LiFeP04, your complete system cost

[john61ct]

You talking second-hand?

Repeated for emphasis, OK for land-based hobbyists.

Not in production on a boat.

[newhaul]

Originally Posted by john61ct

You talking second-hand?

Repeated for emphasis, OK for land-based hobbyists.

Not in production on a boat.

don't take this wrong but don't you mean not on your boat.

[DumnMad]

Originally Posted by boat_alexandra

This must be a sorry autopilot. My autopilot uses 1-5 watts depending on seas on my boat. When we tried it on a 50ft ketch using a hydraulic pump it used about 5x as much power, so it's still always below 50 watts, and hydraulic is not efficient.

24 tonne ketch in big seas. You parked next to us once. 2 litre pump @ 12volts.

I was thinking the Lead batts might have less AH capacity if there was a higher current draw.

[Dockhead]

Originally Posted by a64pilot

. . God, without getting into that 10,000 response thread, is there a decent how to published? I assume maybe that there is a supplier that will ship cells already balanced? To show my stupidity, shouldn’t a BMS balance cells at each charging? My kilowatt Li-Po Dive scooter did, or said it did anyway.

Patience! Just spend a couple of days reading up on it, and you will figure it out. I had the exact same question a few weeks ago, and I discovered that it's not nearly as complicated as I feared. With your level of knowledge in technical things, it will be a piece of cake.



A very short oversimplified summary of what I learned:


* Balance the cells before you use them; read up on top-balancing vs bottom balancing.


* BMS will take care of it from there, but you have to check periodically.


* All charging sources need to be set up to (a) give the right voltage for the right time; and (b) be capable of being shut off safely in case of a HVC event -- a challenge for alternators. This needs very careful study and don't make a mistake.



* You need the BMS, an amp-counting battery monitor, contactors to implement the HVC and LVC, appropriate battery boxes and connectors etc.


* Take care you don't burn up your alternator. Derate it and/or use a really heavy duty one.



* Optional: you might like a bigger alternator and/or a bigger charger to take advantage of the higher acceptance rate.


* Enjoy.


It's not nearly as much of a "science experiment" as I thought.

[Dockhead]

Originally Posted by DumnMad

24 tonne ketch in big seas. You parked next to us once. 2 litre pump @ 12volts.

I was thinking the Lead batts might have less AH capacity if there was a higher current draw.

Now we know what you mean!


You can do your own Peukert Factor calculation based on your actual lead bank, but that does not sound like a significant Peukert issue for a decent sized bank.


Where the lack of voltage sag and very good Peukert Factor of lithium is really valuable is with windlasses and especially bow thrusters.


I figure my 10hp Sleipner bow thruster will have more than 20% more power, and will run cooler, with lithium -- a significant advantage.

[DumnMad]

Originally Posted by Dockhead

Now we know what you mean!


You can do your own Peukert Factor calculation based on your actual lead bank, but that does not sound like a significant Peukert issue for a decent sized bank.


Where the lack of voltage sag and very good Peukert Factor of lithium is really valuable is with windlasses and especially bow thrusters.


I figure my 10hp Sleipner bow thruster will have more than 20% more power, and will run cooler, with lithium -- a significant advantage.

Thanks Dock. We have 600AH but they're getting old.

[john61ct]

Originally Posted by newhaul

don't take this wrong but don't you mean not on your boat.

No.

All kinds of speculative DIY science projects are so much more dangerous on a boat than in a S&B fixed location.

Not in a campervan either, although at least you can walk (run) away there.

New Prismatic cells from a known trusted vendor only.

Even DIY-BMS can be done safely only by a certain type of boater. For 99% out there only a BMS-packaged system (Victron etc) would be safe enough.

[john61ct]

My list of known-good makers

Systems: OceanPlanet (Lithionics), Victron, MasterVolt, Redarc (Oz specific?)

Bare cells: ​Winston/Voltronix, CALB, GBS, A123 & Sinopoly

If anyone has additions to suggest, that would be appreciated.

[a64pilot]

Originally Posted by john61ct

OK for land-based hobbyists.

Not in production on a boat.

And are you even talking LFP? Most cylindricals aren't, therefore dangerous wrt thermal runaway.

Don’t get in a Tesla then, cause that is all it’s packs are

[a64pilot]

Originally Posted by Dockhead

It's not nearly as much of a "science experiment" as I thought.

From what little I have seen it is, or sort of is.
The BMS ought to be the HVC and LVC cutoff, no need for more home made boxes.
Instead of an HVC and LVC cutoff, why not a simple voltage alarm, set it conservatively, and you take action?

Instead of interrupting charge sources, can’t you control charge with voltage? Set voltage for whatever 80% SOC equates to, and won’t it just stop charging when voltage reaches equilibrium?

Ive seen individual cell voltages monitored, is this really necessary if they don’t drift after initial charge?

[john61ct]

Originally Posted by a64pilot

Don’t get in a Tesla then, cause that is all it’s packs are

Tesla has billion$ of top-shelf engineer hours invested just in its redundant thermal management systems.

So NP, the odds are slim I will be burned to a crisp by a control system circuitry failure.

A Victron, Mastervolt or Lithionics packaged LFP system is likewise much safer than something I cobble together myself.

But take apart a Tesla, remove the cell packs from their engineered safety systems and rig up a DIY House bank system from that?

No more protection from thermal runaway?

Do not anchor anywhere near me please, and I'll host sundowners my place OK? Boom bad!

I am pretty sure when the ABYC working group comes up with standards to allow non-lead storage systems to be covered by insurance, similar ideas will be clearly codified.

[john61ct]

Originally Posted by a64pilot

The BMS ought to be the HVC and LVC cutoff, no need for more home made boxes.
Instead of an HVC and LVC cutoff, why not a simple voltage alarm, set it conservatively, and you take action?

Instead of interrupting charge sources, can’t you control charge with voltage? Set voltage for whatever 80% SOC equates to, and won’t it just stop charging when voltage reaches equilibrium?

Float is potentially harmful to longevity even at lowered voltage, tge default state should be low SoC not high.

Relying on the owner to be present to hear alarms and be in a position to immediately take action is not appropriate when a system failure can wipe out thousands of dollars or burn the boat.

BMS is final-layer protection, only used when normal-use charge / LVD controls fail.

The necessity for cell-level monitoring is disputed, many feel even active balancing is required. I do not.

[CatNewBee]

cell level monitoring is necessary, but done by the BMS, so no additional effort. OVP / LVP is based on cell voltages usually. Otherwice the BMS is scrap.

[a64pilot]

So, how do you terminate charge, voltage or time?
I assume a large relay that all sources tie to and disconnect?

[Dockhead]

Originally Posted by a64pilot

From what little I have seen it is, or sort of is.
The BMS ought to be the HVC and LVC cutoff, no need for more home made boxes.
Instead of an HVC and LVC cutoff, why not a simple voltage alarm, set it conservatively, and you take action?

Instead of interrupting charge sources, can’t you control charge with voltage? Set voltage for whatever 80% SOC equates to, and won’t it just stop charging when voltage reaches equilibrium?

Ive seen individual cell voltages monitored, is this really necessary if they don’t drift after initial charge?

You have more technical training and knowledge than I do, so I don't think there is any point in my trying to give a lecture based on my own reading. Better you should do the reading and give ME a lecture.


For whatever it's worth -- this system does not seem complex to me, if you just forget about the architecture of your lead power system and put a clean sheet of paper in your mind.



What "additional home made box"? It's just a couple of contactors. The concept is very simple, and designing and wiring up such a system is well within even my modest technical abilities.


As John61 said, HVC and LVC are last-ditch protection, not daily battery management. For daily battery management, the BMS needs to have the ability not only to sound alarms, but to control the mains charger and the alternator. This is something which may be difficult for some, easy for others. With Balmar, Victron and Outback equipment, gear of that level, should be pretty straightforward.




Actually lead battery banks could use a LVC just as much as lithium could, and they exist ("battery savers"). If I were designing a new lead acid power system today, I would surely include one of these. This is not a complicated system and would prevent probably 80% of battery damaging events even for lead.