LFP FLA hybrid

[tanglewood]

Sorry, I can be dense at times over acronyms. What is ICE?

[Dockhead]

Originally Posted by ramblinrod

. . . With appropriate charge sources an FLA bank is pretty idiot proof.. .

What you consider to be "an appropriate charge source" is simply not an option for very many cruisers.


Besides that, even with a large (relative to consumption) solar bank, you can't say managing lead power is "idiot proof". If we were looking at it from zero, without a lifetime of experience with lead acid batteries like all of us have, we would be amazed at the Dr. Frankenstein gothic 19th century nature of lead-acid power. Our children or grandchildren, I am very sure, will look it just like that, pretty soon. You have to keep them full of water but not overfilled, you have to use the right kind of water, you have to make sure they are fully charged at least every few days, you have to equalize them, you can't over-discharge them and for God's sake you can't leave them discharged, you have to be careful about boiling the electrolyte, etc. etc. etc. They are a very high maintenance system. We are just accustomed to this because we've been using them since childhood.

[john61ct]

Originally Posted by tanglewood

Sorry, I can be dense at times over acronyms. What is ICE?

Dino juice power sources, alts and gennies.

Internal Combustion Engines.

As opposed to agency in need of. . .

[ramblinrod]

Originally Posted by Dockhead

I'm sure you have plenty to contribute, especially what concerns practical experience, but do you actually understand how high voltage transients are produced? Reading this makes me doubt it. Hint: It is not current, but rate of change of current, which figures in the formula. The other parameter is inductance in the circuit. That is why a very low current device like a relay coil can produce a dangerous voltage spike requiring a snubber or a flyback diode.


This is also why a very high current resistive load like a calorifier coil or an electric heater, causes zero problem with high voltage transients, despite the high current.

Yes, I know how high voltage transient spikes are produced.

Yes, it is very easy to produce high voltage transient spikes when suddenly switching a high current source in circuit.

When it comes to LFP emergency disconnects and reconnects, this is exactly what we are facing, low voltage / high current induced transient voltage spikes that may wipe out all electronic devices connected if not protected from such an event.

LFP drop-ins (integral BMS) and discrete BMS may due nothing to protect the boat from this. Hence the need for hybrid LFP / FLA (the FLA acting as a big filter capacitor), or another method to manage.

If one connects the alternator to the LFP with DC/DC charger to the FLA, this can be bad news for the alternator. The other way round, no problem.

However, one now needs a significant DC/DC to take advantage of the high acceptance of the LFP, and they still need to recharge the energy drawn from the FLA, that has the diminishing acceptance to full charge and sustained PSOC issue.

Problem not solved.

[john61ct]

Originally Posted by rgleason

Please substitute LFP in place of LA in this post. Sorry I don't know what I was thinking. Its FLA and LFP. Sorry for the confusion.

I thought so.

Maybe go back and read my amazed corrections of your resulting misconceptions

ideally quoting your misstatements and giving new corrected versions

in order to ensure noobs coming along later via google are not misled.

[Dockhead]

Originally Posted by ramblinrod

Yes, I know how high voltage transient spikes are produced.

Yes, it is very easy to produce high voltage transient spikes when suddenly switching a high current source in circuit.. . . .

High current sources? The qualities of the power source, high current or low current, have nothing to do with high voltage transient spikes



Really, you should read up on this stuff before you post about it. I recommend this: http://www.nhu.edu.tw/~chun/BE-Ch14-...Transients.pdf. Don't be afraid to ask questions.

[evm1024]

In regards to the original topic I came across a book that might be interesting to read.

I have not read it and do not have a copy (perhaps my library will pick up a copy).

The book is:

Lead-Acid Batteries for Future Automobiles

eBook ISBN: 9780444637031
Hardcover ISBN: 9780444637000

It is a bit spendy....

https://www.elsevier.com/books/lead-...-0-444-63700-0

I've looked at some excerpts and there are sections on LFP FLA hybrid cars. Might be worth a look.

[tanglewood]

Originally Posted by Dockhead

Thanks for this, and I believe you, but I guess that we need to think one step further than just a normal shutdown of the charge source (easy on my system with Victron and Balmar), and make sure that even an emergency cutoff will not wreck anything with an inductive voltage spike.



This requires some engineering, but I'm sure it can be done. I believe Charlie Sterling's "alternator linearizer" will deal entirely with all the alternator issues. I don't know about the Victron charger, but the place to find out will be from Victron, who give awesome technical support.


Then I guess we need to think about the LVC and the loads, if there is much inductance in the system, which there is in my case. How did you deal with this, on your system?

I think you need to separate out behavior in a correctly operating BMS, from behavior from a broken BMS.


With a correctly operating BMS, all load sources will be shut off before an LVC occurs. Same with charge sources before an HVC event. And really neither an HVC nor an LVC should happen at all unless there is BMS or cell failure.


So short of equipment failure, I don't think it's an issue. But it does depend on a well implemented BMS. If chargers are uncontrolled and HVC or LVC cutoffs are an occasional occurrence, then protection would be wise.


But I view a failed BMS as no different from any one of many other possible failures in a power system, regardless of battery type, that could result in abrupt on/off current flow. And even in normal operation, consider what happens when you start and stop your windlass or your thruster. Those are some pretty abrupt changes of current, and probably of equal or greater magnitude to switching off an alternator.


I think the big risk is the alternator itself if you cut the output. It has a large magnetic field that collapses and creates a back EMF, and it has rectifier diodes that have a reverse voltage limit. That's what fries alternators.

[tanglewood]

Originally Posted by Dockhead

High current sources? The power source, high current or low current, has nothing to do with high voltage transient spikes



Really, you should read up on this stuff before you post about it. I recommend this: http://www.nhu.edu.tw/~chun/BE-Ch14-...Transients.pdf. Don't be afraid to ask questions.

Hummm, current does play a roll. The magnitude of the magnetic field in the inductor is proportion to the current. So more current means a large magnetic field, and when that field collapses it generates the voltage spike.

[rgleason]

I am too ICE internal combustion engine.

[tanglewood]

Originally Posted by john61ct

Dino juice power sources, alts and gennies.

Internal Combustion Engines.

As opposed to agency in need of. . .

Thanks!

[Dockhead]

Originally Posted by tanglewood

I think you need to separate out behavior in a correctly operating BMS, from behavior from a broken BMS.


With a correctly operating BMS, all load sources will be shut off before an LVC occurs. Same with charge sources before an HVC event. And really neither an HVC nor an LVC should happen at all unless there is BMS or cell failure.


So short of equipment failure, I don't think it's an issue. But it does depend on a well implemented BMS. If chargers are uncontrolled and HVC or LVC cutoffs are an occasional occurrence, then protection would be wise.


But I view a failed BMS as no different from any one of many other possible failures in a power system, regardless of battery type, that could result in abrupt on/off current flow. And even in normal operation, consider what happens when you start and stop your windlass or your thruster. Those are some pretty abrupt changes of current, and probably of equal or greater magnitude to switching off an alternator.


I think the big risk is the alternator itself if you cut the output. It has a large magnetic field that collapses and creates a back EMF, and it has rectifier diodes that have a reverse voltage limit. That's what fries alternators.

Well, I'd want to be sure to think through all these issues and be quite sure you don't cause damage even in an abnormal LVC event.



You are right that these are issues not unique to LFP power systems.



For example, my system has remote control contactors for isolating both battery banks, which was part of the original design of the electrical system. These contactors have large diodes on them to dissipate flyback currents. My bow thruster control box also has some kind of snubber in it.


I suppose everyone knows that you have to protect an alternator from sudden isolation from the load. There are plenty of ways to solve this. The simplest way is to just whack a big Zener diode on it -- which is all the old Zap Stop system was.

[mbartosch]

Originally Posted by ramblinrod

An HVC or LVD event can cause a high voltage transient (50- 100 volts or more).

A voltage spike can happen, but on a correctly designed system this will have no impact.
Only on a badly designed system this might be a problem (e. g. a single contactor for isolating the bank from charging sources and loads at the same time. In this case, yes, dropping the bank will cause a voltage spike seen by the loads. Again, this is bad design and to be avoided.)

A correctly designed LFP system will have separate load and charge buses, both of them with their own disconnect contactors for HVC and LVC events. (This is established common knowledge and not news, so I do not need to elaborate, I think. Refer to numerous posts on the main LiFePO4 thread, to various blog posts, including my own setup documentation for details on how this can be done.)

All non-inductive charging sources can safely be disconnected by a relay/contactor from the rest of the system and can thus be directly connected to the charge bus of the LFP system.

The moment the HVC trips the relay/contactor which connects the charge bus to the rest of the distribution nothing serious will happen. The LFP bank is still connected to the loads and will immediately deliver the necessary power.
Any voltage spike delivered by the charging sources will happen on the now isolated charge bus and will hence not be seen on the distribution/load bus side.
In other words: There will be no voltage spike on the loads.

Inductive charging sources, however, must not be connected to the system (including the charge bus) without voltage spike mitigating measures. It is much better design to devise a system which cuts off the charging source safely. In the case of an alternator this can be done by a NC relay (triggered by the BMS HVC output) interrupting the field supply of the alternator.

In case of a LVC the situation is comparable. The contactor drops the sensitive loads, and in this case there is no spike on the load side because there is nothing providing power anymore. There is an exception, though: If there is a high inductive load on the load side active at the time the LVD happens, there may be a voltage spike from the inductive load to the rest of the other loads. But in my opinion this is a very rare edge case, and exactly the same case as blowing a fuse on a traditional system.

[ramblinrod]

Originally Posted by Dockhead

What you consider to be "an appropriate charge source" is simply not an option for very many cruisers.

I think this statement is misleading.

Very few cruisers (or wannabees) intending to anchor out off the grid, are opposed to wind and solar charging once they learn the benefits and overcome their fears (mostly from the misinformation they have heard).

In your circles it may be "many".

In mine, 95% of cruising sailors are interested in non-ICE charging systems.

About 20% of power boaters are interested in solar to reduce ICE at anchor.

Besides that, even with a large (relative to consumption) solar bank, you can't say managing lead power is "idiot proof".

Yes I can, I did, it is, exactly as I explained.

Wake up, check the voltmeter, carry on with the day most days.

About 2 days out of 7, run the ICE charging system for an hour (likely less duration than an LFP bank with solely ICE charging).

Once per month, check and add distilled water if necessary.

All of the "issues" you list are non-issues if one follows these simple steps.

Since you brought up the FLA vs FLP issue again...

"Fill the FLA bank as soon as possible" is far easier than never overfill the LFP bank or leave it full, or discharge too deeply, or leave it empty, or let the BMS disconnect it and destroy $1000s and $1000s of electronics and your alternator.

How easy?

For every 100 A-hrs of consumption, apply 300 A-hr of FLA bank, and add:

- 20 A of shore power charging capacity.
- 200 W of solar charging capacity.
- 200 W of wind charging capacity.
- 80 A of alternator charging capacity.

All of the devices are preset and suited for FLA.

Connect it and it works.

Done.

If one has no electrical background, they can have the system installed and there is nothing to learn. Other than the simple rule...

- Sun and 12.2, nuthin' to do,
- No wind or sun, need an hour run.

Try that with LFP and no wind or solar.

LFP is way more expensive for the limited "benefit" of not having to check/add water once per month (but having to check/add oil to the ICE charger EVERY morning before start-up.)

[Dockhead]

Originally Posted by tanglewood

Hummm, current does play a roll. The magnitude of the magnetic field in the inductor is proportion to the current. So more current means a large magnetic field, and when that field collapses it generates the voltage spike.

Yes, the power in the inductor is in proportion to the magnitude of the current, but the voltage of the spike is a function of the RATE OF CHANGE of current, not the magnitude of the current:








It's a corollary of Faraday's Law:





Where epsilon is electromotive force and ΦB is magnetic flux.


What this means practically is that high induction loads of very small current can produce very high voltage inductive spikes.