LiFePo4 High Level Schematic

[Steve_C]

Originally Posted by mbartosch

Think outside the box.

You will have a LiFePO4 bank which enjoys being held in the middle SoC ranges and which does not like being held near full SoC. Sure, when cruising you want to store and use every Joule of energy your solar cells produce, but at anchor the story may be different. At least we noticed that is the case for us.

When in "at anchor mode" for prolonged time I found it very useful to be able to completely shut down charging sources administratively, to keep the bank e. g. below 80 % even though the sun is shining.

If I am not mistaken, the BMS you plan to use pulls HVC output to ground if HVC is active, so you can adopt the same idea:

You can pull BMC HVC output to ground externally (e. g. with a switch or a relay) and thus simulate a HVC to cut off all charging sources. If the system is properly designed you can do this in all operation modes without damaging your system.

I have a manual 3-way switch at the console labeled "Normal charging" - "Stop charging" - "Lazy charging".
"Stop charging" connects the HVC output of the BMS to ground, forcing a simulated HVC.
"Lazy charging" connects ground to the BMV700 relay which in turn is connected to HVC output of the BMV700. Then the BMV700 can turn charging off at, say, 80% and on again at, say 60 % SoC. Actually we use "Lazy charging" a lot when at anchor.

This all makes a lot of sense, I actually plan to have the HO alternator as backup for prolonged rainy and/or cloudy days just in case! I plan to use the solar as the primary charging source. My day to day operation i'm sure will vary a lot based on location as I plan to travel a LOT.

I defiantly plan to have "Override" capability with a remote switch to allow me to do just what your suggesting. I like the "Lazy Charging" option.

Thanks mbartosch!

[ronstory]

@Mbartosch

In your experience with the BMV700, how accurate has it been tracking SOC of the LifePO4 pack?

[mbartosch]

Originally Posted by ronstory

@Mbartosch

In your experience with the BMV700, how accurate has it been tracking SOC of the LifePO4 pack?

Quite accurate, over a single cycle I'd assume it's off a few percent. However, inaccuracies accumulate over time if no resynchronization is done (by charging to 100 %, the BMV700 resets to 100 % automatically if its reset criteria are reached).

I heard good things about the Balmar SG200 battery monitor which should be much more accurate because it "learns" the battery properties over time.
There's a thread about the device on CF. If I had to build the system from scratch I'd consider using this device.
Two downsides I see:
- it does not seem to have a relay output
- it does not integrate with my other Victron hardware

[Looking4Neptune]

I see you have a Victron Quattro in the plan. Two comments:
1. You can buy the version for 120v shore power OR for 240v shore power, but you have to choose one or the other. As you plan to travel a lot, that may become an issue. I know you said you'd rarely use shore power, but it is nice to have the option.
2. You mentioned you may get a generator. Is that why you chose Quattro over MulitPlus? Otherwise the MultiPlus is probably less $.

Another option is to go with Victron Phoenix Charger that can handle either 120v or 240v, and a separate inverter. One downside of this is that all your AC loads are driven off the inverter so that, even when running a generator or on shore power, all electricity gets converted to DC and back to AC.

I don't know if someone makes an inverter/charger that can take either 120v or 240 (which baffles me). I looked at Victron and Xantrex and could not find one.

[Steve_C]

Originally Posted by Looking4Neptune

I see you have a Victron Quattro in the plan. Two comments:
1. You can buy the version for 120v shore power OR for 240v shore power, but you have to choose one or the other. As you plan to travel a lot, that may become an issue. I know you said you'd rarely use shore power, but it is nice to have the option.
2. You mentioned you may get a generator. Is that why you chose Quattro over MulitPlus? Otherwise the MultiPlus is probably less $.

Another option is to go with Victron Phoenix Charger that can handle either 120v or 240v, and a separate inverter. One downside of this is that all your AC loads are driven off the inverter so that, even when running a generator or on shore power, all electricity gets converted to DC and back to AC.

I don't know if someone makes an inverter/charger that can take either 120v or 240 (which baffles me). I looked at Victron and Xantrex and could not find one.

I am just now starting to shop for a very lightly used Cat to purchase, I do not yet know if it will be US 120 V 60 hz or European 220 V 50 hz. Once I know that I will pick the exact model of the Quatro. My biggest AC loads will be the all electric kitchen (Stove, Induction Cook-top, Microwave, etc..) I have no problem using 220 V 50 hz appliances if that's the original voltage of the boat.

I will not be spending much if any time in the US so not a big deal. When I actually get ready to purchase I would consider the Multiplus, but all things considered the price difference is not going to be the deciding factor. I like the thought of being able to have two AC sources.

[ronstory]

Originally Posted by Steve_C

I have been talking to Maja at REC and learned they are working on a new version of the REC Q 16s but it wont be out for a long time and he can't release the specs yet because they are still working on them. He did verify that the new one will still have only one relay and the same optical ports.

Just a note, Maja is a 'she'. ;^)

[Steve_C]

Ah, thanks! That's really good to know, especially when I communicate with her.

Not the first time I have embarrassed myself

[notz]

I'm not sure if you resolved your bus bar or distribution worries, but I used the Marinco Pro Installer series because of it's higher amp capabilities in my recent LiFePO4 conversion.



They had much higher ratings and solved some of the fusing and distribution issues I was having without lots of cross connects and small, short wiring.

[Steve_C]

Originally Posted by notz

I'm not sure if you resolved your bus bar or distribution worries, but I used the Marinco Pro Installer series because of it's higher amp capabilities in my recent LiFePO4 conversion.



They had much higher ratings and solved some of the fusing and distribution issues I was having without lots of cross connects and small, short wiring.

That looks interesting, I went to their website and they apparently make the Blue Sea line. I am traveling right now and looking at all of this on my phone, so when I get back home I'll check it out a little better.

Thanks!

[ktowers]

One very important piece that you're missing is the field control signal from the BMS to the alternator. Alternator and their regulators assume that there is a battery load connected at all times. When the BMS opens the battery charge circuit at full battery charge and the alternator is running, you will get a "load dump" event. This is a high voltage spike (caused by inductive kick-back when the charge current suddenly stops flowing) that will take out the alternator diodes at the very least and possibly everything else on that bus.

I looked at the REC BMS specs and it does not appear that they have a field control signal. This would be an output that turns off the alternator field voltage prior to disconnecting the batteries. Most BMS's I've seen appear to be oriented at vehicle charging from AC chargers - not alternators.

A very good article to read is at https://marinehowto.com/lifepo4-batteries-on-boats/

[CatNewBee]

Originally Posted by ktowers

One very important piece that you're missing is the field control signal from the BMS to the alternator. Alternator and their regulators assume that there is a battery load connected at all times. When the BMS opens the battery charge circuit at full battery charge and the alternator is running, you will get a "load dump" event. This is a high voltage spike (caused by inductive kick-back when the charge current suddenly stops flowing) that will take out the alternator diodes at the very least and possibly everything else on that bus.

I looked at the REC BMS specs and it does not appear that they have a field control signal. This would be an output that turns off the alternator field voltage prior to disconnecting the batteries. Most BMS's I've seen appear to be oriented at vehicle charging from AC chargers - not alternators.

A very good article to read is at https://marinehowto.com/lifepo4-batteries-on-boats/

No, thats not true, its about you how you design your system and not about the BMS. The REC has 2 pairs of outputs and with a custom firmware you can have 4 independent outputs, further the system has a CAN bus, where you can hook up CAN devices for even more granular control, there is a firmware that talks to a victron ccgx, octo, venus, you name it, where all cell values are populated and you can then use the victron relays for switching. Endless opportunities to switch what you want whenever you feel you need to. There are automotive alternators that have can bus control for energy efficiency tweaking, you can use those, you can add a relay, that controls the field or adds a resistor to limit the current, you can replace the regulator, even with a no name bms you can add a delay relay to the solenoid input, switch off the field first and a programmed time later the Solenoid finally cuts the battery.

But the easiest and most error free way is to let the AGM startbattery always connected. No need for field control on bms switch off.

[Steve_C]

Originally Posted by CatNewBee

No, thats not true, its about you how you design your system and not about the BMS. The REC has 2 pairs of outputs and with a custom firmware you can have 4 independent outputs, further the system has a CAN bus, where you can hook up CAN devices for even more granular control, there is a firmware that talks to a victron ccgx, octo, venus, you name it, where all cell values are populated and you can then use the victron relays for switching. Endless opportunities to switch what you want whenever you feel you need to. There are automotive alternators that have can bus control for energy efficiency tweaking, you can use those, you can add a relay, that controls the field or adds a resistor to limit the current, you can replace the regulator, even with a no name bms you can add a delay relay to the solenoid input, switch off the field first and a programmed time later the Solenoid finally cuts the battery.

But the easiest and most error free way is to let the AGM startbattery always connected. No need for field control on bms switch off.

I do plan to use a Smart Regulator to allow me to control output of the alternator. As you mentioned there are many ways to control that. I am considering leaving the stock alternator in place just to charge the engine start battery, and adding a second 24V HO alternator to charge the bank, when needed. This will just be backup for the solar, and since I don't plan on having a generator.

I would like to have the ability to manually control the states like "High Output", "Low Output" or "No Output" as well as have the Victron system limit charging no matter what manual state I have the system set to.

I don't mind logging into the system to look at and change the system settings or states, but I would want to be able to have a simple, easy to reach switch that would allow me to set the manual states quickly. The Victron system should easily allow to use one of the many inputs to do this.

Once I actually have the main system in place I will focus on this aspect. Initially I plan to just keep the stock charging setup isolated from everything except the engine start battery.

Thanks for all the input!