Cheap and reliable battery pack?

[dnmun]

everybody has their opinions. i do experiments.

i think the guys who manufacture the BMSs know what they are doing. you have opinions.

i reversed the hack i did to convert the 24S lipo D131 to 20S by resoldering the little 603 surface mount resistor in the LVC signal line on channel #21 and also soldered the resistor back into the HVC signal line on top. i wired up a harness that used some 9 pin plugs i have to the 7 pin JST connectors and connected tot he 25 wires of the snese bundle to the BMS.

charging!

 

[wesnewell]

It's good news because LVC can be set to 3.0V, perfect for lipo under load

Yes, it would be perfect with a high load to where the battery would sag to that point and then come up to 3.4V resting. The problem is that isn't going to happen in real life ebike use where there's never a high load on the battery pack. With a 3.0V cutoff when the cell gets that low on an ebike, you'll be lucky if it comes back up to 3.1V resting. Just say rest in peace to your battery pack and bury it. My 20C 10ah 24s2p pack sags about 3V under a full load from my 40A controller. That's a total of .125V per cell under full load. See the problem? Under normal use, it sags less than 1V, or <.05V per cell. So when it hits 3.0V under that load, it's been fully drained for some time. But don't believe me. Build it and find out for yourself. Be sure and set controller LVC to 3.0V per cell too, so it won't shut off before the BMS. Let everyone know how that works out for you.

 

[methods]

I totally disagree with these conservative lipo numbers that folks are throwing around. (yes I understand that they promote longevity)

Back in the day when Lipo first hit the scene we used to prop our RC planes so that they would pull every cell down to 3.0V under load - just over where the 3S ESC BMS would cut out. I did hundreds and hundreds and hundreds and hundreds of flights like this. Never with a BMS, always charging all the way up to 4.2V and always discharging until the 3S pack was about 9V. Just beating the crap out of the cells. For years - and guess what? I still have most of those packs (the ones I did not lose or poke holes in or run dry). They still have good capacity. Maybe balanced them a few times in a few years.

Then... the crap LiFePO4 started hitting the market (think Thundersag). Everybody justified spending the big bucks because they were going to get 3,000 cycles. Yea... 3,000 saggy ass 2C cycles. The deal is... by the time anyone ever got their monies worth out of a ThunderSag the technology was so old and crapped out that they were hardly good for bulk storage.

Now we have Nano this and nano that - cells that dont even sag at 50C
SO... why I ask... are we so worried about getting thousands of cycles when the rate of change of technology is changing so quickly? I say the best value is to buy as much lipo as you can afford around the 15C to 20C range and enjoy it. Chances are a pack will be ruined by leaving the bike on or an accident or some stupid failure anyway. At least that has been my experience. Packs die - horrible deaths Rarely do they get "worn out" and the whole point is to extract as much pleasure from them as possible before they burst into flames or something better comes out.

But - that is from a high performance perspective. No 40A discharge happening here.

All this worry worry worry about not discharging below 3.4V and not charging above 4.1V
That may extend longevity - on a years scale - but when I am riding I really dont care. I want as much energy in my pack as can fit and I want to ride as hard and as long as I can - with as light of a bike as possible. Push the limits. This means charging all the way up to 4.2V or even 4.25V so that for the first few minutes of my ride I can experience the explosive power of 100V 150A hammering a 20" Cromotor. Blow off all that adrenalin - then my cells are at 4.15V and I can take my 20 mile ride.

This conservative LVC point may work for some (running low current limits) but one should not assume it works for everyone. Case in point:

I run 24S 10Ah 15C cells - the ol'school HObby King packs
10Ah * 15C = 150A rated
Well... My controller is tuned for 150A DC limit - and I hit it - for seconds at a time - and the last thing on the planet I want is a hardware BMS cutting out under heavy load! That is retarded. Ever hit a hard limit while accelerating so hard you are scared? 15KW shuttering and going into oscillation is no good - not for the rider and not for the controller.

Hardware cutt-off is for hardware cutt-off levels. (i.e. NOT TO BE HIT)
It is the job of the Controller pack level LVC or the CA Pack level LVC to start "softening" the discharge curve as the pack gets near the end. The hardware cutoff levels are there as an emergency backup and thats it. That is why they are set to 3.0V (or 2.7V for those of us who have been around a while)

I think folks should set the hardware cut for 3.0V
THEN... set the CA for 4 or 5 volts (pack level) above that - whatever works out to 3.3V or 3.4V or 3.9V or whatever gets you aroused. The CA has a nice soft roll-off, it will let you dip DYNAMICALLY down below 3.4V per cell but over a timeline it will keep you safe. Hardware cutoff without hysteresis stinks.

The hardware in a BMS is for emergencies - not to bounce off of on every ride Anybody who has an 80lb ebike with fixed gears that go 35mph can attest.

More came out there then I intended - but for the last few months I have been hearing more and more of this 3.4V LVC and 4.1V HVC talk. Ok - fine - do that with your charge voltage and your controller LVC - but hardware limits should be set to hardware levels. Anyone who says a pack has 0% charge left with 3.4V on the cells has never ridden 5 miles like that. I have - many times. There is certainly enough charge to get a guy home - pedal assist - at a few hundred watts. So hardware levels should never be set that high - not when there is usable energy left in the pack. This kind of talk is what gives people range anxiety. Ok - so a few cells hit 2.7V... the world is not going to end... Just dont make a habit of it.

Now that I am done writing this I am realizing that I will have to argue the point for hours and hours and hours with new guys on the forum who I dont even know.

Yea... not going to do that.
I concede the point - right now - to anyone who wants to argue with me.

YOU ARE RIGHT
I AGREE
I TOTALLY AGREE
I am wrong and I accept it.

Whatever I have to say to be able to spout my opinion and not argue about it.
Just think some opposing viewpoints need to be interjected from time to time else things might get skewed around here.

lol...

-methods

 

[dogman dan]

Sounds like your early lipo beats the stuff I bought from HK 2-3 years ago.

The first 4 packs I bought only lasted about 50 cycles. I found they got unbalanced every cycle if I took them below 3.6v resting. They were doing 8c max and were 30c turnigys. Those four got rode to 3v at least 10 times.

So I decided to be a bit nicer to the next 20 packs I bought, and other than the ones I killed stupidly along the learning curve, they went closer to 200 cycles before going off a capacity cliff. Now, almost 3 years old, they stay perfectly balanced if I stop by 3.6v, but have half capacity or less. I attribute the capacity loss to storage at 4.2v. These ones never saw 8c either, more like 4c discharging.

The main thing for me is not having to balance them every ride. But a BMS solves that easy eh? However, even with a bms, it will take longer than just zapping a balanced pack full. I just think carrying 5 ah more is a good solution in many cases. Or stopping sooner, if 5 ah more is a bitch to carry, or would give you a ride length that tends to melt your overclocked hubmotor.

Chargers that charge each cell individually have to be the way to go, if you are planning on deep discharges. No waiting for bms's to discharge the high cell.

Do bms haters realize that if they use an RC charger they are using a bms for charging when they select balance charge?

2.7v is 0% IMO. When needed, I don't hesitate to take it all. No way I'm struggling home to keep cells above 3.6v. But I have learned not to pull 40 amps from low cells. I've used 3.5v beepers when intending to discharge deep. I don't stop when they start beeping, I just start riding using 100w.

I have also noticed, that if you pull 40 amps from low cells, they DO sag a lot then. That's resistance growing as you discharge deep. You should see those old dog cells of mine sag now. They act like 2c or worse now. They have resistance in the 100- 150 range these days.

 

[dnmun]

i find that once the cells have balanced, just as with lifepo4, that the balancing phase at the end of charge is very short. i find that even when i drain the pack to where the low cell hits LVC that when i recharge all of the cells arrive at the same voltage when they get to the balance current.

i find that the lipo is easier to balance than the lifepo4, they seem to be on rails and go right to end point. spread is all within 4.19-4.21V and almost all are exactly 4.20V just like they say in the data sheet. never had that happen with the old ping pouches.

 

[methods]

Sounds like your early lipo beats the stuff I bought from HK 2-3 years ago.

ThunderPower V2 were very good cells - never needed balancing. I agree that the early Hobby King stuff was garbage.

The first 4 packs I bought only lasted about 50 cycles. I found they got unbalanced every cycle if I took them below 3.6v resting. They were doing 8c max and were 30c turnigys. Those four got rode to 3v at least 10 times.

So I decided to be a bit nicer to the next 20 packs I bought, and other than the ones I killed stupidly along the learning curve, they went closer to 200 cycles before going off a capacity cliff. Now, almost 3 years old, they stay perfectly balanced if I stop by 3.6v, but have half capacity or less. I attribute the capacity loss to storage at 4.2v. These ones never saw 8c either, more like 4c discharging.

Agreed - short cycling and keeping C rates low will definitely result in less wear and tear on the cells.

The main thing for me is not having to balance them every ride. But a BMS solves that easy eh? However, even with a bms, it will take longer than just zapping a balanced pack full. I just think carrying 5 ah more is a good solution in many cases. Or stopping sooner, if 5 ah more is a bitch to carry, or would give you a ride length that tends to melt your overclocked hubmotor.

Agreed - I balance like once a year lol. My theory (as you know) is to just run cell level LVC and cell level HVC protection - then not worry about it. Carrying extra AH is a good choice if you can afford the cash and weight.

Chargers that charge each cell individually have to be the way to go, if you are planning on deep discharges. No waiting for bms's to discharge the high cell.

I totally agree with that. Charging individual low cells is a better idea than restively discharging the high cells

Do bms haters realize that if they use an RC charger they are using a bms for charging when they select balance charge?

BMS haters have just had bad experiences with bad hardware. Thats why I am so hard on all these new Chinese BMS's that come out. The Detector Boards that I use are actually the hardware backup to our original motorcycle BMS - which was big and power hungry and sketchy. I agree that BMS's do add a huge amount of unreliability to a system and thats why you want to keep the BMS as simple as possible - cell level protection.

2.7v is 0% IMO. When needed, I don't hesitate to take it all. No way I'm struggling home to keep cells above 3.6v. But I have learned not to pull 40 amps from low cells. I've used 3.5v beepers when intending to discharge deep. I don't stop when they start beeping, I just start riding using 100w.

Yea - I always try to quit at like 3.6V but I want to have access to the remaining power if I need it.

I have also noticed, that if you pull 40 amps from low cells, they DO sag a lot then. That's resistance growing as you discharge deep. You should see those old dog cells of mine sag now. They act like 2c or worse now. They have resistance in the 100- 150 range these days.

I should post a picture of my Lithium Table. Like 500lbs of beat to hell cells. I completely understand. I just treat Lipo as an R&D toy on the way to something better - as opposed to coveting it and treating it nice.

-methods

 

[methods]

i find that once the cells have balanced, just as with lifepo4, that the balancing phase at the end of charge is very short.

I find that to be true with new, high quality cells. But with salvage cells (most of what I have) it seems that they are constantly going out of balance and trying to resistively balance them at the end of charge requires a pretty high balance current - like an amp or two. If it is to be 200mA or less then it needs to really go for a long time - which I suppose is fine if there is somewhere for the heat to go.

i find that even when i drain the pack to where the low cell hits LVC that when i recharge all of the cells arrive at the same voltage when they get to the balance current.

YOu must have good packs Apparently salvaged emoli packs are not as friendly

i find that the lipo is easier to balance than the lifepo4, they seem to be on rails and go right to end point. spread is all within 4.19-4.21V and almost all are exactly 4.20V just like they say in the data sheet. never had that happen with the old ping pouches.

That is because of the chemistry right? LiFe has a huge window above the fully charged point - call it "surface charge" - where it is not really 1:1 anymore. That is a nice attribute of Lipo - voltage is a pretty good indicator of state of charge.
-methods

 

[friendly1uk]

I have LiPo and according to wiki most manufacturers recommend 3v-4.2v which seems to tie in with most peoples experiences.

i think the guys who manufacture the BMSs know what they are doing

The bms supplier you recommended for me sets the hvc to 4.28v +/- 25mv, so peeps could be charging them to over 4.3v. He told me this after I had asked for 4.2v

I have seen a lvc on other lipo boards of 2.5v, which is again out of range.

I have tried for some time to find an outlet that gives me confidence. A board member in central europe is stocking a few of the 13s smart bms and programming them however you like. I don't have the board from him yet, but so far his english is alright

 

[methods]

BMS limits are hardware limits that are to be hit only occasionally. That is why they are so far out on the edges.

It is your job as the rider to set your power supply (charger) to the HVC voltage that you want, and to discharge only to the pack level that you want. Any time a rider hits the actual hardware limits of their BMS (be that cell level LVC or HVC during a charge) they are "doing it wrong"

The tide has turned around here... pushed by folks who dont really know what they are talking about... and I intend to come back and waste my time arguing with them to set things straight.

YES short cycling lithium will make it last longer (3.4V to 4.1V)
NO this does not mean setting your hardware protection system to these levels
YES it does mean setting your pack level LVC and HVC to these tighter voltage
YES it means you have to keep your pack balanced and monitor it

This will maximize the energy you can put in and get out on any given ride. Similar to how the Tesla works... For day to day driving you just run the pack in the middle. BUT - BUT - BUT -> You have the ability to charge it all the way up and discharge it all the way down when you need it!

Thats the point
and that is why we dont set hardware limits so high on the low end or so low on the high end.

That is the job of adjustable things - like charge voltage and pack LVC

Again - any ebike ride that ends in the BMS cutting discharge is a Fail.
Any ebike charge session that ends with cells bumping into a 4.25V BMS limit is also a fail
The BMS should not be relied upon on a regular basis... it is a backup shoot... a fail safe.... not a sounding board.

This is not directed at anyone in particular - but rather at the ideas that have been spreading on the board.

Short cycling is good.
narrow hardware limits are bad
narrow software limits are good

-methods

 

[wesnewell]

The problem with setting LVC low and HVC high is that most people either don't pay attention to pack voltages or they want the hardware to protect their pack. Setting lvc to 3.0V per cell won't do that, and setting to 2.5V will just kill them quicker. There's just not enough energy in rc lipo under 3.6V resting to even consider it usable imo. There are all kinds of graphs on the forum that show this. That part is just a fact and not an opinion. Having pack lvc set to 3.5V per cell will let you run it down to lvc and not damage the pack or get it way out of balance, and worse case it won't you discharge it so much that it will go into thermal runaway and catch fire. It just doesn't make sense to me to use such a low cell level cutoff if its really not going to protect anything. If you need more range just make your pack bigger. Set lvc to a voltage that won't let you over discharge it and an rc lipo pack should last years.

 

[migueralliart]

I may not be using lipo anymore but I remember this argument ever since I posted on methods LVC HVC boardsthread that the LVC was a bit too low for the majority of the USERS here.

I remember when I had a small capacity pack in one of my off road bikes that I believe it was a 18S1P turnigy. I had the LVC buzzers set at 3.5v and when I attached the pack to charge after it started beeping the capacity put back to the pack was pretty close to 90%. If I were to discharge that pack to even 3.0V per cell that will just heat the cells more and push them to the limits.

Result; Unbalanced Pack, possibly cycle damage and maybe puffing?

 

[Tommy L]

Methods!

I like a "RANT" that makes sense! Yours was AWESOME! 8)

I get "Mad" (not really) ....... when people talk about LiFePO4 sagging. My A123's or my Headways 38120HP's do not "Sag" because
I understand that the Chemistry requires 3.65v per cell to fully charge them. Under load, the A123 can handle 5-7C and stay between 3.1 and 3.2v
per cell until 100% (or a little more) capacity is used, then they fall off the cliff at 3.0v. The Headways's are 4.5C and stay around 3.1v per cell
until 100% (or a little more) capacity is used, then they fall off the cliff at 3.0v.

For LiCo (RC Lipo) you need 30s for 128v then you finish at 3.5v per cell @ 105v (a 0.7v per cell drop from start to finish) hmmmmmm
I'm not "KNOCKING" RC Lipo or "Promoting" LiFePO4, I'm just saying to build your packs out of the chemistry that you want and know how to use
the pack of a given chemistry with in it's limits. I know that if I want a 128v nominal voltage LiFePO4 pack it needs to be 40s. And I can use it
at 5C until all 100% is used and maintain 128v to the controller. (In my example I use 4s4p 9.2ah packs with 10 units strung in series, picture below)

If you are using LiFePO4 and you want 128v on tap, then use 40s. Sure, Hot off the Charger is 146v, so best that your controller can handle it.
But once under load, it will be 128v. My "RANT" is..... know the Chemistry and it's true "C" rate once placed in a "PACK". When I say: "It's True C Rate"
I mean to maintain a certain voltage. They say a single cell A123 can handle 60C, but there isn't any voltage while it's being hammered like that.

(once I'm up to speed and my current demand drops and I'm more like 132v, when I take off from a stop then I drop into nominal voltage of 128v)

Another "RANT" is wire sizing. For a given amperage (let's say 15 amps) and remember, amps ain't everything, voltage needs to be considered

12v @15 amps 180 watts #14 wire 6 feet max
24v @15 amps 360 watts #14 wire 11 feet max
36v @15 amps 540 watts #14 wire 23 feet max
48v @15 amps 720 watts #14 wire 45 feet max
120v @15 amps 1800 watts #14 wire 68 feet max

As your Voltage increases (it's like higher pressure) and less heat builds in the wire.
This is why I like the High Voltage set ups! Less energy wasted to heat. :wink:

Tommy L sends.....

 

[dnmun]

i don't know of any BMS capable of handling over 100V. the 24S lipo is just over the edge of the irfb4310 breakdown voltage now at 100.8V