LiFePO4 (lithium iron phosphate) batteries

[Graham W]

Large capacity lithium-ion batteries of various flavours have been around for a while but are now becoming more common in everyday use.  LiFePO4 batteries seem to be the favoured version as they are more stable, less toxic and less prone to bursting into flames than other types, such as those allegedly responsible for recent Tesla and Boeing Dreamliner "thermal events" (great euphemism!). LiFePO4's are still around 4-5x more expensive than Yuasa-style sealed lead-acid batteries but they claim to be better in the following ways:
* They charge more quickly and hold each charge for longer when not in use
* In use, their discharge rate is consistently flat rather than slowly petering out like a Pb battery, so that more of the battery's power is available.  I find that by the time my Yuasa battery is half-discharged, the voltage is too low for my fishfinder. An equivalent Li-ion battery would keep pumping out 12v until nearly fully discharged and would therefore give greater autonomy between charges - say five days instead of three.
* They are much lighter than Pb
* They last a lot longer in terms of the number of times that they can be recharged before giving up the ghost

Has anybody actually used one on as a house battery on their boat yet? I think Johan E posted that he was thinking of doing it a while back. Are they as good as they claim?

The orange-coloured ones on this page seem to fit the bill - they are easily small enough to fit in front of a BR centreboard case, are waterproof and come complete with charger http://www.deben.com/tracer-battery-packs.html

There are also lithium batteries with exactly the same dimensions as the Yuasa NP18-12 Pb battery, which some of us are using.  For example, see http://www.batterymasters.co.uk/Product-Li20-12,-12v-20Ah-Lithium-Iron-Phosphate,-LiFePO4-High-Capacity-Deep-Cycle-Battery,-Charger-Included.-L%28mm%29-W%28mm%29-H%28mm%29-181-76-167_2249.aspx

I think prices will come down as more people turn to them - they seem to be particularly popular for powering golf buggies and mobility scooters and (needless to say) are already a lot cheaper in the USA.

[Johan Ellingsen]

Hi guys,

Re the above,(see picture of "Lill-Freja" in the hands of the dock-yard mateys!),I have
on board 2x50/12V Ah LiFe batteries,primarily for propulsion.They supply a 600W Minn-
Kota outboard, the Torqeedo solution having proved totally worthless for cruising purposes.I had the Minn-Kota hanging over the side last summer,to prove that the oomph
was adequate,which it was.The calculation was for me to have available 10-15 hours of
"economy power",sufficient for a week's archipelago cruising without putting plug to socket.In fact, I was running around the harbour on numerous occasions in August,not even denting one battery.Been over-ambitious?Next summer will tell.We have dismembered the outboard,experimentally making a new rudder-power assembly(see
pictures).If this doesn't work well,I think the way forward(!) might be a shallow,sloping
"skeg" with the engine at the aft end.
I am very happy with the SB adaptability concept!

Cheers,Johan

[Graham W]

Those are serious batteries!  This is the nearest that I could find to them, only for sale in the USA http://www.lithiumion-batteries.com/products/product/12v-50ah-lithium-ion-battery.php

I've just bought a 12v 20ah LiFePO4 replacement for my lead Yuasa NP18-12 on eBay. I am currently (no pun intended) trying to make a dent in its charge by running my iPad and anything else I can think of from it.  It may take a while.....

Incidentally, one of Johan's 50ah batteries probably weighs about the same as my old Yuasa (7.5kg or thereabouts), while providing something like four or five times more usable capacity.

[Michael Rogers]

Those are also seriously eye-watering prices!! It makes one realise why complete packages like the Torqeeda Travel 503/1003 outboard (which I shall have to acquire some day, when offspring are self sufficient at long last)), or even my (brilliant) Bosch Li-ion battery mower, seem so expensive. Roll on the day (by prophet bard foretold?) when those of us on pensions can look such batteries in the financial eye. Incidentally, I very seldom buy any batteries other than AA, AAA etc, but my impression is that the cost of lead-acid batteries generally has come down: correct?

Michael

[Johan Ellingsen]

Again,may I tell you what´s wrong with Torqeedo?

I had the misguided idea,that one could have a Tq motor,with a large, "deep reserve" battery
feeding it.Turns out,external power can only go through the battery charging inlet,at a severely
slower rate than any possible ongoing consumption.Thus,when you have exhausted any Tq batteries you may have on board,you´re stuck anyway,all your reserve Ah:s notwithstanding.At least until the next morning...

But the motor/propeller are fine.

/Johan

[Michael Rogers]

I think it's horses for courses, Johann. It sounds as though your requirements are a very great deal more demanding than mine would be, with my light little boat and at my age. I should row when I can't sail, and usually do at the moment. Hey ho, as I implied, I'm dreaming at the moment. Where are those oars?……..

Happy Christmas, by the way!

Michael

[Graham W]

Here's an interesting source of information on extending the range of a Torqeedo's lithium battery http://thetorqeedoshop.com.au/range-extension-options-for-torqeedo-1003-and-ultralight/

The conclusion seems to be that the simplest but most expensive solution is to buy a second lithium battery from Torqeedo. If the resulting doubling of range isn't required, then there are various ways of using the charging socket on the built-in battery to extend range a bit. Virtually none of these suggestions are mentioned by Torqeedo themselves. In sunny climes, the most interesting idea is to use the boat's house 12v battery with a step up converter to provide about half the power (via the charger socket) on a medium speed cruise, and a solar panel to slow down the resulting depletion of the charge on the house battery.

I estimate that with a house LiFePO4 battery of 12v 20ah stepped up to 32v, plus a 25 watt solar panel partially recharging same, the 10nm range at 3 knots could be extended by around 50%. At full speed, the integral battery charge runs down so quickly that reinforcing it from other sources makes very little difference to the range of around 2.5nm.  Unless, once the integral battery has run out of juice, you are prepared to wait for hours while it is partially recharged. So slow and steady gets you both further and at a faster average overall speed.

[Peter Taylor]

Graham, that's an interesting web site. My interpretation is that they are suggesting exploiting the fact that the battery management system charges at constant current rather than constant voltage. Thus if you can supply the 4A current at 24V you will get twice the number of watts into the Torqeedo battery. I'm putting two 12V batteries into my new BC20 so I could take a 24V series connection to the Torqeedo rather than the 12V connection I was planning which is very tempting.

Will I? I'm not sure I will since the Torqeedo supplied mains charger only provides 12v. I'd need to be certain that charging the Lithium-ion battery at a higher power rate doesn't pose an increased fire risk. I know Torqeedo say you can charge from a solar panel at 24V to 60V with maximum 4A current but Torqeedo's own panel is only 45W. If only we could ask Torqeedo if charging at a higher rate is safe but getting information from them seems to be a life's work!!!

If anyone tries this please tell us what happens - and I suggest keeping a close watch on the temperature of the Torqeedo battery!

Peter

[Graham W]

Peter,

For some reason, the Torqeedo charging voltage has to be either 12v or a bit higher than the voltage of its integral battery (29v).  Anything in between, including 24v, doesn't work.  The Australians suggest using a step up controller to get the charge to >30v, which at 4 amps maximum gives you around 120 watts. 

It's easier to find waterproof step up controllers that start from 12v rather than from 24v, so unless you need 24v for the rest of your system, it might be better to link up your two batteries in parallel (12v) rather than in series (24v). This step up controller from Hong Kong seems to fit the bill http://www.ebay.com/itm/WaterProof-12V-32V-3-4A-109W-DC-DC-Step-UP-Power-Converter-Regulator-/301045461741

I'll be trying out various configurations on Lake Bala in the spring. I've also got some lithium manganese batteries for electrically-assisted bikes which I will see if I can plug into the charger socket, with a bit of voltage step-upping. If that works, it might double my 3 knot range.

[Peter Taylor]

Sorry, I didn't read it carefully enough! For a third party supplied solar panel the Torqeedo manual says it must comply with.. rated voltage 24V; Max idle voltage 58V; max power (sic) 4A ...and that using anything else damages the device. I'd taken that to mean you can charge at 24V.

Charging at around 120W does sound tempting but if you really can charge at 4A/30V why doesn't Torqeedo's mains charger do that? I wonder how much experience the Australians have of what they are  suggesting. In any case I've found with experience I can now achieve longer run times with the Torqeedo on my 15' dinghy; often just cutting the speed by a fraction of a knot results in big power savings. Keeping an eye on the gps speed and power consumption readouts does pay dividends!

On the BC20 (assuming it survives tonights gales) I'm actually planning to install two 12v batteries and use them independently either each powering different functions or one powering everything and the other in reserve. To connect batteries in parallel one needs to include diodes which will drop the voltage a little and waste power, I'd rather just switch between them!

Incidently, my shortened Torqeedo did fit in the BC20 well and will tilt up OK - remains to be seen if it has enough power for my purposes - I'll report in due course!

Peter

[Rob Johnstone]

Hope the BC 20 survived the exciting night.

On the subject of connecting batteries in parallel, can I show my ignorance and ask why you need to connect them through diodes? Is it to protect one battery if the other fails?

On another topic, has anyone tried to recharge Li batteries using solar cells?

Vagabond has two Pb 50 batteries connected in parallel ( without diodes), powering sailing instruments and a GPS. The voltage drop at the end of a 12hr sail is quite noticeable, so rechargeing the ipad ( my main nav system) is out of the question. This is despite two 10w solar cells. I usually find a pub to recharge both me and the ipad. Looking ahead to next year, there's a dearth of pubs round the N coast of Scotland, so Li batteries sound a good option, provided they can be charged by solar power......

[Graham W]

Rob,

Since Peter's post above I've been reading up on diodes.  It seems that if the batteries in parallel are identical in every way (including their state of charge), diodes may not be necessary, although for some reason this is extremely controversial!

Lithium batteries can definitely be recharged from solar.  Genasun in the US do a solar MPPT controller specifically for lithium, model GV-5.  Unfortunately it isn't waterproof. Torqeedo also do a 45w flexible panel that plugs straight into their integral lithium battery but at a ludicrous price - £800.

I managed to complete 3.4 recharges of my iPad from my 20ah LiFePO4 battery before the battery management system shut the battery down because of low voltage.

If you already have space for two 50ah pb batteries, you could get a single 100ah lithium battery that would last longer, take up less space and also weigh considerably less - but at quite a cost.  Here's a UK site with a reasonable range of different sizes http://www.batterypitstop.co.uk/18/lithium-iron-batteries/11/all/22/all-lithium-iron-batteries/

[Graham W]

Charging at around 120W does sound tempting but if you really can charge at 4A/30V why doesn't Torqeedo's mains charger do that?

There appears to be a new Torqeedo fast charger on the horizon (part no. 1131-00) which probably does exactly that. No doubt at a high cost.

[Peter Taylor]

Here is my understanding... In theory, if two batteries are identical you can parallel them without diodes. In practice batteries are almost never identical. There are slight differences due to manufacturing, previous history, etc. If you connect two batteries in parallel and one battery has a slightly higher voltage it will drive a charging current through the other one. Since the internal resistance of a lead acid or lithium battery is very low the current that will flow can be very high. At best you will waste power by heating the connecting wires, and not get the amount of useful power you expected. At worst you will have a fire or possible explosion. In the model boat world, unintentional but spectacular fires or explosions due to people using Lithium batteries in parallel are not that uncommon!

I'm glad to say my BC20 survived unscathed although the jetty timbers did show significant abrasion from the fender board I am using! The maximum gust was 24m/s - nearly 54 mph. "Seatern" certainly had a rough welcome to Southampton and there's more on forecast for Friday!

Peter

[Peter Taylor]

There appears to be a new Torqeedo fast charger on the horizon (part no. 1131-00) which probably does exactly that. No doubt at a high cost.

It will be interesting to see how it works. I use Makita power tools and the batteries charge rapidly (20 minutes). The Makita charger blows air through the Li-ion battery to keep it cool. You'd have trouble doing that with the Torqeedo battery!