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Old 08-02-2013, 06:34   #1996
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Originally Posted by goboatingnow View Post

Yeah I reread my post and saw that was a real "brain fart" of mine, Im handing back my electronics degree in shame.

SO if the BMS shunts the charge current, how do you protect the BMS from excessive shunt current, It has no control over the charger, nor has it any idea of the potentially greatest charge current that could be applied. Surely you could just fry the bypass device

ie I set my set point on my charger a little to high, so there is stiull serious current flowing at the BMS setpoint, it detects imbalance, and "lots of magic smoke escapes", or a fuse goes, but the balancing has failed. It all seems a little haphazard
Dave
The BMS flips a switch to parallel the resistor with the cell. It must be rated for the watts at 4V based on the resistance and then the heat dissipation managed. Some solutions use some kind of solid state component shunt, not sure what thats called exactly, but the result is the same.

Excess current continues to charge the cell. Then at some point, all BMS systems need a way to isolate the battery. If the charge voltage overruns the shunt, at say 3.65V, it yanks either the charge path, or all paths to the battery pack.

The EV guys usually have the BMS set to send a CAN bus off command to their charger or switch off the AC feed to the charger. Sometimes at a certain voltage, an EV charger is programmed to reduce the charge rate. There is no standard.

Once the bank is balanced, so long as the charge rate is not really high, the concept is only a couple minutes of shunting is required to maintain the balance.
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Old 08-02-2013, 06:44   #1997
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Originally Posted by CharlieJ View Post
BTW, the owner of the site that Bob Ebaugh recommended in #1991 has written an excellent, albeit expensive, book on BMS. It is relatively academic and not directly applicable to our xPyS configurations, but very fact filled, nonetheless.
A fair amount of that book is "free" in the online Google Book preview.
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Old 08-02-2013, 07:16   #1998
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by T1 Terry View Post

The reality is, a BMS system needs the cells balanced first, the claim is they are designed to keep the pack balanced. A balance pack rarely goes out of balance unless a cell fails or over charging causes a cell run away. A BMS can't do anything for a failed cell, it won't even tell you that the cell is failing, only cell monitoring will do that.
That leaves cell run away, if a high cell voltage charging cut is used there will be no cell runaway, so why is the cell balancing required?
The active BMS system can only actually function if the cells are over charged, that is the point they turn on, at an over voltage point. This brings me back to the question I asked before, why over charge the cells in the first place, there is nothing to be gained is there?
I don't have anything to sell, I have no reason to make stuff up.

T1 Terry
That's what baffles me the most, I know you have no reason to make stuff up, and yet you keep doing it in most of your posts

None of what you said above make any sense to someone who worked with LFP cells for 3 years. None of what you pontificate in your posts actually happens in reality, maybe not your reality, but in reality I see with my own eyes, while working on 100s of projects using LFP cells every day.

With all your fictional stories across this thread you make it look like BMS is some complicated and dangerous boogaboo , which confuses people and probably causes some of them to stay away from LFP all together. When in fact LFP is very simple and BMS is a simple and inexpensive tool, which helps manage LFP bank. Is BMS a must have? No, it isn't, and I never claimed otherwise. Just like having a DVM is not a requirement to use any battery, but it helps most people to have one handy. When one spends $1000-$2000 on LFP cells, is additional $150 spent on an instrument so hard to justify? No. Then why do you need to make up all these stories? What is your goal here? Why do you insist to know a product that you never actually held in your hands?

An where do you see an attack from me? I am simply defending something I do every day with my own hands from armchair experts like yourself.

Yes, I am selling BMS, which I designed and use personally in all my batteries, I have 2 EVs , one converted lawn mower, and bunch of smaller LFP batteries all over the house, all managed by my BMS, plus 100s of satisfied customers, without a single product return in 3 years.

To be honest, I could care less if anyone from this forum buys anything from me, I only make a few bucks on HousePower BMS since its so cheap, it makes no sense for me to spend time on forums from business point of view, because most of my business is with system integrators, who buy my BMS , make complete battery system and then sell at a nice profit to folks, many of whom could have done same thing as DIY if they weren't scared by people like you. I only keep retail business for DIY folks because I want to help people save money. Most likely retail sales will not last long since I have less and less time to deal with individual DIY customers as this market is growing fast and system integrators are more attractive for me because they know what they are doing and don't ask 100 questions with each order.

And what is this notion on forums that if someone sells something they must be evil and lying, while a guy who doesn't sell must be honest and knowledgeable? Its absurd. When I want to learn something new, I listen to people who do it for a living, not to a guy who plays with toys and thinks he knows everything.
This is main reason I stay away from forums, I cannot stand this absurdity.
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Old 08-02-2013, 07:38   #1999
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by mbianka View Post
Typhoon:

I built a monitoring station for my 48 volt AGM electric propulsion bank. I have it mounted at the helm so I can keep an eye on things while underway. Got a photo of it here:
THE BIANKA LOG BLOG: MID WINTER CHECKUP
It's not permanently installed yet but, I can check each battery's voltage as well as pack voltage and current. The main battery monitor (XBM) had to be moved out of the cockpit because the LCD display could not stand up to the sun:
THE BIANKA LOG BLOG: REPAIRING A XANTREX XBM BATTERY MONITOR DISPLAY
The backup Paktrakr battery monitor was located in the cabin and hard to read without glasses and also took it's power from one of the batteries causing an unbalanced condition. Having all the info at the helm with this monitoring station helps a lot in keeping an eye on the batteries.
Hi Mike,

Thats a good idea, this is food for thought , Im thinking maybe to us the USB info from a cell log 8 and feeding it to a lager display with the appropriate software , maybe an i pad of sorts and just build it into the chart table, that way I could check on many aspects of the batteries using a touchscreen. Going to give it more thought and research .



Regards
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Old 08-02-2013, 07:49   #2000
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Li-Ion BMS - Li-Ion BMS options
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Old 08-02-2013, 08:44   #2001

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

Just as a reference point, how far do the cells in a typical 12v wet acid battery vary as they go out of balance?

On vibration specs, I don't think "vibration" really applies to the pounding that a battery would see on a boat slamming around at sea. The repeated impacts would be more like hitting potholes in a truck, fairly large sudden high-g events, occurring way less frequently than something like the vibration from engines or other sources. Given all the talk about how the mebranes in Li-Anything cells can be punctured by crystal growth, I would think "high g" impact events might be a different area of concern.
I'm thinking of a short trip on a highly overpowered RIB slamming across chop, where my kidneys definitely weren't calling it "vibration". And my knees agreed.
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Old 08-02-2013, 09:10   #2002
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Bulging cells

Hi all,

I have a situation I would like to discuss.

We have a 400ah "Hipower" bank on Alchemy. It is comprised of eight, 200ah cells in a 2p4s configuration. Physically, they are grouped into two banks, 4 cells each connected with metal interconnects (6v), with a heavy cable in-between each to form 12v. The cable is only about 18 inches, it is done this way to fit into our existing battery boxes, which previously held 4 t-105 wet cells (two in each box).

Alchemy was on the hard for about 8 months, after some summer storm damaged forced us to pause cruising. We had spent the previous 6 months cruising down to the Bahamas and back, and they performed very well.

I kept them at about 50% for much of the refit period, and only started to charge them with a 120w solar once we were getting ready to go back into the water. By the time we splashed her, the bank was about fully charged, and it was cold.

I ran the engine for about an hour, and towards the end, I noticed that the Link10 voltage, which is usually a bit higher reading then actual battery voltage owning to where it reads in our wiring, was at 14.7 with the engine running. It did not click that this was something really bad right away, so the engine ran for about an hour, and then again for 1/2 a hour moving the boat from the yard to a nearby slip.

At this point, I inspected the batteries. They lie on their sides, so I could only see the top cells in each box. The aft cells, third in series, were at 3.9 volts! Worse, there was bulging in those two cells.

Furthermore, when I pulled the cells out, one of the lugs of the heavy cable came off. This cable was re-used from the original LA install, and it looked like the end, with very nice heat shrink, was never crimped properly!

I figured out where the high voltage came from. We have a Balmar 612 regulator. I had set the bulk to 14.1, float to 13.4, but I failed to change the compensation limit, and yes, I had a temp sensor installed. IT was set to 14.8! So it was cold, and volted compensated the charge up to 14.6-7 ish. It was left-over from the LA install, and I figured it could not hurt. Woa, I was wrong!

I have pulled all the cells out, removed the temp sensor for the batteries (and kept the one on the alternator). I am now charging each cell-pair with a 6a 3.6v charger to top balance. I had drained to top cell with a long 16ga wire.

The bulging seems to be about 2mm on either side on the two parallel cells.

I have an uninstalled mini-bms house bank system, that I may install, but only to balance and buzz, not to disconnect or do anything active (yet). Once the cells are all top balanced, I will put them in, draw them down, and then charge back up.

So, what do I have, are they damaged too far? I will install the bms, but can turn it on or off with a switch. Should I re-order the parallel groups?

Looking for comments.

Chris
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Old 08-02-2013, 09:29   #2003
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
Originally Posted by goboatingnow View Post

SO if the BMS shunts the charge current, how do you protect the BMS from excessive shunt current, It has no control over the charger, nor has it any idea of the potentially greatest charge current that could be applied. Surely you could just fry the bypass device

ie I set my set point on my charger a little to high, so there is stiull serious current flowing at the BMS setpoint, it detects imbalance, and "lots of magic smoke escapes", or a fuse goes, but the balancing has failed. It all seems a little haphazard
Dave
This is precisely why there is no good BMS which does just balancing. There were some early on, all of them failed, went up in smoke. No one does it anymore.
Proper BMS must have HVC/LVC functions first and foremost. It must be able to shut off charging when any cell reports HVC and must be able to shut off load when first cell reports LVC. If you don't have these 2 functions, then you don't have a BMS.

Balancing is a 3rd function, and its optional in some systems, or very weak in other systems. In our HousePower BMS system balancing is limited to only 0.6A on average ( peak at 0.75A ) after which it will shut itself off via PTC fuse, preventing overload and overheating.

This is why BMS cannot do initial balance in reasonable time, it does not have enough shunting capacity. Since initial balance is only needed one time when bank is constructed, it does not make sense to build a BMS with huge shunting capacity. So, BMS has a small shunting capacity, designed to keep the pack balanced over years of daily use. But initial balancing still needs to be done with other tools, such as single cell charger. Initial balance depends on quality controls at the cell maker/vendor. Some make sure they ship cells at well matched SOC, in which case initial balance is not required, or very little is needed. Some vendors ship cells from different batches, different manufacturing dates, different SOC, etc. These require a lot of initial balance. Its like a box of chocolates, you never know what you going to get.
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Old 08-02-2013, 09:44   #2004
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Hi all,
So, what do I have, are they damaged too far? I will install the bms, but can turn it on or off with a switch. Should I re-order the parallel groups?

Looking for comments.

Chris
I don't have any experience with overcharged cells, but there is a picture in a Thundersky manual of a device that compresses bulging cells flat again. If you used a couple of pieces of plywood at each end of the bulged cells and tightened them in a vice for a few hours it would perform the same function.

Hopefully you will find the cells recover. If not, and the others test OK, I'd be inclined to replace only the bad cells. You could pretty much use anyone's cell at the same capacity rating.

I would hook up the House BMS to a disconnect solenoid to prevent future occurrences. The alarm won't save you if the next failure is your solar controller and you are away.
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Old 08-02-2013, 09:45   #2005
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Re: Bulging cells

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Originally Posted by witzgall View Post

I have pulled all the cells out, removed the temp sensor for the batteries (and kept the one on the alternator). I am now charging each cell-pair with a 6a 3.6v charger to top balance. I had drained to top cell with a long 16ga wire.

The bulging seems to be about 2mm on either side on the two parallel cells.


Chris
Chris,

I bet that poor connection resulted in voltage drop and produced extra heat, which was absorbed by the terminal and the guts of the cell. This caused a small amount of electrolyte to vaporize into gas and bulge the cell a little. I have seen this happen a couple of times.

If the bulge is so small, then the cell is not ruined, but its likely lost a bit of capacity and has a bit higher internal resistance now. It will still work perfectly fine as long as reduced capacity does not cripple your needs.

Once you balance them and put them back in use, try to run them down until first cell reports LVC, it will likely be the bulged cell. If amount of AH taken out by that time is not too bad, then you can live with it. If not, then cell must be replaced.
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Old 08-02-2013, 09:50   #2006
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by ebaugh View Post
I don't have any experience with overcharged cells, but there is a picture in a Thundersky manual of a device that compresses bulging cells flat again. If you used a couple of pieces of plywood at each end of the bulged cells and tightened them in a vice for a few hours it would perform the same function.
Its my understanding that this process does not recover any capacity and does not make much improvement in cell's life. Vaporized electrolyte cannot be pressed back into useful form. Perhaps all it does is make the cell physically able to fit back into the box, if its still usable at that point.

If its just 2 mm bulge on a 200AH cell, I think the damage is minimal.
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Old 08-02-2013, 11:54   #2007
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by T1 Terry View Post
From the Winston test information that i have on hand:
Vibration test
Vibrate direction: rack vibration
Vibration frequency: 10^55Hz
Maximum acceleration: 30m/S2
Vibration duration: 2hrs
Discharge: discharge the cell with 1/3 3C (A) current until the voltage reach 2.5V
there should not be significant discharge current transformation, abnormal voltage, case distortion or electrolyte leakage.

It's a bit chinglish but maybe it means some thing to some body

T1 Terry
Those numbers are describing vibe parameters, in units that are pretty standard. Placed on a random vibe table you would experience accelerations of up to 3G (30m/s^2) at frequencies from 10-55 Hz.

At work the environment is determined as a function of the booster and location relative to it, and the number of joints between the booster and your item of interest, but that is on a case by case basis as every gram matters. The unit under test would then be placed on the shaker table and the responses measured against the structural limits. There is a graphic of a typical vibe curve as a spec here: FEMCI Book - Creating a Random Vibration Component Test Specification, with what looks like an example of actual data from which that curve was derived. The text Terry has makes it sound like they are just plugging in a flat line curve to the shaker table and not actually measuring the responses in situ (this is expensive and usually requires a good finite element model to exist to compare predictions against results), just looking at the effect after the test was done.

Presumably for the marine universe someone went out in a storm with some data loggers and made a bounding case of vibrations that can be expected to be seen and units can just be tested against that standard.

Andy
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Old 08-02-2013, 12:06   #2008
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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On vibration specs, I don't think "vibration" really applies to the pounding that a battery would see on a boat slamming around at sea. The repeated impacts would be more like hitting potholes in a truck, fairly large sudden high-g events, occurring way less frequently than something like the vibration from engines or other sources. Given all the talk about how the mebranes in Li-Anything cells can be punctured by crystal growth, I would think "high g" impact events might be a different area of concern.
I'm thinking of a short trip on a highly overpowered RIB slamming across chop, where my kidneys definitely weren't calling it "vibration". And my knees agreed.
I think you're confusing random vibration (many frequencies all at the same time, what you get with most of real life in shaking situations) with sinusiodal vibration (things ringing at specific frequencies, which is relatively uncommon). Random vibe can encompass everything from what your butt feels driving down a smooth interstate to what the space shuttle SRBs feel when they light off, it all depends on the spectrum and values that are specified. Shock values are another (related) regime, where they are extremely high G (thousands) but for very short durations (milliseconds), and are actually relatively unlikely to occur in the marine environment. Typical shock causing events are pyros firing or burst vents blowing, or what you feel when you have your hand on a splitting maul handle when someone hits the maul with a hammer to split a tough piece of wood. Vibe can kill any structure, shock is mostly an issue for very rigid, brittle structures.
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Old 08-02-2013, 12:10   #2009
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

There is supposed to be a reply to Terry's question about the vibration datasheet but it needed moderator approval somehow? It had a reference link to a nasa page, does any link require a mod approval?
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Old 08-02-2013, 12:14   #2010

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

Durundal, I'm not confusing vibration types. I'm suggesting that the only unusual movement on a boat is not vibration of either kind, but is shock. And that both share the common attribute of being motions, as opposed to fixed-installations. The speed (rate) and range of the motions in the environment may vary, but it still comes down to whether the batteries have been installed on inertial dampers or acceleration couches. Oh, wait, you don't have those on this planet yet, do you? <G>
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