Re: Switch to LiFePO4


Scott SV Tengah
 

Kent,

Tom on L'Orient (who we met recently here in Oahu) called me the Lithium Evangelist or something similar. I do love my lithium and the impact that it has had on our comfort aboard, but I will add that I'm also a perfectionist with it so I'll quickly point out what I perceive to be problems that I perceive with my (and others') setups. My experience is not as an engineer but as someone who probably overthinks his lithium setup (because it was damn expensive and I don't want to damage it!) and on my most recent check, have run 2470kwh through my batteries, which is around 350 cycles at my 60% DOD average over the past nearly 2 years and they're as good as new. 

Here are some responses to your questions:

- Check that your charger inverter has a lithium profile. That's the easiest way to do it.

- The Skylla has a lifepo4 profile -  I own one.

- The Victron mppt have lithium profiles, use them. I own the 150/35. No temp compensation except there is a low temp charge cutoff. 

- I have 450AH. That is a good sweet spot IMO because once you have more than the amount of capacity you need to run 24 hours, you should be thinking about your renewable output. I put out about 250AH a day via solar. With our usage pattern, while stationary, we only run the generator to make sure it still works. You will have to do your own energy budget.

Example: If you have 1,000ah and use more daily than you put in with your renewables, all you gain from all that extra money spent on batteries is a longer interval between running the generator. Better to spend that money on renewables, imo. And unlike lead, you can take lifopo4 down to 20% very safely and still get 2000 cycles out of them. In fact, if I had a 1,000AH bank and kept it between 75-100% SOC, I'd probably be worse off because lithiums do not like being kept at the upper end of their SOC range. More is not always better.

Adding batteries later is not recommended, at least per my long conversations with Victron engineers. You really should have them all installed upfront or at latest 6 months later because while the batteries age slowly, they do age. Adding newer batteries to an old bank will cause charging imbalances.

- Making the chargers work together involves making sure they have the exact same charging voltages and durations. My Quattro and Skylla oddly do not talk to each other, but they work together perfectly because of this.

-I met with Peter Kennedy when I was trying to figure out how to safely shutdown my Mastervolt 110 alternator when I have a high cell voltage condition, aka cell imbalance. He seemed reasonably knowledgeable and as a Victron dealer understood how the Victron BMS sends out a signal that could be used to safely turn off my alternator when the BMS detects a high cell voltage condition. He suggested the solid state relay that I ended up using as he had tried it on someone else's setup. I will say that he admitted that he wired it incorrectly and fried it but still thought it would work. What was a bit surprising is that he didn't know that solid state relays cause a voltage drop and that causes problems with my/his proposed method of using the the Victron BMS to control the "reg-on" wire of the Mastervolt regulator. The problem was that the reg-on is also the voltage sense wire for the regulator, so you can imagine that a voltage drop on a sensing wire is not good. I solved that with the help of a very capable automotive ECU tuning engineer and detailed it in a post on my long lithium thread.

The point of that long story is that PKYS knows more than any other group I've encountered but it's your boat and even those who appear to understand lithium do not understand the intricacies of your specific setup and mistakes occur as a result of that or worse, the result of applying lead acid thinking to lithium. 

A few other thoughts in general and on others' responses:

-I chose 12v series pairs rather than 24v batteries to provide a backup to my starting battery. With 12v pairs, you do need to ensure that the individual batteries in the pairs are fully charged with a slow charger before installing them. Once a year, you disconnect and individually charge the 12v batteries in the pairs to ensure that they are balanced between them. I use a few cheap 12v/1.5a Lifepo4 chargers that run on 110-220v that you can get on Amazon for $20. As noted, the BMS will balance between batteries in parallel but not batteries in series. As a side note, each 12v pair is then, of course, put in parallel to create the 450ah capacity and as long as each PAIR is not too imbalanced, each pair will balance out with the other pairs. Hope that makes sense.

24v batteries does solve the problem of imbalance between 12v pairs, so that would be nice. If you go that route, just get a "backup 12v starting battery" that you keep charged via a dc-dc converter or even just a trickle charger that runs whenever you have the genset on, assuming your setup requires you run the generator now and then. That would probably be ideal.

I would be wary of going for a single massive 24v, say 450ah battery bank. Individual cells do die now and then and with a massive bank, unless you're very capable and confident about assembling/disassembling batteries, you won't be able to take it apart and remove those cells and continue on. If I'm in the Tuamotus and one cell dies, I just take that 12v PAIR offline and still have 300Ah of capacity left. Even I can do that without killing myself.

- Stop thinking float. That's lead acid thinking and will quickly kill your lithiums if you set it anywhere near your absorption voltage. If your charger requires you enter a float voltage, set it to 27v float and forget it. Controlling when charging stops with respect to SOC involves setting absorption voltage and duration. That said, it's very very difficult to try to target an ending SOC based on voltage. Lithiums have voltage "knees" on the top and bottom. The voltage with respect to SOC is nearly flat from around 10%-90% state of charge and then hockey stick up at 90% and down at 10%. But voltage is an unreliable indicator of SOC. To give you a real life example, I set my alternator's absorption voltage at around 27.2 volts, I believe. That was done so the batteries aren't kept at 100% during long motoring sessions. If I was going for fully charged, I set it at 28.4volts. During the last nearly 2 years, the alternator will stop charging anywhere from 85-95% SOC, as indicated by my battery monitor. It's not easy to target SOC using charge voltage on lithiums. And it's even harder if you're not targeting high terminal SOC because of the flat voltage vs SOC relationship when you're not at SOC extremes.

This is also a reason why most balancers only work when the batteries are at 28+ volts. When my own batteries were imbalanced a year ago, the cell voltages looked perfectly equal until 90% SOC and then and only then did the imbalance show itself. As a side note - charge your bank to 100% once a month. It helps balance the batteries and also resets your battery monitor since that really only tells you SOC based on amps in vs. amps out and charging to 100% calibrates it.

- You need a way to shutoff your alternator that is related to both overall bank state of charge and high cell voltage. Your state of charge may be at 90% but one cell may be at 4.2v and since your absorption voltage setting look at overall bank SOC and tells the alternator to keep charging, that 4.2v cell will keep getting fed with current and will therefore die shortly. This cell imbalance does not show itself when you look at overall bank voltage, but is detected by the BMS, which monitors cell level voltage.

Solving this honestly took me over a year and the help of aforementioned car tuning engineer to solve. Note that I spoke to countless lithium "experts" including Victron and Mastervolt engineers prior to this without a solution. I took a quick look at your regulator's manual. It says:

"Many LiFePo4 batteries have a Battery Management System (BMS) that may disconnect the battery from the alternator as a protective action or when charging is complete. The regulator must be shut down before the battery is disconnected .Running an alternator without a battery will damage the alternator and may damage any attached system. This is doubly true if the battery can be disconnected during

high current charging, causing a load dump. The load dump can easily cause a high voltage spike
which will destroy the alternator’s rectifier, at minimum. This is not a warrantable failure. To reiterate: THE ALTERNATOR MUST BE SHUT DOWN BEFORE DISCONNECTING THE BATTERY. THE ONLY SAFE WAY TO SHUT DOWN THE ALTERNATOR IS TO TURN OFF THE REGULATOR. The preferred method of turning off the regulator is disconnecting the regulator’s ignition (brown) wire, but if used as
an EMERGENCY ONLY shutdown, disconnecting the regulator’s power input (red) wire in addition to the 
ignition wire has a very low chance of damaging the regulator."


(1) You need a signal from the BMS to tell the alternator to turn off. The BB batteries seem to have an internal BMS that cuts off charging if there's a high cell voltage condition - does it send a signal that you can use to tell the alternator to turn off? Perhaps it's not a problem because with each BB battery having an internal BMS, maybe only that one battery is taken offline?

(2) You need to use that signal and use it in a way that safely turns off the alternator without frying it, per your Balmar manual. 

As noted in my long thread on my install, on my Victron BMS, there's a signal wire called "charge disconnect" that I use to control my Mastervolt regulator's "reg-on" wire. Seems you may be able to something similar on the Balmar as long as your BMS can send a signal when there's a high cell voltage condition.

Also with the alternator you will need to install a temp sensor. Balmar says that in their manual. When you're charging lead /agm/gel, the alternator only outputs full current for short period and tapers off quickly. I understand that internal resistance goes up at higher SOC. Lithium does not have this problem so your alternator/chargers will output full current until the battery is nearly full. That may cause overheating and fry your alternator. The Mastervolt engineers said my 110a alternator can handle that heat, but just to be safe, I installed an alternator temp sensor anyways. I recommend you do the same.

This has been long enough, I hope it helps someone at least a bit.

I will end by saying that I agree with Joerg on using one brand to the extent possible. I only went mostly Victron because I started with a Victron solar MPPT before I even knew what lithium was. Victron does not make alternator charge controllers and that was the source of my main issue, which is now solved thankfully. If you mix brands, be ready to have every company point its fingers at others if your batteries die. My understanding is that MV also allows you to set SOC based charging limits, which would be very useful. I haven't fully researched them, so I don't know what their disadvantages are but I'm sure there are some.  

Biggest disadvantage I've seen - If you think Victron batteries are expensive, Mastervolt will change that opinion.






--
Scott 
2007 A54 #69
SV Tengah
http://www.svtengah.com

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