LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[fallingeggs]

Originally Posted by Maine Sail

That was a very old post and I have changed settings a few times over the years. (sorry CF does not let us edit posts, or keep them current, unless you physically ask a moderator to do it).

For me that worked fine because I manually shut the reg down at voltage & current. On a long windless delivery with some friends I changed it to what you see below rather than explain to them why and when to shut down the alt..

I don't think I have changed it since that reprogramming. I fall short occasionally on bulk & absorb time but not by much. Bumping bulk from 13.9V to 14.0V helped a little bit on that. A few minutes with the magnet and this is where I left it...


bv/Bulk Voltage = 14.0V
b1c/Bulk Time = 24 Minutes
Av/Absorption Voltage = 13.8V
A1c/Absorption Time = 12 Minutes

With 12 minutes fixed the calculated absorption usually drops to float nearly immediately after the 12 minutes because the current drop is so rapid. Ideally I may go back in and tweak the absorb time to 24 minutes or so and for my bank, and charge rate, that is probably just about where it winds up at less than 10A at 13.8V...

Occasionally I will just re-boot the reg, if I really need the battery capacity, but usually I don't. At the setting above I am close to or below 10A at 13.8V by the time the 40 +/- odd minutes are up.

With the original absorb settings at 13.8V you're not going to do any major damage to the LFP bank even if you started it when it was pretty full. You'll just likely get down towards 1-2A acceptance at 13.8V. Plenty of safety margin at 13.8V absorb.

Question about how the MC-614 works... If bulk is set to 14.0, does it keep pumping current to the LiFePO4 bank until the later of: (1) the minimum time set or (2) the voltage sensed at the battery terminal is 14.0?

Once both conditions are met, the MC-614 switches to absorption mode where voltage is held at 13.8 (via tapering current down) until the later of: (1) the minimum time set or (2) the voltage sensed at the battery terminal is 13.8?

Guessing here, but it seems like the time in bulk is unknown and depends on how deeply discharged the bank is. I was thinking why not set the minimum bulk time to 6 minutes to give the greatest flexibility and reduce the chance of overcharging a full bank. But it seems having a higher minimum bulk time can act like a short and controlled absorption phase when the bank hits 14.0 quickly.

I would also guess, as suggested, that the absorption mode can be set to nearly always exit to float/off after the minimum absorption time because the terminal voltage will be at 13.8 (assuming big loads aren't on at the same time).

(PS - Not attempting to factor in the "% of field current" settings yet...)

(PPS - Getting to the end of this post I may have just described what was written in this post on constant current and constant voltage. http://forums.sailboatowners.com/ind....176854/page-2)


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[mrm]

I addressed your question:

Originally Posted by transmitterdan
Why is there no protection left? If all charging sources are off what protection is required?

exactly because:

Originally Posted by transmitterdan

If one removes the field voltage then the alternator cannot produce power.

you seem to overlook the fact, that removing that field voltage is done by an element which may fail in such a way, that the field voltage will NOT be removed when it is requested (for example, relay contacts may weld together or some rust inside a relay will mechanically disable the relay). That is why a second level of protection seems prudent to have, given the cost of a LiFePO bank.

And why can't there be more than one HVC circuit if redundancy is desired?

You seem to mix terminology here. To me, a HV condition means that the bank voltage is higher than it was intended to be, as a result of one or more charging sources misbehaving (not terminating a charge). Therefore a HVC circuit is a bank defense circuit, not a charge source(s) control circuit. It gets into action only when charge control circuits fail to operate properly.

I'm not understanding the desire to reach 100.0% state of charge. With LA banks absorption is important to increase battery life but with LiFePo it doesn't seem necessary.

Please note, that I did not discuss this and see no reason why you brought it back into a reply.

[Maine Sail]

Originally Posted by fallingeggs

Question about how the MC-614 works... If bulk is set to 14.0, does it keep pumping current to the LiFePO4 bank until the later of: (1) the minimum time set or (2) the voltage sensed at the battery terminal is 14.0?

For LFP the regulator v-sense and regulator B- should directly sense the battery terminals. When the battery attains 14.0V the bulk voltage timer starts and runs to what ever you set it for. This is a fixed time clock and runs out as priority. After the time clock the regulator then enters calculated bulk voltage (don't get me going on a CV bulk voltage) and looks at how long it took during bulk.CC to CV in order to clim there. It can then add more time to bulk voltage. You will want to adjust this transition threshold so it drops to absorption quickly, if you set a fixed time..

Originally Posted by fallingeggs

Once both conditions are met, the MC-614 switches to absorption mode where voltage is held at 13.8 (via tapering current down) until the later of: (1) the minimum time set or (2) the voltage sensed at the battery terminal is 13.8?

Like bulk voltage the time at absorption voltage is fixed, the calculated absorption time can vary based on field threshold transition settings.

Originally Posted by fallingeggs

Guessing here, but it seems like the time in bulk is unknown and depends on how deeply discharged the bank is.

The time in real bulk or constant current is the time it takes to get to 14.0V. The regulator applies any "counts" during this time & voltage climb to the calculated bulk stage.

Balmar bastardizes the term bulk voltage (CV) of which there really is no such thing but we work with it.

The MC-614 essentially does two absorption stages Bv and Av. The time parameter you set for bulk voltage is fixed the calculated bulk comes after the fixed time and is based on how long it took to attain 14.0V. It can add time to your fixed time.

Originally Posted by fallingeggs

I was thinking why not set the minimum bulk time to 6 minutes to give the greatest flexibility and reduce the chance of overcharging a full bank. But it seems having a higher minimum bulk time can act like a short and controlled absorption phase when the bank hits 14.0 quickly.

It will all depend on your bank and your charge rate. For my bank it takes about forty minutes from the time I cross CC and move into CV to drop to less than 10A at 13.8V... Remember, even at 14.0V you have plenty of head room for safety.

Originally Posted by fallingeggs

I would also guess, as suggested, that the absorption mode can be set to nearly always exit to float/off after the minimum absorption time because the terminal voltage will be at 13.8 (assuming big loads aren't on at the same time).

Again absorption time, like bulk voltage time is fixed to what you set it for. Calculated absorption looks at the field drop during the fixed time periods to determine if any additional calculated absorption time is required. The calculated stage times are adjusted via the field thresholds.

Originally Posted by fallingeggs

(PS - Not attempting to factor in the "% of field current" settings yet...)

If you choose a time for bulk you will want to adjust for threshold. If you set it at six minutes you still may need to adjust threshold for bulk because unlike lead the reg spends a LOT of time in bulk/CC and can add "counts" to the calculated time. The settings for one bank will not be the same for all banks and require experimentation.

Originally Posted by fallingeggs

(PPS - Getting to the end of this post I may have just described what was written in this post on constant current and constant voltage. Battery Voltage vs. State of Charge | Page 2 | SailboatOwners.com Forums)

The stuff I referred to above..

[Maine Sail]

Originally Posted by mrm

You seem to mix terminology here. To me, a HV condition means that the bank voltage is higher than it was intended to be, as a result of one or more charging sources misbehaving (not terminating a charge). Therefore a HVC circuit is a bank defense circuit, not a charge source(s) control circuit. It gets into action only when charge control circuits fail to operate properly.

Some of these HVC's don't even occur until 3.65V+ with some as high as 3.9V..

I have a pile of severely overcharged, ruined & bloated cells from a $10,000 "factory made" LFP bank on my bench that had been regularly charged to 3.65V per the manufacturers guidance.... That charge votlage guidance BTW has since been reduced but the customer was not covered and was out 10K.......

Using HVC as charge control for LFP, no thanks....

[fallingeggs]

Originally Posted by Maine Sail

The MC-614 essentially does two absorption stages Bv and Av. The time parameter you set for bulk voltage is fixed the calculated bulk comes after the fixed time and is based on how long it took to attain 14.0V. It can add time to your fixed time.

I think this is the crux of the issue. If I understand the response, what MC-614 calls "Bulk" is really a true bulk/constant current phase followed by the first absorption/constant voltage phase.

Beginning from turning the ignition on, the MC-614 will, after a delay, soft ramp the field current to the max. Then we are in the first phase of Bulk, being the true bulk/constant current phase. Once 14.0 is sensed at the terminal, the MC-614 moves to the second phase of Bulk, being the first true absorption/constant voltage phase. This phase runs for the preset amount of time. After this time, the MC-614 moves to Calculated Bulk, which can be managed to end quickly.

The MC-614 Absorption phase is a true absorption, just the second one, followed by a Calculated Absorption (managed to be quick). Then we enter float at 13.2, which effectively turns the alternator off till the bank is highly discharged or the MC-614 is restarted.

If this is true, then it is just a question of adjusting the Bulk (bv, b1c, fba) and Absorption (av, a1c, ffl) settings to quickly and safely move my LiFePO4 bank charging under my alternator from 14.0 at max current to 13.8 at 1% acceptance of the bank's amp hour capacity. Sounds like a lot of testing, monitoring and changing settings, but very do-able.

Does the MC-614 have blinking lights to let one know which phase it is it? Or are we left guessing by what the voltage at the terminal is doing and amp acceptance rate?

[OceanSeaSpray]

There is no "true bulk" or "constant current" alternator charging on boats, these regulators can't control output current. The current is primarily determined by the engine revs, but it strictly doesn't matter anyway.

The charging regime we have is not CC-CV, it is AC-LV: any current, limited voltage.

I have run into a few pre-existing external regulators while dealing with LFPs and the only settings of value really are absorption voltage, absorption time and float voltage. Even very simple ones usually offer that.
If you can set a field current limit, this can be very useful too, otherwise there is a workaround.

In any case, by now you are on the right track.

[Maine Sail]

Originally Posted by OceanSeaSpray

There is no "true bulk" or "constant current" alternator charging on boats, these regulators can't control output current. The current is primarily determined by the engine revs, but it strictly doesn't matter anyway.

The charging regime we have is not CC-CV, it is AC-LV: any current, limited voltage.

I have run into a few pre-existing external regulators while dealing with LFPs and the only settings of value really are absorption voltage, absorption time and float voltage. Even very simple ones usually offer that.
If you can set a field current limit, this can be very useful too, otherwise there is a workaround.

In any case, by now you are on the right track.

I still refer to the maximum the alt can put out (RPM and heat limits aside) as constant current because the reg is essentially driving the alt to its max current potential for the RPM or heat/temperature etc. before it has attained the limiting voltage.. You can call it AC & LV but the charging type we are discussing is most often referred to as CC>CV constant current (meaning the charge source is not limited by a voltage limit) & constant voltage where we limit voltage to a constant.

[OceanSeaSpray]

Sure, if you just run the engine at constant speed and nothing else and wait until the charge is complete, it gives a CC/CV charge profile, but on boats, we don't just charge with alternators, we charge with anything we can get, solar, wind (for some) and engine at times.

This all makes "bulk" at "any current" until the voltage limit is reached, and then it is not even CV, because all it takes is a cloud or lower revs to drop the voltage momentarily, so it is "limited voltage".
To make things worse, we often also discharge back before charging some more and only occasionally manage to get to near-full.

A true CC/CV charger would do exactly what it says, CC until a voltage limit has been reached and then CV until a residual current limit has been reached. This just doesn't happen often in reality on boats (especially if you live aboard) and this is why the pretty CC/CV charge curves from the brochures are not that helpful. The CV part of the curve depends too much on what happened before during the supposed CC charging time.

Another way to look at it would be pointing out that a CC/CV charger actually has dedicated circuitry to deliver a constant current. We don't. We just throw everything we can find at the battery without exceeding a voltage limit along the way and try to stop when it gets about full (which we don't do very well in most instances).

Then the whole discussion revolves on how we try to coax a wide and random range of gear into charging LFPs when it was never intended for that, haha!
But some of it can be made to work within limits and the cells are reasonably forgiving to occasional small imperfections in charge control, so we can do it.

[evm1024]

I don't think that there is a need to quibble about the definitions as much as we do. Bulk, Absorption, CC, CV, etc.

Some engineers and scientist may require a precise definition but I think that we can agree on a common understanding.

True constant current supplies have some major limitations and hazards. For example it is "easy" to do a constant current of 100 A through a 1 meg ohm resistor. You just have to drive it with 100 million volts. (and deal with the power company asking why you shut down the grid)

For our use Constant Current means current limited. Calling it any current misses the mark.

---------------------

OK just forget everything I wrote. I just read the next post and realize that clouds and engine RPM determine the mode of operation our chargers are in.... Can't argue with that.

[s/v Jedi]

Why don't we forget every term invented for older battery tech and/or for land applications and concentrate on lfp charging aboard cruising sailboats.

Why not first come up with the ideal (practical, not maximum theoretic) charging profile (i.e. which stages, if any and to which voltages, timers etc) and then see how this can be done with our charging devices... or come as close to it as possible.

I see the first stage like this: throw everything we have, or can muster under current conditions at it until we reach a voltage of x Volt.
Etc.


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[transmitterdan]

Nick, I agree with you that the old LA names for charging phases are useless with LFP. The charging of LFP can be pretty simple if you want. Charge as much current as you can safely make until pack voltage approaches some preset value and turn off the charge source(s). Then don't discharge below some lower preset voltage. Between these voltages charge anytime you want/can. This "regime" will keep most banks between the 20-80% SOC range and that's more than good enough for 99.4% of cruisers.

One can come up with a much more complex charge profile to eek out the rest of the capacity but there is little point.

[s/v Jedi]

Originally Posted by transmitterdan

Nick, I agree with you that the old LA names for charging phases are useless with LFP. The charging of LFP can be pretty simple if you want. Charge as much current as you can safely make until pack voltage approaches some preset value and turn off the charge source(s). Then don't discharge below some lower preset voltage. Between these voltages charge anytime you want/can. This "regime" will keep most banks between the 20-80% SOC range and that's more than good enough for 99.4% of cruisers.

One can come up with a much more complex charge profile to eek out the rest of the capacity but there is little point.

When a simple timer or current measurement, which could be available in most charging sources, could make that 20-95% SOC range then I think it is sensible to do that. Even if it only does 20-90%.

[agk]

Hello everyone,
I live aboard full time in Panama now and frantically researching my options to purchase LFP cells for my house battery. Being located in Panama makes shipping from US suppliers difficult. I came across evlithium.com. They are located in Hong Kong and have a store themselves and with Aliexpress. They carry Calb and Winston. I have a feeling that they might have taken over the Balqon's business: they are also selling Balqon's 'drop-in' batteres. Anybody has information about them?
Many thanks,
Alex

[senormechanico]

Originally Posted by s/v Jedi

Why don't we forget every term invented for older battery tech and/or for land applications and concentrate on lfp charging aboard cruising sailboats.

Why not first come up with the ideal (practical, not maximum theoretic) charging profile (i.e. which stages, if any and to which voltages, timers etc) and then see how this can be done with our charging devices... or come as close to it as possible.

I see the first stage like this: throw everything we have, or can muster under current conditions at it until we reach a voltage of x Volt.
Etc.


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That's what I do until I reach 13.8 on our single 200 aH bank.
During times of boat non use, I terminate and set float to 13.2.
In the summer when I'm using the boat and running whatever I feel like (everything), I add a half hour of absorb at 13.8 which works for our boat.

[SV THIRD DAY]

Originally Posted by transmitterdan

Nick, I agree with you that the old LA names for charging phases are useless with LFP. The charging of LFP can be pretty simple if you want. Charge as much current as you can safely make until pack voltage approaches some preset value and turn off the charge source(s). Then don't discharge below some lower preset voltage. Between these voltages charge anytime you want/can. This "regime" will keep most banks between the 20-80% SOC range and that's more than good enough for 99.4% of cruisers.

One can come up with a much more complex charge profile to eek out the rest of the capacity but there is little point.

Bingo
It's almost like we score more Sea Scouts Merrit badges by over thinking, over analyzing, and over hyping this issue. We don't need no stinkin badges. what we need is simplicity, because everything else on a boat fails and will screw you.

Using the Old Lead is Dead charge terms of Bulk, Absorption, and Float for LiFePO4 batteries should be a crime punishable by having to scrub out the bilge because it traps people right back into the old LA way of thinking and it confuses people.

There is no spoon....