What charging precedence strategy are you using with your REC-BMS-controlled-Victron-Energy-LiFePO4 marine system?

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MeltemiCaz

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Hello All,

What charging precedence strategy are you using with your REC-BMS-controlled-Victron-Energy-LiFePO4 marine battery system?

I have Multiplus-IIs, a main engine driven alternator using a Wakespeed WS-500 regulator, VE MPPT solar charge controllers, VE battery chargers all connected to the Cerbo-GX with DVCC turned on.

My charging will be through the main engine alternator, shore power connection, and the solar charge controllers. The strategy needs to accmodate dock-side charging, at anchor and underway with the main engine until I raise the sails, at which point I will either rely only on the 1100 watts of solar, or the generator (as needed).

I think that VE has the ability to prioritize charging, but do not know how well it woks. I plan on looking into it today.

What technique are you using to program your system to use the cheapest charging sources given the REC-BMS and the Cerbo GX components?

If there is an existing thread, I have not found it.

Thanks in advance!
 
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I'm not using a REC BMS, but so far I have not found a good way to prioritize charging sources when charging is BMS controlled. Victron does have a feature to prioritize solar, but that it really does is de-prioritize Multi charging. If you just have a Multi and solar, it's the same either way, but if you have other AC (shore or generator) powered chargers, or an alternator, they will not be de-prioritized. So it's kind of a half-baked solution. But if you are sitting on shore power and want your solar to do all it can, then let shore power make up the difference, it seems to work.
 
I'm not using a REC BMS, but so far I have not found a good way to prioritize charging sources when charging is BMS controlled. Victron does have a feature to prioritize solar, but that it really does is de-prioritize Multi charging. If you just have a Multi and solar, it's the same either way, but if you have other AC (shore or generator) powered chargers, or an alternator, they will not be de-prioritized. So it's kind of a half-baked solution. But if you are sitting on shore power and want your solar to do all it can, then let shore power make up the difference, it seems to work.
I'm noticing the same. I had hoped that there is a more automated approach other then manually turning on/off charging sources. VE appears to be actively working on this, but I'm not sure how mature their DVCC and solar charging protocols are at this point. I hear that they are iterating on this issue as they work to perfect their algorithms.
 
in order to use solar via the batteries to power the loads normally supplied with the inverter you need to turn off the AC input to the multiplus.

To do that you can either trip the input breaker or better yet on the cerbo choose inverter only mode.

You might be able to automate that, perhaps with an "assistant" but it won't be valid for all potential situations as the multiplus as far as I can tell cannot descriminate between shore power and generator power.
 
Not seeing a reason to prioritise. Solar is direct to batteries, is it not, so it will either charge or feed loads. The inverter charger from either shore or GEN will charge until it senses full charge based on voltage.

I always thought the charger with a bit higher output voltage fools the other charger which shuts off. That is how I saw it with two alternators, one would back off near full charge.
 
Not seeing a reason to prioritise. Solar is direct to batteries, is it not, so it will either charge or feed loads. The inverter charger from either shore or GEN will charge until it senses full charge based on voltage.

I always thought the charger with a bit higher output voltage fools the other charger which shuts off. That is how I saw it with two alternators, one would back off near full charge.
If your chargers are individually programmed and controlling charger, as they traditionally would, you can prioritize one over another by making slight adjustments to their target voltages.

It's a bit different with DVCC because the chargers are all taking directions from the BMS, and they all get the same directions. So you have no way to bump one up a bit, or bump one down a bit. This was really evident on my boat because when on shore power, I was not getting any output from my solar panels. All the boat's DC loads were being covered by the charger in the quattro, not by solar. Turning on Victron's priority feature causes the quattro to back of a slight amount, and now I get contribution from my solar. It's not a lot, but I'll take it.
 
TT, it sounds like you prefer/want solar to charge in preference to any other charger. I guess I would as well after the investment.
I READ HERE about DVCC and I must say a simple matter of charging batteries becomes complicated.
 
TT, it sounds like you prefer/want solar to charge in preference to any other charger. I guess I would as well after the investment.
I READ HERE about DVCC and I must say a simple matter of charging batteries becomes complicated.
I was very skeptical of DVCC, mostly because it's new, and all the devices need to behave correctly, etc. - basically new tech that needs to be debugged and shaken out. I kind of got forced into it to work around Victron's stupid Multi behavior of not starting a full charge cycle when AC power is applied unless the battery voltage is below a certain level. I'd run a generator to do something else like make water, and expect to opportunistically charge batteries, but the Multi (quattro in my case) wouldn't start charging. DVCC fixed that, so I started using it.

It does have a number of advantages.

- You don't have to worry about what charging parameter's your battery wants because the BMS already knows.
- You don't have to program individual chargers because the BMS tells them what to do, and when to do it.
- If charging needs to be adjusted because of a cell imbalance, the BMS commands that. Individual devices don't have visibility into individual cell status, so can't respond on their own.
- If you want to put the system into some sort of storage mode, like if it will be on shore power for a few months, you can tell the BMS to do that, and all chargers behave accordingly.
- The BMS knows the exact voltage for the battery and shares that with all devices. That gives all devices remote battery voltage sensing, with no need for adjustments of offsets.
- If a battery wants a bit longer charge so it can do cell balancing, the BMS can command that.

So there is a bunch of good stuff that comes from it. The down side is that if something goes wrong, a lot can go wrong. Plus it's one more thing to understand about how your boat works.
 
In the Magnum programming there is a setting for always bulk charge when AC power becomes available when it has been off for 2 minutes or more, but only until absorbtion voltage is reached and then it quickly steps down to LFP controlled float. Have tested it when fully charged and it was minutes before it went back to float.

I have remote monitor and when the power goes out for many hours it is inverting as needed and as soon as it is back on I can see charging bulk>absorb>float voltages.

Victron does not have a bulk always when power comes on?
I think that is a great feature for LFP batteries as as rebulk voltage level would/could take a long time. Maybe it is due to LFP not needing to be 100% charged and the previous thought that it should not be left fully charged.
 
I'm reading through this blog where the author is describing their journey to achieve automatic prioritization of solar over shore-based charging.

The author's quote caught my attention; "It doesn’t make sense to me to use utility power to charge the batteries and run the RV’s loads when I have 1.3 kilowatts of solar on the roof. So, the question is, how do I control shore power-based charging to work for my situation?"

Maximizing solar production with Victron GX

and here is the VE take on Solar & Wind Priority charging
 
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In the Magnum programming there is a setting for always bulk charge when AC power becomes available when it has been off for 2 minutes or more, but only until absorbtion voltage is reached and then it quickly steps down to LFP controlled float. Have tested it when fully charged and it was minutes before it went back to float.

I have remote monitor and when the power goes out for many hours it is inverting as needed and as soon as it is back on I can see charging bulk>absorb>float voltages.

Victron does not have a bulk always when power comes on?
I think that is a great feature for LFP batteries as as rebulk voltage level would/could take a long time. Maybe it is due to LFP not needing to be 100% charged and the previous thought that it should not be left fully charged.
In my experience what your Magnum does is the norm. I was surprised by Victron. Some products have a setting where you can select what you want the charger to do on appearance of AC input, but with Victron it never goes into bulk unless the battery voltage is below a fixed level.
 
I'm reading through this blog where the author is describing their journey to achieve automatic prioritization of solar over shore-based charging.



Maximizing solar production with Victron GX

and here is the VE take on Solar & Wind Priority charging
Thanks. The VE method is what I was describing and am using. It just doesn't cover the case where I'm underway for 8+ hrs and should be using solar to it's max rather than burning more diesel with the alternator. It's small, but small things add up.

The feature Ben found is interesting and not one I was aware of. But I don't think it really covers what I'm looking for when on shore power. I want every watt of power pulled out of the solar panels and used, and I only want shore power drawn to make up the difference between solar and total consumption onboard. I don't think the Ben feature accomplishes that. It think it's more about shifting large loads over to the grid rather than placing them on the battery/inverter system. So, for example, everything runs off your solar/battery/inverters, but when you turn on your HVAC, it kicks over to grid power. Then when the HVAC cycles off, it kicks back to solar. That's certainly useful in that scenario, but different from making sure every drop of solar is harvested and used before consuming grid power.
 
TT, do you have the MPPT direct to the batteries or via a buss bar or is it going into a Victron product? If direct;

Have you tried bumping the MPPT to 0.1v higher than the victron on bulk and absord?
 
We have been running a REC-BMS controlled Victron system for a few years in our previous boat. The system includes Victron Multiplus, Wakespeed WS-500 (alternator), and a Victron MPPT. As discussed above, the REC-BMS controls everything and does not appear to provide any ability to prioritize charging source. As TT mentioned, Victron does allow for "prioritization" of solar (sort of), and we would also see some solar production while siting on shore power (but probably not full production).

We are in-process installing a similar system in our new (to us) DeFever, because overall I really liked how the system operated.

The one thing I am hoping REC has updated is providing a mechanism to control SOC in a storage situation. The REC-BMS likes to keep the batteries fully charged, which did not seem to cause significant degradation - but I like to have more control.
 
TT, do you have the MPPT direct to the batteries or via a buss bar or is it going into a Victron product? If direct;

Have you tried bumping the MPPT to 0.1v higher than the victron on bulk and absord?
I'm not sure I follow what you mean by "direct to the batteries or via a buss bar or is it going into a Victron product?", or why it's significant. All are interconnected, via buss bar, and are Victron products. So the answer seems to be "all of the above", which makes me think I'm not understanding the question.

The issue I have experienced is that my MPPT controllers are controlled by the BMS via DVCC just as the quattro is controlled, and just as my AC power charger is controlled. Via DVCC, all see the same battery voltage, and all are charging to the same setpoints as commanded by the BMS.

If I were not using DVCC, I would do just as you describe and set the MPPTs a touch higher. In theory that would cause them to be the primary contributor. However it's not quite that simple because they don't have remote voltage sense and that will throw things off to some degree.
 
We have been running a REC-BMS controlled Victron system for a few years in our previous boat. The system includes Victron Multiplus, Wakespeed WS-500 (alternator), and a Victron MPPT. As discussed above, the REC-BMS controls everything and does not appear to provide any ability to prioritize charging source. As TT mentioned, Victron does allow for "prioritization" of solar (sort of), and we would also see some solar production while siting on shore power (but probably not full production).

We are in-process installing a similar system in our new (to us) DeFever, because overall I really liked how the system operated.

The one thing I am hoping REC has updated is providing a mechanism to control SOC in a storage situation. The REC-BMS likes to keep the batteries fully charged, which did not seem to cause significant degradation - but I like to have more control.
I don't know if the REC BMS has this ability, but the Victron stuff lets you limit/cap the DVCC voltage. So when I'm going to be sitting on shore power for a prolonged time, I limit the DVCC voltage to 26.5V and that holds the batteries at about 50% SOC. So far it seems to work well.
 
TT. These victron assemblies are foreign to me. You say the BMS controls it, is that the BMS inside the battery or a victron product?
My batteries have BMS and they do decide when they have had enough charge, but do not decide where to get the charge. There is where I am confused when you say BMS controls.
 
I'm not sure I follow what you mean by "direct to the batteries or via a buss bar or is it going into a Victron product?",
I am trying to determine if the load lines from the MPPT go directly to the positive/negative of the battery. Or first to a victron product (like DVCC?)
 
TT. These victron assemblies are foreign to me. You say the BMS controls it, is that the BMS inside the battery or a victron product?
My batteries have BMS and they do decide when they have had enough charge, but do not decide where to get the charge. There is where I am confused when you say BMS controls.
There is a whole class of BMSes that have different forms of "communications" that can be used to control charging. With some it's a simple "allow to charge" signal that can be used to enable and disable chargers. With others it's a set of CANbus message where the BMS continually broadcasts it's voltage, current, temperature, etc., and also what max voltage and max current the battery can accept. Chargers and other devices listen to those messages and limit output voltage and current accordingly. If the BMS wants more, it says give me more, and any chargers that can do so will do so. If the BMS wants less, it says give me less and the chargers make it so. There are two defacto standards for doing this. One is RVC which is commonly used by RVs, and the other is DVCC which is a Victron concoction.
 
I would bypass and go straight the battery terminals or bussbar from MPPT for solar, then add the 0.1v to be higher than the cutout for other chargers. Yup the DVCC is stopping you from doing it your way.
Managed CAN-bus batteries: In systems with a managed CAN-bus BMS battery connected, the GX device receives a Charge Voltage Limit (CVL), Charge Current Limit (CCL) and Discharge Current Limit (DCL) from that battery and relays that to the connected inverter/chargers, solar chargers and Orion XS. These then disable their internal charging algorithms and simply do what they're told by the battery.
DVCC must be enabled for the GX device to control the solar chargers, Inverter RS or Multi RS in a system with a VE.Bus BMS V2.
  1. DVCC charge current limits are not applied to DC MPPTs when ESS is enabled with Allow DC MPPT to export. This is to get maximum output from the solar panels for export.
 
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