Victron MPPT Battery Charging Algorithm

[noelex 77]

Originally Posted by travellerw

That is interesting, mine are usually only a few minutes apart from Absorbtion to Float (max I would say 10 minutes). I wonder if this is due to my solar arrays being very physically close together. They all must "wake up" at the same time.

The other thing my controllers do. If the voltage drops due to load increase or sun loss, then they switch back to Bulk really quickly (within a min or so). At that point all three will go back to Bulk and begin putting in power. They do this even if all 3 are sitting in Float and I kick on my water heater. This seems to line up exactly with your first post.

Our three solar panels are identical located side by side and in a very shaddow free location (for a yacht). They wake up times are identical, or very close together.

If you are only noticing a few minutes difference between the absorption times this is indicates your controllers is not meeting the “tail current cut off” criterion where the problems occur.

The rapid return to bulk is an unusual part of the Victron algorithm. It is necessary mostly because the absorption phase does not track voltage so the SOC at the end of the absorption phase is very variable. A rapid return to bulk helps ensure the SOC is boosted if the SOC is low at the end of the previous “absorption” cycle. It is very unique solution that Victron has adopted.

[Wotname]

Noelex77, now that you have 2.5 years of additional experience, what are your thoughts now about these Victron solar charge controllers?

Or is there a more recent thread about them that I have missed?

[noelex 77]

Overall the small Victron Smartsolar MPPT controllers have been excellent (I have three 100/20 units).

When I first purchased the units the charging algorithm was very quirky, but this was completely changed in one of the software updates. The new charging algorithm is very different to the original and is much better, solving all the original issues. The software updates have also added some good new features and much greater user adjustability.

These units now have an excellent and highly customisable charge algorithm.

The tracking performance is very rapid and probably one of the best, although this is still an area where improvements could be made by all manufacturers.

The parasitic power consumption is very low, and this combined with the relatively low price makes these units excellent for the preferred one panel per controller set up.

There are a few drawbacks. The units rely on passive cooling that keeps them quiet, but they run hot and I wonder about the lifespan, especially if installed in a hot environment and running close to their maximum power. I oversized my units and installed some additional aluminium heatsinking and a larger air gap. I have had one unit fail. It was replaced under warranty. It occurred quite soon after purchase so I suspect it was a simple manufacturing fault rather than a progressive failure due to heat, but the redundancy of multiple controllers is probably a sensible precaution.

The other area that could be improved is the cable connections that are rather small on some of the units. There are also some reports of corrosion so install these units in dry area.

The final concern is a relatively high and non adjustable start up voltage. This is only a concern if you are using “12v” panels, and even then seems to have very rarely caused any practical problems. However, these controllers are perhaps the best choice for “12v” low voltage 32 cell panels connected in parallel, especially if you have other charge sources such as a wind generator, and cruise in a hot climate.

[rslifkin]

On the cooling topic, I know the Victron controllers have internal temperature sensing and will throttle their output if they get over a certain temp (I think it's 40* C) to control heat load. If you're concerned or they're installed in an area that might get warm, I'd either size up by a model or point a fan at the heatsink to keep them cooler.

[Lost Horizons]

Originally Posted by noelex 77

Overall the small Victron Smartsolar MPPT controllers have been excellent (I have three 100/20 units).

Any thoughts on having three smaller units versus a single one with a higher charging current, such as 100/50? How did you route six wires through the deck?

[noelex 77]

Originally Posted by rslifkin

I'd either size up by a model or point a fan at the heatsink to keep them cooler.

As well as upsizing the units (20A capability when 14A is the maximum expected current), I mounted the units on some aluminium profile. This was attached using heatsink paste.

The profile adds some extra area to the MPPT heatsink, doubles the size of the air gap behind the heatsink and also makes the wiring a little neater.

I have no evidence that these measures will make any practical difference to the reliability of the controllers, but the photo below shows how it was done.

[Wotname]

Originally Posted by noelex 77

Overall the small Victron Smartsolar MPPT controllers have been excellent (I have three 100/20 units).

When I first purchased the units the charging algorithm was very quirky, but this was completely changed in one of the software updates. The new charging algorithm is very different to the original and is much better, solving all the original issues. The software updates have also added some good new features and much greater user adjustability.

These units now have an excellent and highly customisable charge algorithm.

The tracking performance is very rapid and probably one of the best, although this is still an area where improvements could be made by all manufacturers.

The parasitic power consumption is very low, and this combined with the relatively low price makes these units excellent for the preferred one panel per controller set up.

There are a few drawbacks. The units rely on passive cooling that keeps them quiet, but they run hot and I wonder about the lifespan, especially if installed in a hot environment and running close to their maximum power. I oversized my units and installed some additional aluminium heatsinking and a larger air gap. I have had one unit fail. It was replaced under warranty. It occurred quite soon after purchase so I suspect it was a simple manufacturing fault rather than a progressive failure due to heat, but the redundancy of multiple controllers is probably a sensible precaution.

The other area that could be improved is the cable connections that are rather small on some of the units. There are also some reports of corrosion so install these units in dry area.

The final concern is a relatively high and non adjustable start up voltage. This is only a concern if you are using “12v” panels, and even then seems to have very rarely caused any practical problems. However, these controllers are perhaps the best choice for “12v” low voltage 32 cell panels connected in parallel, especially if you have other charge sources such as a wind generator, and cruise in a hot climate.

Thanks Noelex 77, very helpful information.

Can you expand on the reasoning of the emphasised portion in your last sentence? Maybe I have missed something but I not sure why this is so.

[noelex 77]

Originally Posted by Wotname

Can you expand on the reasoning of the emphasised portion in your last sentence? Maybe I have missed something but I not sure why this is so.

The tracking, voltage conversion and other processes used by MPPT contollers needs some power to drive the circuitry. In addition, there is some loss of power through the solar panels when connected to the batteries under very dull light conditions. Because of this parasitic drain all MPPT “go to sleep” minimising the power loss from the operating circuitry and disconnecting the solar panels at night.

They periodically sample the solar panels to try and determine if it is time to “wake up”. Most controllers use solar panel voltage as the only, or at least the primary factor in determining if they should “wake up”.

The Victron controllers use a reasonably high start up voltage. The solar panel voltage must be over +5v higher than the battery voltage before this wake up sequence begins. Once “awake” they only require +1v to stay awake, but the initial +5v condition must be met before any power is produced.

Thus if you have solar panels that have a relatively low voltage such as 32 cell “12v” panels in hot conditions, there is a danger this +5v start up condition may not occur until the sun has reached a high altitude, wasting power. As the +5v is relative to battery voltage, a charge source such as wind generator that may keep the battery voltage higher overnight will also exacerbate the risk. This is not a concern if the batteries are fully charged by the wind generator, but a small charge source can keep the resting voltage well above the typical 12.5v (or lower) morning voltage even on a battery that may not have a high state of charge.

As an example, if the wind generator has been running overnight the battery may be 14v in the morning, thus a Victron controller will not produce any power until it senses the solar panel voltage is over 19v. Typically the open circuit voltage of “12v” solar panels is above this value at around 22v at STC conditions. However, this specification is always measured in very bright light with cold cell temperatures, no shadows, clean, new panels. Thus there is a risk the controller may not meet the start conditions using this type of panel in some situations, at least early in the morning.

I would stress that this only concerns those using “12v” panels (singly or in parallel) and that in practice even then it seems very rare, but it is hard to find good data. I suspect many users may not recognise that their chosen controller is not “waking up” at the optimum time.

The easy way to check is ideally at solar controller start up (you need to get up early in the morning ) the controller output should be zero if the start up criterion is ideally set. If the solar controller wakes up and the solar panels are immediately capable of producing significant power then the controller has “woken up” too late. If the solar controller wakes up and there is net power loss from the parsitic drain the solar controller has “woken up” too early. Waking up too late, or too early, both waste precious power, but only waking up significantly too late has the potential to waste (or not collect) large amounts of energy.

On some of the better controllers the “wake up” criterion is adjustable, but this is rare. The setting more often set by the manufacurer and Victron have chosen a high value compared to other controllers. The Victron setting works well with high voltage panels and is usually, but perhaps not always, fine with “12v” panels. Thus I would suggest caution teaming these controllers with “12v” panels (in parallel) especially if the chosen panels open circuit voltage is on the low side.

The Victron literature suggest series connection partially for this reason, but this works less well on a shadow prone boat installation. One controller per panel or parallel connection is generally better, especially for yachts.

It would be great if we could have some more feedback from users to determine if this is only a theoretical problem or something that does occur in real world situations. My panels have an open circuit voltage of around 50v so this is not a problem I can personally check, indeed a higher start up voltage would be slightly better, not worse, for my panels.

[Wotname]

Again thanks Noelex 77 for a great explanation of how the Victron wakes up and yet there seems to an inconsistency with what you have recently posted (OR maybe I'm just thick).

Back in a previous post you stated " However, these controllers are perhaps the best choice for “12v” low voltage 32 cell panels connected in parallel, but now you have stated " Thus I would suggest caution teaming these controllers with “12v” panels (in parallel) "

So I remain confused - are they the best choice or not the best choice. Although after reading your explanation of how they wake up, it seems they aren't the best choice.

[Peeew]

I have two Victron mppt controllers and the smartsense Bluetooth link. My controllers seem to synch well and will start bulk charging as soon as the controller output voltage exceeds the battery voltage at the smartsense device by any small bit of voltage above battery voltage.

[noelex 77]

Originally Posted by Wotname

So I remain confused - are they the best choice or not the best choice. Although after reading your explanation of how they wake up, it seems they aren't the best choice.

There is no perfect solar controller for every installation, but the Victron Smart series are hard to beat.

If you have high voltage panels there are no issues with the Victron controllers. If you have low voltage 12v panels (these are becoming less common) I think you need to be prepared to monitor the output and possibly connect them in series mode, or a combined series/parallel mode.

[Wotname]

Originally Posted by noelex 77

There is no perfect solar controller for every installation, but the Victron Smart series are hard to beat.

If you have high voltage panels there are no issues with the Victron controllers. If you have low voltage 12v panels (these are becoming less common) I think you need to be prepared to monitor the output and possibly connect them in series mode, or a combined series/parallel mode.

OK, that makes sense to me now.

I appreciate your detailed explanations of the Victron controllers upthread and I have learnt more about the fine detail of these units from this thread than hours of reading the Victron on-line literature.

While the overall operation of solar charge controllers is a straightforward concept, the devil is always in the detail and you have 'simplified' such detail.