1400 Ah Lithium from cells

[exitstrategy]

Originally Posted by CatNewBee

Yes, the yellow bricks from Winston

Here is a link to those specific cells. They look great, and at $1100, it is very price competitive.

I totally concede that it would make a much nicer/simpler build. My only concern is what if I had a bad cell DOA. Or one failed later. We are hardly ever someplace where shipping will be cheap.

https://www.ev-power.eu/Winston-40Ah...l-product.html

[exitstrategy]

Originally Posted by PaulinOz

Awesome write up Erik thanks for taking the time to share.

Thanks man!

[exitstrategy]

Originally Posted by LoudMusic

Wow that's a lot of usable power for a relatively low price of entry. Thanks for the write up and images.

Thank you loud music!

[exitstrategy]

Originally Posted by Malabarista

Hey mr Exitstrategy. You have finally done it! I think i now understand. Thanks for such a well written and informative article. I have read lots about LiFePO and been thoroughly flummoxed. Thanks

Thank you, I too found a lot of the LiFePO4 threads confusing at times.

[CatNewBee]

Originally Posted by kmacdonald

... The 30W panel can charge it easily.
I find it hard to believe a 1400Ah bank is necessary on a boat.

Well it depends on what you are up to.

2 Fridges + 1 Freezer add up a lot, the washer / dryer for the Admiral, fresh water (watermaker) + hot showers and warm water for the galley, some AC units for cooling or heating for some hours. Its a condomaran...

My intention is to get rid of propane in the galley and use an induction cooktop plus convection oven instead of the propane stuff. All powered by solar (1600Wp). I will have a propane bottle only for the BBQ at stern.

I guess 12V / 1.000Ah / 12kWh are not so big for this stuff. Also want to fill up some scuba tanks from time to time.

Well, we do have an Onan 9kW as a backup on board, I hope we will not need it frequently, but IF, the battery will be charged from EMPTY to FULL in less than 3 hours (80A stock charger, 220A Victron Quattro 12-500/220, 100A solar)...

[exitstrategy]

Originally Posted by kmacdonald

I use a 20Ah, 12V LiFePO4 battery to power the VHF radio, depth finder, cell phones, tablet, and lights. I used to charge it with a 60W solar panel but found that it was way more than necessary so I replaced the 60W panel with a smaller 30W panel. Without charging, the battery can last over a week. The 30W panel can charge it easily.
I find it hard to believe a 1400Ah bank is necessary on a boat.

I was very honest throughout the article that we use a lot of energy, and our goal was to match the thoughtless, but thoroughly green land-based lifestyle of just having power when we wanted it.

Now, looking over your list I see that you have a nice collection of accessories. You do not actually need a depth finder - you could easily scull ahead on your dink and inspect the shallow water before proceeding. And a cell phone? Who needs that modern toy? And a tablet? What, next you will be telling us you use electronic charts!

I am teasing you. You don't actually need that stuff any more than we need all the stuff for our 5 person family plus guests.

Never was about needs

[LoudMusic]

Originally Posted by exitstrategy

I was very honest throughout the article that we use a lot of energy, and our goal was to match the thoughtless, but thoroughly green land-based lifestyle of just having power when we wanted it.

Now, looking over your list I see that you have a nice collection of accessories. You do not actually need a depth finder - you could easily scull ahead on your dink and inspect the shallow water before proceeding. And a cell phone? Who needs that modern toy? And a tablet? What, next you will be telling us you use electronic charts!

I am teasing you. You don't actually need that stuff any more than we need all the stuff for our 5 person family plus guests.

Never was about needs

He's just jealous.

[exitstrategy]

Originally Posted by nebster

Others have commented on safety issues, and for new readers those are legitimate concerns. Inadvertently bridging an LFP cell can be a ... life-changing experience.

I was actually very concerned about this potential hazard, so outside I experimented with very briefly shorting a terminal across a single cell, and across a 4s and even across a parallel. And for sure you get instant spark feedback - just like lead acid battery, but I found you are naturally on guard and ready to remove the wayward short instantly. I measured the cells after that, and yes there was a measurable not an existential drop in the affected cells voltages.

Originally Posted by nebster

It may be that using teenagers to do pack assembly is an ingenious choice: they have better dexterity, smaller fingers, and superior eyesight. I know all of my sketchiest moments building up my system have come when assembling and disassembling the cells!

I agree, that the team must be especially mission focused during the build up and down. Part of our homeschooling on the boat involves the boys doing anything they are capable of, and learning what they need to do to be capable of the rest. I disagree with coddling them and protecting them from all possible dangers, and then when they turn 18, sign them up for a life of debt... In other words, I believe that kids are much more capable than modern society has normalized.

Originally Posted by nebster

One suggestion on nomenclature would be to make clearer the distinction between power and energy. It is usually possible to infer which one someone means when they mix them up, but sloppiness here can lead to mistakes or confusion. In a larger system, it's a good idea to internalize the difference between the two and to discuss engineering choices around both -- each in the right context. And, of course, the units for each are different.

Good feedback, I will clean up the units and make it more clear on a second edit.

Originally Posted by nebster

There is a mention of high power consumption on a contactor that was going to be used in conjunction with a LVD, but I didn't see the details. It is possible to design a pretty low consumption design that works for this purpose, so I'm curious what happened here. Did you look at contactors with economizer coils? Do you have any numbers or data you can share here?

Yes, here is a picture-diagram of the recommended design from TECC, I was very happy with them overall so I did not spend much detail in the article complaining about the LVD:



The relay in the background is the power hogging one for LVD. As it was upstream from all other instruments I could only hazard a guess of its consumption based on how quickly it drained the much smaller portion of the parallel net that it was wired into on the first wiring. But on the order of 10-15 Ah

Originally Posted by nebster

I see several times either 3.65v or 3.6v mentioned. I imagine you are not actually charging (or even top-balancing) to those high voltages day to day? Other than to trigger an occasional BMS shunt rebalance, staying lower will get you almost the same capacity and probably a lot more cycle life. Shoot for 3.45 or even lower if you can.

Sorry, yes, I should have been much more clear about that. Good feedback.
I use 13.8 / 4 = 3.45v for charging.

Originally Posted by nebster

4. The pack in this thread appears to employ an "active" BMS with top charge-shunting/rebalancing. These BMSes are relatively more expensive and tend to scale the cost unfavorably in a series-first design. It is also possible to design a pack that performs well with only passive monitoring, and then the management component can be much less expensive in absolute terms but also in proportion to the cell costs. This, along with a high ratio of series count to parallel count (say, 16s4p for a 51.2v, 20kWh nominal pack) can certainly tilt the scales in favor of going with s-then-p.

Yes, you are correct using the active BMS, I thought that this would give me better daily performance and peace of mind, and pro-long the need for me to go and pull it all apart for a periodic re top-balance.

[kmacdonald]

Yep guys, I see it comes down to how we use our boats.

As far as being green, I'm not so sure about that. It takes over a gallon of fuel to make a gallon of ethanol that is mixed in our gasoline. We are told it's part of being green but in reality it's not and we are forced to pay more for gas and fund the farm subsidies at the pump.

[kmacdonald]

How does the relatively high failure rate (at great expense) of large LiFePO4 banks affect the rational decision making process? Is is just disregarded or does it only happen to other people? Or is it "I can make it work when the pros couldn't"? Don't get me wrong, I love the light weight, fast charge, deep cycle ability, and being able to be stored at PSOC that LiFePO4 offers but is it really up for prime time to the average cruiser?

[CatNewBee]

I use those for LVP / OVP (low voltage protection / over voltage protection).

They are bi-stable platching relais with built-in electronics, no power consumption in any state, need small positive impulse to set / reset.

I use a 100µF capacitor in series with the signal to create an impulse out of a static voltage from the output of the bms. a small resistor about 1kOhm on the input of the capacitor towards ground discharges the capacitor when the signal goes of, so it can process the next on signal quickly. Its a SET / RESET relay with separate inputs - you can use a small signal relay with3 contacts (NC/NO) and put the middle connector to plus 12V to flip this if you have only a on/off output (NC goes to SET, NO goes to RESET, both over a capacitor as explained above.).

[CatNewBee]

Originally Posted by kmacdonald

How does the relatively high failure rate (at great expense) of large LiFePO4 banks affect the rational decision making process? Is is just disregarded or does it only happen to other people? Or is it "I can make it work when the pros couldn't"? Don't get me wrong, I love the light weight, fast charge, deep cycle ability, and being able to be stored at PSOC that LiFePO4 offers but is it really up for prime time to the average cruiser?

We are not average cruisers I guess - sorry for that.

[kmacdonald]

Originally Posted by CatNewBee

We are not average cruisers I guess - sorry for that.

OK, just what I thought, "I can make it work when the pros couldn't"

I've made my LiFePO4 work for 3 or 4 years but I wouldn't risk it on a large install. Sooner or later I will make a charge or discharge mistake and ruin the small bank. I wouldn't mind a $150 setback but $15000 would be hard to swallow.

[CatNewBee]

Originally Posted by kmacdonald

OK, just what I thought, "I can make it work when the pros couldn't"

I've made my LiFePO4 work for 3 or 4 years but I wouldn't risk it on a large install. Sooner or later I will make a charge or discharge mistake and ruin the small bank. I wouldn't mind a $150 setback but $15000 would be hard to swallow.

Its more a 5.000$ instead of a 15k One cell is about 1.1k€, but it's a lot of money too. on the other hand, good deep cycle GEL / AGM are also very expensive in that capacity. You would need 2000Ah to compare, this makes 10 x 200Ah AGM, well the 5.000$ are not so far away.

[kmacdonald]

Originally Posted by CatNewBee

Its more a 5.000$ instead of a 15k One cell is about 1.1k€, but it's a lot of money too. on the other hand, good deep cycle GEL / AGM are also very expensive in that capacity. You would need 2000Ah to compare, this makes 10 x 200Ah AGM, well the 5.000$ are not so far away.

The difference is the lead batteries are very forgiving compared to LiFePO4. Large commercially available LiFePO4 banks with BMS were well over $5k. I'm not sure anyone is still offering them. Too many failures.