Battery Charge Management System (BCMS)

billr

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My understanding is that the BMS monitors voltage and temperature of each cell. Does it also monitor current for each cell? If there is a fault, either in charge or discharge, can the BMS isolate an individual cell from the battery circuit? That would seem to take a lot of power transistors to selectively take a cell out of the circuit and bypass it; and parasitic voltage loss in the transistors all the time. In pictures of the Tesla batteries, it looks like the cells are connected with a simple buss-bar from cell-to-cell, no isolation possible. I am particularly interested in the Chevy Bolt, any BMS info specific to it would be appreciated.
 

nickb2

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Hi Bill, Or JordanR, I mistakenly posted some stuff on what I think are desing flaws in the BCMS/BMS systems of hybrids in another thread and invited Nick D for debate and sharing, you also.

I am,sorry, not the bolt pertinent, those are to come, we just finished module 2 of 8, so wait for it.

I can't copy paste that here. Can you look into that for me, I don't have admin priv on that.
 

billr

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You had several replies regarding "BCMS" (that is the correct abbreviation, not BMS?). How about I just advise anybody interested to look here:

https://batauto.com/threads/what-are-the-most-common-ev-codes.15598/

In that thread you asked me to comment, but I will do so here and will try to include enough info you posted there so that my comments will seem pertinent to this thread.

Notice that I changed the subject of this thread to "Battery Charge Monitoring System (BCMS)", is that all correct now?
 

billr

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In that other thread, nickb2 noted that there are a couple of "common" problems that relate to the BCMS:

1) Most (all?) EVs, both BEV and hybrid, have two "batteries"; a high-voltage (HV) one for main driving power and a low-voltage (LV) one for controls/accessories. Leaving the car connected to the day-to-day HV charger does not keep the LV battery charged. If the car is left for a long time, the LV battery will run down enough that the car will be inop, even if on the HV charger all that time.
I wonder how long it really takes for the LV battery to go too low, even in the frigid zones? In my area a LV battery will last a few months with the "keep alive" loads of a modern car. That is way longer than would be problem for most folks that can't afford to have a car as just an idle toy, I feel. I also wonder why they even bother with two batteries??? Yes, it is a good idea to keep most of the car wiring at the safer LV, but that could be done easily with a DC-to-DC inverter to get the LV off the HV battery.

2) There is an increasing mix of battery types for the LV. There are "flooded", "AGM", "VRSLAB" and gel in the lead-acid family; and maybe some lithium or nickle variants as well. Sticking with just the LA, charging can be different, so just advising to keep the LV battery on a charger can also cause problems.
I disagree that using a standard charger on AGM is a "huge no-no"; some AGMs are designed to handle higher (flooded) charging voltages OK. However, I do agree that it all depends on the battery design and the charger design; you gotta be sure they are compatible. This problem begs me to ask, why the not-so-recent trend for charging voltages up in the 14.5-15V range? That isn't even real good for a flooded battery. In the "olden days" a 12.6V battery charging system was usually in the 13.4-14V range. That is plenty enough to fully charge the 12.6V battery, and not enough for detrimental overcharge. Of course, if there were no separate LV battery, then this is all moot...
 

nickb2

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Actually, I am a bit confused right now, I thought this was all going to be one thread. But I will adapt. But reasonably, right now, all the info in my head needs to be done in english in my head before I write it, and then I have to self correct. So, yes, BCMS in my head mean battery control management system, some others simplyfy, bms, same thing,

It takes me time to correct myself to actually write this stuff, nuts. I think that is why Billr tolerate my lame arse. I go OCD, need time off.

 

NickD

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Really have not studied hybrid battery charging, for one thing, a bit greater than 12 volts. Temperature sensing relies on a temperature sensor.

Chargers typically are current limited depending on the size of the cells being charged, but the charging leads are also voltage sensitive. Once that voltage is reached, the charge rate is cut back mostly to a so called maintenance charge.

By using inverter and converter technology, any kind of input voltage can be used also in regards to the output voltage. Timers also can be incorporated, like if the charged voltage does not reach a predetermined value in a certain period of time, charging voltage will be stopped, indicative of a shorted cell. Will also ignite a warning lamp, can call this a heart attack lamp as you have to replace that battery.
 

nickb2

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Can someone, plz expain to me, why when you have a BMS, and a US market lets say CCS1, type, why is it not check low scale for convenience? There is a monitor on this all day, but, bms doesn;t give a shyte, only charges HV. Useless up north.

In the blue patches of responses, I don't know if they were billr question, but I will attemp two of three, or one of two, I am still in yestarday work clothes, I went line dancing. New 45ish hobby, my buddies say I should get out more, well now I stink of of line dancing and shots of I cant remember trying to remember why I am asking this question. Oh, yeah, why is the bms monitoring full time hv, but ignoring LV? Is that by design? If so, why??????????
 

nickb2

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BTW, cute old women dance the acky breaky. I feel so old right now, I just want to go to bed. I sure cant party up like when I was 30. :eek::oops::money::money::money::money::money:

 

NickD

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Do know with a lithium-ion cell phone battery, if the voltage drops below 3.7 volts that's the end of that battery. Requires a current cut off circuit so the voltage does not get any lower. If you leave a discharged lithium-ion battery lying around, like any other battery, its dead.

Wonder what will happen to your Tesla battery if the car is left in your garage for a couple of years without a maintenance charger, you could be out a couple of bucks.

Nickel cadmium batteries are entirely different, should be full discharged first before recharging. But they also have a high self discharge rate. If left in a power tool for a month or two, have to recharge them first.

Sulfuric acid batteries will freeze below freezing if not fully charged. If you take a lab type power supply set to exactly 13.5 V should fully charge the battery and show 0 amperes charging current. Had some that would only go down to 3 amperes, this means the battery has a high self discharge rate. But don't try to explain this to the party you purchased this piece of crap from, they are idiots.

Ask that question first before buying a battery, if they agree, they have a sale, self discharge is a very common problem, 60 AH battery will be stone dead in about 20 hours. See signs were frozen batteries are not covered under warranty, but darn things can leak internally just as well as externally, so stay far away from those places.

Anybody remember 15 bucks for a new battery, more like 200 bucks today.

Generally charging a battery looses about 30% of total energy, heat loss in the battery and the efficiency of the charger itself. Discharge runs about 10%, current is flowing inside of the battery that has internal resistance.

Not that really bad for a cell phone, but what about a car? Not sure about the Tesla, on the GM EV switching on the heat or AC will reduce your driving range in half.

For electric vehicles, coal in Nevada is still used for California EV's, power and heat losses in turbines to generator electricity, more in those super long high voltage towers, plus maintenance cost, more in the inefficiency of the chargers and the charging process itself, more in hauling the huge weight of these batteries, and more in converting chemical, to electrical to mechanical energy. And a lot more if you want to ride in comfort.

But the big deal is that the major pollution fall outside of the state of California.
 

nickb2

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quick man, or quick study??
Let's not get this EV forum off "into the weeds" so quick. Dropping below 3.7V is not "death" for a lithium battery, that is more like full-charge. Dropping below 2.5V is more often the cut-off point when discharging. Anybody interested in the true story, peek here:
Thx for the link, I liked it.

Balancing is harder than I thought, but yeah, 2.5v is the standard that a BMS should code at. You can also see that in live data. I think this goes back to series/parallel and why this is designed this way. Cuz if one goes down below specified whole thing would just knock off? No, we are smarter than that.

I will keep that link for class tommorrow. The class will like it, we talked about that last week. ;)
 

nickb2

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