LiFePO4 Batteries - Okay Tear Me Apart ;-)

[electric1]

Now, using typical "top-off" balancing BMS boards, the balancing voltage of the TS cells is rather high (approx 16.8V or 4.2V per cell on a 12V battery), so the only way you would get there using a typical marine charger is to use the "equalization" mode. So, if you know how to do that and monitor the current and cell voltages this can be done just fine. However, if you don't want to mess with it, the full-time balancing of the Genasun/Mastervolt/etc type BMS is probably worth the extra $.

With all due respect, the last thing I want is to start any flaming war here, so I am speaking with utmost respect to OceanPlanet and his MIT guy, but above statement is plain false, as well some other statements made in your post.

First of all, in marine house banks there will not be any need for balancing LFP cells, since they do not get imbalanced at such low discharge rates. So any sophisticated balancing schemes are just waste of money. I know this from personal experience, MiniBMS is the 3rd BMS I designed as well, with a few things learned from previous versions and using LFP batteries every day. I even made shunt/balancing optional feature in MiniBMS and some of my customers use MiniBMS without any balancing and it works perfectly even in EV where LFP cells get much higher abuse ( as long as cells don't see over 2C currents ).

Also, I checked Genasun Web site and their pricing list. OMG, this system is severely overpriced considering its using SkyEnergy cells ( seen in the picture on Genasun site ) and fairly simple BMS that comes with it. I can build dual bank LFP system of comparable size and features at almost half the price using my MiniBMS.

I realize that capitalism is based on supply/demand and market price for a new technology can be high at first while supply is low and demand is high, but LFP is not THAT NEW anymore.

At this time I am only offering BMS for DIY folks who aren't afraid to source their own batteries and put their system together using their own brain and hands, but I am exploring possibility of importing LFP cells and assembling turn key solution similar to Genasun at MUCH lower cost.

If anyone in Tampa/St.Pete area is interested in helping to expand this market and/or test/pilot my product, please PM me.

Again, OceanPlanet, I said everything with utmost respect and hope there are no hard feelings.

[s/v Thea]

Originally Posted by electric1

Actually 3.6V is the "knee" in CC/CV curve for Thundersky cells. So, when using chargers designed for LA it will be basically a straight line, just like Jallum said. Once they reach 3.6V they shoot up in voltage super fast, that is why most chargers and BMS's don't go to the max voltage, its too much risk.

I charge my 160AH pack every night with 20 Amp Zivan charger. The pack stays between 3.3V-3.6V per cell while charging at 20 Amps for several hours ( 4-7 hours, depending on how much it was depleted during the day ). Then once it reaches 3.6V per cell it would shoot up to 3.8V HVC level within 2 minutes if current is not reduced. Zivan is programmed to switch to CV phase at 3.6V , so current is dropping super fast after 3.6V and BMS is there as insurance policy in case charger doesn't slow down fast enough. In my usual routine I don't have HVC tripping at all, but in your case of using LA chargers HVC is virtually impossible and your charging curve will be essentially a straight line.

Electric1,

Do you have a feel for what the charge rate would be (xC) with the cells say 90% charged and 3.6V applied to the cell?

Thanks,

Doug

[hellosailor]

Iain-
"and also for their small size in R/C planes, " Were those the cells involved in some million RC helos and planes that were recalled after a raft of "fire" problems in 2008/9 ?

I understand that good fuel supplies make good explosives, gasoline included. It is just that the small details of production versus stability keep cropping up in lithium batteries. Not to mention, China. (I know, give 'em fifty more years.)

[Viking Sailor]

Electric1,

I don't believe that you fully understand how batteries are used on a sailboat. When a battery get near it's lower limit it is not disconnected and a generator started to pickup the load. Instead a make-before-break switch is thrown to switch to another battery. This type of switching is necessary to avoid interrupting the use of things like navigation lights and other equipment.

So, the question is - if LVC is triggered and the alarm sounds, how long would one have to switch to another battery when drawing 20A from a 200ah battery before the battery is damaged?

[electric1]

Originally Posted by s/v Thea

Electric1,

Do you have a feel for what the charge rate would be (xC) with the cells say 90% charged and 3.6V applied to the cell?

Thanks,

Doug

Doug,

the charge rate will be as much as your charger can supply
LFP cells can absorb as much current as you can throw at them. xC would depend on your cell size, but I suppose anything less than 100Ah is not practical in marine house bank and up to 1C is safe for LFP, so that means any charging source up to 100 Amp is safe, but could be much more if you have larger cells and larger charing source.

Hope this makes sense.

[s/v Jedi]

Originally Posted by electric1

There is also hidden logic in lifecycle numbers, you get more shallow cycles than deep cycles, but since deep cycles last longer, over the same battery life you will end up with less deep cycles, so it all evens out. For example, one battery is cycled 365 times a year and each cycle provides 24 hours of use (deeper cycle), while the other battery is cycled 730 times a year and each cycle provides 12 hours of use ( shallower cycle ). Both batteries are used the same way and provide the same useful work over the same time period, so their number of cycles is not very relevant from this point of view, as long as you stay within normal operating conditions.

Okay, this is good news. But you must understand that some sailors (my kind of sailors ;-) will take a different approach, like this: if we make the bank twice as big, we half the cycle depth on average which will make the bank last twice as long, while giving us a reserve capacity when we need it for some reason that might incl. emergency or long cloudy passages.

My personal experience with Thundersky cells ( which are the cheapest LFP cells on the market ) is that continuous rate under 1C and bursts under 2C have no impact on their health. Further you stay below those rates the better. So again, this makes them a perfect choice for house banks.

Yes, for house banks on boats this means you get virtually unlimited power for stuff like microwaves because with 100Ah you already get away with that and we need much more Ah anyway. With deep cycle LA we need more Ah just to get higher sustained power outputs without voltage dropping too low.

LFP cells are always rated at 1C, but have virtually no derating up to 2C. So, when calculating bank size, you can bet that 200AH cell will deliver 200 Amps for an hour, or 100 Amps for 2 hours, or 20 Amps for 10 hours, etc etc.

It's hard to believe after half a lifetime on LA. This will change life aboard boats.

Shunting has so little impact on capacity that it can be ignored. For example, in my experience MiniBMS shunts for 20 minutes at 0.75 Amp, which corresponds to only 0.25 AH

Yes, fair enough.

While SOC meters designed for Lead Acid do not provide very accurate reading on LFP since LFP has much flatter curve, they are good enough to provide meaningful reading and when combined with simple BMS it makes LFP bank very easy to use.

Like someone else wrote, the Victron monitors can be programmed to handle LFP correctly. I can add the Link2000 to that because I remember changing it's Peukert settings. I guess setting it to 1.00 equals a flat curve.

Also, someone mentioned that Victron chargers can be programmed for LFP. I can confirm that, you can program almost any charge curve you like when you download the free software from the Victron website and buy their serial converter to plug your PC into the Victron communication bus. I spent some time checking that out and even posted screen shots on this forum, so a search should bring it up.

For solar charging it's easy too because the BMS can just interrupt the circuit from the solar array without trouble. Wind generators will have to be switched to a dump load like the water heater element. Nothing that a relay can't handle, so easy.

Electric1: I'm not sure if you have experience programming micro-controllers but I think that with an additional $50 in parts it's simple enough to bring intelligence into the mini-BMS, keep statistics etc. I can see myself playing with this next time I need new batteries ;-)

thanks,
Nick.

[electric1]

Originally Posted by Viking Sailor

Electric1,

I don't believe that you fully understand how batteries are used on a sailboat. When a battery get near it's lower limit it is not disconnected and a generator started to pickup the load. Instead a make-before-break switch is thrown to switch to another battery. This type of switching is necessary to avoid interrupting the use of things like navigation lights and other equipment.

So, the question is - if LVC is triggered and the alarm sounds, how long would one have to switch to another battery when drawing 20A from a 200ah battery before the battery is damaged?

Viking,

your point is well taken. The diagram was designed to protect the battery not the boat. I suppose I need to design the system which will come with 2 banks and automatically switch between banks when one bank hits LVC, which will pretty much do what Genasun does today. I think my current system is still OK for some cases where brief power interruption is not critical.

Thanks for your feedback everyone, this has been a great discussion so far!

[S&S]

Originally Posted by electric1

.

First of all, in marine house banks there will not be any need for balancing LFP cells, since they do not get imbalanced at such low discharge rates.

Well, that's not what I heard from the Thundersky rep. No offense, but I'll follow what the batt. mfr's rep recommends.

[electric1]

Originally Posted by S&S

Well, that's not what I heard from the Thundersky rep. No offense, but I'll follow what the batt. mfr's rep recommends.

No offense taken , I personally use balancing on my own modules, but I realize how little role it plays in overall LFP usage.

Also, working with Thundersky cells for a year and seeing reports from my fellow DIY EV folks, I can tell you to take everything Thundersky says with a big bucket of salt

Their datasheets have been proven to be quite far from reality on many occasions and the fact that they keep changing datasheets every few months makes me even more skeptical of their technical teams.

They make a decent product at a decent price, but you have to learn their true operating data on your own skin. They also have been known to royally screw their customers in the past, which will always remain on their concience.

[S&S]

Originally Posted by electric1

No offence taken , I personally use balancing on my own modules, but I realize how little role it plays in overall LFP usage.

Also, working with Thundersky cells for a year and seeing reports from my fellow DIY EV folks, I can tell you to take everything Thundersky says with a big bucket of salt

Their datasheets have been proven to be quite far from reality on many occasions and the fact that they keep changing datasheets every few months makes me even more skeptical of their technical teams.

They make a decent product at a decent price, but you have to learn their true operating data on your own skin. They also have been known to royally screw their customers in the past, which will always remain on their concience.

So I understand. That's why I tend to believe that the cells can become unbalanced adn rates of less than 1C. It may show up slower, but I see no physical reason why a slow rate of discharge would preclude cell imbalance.

[jallum]

Originally Posted by S&S

So I understand. That's why I tend to believe that the cells can become unbalanced adn rates of less than 1C. It may show up slower, but I see no physical reason why a slow rate of discharge would preclude cell imbalance.

Wouldn't a multimeter and five minutes to check the voltage across each cell every few weeks or so answer this question or warn you of this condition?

[electric1]

Originally Posted by S&S

So I understand. That's why I tend to believe that the cells can become unbalanced adn rates of less than 1C. It may show up slower, but I see no physical reason why a slow rate of discharge would preclude cell imbalance.

Originally Posted by jallum

Wouldn't a multimeter and five minutes to check the voltage across each cell every few weeks or so answer this question or warn you of this condition?

Guys, please don't get hung up on balancing LFP cells. Its needed to some small extent, and can be easily accomplished by simple BMS like MiniBMS, but don't let it distract you from the real issue, and that is how to manage LVC. Balancing discussions tend to get people confused and push them away from LFP technology. It also creates a market for complex balancing BMSs which is complete waste of money. Its very distracting and annoying and all of us in DIY EV world have gone thru it in the past year. You can find some old threads on DIY EV forum where all this has been discussed a million times.

The real challenge in marine house bank is how to integrate BMS and LFP with charging and discharging busses with minimal issues and minimal cost, that's where the focus should be , IMHO.

[s/v Jedi]

I don't see a problem with LVC. You can just set an alarm on your battery monitor that sounds well in advance of LVC so that you can take action. If you get that alarm often enough you know you need to either increase charging or buy more or bigger cells.

I do not agree with the multiple battery setup that Viking Sailor states we have. I don't have that, just a few of the thousands of boats I know have two house banks and switch loads between them, instead of one big bank. I think Viking Sailor confuses a starter battery for a house battery??!!

cheers,
Nick.

[Viking Sailor]

Nick,

No confusion here! I don't even have a start battery. What I do have are two 8D AGMs and two nice big rotary switches. One switch selects for the house loads and the other selects for the starter and windless loads. This arrangement allows me to isolate and charge each battery fully while underway. Which, for the longevity of AGMs, appears to be more important then splitting the depth of discharge between two batteries in a single bank. Additionally, if one battery should fail I am but a switch throw from a good battery.

[OceanPlanet]

Originally Posted by electric1

With all due respect, the last thing I want is to start any flaming war here, so I am speaking with utmost respect to OceanPlanet and his MIT guy, but above statement is plain false, as well some other statements made in your post.

First of all, in marine house banks there will not be any need for balancing LFP cells, since they do not get imbalanced at such low discharge rates. So any sophisticated balancing schemes are just waste of money. I know this from personal experience, MiniBMS is the 3rd BMS I designed as well, with a few things learned from previous versions and using LFP batteries every day. I even made shunt/balancing optional feature in MiniBMS and some of my customers use MiniBMS without any balancing and it works perfectly even in EV where LFP cells get much higher abuse ( as long as cells don't see over 2C currents ).

Also, I checked Genasun Web site and their pricing list. OMG, this system is severely overpriced considering its using SkyEnergy cells ( seen in the picture on Genasun site ) and fairly simple BMS that comes with it. I can build dual bank LFP system of comparable size and features at almost half the price using my MiniBMS.

I realize that capitalism is based on supply/demand and market price for a new technology can be high at first while supply is low and demand is high, but LFP is not THAT NEW anymore.

At this time I am only offering BMS for DIY folks who aren't afraid to source their own batteries and put their system together using their own brain and hands, but I am exploring possibility of importing LFP cells and assembling turn key solution similar to Genasun at MUCH lower cost.

If anyone in Tampa/St.Pete area is interested in helping to expand this market and/or test/pilot my product, please PM me.

Again, OceanPlanet, I said everything with utmost respect and hope there are no hard feelings.

No offense taken. You probably don't know my background and history in the marine biz that has led me to where I am. However, to say that my statements are "plain false" is getting a little carried away. The bottom line is that there are different levels of protection for different levels of users. You are on the right track focusing your sales on the DIY crowd with your system and price point. The good thing in the biz is that there is competition at different price points...one could also buy RaceCell batteries at about half of the Genasun price, so do you have competition at that level.

After a lifetime on the water, starting with family cruising as a kid, 20+ years working in boatyards, leading up to 2 solo circumnavigations, 6 transpacifics, and 6 transatlantics. One learns after a while that a lot more can go wrong on boats than the magazine images suggest, often with dire consequences.

Marine industry professionals need to back up their products and services with the support and warranties that their clients expect. They need to know that their supplier will stand behind them. I agree that for much of the DIY crowd the level of protection offered by the Genasun approch is overkill and beyond their budget. For them, your system sounds good and/or RaceCell. However, a lot of them (and I don't mean to offend anyone here) don't know as much as they think they do, and can (and do) get into trouble. Besides, we ALL make mistakes. I know of more than one case where seemingly knowledgeable folks with TS cells have gotten them out of balance, ran them too low and killed off a number of cells. It should NOT happen, I know....

Regarding TS cells not needing any balancing at low discharge rates, I agree that may be somewhat true for LFP batteries that are being used pretty much like the Pb they replace. However, no certified marine electrician is going to turn their clients loose (or shouldn't) on LFP systems without balancing (preferably full-time), LVC and HVC protection, and knowing that the alternator(s) are looked after. Especially for high-loaded systems like electric propulsion or supporting large AC loads through inverters, etc.

To reach that level of security, provide the support and warranty many clients need, a professional installer need to make a reasonable profit. Keep in mind the Genasun prices you see online are RETAIL, and an enormous amount of support is provided at level, including (in most cases) travel to the boat just about anywhere in the world to sign off and approve the installation. Installers and builders of course get a sizable discount off those prices.

But hey, everyone has different needs and different abilities, and certainly different sized checkbooks. There are plenty of reasons why Genasun, Mastervolt, Valence, etc. are priced the the way they are. No one is trying to rip anyone off. There is plenty of competition at that level too, and compared to Mastervolt & Valence the Genasun is quite competitive especially for the professional installer.