Without BMS

K

k-harvey

100 W
Joined
Aug 5, 2011
Messages
269
Location
New Zealand
Can a made up bike battery from used computer cells last without a BMS as i just met a guy who said his would as on his Bafang unit he has adjusted the LVC etc-------- if hes right I've been doing a lot of work on batteries unnecessarily .
 
As long as you are willing to be the BMS, by manually checking and monitoring the battery, you can run any of them without a BMS.

Some brands of cells are better at staying balance than others (better quality control when made), but anything that's old or used and not all from the same batch will ahve differing qualities between cells, so will behave differently in use.

That means that when not using all good cells from the same batch, until you have tested and monitored them, you won't know if they behave identically. The BMS would do this for you, so without one you have to do it yourself, or live with whatever consequences there are from them not behaving identically.
 
Use them gently,, and the cells are not used up already, and they will last. Use them harshly, and you can kill it nice and quick.

Your question is very vague, but in general,, if you practice using less than 100% of a battery they last and stay relatively well balanced. So that is not draining them completely, and using them at very low c rates. At one point, the advisable c rate for laptop cells was .5c. That might be higher now since cells have improved some. Undercharging is only advisable if that means you still have plenty of room at the bottom. So the bottom line is make that battery huge.

This type of very gentle use of any battery usually results in much less unbalancing of the pack, which makes being a human bms easier.

But I sure don't mean you can ignore the pack. It needs a bms. a machine, or you, but it needs a bms.
 
I've just bought another BMS & hate the job of installing with so many wires , the last one am sure is faulty . Once a guy came to me his 2 batery packs BMS s were too lower amp so he took the risk on one without it & that stuffed half the cells ( these are the big 10---12 ah ones ) ,then I fitted high amp BMS to his other pack. The battery packs I've made up all with these screw together cells on the 24v have worked fine but the 36v several the BMS fails. High amp BMS's are expensive .And i wish they were all the same plugs etc & wired.
I think I'l keep to using the BMS;s as abuse of the battery is not always in my hands-----Thanks guys.
It was good when he told me his estimated cost for his battery pack( these are all used) it was about same as new with BMS .Although it was small cell 48v.
 
Used cell computer batteries need to be built over sized like 10p as to have less stress. Plus a low amp controller. Without bms is best with new quality cells with always monitoring like wearing out sense wires and meters and replacing them.
 
I've been using recycled laptop cells for the whole season right now. My setup has a bestechpower BMS 16s. Pack is 13p. The BMS is completely not needed in my opinion. I always charge at home or work, being nearby. I also stop charging before the BMS enters the balancing mode (it is designed for lipo 4,25V, which is too much). The same with discharge. 16s13p has so much range, that I usually charge when the cells are above 3,3 V at full load (watched with cellogs).

I have run out of juice 2-3 times and even then I would prefer not having the BMS, because it turns the bike off and I want to get home slowly.

My cells are of various capacity, from various vendors. I did ca. 1500 km and they are well balanced (they are top-balanced and have slightly various resistance and capacity for different battery "S" levels, but after recharge each time they meet each other at 4,15V)! Only one thing went wrong: the BMS! It started to discharge my last module of battery! Because of that went to 1V one day. Now I disconnected the BMS for winter and all the batteries wait nicely at some 3,8ish voltage.

So because of the bms I only had problems.
 
I run without a bms but have A123 20ah 24s cells. Mostly taking out 12ah but have used 18ah three times in 960 cycles. worn out three sets of sense wires, 6 cell meters, three charges, a power supply and two motors one controller in 4 years. Same heavy battery. Good as new set controller to 85amps.
 
As a local electronics friend said I'm playing around with what i know little , as i did get a cell log & couldnt use it , will look again for it ,
Am now looking for these used cells from laptops , as we in New zealand, china battery guys can't freight to us unless exorbitant cost.
I've had good luck just buying from e bay & they freight ok but this is usually low current discharge for low wattage motors.
 
Re the bms discharging the pack over the winter. There are two approaches,, the best is unplug the bms while you store it.

If you cannot do that, or don't want to open a case to do it,, then recharge it about monthly, to prevent the bms from the possibility of draining one cell group.

I wish commercial batteries just had a switch you could flip to put the bms in an unpowered, storage mode.

Re bms's failing. It happens. but IMO the average joe can wreck a battery far more often than a bms fails. The typical ES member is NOT the average joe, and can easily be a human bms. But he has to keep learning,, like how to use that cellog or other cell reading device. We can do that. The average joe is not so dumb really,, but he is lazy, and will kill a battery without a bms.
 
The reality is, batteries just aren't really a great thing to store without purpose or use. In many ways, its like keeping a petrol can in your house, then complaining about the smell. There's an inherent, systematic risk they will self discharge and cause problems. This can be reduced by quality, matched cells, periodically monitored, with or without a BMS. Some chemistries and formats tend to be safer than others, sure, but still. Its literally keeping a store of energy in one place.

LVC is not the only reason to have a BMS. BMS itself is a pretty undefined term which can range from being a basic alarm right through to bluetooth alerts via your cellphone including real time voltage per paralleled cells. Balanced charging, temperature cut offs or reporting via bluetooth, high voltage, low voltage, high current, low current... the list goes on, depending on the functionality of the BMS itself.

The lack of clarity on the definition of a BMS, and the subsequent discussions about specific issues has driven me a little crazy recently..... :evil:

A storage mode is right, but switching off the BMS is not the answer. Rather, balancing draw to power it and an ability for store mode to be plugged into the charger charging to an maintenance voltage of 60% (or whatever you deem safe) and leave it to trickle charge when required.
 
My bms is in my ass the battery is losing a lot of power at better not use it. When my drill is losing power I should not pull the trigger. Get it empty is empty only with batteries does empty destroy. Destroy. Destroy . OK. Next. Destroy.? ???
 
Most idiots know when the battery is drained the other idiots use the battery reset the BMS and kill the battery over and over again. Which idiot do you want to be. Idiot just do it . 960 Cycles 4 yrs. No clues.
Why would you have a battery problem.? I have no battery problems? A123 or next grephene. 18650 why ? Tesla moved on ?
 
I often continue to commute with my ebike when I have done extreme hours, both in commuting and in work. At that point, I'm far less reliable than something electronic, by miles. It isn't a question of difficulty, its a question of diligence and personal preference around time.

Its a trade off really. Spend more time planning/testing/soldering in a BMS or more time consider pack balancing, balancing methods, harnesses, controller programming.... as opposed to just plugging in an charging in full once in a while? Each to their own I guess.
 
RE storage,, plenty of people won't ride the bike till the temps are above freezing,, so they must store the battery at least 3-4 months a year.

Every spring we get "battery season" Troubleshoot calls, " my bike won't work this spring". 100% of the time,, " Oh,, I was supposed to charge it before I stored it 6 months? "
 
I wouldn't leave any battery more than 4-8 weeks before recharge. I'd like to know this guy without BMS to see how long his cells all last . He Had what he called 1500w 48v I thought bafang mid-drive didn't get that big . Testing each cell when charging seems nut when a BMS can do that . I've made up lots of packs only problem these people (friends ) have is they need Like I have is lots of chargers & batteries all the same so as to analyze whether full charge or what might be wrong.
Buying these cells & BMS's is a bit like trying to buy parts for a new space shuttle in NZ
 
dogman dan said:
...people won't ride the bike till the temps are above freezing....
Click to expand...

Im in Australia... what is that? :lol:

Either a BMS which will allow cut out at a storage voltage or a means of cycling the battery monthly (i.e. lights or something) is in order... 8)
 
I run my son's electric motorcycle on a pack without BMS by stopping when resting voltage gets to 3.6 per cell or when lowest sagged voltages gets below 3.3. Usually charge only to 4.1v, and go up to 4.2 if it'll be a long ride where the range may come in handy. I always balance charge. One cycle usually results in less than 0.02v of difference between highest and lowest cells.
 
There are cells on the market which dont drift like the Sony US18650V3.
Used a pack of them without a BMS or balancer output for 13000km and when i measured the drift, there wasn't really something to measure.

But even with these cells a BMS is nice to have.

We should distinguish here.....

BMS for monitoring or a BMS for balancing.

Maybe you dont need to balance the pack every charge but for monitoring a BMS is great.
 
Those are the "Konion" cells and have a limited self-balancing capability so were often used without a BMS.

The charge efficiency of the spinel chemistries decreases slightly as it approaches a high SOC. You can see the effect with a CC supply and a temp sensor as plain as day.

This is what causes them to self balance. (and what causes a lead acid to self balance, only they use electrolysis as the energy outlet)

It is not a designed-in feature, simply an inherent property that helps to self correct balance in packs.

In practice, you can start with a pack that is out of balance, run a number of cycles through it, and each time its finishing the CV mode, you see balance creep a little closer each time until it ends up back in roughly perfect balance after enough cycles.
Click to expand...

https://endless-sphere.com/forums/viewtopic.php?f=14&t=48370&start=75
 
999zip999 said:
I run without a bms but have A123 20ah 24s cells. Mostly taking out 12ah but have used 18ah three times in 960 cycles. worn out three sets of sense wires, 6 cell meters, three charges, a power supply and two motors one controller in 4 years. Same heavy battery. Good as new set controller to 85amps.
Click to expand...

A123 enough said :)
 
Seems kind of silly to not have a circuit monitoring each parallel group of cells, if you want to prolong the life of your pack. You really, really don't want any individual groups going above 4.2V, under 2.5V, or significantly over temperature (120F/50C). Judging the voltage of the whole pack can easily disguise problems with individual groups, and isn't reliable for protecting the pack (especially if you plan to charge in series).

I'm designing my pack with removable cells, and plan to use a cheap 59V series charger. I will forgo integrated drain balancers and instead just monitor every group, with a signal to cut the whole pack if an error condition is detected in any group (undervoltage, overvoltage, or overtemp). This will save the energy and cycle life that would otherwise be wasted by the drain balancer. Since I'm buying new identical cells, I expect this to work very well, and don't anticipate having to balance more than once a month (and hopefully only once a season).

The alternative is to use a balance charger (or three, with switches to break up cell groups before charging). But I'd like the convenience of a single charger and cable, without having to pay crazy money for a few 14-15s balance chargers (one for home, one for work).
 
Monitor, monitor and monitor. Know your battery. You have two hobbies one an ebike two a human bms. Take your responsibilities seriously.
 
Jestronix said:
999zip999 said:
I run without a bms but have A123 20ah 24s cells. Mostly taking out 12ah but have used 18ah three times in 960 cycles. worn out three sets of sense wires, 6 cell meters, three charges, a power supply and two motors one controller in 4 years. Same heavy battery. Good as new set controller to 85amps.
Click to expand...

A123 enough said :)
Click to expand...

Are A123 batteries good, or are you ironic?
 
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