Lithium Ion Batteries

CPseudonym said:

BMS would equal Battery Management System?

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Yes

deckofficer said:

Yes

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Thanks Bob

rjtrane said:

Here are my thoughts regarding using LI as your house bank (essentially that is what we are doing).

I like the idea of a BMS - it gives you information on all the cells. The main way to protect your investment is to keep the individual cells within spec this means running them down too low and/or over charging - EACH CELL.

The BMS we installed (custom engineered from Balqon) has a remote display at the helm. It not only shows the pack voltage (total battery, in our case 48 v nominal), but high cell voltage, low cell voltage, charge/discharge rate in amps, cell temp, total amp hours available (and as a percentage), and BMS temp.

Additional pages on the BMS allow for manually connecting/disconnecting the battery from the bus - connecting/disconnecting charging devices - connecting/disconnecting load devices. It also "specks" via CanBus to the Elcon 3kW charger.

But most importantly, it will disconnect charging devices should ANY cell approach its upper limit (in our case 3.8v) AND disconnect the battery from the bus should any cell reach 3.9v - after this, the cell starts to damage itself. It works in a similarly manner on the discharge side, with disconnecting loads .1 v before disconnecting the battery itself. This is the only way the battery can keep from damage unattended.

One big surprise to me (not, I'm sure to the EEs out there), was upon connecting the battery to the bus, we kept welding contactors closed, thus preventing the battery from disconnecting from the bus. Turns out the capacitors in the inverters were causing a voltage surge. A simple resistor wired between the contactors and a delay relay to close the on/off solenoid (after the capacitors were charged) solved the issue.

And, on a boat, you are most likely going to have an inverter. And will want some sort of safety mechanism to disconnect the battery. Reading total voltage of the pack will not do the job by itself - all it takes is one cell at 3.0v to keep the reading of a 12v battery at 13.4v even though one cell could be 4.0v while the other two are at 3.2v each. This is not your grandfather's LA battery!

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That looks like a nice BMS. I wish they would publish the full specs and pricing online.

All the functions sound spot on, however in my opinion 3.8V per cell is too high a value in general, especially if anything other than the Elcon contributes to the charge. And only then if you are charging near the 1C rate, for example, 200A on a 200Ah bank. At the .5C rates, 100A on a 200Ah bank, or less, then 3.6V per cell will get you 100% SOC. Our house bank rates are normally even lower, mine is 150-200A into a 1200Ah bank, under .2C. At 3.5V, My bank is essentially 100% charged and I limit fast charge to that or less. If my electronics allowed it, which it will eventually, I'd stop charging at 3.45V.

But the biggest issue is "floating". I don't know the exact number, and it might even vary a little from one brand to another, but I've seen maximum safe float values quoted from 3.35 to 3.45V. My personal favorite is 3.38. Any higher voltage maintained long enough will significantly overcharge a LiFePO4 cell, causing reduced life. My own tests have demonstrated that 24 hours at sea, with the cell voltage regulated at 3.35V is greater than 95% SOC. I know this by observing 3.35V underway, then right after dropping the hook, charging to 3.6V in 20 minutes at around 150A. The 3.6V here was a test, but it was about 2.5 minutes from 3.5 to 3.6V. We started the trip at about 3.3V.

I can't do it on my BMS, it just pulls the plug at a non adjustable 3.6V, both charge and discharge paths at the moment. But eventually I will have an alarm set for 3.46 or 3.47V, just above the value I plan to never exceed, with the disconnect set a little higher, somewhere near 3.5V. I may separate the charge discharge paths, but it's hard to do with inverter chargers.

The point is Balqon, and the rest of the EV guys are focused on charging and then stopping charge. That's not what happens on a boat. We have alternators underway, solar chargers, shore power "float" chargers etc that don't ever really shut off. And these guys, in my opinion don't have this well thought out.

The problem you mentioned with cell balance is possible and I agree individual cells need monitoring in a marine installation. At the same time, this is not turning out to be a routine issue with healthy cells. I'm probably getting close to 200 cycles since my final installation balance, and the cells are not showing any tendency to drift apart. This is consistent with many other installations Ive followed. So while monitoring is suggested, the automated "balance" function of some BMS systems is not essential. Properly implemented for marine, I see it as an aid to installation and a periodic maintenance function, which can be accomplished manually.

Ive observed the capacitor surge you describe, but no welded contacts yet. Can you be more specific on the fix for this? Are the resistors always in the circuit? Or only on a new momentary relay that is released after the main solenoid closes?

Thanks, Bob

deckofficer said:

I used to work for the oil industry, and believe me they are not nice people.

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Apparently, I am not nice people.

Should I tell my wife?

For the "soft" start:

1. 100w/10ohm resister.
2. Wire the resister from the battery side of the solenoid to a relay and then to the bus side of the solenoid.
3. When the BMS key switch is turned on, 12v closes the relay allowing 48v from the battery to the bus through the resister.
4. Install a time-delay relay that starts timing when the remote BMS key switch is closed (turned on). When this relay closes (about 5 seconds after the initial relay), it actuates the solenoid which then closes allowing full current from the battery to the bus.
5. Since I have yet to build in a delay for the DC/DC converters, the resister gets warm but not unduly hot. It stays in the circuit as long as the key switch is on (all the time unless working on the battery or circuits), but the current is flowing directly through the solenoid at this time, not the auxiliary resister circuit.

This "soft" start is working well.

Reuben,

Do you have any future plans for extended cruising? I have played with the numbers on Sunshine, and other than its current weight I would think extended cruising of the Caribbean would be possible on minimal fuel burn. Tell me if I'm way off base, but since you were able to get 52 KW-hr into the forward end of one hull, and you were using both hulls for the Odyssey LA, any chance of fitting a 2nd 52 KW-hr bank in the other hull? Going by the published boat review tests, at a stately speed of 4 kts (don't laugh, I've averaged less on a 24 hour run in my sailboat), you could cover nearly 100 nm in a day staying within a 80% DOD. Then your choice would be 3~4 days on the hook before another 100 nm passage or pull into a marina and feel like you get your money's worth from your slip fee when you suck down 85 KW-hr.

rjtrane said:

For the "soft" start:

1. 100w/10ohm resister.
2. Wire the resister from the battery side of the solenoid to a relay and then to the bus side of the solenoid.
3. When the BMS key switch is turned on, 12v closes the relay allowing 48v from the battery to the bus through the resister.
4. Install a time-delay relay that starts timing when the remote BMS key switch is closed (turned on). When this relay closes (about 5 seconds after the initial relay), it actuates the solenoid which then closes allowing full current from the battery to the bus.
5. Since I have yet to build in a delay for the DC/DC converters, the resister gets warm but not unduly hot. It stays in the circuit as long as the key switch is on (all the time unless working on the battery or circuits), but the current is flowing directly through the solenoid at this time, not the auxiliary resister circuit.

This "soft" start is working well.

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Thanks, I see how it works!

FYI: It's "resistor", not "resister".

Bob,

I love your thinking - use up as much energy and then glom onto the grid for a refill!

We actually fit the LI battery on centerline under the master berth. And, since the new battery has essentially the same weight as the original AGMs, we have no more reserve buoyancy forward for another battery.

Of course, the other option is to get rid of the Steyrs entirely and replace with steerable, 10kW pods that weigh almost nothing when you take into account the amount of water they displace. That would free up enough buoyancy aft for another battery and perhaps a small 48v DC genset.

Most of my current thinking for a marketable product uses this approach - steerable pod, LI battery, PV array with wind and generator optional - and parallel hybrid another option. Using only electric propulsion is by far the most simple solution.

Ron: Thanks for the spell check!

Well Reuben, here's to you having a product for all the upcoming baby boomers that want to cruise but don't want to learn to sail. From my social interfacing I think it might be a rather large group. When I'm introduced at a gathering, they always throw in what I do, so the conversation is steered to long ocean passages, then it settles down to "I'd love to island hop through the Caribbean".

I'll be the first to admit that I'm a big dreamer, but I believe a boat can offer both, the ability to island hop on stored electrons (your there now) and pull off an ocean passage without the sails and rigging. Have you followed propulsion kites, deployed from the bow? Between a light weight Chris White designed hull like a scaled up Buzzard's Bay 34, hybrid pod propulsion, and the kite sail KiteShip - Innovation in Tethered Flight a lot of re-gen under sail, along with large solar and LiFePO4 energy storage, I believe that a world cruiser is just around the corner.

I've done the sailboat cruising.

I've crossed many oceans in ships.

Now I want to continue on, but with an almost zero carbon footprint. Reuben, will you help me and other baby boomers realize our dream?


For folks that aren't familiar with Chris White's designs, most are sailboats, cats and tri's, but he did a design for the power boat market, that takes the hull efficiency of a PDQ 34 to a whole new level, and no pounding in large seas. As you probably know the PDQ 34 can top out at close to 20 kt with twin 100 hp, and at slower speeds be fuel efficient. The Chris White designed Buzzard's Bay 34 with its knife edge hulls slicing through the water will do 35 kt on about the same power and can also be fitted for outboards, with the larger offerings taking his hull to almost 40 kt.

You sure get around from your Friday Harbor base. I used to live over looking False Bay on SJ Island.

Here is some of the weight savings when you get to choose your rpm for DC gen set vs an AC gen set at a fixed rpm. For an AC gen set to be close but still heavier than its DC counterpart, it will be screaming at 3600 rpm to produce its output. If it is a 1800 rpm AC gen set, then for the same output as these Volvo Penta DC gen sets, it will be twice the weight.

Polar DC Marine units

Ratings kW (continuous)


5.5 kW @ 2900 246 lbs
8 kW @ 2900 290 lbs
14 kW @ 2900 337 lbs
20 kW @ 2900 396 lbs

Now to power your AC loads while on the hook, it is much more efficient to run them with an inverter and enjoy the silence of a pristine anchorage and when the need arises for the batteries to be charged, you have a diesel running under a good load for a short time, then back to silence. If sized right, could power loads such as A/C and galley. Adding some solar panels would cut down the run time of the DC gen set.

When I designed off grid power for homes it was before LiFePO4 cells, so had to use lead acid batteries. A real short coming of LA batteries is the Peukert effect which basically means the higher the draw, the less total capacity. To minimize this I always used 48 VDC input inverters which for the same wattage out pulled 1/4 of the amps that it would from a 12 volt battery bank. A typical battery bank for one of these mountain off grid homes was (24) 2 volt, 700 a-hr cells. Since LiFePO4 cells only have a fraction of the Peukert effect of LA, and most the systems on a boat are 12 volt (lights, electronics, watermaker, fridge, radio), then for the trawlers that want peace and quiet in a remote anchorage, that would be the way to go. A pack 1/4 the size that Reuben is using would handle house loads for a week without solar or running the gen set. Even the smallest 5.5 kW 246 lb DC gen set would charge a 12 volt bank at 370 amps, so run time after a week of quiet bliss would only be 2 1/2 hours. Not a bad deal for being a good neighbor in an anchorage.

Kite sail propulsion has been split into a new thread located here.

http://www.trawlerforum.com/forums/s6/kite-sail-propulsion-9728.html

Here is something those lithium cells can power up via an inverter......

Induction cook top for the galley.


While Reuben is away I'm going to toot his horn. His boat "Sunshine" has employed what I see is the future for cruising. Small things that you didn't know how much you would have wanted on a boat, but after using, you would never go back, induction cook top comes to mind. I've used it and will never go back because I'm lazy. A cooking surface that is flat and doesn't get hot, doesn't bake spilled food into nooks, crannies, and inaccessible areas, instead it is a single wipe across the surface and done. Here is a picture of the galley on Sunshine.

induction cook top comes to mind. I've used it and will never go back because I'm lazy.

How well does an induction cook top work from a NON sine wave inverter?

I don't know, never tried it. By non sine wave you mean a modified sine wave, not pure, right?

We have two 3.6 kW Outback inverters. The induction cooktops work perfectly. I'd recommend these inverters over any others I've used. We now invert all our 120 VAC using shore power only for battery charging AC loads include air conditioning, hot water, TVs, Hitachi refrigerator, Bose 3.2.1.

I just love hearing ".....AC loads include air conditioning, hot water," on batteries and inverter(s).

Like I said, the way of the future.

deckofficer said:

A cooking surface that is flat and doesn't get hot, doesn't bake spilled food into nooks, crannies, and inaccessible areas, instead it is a single wipe across the surface and done.

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What brand of Induction top do you have shown - nice job. We are considering various induction top alternatives to replace the Princess 3 burner. Right now we have portable that does OK. We took out our home gas stove and installed induction some years ago, great choice so far.

For the boat I would stay with the inexpensive portable (like a hot plate) type induction cook top. They run 1500~2000 watt 120 VAC, not as powerful as the 2500~4000 watt 240 VAC built ins for the home kitchen, but the only time I use the highest setting is to quickly bring water to a boil, all cooking the lower power portable works great

I'll bet Reuben with 15 kW surge on those (2) 3.6 kW inverters is probably running home type unit in the 2500+ watt range.

When we build Sunshine, we could not find a good, inexpensive induction cook top that would mount in the counter top. And, the quality home units that had more than a single burner were operating at 240 VAC (something we did not consider, though with the pair of inverters we did install, we could have easily ganged together for 240 VAC). So, we ended up with highly recommended commercial, drop-in units (120 VAC each), designed essentially for buffet, omelette stations, etc., in hotels and restaurants. Cost - $689.95 each. CookTek MCD-1800 - 1,800 watts each at full power.

Now, there is a good selection of home units that would do the same job at affordable pricing. On our smaller e-boats, we'd use inexpensive cook tops matching them with a good microwave/convection oven. On a higher-end unit, we would look closely at 240V quality home-style. I do love the CookTeks though!

Bob: I perused the kite flying thread - not sure if I'm ready for that yet! I'd go much sooner with a pair of folding masts and wind turbines! My guess is we'd get the same benefit as kites on a windy day in broad-reach cruising - straight down wind, not so much. And as I have done my share of off-shore cruising, I now prefer coastal and inland waters - can't see deploying a kite on the ICW!!!

can't see deploying a kite on the ICW!!! __________________


At least the bridge tender would have a better reason to open than a boat that doesn't bother to strike a VHF antenna .

Has anyone used a kite? Just how much work are they?

My colleagues have on a commercial ship. Their system is a hands off, deployed and retrieved from the bridge type of system.

Since you are currently cruising the keys, isn't wi-fi nice? You can cruise and stay active on the forum. Are you cruising under electric power alone?

When looking at the cost of a boat/house bank conversion to LFPs on a ROI cost comparison basis you "must" include total system impact. For example, the incredibly low resistance of the LFPs can destroy alternators, so having some means to regulate their output to control thermal shutdown or burn up must be factored into design and cost. Seems the current thought is to add a smart regulator with temperature sensor to alternator frame that gradually reduces output as temperature increases. This same issue becomes important if the BMS actuates the bank disconnect solenoid while the alternator(s) are outputting power...your diodes die. On my boat (in progress lfp conversion) this involved leaving the agm starters batteries in line as a buffer for the alternators. The use of our existing Victron inverter/chargers involved agonizing hours(read billable) of programming questions and attempts that eventually lead to a solution. In summary, this project has multi-layered costs well beyond the purchase price of the batteries and a bare BMS. These "unanticipated costs" have rendered any direct ROI benefit very upside down (not with standing indirect intangible benefits).

Joe Pica said:

When looking at the cost of a boat/house bank conversion to LFPs on a ROI cost comparison basis you "must" include total system impact. For example, the incredibly low resistance of the LFPs can destroy alternators, so having some means to regulate their output to control thermal shutdown or burn up must be factored into design and cost. Seems the current thought is to add a smart regulator with temperature sensor to alternator frame that gradually reduces output as temperature increases. This same issue becomes important if the BMS actuates the bank disconnect solenoid while the alternator(s) are outputting power...your diodes die. On my boat (in progress lfp conversion) this involved leaving the agm starters batteries in line as a buffer for the alternators. The use of our existing Victron inverter/chargers involved agonizing hours(read billable) of programming questions and attempts that eventually lead to a solution. In summary, this project has multi-layered costs well beyond the purchase price of the batteries and a bare BMS. These "unanticipated costs" have rendered any direct ROI benefit very upside down (not with standing indirect intangible benefits).

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I was able to address these issues with minimal cost, but countless hours of effort researching and implementing my install. But outside of the BMS and the cells, I was able to make it all work without additional system modifications. I do need to spend a couple hundred on an upgrade to my Magnum I/C firmware and controller to simplify the operation. I use the same solution for alternator diode protection.

And if you are paying hourly rates for the conversion, it will be hard to quantify the time/cost required. There just aren't many marine electricians out there familiar with the technology.

But the biggest barrier to ROI analysis is cycle life. At this point we only have a few data points, mostly from lab testing and a little from the EV community. Neither match our operating profiles in a real life system. Further there are open questions on "calendar" life, especially for occasional use.

I believe we will find cycle life in the 2X to 6X what we see with FLA/AGM. And calendar life somewhere between 6-12 years. But these unknowns make analysis only a best guess, no matter what values used in the analysis.

Then there are hard to quantify benefits like I think I am running my generator fewer hours. I have enough data now, need to see if I can boil it down and quantify that a bit more. Both my inverters and my DC water maker especially are happier with the extra 1/2 volt. Will that lead to longer life? Who knows. The water maker does make 5-10% more water per hour.

You have to like tinkering with new technology right now. I'm working on a better BMS for Marine derived from Industrial Automation components. In part since I'm not happy with my BMS flexibility, and a hope to have an application to simplify the installation equation for others. But it remains to be seen how well it will work when complete.

Anyone who claims a big ROI right now, ask for proof not promises. The potential does exist, but it's not proven. The exception is those with size/weight restrictions that can't be met otherwise.

Some really good info from the above posters, thanks guys.

A review of records for generator runtime shows:

From our trip departure from St Pete FL on 4/2/2011 to our LFP install in Grenada on 7/10/2012, we spent 295 nights at anchor, 1533 hours of generator time and averaged 5.2 hours of generator runtime per day.

We normally do 2 cycles per day, morning and night, consume 150Ah - 300Ah each cycle. My best over all guess is 500 Ah average daily, but it's not logged anywhere. The morning charge at 11-12AM has more to recover than the 7-8PM evening one. Primarily this runs 4 refrigeration systems and the DC water maker a couple times a week.

The 12 Trojan golf carts were still functional, but well below their original 1350 Ah rated capacity, maybe good for half of that at replacement. I think the engine room temps in the tropics may have accelerated their demise.

From the LFP install to today, we spent 127 nights at anchor, had 607 hours of generator time and averaged 4.8 hours of generator time per day.

We did not count days underway >3 hours of engine time, or days with shore power.

So...it looks like we can at least on a preliminary basis claim .4 hours a day less generator with the same loads. That's maybe $2 per day savings in fuel and maintenance? $400 a year. Not a big number, but not trivial either.

Overall in both cases the numbers were a bit higher than I expected since 4 hours per day of charging should have kept up with a 150Ah charge rate. But we must also run the generator to cook, maybe that counts for some. We do find "cooking" is the reason to hold off genset shutdown a bit more frequently than before.

Also not factored in is toward the end of life on the Trojans, we only ran the ice maker once a week and kept the supply in the chest freezer to reduce consumption. We also did not do a good job of restoring full charge to the FLA once a week or so while at anchor for extended periods. Both of these items would increase the generator time for FLA.

YMMV....

Ebaugh

In the PNW we average very close to 4 engine hours per generator hour with genset currently at 410 and engines at 1750 hours. Without AC needs our situation is very different. Maybe your lavish boating E needs lifestyle is unusual, or you should do more swimming to cool off. How do sail boaters without AC manage in your cruising grounds?

Do you have high capacity engine alternators?

sunchaser said:

Ebaugh

In the PNW we average very close to 4 engine hours per generator hour with genset currently at 410 and engines at 1750 hours. Without AC needs our situation is very different. Maybe your lavish boating E needs lifestyle is unusual, or you should do more swimming to cool off. How do sail boaters without AC manage in your cruising grounds?

Do you have high capacity engine alternators?

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It's hard to compare I think? We live aboard 365 days a year, off grid at anchor more than 50% of our nights. We used to run the AC about an hour or two a day at anchor during the evening, but for the last year its only normally run when at dock with shore power. At anchor with the trades, almost everyone does without A/C until you get to large crewed boats. True cruising trawlers are very rare compared to sailors. At least 50, maybe 100 sailboats for every trawler.

Refrigeration power is much less efficient due to much higher ambient air or seawater temperature.

We tend to spend several days at each stop, and the distances between stops are much greater. Our last "run" was 415 NM from San Andres Island to Roatan Honduras. This is a bit unusual, in fact it's the longest single leg of our trip. But overall, legs are much longer than we had on the West Coast of Florida. As a result of the longer legs and the consecutive days at anchor, I don't think we would save much with big alternators. Ours are only 90A each, but we run them much lower than that.

The answer here is solar and wind, most every sailboat has one or the other and quite a few have both. I would add solar the next time around if at all possible.