21st century electrics

[davidknell]

I've just started down the road of bringing the batteries in our 43DS into the 21st century. Lead acid's out, lithium's in - I know they've been problematic for Boeing, but we're unlikely to be sailing at 37,000'. I've been seduced by more capacity, more available capacity (at least 80% of the nominal capacity is usable, as opposed to 50% with lead acid), and, provided that the things are property treated and that the manufacturer's spec can be believed, they should still provide 80% of their capacity after 3000 charge/discharge cycles.

On the flip side, they're more sensitive to abuse than lead-acids. Don't over-charge, don't over-discharge, and keep the cells as equally charged as possible are the key rules. In practice, this means a cell management and monitoring system which sounds more complex than it really is: it has to measure the voltage across each cell, and be able to place a load across cells which reach full charge during charging in order to allow less-charged cells to catch up. And they're quite a lot more expensive than lead-acids.

The first step which we've taken is to fit 8 200AHr cells in the existing battery compartments, wired up as 2 batteries of 4 cells in series. Each battery of 4 cells has a nominal working voltage of 12.8V and is pretty much fully charged at 14.4V, so they just drop in. The two batteries are wired in parallel and used to supply both the house and starter motor (I've a fully charged lead-acid battery and some jump leads in a locker just in case..)

Impressions so far are that everything works just as it should. The engine starts, the anchor windlass pulls maybe a bit harder than it did, I can run the inverter and the microwave without tripping the fridge's under-voltage shut-off, and the alternator pushes plenty of amps into the batteries when the engine's running.

If anyone's interested, I'll keep this thread updated with our progress and experience with the installation and use of the things.

--Dave

[Zanshin]

I'm quite interested in the topic, as I thought about going down the road that you've gone but felt that the cost was prohibitively high for me (I've got over 1000Ah).
How are you regulating your charging cycles to ensure that your engine's alternator doesn't inadvertantly fry the batteries? I believe that Lithium batteries have their own circuitry to prevent discharging past a certain point, but thought that one would need a special charge regulator as well. Can you determine the state-of-charge by measuring the voltage and do you use a battery monitor?

[davidknell]

The battery monitor is currently very crude - it involves me and a multimeter. The next generation (currently on my bench being debugged) has a little board which goes across the terminals of each cell, measures its voltage and can add a load if necessary for balancing, and talks back to a host which can talk to a laptop. I've some more bits - a proper charge controller and supervisor - under development. Determining state of charge from voltage is iffy as the voltage/charge curve is very flat; I'm expecting to have to measure energy in and out to keep decent track of things.

An alternator actually isn't a bad source of charge for the things - it should be constant current up to a certain voltage/cell and constant voltage after that, and the numbers are OK for a battery of 4 cells in series. Provided that the alternator's regulator's working properly..

The cells aren't cheap - that's for sure. Each one was just over €200, ex. VAT. On the other hand, each one has roughly the same usable capacity as a 12V/100AH lead acid battery, and the whole lot cost less than a full tank for my friend's sunseeker..!

[sitara]

Keep us posted David, this is something I would like to investigate when my lead/acid batteries fail.

[chaika]

Very interesting... I installed lithiums on my 36i at the beginning of this year and I am more than pleased with them. I took a very cautious approach. An article I wrote for the Cruising Yacht Club of Tasmania briefly describes my approach, this can be downloaded from here:

www.turo.com.au/support/downloads/downloads.html

By the way. The lithium battery on the Dreamliner is a lithium cobalt oxide chemistry, whereas mine (and I presume other boat installations) uses lithium iron phosphate chemistry. Very different chemistries – and with very different risks. Lithium Iron Phosphate (LiFePO4) chemistry is in the very less dangerous category (much higher thermal runaway temperature than the cobalt), in fact, with a battery management system I think they are safer than lead acid.

[davidknell]

Thanks - that's interesting, and I'm not about to publish photos of my current lash-up having seen those of your neat installation..

Original endgame here is to end up with 15 cells under the bed in the main cabin (there's a compartment there for dividers to split the cabin in two; we don't have them, and it's just the right size for the cells) to provide a main 48V bank with a big inverter, a step-down converter for the existing 12V stuff and probably one lead-acid battery for starting the engine. Plus a thing to step up the 12V from the alternator for charging, and possibly something to float-charge the starter battery.

I'm becoming convinced that this is wrong-headed and over-complicated, and that the right approach is to fit 16 cells (4 x 4 - 12V, 800AH) to provide everything, and have the BMS disconnect the house side once a cell falls to 3.0V or so, when there's still ample available energy to start the engine.

The point you make in your article - that you just turn stuff on now without worrying about it - echoes our experience to date. It's liberating.

Last off, ours has two battery compartments, each of which can take two 017 size (or thereabouts) lead-acids. I'm pretty sure that the 800AH of lithium cells would fit in those two compartments if the moulding which provides location for the base of the lead-acid batteries were removed.

[davidknell]

OK - first update after a couple of weeks pottering around the Aegean.. fantastic - a world apart from our old (admittedly probably pretty badly shot) lead-acids. We're currently using 8 200AHr LiFePO4 cells to give us a single 400AHr bank which is used for the engine and house, charged from the existing alternator.

We're a couple with two small children, one 5 months old, and so we use a microwave on an inverter a lot for warming milk, sterilising bottles, making coffee, etc., run a blender on the inverter, we keep the fridge reasonably cool and turn the lights on (and they're the originals, my LED bulbs having failed to arrive before we set off) when we need them. We have two laptops, an iPad and a couple of phones to charge. This tots up to something between 80 and 100AHr out of the batteries a day, as far as I can tell.

Good points: we have 400 AHr available to use - none of this "don't discharge below 50%" nonsense that one has with lead-acid. The batteries charge more quickly - they maintain a terminal voltage of about 13.5V until they're almost full. This is low enough for our stock alternator/splitter combo to put a steady 75->60A (dropping over time as the alternator gets warm, I think) into them. They also return 1AHr for every AHr that goes into them - unlike lead-acid, which might return 0.7-0.8. They can supply a lot of current: our existing bank is rated for discharges up to 2000A with a drop in terminal voltage of 1V. In practice, I can be warming something in the microwave and start the engine, and the voltmeter hardly moves.

Bad points: if you overcharge or overdischarge a cell, they're permanently damaged. Cell equalisation is important but is harder than lead-acid: you can't just overcharge the thing and then top up the water. And the things aren't cheap.

--Dave

[Zanshin]

Dave,

I'm pottering about with making my own BMS system for Lithium batteries. I've got a crude setup on my breadboard right now, using an ATMEL microprocessor, digital thermomenter and playing around with the Maxim and Texas Instrument BMS chips. I will most likely use just resistive balancing instead of active balancing for my cells and will hook everything up with a display that looks similar to the Victron or Xantrex ones, but it will have an ethernet plug and the controlling software will run on web pages instead of proprietary stuff. Since I like numbers, each cell will report resistance, temperature, voltage and (if I can source a cheaper shunt or hall-effect device) also current. With those numbers in real-time and kept for several months or longer the state-of-charge values are going to be very accurate. I'm thinking of "productizing" this, both for Lithium but also for more accurate Lead-Acid systems but am not sure that the boat market (plus the RV market) is going to be big enough for the effort.

How are you balancing your Lithium bank? Resistively during charge?

[Zanshin]

Jul 15, 2013 22:59:12 GMT chaika said:

... www.turo.com.au/support/downloads/downloads.html..

Nice job indeed! And a clean installation as well as being cutting edge.

What balancers are you using for your bank? Are the homegrown or from that Dutch company whose name evades me right now (not Victron or Mastervolt, but one that specializes in Lithium cells)?

[Anwen (Deep Joy)]

This is a fascinating thread, and I have been following with interest. I would be very grateful if you could point me in the direction of a supplier for the 200Ah LiFe cells, as Google hasn't really been very helpful. I have a fair amount of experience with lithium cells, and understand the issues and risks.

[Zanshin]

There are lots of suppliers for Winston cells, which come in many shapes and amperages.

Where are you located?

(Click on the text for "Winston Cells", it is a hot-link but somehow the forum software never shows that. I'll see if I can underline and bold it to make it more obvious.

[debenboy]

Chaika,
ASbsolutely fascinating thread. I have pm'd you.

[chaika]

Aug 15, 2013 8:45:28 GMT Zanshin said:

What balancers are you using for your bank? Are the homegrown or from that Dutch company whose name evades me right now (not Victron or Mastervolt, but one that specializes in Lithium cells)?

Rather than design it myself, it was much cheaper and quicker to just buy the balancing modules and safety monitoring and cut out units. I looked at various units on the market then homed in on one system. After studying them carefully and how they operated I decided to buy them. They were from a Western Australian company EV Power (http://www.evpower.com.au). I bought:
4 off BMS cell modules
1 off BCU-PPA to suit, with 3 pole latching relay

Each cell has a balancing module (BMS) across its terminals. A single current loop connects the BMS's in series and then to the Battery Control Unit (BCU-PPA). The BCU controls a relay that can shut off the 12V lithium bank. The shut off is triggered by
1) if any cell is over an upper preset voltage
2) if any cell is less than a lower preset voltage
3) if the 12V bank is over an upper preset voltage
4) if the 12V bank is under a lower preset voltage.

Just before a cell reaches its upper preset shut down voltage, it connects a drain resistor across the terminals. This drains that cell a bit. The first time I charged the batteries this took place (the initial balancing). Even though the drain was less than the charge current, it didn't matter because after a short while the shut off (see 1 above) took place to prevent further charging. With no further charging, that cell continued to be drained by the BMS unit until it fell to within its operating voltage range. And having got there the auto shut down reconnected the 12V bank. It worked very well to bring the system to initial balance - and if ever it gets out of balance it will do the same, with no intervention on my part.

[Zanshin]

Chaika - thanks for that information. The "EV-power" units are ones that I looked at as well, I thought it was a Dutch company, but now it turns out that they are actually a Czech company that has subsidiaries in Oz and the Netherlands.

I really want to use the existing balancer modules but also use a central unit that I program and that stores more statistical information for evaluation purposes. I'll contact EV-Power to see if they will document the protocol they use to see if I can integrate it. They are abou 35Euros per unit, there is a similar unit on offer in the USA with a 1-wire protocl for about US$20 per unit which might be better (1-wire means they are using the DS4328 chip, and that interface is well-documented).

Thanks for all the information!

[chaika]

There is a company in Europe called EV Power, but I think they are unrelated to the one in Western Australia. The web site for the WA one is www.evpower.com.au

[Zanshin]

Chaika - you are correct, same name but very different product indeed. Yours looks like exactly what I'm trying to build, but perhaps I can purchase instead! Can you look at the chip on the BMS and see if it is an 8-pin SOIC (150-mil) chip labelled DS2438? If that is the case, then I'm buying a boatload of those BMS, since that is a public protocol that is very simple to integrate and use! I couldn't see from their web pages how they implemented it. Do you have a small wire going from each balancer to the next and then to the controller?

[davidknell]

I designed my own - I've built more than I need. You're welcome to a small handful of them if you fancy hours of frustration dealing with someone else's hardware - they're based around an MSP430 uC (you'll need a Launchpad to program them, $9.95 from TI, can also act as a host) and built to fit across the terminals of the cells I'm using, which are 200AHr Sinopoly ones. They've a serial interface on which you ought to be able to use to talk back to a host - it should either work as a bus or as a controller<->BMS1<->BMS2<->.. chain - not tested this bit yet. I was expecting to have plenty of spare time this summer, but sailing with a 4 year old, a 5 month old and a wife doesn't leave me with much :-)

--Dave

[chaika]

Zanshin - Looks like you're ok for the cell balancing modules with a digital i/f. The ones I'm using do not have the digital link. The current loop that passes from one BMS to another, etc, is just that, an analogue current loop. The current source (about 1 mA) is supplied by the battery control unit (BCU) and each BMS can break the continuity if its over/under voltage conditions are breached. The BCU then triggers the relay to disconnect the 12V battery bank from the charger/alternator/house system. It's balancing function is done by switching in a drain resistor when a cell approaches and gets close to, its upper voltage. A very simple analogue system, very reliable and resets itself when conditions are restored.

But you won't get all the monitoring you'd like. I just use the Victron battery monitor which I have found to be quite good for every day use.

[Zanshin]

David - I actually enjoy the work on getting my own BMS up and running. I use the ATMEL boards and am currently using two Arduinos that I have lying around. So far I have one working as the BMS and the other as a monitor and data collector. I'm waiting on an order of battery monitor ICs, but didn't realize that the form factor was so small that I don't think I'll be able to mount them on a board.

Chaika - I see the setup now on their pages. Sounds efficient and inexpensive.

I think I will go the Lithium route and am trying to find a source for Winston Cells in the Caribbean, since buying them in Europe and then shipping them over isn't the cheapest or quickest method.