Any thoughts on the following plan and comments to the open questions are appreciated.
Current setup: Boat in the Nordics, 12V systems, currently AGM batteries with Charger, no solar.
Open questions:
Option 1 or 2 for battery connection (see picture)
Personally I’m leaning to option 1.
Victron or Sunbeam MPPT, 1 or 2 each? (see picture)
Victron:
* Pros: VE.Direct comms
* Cons:+5V for startup
→ Might not startup on cloudy mornings/shading? but will show up on Cerbo and talk with BMS Sunbeam
* Pros: +1.25V for startup
* Cons: No comms (except BT to proprietary app)
→ Starts up reliably but does not talk with BMS. Might need a shunt to view solar input on Cerbo? Need to setup MPPT lower float and/or absorption voltage than MP-II to overcome the missing comms?
3. Does MPPT-battery side need a switch? Some designs have, but some people point out that if that switch is turned off when panels are not covered/disconnected, mppt might blow.
4. Add Battery protect behind main switch to cutoff loads if needed? Or is this redundant and if I’d forget to turn the mains switch off when leaving the boat and if battery SOC would go low enough then BMS would just cut all power? (although then the bilge pump etc would be without power)
5. Should there be a battery isolator switch? Placed to the left or right of BMS? Just in case boat is on-land over winter and for some reason the batteries would have to stay in the boat. Or as an emergency all systems cut-off switch.
Not in the diagram but I’m curious why there is a fuse on the neg wire (in addition to pos wire) from batteries to the main busbars. Can anyone think of a reason?
Battery wiring choice is yours. opt1 requires additional hardware.
2 - solar wiring: one may only wire panels in parallel if the Voc matches to within 5% so you may need to look more closely at the PV module ratings.I would avoid these modules as the system voltage is so limited - why?? This may lead to lack of isolation and current leakage.
Better to have modules rated to better than 100v system voltage, and be able to wire 2 in series for better MPPT performance.
3- MPPT’s should at least have a fuse for the input,switch is not strictly necessary. PV should always be turned off first.
4&5 are related. there should be a battery isolator switch, however, the bilge pump may be connected to the battery side of that switch. The fuse in the negative cable should be removed.
Thanks Mike.
Battery wiring I’m leaning to Opt1 because EF fuse that should fit the distributor seem to have AIC rating of up to 50kA whereas MRBF fuse is up to 10kA. Some would say that with Lithium should use T-Class but with 12V I’ve read that arching is extremely unlikely to happen in the event of fault. Theoretically MRBF could fail but EF should be safe.
Solar wiring/MPPTs - There will be a fuse in the distributor so MPPT battery side, and a fuse/dual-pole breaker on the PV input side. I was just wondering when I might need to disconnect the MPPT battery side with a dual-pole breaker, which would also be a fuse so then I’d have double-fuse But good point about putting different panels in parallel, it might be best then to go with option 2 on the solar so two MPPTs. Unfortunately I don’t have space for bigger panels and since they’ll be installed on the deck, they need to be robust, something you can walk on so, have cable coming from underneath (so look nice) so there aren’t a ton of options. Also to my understanding series installations suffer if one panel is even partially shaded, and that is very likely on a sailing boat. Therefore I’m thinking parallel would be better, even with reduced MPPT performance. Which MPPT would be better - I still don’t know.
There is already a mains switch as can be seen on the picture (on the right side), behind which almost all of the loads are already connected. We use that when leaving the boat for a longer time, but have forgotten it once and I guess the charger or something had almost drained the battery when we were away. So a battery protect might be good to have so there would be some power left for bilge pump, since if BMS cuts the batteries off than nothing will have power.
Currently there isn’t a battery isolator switch, so something that would give the ability to cut batteries from everything, and not sure if something like would be needed. I’ve seen some people putting those in, but not sure if there is a specific reason related to Lithium. Most of the Victron example diagrams don’t have one.
And yeah, the negative cable fuse is strange. It’s factory installed and is in the electrical diagrams. Just wondering why it’s there.
If anyone has sunbeam or similar panels and have real experiences with either MPPTs please chime in.
But good point about putting different panels in parallel, it might be best then to go with option 2 on the solar so two MPPTs. Unfortunately I don’t have space for bigger panels and since they’ll be installed on the deck, they need to be robust, something you can walk on so, have cable coming from underneath (so look nice) so there aren’t a ton of options. Also to my understanding series installations suffer if one panel is even partially shaded, and that is very likely on a sailing boat. Therefore I’m thinking parallel would be better, even with reduced MPPT performance. Which MPPT would be better - I still don’t know.