Baqon drop-in LiFePo battery systems with BMS

[Maine Sail]

Originally Posted by SV THIRD DAY

Main Sail can certainly comment, but he is running his tests more in a lab/data collection style than how a cruising boat may actually operate. Meaning, he is looking to count cycles by turning his charge sources on and off. While this is great for data gathering, it's also not how it works on a real cruising boat. (now everyone this is in NO WAY a ding on Mail Sail, he is a great guy and deserves many kudos for the time and energy he puts into his testing and willingness to share it). On a real cruising boat, solar is always charging during the day, alternators are charging when under way, shore power is plugged in while at the dock, and a wind generator is charging when the wind blows.

It's this active charge/discharge condition that I think needs more thought and focus rather than the on/off charging when gathering data for cycle count. In this condition, a simplier charge value could be 13.4v. Why not set all of your charging devices to 13.4v and all but eliminate the risk of over-charging by using 13.8v or 14v? Alternator, Solar, Wind, Battery Charger, and Flux capacitor, just set them all to charge at 13.4v.

Sure you should still have your high and low cell alarms, but this way you effectively have taken away the over-charge issue. Because at a 13.4v charge voltage on a cell with a 3.33v resting voltage (13.4/4=3.35)...well you can't put any more amps into the battery once you reached that resting voltage. Easy to do, easy to set-up and no risks. I have not seen data that says charging at 13.4v vs 13.8-14.0v hurts the cells. So what is to be gained by charging at a higher value and then dropping back down to a lower valve for "resting" or turning off the charge, since there is no "float stage" on a LiFePO4 bank the way we think of it on a Lead Acid battery.

I think this need and want to adjust charging voltage and resting voltage comes from the Lead Acid mindset and in all honetly is part of the BS Marketing of why you need a Gazillion Dollar BMS in the first place! Let's make it sounds like rocket science and scare people to death or better said into buying our BMS that has this fancy 7 stage battery charging and conditioning...again the old Lead Acid Games that may not apply here.

Even after I hit 500 cycles, sometime in September, I will probably continue to use the bank the way we have, but may turn solar on to get more days in-between re-charges. It is nice to have the piece and quiet and nice to walk away from the boat at 20% SOC and not care....

As our boat works I live about 1.5 miles from her and work in the harbor all day long. I am on her multiple times per day.

The only thing I don't do is sleep on her every night but the systems are very often still running, as if she is a live-aboard.. The bank is constantly cycling all summer, on purpose for testing purposes and my own learning.

The only thing I do differently is discharge all the way to 20% SOC before re-charging with any charge sources. This allows me to accelerate this banks cycle life to see how it does. My cycling does slow down in the summer because I simply do not have a .25C load that I feel comfortable walking away from. When I am on board I flip on a .35C load and that discharges her pretty quickly. This load is not really representative of how we use the boat but it gets the cycles in. This kind of treatement would have seen the typical LA bank dead by 200 +/- cycles, I am at 454 with no notable changes in capacity. On the last capacity test I got 423Ah's. My first baseline capacity test, using the same test protocol and same test equipment, yielded 425Ah's.

I admit I got a little impatient on this last capacity test and did not let the acceptance go all the way to the 5A I usually do when capacity testing. I stopped at 9A/13.8V... Still it was within 2Ah's of 450 cycles ago and the bank has never been re-balanced. This data tells me that 13.8V is a comfortable charge voltage for the cells. Even with fairly heavy cycling the cells are surviving quite nicely. I keep expecting them to fall off a cliff, but they have not. I am testing the bank at a .25C rate not .5C and this is where the extra capacity beyond the 400Ah rating comes from..... When tested at .5C (done that twice) she put up 397 and 399 Ah's..

As to 13.4V, you will hit current limiting far earlier. With LFP you still need more of a spread in voltage than .5V above resting voltage but not as much as LA..

As I see it you have about 200 +/- amp of charging current available in various forms.. I would set the alt and charger at 13.8 - 14.0V, for fast charging, and the solar and wind at 13.7V. Perhaps set the wind to brake at 13.6V.... I experimented down to 13.4V and hit current limiting too early.. I run my alt at 120A for a 400Ah bank. At 13.8V I have a fairly short taper. At 14.0V very minimal taper...

I have even run my bank at 13.8V until the chargers power supply cycled off to 0.0A and every now and then would blip on for a few seconds and then turn back off and drift back down again. I left it this way for about three days. The cells were still within 7mV the entire time and the cell temps never budged an iota.

Keeping them at this SOC is reportedly not good for them long term, but it showed that 13.8V is quite safe and does not lead to cell drift or temp increase even if held there for a few days.

My bank is more for experimentation purposes so I really did not care that I let them sit on the charger continuously for three days at 13.8V. Not what I do in practice, but I wanted to see and be able to measure the effects of temp and any potential for cell drift..

Course if you are happy with those acceptance rates then there is no issue I can see. Personally I would not be happy at those acceptance rates, and I assume you are more concerned with cycle life than acceptance, but you have made points about LA acceptance and they need to get to 100% as often as possible where LFP do not. The 100% SOC regularly vs. not necessary is a HUGE benefit of LFP...

I want to be able to charge fast, when I do charge, so my voltage for alt is 13.9 absorb 1 for about 30 minutes then dropping to 13.8V absorb 2 for the duration. When it hits 13.8V and 10A of net accepted current charge sources are simply turned off. Very simple..

This winter I will be throwing in a much larger alt in so will likely bump the regulator up .1V to a max of 14.0V for 30 minutes then down to 13.9V..... Solar will stay at 13.8V... With LFP proper voltage sensing is critical and the regulator v-sense + & B- need to sense the bank terminals for the fastest charging. Many forget the regulator B- is part of the v-sense circuit if using a Balmar regulator.

[IdoraKeeper]

Just happened upon this thread. Fabulous amount of info here about optimization for real world use.
Please consider the following .

A friend of mine running a 100+ foot motor yacht with a large LifPo4 bank and rediculous house loads had one hell of fire (thankfully at the dock) when a large inverter failed and induced a transient that was faster than the protection. The failure mode of the battery was the same as on the 787. Same result, fire. Fortunately the bank was in a compartment that could be sealed and flooded with halon. Nevertheless the damage was more than most mortals could pay for.
In the quest for real world usability of these systems perhaps its harder than we wish. Just ask Boeing.

[Moonos]

Regarding charging and monitoring cell voltage I wonder if the following would work.

Assume you have multiple dc charging sources. And 4 lifepo4 cells in series to make ~ 12 volts.

* 12 volt generator
* 12 volt alternator
* 12 volt solar

All power sources feed into a "black box". This black box has 4 discrete variable dc output channels which each feed into 1 cell.

The black box monitors each cell voltage and controls the voltage feed to it. Once a cell gets to set point charge is stopped for that cell. When all cells are at high set point charging stops.

The black box would need output channels to control an externally regulated alternator, solar controller or generator controller.

Charging begins once voltage reaches low set point and continues with generator until it gets to high set point.

If you still have charging from solar or alternator I s'pose it allows it to feed to batteries until high point is reached, perhaps with hysteresis.

Although an expensive setup, I think I would like to make a system from an 8kw polar dc marine generator, ~1600aH lifepo4, victron multiplus, and small solar.

I would like something that can handle a 12000-16000 btu A/C, but when A/C isn't needed the generator only runs a few hours a week @ anchor for other loads.

[poiu]

Originally Posted by SV THIRD DAY

... Why not set all of your charging devices to 13.4v and all but eliminate the risk of over-charging by using 13.8v or 14v? Alternator, Solar, Wind, Battery Charger, and Flux capacitor, just set them all to charge at 13.4v. ...

This specific question was looked into already on another thread by Ebaugh. Here's his post:

http://www.cruisersforum.com/forums/...ml#post1344170

He shows at 3.35v you get to fill only 80% of your battery after a nearly 1 hour taper down at the end of charge. Clearly it would continue to charge the battery, but at an end charge rate of .02 in his test it indicates it would take maybe 16 to 24 hours (my guess) to get to 100%. It's a big chunk of purchased capacity to not use.

If you bought that extra 20% of capacity it would cost say $400 on a 400Ah 12v system and that would be less than the cost time and hassle of designing and installing a BMS. It might be tempting to not get one, however I can see it would eventually lead to failure. Sooner or later the charger will fail or you will make a mistake in monitoring, it will over-discharge, destroy the pack or one or more cells.

All that said, I am doing just as you suggest on my alternator settings right now as a temporary measure. My reason is that I haven't got round to doing the disconnect circuit for the field winding and to protect the system I dialed down the voltage output from the regulator to 3.4v. Because I use the engine so little I am not loosing much, but am taking a risk. It does work fine and charges most of the battery capacity. Loads up the alt a bit less too, which I am more comfortable with.

[poiu]

Originally Posted by IdoraKeeper

Just happened upon this thread. Fabulous amount of info here about optimization for real world use.
Please consider the following .

A friend of mine running a 100+ foot motor yacht with a large LifPo4 bank and rediculous house loads had one hell of fire (thankfully at the dock) when a large inverter failed and induced a transient that was faster than the protection. The failure mode of the battery was the same as on the 787. Same result, fire. Fortunately the bank was in a compartment that could be sealed and flooded with halon. Nevertheless the damage was more than most mortals could pay for.
In the quest for real world usability of these systems perhaps its harder than we wish. Just ask Boeing.

A fire on a LiFePo battery!? That's a first. Are you sure it wasn't another chemistry - Lithium-cobalt/manganese/polymer etc? Maybe the fire was started in the charger Can you find out what make and spec of battery and more information? Pictures would be great as there would be very important lessons if the info is correct.

[Colin A]

I was recently discussing this with a maker of, I will call less expensive marine chargers. They mentioned they had done testing and felt the safest way to charge lithium was at a steady voltage and not go into the upper voltages. They also mentioned the possibility of having a settable acceptance rate IE shutting off the charger when acceptance drops below a certain level. Again I'm new to this and still learning.

[SV THIRD DAY]

Originally Posted by DotDun

Point taken, but you also have to consider...

"Rich is a smart guy and says 13.4v will never cause a fire, so that must be best."

When in fact your LifeP04 will die prematurely due to lack of proper charge voltage.

Don's stuck living in the Lead Acid World stating myths as Facts....something I deal with all the time as a gear manufacturer and supplier. Your LiFePO4 battery won't die early do to lack of proper charge voltage by charging at 13.4v....but hey...Don has a LiFePO4 battery bank on his own boat and is working with the battery supplier engineers...right...

[nimblemotors]

I'm not sure why some people thnk they know better than the maker of the battery. The battery makers want you to kill the batteries to sell more???
You are kidding right?

The MIT guys at A123 say 3.6 volts, that is 14.4 volts for 4 cell pack.

[SV THIRD DAY]

Originally Posted by nimblemotors

I'm not sure why some people thnk they know better than the maker of the battery. The battery makers want you to kill the batteries to sell more???
You are kidding right?

The MIT guys at A123 say 3.6 volts, that is 14.4 volts for 4 cell pack.

Then run yours at 14.4v...what's the problem here?
How's your LiFePO4 bank doing, what's it's size, cost and how do you charge?

[DotDun]

Originally Posted by SV THIRD DAY

Don's stuck living in the Lead Acid World stating myths as Facts....something I deal with all the time as a gear manufacturer and supplier. Your LiFePO4 battery won't die early do to lack of proper charge voltage by charging at 13.4v....but hey...Don has a LiFePO4 battery bank on his own boat and is working with the battery supplier engineers...right...

How dumb of me, what was I thinking? I equated LifeP04 to anode/cathode/chemical reaction. I didn't realize they are actually magic that only those that own them understand how they work.

[SV THIRD DAY]

Originally Posted by DotDun

I really don't care, I'm not arguing with you...You can do what you like.

Originally Posted by DotDun

How dumb of me, what was I thinking? I equated LifeP04 to anode/cathode/chemical reaction. I didn't realize they are actually magic that only those that own them understand how they work.

For someone that says they don't care, we sure feel the love.

But seriously, it's not dumb of you, don't be so hard on yourself Amigo.
We are just happy to see you care enough to come back and take the time to contribute to the discussion.

So you setup your own 400AH LiFePO4 battery bank on your boat.
How do you intergrate your 4 charging devices and cruising/live aboard lifestyle? Help us learn the magic of battery chemistry, by sharing with us what you would do on your boat. Or is it more fun to shoot spit balls from the back row?

[olaf hart]

This is getting hotter than an anchor thread.

[SV THIRD DAY]

Originally Posted by olaf hart

This is getting hotter than an anchor thread.

but the good news is that LiFePO4 batteries don't need Temperature compensation...ha ha ha...

If you can't have a little fun now and then...what good is the power in the battery bank anyway.....

[DumnMad]

Originally Posted by SV THIRD DAY

It's this active charge/discharge condition that I think needs more thought and focus rather than the on/off charging when gathering data for cycle count. In this condition, a simplier charge value could be 13.4v. Why not set all of your charging devices to 13.4v and all but eliminate the risk of over-charging by using 13.8v or 14v? Alternator, Solar, Wind, Battery Charger, and Flux capacitor, just set them all to charge at 13.4v.

Sure you should still have your high and low cell alarms, but this way you effectively have taken away the over-charge issue. Because at a 13.4v charge voltage on a cell with a 3.33v resting voltage (13.4/4=3.35)...well you can't put any more amps into the battery once you reached that resting voltage. Easy to do, easy to set-up and no risks. I have not seen data that says charging at 13.4v vs 13.8-14.0v hurts the cells. So what is to be gained by charging at a higher value and then dropping back down to a lower valve for "resting" or turning off the charge, since there is no "float stage" on a LiFePO4 bank the way we think of it on a Lead Acid battery.

I think this need and want to adjust charging voltage and resting voltage comes from the Lead Acid mindset and in all honetly is part of the BS Marketing of why you need a Gazillion Dollar BMS in the first place! Let's make it sounds like rocket science and scare people to death or better said into buying our BMS that has this fancy 7 stage battery charging and conditioning...again the old Lead Acid Games that may not apply here.

I like this thinking. Makes sense to me but I know little about these things.
Would the LiFePO4 charging rate be seriously penalized at 13.4 vs 13.8?

[CharlieJ]

I design and install LFP systems. One issue I have had is whether to use temperature monitoring as part of a BMS, and if it is used, how many TC's should be deployed? One per cell? A few scattered around the bank? I had reached the conclusion that, unless the designer is concerned with high temperature in a battery enclosure and wants to cycle a fan on or off, that temperature monitoring is not worth the cost.

I was talking to a BMS manufacturer early this week and the discussion drifted to temperature monitoring. His position is that by the time a BMS has sensed a temperature rise in a cell, the damage may well be done. That makes sense to me so I asked what their protocol is. The answer is that they use the string voltage measurements to derive the AC and DC resistance of the parallel string and alarm if that resistance is out of spec. Since the resistance or lack thereof (shorted cell) is what would cause the temperature rise it makes sense that the cause is monitored rather than the effect.