Victron solar charge controller for LFP?

[john61ct]

A short time on the Victron web site or google-foo will clarify all.

Venus or Color GX are the best comms hubs.

https://www.victronenergy.com/suppor...nloads/manuals

[dutch-barge]

[QUOTE=tanglewood;2786994]I have been considering using one or more Victron MPPT solar charge controller on an LFP bank, but some of the things I have been reading make me wonder how suitable it is for the. The issues/questions are:


1) I have seen comments about voltage control of at best 0.1V. That seems very imprecise for LFP.

<<<
It all boils down to the battery management system with should be integral with the batteries.

LFP is not simply a drop in place option.....Each battery bank should have its own management system which has the FINAL say over what others. the MPPT, the smart alternator etc TRY to do

[CatNewBee]

All this is a non issue. Voltage measured is dictated sole by the battery SOC, the LFP have a very low inner resistance, no MPPT charger can dictate the voltage at all, so the output voltage does not matter.

It is only important to stop charging when the cells reach a specific voltage. This can be done on different ways, like a signal from the BMS or from the battery monitor BMV - whatever makes you happy. The most Victron MPPT controler have a control input to turn them remotely on and off if you are too paranoid about the voltage. Some can be controlled by the Venus devices too if you trust more CAN busses and digital datagrams instead of digital on/off signals.

Any way, the internal logic is more than capable to do all necessary switching reliably herself, and she recognizes automatically if there is a communication fault than falls back to the pre-settings - if you do not trust the BT wireless interface, so safe enough too. And WHEN there is a voltage drop, that means an earlier switch off BEFORE the cells reach 100% SOC, so even safer for battery life.

There is no reason to discard the Victron controllers, they are pretty good and fit great in a LFP setup.

[tanglewood]

Originally Posted by john61ct

A short time on the Victron web site or google-foo will clarify all.

Venus or Color GX are the best comms hubs.

https://www.victronenergy.com/suppor...nloads/manuals

I understand there are ways to connect the wires. But to work, the Quattro (for example) needs to send the measured voltage over its network, the hub needs to receive and convert that to the other network(s), and the MPPT needs to be able to receive and act on the data on its network. I don't know if I should expect this to work, or not.


It seems the consensus advice is to use the BMS to control chargers rather than relay on the chargers themselves.

[CatNewBee]

Best is to program the chargers correctly, anything else is a bonus.

[tanglewood]

Originally Posted by CatNewBee

Best is to program the chargers correctly, anything else is a bonus.

That's what I've been striving for, with BMS intervention as a secondary safeguard.

[john61ct]

Just read the Victron manuals for Venus or Color GX, and the other specific gear, they make it clear which connections work for each.

BMS is functionality, all this gear where it protects the battery is included AFAIC.

A centralized point that controls all charge sources is an abstract ideal IMO.

Or at least beyond what I consider good value.

Each charge source should have reliable and user-adjustable regulation, whether internal or external may depend on the source.

Or a DCDC charger may provide that, perhaps for all primary sources.

Then, for an expensive LFP bank, there should be an additional layer of defense to protect it in the event one of the usual daily-use regulators fail.

If you have "a BMS", that usually works as that innermost last layer of defense.

[dutch-barge]

Originally Posted by tanglewood

I understand there are ways to connect the wires. But to work, ........ I don't know if I should expect this to work, or not.


It seems the consensus advice is to use the BMS to control chargers rather than relay on the chargers themselves.

Have you emailed Victron? they can easily answer this..I always found them very responsive to questions, even during off hours, holidays and closed times

[john61ct]

Originally Posted by tanglewood

I understand there are ways to connect the wires. But to work, the Quattro (for example) needs to send the measured voltage over its network, the hub needs to receive and convert that to the other network(s), and the MPPT needs to be able to receive and act on the data on its network. I don't know if I should expect this to work, or not.

Note with lead banks like GEL, where it is important for longevity to regularly get to 100% Full as per endAmps,

no matter what Victron gear you have, they removed the ability to stop charging (drop to Float) based off BMV measured trailing amps directly in a firmware update.

Therefore the user must tweak Absorb Hold Time upwards until that goal is reached, and perhaps check it when usage / conditions change if overcharging is a concern.

Not an issue with LFP, where there is no need to get right up to Full, when in doubt just stop short, set AHT to minimum, lower voltage a bit. . .

[CatNewBee]

Originally Posted by tanglewood

I understand there are ways to connect the wires. But to work, the Quattro (for example) needs to send the measured voltage over its network, the hub needs to receive and convert that to the other network(s), and the MPPT needs to be able to receive and act on the data on its network. I don't know if I should expect this to work, or not.


It seems the consensus advice is to use the BMS to control chargers rather than relay on the chargers themselves.

There are two different ways, one is the data bus with messages and the other more reliable is by switching on and off of a contact that controls charging. You can program this on the Quattro and on the MPPT to either stop charging or force to float at a pre set voltage. So you are flexible to do what you think you need to do.

The quattro has various inputs and outputs you can use for different tasks using macros too. Just RTFM, it is all there.

It is really easy to create the automation you are envisioning.

[tanglewood]

Originally Posted by CatNewBee

There are two different ways, one is the data bus with messages and the other more reliable is by switching on and off of a contact that controls charging. You can program this on the Quattro and on the MPPT to either stop charging or force to float at a pre set voltage. So you are flexible to do what you think you need to do.

The quattro has various inputs and outputs you can use for different tasks using macros too. Just RTFM, it is all there.

It is really easy to create the automation you are envisioning.

We are talking about different things. I'm aware of the various programming options on the Victron products, programmable control inputs and outputs, and actually have RTFMs.


I was asking a specific question about whether the voltage remotely sensed by a quattro is communicated to other devices over the ve.bus and other Victron data communications buses. There are at least three such coms buses used in different products of different generations. A product like the Color display has connections to all the different coms buses, so there is a way to connect the wires. But that says nothing about what information is conveyed over those buses, what's bridged by the Color display, and what's listened to by the MPPT. That's not in the manuals.

[tanglewood]

Originally Posted by john61ct

Note with lead banks like GEL, where it is important for longevity to regularly get to 100% Full as per endAmps,

no matter what Victron gear you have, they removed the ability to stop charging (drop to Float) based off BMV measured trailing amps directly in a firmware update.

Therefore the user must tweak Absorb Hold Time upwards until that goal is reached, and perhaps check it when usage / conditions change if overcharging is a concern.

Not an issue with LFP, where there is no need to get right up to Full, when in doubt just stop short, set AHT to minimum, lower voltage a bit. . .

OK, but has nothing to do with the question.

[CatNewBee]

Originally Posted by tanglewood

We are talking about different things. I'm aware of the various programming options on the Victron products, programmable control inputs and outputs, and actually have RTFMs.


I was asking a specific question about whether the voltage remotely sensed by a quattro is communicated to other devices over the ve.bus and other Victron data communications buses. There are at least three such coms buses used in different products of different generations. A product like the Color display has connections to all the different coms buses, so there is a way to connect the wires. But that says nothing about what information is conveyed over those buses, what's bridged by the Color display, and what's listened to by the MPPT. That's not in the manuals.

OK, now got it.

The Quattro indeed has a sense wire for the voltage, and also internal shunts and SOC calculation, like a built in BMV, but not so usefull and precise, it is meant for a battery buffered 240V system like a UPS.


If you have other charging sources and loads, you want the shunt to monitor all sources and loads, so Victron recommends in all circuit blueprints a BMV for the measurement of the voltage and the current, connected to the CGX as the brain of the system, that controls the quattro, the MPPT chargers etc. The voltage sense wire is only used in stand alone configuration of the Quattro as far as I know, but the data gatheted is shared over the CAN protocol to be displayed, you can see it on the MK2 USB interface on the PC along with grid input voltages, currents, output voltages, current, battery voltage, current, power, frequency etc.

I guess, it can be used, but Victron recommends to use a dedicated battery monitor.

[newhaul]

Originally Posted by Cpt Pat

I can't stress this enough: you can overcharge a 12 volt (4 series cells) LFP battery with a terminal voltage as low as 13.6 volts (with some chemistries, even lower). This is especially insidious when charging the battery with a low current - like a solar array. This is why "trickle charging" an LFP is so strongly discouraged. Charging begins at about 13.4 volts -- and with a low current charging source it needs to end after 13.6 volts has been achieved for some random amount of time. That's only a 0.2 volt difference! When charging at higher constant currents, such a 0.2C rate or higher, you can detect the 100% SoC point by a tapering off of the charging current. That detection cannot be performed with low and varying charging current from a solar controller.

Employing only terminal voltage detection to determine when to stop charging is "lead-acid thinking." This is the hardest concept to get over with LFP batteries: terminal voltage only reflects state of charge at a very specific charge current and temperature. That charge current is neither constant nor achievable with a solar power source (unless you have thousands of watts of panels).

The manufacturer's voltage curves assume you are charging the battery with far more current than you are likely to ever see from a solar charging source. If you have a 100 AH battery, you'd need a constant-current source of 50 amps for those curves to be valid.

The charge/discharge versus voltage curves for LFP batteries presume a high charge current. Usually the lowest charge current shown in those curves by the manufacturer is 0.2C (if you can find the curves at all). When charging with a solar controller with 10% or less of that current, you need to use a combination of "coulomb counting" (counting amp/hours in and out) and terminal voltage to detect SoC. Here's a paper on the topic: https://arxiv.org/ftp/arxiv/papers/1803/1803.10654.pdf.

Fortunately, the charge controller can do terminal voltage detection (within the accuracy constraints you have already described) and the BVM-712 can do coulomb counting by configuring it to open its internal relay contacts at your chosen SoC set point (I use 80% SoC) for charge discontinuation. I also set a charge cutoff voltage at 13.8 volts, but that only applies to charging with my (0.2C) shore power charger. With solar panels, 80% SoC occurs at 13.6 volts (with some small variance due to temperature). That a per-cell voltage of only 3.40 volts.

I calibrate the BMV to 100% SoC every few months by continuing the charge from my shore power charger at a constant current rate of 0.2C, at or near an ambient temperature of 25 degrees C, until the charge current tapers to 0.05C.

Since you can safely use terminal voltage for discharge discontinuation, I use the BVM low voltage detection for stopping discharge (I use 12.7 volts). In my installation, the BVM relay contacts drive a high-current external relay (be sure to install a reverse polarity snubber diode across the relay coil to absorb inductive flyback).

I would not trust the BMV switch contacts to carry more than 2 amps, so beware of some high current latching relays that draw 7 amps when actuated. Such as this one: https://www.bluesea.com/products/cat...Relays/ML-ACRs.

The reason I chose 80% SoC as the charge cutoff threshold (which appears wasteful) is to accommodate the reduced charge capacity of the LFP at lower temperatures. I couldn't get temperature-dependence data from the manufacturer for inclusion of temperature compensation to the charge cutoff threshold. It's a tradeoff. If the LFP has a built-in BMS that takes the battery offline, I would only trust that as a last ditch "ejection seat" control.

please provide some white sheet references. As well as actual hard data on all of the items you profess to have.

[john61ct]

Cross fertilization

http://www.cruisersforum.com/forums/...oc-212196.html