Headway Battery sag

[johnnyz]

Ok ive had numerous posts on this forum and heres the latest. I have a trike with 27 headway batteries wired serially ( I had 28 but when torquing down the bolt twisted the negative cap and although still working I dont trust it). These cells I got last summer and have about 2000 kms on them. I have not run a BMS but have bottom balanced them. When the highest cell is fully charged (around 3.7 volts), the lowest is around 3.45 volts and most others around 3.5-3.6 volts. I have a Crystalyte 18 Fet controller pulling a max of 60 Amps. Under full throttle it will sag down to about 75.8 volts from a nominal full charge of 89.5. I have split the pack into one 48 volt and one 44 volt pack so that I can use the Satiator to charge each. Each pack is connected using 8 gauge wire.

There appears to be so little usefull information on these cells especially under performance...this sag as a percentage represents 16% sag. The trike weighs 120 lbs and Im 175 so total weight of around 300 lbs.When cruising at around 40 kph using maybe 8 -10 amps it only sags to about 85 volts. Does anyone have data to support that this is too much sag or acceptable?

Thanks

John

 

[wesnewell]

There's lots of specs on their website, including how much they sag under different loads from 1-20C. At just a 1C load, they sag down to ~3.25V per cell. For a 27s pack, that would be 87.75V from a full charge voltage of 97.2V. If you're only charging to 89.5V, you are a long way from a full charge, although the voltage sag will still be about the same percentage wise. Their 15ah cells sag even more.
http://www.headway-headquarters.com/lithium-lifepo4-cells/

 

[johnnyz]

There's lots of specs on their website, including how much they sag under different loads from 1-20C. At just a 1C load, they sag down to ~3.25V per cell. For a 27s pack, that would be 87.75V from a full charge voltage of 97.2V. If you're only charging to 89.5V, you are a long way from a full charge, although the voltage sag will still be about the same percentage wise. Their 15ah cells sag even more.
http://www.headway-headquarters.com/lithium-lifepo4-cells/

Ok digging a little deeper, on this site i see that some other lifepo4 cells had sagged to under 2.5 volts at 4C http://evtv.me/2010/07/4c-lifepo4-power-tests/....actually the best cell was 2.25 volts...so if you take my sag of around 74 volts / 27 cells thats an average of 2.7 volts at 60 amps which is 4 C for the 15 Ah Headway cells. The reference you gave me doesnt show any data on these cells especially when it comes to testing, just price. Maybe I missed it?


John

 

[wesnewell]

You missed it. Assuming you have this cell;
http://www.headway-headquarters.com/38120s-10ah-headway-energy-cell/
Click on the boxes below the picture of it for specs. The third box gives a discharge curve.

 

[dogman dan]

The way you are beating them with a huge club, the sag sounds about normal to me.

Measure sag from the current state of charge though, not what you charged them to. You'll lose several volts in the first few blocks. That's normal for lifepo4. It shouldn't be that bad at 10 amps cruise, from whatever resting voltage is at that moment. Most likely you only see about 2-3v of sag in cruise mode.

 

[johnnyz]

The way you are beating them with a huge club, the sag sounds about normal to me.

Measure sag from the current state of charge though, not what you charged them to. You'll lose several volts in the first few blocks. That's normal for lifepo4. It shouldn't be that bad at 10 amps cruise, from whatever resting voltage is at that moment. Most likely you only see about 2-3v of sag in cruise mode.

Beating them with a big club?...lol...60 amps is 4 C and well within the parameters ans specs...60 amps only occurs for a brief time perhaps 2-3 seconds as the amps taper off. You right about cruising.. 40 kph uses about 8 amps and that equates to about 85-84 volts. Yes, the voltage usually drops a volt in the first 5 mins and equalizes..

This is why I think thee cells are over rated..they sag quite a bit and then when your through half of the SOC they sag even more..alot actually...

John

 

[johnnyz]

You missed it. Assuming you have this cell;
http://www.headway-headquarters.com/38120s-10ah-headway-energy-cell/
Click on the boxes below the picture of it for specs. The third box gives a discharge curve.

Ok i found it...lol..pure rubbish...outright lie. I had the cells from new and they are sagging the same as when new...If I take one cell and discharge it from fully charged with 1C , thats 15 amps it will sag alot...down to about 3.15 volts.

John

 

[wesnewell]

Well that's not far from what the curve shows for the 15ah cells. Looks about like 3.2V to me. The 15ah cells sag more than the others do.

 

[johnnyz]

Well that's not far from what the curve shows for the 15ah cells. Looks about like 3.2V to me. The 15ah cells sag more than the others do.

First off the specs on voltage sag vs load is a bunch of rubbish. If I give my 15 ah headway cell pack a 15 amp load (1 C) on a full charge, they will sag (from currently a full charge of 27 cells x 3.3 volts=89.1) to about 84 volts , thats about 3.11 volts and they have done this since they were new. You say they sag more than the other cells...that doesnt make sense to me...are you saying that a 15 Ah headway cell given a load of 15 amps will sag less than a 10 ah headway cell given the same load??....explain...

John

 

[riba2233]

Yes, they do sag like shit, I was very happy once I got rid of them :lol:

They should be rated as 2 C cont, 3 C peak and that's it! I don't know why are they even so overhyped, they are expensive, large, and heavy.

 

[johnnyz]

Yes, they do sag like shit, I was very happy once I got rid of them :lol:

They should be rated as 2 C cont, 3 C peak and that's it! I don't know why are they even so overhyped, they are expensive, large, and heavy.

So your saying this is normal for these cells?...whats a viable replacement (Lifepo4)??

John

 

[riba2233]

Yeah, unfortunately it's normal. Only lifepo4 of which I know that is better are a123 and calb...(newer - liyuan?). But why limit yourself to this dinousaur chemistry? Buy some of new generation cells with much better chemistry, NCA.

 

[johnnyz]

Yeah, unfortunately it's normal. Only lifepo4 of which I know that is better are a123 and calb...(newer - liyuan?). But why limit yourself to this dinousaur chemistry? Buy some of new generation cells with much better chemistry, NCA.

Dinosaur chemistry?...ok...tell me something I dont know...there is something better out there (NO im not going to even consider lico)....Tesla uses Lithum Ion, and I would assume the company is at the forefront as far as battery technology is concerned, but hey if theres something else I havent heard about??


John

 

[riba2233]

Yeah Tesla uses NCA. Its Li-Ni-Co-Al, not only Li-co which is used in polymer cells. They use 3C nominal cells, but you can find NCA cells with higher nominal discharge rate

Lifepo4 is dinousaur because it's 2-2.5 times heavier, and 3-4 times larger for same capacity and C rate, and also around double the cost.

 

[wesnewell]

My current 10ah 24s 888wh rd lipo pack cost me $275 and is almost 3.5 years old with over 13K miles on it. After a year or more and ~5K miles on it it sagged ~3.5V total with my 270 lbs and at a 4C load. When i first switched to lithium, people here tried to talk me into lifepo4. I researched it and found it to be worthless for ebike use unless you built a huge ah pack which wouldn't even fit on the bike good. That's one reason I went with rc lipo and have never regretted it.I keep looking for something better, but still haven't found anything yet at a similar price. NMC, NCA, and all the newer stuff still doesn't cut it imo. And it all cost a heck of a lot more than rc lipo and I don't want to wire 100 flashlight batteries together anyway, when I can throw a 24s rc lipo pack together in a few minutes.

 

[johnnyz]

My current 10ah 24s 888wh rd lipo pack cost me $275 and is almost 3.5 years old with over 13K miles on it. After a year or more and ~5K miles on it it sagged ~3.5V total with my 270 lbs and at a 4C load. When i first switched to lithium, people here tried to talk me into lifepo4. I researched it and found it to be worthless for ebike use unless you built a huge ah pack which wouldn't even fit on the bike good. That's one reason I went with rc lipo and have never regretted it.I keep looking for something better, but still haven't found anything yet at a similar price. NMC, NCA, and all the newer stuff still doesn't cut it imo. And it all cost a heck of a lot more than rc lipo and I don't want to wire 100 flashlight batteries together anyway, when I can throw a 24s rc lipo pack together in a few minutes.

Ok...still going strong after 13k miles??? wow...that is impressive...my concern is the safety factor..I can builda metal enclosure for the batteries in case something goes wrong..tell me that they are safe..safe how?...when Ihear stories of fires and the like, is this the resut of people making mistakes (over charging, over-doscharging etc) or is the nature of this battery chemistry inherently unsafe?.. You said t sagged a total of 3.5 volts...what was the total voltage?...if I wanted to replace what I currently have (92 volt 15 ah) pack what would be the best way of doing that going the RC route?

Thanks

John

 

[wesnewell]

How safe they are will depend on you. Don't over charge or over discharge and they shouldn't be a problem. But like any battery, do something stupid and you could have a fire. When I tested the sag, they were charged to ~96V iirc. This 10ah of 24s 20C cells rated for 200A that I normally full charge to 100.8V. I didn't pull more than 40A from them. Normally I don't go below about 20% soc and with my lvc set to never go below 10% soc. I just use a volt meter to monitor the voltage. Set LVC to 3.5V per cell and you'll never go below ~4% soc. I've got mine set to 3.65V per cell. How safe are they?
https://endless-sphere.com/forums/viewtopic.php?f=14&t=27241

 

[riba2233]

Forget about lipo now that NCA costs very close, and it's like million times safer. No need to risk your house, EV, whatever. NCA costs slightly more, but lasts more so it's effectively not much more expensive.

 

[johnnyz]

Forget about lipo now that NCA costs very close, and it's like million times safer. No need to risk your house, EV, whatever. NCA costs slightly more, but lasts more so it's effectively not much more expensive.

Give me an example of this chemestry....a link?

John

 

[Hillhater]

Do some more research.
look for Samsung, Panasonic, or LG 18650 cells.
or, look at used Nissan leaf modules or similar large EV pouch packs
..it just depends on your particular priorities, capacity, power, weight, cost ...its all a compromise.

 

[riba2233]

Forget about lipo now that NCA costs very close, and it's like million times safer. No need to risk your house, EV, whatever. NCA costs slightly more, but lasts more so it's effectively not much more expensive.

Give me an example of this chemestry....a link?

John

High rate:

http://eu.nkon.nl/rechargeable/18650-size/samsung-18650-inr18650-25r.html

http://eu.nkon.nl/rechargeable/18650-size/samsung-inr-18650-30q-3000mah.html

http://eu.nkon.nl/rechargeable/18650-size/lg-18650-hg2-3000mah-20a.html

3C:

http://eu.nkon.nl/rechargeable/18650-size/panasonic-ncr18650pf-3-7v-2900mah.html


Topic about high rate cells:

https://endless-sphere.com/forums/viewtopic.php?f=14&t=57291

NOTE - sony vtc5 and lg he2 are NMC chemistry, not NCA

 

[wesnewell]

Rated for only 8C, I don't consider any of those as high rate cells. I use 20C rated rc lipo and don't even consider that high rate.
http://lygte-info.dk/review/batteries2012/Common18650comparator.php

 

[kiwiev]

Where are you from John?

There are some cheap 18650 packs in Aldi Australia ATM they are 20 volt 2ah packs and have Tabs spor welded on so you could buy a few link together.

Also I have a headway pack in my gaint trance it doesn't sag much 22 cells 10 ah I can draw 75 amps with not much sag, temperature is the biggest killer they sag 20% easy in the winter tripping the BMS hot off the charger.
Cheers Kiwi

 

[johnnyz]

Where are you from John?

There are some cheap 18650 packs in Aldi Australia ATM they are 20 volt 2ah packs and have Tabs spor welded on so you could buy a few link together.

Also I have a headway pack in my gaint trance it doesn't sag much 22 cells 10 ah I can draw 75 amps with not much sag, temperature is the biggest killer they sag 20% easy in the winter tripping the BMS hot off the charger.
Cheers Kiwi

Thanks for all the responses...Im from London

It now seems that something somehow has drained 8 of my headways to below 2 volts..the worst being 1.4... I did a drive last night and pushed them a bit more than I usually do, thinking though that they would all reach the same voltage due to the bottom balancing procedure..but they completely discarged all over the map..some were at 2.5 volts others were 2.8 some 3.2...the lowest one was 2.3 volts so I left it for this morning..I checked them and they drained down..8 of them to below 2 volts, and the cells on the other side were actually higher..all 3.25 volts..it seems either the Battery Medics (that were attached) somehow drained the cells or somehow i dont know how they got drained from the other cells.....

Im trying to revivie these cells...with a nice .02 amp charge from my Imax....ive done it before, Im hoping they will take a good charge since they were not drained to this critical level under lots of load...what a bummer...

John

 

[Hillhater]

..... . When the highest cell is fully charged (around 3.7 volts), the lowest is around 3.45 volts and most others around 3.5-3.6 volts..

This is the root cause of your problems....unbalanced cells.
those Headways have such a flat discharge voltage curve profile, that the difference between a 3.7v cell and a 3.45v cell could be 80% of capacity. !
..IF they come back to life, ...try top balance for a change . :wink: