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LiFePO4 batteries for an electric boat

Posted: Mon, 24 Oct 2011, 00:31
by boatie
My apologies for posting electric boat question on EV forum, but where else to ask the battery question?

I have a 3.7m boat with 24V electric engine Torqeedo 801 and two 12V 55Ah Optima led acid batteries that I bought about year and half ago. The maximum power is 800W but boat goes well with around 300W so this setup gives me a range of around 3 hours. I found that a bit limiting even for day trips. When I bought the batteries I was aware of only very expensive lithium batteries for such purpose. A few days ago I came across EV Works and EV Power selling LiFePO4 in Australia for a reasonable price. I am considering replacing the existing batteries with two 12V 90Ah LiFePO4 batteries that would double the existing range. It would suit me to use two 12 volt batteries because of the available space and ability to use a standard led acid battery charger that I already have.

I considered assembling the batteries from 3.2V cells, the price seems to be close. Would that be a better option?

The boat is not used too often, on average ones a month.

At the moment the setup is very simple with only one circuit breaker in the circuit.

I will be grateful for any information that you could provide. Are both EV Works and EV Power reliable companies to deal with? Is anyone else selling batteries at similar price point? Any technical traps that I need to be aware of?

Best regards

Alan

LiFePO4 batteries for an electric boat

Posted: Mon, 24 Oct 2011, 02:48
by Electrocycle
you'll need a BMS ideally to monitor the cells and make sure you don't over charge or discharge them, but the end result should be much better performance.

The ready made 12v batteries will probably simplify things a bit, especially in a marine environment where any exposed connections are likely to cause you problems.

LiFePO4 batteries for an electric boat

Posted: Mon, 24 Oct 2011, 03:07
by T1 Terry
Trev from Basicly Natural up the top end of Qld has the 90Ah cells for $1.40ah so roughly $500 for a 90Ah 12v battery. For a few extra $$ I believe he will build them into what ever size packs you want with end plates and straps.
as you will probably be charging them as 12v batteries I wouldn't worry too much about a BMS, there are only 4 cells to watch. I'd buy a Cell Logger so you can watch the cell voltages while charging and discharging and balance them as needed using a light bulb to drain the high cells. Once they are balanced they stay that way for ages. my pack of 16 X 90ah cells to make a 360Ah 12v battery to power my house stuff has stayed in balance for 2 mths now , in use 24/7, solar charged and dragged down to around the mid 40% SOC each night.
The 4 cells are smaller than a 100Ah AGM battery so they would fit in a plastic battery box.
Don't charge them over 14v (3.5v per cell) and if you are going to leave them on a charger for any extended time drop the charge back to 13.8v (3.45v per cell)so you don't cook the cells. No trickle chargers though, these kill LiFeP04 batteries very quickly.
Usual disclaimer, no financial connection with Trev at Basicly Natural, just a very happy customer, he is a good guy to deal with.
http://www.thebackshed.com/basiclynatural/default.asp

T1 Terry

LiFePO4 batteries for an electric boat

Posted: Mon, 24 Oct 2011, 13:05
by a4x4kiwi
Hi Alan,

I would have to agree with Electrocycle, that you must use a BMS so you can charge and discharge unattended with piece of mind.

The last thing you want is to damage your cells, or your boat due to over charging or discharging. If nothing else call it an insurance policy.

Your 12v / 24v charger most probably wont be suitable for charging the lithium cells as the charge profile is quite different due to the different batter chemistry.

Have a look at this to get an overview of balancing

Also very useful would be the Cycle Analyst to keep track of your battery state of charge and range from EV works

LiFePO4 batteries for an electric boat

Posted: Mon, 24 Oct 2011, 14:40
by woody
boatie wrote: I have a 3.7m boat with 24V electric engine Torqeedo 801 and two 12V 55Ah Optima led acid batteries that I bought about year and half ago. The maximum power is 800W but boat goes well with around 300W so this setup gives me a range of around 3 hours. I found that a bit limiting even for day trips.
I see no reason you couldn't get 2 more batteries the same and put them in parallel (or even with a cut over switch) to double your range...

cheers,
Woody

LiFePO4 batteries for an electric boat

Posted: Mon, 24 Oct 2011, 19:38
by zacjupiter
Hi,

Thanks for your answers. Considering a low value of my setup, what economical charging/balancing system would you recommend?

I was hoping to use my existing charger that has maximum voltage of 14.6V – 3.65V per cell. Is that too risky? On PV works site they advertise 12V batteries as a straight replacement for led acid car batteries that can be used with the standard chargers. I suspect that those batteries and just boxes with four 3.2V cells connected in series. The batteries would be charged 10-20 times per year.


LiFePO4 batteries for an electric boat

Posted: Mon, 24 Oct 2011, 19:57
by T1 Terry
zacjupiter wrote: Hi,

Thanks for your answers. Considering a low value of my setup, what economical charging/balancing system would you recommend?

I was hoping to use my existing charger that has maximum voltage of 14.6V – 3.65V per cell. Is that too risky? On PV works site they advertise 12V batteries as a straight replacement for led acid car batteries that can be used with the standard chargers. I suspect that those batteries and just boxes with four 3.2V cells connected in series. The batteries would be charged 10-20 times per year.
You will need a cut out device that stops charging at 13.8v to 14v, link it to a Cell logger, about $14 from Hobby King, and set the high cell alarm to 3.8v and link the alarm port to the cut off relay, simple as that. My system incorporates a solar regulator so the high volt cut is already a function of the regulator, it was just a matter of linking a 12v controlled 240v relay to turn the charger off and the cell logger alarm to turn every thing off.
It’s worked fine for a number of mths now, 24/7 around 200Ah flowing in and out of the batteries. A balanced 4 cell battery stays in balance for a long time, just don't push the parameters, cell over voltage/under voltage, the cell logger gives an audible warning for all these parameters.

T1 Terry

LiFePO4 batteries for an electric boat

Posted: Mon, 24 Oct 2011, 20:12
by Johny
zacjupiter wrote: Hi,
Thanks for your answers. Considering a low value of my setup, what economical charging/balancing system would you recommend?

I was hoping to use my existing charger that has maximum voltage of 14.6V – 3.65V per cell. Is that too risky? On PV works site they advertise 12V batteries as a straight replacement for led acid car batteries that can be used with the standard chargers. I suspect that those batteries and just boxes with four 3.2V cells connected in series. The batteries would be charged 10-20 times per year.
If you are happy with the price of a couple of 12V LA replacement LiFePO4 packs from EV Power then that's the way I would go. Get their advice on the best replacement setup for your requirements - they can purpose build it for you. You may be right in that your current 12V charger will do fine as long as the BMS can turn it off when the pack(s) are fully charged. Again - I'd ask the guys who are supplying the packs.

LiFePO4 batteries for an electric boat

Posted: Tue, 25 Oct 2011, 21:06
by Richo
a4x4kiwi wrote:Your 12v / 24v charger most probably wont be suitable for charging the lithium cells as the charge profile is quite different due to the different batter chemistry.


Most SLA charges pump in lots of current (CC) until they get to their maximum voltage (CV).

I don't really see the difference..

LiFePO4 batteries for an electric boat

Posted: Tue, 25 Oct 2011, 22:20
by a4x4kiwi
Most smart chargers I have used is a CC-CV-CV mode.

CC at a constant current, up to a voltage of 14-15 volts, then float at 13.8.

I guess it very much depends on the charger, but given the cost of the cells, I would use a charger with a lithium charge profile.

Mal.

LiFePO4 batteries for an electric boat

Posted: Tue, 25 Oct 2011, 22:40
by Electrocycle
otherwise a simple charger with the BMS turning it off should be ok.

LiFePO4 batteries for an electric boat

Posted: Wed, 26 Oct 2011, 18:30
by boatie
Thanks again for advice.

Has anyone ordered batteries from EV Works? They seem to have a good range on their web site including 12V batteries.

I wonder about individual cells in 12V battery. Do they have some sort of management system within these batteries?

Link: http://www.evworks.com.au/index.php?pro ... -LP12V90AH


LiFePO4 batteries for an electric boat

Posted: Wed, 26 Oct 2011, 20:29
by Richo
Ah there is plenty of eV's around Perth with batteries from EV Works for proof.

I can't comment on the internals of the 12V battery.
But since a cars alternator will never get to the max of 4 cells in sereis I doubt it matters.

You would have to just watch over discharging them and even a cheapo voltemer/panel meter would probably give enough indication for that.

LiFePO4 batteries for an electric boat

Posted: Thu, 27 Oct 2011, 19:58
by bga
Thundersky cells are almost universal in road-going EV conversions around the country. EVWorks also has a controller for their cell-top BMSses to provide an undervolts lockout and charger control.

As for the 12V battery block option, you will probably get more bang for your buck with individual cells, say the popular 160AH type, which will deliver about 3.5kw. An alternative would be to use 90AHor 60AH cells.

EVWorks has just recently specified a system to do exactly this for a work project. We were most happy with the price.

LiFePO4 batteries for an electric boat

Posted: Fri, 28 Oct 2011, 14:37
by boatie
I enquired about 12V batteries with EV Works.
The answer:
“The 12V cells are made up of four individual cells, they are moulded
together from the factory. No BMS is installed in the pack so it is
important they are not over discharged.”

So no balancing of those 4 cells through the battery life - interesting.

LiFePO4 batteries for an electric boat

Posted: Fri, 28 Oct 2011, 15:09
by lithbattboss
boatie wrote: My apologies for posting electric boat question on EV forum, but where else to ask the battery question?

The source for electric boat information is the Australian Electric Boat Associoation-
http://www.electricboats.org.au/

LiFePO4 batteries for an electric boat

Posted: Sun, 30 Oct 2011, 15:26
by coulomb
lithbattboss wrote: The source for electric boat information is the Australian Electric Boat Association-
http://www.electricboats.org.au/

Admins: perhaps this could go onto the AEVA Links page, perhaps under Other Australian Organizations ?

While I feel that electric boats definitely are electric vehicles, I think that there would be enough unique problems with E-boats, and issues relevant to land vehicles that are not relevant to boats, that encouraging a separate web site and perhaps association makes sense.