Rocksnsalt
Solar Enthusiast
It’s true!
SOK 206AH BATTERY CONCERNS
- Thread starter Rocksnsalt
- Start date
Yes, external regulator. I'm pretty sure all of the aux alternator products use external regulators for control purposes, charge profiles and the like. Balmar has the lion's share of the market, but Wakespeed is now coming up to speed (so to speak) as well. Wakespeed indeed designed their suite of products for the marine world, but they work great in RVs, particularly for lithium systems.
My system has a DIY battery based on Fortune cells (thanks, Will), Wakespeed regulator and REC BMS. The BMS is connected to the regulator via a CANbus. The BMS actually controls charging based on its fine-grain visibility into what the cells are doing, and sends current requests to the Wakespeed which in turns sends exactly that much current to the battery. They call this a remote-battery-master configuration. There's no charge profile because the regulator is simply doing what the BMS tells it to do. The BMS has settings for battery size and your desired C rate which it uses in conjunction with cell voltages to calculate how much current to request. Usually it's requesting your full desired C rate until it's full. So with my 200 AH battery, I'm generally charging at around 100 amps. I will be adding another 8 cells to for 400 amps total. I'll only need to change the battery size parameter and I'll be charging at 200 amps with no other changes.
I was an early adopter of this technology for use in a van and pretty bullish on it. The install is actually pretty easy and logical and nothing that anyone who works on charging systems can't handle. Setup is easy too. As an early adopter, I had some bugs bringing up the system that were worked around in firmware by Wakespeed. But the system is rock solid now and should work for anyone else right out of the gate.
Sorry, I get carried away talking about this stuff. I have a build thread about it on the Sprinter forum here. https://sprinter-source.com/forums/index.php?threads/89088/
Rocksnsalt
Solar Enthusiast
It’s ok, these are your people to talk that stuff to.
fratermus
Solar Enthusiast
- Joined
- Mar 19, 2021
- Messages
- 509
Welcome to the forum. I think you'll fit right in. 
Are you idling to recharge? If so, faster charging does makes sense as one can reduce time idling the engine.
If one doesn't have time pressure (driving from place to place, or maybe solar is helping out) I'd think the lower 0.25C rate would be gentler on the batteries than 0.5C, especially in colder temperatures.
If vanlife means Instagram hashtag-vanlife with apartment-style amenities then I agree. If it means people who live in vans in my experience meeting a few hundred vandwellers over the past few years I'd say the majority (or at least plurality) are using solar to recharge ≤200Ah lead banks. Those folks would likely be delighted with the smaller SOK 100Ah.
My fulltime boondocking use case: maximum load is ~300w, typical loads ~150w, all loads run off solar in the daytime, and I use 30-40Ah overnight. For me a SOK 206Ah would be overkill and unnecessary expense. Horses for courses, as they say.
0.25C is paltry compared to your charging capacity, but not paltry for LFP in general. I'd be surprised if the typical member of this (admittedly solar-centric) forum was charging lithium at ≥0.25C. I have 750w of solar charging a 100Ah LFP and under normal conditions it charges at less than 0.25C.
Are you idling to recharge? If so, faster charging does makes sense as one can reduce time idling the engine.
If one doesn't have time pressure (driving from place to place, or maybe solar is helping out) I'd think the lower 0.25C rate would be gentler on the batteries than 0.5C, especially in colder temperatures.
If vanlife means Instagram hashtag-vanlife with apartment-style amenities then I agree. If it means people who live in vans in my experience meeting a few hundred vandwellers over the past few years I'd say the majority (or at least plurality) are using solar to recharge ≤200Ah lead banks. Those folks would likely be delighted with the smaller SOK 100Ah.
My fulltime boondocking use case: maximum load is ~300w, typical loads ~150w, all loads run off solar in the daytime, and I use 30-40Ah overnight. For me a SOK 206Ah would be overkill and unnecessary expense.
Horses for courses, as they say. 0.25C is paltry compared to your charging capacity, but not paltry for LFP in general. I'd be surprised if the typical member of this (admittedly solar-centric) forum was charging lithium at ≥0.25C. I have 750w of solar charging a 100Ah LFP and under normal conditions it charges at less than 0.25C.
Thanks!Welcome to the forum. I think you'll fit right in.
I don't understand your question about idling. I charge whenever the battery is below 100% and the engine is running, and it's generally charging at my preferred 0.5C. Once I populate the rest of my cells and increase my battery to 400 AH then there will be some roll-off of current at idle. Although I've already seen it put out around 150 amps at idle, so not much degradation. The van is diesel, btw, and idling for extended periods is bad for them.
I'm not aware of any downside to charging at 0.5C. The batteries can handle 1C, so 0.5C is already conservative. If you have references to such information, I'm all ears. My batteries are always warm because they live inside the van. The BMS is temperature savvy, so if there were temperature ranges that needed less current then it would call for less power. It does kill the power at low temps close to freezing, as those charging at those temps can damage the battery.
If vanlife means Instagram hashtag-vanlife with apartment-style amenities then I agree. If it means people who live in vans in my experience meeting a few hundred vandwellers over the past few years I'd say the majority (or at least plurality) are using solar to recharge ≤200Ah lead banks. Those folks would likely be delighted with the smaller SOK 100Ah.
My fulltime boondocking use case: maximum load is ~300w, typical loads ~150w, all loads run off solar in the daytime, and I use 30-40Ah overnight. For me a SOK 206Ah would be overkill and unnecessary expense.
0.25C is paltry compared to your charging capacity, but not paltry for LFP in general. I'd be surprised if the typical member of this (admittedly solar-centric) forum was charging lithium at ≥0.25C. I have 750w of solar charging a 100Ah LFP and under normal conditions it charges at less than 0.25C.
Ha, you should check out the Sprinter forum. We have guys there with 1100 AH lithium batteries running AC all day. I'm more towards your camp, but I like hot food and hot coffee and my heated mattress pad in the winter.
Rocksnsalt
Solar Enthusiast
And 48v/12kwh systems that can run ac all night… Having and 800amp alternator helps for a quick charge… as they
(Storyteller Overland Vans) only have a token 100w of solar, but room for 300 to 400w more if they give up the rooftop deck space. That would be me, given the choice.
I'll be looking at a 48V system for my next van, it has its benefits, i'd hate to weight all the copper in my van with my 12v system.
It'll be interesting to see how bigger the systems get in the next few years, with people moving towards AC and and induction cooking we will see 16-20kwh systems.
Rocksnsalt
Solar Enthusiast
Perhaps
I believe they are just asking whether you idle the van to charge the batteries (i.e. use the van as a big inefficient generator) as opposed to just taking advantage of charging when driving.
There is a three way relationship between temperature, c-rate, and state of charge. Or to simplify it a bit a two way relationship between temperature and c-rate. A certain C-rate will cause more wear and tear on the battery at a low temperature than it will at a moderate temperature, or put another way charging at a low c-rate at a low temperature is less bad than charging at a high c-rate and low temperature, this is more pronounced at higher states of charge.
There are some high temperature considerations as well.
The fact that the batteries can handle 1C doesn't necessarily make 0.5C conservative, but it does mean it is well within spec. If your cells can handle a max continuous charge rate of 1C, its likely the manufacturer recommends 0.5C as the max recommended charge rate, depends on the manufacturer but that is a pretty standard recommendation. None of this is meant to imply that your 0.5C charging target is unreasonable or unrealistic or wrong, just that it is about the upper edge of the range of what many people here consider to be conservative.
Maybe I misspoke about the 1C max charge rate. I'm using Fortune cells and went back to look at their specs to refresh my memory. What I went by is what they call, "Standard Charge Current" which is 0.5C. They don't actually give a max charge rate except for a "Max Pulse Charge Current (<10 sec)" which is 6C. I'm used to seeing the 1C maximum charge rate quoted by other people that apparently I assumed mine was the same.
Here's the link to their specs: https://www.electriccarpartscompany.com/fortune-100ah-aluminum-encased-battery
Here's a spec to another 100 AH prismatic cell and they give a "Best Charging Current" of 0.5C. https://www.batteryspace.com/lifemn...3-2v-100ah-3c-rate-320wh---un38-3-passed.aspx
Note that their Max Charge Current is 3C.
So I doubt I'm doing any harm at 0.5C and so far I haven't seen any degradation in my batteries from over a year of heavy usage running them that way.
|
I have tested the 206ah SOK BMS to try and hit its programed current cutoff limits and have not yet run into them. They are definitely not 40 or 50 amp charge as I have done close to 110amps into a single battery for 15 minutes with no BMS cutout, I have also pulled close to 140 amps discharge from a single with no cutout. There is a post on this forum from Cinergi who got a response from SOK that the BMS is actually designed to handle 150 amps continuous charge/discharge and will not cutout until that is exceeded, lines up with what I have seen in testing.
I have a theory why SOK lists 20a recommended charge rate 50a max for the 100ah and 40a recommend 50a max for the 206ah as even though the BMS can handle much more. The Ganfeng cells SOK uses list 0.2C recommended charge rate at 0-7*C temps, so SOK seems to be trying to account for worse case low temp charging conditions. At 25*C they list 1C charge rate and cycle test are done at 1C charge/discharge at 25*C and they have 3000+ cycles there.
My 125 amp charger ends up with about 0.25C with two 206 so I am not concerned in the slightest and my 3000w inverter can pull up to 300 amps without issue split between them although that is very unusual (say microwave and coffee maker at same time).
I like that SOK is very conservatively rated in their docs although I wish they where more clear what the actual programmed limits are vs just recommendations and why.
I have a theory why SOK lists 20a recommended charge rate 50a max for the 100ah and 40a recommend 50a max for the 206ah as even though the BMS can handle much more. The Ganfeng cells SOK uses list 0.2C recommended charge rate at 0-7*C temps, so SOK seems to be trying to account for worse case low temp charging conditions. At 25*C they list 1C charge rate and cycle test are done at 1C charge/discharge at 25*C and they have 3000+ cycles there.
My 125 amp charger ends up with about 0.25C with two 206 so I am not concerned in the slightest and my 3000w inverter can pull up to 300 amps without issue split between them although that is very unusual (say microwave and coffee maker at same time).
I like that SOK is very conservatively rated in their docs although I wish they where more clear what the actual programmed limits are vs just recommendations and why.
Last edited:
Frey (the company that manufacturers the cells ECPC sells under the name "Fortune") makes really solid cells from everything I've heard, and I have heard they are a little more geared towards power rather than energy storage applications (IIRC electric forklift batteries may have been one of their original markets). Generalizations made about the larger cheaper commodity prismatic cells popular here may not always apply to your cells, and likewise, things that apply to your cells may not always apply to larger form factor prismatics.
You've got good robust cells and a nice BMS (that can apparently taper current when it sees fit), and you are within the manufacturer recommendations for your cells, I don't think you have much to worry about.
You left off the less than sign, the spec in the link says "Best charging current <0.5C" further you can see a few lines above that the cycle life estimates are based on 0.2C
Which is inline with what I was attempting to articulate in my previous comment:
But we don't need to get into the weeds here. Different cells will have slight differences, and some will be better optimized for power (high c rates) while others (particularly the larger cells popular right now) will often be more optimized for energy storage and cost. Also different manufacturers will be more or less conservative in their recommendations and cycle life estimates. As a generalization lower c-rates are less taxing, this particularly comes into play at low temp, high SOC or both.
'harm' isn't the term I would choose to use. I'd think of it more like a rate of degradation. There isn't a magic number below which you are fine and above which you are not (even if we leave out context/other variables). I think of it more like a gradient/spectrum of wear and tear, you are not 'harming' your batteries by cycling at 0.5C, but capacity loss/degradation will likely be faster than it would be at 0.25C and slower than it would be at 1C. In normal operation 0.5C may be at the upper edge of the 'sweet spot' but in colder weather or high SOC 0.5C would exceed manufacturer recc's for many cells. Here is an example from the 206Ah Ganfeng datasheet (what SOK uses in their batteries):
Bottom line, stay within the manufacturer recommended specs, and you should be fine, go beyond that (more conservative) and you should be extra fine.
Last edited:
This excerpt from what I consider one the best introductory articles on LiFePO4 (See Nordkyn Design in my signature) sums up the considerations I was trying to articulate much better than I can:
Last edited:
fratermus
Solar Enthusiast
- Joined
- Mar 19, 2021
- Messages
- 509
@Dzl covered it, but I will flesh it out a bit to lay out my thinking.
My thinking was that if one is idling the vehicle to charge then a higher charge rate is likely a good economic move. Any theoretically-shorter battery cycle life would be offset by reduced wear/stress on the engine and alternator (auxilliary or otherwise).
If one is charging by multiple methods or if normal driving is sufficient to meet needs I am suggesting that lower charge rates increase LFP longevity. I understand this is not a universally-held position. Perhaps I am deluding myself and it is merely a form of Pascal's Wager.
I suspect 0.5C is a compromise between charging speed and longevity. Joe Sixpack wouldn't be happy if his new $1000 battery took 5 hours to charge. OMG, that's like one of those lead-acid plebes!
So give them a rate high enough to keep them happy while making it through any warranty period.I have seen manufacturers give the rated/warranted cycle life at 0.5C then give "and up to..." even higher cycle numbers with an asterisk ("when discharged 80% DoD and charged at 0.2C rates"). This isn't dispositive but it's food for thought.
Even more speculative: Battle Born says "We don’t recommend you exceed this [0.5C] charge rate as it can lead to a shortened battery cycle life." What is more likely, that 0.5C is a hard cutoff beyond which cycles will be reduced, or the top end of a sliding scale? More on this below.
Note: certainly not trying to tell you how to charge your bank. I am talking out loud about the factors that informed my own charging choices.
I looked over the the REC ACTIVE manual and website and didn't see any claims that it can regulate charging current from the alt beyond on/off. It was admittedly a cursory reading so maybe I missed something. You will certainly know more about it than I do.
It appears to be a sliding scale rather than hard cutoff -- see these data sheets.
In the charts the average low temp at which 0.5C is allowed is 9.75C (49.55F) and the mean is 10C (50F). I hope I used those math terms right. The lowest of them is 5C (41F). Lower charging rates are allowed at somewhat lower temps, which might or might not tell us something about charging rates at warmer temps.
Same. Cooking and making coffee over a $40 stove allows me to run all my loads (including the heated mattress pad) on 100Ah LFP. I do cook with electricity when there is excess solar power available which helps stretch the fuel supply. Right now I am cooking broccoli and cauliflower in a crock pot.
Same on the Promaster and Transit fora. I fully support each vandweller building the rig that meets their particular wants and needs.
My own are minimal since there is no Wife Acceptance Factor and I follow mild weather. Once I had the van my total build cost was about $2250. I've been boondocking off-grid in it for the last (...checking...) 1,214 days. This low-cost approach allowed me to retire about 8 years early, so doggo and I are quite happy.
Early adopters were DIYing LiFePO4 in vans by 2014-2015 (example), leveraging information from the boating world that started showing up in 2010-2011. In those days many people were running LFP "barefoot" because the BMS were so crude they were doing more harm than good. I am grateful the technology has advanced and come down in price.
Thank you for your thoughtful input.
Gotcha. Yeah, idling isn't good for modern diesels so I do it as little as possible. What I like about my fast charging is that I can camp 20 minutes from the ski resort and pretty much generate enough power for 24 hours, especially if I stop at the grocery store.
Good thoughts. You guys are pretty much convincing me that I definitely don't want to go faster than 0.5C. Ya know, since the C-rate on the BMS is adjustable, I could crank it down when I don't need fast charging. There's actually an app for the BMS, so I can set the charge rate any time. But the wifi is point-to-point, and not as convenient as I like. They have a Bluetooth app which I use all the time but it only monitors and and is unable to set parameters for the most part. Maybe I can cobble up a dedicate device for it. A knob on the dash with an ammeter would be perfect.If one is charging by multiple methods or if normal driving is sufficient to meet needs I am suggesting that lower charge rates increase LFP longevity. I understand this is not a universally-held position. Perhaps I am deluding myself and it is merely a form of Pascal's Wager.
I suspect 0.5C is a compromise between charging speed and longevity. Joe Sixpack wouldn't be happy if his new $1000 battery took 5 hours to charge. OMG, that's like one of those lead-acid plebes!
I have seen manufacturers give the rated/warranted cycle life at 0.5C then give "and up to..." even higher cycle numbers with an asterisk ("when discharged 80% DoD and charged at 0.2C rates"). This isn't dispositive but it's food for thought.
Even more speculative: Battle Born says "We don’t recommend you exceed this [0.5C] charge rate as it can lead to a shortened battery cycle life." What is more likely, that 0.5C is a hard cutoff beyond which cycles will be reduced, or the top end of a sliding scale? More on this below.
Note: certainly not trying to tell you how to charge your bank. I am talking out loud about the factors that informed my own charging choices.
Well, the BMS in my system does fine-grain control over the charging, not just off and on. It gives a specific current target to the regulator which varies while certain stuff is going on. Cell-balance mode is one of those cases, it backs off the charging by 10 or 20 amps or so. There's probably some technical why they do that, but I don't know why it is. Further the BMS does have a battery temperature control which it uses for hard disconnects if battery temps are too high or too low. It could certainly implement the temperature/charge rate curves you guys are talking about if it doesn't already. The hardware is all there, just a matter of adding firmware.
Interesting, thanks. Usually I'm well above 50F since I leave my diesel-fired heater on constantly even when I'm parked in the winter.
I have a nice backpacking stove that would work great. But I'm pretty happy with being all electric, single energy source (except for the diesel fuel my heater consumes).
That is awesome. Hats off to you. I retired early myself, although I've still have small business that that makes me money sporadically. I've got a family situation, but even then I managed to put 36K on my van in my first year. My longest trip was 3 weeks and that went great. If it weren't for the wife I might be a full-timer myself.Same on the Promaster and Transit fora. I fully support each vandweller building the rig that meets their particular wants and needs.
My own are minimal since there is no Wife Acceptance Factor and I follow mild weather. Once I had the van my total build cost was about $2250. I've been boondocking off-grid in it for the last (...checking...) 1,214 days. This low-cost approach allowed me to retire about 8 years early, so doggo and I are quite happy.
And you for yours. ?
Last edited:
That is great to know, thanks. I love the build quality on them, the huge M10 terminal studs and the end caps with threaded rod holes, and the top caps to protect the terminals and bus bars. Plus there are built-in wire troughs to keep things tidy.
Oops, my bad. I missed that.
I get it, thanks. Maybe my cells will only last 10 years, not 20. Or even 5 years is fine. I may start dialing down my C rate when I don't need fast charging. It's just a single parameter in the BMS and I can do it from a phone app.
It's been a great discussion, thank you.
fratermus
Solar Enthusiast
- Joined
- Mar 19, 2021
- Messages
- 509
That is very cool. Thank you for the gentle correction.
You don't need to put anymore solar on that Storyteller van since the alternator can charge it in very little time. That's the whole idea about putting a huge dedicated 48V alternator in them.
Rocksnsalt
Solar Enthusiast
Thanks for the elucidation.
800 amp alternator.
Yes that’s true.
I don’t have a STO yet so it’s not an issue for me yet. ?
Last edited:
My friend has the Metro ordered. He should get it in April. He as ZERO plans of adding more solar. Makes no sense.
