Headway Pack Builders thread

you should not have any reason to need to monitor the cell voltages any more. once they balance, they will stay balanced. it is usually just the first few cycles where they are out of balance.

if they are .1% out of balance and you use up 7Ah then that is 7mAh or about (7/182)x60=2.3minutes to balance. and all the off cells will be balancing at the same time too so once it has settled into its permanent state, the charging will be very efficient.

adding more cable increases the chance of a short eventually too, and if it was a ribbon cable tied directly to the cells then they could discharge outside of the BMS control so that is too big a risk. imo

mondo monday! you can get the smaller soap tubs with a locking lid to keep out the rain.

i have some cedar paneling, 5/16" thick i may use for a frame, but now i am thinking i can also use up some of my old linoleum i saved from putting some in the bathroom in my shed. ineed to build a 12S headway/ping BMS to go with the E-Bikekit.com 36V10Ah lifepo4 pack i have too. wanna be able to get to 72V.
 
you should not have any reason to need to monitor the cell voltages any more. once they balance, they will stay balanced. it is usually just the first few cycles where they are out of balance.
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Unless one fails, it won't balance, and it'd make it super simple to measure to see if one is bad. Sure he could increase the chances of a short, but that's why you make sure that doesn't happen.
 
What I was thinking was to nick the insulation near the BMS connector and solder on 1/8 watt 1K resistors with wires extending to a shrouded DIP header (ATI connector from old computer motherboard, easy to buss with a stock 2 pin jumper), with heatshrink over each resistor and connections. Worst case short on that external connector would pull only 25 ma.
 
Haven't hooked up the BMS yet. Used a hole saw on a plastic cutting board. 1.5" hole on one side, 1.375" on the other side. Needed to dremel out the 1.5" side a bit though to get the batteries to fit well.

batteryf.jpg
 
Nice. Julesa, what did you use for those connection bars?
 
patrickza said:
Very neat looking Jules, what are you using it for. I count 30 cells rather than the usual 24 or 32. is it a 15s2p?
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Thanks! Yeah, there are another two cells on the far end, it's 16s2p. I have a couple 9C kits from Ampedbikes, this is the first pack of two.

Jay64 said:
Nice. Julesa, what did you use for those connection bars?
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3/4" copper pipe, cut into sections first, then cut lengthwise, opened and flattened with pliers and a hammer, then I took a grinder to the edges to remove the sharp bits.

The plastic frame was pretty labor intensive, mostly because I don't have very good tools for the precision needed, just a cordless drill with a hole saw. The cells are each separated by about 1/16", and each hole in the plastic narrows in the last 1.8" to keep the cells from poking through.

I was thinking for the next one, I might skip the plastic frame and just buy a bunch of foam tape. Originally I was going to use the sticky-on-both-sides foam tape, but then I decided that would be a mess if I managed to kill a cell down the road. My wife suggested buying foam tape that's just sticky on one side, and wrapping it around the ends of each cell. Should keep the cells from rubbing against each other and shorting when the plastic wears through, and still allow a little airflow between cells. Not that I'm expecting then to heat up much with what I'm using them for. On the downside, the tape won't look as cool. :)
 
I just did a 3 mile ride with the first balanced 12 cell 10AH pack. 39.8 volts at start, 39.2 at end. Opened it and found all cells at 3.30 or 3.31. Charged with the 2 amp bionx charger which cut off after 70 minutes with 110WH on the killawatt meter. All cells at 3.4 volts except for one 3.38.

That might be enough for routine use. So it appears the boinx charger, which cuts out at 41.8 volts, will work after all once the pack is balanced. Then use the 43.7 volt supply as needed for topping off the balance, with 5 ohm series resistor to limit current to ~100 ma through the BMS shunt resistors.

Now for a longer ride...
 
frodus said:
recount

7 rows of 3, and 2 in the last one, that's 32.
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The last two were in hiding, but at least I counted all 10 rows or 3 :lol:
 
julesa said:
I was thinking for the next one, I might skip the plastic frame and just buy a bunch of foam tape.
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Nah, changed my mind. It would be easier, but... I'm obsessive. :mrgreen: Might as well get rid of the zip ties too, those have been bugging me. Think I'm gonna replace those with threaded rod and nylocks.
 
I like VHB. Use it for securing solar panels to aluminum roofs at 60 mph.

It might be a pain to change out a cell though.
 
Hal, can't help to notice big metal watch on your hand as you were holding the cells. Must be useful in shorting things ;)
On a more serious note, what are the typical cases used for these packs?
Trying to find something that would just fit has not been to easy so far
HAL9000v2.0 said:
I did it with foam tape...
It is 3M VHB tape.
Click to expand...
 
I took some photos of the copper work to show how low tech it can be. One-pound copper flashing is great to work with, cuts with scissors with minimal risk of skin laceration.
View attachment cutting_straps.jpg
It is easy to form in a vise, and a jig allows for accurate holes.
View attachment drilling_straps.jpg
A belt sander makes fast work of rounding the corners.
View attachment sanding_straps.jpg
A butane torch is useful for initial soldering, then a smaller iron can be used for soldering wires to the stub.
View attachment soldering_straps.jpg
Because of the U, the hole spacing can be adjusted using hand pressure. I measure 1 millivolt drop across each strap at 1 amp = 1 milliohm DC resistance, and the flat geometry should also give minimal AC reactance.
View attachment top_view.jpg
After ~50 km one of the cells cracked the bottom acrylic cover, so I have added sticky foam to keep the cells from hammering it on bumps. A sideways orientation might be better on the cells, but this way there is now some damping.
View attachment foam_padding.jpg
 
Hello
I am trying to lay out a battery box while the batteries are on there way,
does anybody out there have the dimsions of the headway blocks and the length of 38120s cell with the blocks installed
Thanks
 
Quick question for you headway pack builders out there.

I built a 10ah 36volt pack with 12s headway 38120s batteries (pictures and how-to video forthcoming). I have been riding with it for a few days all seem good.
I am charging with a 43.8volt LifePo battery charger. Never-the-less i am monitoring cell voltage until the pack is "broken in" for lack of a better term.

After the initial charge sequence pack is at about 41volts at which point the charger moves into a trickle phase where it slowly gives the pack juice then lets it balance at bit, then more juice etc.

When i monitor the individual cell voltage i notice that the first cell (B-) and the 4th cell (from the negative side). Are reading around 3.8 and even 3.9 volts (which is a bit above the 3.65 max of the specs). Now this balances out fairly quickly if i unplug the pack and let it balance.

Should i be concerned about this charge in these two cells even though its only temporary and bleeds off?
Why would it only be these two cells?

everything seems to be working properly and the pack ends up balanced in the end. I am just afraid to leave it on for too long which means i top out at about 41 volts for the pack.
any thoughts or suggestions would be much appreciated.
thanks!
 
enso said:
After the initial charge sequence pack is at about 41volts at which point the charger moves into a trickle phase where it slowly gives the pack juice then lets it balance at bit, then more juice etc.
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The charger is cutting off on it's own, or the BMS is disconnecting the pack? What is the trickle current when it is on?
When i monitor the individual cell voltage i notice that the first cell (B-) and the 4th cell (from the negative side). Are reading around 3.8 and even 3.9 volts (which is a bit above the 3.65 max of the specs). Now this balances out fairly quickly if i unplug the pack and let it balance.
Click to expand...
I had the same behaviour. At 130 milliamps the 20 ohm resistors in the Headway BMS can hold the cells to within a couple of millivolts of 3.65. At 300 milliamps the voltage across fully charged cells goes up, and at 3.9 on any cell the pack is disconnected. The shunts continue to operate for tens of seconds till the cell goes down to 3.65, then the pack is connected and the cycle repeats.
Should i be concerned about this charge in these two cells even though its only temporary and bleeds off?
Why would it only be these two cells?
Click to expand...
Well presumably those are the fully charged cells, and it can't be good for them. I put a couple of 5 ohm resistors and an ammeter in series with the charger and use an alligator clip to tap the string to get ~100 milliamps. As the cells come up the current drops and I move to the next tap. It took about 30 hours to balance that pack (the lower one below) The next pack had one fully charged cell to begin with, so I clipped a 10 ohm resistor across it and charged at 300 milliamps. As the other cells came up I clipped them too. It only took 10 hours to balance that way, but the ATTiny85's were set to shunt at 3.55 volts (the upper pack below).View attachment Balancing_with_ATTiny85s.jpg
 
Dak,
Thanks for getting back, LOL I saw your post about this issue on another thread so I'm glad its you answering. (by the way i love your cedar boxes was going to go that way but i opted for the easy way out a plastic tool box).

I'm on hold for a bit as far as answers go because as a total NOOB, i fried my multimeter while probing, (forgot to switch it to Ammeter side that can handle 10amps now it says random numbers, either that or i have 50volts running out my fingers.)

I am not sure whether it is the Charger or the BMS that switches. Basically charger runs for a while (ie red light charger function and fan) then the light turns green and it stops and every few minuets its turns on again for 10sec bursts). Perhaps the BMS is tripping it because of the high cells. As soon as i get a new multimeter ill test the amps. For clarification you put the ammeter in series with the charger, does it matter polarity side it is in series with? I think i'll have to get fatter alligator cables because the ones i have are like 18gauge or smaller and might not handle the juice (it says 5amp charger perhaps thats only when its fully on?).

As you can tell, i'm no electrical engineer I know just enough to be dangerous. :p
If there are other places that need measuring ie across shunt resistors please be specific. I've already fried one BMS (or at least a mosfet on it), in my learning curve, and now that things are working fairly well don't want to jink it. Everything seems to discharge well and the bms seems to balance after a bit so... By the way what sort of voltage sag do you experience with these packs? I am running a tidal force 750x so at full bore I am pulling serious amps but the Sag seems big to me perhaps it is because i have yet to be able to fully charge the pack for fear of damaging those 2 cells. (on some hills the volts are saging down to just over 30v which is where the Tforce electronics cut out to save the batteries).

I sort of understand your tapping technique but not enough to try it yet any diagrams or further explanation would help. the ATTiny85 are the bms chips? I do not have a Headway BMS, I sourced my Batteries and BMS from Joe at Kennedy Alternative Energy. not sure what the shunt voltage is on the BMS but i will ask.

So after you did the 10hour balance, has the pack stayed balanced so you can charge normally now or do you have to make a science experiment of every charge cycle?

Thanks again for your help
 
enso said:
I'm on hold for a bit as far as answers go because as a total NOOB, i fried my multimeter while probing, (forgot to switch it to Ammeter side that can handle 10amps now it says random numbers, either that or i have 50volts running out my fingers.)
Click to expand...
Buy two more, dedicate one for amps and tape the probes so your fingers will know the difference.
I am not sure whether it is the Charger or the BMS that switches. Basically charger runs for a while (ie red light charger function and fan) then the light turns green and it stops and every few minuets its turns on again for 10sec bursts). Perhaps the BMS is tripping it because of the high cells. As soon as i get a new multimeter ill test the amps. For clarification you put the ammeter in series with the charger, does it matter polarity side it is in series with? I think i'll have to get fatter alligator cables because the ones i have are like 18gauge or smaller and might not handle the juice (it says 5amp charger perhaps thats only when its fully on?).
Click to expand...
I wouldn't worry about the alligator clips, generally the more resistance the safer the circuit. If the wires don't glow within a few seconds they are probably safe long term. If the meter misbehaves try switching the polarity.
IANAL and YMMV of course :)
If there are other places that need measuring ie across shunt resistors please be specific. I've already fried one BMS (or at least a mosfet on it), in my learning curve, and now that things are working fairly well don't want to jink it. Everything seems to discharge well and the bms seems to balance after a bit so... By the way what sort of voltage sag do you experience with these packs? I am running a tidal force 750x so at full bore I am pulling serious amps but the Sag seems big to me perhaps it is because i have yet to be able to fully charge the pack for fear of damaging those 2 cells. (on some hills the volts are saging down to just over 30v which is where the Tforce electronics cut out to save the batteries).
Click to expand...
Well I have yet to trigger any Headway BMS cutout. Worst case I run 160 seconds WOT up a 7% grade at 20kM/H, and have no particular need to boost the performance. That is somewhere around 30 amps from the pack.
I sort of understand your tapping technique but not enough to try it yet any diagrams or further explanation would help. the ATTiny85 are the bms chips? I do not have a Headway BMS, I sourced my Batteries and BMS from Joe at Kennedy Alternative Energy. not sure what the shunt voltage is on the BMS but i will ask.
Click to expand...
Back when I was spending a great deal of grant money I wouldn't buy anything that didn't come with a schematic diagram. However vendors have become increasingly reluctant to provide such details.
Code: 
                              +--------------------> Ammeter -------> Battery plus
                              | <----Alligator clip tap
Charger +  ------\/\-----\/\-----\/\------\/\-
                5 ohm   5 ohm   5 ohm    5 ohm 
Charger - ----------------------------------------------------------> Battery minus

So after you did the 10hour balance, has the pack stayed balanced so you can charge normally now or do you have to make a science experiment of every charge cycle?
Click to expand...
I don't have to, but I find it kind of interesting. The first pack, charged with the Bionx "36 volt" (41.8 max, NiMH) charger to ~3.5 volts per cell, has stayed in <10mV balance after eight cycles. My daily ride is 20km and 200WH, and up to now the Headway BMS has just been a reassuring parasite.
 
The pack I am building is a 20s1p Headway configuration to attain 60V (if you consider per cell to be 3V, which they r not)..

The pack will have a BMS capable of 45A Continous and 90A burst (slightly under the limit of the headway cells), which is good as it assist in squeezing more cycles before I reach 80% capacity point.

The pack will sit in a clear 0.5 cm plexi-glass. If the casing seem inadequate, I will make a aluminuim casing for it.

The picture below illustrates How I started building the pack

The batteries out of the box
p1020876f.jpg


Will I either use this shape? with four rows, with a small gap for BMS? OR..
p1020898y.jpg


This pack with Slightly more length, but will help in keeping the ceter of gravity a bit low :p
p1020900d.jpg


Starting to Hot Glue the cells together
p1020902t.jpg


Adding more cells, using a metal bar to keep things straight :S.. METAL :O! good thing I didnt go about shorting stuffs :twisted:

p1020903a.jpg


Packed of Hot Glue (just incase someone is thinking which glue I am using :p )
p1020906ky.jpg


Finally all cells joined in nicely :)
p1020909f.jpg


Adding some Foam tapes for stopping the batteries to get bashed inside the plexiglass box that I plan to make

p1020910.jpg


A side view again, btw dont under-estimate the potential of those tapes :) AND THE HOT GLUE.. I had to pry one cell out when someone had put it in the wrong direction by mistake

p1020911d.jpg


The Plexiglass box should be done by monday..

Btw, this BMS is a 16Cell BMS.. I am waiting for my 20cell BMS from Kennedy, which will arrive next week
 
kadir said:
Finally all cells joined in nicely :)
p1020909f.jpg
Click to expand...

Nice looking pack, kadir!
Could you tell me how wide the pack is with the cells staggered like that? I'm wanting to know if it would fit between the pedals in that configuration.
 
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