Lithium Conversion

kennharriet · Posted: Sat Apr 12, 2025 10:08 am Post subject:

Sure appreciate all of the experienced wisdom from the group. I ended up ordering the Renogy 20amp non MPPT dc-dc charger (50% of BF90D alternator output of 44 amps). I also ordered two 100ah Renogy Core mini Li batteries, mostly because of their small size and fit in the lazerette. My planned layout is AWG 4 ga wire from the motor to an 85 ah Vmax AGM located in the port lazerette. Then 8 ga wire from the AGM through a 30 amp ANL fuse to the dc-dc charger in the starboard lazerette. From the charger through a 40 amp ANL fuse to the Li batteries also in the starboard lazerette. 200w of solar will also feed the Li batteries through a 40w MPPT charger and 50 amp ANL fuse. The house load will be fed through a 60 amp breaker to a new Blue Seas distribution panel and fuse panel. Everything is marine tinned wire and connectors. Per Bobs earlier advice the windless is on the house battery. I like he simplicity of this set-up. I removed the Yardina Combiner used in the previous system.

Does anyone see any holes in this setup? Looking forward to three months on the water starting in Skagway May 18, with our heads full of stories from Jay and Jolee. Thanks again for the discussion, Ken

shad · Posted: Sat Apr 12, 2025 11:44 am Post subject:

kennharriet · Posted: Sat Apr 12, 2025 1:46 pm Post subject:

Great points Shad! I’ll incorporate your suggestions. 🙂. I will need to make a custom battery tray for the group 22F lithiums as I don’t see anything commercially available that small.

robhwa · Posted: Mon Apr 14, 2025 1:22 am Post subject:

Depending on your usage and need for charging from the alternator, it seems a shame to only get 20A from the alternator. If you look back at my configuration with the 50A (max) charger, you can set the DC/DC charging between 10-50A in 10A increments. Mine is currently set to 40A and it shows no sign of overheating. I earlier set it to 30A and then, with experience, upped it to 40A, nearly the Honda 44A output. The setup with the single DC/DC MPPT unit saves a little money and simplifies wiring a bit. You would also only need to buy one BT2 if you want to monitor charging with a smart phone (a nice touch). The only downside I can see is that if there is enough sun for solar charging, my system won't also charge from the alternator, but that hasn't been a problem that I can see. I have a switch to cut off solar when motoring. With your configuration, I guess you could possible get 60A total charging (40A from solar plus 20A from alternator) when you are running on a sunny day. The downside is that it doesn't appear that your system will use your solar panels to keep your charging battery charged when the boat is sitting unused. You should always run your motor when using the windlass, and mine works fine from the house batteries. I also often use the house batteries to run a bow-mounted trolling motor, which is a heavy load on the batteries when trolling.

thataway · Posted: Mon Apr 14, 2025 1:39 pm Post subject:

kennharriet · Posted: Mon Apr 14, 2025 2:38 pm Post subject:

Thanks Rob and Bob. My newer Honda BF90D is fuel injected with 44amp output. Everything I read suggested the dc-dc charger should be rated not more and preferably less than 50% of the alternator output. I may have errored on the side of caution and ordered the 20 amp non MPPT unit. I will have the BT2 for remote monitoring. When motoring, the Alaska series dingy will be on the roof and cover the 200w solar panel. It is true that I will not be able to maintain the start battery with solar but then its only load is motor starting when it is immediately getting charged by the alternator. Worse case scenario the Honda 90 can be started with a pull rope which I have practiced just in case. After this season if not adequate, I may want to upgrade to the MPPT dc-dc charger. I’ll report after I’ve used the system.

Thanks again for the great advice. Interesting stuff. I’m enjoying learning from you all. Good thing I made a living as a wildland firefighter rather than a marine electrical engineer. 😂

thataway · Posted: Mon Apr 14, 2025 3:00 pm Post subject:

It will be interesting to see to what the actual output is. With the magneto type of "alternator" it should not overhead, as a belted alternator may. Let us know how it works out!~!!

Punkin Drublic · Posted: Mon Apr 14, 2025 7:12 pm Post subject:

robhwa · Posted: Fri Apr 18, 2025 7:05 pm Post subject:

Bob had asked what kind of output I actually see (I read that as amps from the alternator) from the nearly-new Honda BF100, and Ken had cautioned that conventional wisdom is that you shouldn't use a DC/DC rated or set to more than 50% of rated outboard output, which I have greatly exceeded at 40A for my BF100. Since the outboard charging system isn't a belted alternator I thought temperature wouldn't be as much of a problem as with a conventional alternator...maybe a mistake. I'm currently fishing in Brazil, but will put a shunt on my alternator side when I get back to test output. I'll also test the system charging depleted batteries and monitor temperature with my Flir. Normally, you connect a DC/DC between the starting and house batteries, as I have, so alternator output might be "filtered" a bit by the starting batteries resistance (it is standard Pb-acid). I'll put the shunt on the other side to see, and see if I can get temperatures high enough to be concerned. I don't want to dial back (via reduce the DC/DC setting) the potential charging from the engine if I don't have to. I want all of the charging I can get. Ken; I was a forestry professor for almost 40 years, and greatly appreciate the firefighter community. I wish you luck in the future.