Good thesis on preserving the life of LiFePo4 lithium batteries

[tanglewood]

Originally Posted by travellerw

Alright.. I have to say that I think you guys are crazy to be nitpicking this kind of draw. Seriously, lets do the math.



First I will assume the 13 Milliampre in the spec sheet to be safe.



That would mean the following.

0.312ah/day

or

9.6Ah/month

or

56Ah/6 months



So if you were to park your boat for 6 months, with the relay left on (I would never do that) it would only take 56ah. F$&K all in a big ship partner.



I made this exact same mistake when I was designing my system. I was so caught up in the "waste of power" that I actually opted for a 7700 instead of the 7713. Stupid as I let my previous life of designing circuits cloud my brain. Hell, I could fly to the moon on 13 milliamps, I thought. Dumb as I traded a valuable safety check over a mere 0.312ah/day.



For 0.312ah/day, I now wouldn't even expend the energy to search the internet for a better solution. The BlueSea gear is used by tons of people and trusted stuff.

At 13mA, I agree completely. That’s an impressive number.

[tanglewood]

Originally Posted by Maine Sail

It is actually quite easy with the right equipment. An externally regulated alternator can simply have the field cut/turned off & have "float" set to a point the battery will never drop to and this simply disables the alternator. Our BMS does not "manage" charging the charges sources do that on their own through programming.

Exactly. And over time, I think we will see charge control moving from the chargers to the BMS. Most BMSes have OK-to-charge and OK-to-load signals already, and more and more charging devices have corresponding inputs. But for now we have a lot of legacy charge devices that need to be fit in my hook or by crook. Programmable charging parameters and simple enable/disable controls can almost always be made to work.

[Maine Sail]

Originally Posted by tanglewood

Exactly. And over time, I think we will see charge control moving from the chargers to the BMS. Most BMSes have OK-to-charge and OK-to-load signals already, and more and more charging devices have corresponding inputs. But for now we have a lot of legacy charge devices that need to be fit in my hook or by crook. Programmable charging parameters and simple enable/disable controls can almost always be made to work.

Unfortunately today many BMS’s have only catastrauphic level charge/no charge control. Some only feature a few seconds of hysteresis or lack logic to determine when to re-engage charging.

I personally do not want to rely on a 4VPC or even 3.65VPC stop charge signal. There are some more expensive BMS systems that allow more custom control but they certainly cost more than the $39.95 some LFP owners expect to budget for to protect their 3K in cells. We have a hard enough time getting folks to cough up a few bucks to tap into an alts field circuit so it can be safely shut down if the BMS exceeds cell level protection for charging.

I say that because the destroyed LFP battery in our shop right now was ruined prematurely, in an RV, by an owner who knew he should not use his stock alt with a continual non-stop absorbtion. It was an expensive experiment and now he gets to buy another bank and configure his charge sources more optimally, something he admitted he should have done up-front.

[tanglewood]

Originally Posted by Maine Sail

Bingo! The best part is the 7713 fails open/safe when or if the BMS goes teats up... It also has a manual override so you can open the LFP battery switch, thus manually isolating it, and manually turn the 7713 back on. Now your reserve battery, I use a Firefly, can now power the vessel until you sort out the BMS issue.



I initially started with a Tyco EV200 (with the coil economizer) because Blue Sea did not have a hold voltage that low back then on the RBS's. The EV200 is 130 mA vs. 13 mA for the BS 7713. It's really pretty tough to beat the 7713 as a main last ditch "ejector seat" contactor..

I'm using a TE LEV200 on my 48V house system. If only the BlueSeas was available in 48V.......


Another thing I see with the BlueSeas that at least for me is undesirable is that the transition from manual override back to remote control requires that you go through a disconnect. If I'm not understanding the datasheet correctly, please let me know. In addition to manually connecting and disconnecting the batteries, I want to be able to lock the batteries on while I screw around with the BMS, conduct repairs, etc., then turn control back over to the BMS once everything is back on line. But I'd rather not blink the power in the house every time. But I suppose I could do that with some extra switching for the remote control....

[tanglewood]

Originally Posted by Maine Sail

Unfortunately today many BMS’s have only catastrauphic level charge/no charge control. Some only feature a few seconds of hysteresis or lack logic to determine when to re-engage charging.

I personally do not want to rely on a 4VPC or even 3.65VPC stop charge signal. There are some more expensive BMS systems that allow more custom control but they certainly cost more than the $39.95 some LFP owners expect to budget for to protect their 3K in cells. We have a hard enough time getting folks to cough up a few bucks to tap into an alts field circuit so it can be safely shut down if the BMS exceeds cell level protection for charging.

I say that because the destroyed LFP battery in our shop right now was ruined prematurely, in an RV, by an owner who knew he should not use his stock alt with a continual non-stop absorbtion. It was an expensive experiment and now he gets to buy another bank and configure his charge sources more optimally, something he admitted he should have done up-front.

Right, that's a whole other set of problems. I'm glad I don't have to deal with that.


The PLC BMS that I'm doing is DEFINITELY not an inexpensive route, but it's still a good bit less than a fully packaged/integrated system like Victron, and infinitely flexible. So I remain cautiously optimistic. The per-cell monitoring and alarming is all working well, including panic disconnects, and I just go it sending me emails when anything changes alarm state. And all thresholds are adjustable...

[CatNewBee]

Originally Posted by Maine Sail

Unfortunately today many BMS’s have only catastrauphic level charge/no charge control. Some only feature a few seconds of hysteresis or lack logic to determine when to re-engage charging.

....

I say that because the destroyed LFP battery in our shop right now was ruined prematurely, in an RV, by an owner who knew he should not use his stock alt with a continual non-stop absorbtion. It was an expensive experiment and now he gets to buy another bank and configure his charge sources more optimally, something he admitted he should have done up-front.

Can you please elaborate a liitle more about the failed LFP system. What cells, what BMS and what settings were used?

What was the damage caused? (single cell runoff, all celks reduced capacity...?)

[travellerw]

Originally Posted by tanglewood

I'm using a TE LEV200 on my 48V house system. If only the BlueSeas was available in 48V.......


Another thing I see with the BlueSeas that at least for me is undesirable is that the transition from manual override back to remote control requires that you go through a disconnect. If I'm not understanding the datasheet correctly, please let me know. In addition to manually connecting and disconnecting the batteries, I want to be able to lock the batteries on while I screw around with the BMS, conduct repairs, etc., then turn control back over to the BMS once everything is back on line. But I'd rather not blink the power in the house every time. But I suppose I could do that with some extra switching for the remote control....

The disconnect from manual to BMS remote control would be something the BMS does, not something the ML-RBS does. I can manually disconnect my bank (using the switch on the ML-RBS), and then reconnect it without the BMS even knowing I have done it. Once I have manually switched the ML-RBS back on, then its again under control of the BMS. Or, I could switch the control wire on the BMS off and on again, and it would electrically pull the ML-RBS back closed (instead of manually turning back on). However, this functionality would be different depending on what BMS you are using, how its wired, and what functionality it offers (e.g. If your BMS monitors pack voltage and takes its reading on the house side of the ML-RBS, then its going to freak out when you do a manual disconnect as it will see low or no voltage).

As to the "blinking" of the house. You could simply add a smaller jumper wire across the terminals of the ML-RBS. I would actually put a flat fuse in line, not to protect anything, but as a conveinient method to jump across the ML-RBS. Put a fuse in while you are testing, then when you are done you simply pull the fuse to disable the jumper link. No house blinking and you get to see the ML-RBS in action.

[Delfin]

Originally Posted by senormechanico

You asked....

See, I told you we would see that first.

[Delfin]

Originally Posted by rgleason

Highway engineers have taught me that there is always another way to skin the cat.

John wrote:
"Plus there's always a Reserve or Starter bank in lead, could be the power source for the contactor.

So in that context maybe both the NO and zero-discharge features " less critical"

So does it make sense to power the relay and BMS off the starter battery?

John thanks for answering for Cpt Pat about the trigger for 20% SoC probably being ah. It would be nice to have the other answers too, so I continue lurking here.

The BMS has to be powered by the bank it is protecting.

In my installation, the relay is powered by whichever bank is online. I'm using an ML series ACR from Blue Seas. The LFP bank is the primary bank and the starter the standby bank. The ACR sniffs the voltage of the LFP bank and when it reaches a target voltage, closes and connects the two banks. Using a three position switch, I can manually combine the banks via the ACR, then turn off the BMS. This results in the starter bank being the end point for charging sources and the LFP bank is completely disconnected, which is appropriate if underway and the LFP bank is full, or when on shore power. At anchor, the switch is in auto combine, which means the voltage will be below the target voltage for combining, so the starter bank is isolated and the LFP bank powers all loads.

[CatNewBee]

The latching ML-RBS has a yellow turn-switch with a push button and 3-states. Maintenance-Off, Operation mode with On and Off either manually or by signals.

So you can permanently override the BMS in maintenance Off or you can just override it once during a cycle (either turn off or push button on.

In maintenance it stays off, no matter what the signals are, in Oeration mode it acts as a R/S flip flop on impulses.

That ic very handy. Because there are only impulses you can also use more than one source to flip the switch - like emergency remote on-off switch or another logic that can override the BMS / disconnect the battery or what ever.

[tanglewood]

Originally Posted by travellerw

The disconnect from manual to BMS remote control would be something the BMS does, not something the ML-RBS does. I can manually disconnect my bank (using the switch on the ML-RBS), and then reconnect it without the BMS even knowing I have done it. Once I have manually switched the ML-RBS back on, then its again under control of the BMS. Or, I could switch the control wire on the BMS off and on again, and it would electrically pull the ML-RBS back closed (instead of manually turning back on). However, this functionality would be different depending on what BMS you are using, how its wired, and what functionality it offers (e.g. If your BMS monitors pack voltage and takes its reading on the house side of the ML-RBS, then its going to freak out when you do a manual disconnect as it will see low or no voltage).

As to the "blinking" of the house. You could simply add a smaller jumper wire across the terminals of the ML-RBS. I would actually put a flat fuse in line, not to protect anything, but as a conveinient method to jump across the ML-RBS. Put a fuse in while you are testing, then when you are done you simply pull the fuse to disable the jumper link. No house blinking and you get to see the ML-RBS in action.

I think a bunch of this may be specific to my setup, or perhaps applicable to a set of systems and not all...


My BMS controls the disconnect relay, as you would expect. But I want to be able to power down the BMS for repair, service, reprogramming, etc. But if I power it down, it will release the disconnect relay and the power will go out in the house.


Enter the override switch/mechanism. A manual switch that simply provides another source of power to keep the disconnect relay closed will solve the problem, and is my current approach. I can turn on the override switch, turn off the BMS, and the house still have power, albeit without the supervision of the BMS. Then once the BMS is back on line and is itself holding the disconnect relay closed, I can turn off the override switch and return control to the BMS, all without power interruption to the house.


With the 7717 (24V version), it would be nice to use the override that is built into the relay. But reading the data sheet, to return from manual override control to remote control, you have to switch the relay off. After doing that, remote control is again active. That would force a loss of power to the house, which I'd rather avoid.


Unless of course my read of the datasheet is incorrect.....

[JPA Cate]

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[rgleason]

I haven't been able to read everything lately, but this is a first effort at figuring out the controls needed for LiFePo4 using BVM702.
I am certain I am misunderstanding some of the relay controls and I know I haven't got this right yet, but it is a far as I can take it.

Perhaps some more experienced people have suggestions.

I also have not figured out how to use the BVM702 for this action.

• 16 Discharge Disconnect at 20% SoC (is this 12.7v?) *

There are two versions attached, a PDF file and an XLS file that you must remove the ".doc" first.

[CatNewBee]

Originally Posted by rgleason

I haven't been able to read everything lately, but this is a first effort at figuring out the controls needed for LiFePo4 using BVM702.
I am certain I am misunderstanding some of the relay controls and I know I haven't got this right yet, but it is a far as I can take it.

Perhaps some more experienced people have suggestions.

I also have not figured out how to use the BVM702 for this action.

• 16 Discharge Disconnect at 20% SoC (is this 12.7v?) *

There are two versions attached, a PDF file and an XLS file that you must remove the ".doc" first.

You can checkout my thread "1000Ah LiFeYPO4 and a all-electric galley" there are all the schematics how to connect the BMV relay (static NO/NC contacts) to impulse inputs on the ML-RBS latching relay 500A and how to program it.

You still will need a BMS for cell monitoring an balancing, also described in detail there.
http://www.cruisersforum.com/forums/...d.php?t=201795

[rgleason]

Catnewbee, thank you for the suggestion to review your excellent thread LifeYPo4 1000ah Winston.

The diagrams and explanations are good but I am finding them somewhat difficult to follow. I think there are some things I will be able to use here, including wiring of the BVM712 with the ML-RBS, however my installation is about 1/5 the size of yours, does not utilize, solar, quatro inverter charger and does use the alternator as the primary charger.

When I got to this point:
http://www.cruisersforum.com/forums/...ml#post2640576

The alternators will be disconnected from the house bank too, they will only charge the start batteries.
your following posts do not seem to reflect that. If you are setting up a system where you can connect/disconnect the alts to/from the house bank I'd be interested to know more.

I expect there is more valuable information to be gleaned, but I wonder if the REC-ABMS is too overpowered and expensive for my simple 200-270ah system, without much AC equipment?

• 4 series connected cells per unit
• high efficiency 2 A bi-directional active balancing (pack to cell and cell to pack)
• IP65 protection enclosure, AMP 35 pin water resistant connector
• 2 – 5 V measuring range, 2 mV accuracy
• up to 2 digital temperature sensors
• shunt current measurement
• CAN communication protocol
• two programmable fused relay output
• two programmable fused digital output
• ON/OFF switch
• Active Balancing

I have looked at thispreviously, what do you think for my application?
REC active ABMS $524

Wouldn't Victron BMS be more appropriate and less cost?

BTW did you happen to look at one of the two attachments below?