alternator amps, or even knows what source is present at any time.

Mark

Mark,

The answer very often lies within how you programmed the monitor and how it came from the factory.

This is how Victron describes synchronization: (Note: Xantrex uses identical parameters for re-set likely because their monitors used to be built by the same company)

Originally Posted by Victron Energy

"1.2 Synchronising the BMV

Originally Posted by Victron Energy

For a reliable readout, the state of charge as displayed by the battery
monitor has to be synchronized regularly with the true state of charge of
the battery. This is accomplished by fully charging the battery. In case of
a 12 V battery, the BMV resets to “fully charged” when the following
“charged parameters” are met: the voltage exceeds 13.2 V and
simultaneously the (tail-) charge current is less than 4.0 % of the total battery capacity (e.g. 8 A for a 200 Ah battery) during 4 minutes.

Tail current. When the charged current value is below this percentage of the battery capacity (Cb), the battery can be considered as fully charged. Make sure this is always greater than the minimum current at which the charger maintains the battery, or stops charging.

That last sentence tends to sum up why I mentioned solar. Unlike a battery charger or alternator solar does not always have the oomph to hold the current above "tail" even if the battery can take it. This can lead to tricking a monitor into synchronizing too early. Solar late or early in the day or with clouds or rain can mimic a charger or alt tapering the current even when the bank will take more...

We also have all sorts of other reason why they get out of sync like CEF, Peukert, capacity loss etc..

I only post this information because I see so many out of whack battery monitors that are either improperly programmed, improperly wired or where they are likely getting tricked into an early reset when a charge source mimics low tail current & voltage parameters...

It sounds like you've done a good job programming your monitor I just wish I could say the same for more of them..

[colemj]

Ah, I see where I was confused. I don't have our BM programmed to automatically reset itself. I just let it count. What you say about solar is only applicable if the BM is allowed to reset itself automatically. Personally, I think allowing it to do this removes valuable insight into the system - which is why I have ours set for manual reset.

Mark

[Maine Sail]

Originally Posted by colemj

Ah, I see where I was confused. I don't have our BM programmed to automatically reset itself. I just let it count. What you say about solar is only applicable if the BM is allowed to reset itself automatically. Personally, I think allowing it to do this removes valuable insight into the system - which is why I have ours set for manual reset.

Mark

And why I always recommend manual resets, even when set for automatic...

[chicodesouza]

Sorry if my question is stupid, I'm really a dummie and I'm studying to learn more about the electric part of a boat.
Whereas a battery charge, it is an energy receiver and is connected in parallel with the circuit of service.
Without the use of an MPPT circuit, I understand that the service may receive a relatively much higher voltage than supported, which could cause burning of many components!
Is this correct?

[noelex 77]

Originally Posted by chicodesouza

Without the use of an MPPT circuit, I understand that the service may receive a relatively much higher voltage than supported, which could cause burning of many components!
Is this correct?

The solar panel should be connected to a controller (or sometimes called a regulator) and the controller is connected to the battery. The controller stops the battery voltage going too high.

There are several types of controllers MPPT and PWM are the most common.. MPPT extract a little more power from the panels, but they both do an equally good job in stopping the battery voltage going too high. Good MPPT controllers are expensive and cheap ones do not work well, but PWM controllers are fine.

If your solar panel is small (under 10w) you can connect it directly to the battery otherwise you need a controller to protect the battery and electronics.

[careka]

Victron 150V-70 amp MPPT ? or Outback 150V-80amp which one is the best ?