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Old 04-07-2012, 13:05   #451
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Quote:
Originally Posted by bdbcat
Bob...

I really like the look of the EMS panel you have. LCD display, switches, etc.

I see nothing like that on the Elite webpage. I do see the guts, however. Did you build the panel from scratch?

Thanks
Dave
I drew a schematic for it and Electric Blue Motors had the equipment to cut the plastic box for the LCD and switches. I attached the schematic to the post. The battery combiner light shown was a late addition that did not make the final panel.
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Old 04-07-2012, 18:41   #452
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Bob...

Nice job on the panel. Really. I might tackle something similar to replace my ancient Link10 setup.

Dave
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Old 04-07-2012, 19:45   #453
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Originally Posted by bdbcat
Bob...

Nice job on the panel. Really. I might tackle something similar to replace my ancient Link10 setup.

Dave
Thank you!

Just keep in mind this system is pretty good for lithium, but there are better battery monitors for other battery chemistries. The video display is via RCA RG6 composite video. Works OK so far, but I've not started the motors yet....Not the most robust architecture for a marine display 50 feet from the source.
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Old 05-08-2012, 06:06   #454
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First Impressions on Lithium Battery Install:

We have been on anchor about 3 weeks now since leaving Grenada, our first real trial of the lithium installation. Thought I'd share my initial impressions.

First, and important, is I don't recommend lithium for either the technical challenged, or for those who don't really abuse a lead acid or AGM house bank like we did. The primary reason to do this is cycle life, and until a few of us have 3-4 years using them and see how it works out, there just isn't any real world data. Solar and wind are better, proven investments. We did not go down that path because we would have needed a complete redesign of the fly bridge canvas and structure to house solar panels. And we probably need a redesign of our refrigeration systems. So in our case, this was easier and cheaper to implement to get us home, and partially paid since the old batteries needed to go anyway. But it's still a stop gap measure overall.

Below and in no particular order are some observations:

1) You really have to try to get the pack voltage under 13V. This is great for the inverter and water maker which operate better on higher voltages. Charging time for us is more flexible since the lithium have a larger usable discharge capability, but seems to require the same generator time to charge eventually. I expected generator time to decrease some since the lithium are advertised as more efficient at accepting a charge. This may appear this way since we rarely went through a full absorption charge with lead acid on anchor.

2) The StartNow by Charles does not work as designed and mentioned in previous posts. During the trip from Grenada to Bonaire, it dropped the parallel connection between the engine batteries and the lithium bank when a refrigeration compressor started. So if the BMS had isolated the lithium bank, and a refrigerator started, the lights would have gone out. The only reason the StartNow was installed was to parallel the batteries with the engines running and it did not work. Underway, I'm going to have to set the physical battery switch to parallel the lithium to the engine start batteries to prevent this from happening in the unlikely event the BMS pulls the plug. I'm tinkering now to determine the impact of the parasitic current if I leave them in parallel all the time.

3) Battery chargers designed for lead acid work with lithium, but not perfectly. I have three charging sources running off the generator. A Magnum inverter/charger, a Xantrex/Trace inverter charger and a Pronautic 1260 C3. The Magnum, is the biggest problem since it wants to switch from Float to off and wait for 12.7 or 12.6V. It also wants to start every charge cycle in Float mode. I have programmed it to a custom equalization voltage, and invoke that mode while charging at anchor. This can be fixed with the latest remote and firmware from Magnum. The remaining two chargers seem to work OK set to the gel battery settings. I'm charging to 3.4 to 3.45 V average per cell.

4) There is still a .1 V difference from the highest cell to lowest at top of charge. 3.39 to 3.49V. In the normal operating range, they even up to within .01V of each other. I'm watching this to see if they even out or get worse over time before I intervene. Temperature of the cells runs around 102 F under charge. With the generator running, it's probably 95 or so ambient, so only few degree rise. The old batteries ran more like 110F under the same conditions.

5) If a full charge is desired underway, it probably requires an intelligent alternator controller. I don't have one, just a voltage adjustment pot on both engine alternators. I can get it to hold about 70-80 percent charge, but set to more than about 3.35 V per cell, it wants to overcharge when the house loads are low. Even at the 3.35 setting, the batteries discharge slightly under load and then charge when lightly loaded. The load varies based on how many of my 4 refrigeration compressors are running. All of them on is about 50 amps. The pack voltage difference between 50 amps charging and 50 amps discharging is very small. Something close to 1/5 V or 13.3 to 13.5. Normal batteries would probably be closer to 13.5 to 12.6 where the voltage fluctuations don't matter as much. I'm not sure this is really a big problem, the primary charge source is the generators and inverter/chargers, so as long as I don't lose ground underway and can hold 70 percent charge, it will work for us.

That's about it for now...ask me in 12 to 18 months and I will know if they last longer than a set of T105's. And in 3 years or so, I may be able to tell you if they really live up to the promise.
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Old 05-08-2012, 17:05   #455
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Hi Bob,
Not sure if this will help but I'll try to come up with a few suggestions.
Quote:
Originally Posted by ebaugh View Post
First Impressions on Lithium Battery Install:
Quote:
Originally Posted by ebaugh View Post

We have been on anchor about 3 weeks now since leaving Grenada, our first real trial of the lithium installation. Thought I'd share my initial impressions.

First, and important, is I don't recommend lithium for either the technical challenged, or for those who don't really abuse a lead acid or AGM house bank like we did. The primary reason to do this is cycle life, and until a few of us have 3-4 years using them and see how it works out, there just isn't any real world data. Solar and wind are better, proven investments. We did not go down that path because we would have needed a complete redesign of the fly bridge canvas and structure to house solar panels. And we probably need a redesign of our refrigeration systems. So in our case, this was easier and cheaper to implement to get us home, and partially paid since the old batteries needed to go anyway. But it's still a stop gap measure overall.

Below and in no particular order are some observations:

1) You really have to try to get the pack voltage under 13V. This is great for the inverter and water maker which operate better on higher voltages. Charging time for us is more flexible since the lithium have a larger usable discharge capability, but seems to require the same generator time to charge eventually. I expected generator time to decrease some since the lithium are advertised as more efficient at accepting a charge. This may appear this way since we rarely went through a full absorption charge with lead acid on anchor.

I don't understand why you would want to get the pack under 13v, this is nearly all the pack capacity used but it would certainly extend the period between generator runs.
The generator time would be similar, the difference is the lead acid batteries were only 80% when they hit the absorption stage and the lithiums are very close to 100% so you have actually gained 20% capacity for the same charge time. Probably more in reality because the lithiums would have been pulled a long way down before you started charging if it was when the batteries dropped below 13v, that would be close to 80% DoD if not lower, not the 50% DoD the lead acid batteries were down to before the voltage dropped below anything useable under high load.

Quote:
2) The StartNow by Charles does not work as designed and mentioned in previous posts. During the trip from Grenada to Bonaire, it dropped the parallel connection between the engine batteries and the lithium bank when a refrigeration compressor started. So if the BMS had isolated the lithium bank, and a refrigerator started, the lights would have gone out. The only reason the StartNow was installed was to parallel the batteries with the engines running and it did not work. Underway, I'm going to have to set the physical battery switch to parallel the lithium to the engine start batteries to prevent this from happening in the unlikely event the BMS pulls the plug. I'm tinkering now to determine the impact of the parasitic current if I leave them in parallel all the time.

Any chance of posting a wiring schematic of the "Start now" unit? If you leave the two banks parallelled the lead acid batteries will drain the lithium batteries as the lead acid battery fully charge standing voltage is 12.8v so until the lithium batteries dropped to 12.8v (virtually flat) they will continue to feed charge into the lead acid batteries and they will continue to use it boiling the acid because they are being over charged. A possible solution would be very big Schottky diodes in a heat sink to act as a one way valve yet limit the voltage drop. Normal diodes drop 0.7v as the current passes through, between 0.5v and 1.2v when they reach the their max capacity. Schottky diodes only drop around 0.4v as the current passes through producing far less heat and improving the voltage differential seen between the two battery banks, the higher the voltage differential the higher the current flow so the faster the recharge.
Do you have a Junsi cell logger or something that will trigger a relay if cell voltage goes high? If so, a solid state relay that will cut the link when a cell goes over 3.6v. You would need a relay with a low on state resistance such as these
HFS33/D-30D100M //http://www.hongfa.com/pro/HFS33_en.html These also need a heat sink so possibly a heat sink tunnel with a fan and the diodes on one side and the relay on the other and a thermostat to turn the fan on, simple to make, I will give you all the part numbers etc. if you are interested in this system, even make you one if you want but freighting it to you could be interesting.
Quote:
3) Battery chargers designed for lead acid work with lithium, but not perfectly. I have three charging sources running off the generator. A Magnum inverter/charger, a Xantrex/Trace inverter charger and a Pronautic 1260 C3. The Magnum, is the biggest problem since it wants to switch from Float to off and wait for 12.7 or 12.6V. It also wants to start every charge cycle in Float mode. I have programmed it to a custom equalization voltage, and invoke that mode while charging at anchor. This can be fixed with the latest remote and firmware from Magnum. The remaining two chargers seem to work OK set to the gel battery settings. I'm charging to 3.4 to 3.45 V average per cell.

This problem can be solved by linking all the charging sources to the start battery then linking the start batteries to the house batteries via the system mentioned above.
Quote:
4) There is still a .1 V difference from the highest cell to lowest at top of charge. 3.39 to 3.49V. In the normal operating range, they even up to within .01V of each other. I'm watching this to see if they even out or get worse over time before I intervene. Temperature of the cells runs around 102 F under charge. With the generator running, it's probably 95 or so ambient, so only few degree rise. The old batteries ran more like 110F under the same conditions.

5) If a full charge is desired underway, it probably requires an intelligent alternator controller. I don't have one, just a voltage adjustment pot on both engine alternators. I can get it to hold about 70-80 percent charge, but set to more than about 3.35 V per cell, it wants to overcharge when the house loads are low. Even at the 3.35 setting, the batteries discharge slightly under load and then charge when lightly loaded. The load varies based on how many of my 4 refrigeration compressors are running. All of them on is about 50 amps. The pack voltage difference between 50 amps charging and 50 amps discharging is very small. Something close to 1/5 V or 13.3 to 13.5. Normal batteries would probably be closer to 13.5 to 12.6 where the voltage fluctuations don't matter as much. I'm not sure this is really a big problem, the primary charge source is the generators and inverter/chargers, so as long as I don't lose ground underway and can hold 70 percent charge, it will work for us.

That's about it for now...ask me in 12 to 18 months and I will know if they last longer than a set of T105's. And in 3 years or so, I may be able to tell you if they really live up to the promise.

I think the above set up should solve most of the issues you are having with the lithium set up. They do take some adapting to but it does become the norm after a short time and you wonder how you ever tolerated the fuss the lead acid batteries needed.
With the cell balancing, if you have a cell logger set it for a 30 sec sample rate and log a week, look at it on the computer in your spare time and decide if it's only one cell going high every time. A simple load like a 12v water heater element across the offending cell for an hr and then at the next charging cycle see it is still the cell that hits 3.6v first, if so, apply the load for another hr, it will settle down, just an over achiever at the moment :lol:

Sorry, this turned into a very long post, hope no one has gone into a comma or something

T1 Terry
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Old 06-08-2012, 05:06   #456
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Hi Terry,

Thanks for responding....I won't quote your reply, but will try to address the topics.

The "nominal voltage" of lithium phosphate is supposed to be 3.2 V per cell. That's 12.8 V at the pack level. Not sure where "nominal" comes from, but at 12.8 V the discharge curve for my batteries shows 25% remaining. At 13V, it shows 75% remaining. That is at .5 C discharge, so much higher than my normal rates. The impact will be to lower the capacity at both numbers I just quoted. But I think 13V should still represent 40-50% remaining. 12.8 V is probably essentially zero. The curves are on the Elite Power website.

I agree the charge time is difficult to compare since we never normally went beyond bulk charge on lead acid. But I still thought the lithium "accepted" more of the charge than lead acid, even during the bulk phase and I'm not seeing that.

I drew and attached a very ugly schematic showing the wiring. The StartNow is a special purpose battery combiner and one of the switches in the schematic. The other is a manual battery switch. Unless I change the wiring, charging underway has to come from the lead acid start batteries, but the inverter chargers at anchor powered by the generator are connected on the lithium side.

You can lookup the StartNow on the Charles Industries website. It's connected with the lithium house bank as the "reserve battery". If it had a timer to delay the disconnect on a momentary voltage drop it would work fine. But it doesn't, and I'm asking it to do something it was not specifically designed for.

I'm only running the alternators at a float voltage of about 13.4V. This should not boil the lead acid unless I run that way for days with the lead acid at high temperatures. When discharging, they only run about 13.2 so this is pretty much a lead acid float. It does rob power from the lithium bank, but I think it's only about 2 amps. I need some marina time and a cool engine room to get better measurements.

What I need is a battery combiner with a separate voltage sense wire connected to the alternators. On at 13.3 V, Off after 3 minutes below that. Adjustable, since those values might need to change a bit. I might have to make one eventually if I can find a board to drive another solenoid.

I thought about using diodes for a one way bridge from the start batteries to lithium, but with the voltage drop I would have to overcharge the lead acid. To get 13.4 at the lithium would require 13.8 or 14 at the lead acid side? At my engine room temps this would boil the lead acid. Going the other way prevents the lead acid from backing up the lithium if my management system takes them offline.

I may not understand your suggestion correctly? Am I missing something?

I don't have a cell logger, but I do have display of cell voltages at the BMS display at the electric panel. I have one cell slightly overcharged and one cell undercharged by .05V when the others get to 3.4V or so. The undercharged one was the same one I charged to balance the last time, so I will add some more. I'm hoping this is not going to be a chronic condition. That would probably mean one of the individual cells in that string is bad?

Thanks, Bob
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Old 06-08-2012, 06:38   #457
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

The Nom. voltage for lithium ferrous cells is 3.2v, nom. does not mean normal, it's just a reference voltage the same as 12v for a lead acid battery. A lithium ferrous cell should be operated between 2.8v and 3.8v, the two extremes are under high load or under a high charge rate, rested voltage should be 3v min and 3.45v max. It won't harm a lithium cell going to 3.6v as long as the charging system doesn't hold it at that voltage, the system we are using has an alarm and an alarm port to drive a relay circuit that we set to 3.6v. The units we use are Junsi Cell loggers, around $28 from a hobby store, they can read up to 8 sets of cells in parallel series format so they can handle 12v or 24v systems. The alarm port can be linked to either a ratcheting relay so a manual reset is required to reconnect the charging system or a timer circuit that allows the normal loads to pull the high cell back down, then charging resumes till another high cell alarm sets it off again. We set these units to trip at 3.6v per cell, a sort of back up insurance in case a cells voltage runs away while we aren't monitoring the system.

The low charging voltage you are using for the lead acid makes linking the two systems a tough one, 13.4v won't fully recharge a lithium battery bank, it requires 13.8v. The cell pack that is giving you grief simply hasn't been fully charged yet, they need that full charge initially to settle them in, they are fully charged when resting voltage is above 3.45v after 1 hr, 3.4v while charging isn't nearly fully charged, it's some way from it, rested after 24hrs 3.4v would be accepted as fully charged. Once a cell has been fully charged the difference between charging and discharging is a min of 0.1v per cell, 0.05v above rested voltage before any charging will happen and 0.05v below resting voltage as soon as even the slightest discharging takes place, as soon as you stop either functions the cell will return to it's rested voltage.
As far as the battery combiner, no one makes a unit to link lead acid and lithium batteries together.

Thinking out loud here so view it this way and point out any short comings in this next idea. If you were to link the lead acid batteries and lithium batteries to each charging unit with separate cables and put a diode in line to the lead acid batteries the lithium batteries would receive a higher voltage charge. If the charging cables to the lithium batteries were fed through a relay that the cell logger could turn off when a cell reached 3.6v the charger would still have a path to the lead acid batteries so they would not be damaged. Sound feasible?

T1 Terry
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Old 06-08-2012, 07:18   #458
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

It is my understanding that, in the case of motor vehicles, the thin-plate Lead-Acid start battery is recharged by the alternator within a relatively short time after starting the engine.

So, to keep things simple, can you do the following:

1) After starting the engine, let the alternator immediately "top up" the engine battery (could take 5-10 mins; can use a timer)
2) After that, manually switch over to let the alternator direct all charge to the Lithium house bank

This means there should never be any cross-draining between engine (lead-acid) and house (lithium) banks, and no reliance on electronics like battery combiners, diodes, intelligent relays etc.

It also means that the engine bank is only ever routinely charged by the alternator, while other charging sources are permanently set up to charge the house bank (except in an emergency circumstance, when they could be manually connected to charge the engine bank).

Has this option been canvassed and faulted before, or can anyone contribute an opinion on the pros/cons of doing it?
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Old 06-08-2012, 12:13   #459
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Terry,

I understand the first couple of paragraphs. It all makes sense and follows my research, much of which is your own earlier posts on this thread.

I sort of added a layer based on some other research. I'm intentionally not going to full charge on normal cycles. I have done so one time with each individual 100 AH cell prior to install and again two times with 12 of those in parallel each time to 3.6 V each. But not again for several weeks now.

The reasoning is that I found information that extended cycle life is possible by avoiding voltage extremes and using shallower cycles. I could not find one of the articles I remember, but here are a couple of references I did find:

1) Google this: "proper care extends li-ion battery life" and read the article where the author claims avoiding both high end and low end voltages with shallower cycles extend cycle life. Not just since less energy is used, but over a lifetime more energy can be stored and reclaimed overall during the life of the battery.

2) A brief note attached as a picture copied from an Aussie blog I'm pretty sure you've seen. Somewhere there is a more in depth look at this but I can't find it now.

So I think to maximize life, you should stay within a range of something like 20 to 90% SOC. Further, since the batteries are expensive, I think you should plan for 20 percent loss of capacity over the life of the pack. I need 600 AH maximum normally between charges, hence my 1200 AH pack. Guess what, we're back near that 50% number with other chemistries, but this time I'm hoping for 5000 cycles, not 500 or so. The research says the chemistry will do this, but who knows if my GBS cells will or not in real life.

What I've never found is the voltages for SOC at .01-.05C discharge and .15C charge. So I'm guessing, hopefully conservatively. It may vary a little bit on the chemistry and GBS are a slightly different LiFeMnPO4. Do you have any data here?

I have with my BMS a way to engage different relays for HVC and LVC already. At the moment, either trips the same solenoid and isolates the pack from everything and sounds an alarm. I could add the system you describe between the alternators and the batteries and it would work perfectly for an "early" HVC prior to the BMS...but if the BMS burped or LVC occurred, then underway I still lose all lights and electronics.

On the inverter charger side, the physical cables to the inverter are both the charging source and the discharge source and can't be separated. So while the generator is running, it could yank the connection and the generator would power the AC sources. But I'd still have to flip a switch somehow to insure the connection was restored prior to turning off the generator or risk forgetting the refrigeration.

How about this....replace the StartNow with a solenoid engaged by either engine ignition key in the on position? This only parallels the bank when an engine is running and at that point the voltages are more or less compatible in my installation. Seems too simple doesn't it? Hmmm. Just came to me writing this reply. But that might be the ticket.....and gets me back to the original design.

Best Bob
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Old 06-08-2012, 12:39   #460
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Marqus,

That would work fine. In fact I would really like to throw out my last two lead acid batteries and just start off the lithium ones. Before lithium it was just one large bank.

The problem is I elected to add a minimal Battery Management System. It sits there and monitors each cell and isolates the entire bank if I accidentally overcharge or over discharge any cell. It also has logic that if one of the cell monitoring boards fail to report it isolates the bank. Given this is all new technology, I was concerned about everything going dark due to a glitch in the system. So that's why I kept the lead acid start batteries. But underway they have to be paralleled to provide the redundancy if something happens.

Best Bob
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Old 06-08-2012, 13:24   #461
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Bob,

We too have a lead acid start battery, but I think a much simpler system. The start battery is wired to the engine directly. All charging sources go to the LIFEPO4 house bank. There is a combiner switch to add the house to start if required. The start bat is charged by an echo charger.

So the start batt gets it's preferred voltage from the echo charger. The alt regulator has been adjusted for optimal LIFEPO4 settings, per Terry's recommendations.

I have a BMS that thusfar I have elected not to use, and a cell log which I have plans to wire up for monitoring.

Chris
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Old 06-08-2012, 14:43   #462
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Chris,

That's simple. Once I learn to trust the BMS, I may do likewise, Do you have an "ACC" or "accessory" load on the engine? I think the only thing on mine is the engine gauges, a small load, but still something that would eventually deplete the engine battery without charging underway.

I think this load could be relocated to the house if needed, then the start would be a start and nothing else.

Bob
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Old 06-08-2012, 15:33   #463
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Bob,

The engine battery is charged FROM the house battery, whenever a need is sensed. So, all loads are taken care of. The echo charger will deliver up to 15a to the start batt. If you need more, then the similar unit from Balmar, the Digital Duo Chrage, can deliver more amps, if used with a relay.

Chris
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Old 06-08-2012, 19:34   #464
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Hi Bob,
Is this the articlehttp://powerelectronics.com/portable_power_management/battery_charger_ics/804PET22li-ion-battery-life.pdf
The majority of that article refers to lithium polymer batteries, the high float voltage is the give away, if you held lithium ferrous cells that high they wouldn't last long, it is the voltage specified in the manufacturers literature but a lot of studying chinglish is required to understand where the relevance of such a high voltage fits into the charging regime. We don't have the sophisticated chargers that use those extreme voltages so the figure is of no value to us. If you look at the voltage curve as a cell reaches fully charged the full point is fairly easy to observe, the charge can continue to 4.2v but all it's doing is creating heat in the electrolyte, this is the cell life shortening he's talking about. The chart showing the red sections at the top on bottom I believe refer to above 3.6v and below 2.8v per cell but the lower mark could be 3v per cell at rested voltage, that far down in the DoD the voltage drops a lot more under load. At 3.6v peak the lithium ferrous cells never see their max voltage, so the effect of top end charging shortening the life doesn't occur. I do agree with his reasoning that it's better to full charge regularly than deeply discharge but charging to a peak of 3.6v is not the same as holding the cells at 3.6v, especially if the charging current is 0.5C or less. As you have a 1200Ah battery pack I doubt is you charge at 600amps but even at 0.1C or 60 amps in your case, the quick blip to 3.6v will do no harm to the cells. The 4.2v per cell refers to charging at 1C.
When we first commission a cell pack we take all the cells to 4v, this is only suitable for house batteries, not for heavy rate discharge batteries like electric propulsion because it effects the high discharge rate but it does extend the cell life because it evenly coats the graphite anode with a thin film of lithium, this stops spot build up but rather an even layer build up as the cells cycle and limits damage during an accidental over charge as it eliminates any spot lithium build up that could lead to interplate shorting as mentioned in the article.
Quote:
What I've never found is the voltages for SOC at .01-.05C discharge and .15C charge. So I'm guessing, hopefully conservatively. It may vary a little bit on the chemistry and GBS are a slightly different LiFeMnPO4. Do you have any data here?
Quote:
The only data I have and I have tested to see if it matches up is the Winston charts, I couldn't find anything to do a 3C test or 5C test but the 0.5C and 1C are about the same as the graphs by a around 10 millivolts, as can be seen, one cell is a little less charged than the others, the cells had roughly 400 cycles on them, the cell logger graph is at the bottom of the post http://en.winston-battery.com/index.php/products/power-battery/item/wb-lyp100aha?category_id=176 is for Winston LiYFeP04, lithium yttrium ferrous phosphate cells so the LiFeMnP04 may be a little different, I see the quoted life cycles are shorter but these cycles are rated at EV use not house battery use so they are a tad on the pessimistic side. The Winston cells are rated at 3000 cycles to 80% DoD using a 0.5C discharge and recharging to 4.2v per cell stopping when the current reduces to 5% of the original 1C charge rate, I doubt any house batteries would be subjected to that sort of punishment so a longer life would be expected. The other thing is these batteries don't just die unless they have suffered an internal short, the just gradually loose capacity. This is what the cycle life charts are really saying, 1000 cycles to 100% DoD, then a further 4000 cycles with 80% capacity remaining at the end and a further 2000 cycles with 70% capacity remaining, 1000cycles 100% discharge, 5000 cycles 80% discharge and 7000 cycles 70% discharge. We know the first part is correct as the EV people do this to their batteries and have mentioned that after 3 yrs use the capacity is starting to reduce yet others who have stopped discharging their cells before they drop to 2v unload say they have not seen any capacity reduction yet. Naturally the ones who force every last bit out of the pack and drag their cells to zero volts or reverse charged report early failures, I guess they will learn when the wallet is empty not to torture their cells like that.

With your BMS system may I suggest you connect the LCV output to an alarm only and the HCV output to the charging relay, probably a solid state type like I mentioned before so any possible rapid switching would not cause any stress or reduced cycle life to the relay. If you find there is a rapid switching occurring a simle timer circuit could be added to hold the charging relay open for a period to allow the normal loads to pull the high cell down.
Here is the 1C plus test on a 90Ah LYP Winton 12v cell pack
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Old 06-08-2012, 21:35   #465
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

FWIW, we just returned from a Canada vacation where our 200 aH LiFePo4 battery bank with a MiniBMS was the sole electrical power for our boat.
We had 320 watts of well distributed solar panels on our trimaran, one each 100 watt on the amas and a 120 watt on an arch aft with a BlueSky MPPT controller.
We never needed to run the engine for electrical at all.
All the toys aboard, including watermaker and ice cream in the freezer (see Aerogel and LED lighting threads).

It doesn't need to be complicated.

For the whole month, we used 4 gallons of diesel for propulsion and furnace at night.

Starter batteries and all that switching? Who needs 'em?
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