Gel AGM LA v LiFePo4 > electric outboard

[T i m]

Hi all,

We managed to test the electric outboard on a dinghy the other day and on speed 3 (of 5) got over 2 hours out of a 60Ah 12V 'mobility scooter' battery. With the outboard on full speed the current is supposed to be ~30A.

The thing is that whilst the battery is only 60Ah it's f'in heavy (17kgs), especially when trying to load / unload from a small boat.

So, rather than going to an equally heavy 4/ 2.5hp outboard motor, I have been considering the use of LiFePo4 batteries for those 'pottering about' days.

Now, the Lead acid battery should only really be discharged to 50% so my ~60Ah battery is really only 30Ah whereas a 40Ah Lithium can be discharged more deeply (without harming the total cycle count) and so much nearer the 40 Ah capacity. Even if it's only 30Ah it would match the capacity of the LA but be less than 1/3rd of the weight. The other pros for the Lithium battery is the theoretical max cycles (2-3x that of the LA) and a faster recharge time (3-4 hours). A con would be the price but not by as much as I first imagined (~£200 for the LA v £350 for the Lithium).

So, I was just wondering if anyone here had any real world usage experience of this sort of size Lithium battery please and especially when used as a replacement to a lead acid. Golf trolley or mobility scooter perhaps?

Cheers, T i m

[GB]

Sorry to go off at a tangent, but £200 for a lead acid battery?!

That's a 70 Ah deep cycle battery. It weighs the same as your present one, and costs £65. It's still f'ing heavy though.

Could you get two smaller ones and link them in parallel? Each one would then be a bit more manageable.

[Bill]

In message , GB writes

The Halfords one is not a sealed gel-type.

We use 2 car batteries with a 1,2 or both switch in our boat, but I wouldn't want any chance of acid spillage in a boat small enough to use an electric outboard.

[Lee]

Apples and oranges. No way is that a proper deep cycle battery. And it isn't AGM, nor is it listed as spill-proof. Regulations for some types of craft can be quite strict, non AGM/gel may not even be allowed.

That may be a good idea, though it does then mean charging and looking after two batteries instead of just one. Or four instead of two :)

[T i m]

Apparently (average/ round figures) if you had bought it new. ;-)

Apples and pears though mate. The one you show is a 'wet / flooded' battery and the one I have is a gel. Also there is often a difference between a battery marketed for 'leisure' use and one for semi-traction.

I would put them as:

SLI. High cranking current but pretty intolerant to sustained high currents or deep discharges (very thin plates).

Leisure. Don't like high current loads (especially engine starting) but can be deep(er) discharged with less risk of capacity loss than an SLI battery.

Semi Traction. Don't like very high current loads (engine starting) but can sustain moderate high current loads and fairly high depths of discharge with no cycle loss.

Full traction. As above but will sustain even higher continuous loads and depths of discharge (tubular plates forklift / EV etc).

And then you get things like 'Marine' which are a like a SLI / Leisure battery hybrid. ;-)

Or something like that anyway. ;-)

Not sure I would want to run them in parallel but could use them individually, one out and one back (as I was thinking of doing with 2 lithium batteries as the voltage cutoff is even more severe than with lead acid or any other (non Lithium) chemistry actually).

However, when you push a battery harder the capacity also drops so I'd probably get less out of two 30Ah batteries than one 60Ah one (at that sort of loading).

Cheers, T i m

[T i m]

Doh, I said 'apples and pears'. ;-)

But apart from that ... ;-)

Good point, but I don't think it applies (in this instance) to the size of 'portable' craft I happen to be using here.

Just for the S&G's I put the depleted battery on my little Optimate charger and it took a good few days (at 800mA) to charge the battery fully again. ;-)

I think there is an advantage re charging a (LA?) battery slowly, if you are looking for as high a capacity as possible (finer grains but less surface area for higher current or summat).

I am also keen to try the electric outboard on our 16' Canadian canoe and again two LiFePo4 batteries could give us a reasonable range at a reasonable speed and with the knowledge that if we change the first battery over and turn round, we should get back ok again on the second (wind and current allowing etc). Plus we also still have the oars / paddles. ;-)

Cheers, T i m

[Lee]

Hehe fairy snuff :)

That's certainly the conventional wisdom, though I don't know how it stacks up in proper tests.

Is it appropriate to post

again?

So up the creek *with* a paddle lol :) :)

[T i m]

Which is a good / tested plan, especially when you might be 'out on the ocean waves'. ;-)

I think some people do use the bigger and salt-water versions of these 'Trolling motors' (as opposed to 'real' electric outboards that are appearing now [1]) as aux or berthing propulsion on their bigger boats.

It was just really nice to be pootling along (speed 3 equals a casual walking pace on the towpath) in near silence and to be able to talk to your crew and hear all the nature sounds around you.

My favourite sound is that of the wavelets lapping underneath the bow as you also get when sailing (our next use / test of the boat).

Cheers, T i m

[1] We have the M12:

(It's neither me nor my boat and I wouldn't set the motor at that angle nor travel with the rowlocks mounted. ;-)

You then go to something like this (as electric version of a small self-contained (integral fuel tank) IC outboard):

Typical German efficiency and design. ;-)

Then this:

To this (and beyond no doubt): ;-)

[T i m]

Ok and nor me. It sorta makes sense though ... crystal size V surface area etc.

I don't you can post something like that too often. ;)

Better to be safe than stranded, even up a inshore waterway. ;-)

I have an outstanding question with the river authority people re licence fees and what constitutes 'powered' craft?

Like, I know anything powered by a petrol or diesel engine would be 'Powered' by their terms ... and something paddled, rowed or peddled whilst also 'powered' is only done so by 'human power'. Similar with something pulled by a horse then I'm guessing?

Then you have a sailing boat ... that is being powered by the elements but then what of something *mechanically* powered using a onboard windmill connected to a paddle wheel or propeller? Then what of solar electric? It's not using fossil fuels and is also being powered by the elements?

At least the body that cover the licensing on the Norfolk (and Suffolk) Broads give a 30% discount for anything electric powered but why not free like they do with road tax and electric cars as they are both equally making use of the infrastructure?

Cheers, T i m

[Lee]

Because it's assumed that people who want to use a craft in inland waters are (mostly) well-off and thus a soft target? Anything to do with water craft seems to be an excuse to charge disproportionately...

[GB]

Yes, I suppose that sealed gel is a really really big advantage for that purpose. :)

Does the gel really triple the cost?

[GB]

Thanks for explaining it all so patiently. I was genuinely surprised at the cost difference.

I suspect that at least part of the cost difference is down to economies of scale, as far more wet batteries are sold than gel. Similarly with the different types. I wonder whether that explains it all, or is there a bigger dealer margin for all things disability related?

[T i m]

Probably.

True. ;-(

My Dad used to say that 'a boat was a hole in the water into which you could pour money ... ". ;-)

Cheers, T i m

[T i m]

You are more than welcome. It was only my rough understanding of it all. ;-)

So was I (as I bought the battery second had for a fraction of that). I only found the real / current cost when Googling earlier as I was trying to get insurance for the boat and either the electric outboard and batteries ... or the boat plus 4/ outboard.

You could be right. That said, there are quite a few gel / sealed batteries in use out there, from burglar alarms to golf buggies, UPS's, motorbikes and mobility scooters etc.

Again, as Lee mentioned elsewhere re things 'boating', I'm sure there is some of that as well.

Cheers, T i m

[Bill]

In message , T i m writes

Errrm, with all the weight, battery, driver, motor and water in the bottom of he boat at the stern, about half the hull length is out of the water. So the hull speed will be very low, and energy will be going into generating the stern wave rather than moving the boat.

But I've always fancied an electric outboard or a small inboard with battery charged from solar cells. Not sure whether it's feasible, though.

I'm not sure our old Seagull is actually legal anywhere anymore.

[Brian Gaff]

Putting batteries in parallel like this if not actually charging or being used does tend to shorten their charged time I have found. I wonder what special features his 200 quid battery has over a normal one? Brian

[Brian Gaff]

I thought that these days most of these batteries claimed to be anti spill, assuming you make sure everything is secured. Most venting is done in a way that won't let the acid out. There can be, however a very naff smell if its charged in an enclosed area. Brian

[Brian Gaff]

Of course if you use it on a proper like sailing bot, stick the battery down the keel as ballast grin. Brian

[T i m]

I'm not sure that last bit is right Bill. ;-)

Horrible, but if you are talking about the video linked above it's an inflatable and I'm not sure trim makes any difference on them. ;-)

However, Dad (an ex Merchant marinier) impressed on me the need for good boat trim at a very early age (especially when rowing).

Quite.

You can always tell a good dinghy sailor when you see then move forward when on a run to live the stern out of the water if they can.

I'm drying to keep enhance the electric propulsion theme as it makes good sense where low levels of acceleration and low peak / near constant loads are in play (so unlike an EV then). I think the ideal utilisation of that would be an electric narrow boat where you require ballast anyway (so cheap lead acid batteries are still viable), the batteries rarely suffer much in the way of mechanical shock or vibration and there is a fairly large roof, ripe for flexible solar panels. A heavy narrow boat also makes for a good stable platform for a reasonable size wind turbine when moored (or traveling down wind). ;-). [1]

I think the use of 2/'s are still allowed on many rivers and canals (even them running at 10:1) and of course the sea but I'm sure they are being banned on many reservoirs (if IC engines were ever allowed in the first place) or places with sensitive environmental interest. I also understand it's illegal (over here) to sell new 2/'s now days?

Funny you mention Seagulls ... I think I have spent more hours in front of a BS (mostly 40+ and 40 Featherweight than the Silver Century) than any other make or model of outboard and my first formal 'fitter' role was to fit the long range tank and recoil starter upgrades for Dad on any new BS we bought.

We also recently sold a nearly new 40+ that had been hanging in Dads workshop for probably 20 years to a mate who had his BS nicked out of his shed. And another mate has one in his loft he said he would give to me the next time I see him. ;-)

However, as 'tough reliable' as the BS's were, I don't think there is much that would beat the little Yamaha 2hp 2/ for lightness and efficiency.

Cheers, T i m

[1] We hired an electric dayboat / launch from somewhere (can't remember now) and it was quite eerie moving along at the speed limit in near silence ... and hearing all those on motor boats shouting at each other just to communicate. ;-)

[T i m]

Funnily enough, that's exactly what we did when we took the dinghy out the other day. We aren't sailing but I placed the battery under the centre thwart, up against the dagger board casing because there were three of us anyway so I didn't need the battery to act as trim ballast. ;-)

Cheers, T i m