Ideas for Charging My Dinghy

[john61ct]

Originally Posted by Peregrine1983

what’s the best resource you have found for how to build my own LiFePo4s?

Here's my "boilerplate" LFP summary, mostly from Maine Sail

Any and all feedback is welcome, especially if more "canonical" information from the links cited conflict with my summary.

____
Bare cells: ​Winston/Voltronix, CALB, GBS, A123 & Sinopoly

Systems: OceanPlanet (Lithionics), Victron, MasterVolt, Redarc (Oz specific?)

Note nearly **every** vendor, also those of ancillary hardware touted as "LFP ready", gives charging voltages **way too high** for longevity.

My (conspiracy) theory is that manufacturers would prefer their cells get burned out in under 10 years.

EV usage is very different from much gentler House bank cycling. Most EV people talking "lithium-ion" mean other chemistries not as safe as LFP, much shorter lifetimes, and with completely different setpoints and behaviors.

My charge settings for LFP: 3.45Vpc which = 13.8V max for "12V".

Either stop when voltage is hit, or if you want another couple % SoC capacity, stop when tailing amps hits endAmps of .02C, or 2A per 100AH. Note even at the "low" max charge voltage, letting the charge source continue to "push" even low currents long past the endAmps point is **over-charging, and will** greatly reduce lifecycles.

If you can't then "just stop", set Float at 13.1V, but that is a compromise, and *may* shorten life cycles.

With LFP, you don't need to fill up all the way at all, as far as the cells are concerned, in fact it is bad for them to sit there more than a few minutes. Therefore only "fill up" if loads are present, ready to start discharging, ideally right away.

Store the bank as cool as possible and at 10-20% SoC, or maybe higher to compensate for self-discharge, if not getting topped up regularly (I would at least monthly). Letting the batts go "dead flat" = instant **permanent unrecoverable** damage.

Same with charging in below 32°F / 0°C freezing temps.

Persistent high temps also drastically shortens life.

Charging at 1C or even higher is no problem, as long as your wiring is that robust, vendors may spec lower out of legal caution.

Going above 14V won't add much AH capacity, but will shorten life cycles dramatically.

The point is to look at the SoC vs Voltage chart, and avoid the "shoulders" at both ends, stay in the smooth parts of the curve. And of course, we're talking about gentle "partial C" House bank discharge rates, size appropriately and be careful feeding heavy loads like a winch or windlass.

Following these tips, letting the BMS do active balancing is unnecessary and potentially harmful, just look for LVD / OVD and temp protection. Multiple layers of protection are advised if it is a very expensive bank, don't rely on any one device to work.

Check cell-level voltage balance say monthly to start, then quarterly, finally every six months if there are no imbalance issues, but only if that seems safe to you.

This thread is long but informative
http://www.cruisersforum.com/forums/...nks-65069.html

, make sure to give both Maine Sail and Ocean Planet your close attention.

Also MS' summary notes here
https://marinehowto.com/lifepo4-batteries-on-boats/

**Everything** at that site is worth reading, very valuable. He also has great articles in Practical Sailor. His new site under development transitioning the pbase content is here

https://marinehowto.com/support, feel free to make a donation to help with those expenses.

Best of luck and do please report back here

[fritzdfk]

My boat has an Echo-Charge for the starting battery. I would like to also charge a dinghy battery. Can I use a second Echo-Charge? I have looked at battery to battery chargers but they are quite expensive granted they can be much higher amps.

[john61ct]

Yes, as many ECs as you have separate target banks. Just that, in general, larger/fewer banks is a better idea.

Also, watch out for voltage drops, and be aware EC's are limited to 15A and one-way only.

Combiners, VSR / ACR have greater ampacity, suffer less voltage drop and are two-way.

[CFS Klopas]

My plan to charge my 100 Ah dinghy battery is to wire it in parallel with my starting batteries straight to the alternator or shore power. I inherited a battery charger and a 20W solar panel from the previous owner, don't know whether either of those work. The 2500 W inverter does work. All of the batteries are lead acid.

[john61ct]

Be careful if you drain the bigger battery way down and connect to even a full Starter, you may not be able to crank until after charging.

If that possibility concerns you, use a VSR so the connection only happens once charging is underway.