LiFePo4 -- Parallel or Not?

[nebster]

Originally Posted by mbartosch

And this is a very important one. One of the things I have learned over time is that it may look very easy on paper, but it may be difficult to execute in limited and inaccessible space.
A simple connection line or a connector dot in the schematics may cost hours of work in real life.

Wise words, those.

In my case, I found a way to squeeze 96 cells into my available space. Doing that, though, made it impossible to correctly wire for 6p then 16s. It turns out I could have done 2p16s3p, but at the time I decided to go with 16s6p, partly because it made everything prettier and symmetric, and partly because that left open the option to add additional 16s1p strings piecemeal (in a different location on board) if I determined that I wanted/needed to expand my battery.

Now that I have convinced myself that BMS is not even really necessary in my setup, it makes it even easier to justify the string approach, because BMS-per-string is quite expensive.

[Kenomac]

Unless you plan to retain your present boat for another five years or more and cancel your planned “next boat” often discussed, my advice to you is to drop in $2,000 worth of Trojan batteries and find out what caused their very early demise and correct the problem. Our Trojans are going into their 9th year and still going strong. Your issue might also be just one bad Trojan battery with a replacement cost of about $200 USD.

You’ll never get back any of the money spent on lithium when you sell your boat... especially in the short term. But is your money...

[tanglewood]

Originally Posted by nebster

Well, there is at least one other consideration: geometry. It can be easier or harder to wire up a particular topology, with a selected cell of a certain size, in a given space, properly.

True. Hadn’t considered that.

[Delfin]

Originally Posted by Kenomac

Unless you plan to retain your present boat for another five years or more and cancel your planned “next boat” often discussed, my advice to you is to drop in $2,000 worth of Trojan batteries and find out what caused their very early demise and correct the problem. Our Trojans are going into their 9th year and still going strong. Your issue might also be just one bad Trojan battery with a replacement cost of about $200 USD.

You’ll never get back any of the money spent on lithium when you sell your boat... especially in the short term. But is your money...

The performance advantages of LFP over LA are sufficient justification for the former, IMO. Having lived with both, unless a sale of the boat was imminent, I'd still invest in LFP.

[Dockhead]

Originally Posted by Delfin

The performance advantages of LFP over LA are sufficient justification for the former, IMO. Having lived with both, unless a sale of the boat was imminent, I'd still invest in LFP.

Indeed.


What Ken says about not getting the money back is true, of course, but that is true about any improvements to any boat. I will probably sell my boat in the next couple of years, but I'm not going to stop keeping her in good condition and making her more and more suitable for MY needs.



I use her a lot and sail many thousands of miles a year, and I want to enjoy those miles. I'm tired of lead acid and am looking forward to this improvement.


Plus it will be good training for the next boat.

[a64pilot]

I believe most with lithium’s carry them to the next boat. It’s tough to sell a boat with a Lithium bank, you really restrict your market.
It’s just about impossible to get a lead acid battery to run away if the charge voltages are correct.
How many automobiles have you heard or whose battery ran away and caught fire?

[witzgall]

I would echo Delfin's recommendation for Lithionics. They are well built, tested and profiled before they leave manufacturing. I would also consider Victron and MV. THey all have good BMS designs.

If doing things DIY, the old advice was to only parallel cells, not modules. I think that some of the more recent BMS designs have addressed some of the concerns around the issues of paralleling modules. It does make the BMS and control system more complicated though. .



Chris

[Dockhead]

If you have multiple modules, you could use them alternately or sequentially, rather than paralleling them. The reasons we don't do this with lead don't apply to lithium.

Originally Posted by witzgall

I would echo Delfin's recommendation for Lithionics. They are well built, tested and profiled before they leave manufacturing. I would also consider Victron and MV. THey all have good BMS designs.

If doing things DIY, the old advice was to only parallel cells, not modules. I think that some of the more recent BMS designs have addressed some of the concerns around the issues of paralleling modules. It does make the BMS and control system more complicated though. .



Chris

[Kalimniosjohn]

I am in the early stages of reading/learning/planning for a lifepo4 bank. I think I’ve decided on 16 CALB 200 amp cells that I’d run 4s4p. Basically making 4 200 amp 12v batteries that I’d then wire in parallel. This thread has me a bit confused though. Is there a different way?

What are the complications adding bms to a setup like this?

[CatNewBee]

Originally Posted by Kalimniosjohn

I am in the early stages of reading/learning/planning for a lifepo4 bank. I think I’ve decided on 16 CALB 200 amp cells that I’d run 4s4p. Basically making 4 200 amp 12v batteries that I’d then wire in parallel. This thread has me a bit confused though. Is there a different way?

What are the complications adding bms to a setup like this?

Each separate battery should have it's own BMS. If you want to use only one bms with solenoids, contact the cells first in parallel and then the packs in series.

Best solution however would be to chose the cells to your desired capacity. Like 700Ah cells or 1000Ah cells.

[JuliaYu]

The 300a/h 24v module looks good to me. I'll investigate whether it will fit and whether I can actually buy it over here. It costs $8,800 in the U.S., which with VAT will be over $10,000 in Europe if not more. I'll have to think whether that's worthwhile compared to $3,000 worth of cells plus maybe $1,000 more for BMS and battery box.
[/QUOTE]

$8800 for 24V 300Ah is too much... I can help you figure out the best cost for 8×300Ah＋BMS＋battery box

[JuliaYu]

If you raise up this question to Winston factory, they would give you the same answer as experts mbartosch and alctel said Stay less P as much as you can.

[hzcruiser]

Follow-up to a different thread to avoid drifting off-topic there:


https://www.cruisersforum.com/forums...ml#post3285361

Parallel linking the cells first, then putting 4 of such blocks in series to get nominal 12V would present an arguably bigger disadvantage IF one cell goes bad: it would still pull down the other cells that are linked in parallel which causes all the batts to deteriorate until it is being noticed by the user.


To my knowledge there is no BMS that can differentiate between an acceptable (or 'normal') balancing current and one caused by a faulty cell.
Hence I'm not applying such a setup nor do I recommend it.


My suggestion, albeit not called "best practise" yet, is to put the power where it's needed: e.g. an LFP for the windlass up front, one for the inverter located close to it, one for the other consumers on board. They're still connected with wires big enough to carry the maximum current in case one of them goes bad, but for normal operation the charge currents will be smaller (hence fewer losses given the same cable) and the high discharge currents suffer only minimal losses as the wire run to the active consumer is very short, less than a foot in most cases.
For example on my boat right now (it's midnight in Sydney but I'm overseas, stuck due to <you know what> ):


Screen Shot 2020-11-30 at 1.10.00 pm.jpg Views: 107 Size: 303.3 KB ID: 227906" style="margin: 2px" />


The different LFPs are of different capacity between 40 and 100Ah. Some are active on the bus, one is disconnected to prevent it from daily shallow cycling while I'm not on board.

[hzcruiser]

(A timeout occured when I added some more text):

The different LFPs are of different capacity between 40 and 100Ah. Two are active on the bus (relay is closed), 'Settee top' is disconnected

• as it is not needed right now,
• to prevent it from daily shallow cycling while I'm not on board and
• to check its self-discharge rate.

The starter batteries are lead-acid and are disconnected also. Since I haven't been on board for several months I want to be able to top them up when needed, in which case I can turn on the relay for a day and we are good to go again. The boat uses about 500mA at night for the few devices that are left on.

The second screenshot shows the daily shallow discharge and limited charge current to 14.1 V as I don't want the LFPs to get charged to 100% when not in use.


Hope this helps clarify a few things and maybe pique some interest in, what I would call, "modern battery management" in a diverse setup using different chemistries and different size batts.


The goal is to have the most economical power management setup possible, where

• I don't have to replace all batteries because there is a dud one,
• I can detect the faulty batt and disconnect it from the bus, even remotely
• I can source batteries at different times/years depending on boat consumption,
• I can source batteries at the best market price at that time; yet
• I can replace individual batts because they are old, dead or too small by then (e.g. if a bigger inverter gets added).

Last not least, being able to place batteries in different spots can be important in terms of balancing the boat properly.

[T1 Terry]

Originally Posted by hzcruiser

Follow-up to a different thread to avoid drifting off-topic there:


https://www.cruisersforum.com/forums...ml#post3285361

Parallel linking the cells first, then putting 4 of such blocks in series to get nominal 12V would present an arguably bigger disadvantage IF one cell goes bad: it would still pull down the other cells that are linked in parallel which causes all the batts to deteriorate until it is being noticed by the user.

That doesn't make logical sense ... 4 x 100Ah cell in parallel is way in front of 1 x 400Ah cell. If one plate in the 400Ah cell develops a rubbish build up that shorts the graphite plate to the LFP plate, the whole 400Ah cell is stuffed. If that were to happen in a 4 x 100Ah in parallel arrangement, the dropping cell voltage would be just as apparent as it would be for the single 400Ah cell, but it would be easy enough to determine which cell was the problem by simply dropping one cell out and see if the problem went away. A short cable made up to jump from one cell over the next cell so the cell in between was bypassed, only need to do one side, the negative or positive and measure the by passed cell voltage 12 hrs later. If the voltage is much the same as when you disconnected it, this is not the problem cell.

The issues raised with multiple cell links causing a problem just means the job wasn't done properly the first time.
Use a nylon scourer pad like the 3M discs that fit the rubber drill adapter and polish the cell terminal until it is shiny all over, then paint the surface with a generous coating of Alminox to stop further oxidisation from occurring.
If you only plan to pull a 300 amp load or less from the battery , split the heat shrink on the copper links pack supplied, polish both faces of the link where they will bolt onto the terminal and the next links will bolt on top, a generous coating of Alminox on all faces and a new piece of heat shrink to build a two pieces of the thin copper links into a single link. Make sure there is plenty of Alminox coating each contacting surface and bolt them down snug. The Winston LYP cells now come with helicoils in the terminals so less likely to strip out a thread when tightening down the terminal bolts.
Remember, it is the contact between the terminal and the link that carries the current, not the stainless bolt, it just holds the contact tight. Never try to use aluminium cell links or flattened out copper pipe, you need that flexibility provided the thin copper links with the hump in the middle between the cell terminals or the link itself will move under the bolt and slowly wear away loosening the clamping effort the bolt applies and a high resistant joint will result.
Been doing this for over 10 yrs now, a lot of systems installed in that time and no problems, but those that decided using a single cell of the capacity they required was the better choice quickly regretted it because balancing issues between cells was a constant headache and they had no way to determine if there was a fault in one of the cells or if it was just a dirt connection causing the problems.
If you think the battery copes a rough time in a boat, you need to see what happens with a battery in a caravan dragged up one of the many dirt roads in outback Australia.

T1 Terry