72V 20Ah Headway pack

[frodus]

For my education;
1. How different is the LiFePO4 in a Headway from a TS cell?
2. How can it be any different if people are using the identical BMS?
3. How can a fully charged Headway cell at 3.65V go down to 3.3V after being off the charger for only one hour?
Thanks for the enlightenment.

1. Differeny chemistry. TS uses yitrium. The paste of different batteries may be the same, but some manufacturers add chemicals for different reasons, and some use different anode/cathode material. Otherwise we'd have the same discharge curve for all Lifepo4 batteries. They're also built differently.

2. Different chemistries act differently. But I have a hunch that his BMS isn't actually getting to where it cuts out the charger. The charge shuttling shuttles charge between cells automatically (which is why his pack is so close in voltages). I think his charger is to blame, not the BMS. Two of the same BMS acting differently because one is never getting to that upper charge where it shuts down a charger.

3. It's called surface charge. All of these cells (TS, SE, headway, A123) are made as 3.3V nominal. You may take them to 3.65V, but it can actually take a bit longer for the charge to equalize within the cell to it's nominal voltage. It also depends on the size of the cell and how it's made. Prismatics may take longer than a cylindrical cell to equalize within the cell. I assure you, they rest to 3.3V fairly quickly. Hell even halfway charged cell will sit at 3.3V, but as soon as you load it, it'l drop like a rock if there is no charge within the cell. Cells don't hold the charge at 3.65V, otherwise that would be nominal voltage. The lifepo4 we're talking about settles to 3.3V, and it all depends on how readily the cell dissipates the charge internally throughout it's electrolyte.

 

[Gordo]

removed on request

 

[Beavinator]

Like I said in the post before the results one, I measured the voltages immediately after the bms cut off the charger. I will do another one and measure the voltage that the pack is at when the BMS stops charging. One thing that I find strange though is that when I hook the charger up it immediately is cut off by the BMS so maybe the numbers I posted are because the pack has been stored for a month fully charged and it is still fully charged. I have no working bike to do a drain and recharge so Ill just wait a few weeks until I order a new motor.

 

[Gordo]

removed on request

 

[Evoforce]

Gordo I would not do that and I hope the beave doesn't either.

 

[Spacey]

If a couple of cells are low/out of balance then charging without the BMS will overcharge other cells to compensate for the low ones i.e charger doesn't care if cells are balanced as long as they add up to the charge cut off voltage.

Beavinator.... if the cells are not balanced as they should be then maybe you have one of those Lifepo4 chargers that are actually set up for Lipo and NOT Lifepo4. What this means is that once the battery hits the voltage that the charger thinks is charged...that is it.... no bleed power coming from the charger to allow the BMS to do its job.

All the chargers I had from Evassmeble did this, it's an easy fix. Ping pointed it out a long time ago on this forum, it's just a little transistor that needs breaking off on the daughter board. If the 3 legged transistor is there then you might as well not have a BMS for charging.

I found this out whilst monitoring a Headway pack when charging. Best way to know for sure is to hook up a Turnigy Watt meter in between your charger and battery, if the charger is set up for Lifepo4 then it will allow a small amount of power 1 to 20 Watts to feed the BMS some power to do its job. If the Turnigy Meter shows nothing other than maybe a couple of on/offs from the charger then you need to look for the transistor.

It's not just the ever crap Evessemble that supplied these, they are a common mistake with some KP Model Lifepo4 chargers. Just recieved 2 more chargers so I will check those as well.

 

[Barry]

$16.66 a cell is not bad price for headway 10AH cells. Unfortunately I just received a shipment from China.

Somehow all discussions about Headway cells turn into BMS and balancing problems. I have gone through 4 BMS’s, 2 bulk charges and 12 single cell chargers over the past two years.

The best solution I found is to use a Hyperion 1420i to charge and balance the 36v packs. I don’t discharge the pack past 80% its capacity and everything works fine.

 

[Spacey]

As long as you have the correct charger and a decent BMS they work just fine.

 

[frodus]

I agree that the nominal voltage of LiFePO4 is 3.3V but it was not arrived at by measuring the resting voltage after charge. A nominal "12V" automotive battery has a resting voltage of 12.6-13.2 depending on the construction and electrolyte. Nominal = named, nothing else.
My scoot with 20 cells is described by the manufacturer as 60V which does not seem to follow any convention. A further confusion is the charger stamped as 72.8V which is 3.64V per cell, yet when the pack is balance, the cells are all 3.65 when the charger shuts itself off.

My Headway cells rest at ~3.33V, other batteries may differ (I think I remember TS and CALB resting slightly higher). Yes 12V is just a name, but 3.2V on these batteries is more like it's normal operating voltage, so the voltage of the battery under a small load (1C or lower), at least that's what I've seen in my testing and experience. I agree, it's all confusing, which is why we gotta check cheap BMS and Chargers from china. The charger cutoff should be: n * 3.6 up to n * 3.7 for Headway batteries. I know TS and CALB are higher. The BMS should work within the limits of the cell that it's working with, which is why I think some of these BMS's aren't doing the job right.

Anyway, my WAG is Beav battery is probably perfect, but I suspect the BMS is faulty. I wonder why, with a perfectly balance battery, he does not disconnect the BMS and let the charger pound the battery until it quits on it's own? Then measure each cell.

I wouldn't suggest disconnecting the balancer, but I think if he kept the BMS connected and bypassed the BMS (so it doesn't cut off the charger) to see if the pack charges fully, it would be acceptable. Then at least he'd know if the charger or the BMS is the problem. Keep the BMS there so it can do it's job balancing the cells.

 

[Gordo]

removed

 

[frodus]

The charger cut off is based solely on the pack voltage, not on any individual cell voltage. All the BMS does is use parallel to balance a pack being series charged or discharged. The BMS doesn't tell Beav's charger to shut off at 80V, the charger does this with or without the BMS. The BMS is not telling the charger that the pack voltage is more than what it is. The charger does not see the individual cell voltage.

Yeah, duh...... but..... what we have to go by is the BMS here:
http://www.evassemble.com/index.php?main_page=product_info&cPath=6&products_id=46
shows a max charge current, so it's safe to assume that the BMS manufacturer expects the charger to go through the BMS like most cheap BMS do (using a FET to disconnect charger from batteries), that's all I have to go by. If the CHARGER goes through the BMS and the BMS is somehow cutting off the charger, the charger isn't stopping itself, the BMS is stopping it. This can happen for several reasons, HVC (cell level), Overtemperature, Overcurrent or from some flaw in the circuit. So the BMS COULD be telling the charger to shut off prematurely, that was my point. By bypassing the BMS cutoff, and leaving the BMS connected and just connecting the charger directly to the pack, he can see if it's the charger OR the BMS.

And, TS, Calb chargers are not higher than 3.6V to 3.7V as you state.

Maybe the TS or CALB rebranded chargers actually cutoff at 3.7 or lower, but they state, on their actual datasheet for the actual cell 4.2V max. I didn't state what the chargers cut out at, I stated that the charger can be slightly higher for CALB and TS, which is true.

My 20 cell TS charger cuts off at 72.8V which is 3.64V per cell and every cell is very close to that. And they stay there for weeks.

Yeah, but as soon as you draw a load, you're back down to 3.xxV, just like the rest of the lifepo4 cells out there. So you fall to ~60-66V immediately.

I'm just very curious as to why most people praise Headway which rest at 3.3 and bad mouth TS which rest at 3.6+? Do TS cells sag much worse that Headway. I know TS only do 2C vs 10C from Headway. Watts are watts and I would much rather have 72V X 40A than 66V x 40A.

Who badmouthed TS? Resting voltage has nothing to do with cell quality whatsoever. TS sag more than an equivalent headway pack, that is what makes people badmouth them. Resting voltage has NOTHING to do with it. Look at a discharge curve, it tells you all you need to know. The voltage drop is huge at 5C, not even in the same league as headway.

I'd rather have a REAL 72V pack (24s) of 40Ah cells that I could discharge at 40A and know it'l stay right around 3V, than have a 20s pack of 40Ah cells that "look" like they're 72V off the charger, but sag down to 60V at 40A of discharge.

I'll take my 5kwh pack of headway over a 5kwh pack of TS any day, the voltage drop is much less for an equivalent pack. I'll be hitting 70mph while other people hit LVC on their cells because of voltage sag.

 

[Gordo]

removed

 

[frodus]

Beavinator, what have you found? How is your charger wired? Does it go through the BMS? Any more info?


Gordita,
You're getting way off topic.... which is why is his charger not fully charging the batteries, not discharge current, voltage sag, nominal voltage, how a BMS works, blah blah........

FYI, I used to work for EVComponents as their resident EE in Tech support (worked with batteries, BMS, chargers), now I test cells and help design packs (I work for Manzanita Micro and Elithion currently as well as contract for some customers that need help building or testing packs). You're talking a scooter in the neighborhood of what, a couple thousand watts and only a couple C? I'm talking about actual street vehicles over 20,000W. I've physically built packs using Headway, K2, TS, HiPower and worked with 3 different motorcycle companies testing cells and helping lay out the electrical system.

You don't say much about your setup, how many batteries in series/parallel, what Ah the batteries are, how many amps you're pulling on that hill, what C you're discharging at... 65V doesn't tell you jack.

my setup:
1986 Honda VFR700 motorcycle
160 Headway 38120S cells 32s5p (~5kwh, 40kw+ peak output)
DeltaQ 96V charger (116V peak)
AC20 motor/Curtis 1238-7501 controller
Elithion Lithiumate BMS

 

[Gordo]

removed

 

[frodus]

Please read my posts. I have already answered all of your questions.

How about you read my posts again since you can't remember anything I've actually said.

I am even more puzzled as to why with your vast qualifications, education and experience, you make errors in your statements as in the charging voltage of a TS charger is more than 3.7V per cell?

I'm puzzled why you can't read. I said:

Maybe the TS or CALB rebranded chargers actually cutoff at 3.7 or lower, but they state, on their actual datasheet for the actual cell 4.2V max.

The cell SPECIFICATION lists 4.2V as the charging voltage limit. I said that the chargers can be higher than 3.7V, in fact, I know quite a few people with cars, trucks, motorcycles that charge at 3.8V or higher, with a charger that is NOT a TS charger.

And you contradict the fact that many of my cells will sit at 3.62 volts for weeks after being off the charger. They do not rest anywhere near 3.3V until they have been discharged under load for an hour.

So what if many of your cells sit at 3.62V for weeks, sitting, with no load. Remember this:

3. It's called surface charge. All of these cells (TS, SE, headway, A123) are made as 3.3V nominal. You may take them to 3.65V, but it can actually take a bit longer for the charge to equalize within the cell to it's nominal voltage. It also depends on the size of the cell and how it's made. Prismatics may take longer than a cylindrical cell to equalize within the cell.

So it sounds like your cells (and it's a little hard to believe they can sit for "weeks" with such a high surface charge) actually keep that charge for a while (which I actually talked about)..... I said prismatics are different. Headways rest at 3.2-3.4V within 24-48hours from my experience (and I've played with over 400 of them so far). Remember, this thread is about headway batteries, not TS. Most of the TS I've been around (Much larger cells, 100Ah or larger) tend to rest between 3.3 and 3.5V within a few days of charging them with a single cell charger.

Some of your information may be correct & therefore helpful, but it is a little hard to know what is factual?

I mean, feel free to correct me Mr. Almighty battery guru, but I'm still not sure what you're even arguing, you can't even get your facts straight about what I have or haven't said.

Just stop, it's not being productive.

Beavinator,
Any update?

 

[icecube57]

I agree with frodus.. Its hard to believe that with your Lifepo4 that unless its a brand spankin new un-used and abused cell that it holds its float voltage. Unless you had the equipment to match cell by impedence and lot # its hard to get cell to sit at the same voltage. After 3.45 the internal resistance and cell capacity starts showing its head and voltages start skyrocketing. Just as easily as those cells go up they come down. I had a 24cell TS pack that was a pain in the ass to keep balanced unless it was constantly on the charger with balancers running to combat the self discharge demon. Within days I was sitting anywhere between the high 3.4s to the high 3.5s if it was left off the charger. Not many people go the extra mile and check all their cells but I made sure my cells had some type of monitoring. In my case 4 battery medics the the degree of misbalance on the slightest discharge was retarded to where it took 30 min to several hours to get back in balance.

 

[Gordo]

moved

 

[Spacey]

Lifepo4 discharge curve after the initial half a mile burn off is very very straight. In that a cell at 20% discharge and a cell at 35% discharge will both be at 3.3v because 3.3v is where they sit until they are nearly empty.

But when a cell is 5% out of balance with another cell it will suddenly shoot to 3.65v while the lower one is at a much lower voltage due to not being full yet.

 

[Gordo]

Lifepo4 discharge curve after the initial half a mile burn off is very very straight. In that a cell at 20% discharge and a cell at 35% discharge will both be at 3.3v because 3.3v is where they sit until they are nearly empty.

But when a cell is 5% out of balance with another cell it will suddenly shoot to 3.65v while the lower one is at a much lower voltage due to not being full yet.

From this piece of wisdom and the fact that I clearly see 3.35V on the graphs until you hit the knee, one can assume both my meters are accurate. So the remaining puzzle is how some of my cells will sit at 3.62V to 3.7V (and some won't) for weeks after being off the charger? Have you ever seen this or have I somehow got the only LiFePO4 cells in the world that don't quickly loose their "surface" charge and go to a resting voltage of 3.35 as others have found? 20 of my cells are 3+ years old and 3 are only 8 months old.
Thanks

 

[oatnet]

or have I somehow got the only LiFePO4 cells in the world that don't quickly loose their "surface" charge and go to a resting voltage of 3.35 as others have found?

Yes, Thundersky is a unique LiFePO4 chemistry, with a fully charged voltage of 4.2v and a resting voltage of 3.6v-3.7v. It is the only LiFePO4 chemistry that I know of that does not have a fully charged voltage of 3.65v and a resting voltage of 3.3v-3.4v. Comparing the voltages of Thundersky cells to other LiFePO4 is as specious as comparing voltages to Lipo Cells - they are different chemistries with different base voltages.

If you have been using a T-Sky charger/BMS, your cells would have charged to 4.2v each, and dropped back to a resting voltage of 3.6-3.7v. If you have been incorrectly using a charger that is designed for 3.65v LiFePO4, and not 4.2v Thundersky, then you have not been fully charging the cells, and there is no "float" charge to dissipate. This is not all bad news, because the top of a charge or discharge cycle does the most damage to cycle life, and it is usually just small amount of current, but the rise to 3.65v (Or 4.2v in the case of your T-Sky cells) tells us they are topped up. If you are getting enough WH from your pack without hitting LVC, then you are actually better off not fully charging them. The downside is that your cells will not necessarily be balanced.

-JD

 

[Gordo]

 

[oatnet]

The CanEV guy manufactured the adaptor plate I used in my '74 VW Bus conversion, quality Kit.

you make errors in your statements as in the charging voltage of a TS charger is more than 3.7V per cell?

Our Battery Guru Frodus was correct. T-sky used to be 4.2v peak charge, I did I quick lookup and now they advertise 4.0v, maybe that is the 3G cells, or another marketing gimmick.
BTW: Frodus thanks for all the advice you've shared over the years, from your wealth of technical knowledge, I know I have learned a lot from you. A lot of folks appreciate the Huge group buys you arranged here too. You have many freinds.

So Gordo I wanted to find out more about your pack, so I looked at some of your old threads. In this thread, you report:

And you contradict the fact that many of my cells will sit at 3.62 volts for weeks after being off the charger. They do not rest anywhere near 3.3V until they have been discharged under load for an hour.

But 9.5 months ago in this thread, you report:
http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=20665&p=302182

...Since new, I have had 3 weak cells that quickly go lower than the other 17. They drop to 2.7V when the others are all @ 3.2 to 3.4.
...I want to go for a ride so I decided to individually charge them to the level of the other 17 and was very surprised to find all 20 cells at 3.30V EXACTLY.
...After the second to the last charge I found all the cells at 3.35V after sitting all night.

...I plugged the charger in and when it quit, I immediately unplugged it and checked all the cells. They were from 3.65V to 3.85V.

...I have emailed them to check if it will handle the 40Ah TS cells as they actually put out 55Ah?

At what point did you notice that the behaviour of your resting voltage had changed from what you reported in the first 3 excerpts?

Also, in the 4th excerpt, if your cells were charged to a mix of 3.65 and 3.85, the aggregate voltage would be higher than the 72.6v you are seeing on your charger.

In the 5th excerpt, if you were reading 55ah discharged from a 40ah T-Sky cell, that has not been my experience, I'd speculate whether your meter (CycleAnalyst?) is accurately calibrated to your shunt.

-JD

 

[Gordo]

Moved as requested.

http://www.endless-sphere.com/forums/viewtopic.php?f=10&t=28783&p=415143#p415143

 

[frodus]

why don't you start your own thread and we can chat about TS cells, you've completely thrown this posting off topic. Start a new thread, this is the for sale thread....

We came here to talk about his headway cells and you keep wanting it to be all about you and your cells, which Oatnet and I have pointed out are different chemistry.

And Beavinator hasn't posted again, I'm wondering what he found out?

 

[999zip999]

Are there T.S. cells in a headway pack of 24s and how many ?