Charging lithium dinghy battery?

[kayakerChuck]

We're planning to cruise to the North Channel later this summer. We have a small dingy with an electric trolling motor & 100 amp Lifepo4 battery. In the past, we've never needed to recharge while on the boat. I've always been able to take the battery back to my shop. We will be away from shore power for a week or more & will need to recharge the dingy at some point.

I've done very well getting deals on goodies for our O'Day 30. She has a Balmar 70 amp alternator, ARS-5 external regulator with battery & alt temp sensors, and 240 watts of solar.

Am I correct in thinking that I just need a 12v dc to dc charger suitable for lithium batteries? Something like a ORION TR 12/12-30A? This would get wired to my main dc bus- I think. I suppose I could also use a 110v charger powered by the inverter. That would not be terribly efficient, but this is for occasional use only. "Frugal" is good.

thoughts?

[Orin]

You could use a Orion TR Smart series. It’s important that it’s the smart series if you’re charging lithium batteries.

What’s the exact model of the battery?

[Jammer]

Most often the lithium batteries people use for trolling motors have an integral BMS, e.g. Dakota Lithium and most others specifically sold as trolling motor batteries.

For a one-off trip, if you can use the inverter and your existing charger, that's what I'd do.


Otherwise, if the trolling motor battery has an integral BMS, you can use any DC-DC charger with it. Follow the instructions that came with the battery on the permissible maximum amps.

[kayakerChuck]

Currently, I'm using a pair of PowerPSonic PSL-12450E batteries, which do have an internal BMS. Before our trip, I will likely replace them with a single 100 amp Lifepo4, probably a KiloVault HLX+ 1200.

The charger I'm currently using for the lithium is a giant, precision power supply at my shop. It's a bit of overkill :-)

It sounds like I'm overthinking this, which will hopefully prevent future problems.

[Adelie]

Mount a 50-100W panel above the transom of the boat.
Anecdotally that is enough to keep the battery charged except days where you take hours long motoring trip.

[Fuss]

Originally Posted by Adelie

Mount a 50-100W panel above the transom of the boat.
Anecdotally that is enough to keep the battery charged except days where you take hours long motoring trip.

Do you have any pictures of your dingy Adelie?

[Adelie]

I have not done this myself yet, I have seen it and heard from folks that did, hence anecdotal.

2-1.5” square aluminum posts bolted to transom sticking up 30-48”.
Panel sits flat atop posts. Leaves room for trolling motor under and is aft so not where people sit. High enough to decrease splashing somewhat.
Photo below shows what I’ve seen but on a larger hard dinghy with a panel that would be too big for an inflatable.

100W panel would give you about 33Ahr/d using MPPT controller. That’s approximately 1hr at full throttle.

I would mock it up with 2x2s & plywood to figure out height, geometry, maximum reasonable panel size etc before committing to aluminum.

For the trolling motor get a Kipawa prop and keep the stock prop as a backup.
Stock props are optimized to better acceleration and for throwing off weeks.
Kipawa will give you a bit high max speed or 15-20% more range as time speed.
https://www.kipawapropellers.com/

If you get a MinnKota get one with DigitalMaximizer.
This is a PWM motor controller that uses less power at any speed except max speed.