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Discussion Starter #1
Aloha, I am trying to plan my Lithium purchase. Probably 50 Calb cells @200ah. But I am hearing conflicting heated, (even namecalling) arguments about weather to use a bms or not. So will the person with the most Lithium-use-hours experience stand up and give me the "skinny"? thanks
Francis
 

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I'm not sure if hours has anything to do with it, otherwise that might well be Jack R. one of the no-bms guys. But he does have a few cars, all BMS free and what he reports as working perfect. Others use a BMS and are working perfect, I'm kind of in the middle, I would love to go BMS free as I think it is the best solution, however it might not be the right solution. I've decided to charge individual cells instead of a series string eliminating the need for a BMS during charging. (I will have monitoring during discharging).

To all others, I hope this is a nice discussion even though there probably isn't an answer to this question. It's your choice to make, and your responsibility to research on your own and make the choice that's right for you.
 

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Discussion Starter #3 (Edited)
I guess I should first ask "What is the function of a BMS? Does it regulate down a charge for each individual cell attached to it from a series string of cells? Or does it actually boost a charge coming from a series of charging cells? In my mind individual chargers would be the go, but using one for each cell (50) would start to get $ and heavy as it needs to put out to charge a 200ah cell. Maybe get a good 12v charger and group 4 cells??

***also what is the best instrument brand name that shows the state of charge of each cell simultaneously? ie can any show 50 cells at the same time?

francis
 

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I guess I should first ask "What is the function of a BMS? Does it regulate down a charge for each individual cell attached to it from a series string of cells? Or does it actually boost a charge coming from a series of charging cells? In my mind individual chargers would be the go, but using one for each cell (50) would start to get $ and heavy as it needs to put out to charge a 200ah cell. Maybe get a good 12v charger and group 4 cells??

***also what is the best instrument brand name that shows the state of charge of each cell simultaneously? ie can any show 50 cells at the same time?

francis
The function and even meaning of a BMS can vary wildly. "Battery Management System" or "Battery Monitoring System" are two entirely different things. Then there is Shunting, or non-shunting, and some that can re-distribute power to reduce wasted power. Some trigger chargers to turn off with a HVC, some trigger controllers to reduce power with a LVC.

The main thing to remember is safety, anything can be dangerous. Nitrous in street racers can explode and destroy cars, garages, houses. The same goes for anything that you attach to you high voltage pack. All wiring must be safe, ideally fused and properly secured.

I've seen a car burn to the ground from an improperly installed car stereo using a single 12v battery, it can happen to anyone.
 

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I'm going free when mine arrives. For one, it will a large chunk to your battery cost and a lot of time to install. The costs can be over $1000 even 2000.

After watching this and this you'll have a good idea of what you want to do.

My plans are to not discharge to the edge of the cliff and not charge to the hilltop. Discharge to say 90-95% and charge up to within 5-10% of max. You will need to educate yourself if you plan to DIY or you may toast $12000 worth of batteries.

That guys philosophy is that in order to know how deep to discharge you MUST have an amp-hour counter installed. So if you have a 200Ah cell you can discharge the pack down to within 10Ah or so of being dead. However to do so, you MUST bottom balance the cells in the pack so they are at the same state of charge at bottom.

Jacks testing shows that using a BMS to "Top Balance" cells to get them charged to the MAX will cause them to likely be out of balance at the bottom (discharge end) thus when you're running the pack low you risk one cell bottoming before the rest and if that happens it's toast!

Yes IF, and that's a big IF, the BMS works correctly it should prevent that from happening. But doing so in the first place is placing a needless burden on the batteries if you want them to last longer. Discharging cells very low shortens their life as does over charging them. However if you stop before getting too low and before getting too high, you'll get longer life anyway.

Here's a bit of my reasoning for staying away from a BMS. My career for about two decades was in electronics and circuit board repair. Have you ever known electronics to fail? I have seen MANY. Electronics, no matter how well designed do fail from time to time. Lightning striking a tree NEARBY gives off enough EMI to destroy electronics from a distance, even in your garage.

Here's a scenario. You're asleep and a storm comes through, strikes a tree nearby and the EMI radiated from it torches a circuit board on one of your cells. If that cell shorts across the battery who knows what it could take out, the BMS controller it's attached to, wiring between the two, could fry the harness starting a fire etc. Who knows what could happen with a failure but there have been many fires documented due to BMS board failures. I don't want anything capable of failing and shorting a battery in my car while I sleep or while I drive!
 

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there have been many fires documented due to BMS board failures
Actually there have been ZERO fires documented due to BMS failure. Lets not propagate baseless stories here. In every reported fire there were a dozen of things that could have gone wrong not even counting the BMS.

I am biased and I am not promoting my BMS or any others, but let's stick to facts and leave the fiction where it belongs, in TV shows and books.

Yes, electronics fail, but so do all other things. Based on your logic you should live in a cave and never step outside since you can be killed by lightning. I'm sure many people who are hit by lightning every year regret leaving the house that particular day, but it doesn't turn them or most others into hermits.

My point is there are 2 sides to every story. Even if I wasn't selling MiniBMS but just made one set for my own use, I would not regret it. Even though you have a solid theory of how not to damage your pack you have not had any practice yet. I have been using mine every day for 2 years. let's compare our notes after you get 2 years from your BMSless pack. Including how much time you spend caring for your pack and how much your time is worth to you.

I'd be the first one to tell you that its certainly possible to go without BMS if several other conditions are met. However, just because all these conditions are met by one person's project, it does not give him the right to yell all over the world that everyone else SHOULD BE FINE because he has shown that HE IS FINE. Almost every EV conversion has some unique combination of parts and you can't judge one from looking at another.

I wish that every one who supports BMS'less approach had guts to come back and tell the story when something goes against their theory, few people do that. The judgement is still out which way works better.
 

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Wait, Didn't Jack Rickard ruin an entire pack of thundersky because there was nothing to stop the charger from overcharging? Had he had a cell-level HVC installed (one form of BMS) he'd have saved the pack. Not something you hear much about on the forums.... Very interesting. Not someone I'll be taking advice from.

IMHO, you ABSOLUTELY need monitoring on a cell level. You need something to look for overvoltage while charging (not on the pack level, on the cell level). If it senses a high cell, it turns off the charger. Then you need to look for overdischarge (LVC) and throw an alarm and reduce the throttle somehow.

In regards to cell balancing, I don't care if people want to top balance, bottom balance, coulomb count, individually charge. There's no RIGHT way. They all work. My point is, and I think most agree, you should monitor the cells individually. Even if you're using a cheap Cell-Log 8 with the alarms optoisolated and linked together or have a fully fledged BMS balancing/monitoring system.


So what am I using? Elithion. Why? Because I could afford it at the time and because I worked at EVComponents providing support for that system. Now I work for Davide as a consultant and own his BMS book, which is a great read. Not only does Elithion balance, it monitors temperature, voltage and SOC and gives me a TON of useful information back from my pack, which I intend to publish reguardless of results. I want the data and thats why I bought it. It'l be logged via Canbus through bluetooth on an Android device.
 

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Actually there have been ZERO fires documented due to BMS failure. Lets not propagate baseless stories here. In every reported fire there were a dozen of things that could have gone wrong not even counting the BMS.
Do the statistics exist? Of all the fires reported, how many had BMS systems and how many did not? I know stastics lie, but if there are no BMS absent fires, lets think.
Gerhard
 

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If I'm going to throw $5000 - $10,000 at pack. I'm going to spend a little more to protect it. I just haven't decided which BMS to use.
 

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Do the statistics exist? Of all the fires reported, how many had BMS systems and how many did not? I know stastics lie, but if there are no BMS absent fires, lets think.
Gerhard
This just makes no sense to me. From relatively small number of EV conversions on the road, and even smaller percentage of those using Lithium packs where BMS is typically used, it will be hard to get meaningful stats based on the fact that car had BMS or not vs. same car burning down or not. Especially that Lithium packs are relatively new, making the count even more difficult. I can't see any logical connection here.

If 1000 cars had Lithium packs, of which 900 had BMS and 100 did not and there were 5 fires reported, all of which had BMS in them. Does that say anything about BMS causing it or simply that vast majority had it to begin with, hence larger chance of fire in a car with BMS than without one.

90%/10% was a very generous split too just to make the point. I think in real life its more like 98%/2% of BMS vs. no BMS conversions.
 

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Dimitri I haven't studied and read exhaustively the details of purported BMS fires but I've read others writings about them and it coincides with my experience and knowledge of electronics, enough so that I'm convinced that BMS is not needed and is IMO a liability. Unlike you, I have no dog in this fight. I'm only answering the OP's call from my perspective.

I'm glad we agree that electronics do fail. As I said, I've seen lots of failures in 20 years of electronics, some dangerous, some benign. That said my charger could fail and torch the pack left to it's own devices but that is easily rectified without a BMS. Actually BMS circuitry could be modified or configured in a circuit to kill the charger at a predetermined voltage. But again, nothing is certain but death and taxes.

My point, as is Jacks to the best of my knowledge is this. One can buy your BMS and install 50 electronic circuit boards assembled of the finest components with the greatest care, spend hours wiring 5 pounds of cabling running through the vehicle to the dash and elsewhere, confident it is the holy grail of battery protection and will prevent battery failure.

Or one can buy a meter with Ah counting capacity, set the low levels to notify the driver at 20% remaining and again when the tank is empty and I'm about to destroy my pack, even have it shut down the vehicle or take it to limp mode. I'll have the charger set to charge to a voltage less than full which will give me more life according to the OEM. All I need to do is bottom balance and keep from bottoming out a cell. Even that may be unnecessary, not real sure. I can also install redundant protection on the pack to kill the charger should it decide to fail. Simple and inexpensive.

Should I take your advice and one of your quality boards fail shorted, that cell is dead and come hell or high water you (the driver) nor your BMS is likely going to stop it. No, Lifepo4 isn't going to catch fire from what I've read but don't throw me under the bus because I haven't consulted an expert directly nor have I proven to myself that it can't. Again that's what I've read. And one or two cells is likely less than your BMS system if somehow one of them does go south.

You guys hocking your BMS wares certainly have reason to bash those of us who rationally decide NOT to send you our money and chose another route, a route that is much less potentially harmful and blatantly simple. So go ahead if it makes you feel better brother!
 

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The only reason I responded to your post is this statement you made, which is as blatant lie as it gets, with very serious consequences to people involved in these issues.
there have been many fires documented due to BMS board failures
I know you did not make this up yourself, you just repeat blindly what you hear on EVTV.

I have full respect for your plans to go without BMS and I am not pushing anything to anyone, I just try to stop lies from propagating, which seems a futile effort since everyone likes drama more than facts. Pros and cons of BMS have been discussed to death on this forum, no reason to repeat everything again, so I stay away except when lies are posted as facts.

As for your plan, it sounds great. I only ask one thing, come back 2 years from now and honestly share how real life experience differs from your plans and how much time/money you spent avoiding to use BMS.
 

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If 1000 cars had Lithium packs, of which 900 had BMS and 100 did not and there were 5 fires reported, all of which had BMS in them. Does that say anything about BMS causing it or simply that vast majority had it to begin with, hence larger chance of fire in a car with BMS than without one.
Sure, you can correct for unequal sample sizes. The difficulty would be in getting unbiased data. Many people don't like to admit their mistakes.

Did Jack really destroy an entire pack? I don't recall hearing about that.
 

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Did Jack really destroy an entire pack? I don't recall hearing about that.
No, he just killed a couple cells, not a huge deal. This "killing whole pack" is another urban legend that just keeps spreading itself. I can't imagine how you can kill the whole pack at once, other than having BMS set it on fire :D

You would kill the weakest cell in each incident, replace it, then kill the next weakest cell in the next incident, etc etc, but not the whole pack at once.
 

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Discussion Starter #16
Aloha, all. Best to keep an open mind on the bms as there is a lot of testimony coming out for pros and cons, so best to take it all in Objectively and decide on the merits. Jack R has a lot of good info and so do the pro guys. I think some sort of balancing will win out, (either top or probably bottom) as I see cells wandering off over time. (at least in AGM). So far I think charging to 90-95% and discharging to no less than 35-40% is in order, so I think it pays to buy bigger ah than absolutely needed and treat them with care. Using a good individual cell monitor and culling out a cell that is out of range is a good idea. For my agm setup I see the suggestion of using this homemade cheap "BMS" is a great idea. http://www.evdl.org/pages/hartregs.html (since I bought my car with AGM from a guy that only series charged and never balanced, and was only getting 5 miles on his pack. I balanced and am up to about 15 miles and hope to get to 20 miles after a little more TLC on the batteries) But lets wait and see.
Francis
 

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Here's something I would love to see: Run a BMS on half the pack, and go BMS free on the other. May the best half of the pack win!

Also, test for yourself! You can buy Headways for ~$20 each, an RC charger for ~$75, and a load tester with Voltmeter and Ammeter for $50 at Harbor Freight. Get an IR thermometer, a voltmeter, and a timer, and you are ready to rock.

Here's my limited experience:

Lead acid: On an Optima pack, it would go very quickly out of balance with weak regens. Doing a small number of 500+ Amp regens during a drive keeps the batteries well balanced, within about +-0.02 V.

Lithium: Once bottom balanced, 4 China HiPower 10 Ahr cells stayed well balanced over about 20 severe cycles, without BMS. It appears Jack was right for this small number of cycles.

I pushed them until 2 of them vented. How's this for an idea, discharge one cell and fully charge the other. Then do gentle charge/discharge cycles, and see if they'll grow into balance like Jack claims. I think this would be a good test for if a BMS is needed -- do cells naturally balance? Anyone else out there game to test this idea and see if we get the same results?

I just got some Headways and have more China HiPowers on order, the testing continues. I'll post up details, good or bad, when I'm done.
 

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I don't use a "BMS" in my car.
Why? I haven't found one that monitores my LiFePo-pack the way I want to a price that I could afford and with the safety issues I need.

Do I monitor the whole pack? Yes, that's neccessary I think.
Whole voltage, amphours, amps, but no tiny boards or "spaghetti"-wiring.

After ~40 - 50 charges (Zivan NG3), all cells (SkyEnergy/CALB 121AHA) are still close together in voltage.

there have been many fires documented due to BMS board failures
I have read about only one car that burned to the ground because the owner overcharged his pack dramaticly.
Every other case of fire I read (six I guess) was a vehicle with a mounted "BMS" on it.
Thats my personal statistic. Fell free to widen it :)
 

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When you have thousands of dollars/pounds tied up in your pack, a fire isn't the only problem that can ruin your EV day.
I've run a conversion business for years, and tested a huge quantity of cells and system setups, and I'd like to say that I'd never run a Lipo or LifePo4 (especially LifePo4) pack without a BMS for more than 2 or 3 cycles. You can take that advice or leave it, I have written this only because I am so alarmed that so many would advise a BMS is not nesaccary.
It cost many hundreds worth of cells to come to this conclusion, over a large number of EV's (no fires however). You don't have to replace many battery's to cover the cost of a BMS, not to mention the inconvenience of stripping down a pack to replace cells (not all packs are as easily built as cheap thundersky's!).

Steve

PS, for Gottdi, I've lost 4 banks of cells due to BMS failures (mainly during a prototyping and testing period), this in no way compares to the hundreds of cells I have sitting around that were damaged by NOT being managed, or the several customers who have homebuilt EV's rotting in their garage because they believed they would not need a BMS and lost thousands worth of cells, 3 users did indeed lose the whole pack (or more than 70% therof), 2 by overdicharging and 1 by overcharging.
 

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How's this for an idea, discharge one cell and fully charge the other. Then do gentle charge/discharge cycles, and see if they'll grow into balance like Jack claims. I think this would be a good test for if a BMS is needed -- do cells naturally balance? Anyone else out there game to test this idea and see if we get the same results?

I just got some Headways and have more China HiPowers on order, the testing continues. I'll post up details, good or bad, when I'm done.
I've been thinking about a test almost like the one you propose:
Take three matched batteries. Discharge them all in parallel to 2 volts. Put 10% of the capacity into one, 20% into another and leave the third one at zero.
Connect in series and then repeatedly charge and discharge at 1C, stopping when one battery reaches 3.8 volts on charge and 2 volts on discharge. See if they drift closer to balance or not.
At the end of many cycles, remeasure the capacity to find out which is more damaging, running near the bottom or near the top.
 
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