Electric boat design review request and specific questions

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ev-gavia asked Jul 3, '21

Electric boat design review request and specific questions

Hello! We are building a 25' all-electric boat, with various Victron components and hoped to get some advice from the community. Questions are up top with details of the system farther down.

Questions:

Battery Protection: We need to have battery under/over voltage protection on the 48V bank, but the largest 48V battery protect from Victron is 100A, which isn't high enough to have just one (We anticipate a potential burst load of say 8kW for 30 seconds or so, which is a 166A load). We could monitor each individual 48V battery with a separate BatteryProtect, but is this the best way to monitor and protect the batteries?

General System Design: Does anyone see a problem with what we have proposed in the diagram below? Any gotchas to watch out for? We are hoping the Cerbo GX and GX Touch 50 + iphone apps will provide monitoring and alarms for system operation.

12V system and battery: We need a 12V battery and require monitoring and protection for it, ideally victron branded and something we can monitor using with the GerboGX alongside the rest of the system. It doesn't appear that the 12V batteries from Victron natively connect to the Cerbo GX, will this require a BMV712 or smartshunt to be monitored? And if so, which is recommended?

Solar System: We will probably have two different sizes of solar panels on the roof of the boat, potentially with different nominal voltages, would that require two different solar charge controllers? Thoughts on flexible vs rigid panels, and the Victron charge controllers that would be best? We haven't purchased the panels yet so needed details are missing but any general advice is appreciated.

Diagram:

Background:

Gavia Electrical System Design

Description: Gavia is a 25’ all-electric solar motor boat under development.

48V DC System: The motor is a brushed 7.5 kW DC 48V Thoosa Electric Motor. We hope the nominal draw will be around 1-2 kW while under way, but short bursts (1 minute) of 7.5kW are expected (we have not tested the boat in the water yet). Energy will be provided by a 48V lithium-iron battery bank. Solar cells on the roof will be the primary recharge method, hopefully 1kWp or greater, with AC shore power and backup 1kW generator for AC charging on-the-go. A hybrid inverter/charger should be a convenient way to pack lots of functionality into one box, and AC input/output should be 120V (we are in the USA).

12V DC System: The 12V DC system will be used to run low-wattage house electronics (navigation, radio, windless, house lighting, etc), and 12V bow thruster whose max draw is 1500W. This larger 12V draw necessitates a 12V energy bank (vs relying on DC-DC converter), so a 12V 100+A lithium battery will be used and it should recharge from the main 48V system.

120V AC: 120V AC will be used for a minimum number of appliances onboard, the largest of which is the induction cooktop with a 1800W maximum draw. This will be provided by the hybrid inverter/charger.

Note that we do not anticipate running the high power loads at the same time. For example, we won’t run the induction cooktop while the electric motor is running.

Here are some system components:

Inverter/Charger: "PMP482305100 MultiPlus-II 48/3000/35-50 120V"
48V Bank: SimpliFi PHI 3.8-M ("PHI3.8 48V 60 VTE BRK") wired in parallel (x4)
Onboard component monitoring (interior): "Victron Energy BPP900455050 GX Touch 50" with "Victron Energy BPP900450100 Cerbo GX". Onboard component monitoring (exterior helm station): ipad similar device running victron app, with weatherproof case
Battery Capacity Shunt: "Victron Energy SHU050150050 SmartShunt 500A/50mV"
Battery Protect: Undervoltage/overvoltage protection: The batteries have a BMS, but we need an additional protection for the battery bank as a whole or the individual batteries.
12V DC Charger: We will use an AC battery charger to charge the 12V bank. We cannot use a DC-DC charger for this because the Victron DC charger is not isolated; the motor requires no other DC systems on the negative side of the 48V system
12V House Loads Battery: something with 1kWh of energy and built-in BMS, and some way to monitor the voltage.

MultiPlus Quattro Inverter Charger Battery Protect 48v battery

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Answer 1 · 2021-07-03T17:21:29Z

Battery Protection:
The BMS in the battery will provide this protection. I would get the new 3.8 with Coms. You should confirm with SimpliFi but once all connected it should act as one big battery and you don't have to worry about Over Current, Overvoltage and Undervoltage. This should be handled by the BMS.

General System Design:
Use a DC-DC, Victron make Isolated Converters
https://www.victronenergy.com/dc-dc-converters/orion-tr-dc-dc-converters-isolated
You do not want to be running the inverter to charge your 12V battery.
Orion-Tr 48/12-30, you can control it via the remote input. Turn it on and off with a switch or Cerbo relay.

12V system and battery:
You can't monitor the 12V battery with that one GX as the coms cables will break isolation.
Probably just install a smartshunt and use bluetooth to see status. If you would like automated charging of this battery, I would install second GX.
You would also probably want to install 2x 100Ah BattleBorn batteries so you can output the enough power to run the Bow Thruster and all the other electronics, Radio, Nav, etc at the same time.
or you could parallel 2x Orion-Tr 48/12-30 and have them automatically enable if the bow thruster is turned on to give you an extra 700W. Which would be way cheaper.

Solar System:
You are going to want to have diffrent MPPTS for the diffrent arrays to get the most out of the panels. I would go with a lot of smaller MPPTs vs 1 big one so that you get the most out of the panels.

Diagram:

Looks good except DC-DC.
Multiplus Fuse : 125A
Over-current protection: None, BMS will do it.
Battery Protect: None, BMS will do it.
Battery Fuse: Min 400A, this should be a secondary backup if battery breakers fail. I would personally install 4x 125A, one on each battery lead. Victron Lynx is a nice 1000A bus system.
Solar Fuse: Depends on MPPT, if you are using 250/100 then 125A, if 250/60 then 75A, etc.

I would also move the battery disconnect to the motor controller and not on the whole pack. As you can just turn off the battery breakers if you need to do maintenance or would like to shut the system off. You would probably want to leave the PV connected when the boat is not in use to keep the batteries charged and maintained.

Generator and Shore power should both be connected through the 3 position selector switch (also know as a change over switch), so you can only chose one or the other. You can not have grid and generator connected together.

Just my thoughts

Answer 2 · 2021-07-06T20:46:52Z

hoeken answered · Jul 06, 2021 at 08:46 PM

Love to see a cool project like this. Here are my suggestions:

1. With a small portable gas generator like that, just make a short 'shore' power cable to plug it into your shore power inlet. Much easier than wiring in a switch. If its permanently installed, then nevermind. If you have shore power you won't want to be running a noisy gas generator anyway.

2. Smartshunt should be fine. I just saw you need to keep the 48v stuff isolated. For the 12v smartshunt, you can use bluetooth to monitor it, so no problem. If you really want that integrated with the Cerbo, maybe you could try a USB isolator from Amazon and a VE.Direct to USB cable?

3. Is this a new build? If so, highly suggest getting 48v windlass and bow thruster. Current will be much less and you can use smaller cables. If working with existing stuff, stick with 12v.

4. Rigid solar panels have much better life than the flexible, and if you mount them with a gap so there is airflow, they will give you better output. I've heard good things about Sunpower modules. A lot of marine installs use one regulator per solar panel in case one panel gets shaded, then only that module reduces output instead of all the panels in parallel/serial. For different size panels you will want one charger each.

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Answer 3 · 2021-07-08T23:28:25Z

northwestnick answered · Jul 08, 2021 at 11:28 PM

I am also using a Simplihi 3.8-kW 48V LiFePO4 battery to power a boat. In my case, a 16' sailboat with a 1-kW electric outboard.

SimpliPhi techs advised me to use a Battery Protect or equivalent to disconnect the motor if the battery voltage ever goes below 50.2V (80% DOD).

The only device I've found that can be programmed for low-voltage disconnect at that setpoint is the Victron SBP 48/100. So I bought one, carefully designed my system so it would never see backfed current, and...

...immediately destroyed the thing by connecting it to an inverter. Actually I'm not sure if it was the inverter or the outboard motor. Both presumably have capacitors on the input, which (I now know) is instant death for BP's. Mine welded itself in the "on" mode, so it never disconnects. Now it's a pretty doorstop.

So beware. The Battery Protect cannot handle even the slightest whiff of reverse current, from a charger or a charge controller or any device with a capacitor. Zero. The installation manual says nothing about damage from inverters, but it's very real. What the manual DOES say is that connection to an inverter will cause the BP to activate "short circuit protection". This is untrue. No E1 error ever occurred. It just cooked itself silently and I would have never known had I not tested it.

I would assume that a significant fraction of BP's out in the field are similarly damaged and their owners have no idea.

At least with 12V and 24V systems, there are other options. But for 48V, especially with a custom setpoint, the SBP 48/100 is pretty much the only choice. So I'll be buying another one, but this time I will have it power a contactor rather than the load itself. I'd advise you to do the same. Hopefully the back EMF from the contactor coil won't ALSO fry the SBP.

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shaneyake commented · Jul 09, 2021 at 12:27 AM

Yes, you will need to use a contactor but even a contactor will fail over time. You need a pre-charge circuit if you are going to put something in between inverter or motor controller and battery. Victron recommend you use AC or MPPT to pre-charge the bus before connecting batteries.

Most motor controllers can programmed for low-voltage shut off and all victron inverters can also be programmed for low voltage shutdown. This is a much better way to do it and then possibly have a shunt trip breaker or contactor as a last resort controlled by a Victron BMV but the BMS will disconnect the pack at this point anyways so it is also unnecessary.

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northwestnick shaneyake commented · Jul 09, 2021 at 12:54 AM

Thanks for the reply! I've got multiple loads, not just a motor and inverter, so I'm looking for global low-voltage protection. Yes, contactors fail too, but generally in the open position (whereas mosfets usually fail in the closed position).

What I'll really miss is the super low current draw of the Battery Protect. The most efficient contactor I've seen for my application draws around 44 mA, compared to < 2 mA for the BP 48/100.

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shaneyake northwestnick commented · Jul 09, 2021 at 02:37 AM

You could also always use both.
BP 48/100 for other loads and Contactor or built in control for inverter and motor controller. Have a switch that you flick if you want to use the motor. So the contactor is only enabled then motor is needed an not all the time but the power to the switch comes from the BP so it would still shut off at low voltage.

I have had contactors weld closed (from startup inrush current) but you are correct most times the contacts inside burn up and it goes open circuit.

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ev-gavia commented · Jan 06, 2022 at 04:19 PM

Thanks for the reply! It is good to know there are more SimpliPhi's being used for marine applications. The tricky part regarding the low-voltage disconnect with our boat is that this boat it is 100% motor powered, so we can't disconnect the motor at 80% state of battery discharge; we will certainly alarm on that condition but we can't disconnect since the boat will lose propulsion which could potentially be dangerous.

I would love to see results of low and high voltage disconnect testing on the SimpliPhi 3.8

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