LiFePo4 Power -- Controlling Alternator and Inverter/Charger

[s/v Jedi]

Originally Posted by CatNewBee

Bad idea.
And this is why.

A full module has a higher cell voltage than a empty module.
Having modules connected to the load bus, lets say at 50%SOC, getting one module out for charging will deplete the remaining modules even faster, with high loads like inverter, and turned off modules, the remaining will be punished even more, the voltage drop is higher and very likely you will trigger low voltage protection, that can lead to a cascaded shutdown, like the blackout in London recently.

Then the full module connects to this mess with a voltage difference above 1V and very low inner resistance causing high cross module currents due to equalization, this will charge the empty modules on the load bus and somewhat drain the charged module, also stress for unnecessary cycles. You can prevent cross currents by using diodes to connect to the bus bars, but then there will be power loss by heat in high current applications, also the load will be inequally distributed, resulting the drain of the fresh cell first with much higher current due to the higher module voltage.

You can mitigate this by usung b2b charger per module and limit or control the currents but is it really worth it?

To answer your question,
Yes, I have a separate charge bus, load bus and inverter charger bus, that is a mix of both, but separately controlled by the BMS. I use a single 4S 1000Ah LiFeYPO4 battery, so no mess with cross currents. The battery is connected in normal conditions to all three busses, allowing direct supply from charge sources to loads - another advantage of this dessign. Busses are only separated and disconnected in case of an unusual cell voltage ot cell temperature to protect the battery.
Another advantage of having the busses combined in normal operation is, all charge sources contribute directly to the energy balance and feeding the loads before current is flowing into the battery, what leads to less and shallower cycles, resulting in a longer life.

Yes it's possible to come up with ways to make bad things happen but this is true for every scenario. When one is at 50% SOC and has high loads running, then why would you disconnect a battery module? But when there are only light loads running on a 90% SOC system, then I can see the advantage of isolating modules one by one to give them a full charge cycle to erase any capacity loss by memory etc.

A disadvantage of your single battery bank 1000Ah setup is that a shorted cell can bring your system down while a system with 5x a 200Ah bank will probably blow the fuse of the bank with the shorted cell or otherwise it can be quickly isolated and things continue at 80% capacity.

I can think of several more advantages (as well as disadvantages).

Inverter/charger bus... hmm, let me think about that one :-)

[CatNewBee]

I had a BMS for lead acid, GEL and AGM batteries that was dealing with independent batteries, capable to combine and separate them, even with different sizes and chemistries, ages to charge and load. Was a nice product for an RV, downside was maximum current limited to 150A.

It was quite smart, it switches on low loads between the banks to equally discharge them allowing maximum divergence of 5%, but keep them isolatad, on higher loads it combines them temporary to distribute the current across the banks, when a charge current was there, it charges the deepest discharged first to the level of the other, then combines them and charges to 80% SOC, after that, it disconnects one and charges individually the remaining 20% according to the chemistry specifications in the set up. You could also manually control the system and isolate one or both banks for maintenance. Came with a nice display and BT.

NDS iManager was the brand, small company in Italy.

https://www.ndsenergy.it/prodotto/imanager/?lang=en

[john61ct]

I think there would be no "macro" problem if the sub-bank modules were a low enough percentage of the full bank capacity, and you only rotated one out at a time.

I'm considering the same in order to include "portable powerpaks" to power an electric dinghy motor, taking ashore when roughing it overnight off-grid, backup/reserve packs for essential nav / comm gear, dedicated windlass or bowthruster packs etc.

Keeping the wear & tear (roughly) even by rotating identical modules in and out of the main bank, also not having to deal with separate charge sources at different voltages.

A safe and gentle current limiting arrangement is of course required when joining LFP modules at different SoCs to avoid too-high-amp surge flows from higher to lower.

[john61ct]

Originally Posted by CatNewBee

NDS iManager was the brand, small company in Italy.

https://www.ndsenergy.it/prodotto/imanager/?lang=en

Looks interesting, worth exploring further, for DIY ideas if nothing else.

Thanks!

[Dockhead]

Originally Posted by s/v Jedi

Yes it's possible to come up with ways to make bad things happen but this is true for every scenario. When one is at 50% SOC and has high loads running, then why would you disconnect a battery module? But when there are only light loads running on a 90% SOC system, then I can see the advantage of isolating modules one by one to give them a full charge cycle to erase any capacity loss by memory etc.

A disadvantage of your single battery bank 1000Ah setup is that a shorted cell can bring your system down while a system with 5x a 200Ah bank will probably blow the fuse of the bank with the shorted cell or otherwise it can be quickly isolated and things continue at 80% capacity.

I can think of several more advantages (as well as disadvantages).

Inverter/charger bus... hmm, let me think about that one :-)

I think we are all suffering from hangovers from lead mentality.


Why would we need to combine cells in parallel to create redundancy? There is very little Peukert effect with these batteries so why would we need to struggle so hard to keep them all combined in one big battery?


I think creating batteries out of cells connected only in series, and having a couple of completely separate batteries, would be the ideal configuration, with total redundancy (if anyone thinks we really need it).


The separate batteries might be combined at the battery level (not the cell level) if desired. For light usage one could leave one out of commission altogether at storage charge.




Concerning the "inverter bus" -- mine would have this as well, since charger/inverter connection is both charge and load depending on the operation mode.

[Dockhead]

Interesting that the Wakespeed alternator regulator has this function:


"Zero Output Technology™ -- Enables charge controller to use current monitoring capabiltiy to limit output to match house loads only when batteries are fully charged."


http://www.wakespeed.com/WS500%20data%20sheet%20web.pdf


Interesting, how does that work? That would seem to fit the bill exactly.

[Nicholson58]

Originally Posted by Dockhead

Do we need to control the charging sources with the BMS, or not?


It would seem prudent to me to be able to force the charging sources into float when the battery is full as determined by amp/hour-counting. Or do we think this is unnecessary?


I note that the Batrium BMS system can be connected to the Victron Multiplus by Canbus, but it's not clear to me exactly what it does:


https://secondlifestorage.com/t-Batr...24561#pid24561


This:



https://support.batrium.com/article/...-with-watchmon


seems to suggest that the BMS can control the charging profile.






What concerns Balmar, this:


http://www.balmar.net/wp-content/upl...re-7-19-17.pdf


strongly warns that the alternator should be shut down before a HVC is activated, which should be done by interrupting power to the brown ignition wire. Interesting question whether there needs to be a small time delay between this interruption, and activation of the HVS, and whether an alternator protector like the Sterling one makes this irrelevant.


I don't see anyway for the BMS to force the Balmar into float, but I note that the default LFP program in the Balmar has "absorption" voltage at 13.6, which is basically float I think, so it seems the Balmar automatically drops the voltage when the acceptance tapers off. Don't know if that is an adequate control and will be glad to be educated.

Read this.
There is NO FLOAT for Lithium. Float will wreck them.
https://marinehowto.com/lifepo4-batteries-on-boats/

You need to reprogram all of your charging devices; solar, alternator, inverter-Charger. Most of these have downloads to do the change. Alternators need external controllers.

[Inkog]

Originally Posted by Nicholson58

Read this.
There is NO FLOAT for Lithium. Float will wreck them.
https://marinehowto.com/lifepo4-batteries-on-boats/

You need to reprogram all of your charging devices; solar, alternator, inverter-Charger. Most of these have downloads to do the change. Alternators need external controllers.

A battery needs potential to charge. This means that the voltage of the charger has to be higher than the voltage of the battery. If your Li bank has been charged to 100% at 13.8v (resting) and your charger goes into Float mode at 13.6v, the battery cant and wont take a further charge. There is no harm done to the battery if the "float" charge is below the nominal battery voltage.

The only reason you shouldn't pull a lot of amps from your bank while in Float is that any voltage sag from the load could cause the charger to go back into Bulk and/or Absorption which is at higher voltage, so you'd be back to charging your full battery. The key here is that you want a charger that has a highly configurable absorption mode. If you can turn it off or adjust the voltage to be the same as your float voltage (13.6v in this case) that's ideal. Otherwise set the absorption for the shortest time possible. Often this is defined as a fraction of the time spent in bulk.

If you can turn off or configure absorption voltage, and configure float voltage to be below the banks nominal voltage there is no need to micro manage your charging system. Going into Bulk as needed is perfectly fine. You can adjust the bulk voltage down 80%-90% resting for longevity vs max capacity.

[Inkog]

The main killer of LiFePo is charging too fast, not too much. Most manufactures recommend charging at a max amperage of .5C, or half the bank capacity. Less is better. A small bank of 200Ah should never be charged at a rate higher than 100A, although they'll happily consume twice that if depleted and you let them. This makes current limiting very important for small banks. Large banks of LiFePo will happily meltdown your alternator, easily sucking down their total Ah capacity in amperage if depleted. Making current limiting very important for large banks also

[CatNewBee]

Originally Posted by Inkog

The main killer of LiFePo is charging too fast, not too much. Most manufactures recommend charging at a max amperage of .5C, or half the bank capacity. Less is better. A small bank of 200Ah should never be charged at a rate higher than 100A, although they'll happily consume twice that if depleted and you let them. This makes current limiting very important for small banks. Large banks of LiFePo will happily meltdown your alternator, easily sucking down their total Ah capacity in amperage if depleted. Making current limiting very important for large banks also

LFP can be charged and discharged continously at 1C and even quick charged at 3C, if necessary. Limiting factor is the ability of the source.

[john61ct]

Yes but such high rates, especially charging, does reduce cycle longevity.

Which of course may not be important to everyone, especially if you're already confident of getting over a decade.

[Inkog]

Originally Posted by CatNewBee

LFP can be charged and discharged continously at 1C and even quick charged at 3C, if necessary. Limiting factor is the ability of the source.

Sure you can, I said as much, but that doesn't mean you should. The quickest way to kill a LiFePo is charging too fast (Other than trying to charge below freezing) . I don't know a single manufacturer of 12v packs that recommends over a .5C charge rate. I'd love for you to prove me wrong and show me one.

[john61ct]

If by "12V pack" you mean drop-ins, that's because they cheap out on the BMS.

Proper packaged system vendors like Lithionics/Ocean Planet), Victron, MasterVolt, I dunno.

I agree not a good idea if you want max longevity, but a 1C rate charge only occasionally when required will have much less of a longevity hit than going below 50% DoD.

In an EV context even 3-5C is often considered worth the lost cycles, motorists want to get back on the road ASAP.

Of course assuming no heat issues, the surrounding infrastructure all has to be up to snuff.

Discussions about LFP technology in general really should be segregated from drop-ins, comparing apples to oranges.

[Inkog]

Originally Posted by john61ct

If by "12V pack" you mean drop-ins, that's because they cheap out on the BMS.

Proper packaged system vendors like Lithionics/Ocean Planet), Victron, MasterVolt, I dunno.

I agree not a good idea if you want max longevity, but a 1C rate charge only occasionally when required will have much less of a longevity hit than going below 50% DoD.

In an EV context even 3-5C is often considered worth the lost cycles, motorists want to get back on the road ASAP.

Of course assuming no heat issues, the surrounding infrastructure all has to be up to snuff.

Discussions about LFP technology in general really should be segregated from drop-ins, comparing apples to oranges.

I'm speaking of any manufacture that produces and/or warrantees LiFePo4 batteries meant for boat and RV applications. You can call them Drop-ins or whatever you'd like. Most people here are looking for turn key, safe solutions, not EV or even fringe DIY. I would think in this context we would be talking about the same things.

[john61ct]

Maybe you should read some past threads here to become familiar with the community.

The usual turnkey packaged systems here are from the vendors I cited, usually installed by professionals and cost thousands.

The drop-ins you're talking about are widely considered sub-par by those whose opinions are most respected here.

There are hundreds of systems in use where the owner has bought bare cells from a known-good LFP maker - e.g. Winston/Thundersky/Voltronix, CALB, GBS, Sinopoly - then selected an appropriate BMS - as with Batrium as discussed in the OP - and put in a well designed architecture of quality gear far superior to what's inside any drop-in.

DIY does not mean poorly implemented, but does take a decent level of knowledge and skill.

Trojan's Trillium line has recently started shipping, apparently OEM is K2, and their more sophisticated approach, along with Victron's lower end lines, are a sort of "hybrid drop-in", perhaps closer to the top packaged systems.

Of course it will be years before we know whether they measure up or not.