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Old 21-01-2016, 12:46   #4876
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by mbartosch View Post
Agree with the notion that the House Power BMS is not an optimal choice for marine applications, but you can work around a few of its limitations.

For example you can achieve this "OK to load" and "OK to charge" completely without a main contactor.

...

(BTW, I actually sat down and created freaking logic tables when first designing that, and converted them to relay logic - only to find out it's that simple )

HTH

Martin
Haha, yes I know, but why procrastinate with a gadget that was only ever intended for playing at the cheap end of the EV market at the very most... it even lacks the features to make it a decent EV BMS.

Adding relay logic around it to try and fix it only decreases its overall reliability and you lose the ability to have a control signal saying "stop" before a DC disconnect takes place, which should be the last resort.
You can blow up a MPPT by disconnecting its output at high load and if you have a wind generator as well, things get more challenging again.

Meanwhile you are still stuck with cell boards, high intrinsic consumption, no temperature sensing, zero redundancy in electronics that are not fail-safe and the list goes on.

When I looked at it, I laughed and headed for the drawing board. No way I was going to use that on a high-value asset.
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Old 21-01-2016, 13:17   #4877
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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I build my own when I need them and this is what I have been using. It is technically a BPS and I designed it specifically for this application.
I am designing a new model (BMS) at the moment based on everything I learned along the way, but it hasn't reached the stage of the first prototype yet. An alternator control project got in the way, but this is now near finished.

Not long ago I needed to identify a pathway for a 24V system and after reviewing a great many of them, I found that you could use an Orion Junior for that with benefit...
It would work for 4-cell/12V too and it has the capability of monitoring many pack temperatures etc. Unlike the other one, I see it as a decently engineered product.

Check it out and I hope this can help...
Eric

Thanks Eric.
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Old 21-01-2016, 13:39   #4878
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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I personally like the idea of a manual main battery shutoff in order to isolate the batteries to do work on them (replace, repair, cell boards, etc.) without worrying so much about an accidental short circuit to ground. It would normally be left on in an installation while the BMS and relays and contactors manage the LV and HV. I don't think I would shut it off while charging, although the solar panels would be "on" during daylight. I just rechecked my Outback MPPT solar charge controller and it gives no warning about disconnecting the battery while charging, and I have done that with on my previous boat by pulling the fuse and never noticed a problem. It may be I missed the bullet?
A main battery switch is of no help to "work on the battery" as you describe, really... it doesn't shut the cells off. Meanwhile, using it on some deficient designs results in leaving the charge bus connected to the load bus.
Triggering a disconnect of the load and charge buses disconnects the battery without having this problem.

Some MPPTs will disconnect under load and manage the transient, others may not. You are always taking a bit of a chance. An Outback is a fairly serious piece of equipment.
A common issue I see in many designs is that a HVC disconnect leaves all charging sources connected together with nothing to charge. If it happens under load, the spike produced by one of them (like a wind generator) can be enough to blow another device that was never designed to handle that much voltage on its output suddenly. An event like this can get expensive, so always wary there.

The more current you are running at the time, the higher the risk. You might disconnect 50 times without incident and then suddenly face a major because it happened to be blowing a gale this time and the battery was bulk-charging. Anyway...
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Old 21-01-2016, 16:03   #4879
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

I am only running one contactor right now for the main. I'll add more for the hvc and lvc later on.
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Old 21-01-2016, 17:50   #4880
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by OceanSeaSpray View Post
A common issue I see in many designs is that a HVC disconnect leaves all charging sources connected together with nothing to charge. If it happens under load, the spike produced by one of them (like a wind generator) can be enough to blow another device that was never designed to handle that much voltage on its output suddenly. An event like this can get expensive, so always wary there.
I really don't understand why more people don't use a small 'oh crap' type lead battery on the charge bus to avoid any spikes. Put some diodes in front of it to isolate it from the lithium batteries and adjust for voltage differences and Bob is your uncle.
Even a small motorcycle battery will absorb any spike that should ever show.
I would suggest a super capacitor but it would probably be more expensive than a motorcycle battery.
While I am at it, may I suggest that more people isolate their different charge sources in case of voltage regulator failure? Put a diode or FET isolator on every charge device so that a failure in one doesn't blow the others. Hopefully the battery bank is protected already by an overvoltage relay and of course you do (don't you?) have a separate charge and load bus so a failed voltage regulator will not blow up your entire electrical system .....
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Old 21-01-2016, 17:54   #4881
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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You need to read about a concept called "shuttle reaction" and learn how each type of battery deals with current once fully charged, why LAs are able to equalise and LFPs can't etc. They simply have nothing in common...
I'm familiar with battery electrochemistry generally and with the redox shuttle approach to overcharge protection specifically. If you ever apply an over-voltage sufficient to oxidize redox shuttle additives so that they can shunt current, then you're already well past abuse. Those electrolyte additives are to minimize the risk of Li cells bursting, not to extend their service life. They have absolutely nothing to do with voltage balance among cells.

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What you are saying above is completely wrong.
We have a difference of opinion. My opinion is based on having a minor in physics, deep knowledge of LiFePO4 electrochemistry, and years of experience playing with LiFePO4 cells. I'm not trying to sell anything. My opinion is that vendors are exploiting, whether consciously or unconsciously, people's natural fear of anything that is new and different to sell BMSes that people don't need.

If you want a basic introduction to LiFePO4 electrochemistry, I suggest starting with this lecture by Prof. Jay Whitacre:
http://media2.ev-tv.me/chargecar.mov

Note that while Prof. Whitacre advises these students that they should do cell level monitoring (to learn about battery chemistry), he suggests the cost of cell level monitoring does not justify any potential benefits, emphatically noting that none of the electric vehicle manufacturers do cell level battery management.
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Old 21-01-2016, 18:24   #4882
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

A redox shuttle mechanism is intrinsic in lead-acid batteries and doesn't exist in lithium batteries. While there have been considerations about adding stuff into them to create one, all the cells we can buy don't have one and can't be trickle-charged, equalised and what not for this reason.

Proof? Current goes down to ZERO if you overcharge a LFP cell and then the voltage rises up to 4.2-4.3V, which is the next reaction potential where you break the electrolyte down. If there was a shuttle reaction, we would see the voltage stop there with some current flowing.

The creation of a redox shuttle would precisely allow cells to be balanced through moderate over-charge (while heating them too...) and the presence of such a shuttle mechanism in lead-acid cells has never prevented boiling them, damaging them or worse because the capacity of the reaction is still easily overcome.

So in spite of the claims, credentials and advice, I maintain my earlier comment: completely wrong, even more so now. Sorry.
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Old 21-01-2016, 19:31   #4883
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Note that while Prof. Whitacre advises these students that they should do cell level monitoring (to learn about battery chemistry), he suggests the cost of cell level monitoring does not justify any potential benefits, emphatically noting that none of the electric vehicle manufacturers do cell level battery management.
This thread Pics/Info: Inside the battery pack would seem to contradict that assertion. The Tesla model S pack looks like it has a BMS and what appears to be dedicated cell monitoring and balancing (albeit very slow) capability.
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Old 21-01-2016, 19:33   #4884
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by OceanSeaSpray View Post
A redox shuttle mechanism is intrinsic in lead-acid batteries and doesn't exist in lithium batteries. While there have been considerations about adding stuff into them to create one, all the cells we can buy don't have one and can't be trickle-charged, equalised and what not for this reason.

Proof? Current goes down to ZERO if you overcharge a LFP cell and then the voltage rises up to 4.2-4.3V, which is the next reaction potential where you break the electrolyte down. If there was a shuttle reaction, we would see the voltage stop there with some current flowing.

The creation of a redox shuttle would precisely allow cells to be balanced through moderate over-charge (while heating them too...) and the presence of such a shuttle mechanism in lead-acid cells has never prevented boiling them, damaging them or worse because the capacity of the reaction is still easily overcome.

So in spite of the claims, credentials and advice, I maintain my earlier comment: completely wrong, even more so now. Sorry.
Even if Li cells didn't have redox shuttle additives (they do), none of what you wrote above makes a case for cell level voltage monitoring. LiFePO4 cells that are well-matched, properly balanced, not abusively charged, and not abusively discharged do not drift out of balance. Several members of this forum (including me) have many hundreds of cycles on LiFePO4 with zero voltage divergence among cells. No one has reported a contrary result here or anywhere else as far as I can find. I've searched the academic literature and cannot find any reports of voltage divergence among well cared for LiFePO4 cells. People are selling expensive "solutions" to a "problem" the existence of which has not been shown to exist.
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Old 21-01-2016, 19:44   #4885
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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This thread Pics/Info: Inside the battery pack would seem to contradict that assertion. The Tesla model S pack looks like it has a BMS and what appears to be dedicated cell monitoring and balancing (albeit very slow) capability.
Tesla use LiCoO2 (Lithium Cobalt Oxide) which is a very different chemistry from LiFePO4. Prof. Whitacre's assertion was specifically about LiFePO4 cells. LiCoO2 has a higher energy density and is much more dangerous than LiFePO4.

Other than the relatively small LiCoO2 batteries in my iPhone, iPad, and laptop, I would not want a LiCoO2 battery anywhere near a boat or airplane. I'm not entirely comfortable with LiCoO2 for electric cars, but at least cars are easy to abandon when they catch fire.
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Old 21-01-2016, 23:01   #4886
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by mcarling View Post
Tesla use LiCoO2 (Lithium Cobalt Oxide) which is a very different chemistry from LiFePO4. Prof. Whitacre's assertion was specifically about LiFePO4 cells. LiCoO2 has a higher energy density and is much more dangerous than LiFePO4.

Other than the relatively small LiCoO2 batteries in my iPhone, iPad, and laptop, I would not want a LiCoO2 battery anywhere near a boat or airplane. I'm not entirely comfortable with LiCoO2 for electric cars, but at least cars are easy to abandon when they catch fire.
Oh well, I have now learned about the unique mcarling one-way redox shuttle reaction that stuffs the electrolyte at 4.3V with no come-back, that Tesla uses LiCoO2 chemistry (wrong) and that mcarling's iGadgets are LiCoO2 powered too, which is unfortunate because everyone else's use lithium polymer. Or could he just be wrong too? That would make him beyond completely wrong, as he has been completely wrong on all fronts from the start already.

Meanwhile several people have reported here occasionally adjusting the balance of their packs by discharging the odd high cells - can't always be lucky when buying them - and there is a good explanation for this to happen, but whatever. Got much better things to do than arguing with opinionated ignorance...
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Old 21-01-2016, 23:47   #4887
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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What you are saying above is completely wrong.
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Originally Posted by OceanSeaSpray View Post
I maintain my earlier comment: completely wrong, even more so now.
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That would make him beyond completely wrong, as he has been completely wrong on all fronts from the start already.
Just keeping repeating that mantra. Saying I'm wrong is the strongest argument you've put forth.
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Old 22-01-2016, 08:20   #4888
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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My opinion is based on having a minor in physics, deep knowledge of LiFePO4 electrochemistry, and years of experience playing with LiFePO4 cells. I'm not trying to sell anything. My opinion is that vendors are exploiting, whether consciously or unconsciously, people's natural fear of anything that is new and different to sell BMSes that people don't need.

If you want a basic introduction to LiFePO4 electrochemistry, I suggest starting with this lecture by Prof. Jay Whitacre:
http://media2.ev-tv.me/chargecar.mov

Note that while Prof. Whitacre advises these students that they should do cell level monitoring (to learn about battery chemistry), he suggests the cost of cell level monitoring does not justify any potential benefits, emphatically noting that none of the electric vehicle manufacturers do cell level battery management.

OOOOPS you are talking too much sense here. You are trying to change opinions with facts......that just confuses and upsets some people and causes deeper entrenchment in their beliefs and the results are not nice to see or read.

As I am seeing 0.001V of a difference in cell voltages in my three seperate batteries.......using cheap and chearful RC/ cell monitors, producing results which had me thinking this cannot be right. That was until I pulled out my FLUKE DVM which displays to three decimal places at low voltages and confirmed that these <$10.00 monitors were accurate.

Well this after a year has me thinking - I have FOUR BMS/ 200A relay units and TWELVE Cell Boards....(and some spares) PLUS I know from experience that my Delco Remy 10SI alternator is a solid as a rock and is incapable of generating an HVC voltage..........

Since I have no idea of the MTBF of these 'BMS and associated components' and since i am monitoring individual cell voltages and it would be very easy to set up some HVC alarms with parts I have already.

Maybe I really should go total KISS and remove the BMS's and the Cell Boards as they could quite easily be the weak link in the chain, doubly so as I never expect to see an HVC or LVC and have triple redundancy having three seperate 200AH batteries as my house bank..........NOT that I see even if all three went offline simultaneously this being a critical situation.

I see few 'real' differences between LA and LIFePO4, in a how should we look after them way.....

LA has generated a nice wee idustry in LA Battry 'things' POWERFUL WHITE alternators (why would you ever want to insulate the case of your alternator and make heat dissipation more difficult).....three stage external alternator control......you want to run your main engine for long enough for the third stage of the charging profile to kick in do you? Battery monitors that tell lies lies and more lies BUT look good and convince people that they are maintaining their LA batteries 'properly'.

I think I know how to take care of my batteries since my Gel Cells were dumped at 14 years old ONLY because while the F/F was happy (well the batteries were able to handle the loads) the minute I tried to move over to electric cooking, the Gel Cells were not up to supporting these loads.

While I am not suggesting LIFePO4 is a drop in replacement for LA the changes needed are minimal for a KISS system........the more complexity you add the more things you have to go wrong and cause issues.......which is why having some experience now I think one should monitor cell and battery voltages as a minimum, a HVC/LVC alarm yes too, is a nice to have thing......but how often are you going to test it? and a BMS with Cell Modiules is also nice to have BUT NOT neccessary IF you look after your batteries properly........

Probably for the masses who seem to have constant battery issues (certainly here in SXM) a BMS is eseential.

Just my views of course but feedback based on having installed a LIFePO4 house bank myself and using them in a cruising liveaboard situation .
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Old 22-01-2016, 09:09   #4889
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by OceanSeaSpray View Post
A main battery switch is of no help to "work on the battery" as you describe, really... it doesn't shut the cells off. Meanwhile, using it on some deficient designs results in leaving the charge bus connected to the load bus.
Triggering a disconnect of the load and charge buses disconnects the battery without having this problem.

Some MPPTs will disconnect under load and manage the transient, others may not. You are always taking a bit of a chance. An Outback is a fairly serious piece of equipment.
A common issue I see in many designs is that a HVC disconnect leaves all charging sources connected together with nothing to charge. If it happens under load, the spike produced by one of them (like a wind generator) can be enough to blow another device that was never designed to handle that much voltage on its output suddenly. An event like this can get expensive, so always wary there.

The more current you are running at the time, the higher the risk. You might disconnect 50 times without incident and then suddenly face a major because it happened to be blowing a gale this time and the battery was bulk-charging. Anyway...
Perhaps I wasn't very good at expressing myself. I like a manual battery switch to work on other downstream components, such as the inverter, etc. so I do not have to remove fuses or other cables first. It depends on the situation but it has been a regular thing with me in my work. To each his own. If you don't need it don't do it.

I find your discussion of the issues of spikes interesting. It should be discussed at length in other threads other than just LiFePO4 threads as it would seem to be just as applicable. Most all battery installation have all the charging sources effectively connected together and it makes no difference whether you disconnect a battery with one type of switch or another or removing a cable. I make it a habit of turning off charging sources before I do any work on my batteries anyway so perhaps it doesn't matter that much to me. If there are other threads on this could you please direct me to them?

All batteries are accidents waiting to happen as you cannot isolate a battery below its external terminals. So a battery switch does not prevent grounding issues between terminals. I use shorty wrenches on my batteries for that reason and even still they have a few scars where they jumpered between plus and minus. Sloppy work on my part, I know.
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Old 22-01-2016, 09:34   #4890
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

I am sure someone will help me out here, perhaps by attempting to put me out of my misery with some excruciating witty sarcasm, but, it seems to me that cell balancing is only a part, and it would seem from most all posters a small part, of the role of "practical" BMS's . Is seems that some BMS's attempt to do balancing and some don't. From what I have gleaned from here is it is good to started with cells balanced. It also seems that as a practical matter (as reported by all posters that have reported on it) that cells rarely get out of balance except when there is a bigger issue causing it (e.g. high voltage application).

Am I off base here? Should we, or should we not, really be debating the importance of, and competing ideas on, this issue? It is interesting to some of you for sure.
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