Re: Converting my Amel 54 to lithium batteries: what I did, what I like and what I don't like (after one year of full time live aboard use)
Scott SV Tengah
Good timing on your question. I have figured out a way to have the Victron BMS control the Mastervolt Reg-on wire. I purchased this solid state relay at the suggestion of Peter Kennedy (PKYS):
It is very low current draw so the Victron BMS successfully triggers it. However, as a solid state relay, there's around a 1 volt drop across the relay! So I ended up up adding two more Hella relays. Excuse my layman's explanation but this is how it works:
1) The Crydom solid state relay coils are triggered by the Victron BMS. As you may recall, the Victron BMS sends a voltage-high on the charge disconnect wire (a bit less than battery voltage) when all is good and then goes open circuit when there's a problem and charging needs to be stopped.
So I have this charge disconnect trigger the solid state relay.
2) Because the reg-on wire is also the alternator voltage sense wire, the 1 volt drop across the Crydom relay isn't acceptable. So the load circuit (is that the right term? I'm talking about what is passed through when the Crydom relay is closed) controls a 24v Hella relay's coils. The 24v Hella relay connects battery positive to the reg-on of the Mastervolt. So when the BMS is happy, this 24v relay provides the battery voltage to the reg-on wire, which turns on the Alpha Pro and allows the alternator to charge but also provides the voltage sense to the regulator. We'll call this Relay2
3) However, I didn't want that 24v hella relay triggered 99.999% of the time, which it would be because 99.999% of the time, the Victron BMS charge disconnect "all is ok" signal would activate the Crydom relay and consequently activate the 24v Hella relay. So, to solve this problem, I added a 12v relay that is controlled by the Volvo ignition. We'll call this Relay3. It's easy to get that because the original Amel setup has a 12v relay there already, so I just spliced off that. When the ignition is on, the 12v relay closes and pass through 24v, which is used to power Relay2. In that way, Relay2 is only energized/activated when the ignition switch is on.
I hope this makes some sense and perhaps if you do understand it, you could make an electrical diagram that explains it to others in a simple way.
Note: The Crydom's terminals are exposed, as you can see. I put liquid electrical tape over the whole thing to protect it. Your ELK-924 relay seems to be a good solution too. I didn't see a voltage drop across the relay, so maybe that allows you to get rid of what I call Relay2. However, I think the Crydom is bi-stable and I believe it draws little to no current when activated. Not sure about your proposed relay.
I noticed you don't have an external BMS. I suppose the Battle Born batteries have an internal BMS that disconnects the battery when it detects overly high or overly low voltage? My understanding is that if your chargers (alternator/solar/multiplus) can get damaged if they are outputting a lot of current and you suddenly disconnect the battery. The way the Victron VE.BUS BMS charge disconnect works is that it tells the chargers to stop charging. Seems the Battle Born system just disconnects the batteries and does nothing to turn off the chargers? Maybe that is ok, but you will need to investigate.
I have installed two simple switches to control my Victron Quattro. Pretty sure you can do the same with the Multiplus
1) The first switch is to turn the charging portion of the Quattro on/off. I run the VE-Config software and added an assistant called "charge current control". The switch simply passes through 24v that I got near the autopilot above the galley sink and goes to an Aux Input 1 on the Quattro. The charge current control assistant then dictates what happens. When the switch is activated, the Quattro charges at 120amps. When it is inactivated, it doesn't charge. This allows me to easily turn off this big load to assist with warm up and cool down of the generator.
2) The second switch turns the inverter portion on/off. There's a remote switch input built into the Quattro. I measured Quattro inverter's idle consumption to be 40watts! That's nearly 40 amp hours a day! So now we just turn the inverter on when we need it. Sure, you can get the $125v Victron control panel to do this, but I find this simpler, cheaper and it doesn't consume energy.
Keeping state of charge low when I leave the boat for extended periods
I think I figured out a way to keep the battery in the healthy SOC range for lithium batteries when I am away from the boat for extended periods. Keep in mind I have 960w of solar, but you can easily apply the same solution if you're just plugged in. When we left the boat over the summer for a month, the batteries sat at 100% for a month in hot Southern Virginia. Not good for the batteries.
When I leave the boat, I will use the BMV-712's built-in bi-stable relay to turn on the inverter (using the remote switch wiring I mentioned above). I have a 220v AC (200w) dehumidifier that will be plugged in. When the BMV-712 hits 65% SOC, it will close the relay. That will turn on the inverter and the humidifier will start running and drawing down the SOC. The relay will stay closed until the battery SOC gets down to 45% and then the relay will open, which then will turn off the inverter.
I think by using this method, I'll keep the batteries in their optimal 45-65% SOC range and also have the dehumidifier run daily. Win-win. I don't recall you having solar, but you could probably achieve something similar with shore power. Just remember to dial down down your charge current on the Multiplus, otherwise the dehumidifier could never draw down the SOC otherwise.
Generator Start-Stop and "load disconnect"
There's a way to have the BMV-712 trigger the Quattro's programmable relays to start/stop the Onan. I have started to think it through but haven't implemented it yet. I am thinking of having the generator automatically start when the SOC drops below 30%. See the 'Alternatives Using Assistants' by Thierry Cortasa below.
Two differences in my plan:
1) Rather than have voltage trigger the start/stop, I will use the BMV-712 bi-stable built in relay to do that. The output of the BMV-712 relay will go to the Quattro's Aux Input 2. Then I will use the Quattro programmable relay assistants perform the start/stop. I am thinking of having the generator automatically start when the SOC drops below 30% and run the generator until SOC reaches 75%. Note that I can't have this active when I leave the boat for extended periods and setup the BMV-712 to turn on/off the inverter, as described above, since the BMV-712 only has one programmable relay.
2) Another improvement I will make is that I will have the Quattro "Ignore AC" for 30 seconds upon the 30% lower SOC generator startup threshold, to allow the oil to circulate before imposing the huge charging loads. I will do the same when the SOC hits 75% to allow the generator to cool down a bit.
I have been struggling with the load disconnect and have decided I will not add it. Here's my nightmare scenario: I am sailing at night in 45 knots and focusing intently on keeping us safe. The batteries are severely imbalanced somehow and even at 35% overall state of charge, there is one cell that has dropped below the voltage threshold and triggers the BMS to disconnect the load. At this point, I would lose navigation, autopilot, everything electrical. It's an unlikely scenario, but it could happen and the results could be very unpleasant.
To solve this, I will add the load disconnect as an additional trigger to start the generator. If the Victron BMS load disconnect signal is triggered (aka goes open circuit), it will start the generator and charge the batteries to remove that low cell voltage condition. I think this is far preferable to simply disconnecting all electrical devices because it actually solves the cell low voltage problem.
So the generator start/stop will be triggered by either SOC or the BMS sending a "load disconnect" signal. I just need to figure out a way to make sure I can connect both the BMS load disconnect wire and the BMV-712 relay output to the same Aux Input 2 on the Quattro without causing any trouble. Also need to think it through to ensure that if the BMS triggers a generator start, the BMV-712 relay will still turn off the generator when it hits 75%. Just need to test I guess. Thoughts?
Some thoughts/comments on your choices specifically:
- You will need the Mastervolt Masterbus-USB interface to adjust the charging profile in your alternator. Or just borrow one.
- One advantage of using 12v batteries in serial to create our 24v house bank system is that if you have a problem with the engine/genset battery, you can easily borrow one from the house bank. You won't be able to do that with your 24v Battle Born batteries. That said, one huge annoyance of my system using 12v batteries in serial to create 24v is that, annually, I need to disconnect by batteries and charge them individually to balance them out. The cells in a 12v individual battery will balance automatically but two 12v batteries in serial to make 24v will not balance themselves.
Maybe a solution for you is to get a backup 12v starter battery that is connected a battery tender that keeps it topped off whenever you run your generator. That way, you have a backup that stays fully charged in case the single engine/genset starting battery fails in the middle of nowhere.
- Your idea of being able to charge and invert simultaneously is good. I was considering doing that by having my Skylla charge and then my Quattro invert to avoid the 50hz/60hz problem you describe. But frankly, we are going through the P-Canal soon and I think most our cruising route will be in 50hz land and in any event, we're rarely at marinas. In Panama/Colombia I got 230v/60hz power, which my appliances don't love. So what I simply did was turn off the 230v outlets and appliances, run the charger for an hour or two to charge the lithiums and then disconnect shore power. That's good enough for us at the moment. Your solution is obviously preferable if you're going to be spending lots of time in 230v/60hz marinas.
Hope this helps you and everyone else. I welcome comments/criticisms/improvements.
2007 A54 #69