Good subject and lots of useful info.  
I have to say that soldering wires is an art I have never mastered, copper pipe fitting I can do.

Plain, un-tinned  copper will corrode at the joint, would solder tinning the wire ends before crimping be a good idea?  Likewise a copper strap.

Anonymous wrote:

Darren,

Excellent tips regarding the charge controllers, thank you!

Jami,

As for LiFePo4 in general I really don't see any practical reason* for anyone to use lead acid batteries for anything anymore, so I would've switched even without converting to electric motor. When you factor in usable amp-hours and overall life expectancy, LiFePo4 is actually less expensive and a far superior battery technology.

*) except short-term financial

LiPO4 do have some problems, that mean they're not the best choice for everyone:

1) They are damaged if charged below freezing temps.  This can be overcome, but if you have depleted batteries and can't use them to warm themselves you can get yourself into a pickle.

2) They have a habit of destroying alternators if all you do is add them to an existing boat.  Their high charge acceptance rate will cause many alternators to kill themselves trying to supply the batteries.  This can be overcome, but it means LiPO4 is not a drop-in solution.

3)  You have to have a functioning BMS to keep them working.  With lead-acid batteries you can charge them in all sorts of unsophisticated ways in a pinch.  Not so with LiPO4.

4)  With LiPO4, a single error in over-discharge can destroy the batteries and leave them inoperable.  A BMS should prevent this, yet there are lots of examples of LiPO4 being destroyed this way.

They're still a fantastic battery choice, but there are ways in which lead acid are better.  Something like Firefly carbon-foam AGM can offer a better compromise for someone who wants high-performance with fewer headaches.  For someone who is technically inclined, or with deep pockets, Lithium might make a better choice.

Anonymous wrote:

Do I understand correctly: with those CALB cells you don't even need to solder to make a battery yourself? Soldering (which I just don't seem to master) is the main problem I've been afraid of so far, when thinking of a DIY lithium battery.

To keep the budget down, one could make a 100Ah 24V battery first, and add another one later - right?

It depends... for making the cells into a battery, they provide copper straps which need no soldering (most other cells would be similar having screw on terminals). However, if you are going to make your own cables (which will probably be needed) most people like to use solder even with crimp ends to keep oxygen and water out of the join. There are others who say crimp only as the join may heat and the solder run out and the join fail. Certainly crimp first and solder after as the crimp is what gives a good mechanical join.

Copper straps are easy to make. Use copper water pipe pressed flat, cut to size and drill holes for the terminal screws. The shrink wrap is a nice touch but electrical tape will serve as well.

Yes more cells can be added in parallel later. Most people suggest the exact same kind or at least the same AH but in practice with a slower charge rate that is not needed.

Darren,

Excellent tips regarding the charge controllers, thank you!

Jami,

The cheapest option (apart from buying second-hand cells, which would be a viable option) I've found would be CALB cells. Example:

https://www.aliexpress.com/item/4000303299745.html

With these 12V/100Ah would be about €400 (€800 for 24V/100Ah, €1.6k for 200Ah).

In addition you'll need a BMS, which will set you back between €30-200 depending on type/features. If you aren't planning on sailing in freezing temperatures you don't need low temperature cutoff and a Daly would work fine, although it would be a good insurance to have it anyways (if you forget to unplug chargers when wintering).

So for 24V/200Ah €1800 would be in the ballpark.

If buying used cells (90% capacity) it could probably be closer to €1000 although I haven't looked into this extensively. Another cheaper option that some go for is to buy a used electric car battery pack. The problem with this is that they are mostly lithium-ion, which can be a fire hazard, so LiFePo4 is the way to go. LiFePo4 also has better discharge rate and is non-toxic.

Another option (probably better but slightly more expensive) would be to get 200Ah cells.

As for LiFePo4 in general I really don't see any practical reason* for anyone to use lead acid batteries for anything anymore, so I would've switched even without converting to electric motor. When you factor in usable amp-hours and overall life expectancy, LiFePo4 is actually less expensive and a far superior battery technology.

*) except short-term financial

PSA: You can find a lot of good information, reviews and tests in Will Prowse's Youtube channel.

Yes, I was thinking of something of the sort. The magnetic key comes with a lanyard and a clip which will attach to the pushpit, but I was thinking of an additional Velcro band or perhaps just duct tape, though it would be good to be able to remove the key easily to prevent unauthorised use.