Yet another custom battery pack

[OleTC]

I can cruise 6 km as a max. on my cheap noname EU with a nominal 132 Wh battery-pack. I opened the battery-pack wrap and found that the cells, allthough

apparently good quality Samsung 18650 cells, are obviously second hand. Discoloured from glue, with holes in the wrap and smeared printing. All

indications of these being taken out of worn laptop batterypacks.

I charged the pack fully and connected it to a 51 Ohm resistor in series with an ampmeter. Then took readings every 2 minutes 'till the BMS suddenly cut

the connection to protect the cells from being overly discharged.
Starting value said 63,3 Volts and discharging dropped the voltage allmost linearly down to 55 Volt. Then it started to drop at an increasingly faster

rate. Next it soon reached 45 Volts, at which time the BMS cut the connection. This is equivalent to about 2,8 Volts over each single cell.
I conclude, that the useable range is from fully charged, down to about 55 Volt, so I drew a curve with time out the horizontal axis and current out the

vertical axis, on squared paper. Counting the number of Squares in the area below the curve summed up to a total of just below 70 Wh. This is what I

consider usable energy in the pack. There might even be less, since it took 68 minutes to reach the 55 Volt level and I never were able to ride more

than 48 mins. on a charge. Higher drain will mean lower available power.
Comparing this to what others have stated about range, compares well. It seems that I can cruise 1 km in smooth terrain, using 11,7 Wh per kilometer.
Not in any ways a scientific measurement described above. Just an indication. Seems to be in the ballpark, though.

Next up is building a replacement battery-pack, using a BMS for a Solowheel, rated max. 15 Amps of discharge current, before the protection cuts the

battery off. My motor will never reach this level of drain, so I should avoid the mod that hobby16 has described and still have the short-protection of

the MOSFET transistors available. If I have understood everything correct.

http://www.aliexpress.com/item/16S-unicycle-lithium-ion-battery-BMS-60V-li-ion-battery-protection-circuit-board-for-solowheel-battery/32256690244.html

The cells will probably be 16 pcs of National 18650B's, which I understand is the state of the art today.
In theory it should give 204 Wh of available power but my guess is, it will be closer to 175 Wh for a fresh pack.
This is still pretty good and will - again in theory - allow me to cruise distances of about 15 km on a charge.

 

Stay tuned for updates. It WILL take some time to reach completion. If I reach the goal.

[dmethvin]

I can cruise 6 km as a max. on my cheap noname EU with a nominal 132 Wh battery-pack. 

That definitely seems on the low side. I get 6.5 to 8km on a charge on my noname before it gives me the fast-beeping battery warning. But it sounds like they cheated you by saying they were "Samsung cells" but didn't say they were used cells. 

Starting value said 63,3 Volts and discharging dropped the voltage allmost linearly down to 55 Volt.

Even that seems low, my pack is 67 volts fully charged (it's Sony cells tho).

Next up is building a replacement battery-pack, using a BMS for a Solowheel, rated max. 15 Amps of discharge current, before the protection cuts the

battery off.

Really interested in your work there, to see if maybe it's possible to build an even better pack!

[hobby16]

Comparing this to what others have stated about range, compares well. It seems that I can cruise 1 km in smooth terrain, using 11,7 Wh per kilometer.

Not in any ways a scientific measurement described above. Just an indication. Seems to be in the ballpark, though.

.

Absolutely, I do confirm with my data (bike computer for counting km and a "charge doctor" for counting Wh). I have about 11 to 13 Wh/km, taken on many 10km trips (5km round trip), for 65kg at tyre pressure = 3 bar.

Interestingly, that ratio doesn't change much wether I ride at very "high" speed (up to 22km/h mean speed, so with many peaks at 28km/h, yeah, my Firewheel rocks!) or at much lower speed (around 12km/h mean speed).  Whatever the riding conditions, I get around 24km distance on my fully charged 260Wh Firewheel. BTW, I can easily test the maximum distance since I have a mobile charger : when the wheels stops because of empty battery, I plug in my mobile charger and I restart again (at reduced speed), no more "range anxiety" syndrome. More on it later.

 

 

 

Next up is building a replacement battery-pack, using a BMS for a Solowheel, rated max. 15 Amps of discharge current, before the protection cuts the

battery off. My motor will never reach this level of drain, so I should avoid the mod that hobby16 has described and still have the short-protection of

the MOSFET transistors available. If I have understood everything correct.

http://www.aliexpress.com/item/16S-unicycle-lithium-ion-battery-BMS-60V-li-ion-battery-protection-circuit-board-for-solowheel-battery/32256690244.html

It's stated as a "Solowheel BMS" but I highly doubt it, Chinese vendors can be very sloppy and even deceitflul as to their product page.

Theorically the BMS doesn't cut power before the wheel warns you of low battery. Theorically.

But in reality, it can cuts for many reasons, low temperature, high internal resistance, voltage drop because of high current drain in an acceleration or a steep climb...Even a cell defect would trigger a cut-off which is totally crazy for a monowheel. So if I were you, I would shunt the BMS, it's NOT avoidable.

A short-protection or low-voltage protection SHOULD NEVER EXIST on a monowheel's BMS, period. The highest priority must be user's protection, which is incompatible with a battery protection. Who cares about short-protection if it costs you a broken arm ?

A correct monowheel's BMS should be like the latest ones from Gotway : with the raving crazy stupid short-protection circuitry removed alltogother. There is no way to do otherwise, if there were, I would like to know.

 

BTW, from what I know, the stated nominal capacity of noname batteries from wheels clones is often untrustworthy so if it were of some solace, your case is quite commonplace. On my X3-clone, I have a 132Wh nameplate, but only 110 Wh real . On my TG with 132Wh name plate, it's worse, only 90 Wh real. On the other hand, on my Firewheel, the battery is 260Wh nameplate and I can charge up to 280Wh, but it's Firewheel.

 

Don't want to rock your boat but you must know it's difficult to make good battery blocks if you don't have a lot of cells to sort and pair them by capacity. That's what manufacturers do even with brand new cells. Well paired cells required few or even not at all "equilibration" discharge and they age uniformously and gracefully.

If you go ahead anyway, please give us news, it would be interesting to know.

[MetricUSA]

Wow, thanks for sharing, it is good to know what shady practices might go on, selling 'new' eu with used batteries, and at times premium prices....Why must Chinese Businesses go to such gross lengths to cheat their own consumers? I wish they would take more pride in their work, makes all the more 'hated' praise of them. And more 'hated' praise of any American company using Chinese companies...

[OleTC]

Thank You for the replies. Feedback is very valuable and there are good points made.

 

As for the noname Wheel I bought, I had a feeling that the seller had been cutting some corners here and there and was prepared for the worst. The EU has actually, with a few ajustments,  turned out to be very reliable and unproblematic to ride - within its limits! It also creates good attention by most people who sees the 'magic wheel'. You've recognized that Youself, no?

 

A fix I did, was to take the Shells of and glue the magnets inside them, that hold the pedals in place, to the Shells on each side. They were simply attached with a small string of tape and had been attracted by the axl (iron). A sloppy production detail. Now the magnets stay whre they're supposed to be. The footplates stay up and I also have glued a felt floor-protection pad on the outside of the Shell, to dampen the massive 'klonk' when the pedals were raised and hammered on to the Shell. Works nice. Small detail that gives just a bit more luxurious feeling in operation.

 

As for the batterypack, I'm planning - I know this is probably not a BMS for a Solowheel. The Solowheel uses a different battery-type LiFe-something which would probably require different properties of the BMS.

This one is likely intended for LiPo-cells but maybe with a higher allowable discharge current.

 

I don't know how well the cells are supposed to be matched. I have noticed that the BMS on my noname EU Works well. I measured the voltage over each single cell a couple of times during the discharge and they were absolutely uniform. I mean same voltage, spot on! So even though theory dictates matched cells, I believe, I can get away with it.

As long as I sort out cells that are outside the manufacturer specs.

The Panasonic specs of the 18650B's say 3400 mAh nominal capacity per cell, with a minimum capacity of 3200 mAh. So I plan to buy 16 pcs, charge each of them and measure the capacity during discharge. If any falls outside, it will be returned to seller. The Panasonic cells are japanese production cells and have a very good rumour as for quality control. So hope I get genuine Panasonics.  

I follow my gut-feeling here but time will show if I'm right or wrong.

 

The point that I'm concerned about is, that assembling the board requires spotwelding of nickel-strips to each cell. So I have to build my own spotwelding device and Work up the handycraft to make reliable welds, without melting Down the poles of the cells.

 

I have the BMS and the nickel -strips. Also have a transformer out of a discarded microwave-oven, with just the primary Circuit in. And 40 mm^2 of insulated wire for making the secondary Circuit. Let's see if I can pass this hurdle. Will make a few practice welds before I actually order the cells. Can practice on aluminum beveridge-can metal and bits of nickel-strips.

If it doesn't turn out well, I will stop the project and at least save the Money for the cells, which are by far the most costly part of a battery-pack.

[sunny]

Please keep us updated! This project sounds very interesting!

[Gimlet]

Thank You for the replies. Feedback is very valuable and there are good points made.

 

As for the noname Wheel I bought, I had a feeling that the seller had been cutting some corners here and there and was prepared for the worst. The EU has actually, with a few ajustments,  turned out to be very reliable and unproblematic to ride - within its limits! It also creates good attention by most people who sees the 'magic wheel'. You've recognized that Youself, no?

 

A fix I did, was to take the Shells of and glue the magnets inside them, that hold the pedals in place, to the Shells on each side. They were simply attached with a small string of tape and had been attracted by the axl (iron). A sloppy production detail. Now the magnets stay whre they're supposed to be. The footplates stay up and I also have glued a felt floor-protection pad on the outside of the Shell, to dampen the massive 'klonk' when the pedals were raised and hammered on to the Shell. Works nice. Small detail that gives just a bit more luxurious feeling in operation.

 

As for the batterypack, I'm planning - I know this is probably not a BMS for a Solowheel. The Solowheel uses a different battery-type LiFe-something which would probably require different properties of the BMS.

This one is likely intended for LiPo-cells but maybe with a higher allowable discharge current.

 

I don't know how well the cells are supposed to be matched. I have noticed that the BMS on my noname EU Works well. I measured the voltage over each single cell a couple of times during the discharge and they were absolutely uniform. I mean same voltage, spot on! So even though theory dictates matched cells, I believe, I can get away with it.

As long as I sort out cells that are outside the manufacturer specs.

The Panasonic specs of the 18650B's say 3400 mAh nominal capacity per cell, with a minimum capacity of 3200 mAh. So I plan to buy 16 pcs, charge each of them and measure the capacity during discharge. If any falls outside, it will be returned to seller. The Panasonic cells are japanese production cells and have a very good rumour as for quality control. So hope I get genuine Panasonics.  

I follow my gut-feeling here but time will show if I'm right or wrong.

 

The point that I'm concerned about is, that assembling the board requires spotwelding of nickel-strips to each cell. So I have to build my own spotwelding device and Work up the handycraft to make reliable welds, without melting Down the poles of the cells.

 

I have the BMS and the nickel -strips. Also have a transformer out of a discarded microwave-oven, with just the primary Circuit in. And 40 mm^2 of insulated wire for making the secondary Circuit. Let's see if I can pass this hurdle. Will make a few practice welds before I actually order the cells. Can practice on aluminum beveridge-can metal and bits of nickel-strips.

If it doesn't turn out well, I will stop the project and at least save the Money for the cells, which are by far the most costly part of a battery-pack.

I played around with battery packs for remote control car racing about 12 years or so ago. As I remember it all the cells default to the output of the worst cell and spot soldering them together with as little heat getting into the cell as possible was a nightmare.

Mess up one cell with too much heat and all the others default down to that cells output. I gave it up in the end and paid out for the very best battery packs that were available at the time.

[OleTC]

I played around with battery packs for remote control car racing about 12 years or so ago. As I remember it all the cells default to the output of the worst cell and spot soldering them together with as little heat getting into the cell as possible was a nightmare.

Mess up one cell with too much heat and all the others default down to that cells output. I gave it up in the end and paid out for the very best battery packs that were available at the time.

 

Wow, not really what I wanted to read. I AM concerned about the spotwelding part. But appreciate the warning! I only will have myself to thank, if I mess up here.

I have spent some hours today, building on my amateur spotwelder and will continue, just to see how it works out, testwelding some nickel-strips, since I allrady have them at hand. I only use recycled parts and will have no expenses on this experiment.

I even have 4 old and very worn size AA NiMH cells to experiment on, so will definitely build some experience and take time to consider things, before I jump the deep end and maybe order 18650B cells.

 

By the way, the symptoms You describe is the reason why I wouldn't be worried about putting together 16 different cells of good quality, the stronger ones will be worn a little faster 'till they all are in line performancewise and from then on they will age more or less uniformly.

But ofcourse - none of them must be outside the acceptable range from start, since they will degrade towards the least quality cell specifications.

 

Once again, thank You for the warning.

 

Will also say, I don't advice anyone who don't know exactly what they are doing, to build their own spotwelder and operate it. Lethal voltages are involved as well as currents that could melt a finger-ring right down through Your finger, if it was the shorting part of the secondary circuit. Firehazard is another danger. So pls. be very carefull or stay away from this kind of equipment.

And I will not come up with any descriptions of the circuit I'm building. Just update on progress of the battery-pack or wave the white flag.

 

Best

[Gimlet]

I suggest you take a note of the outputs of your old test batteries before and after to see if the heat has affected them at all.

As I said, on the racing car where we were trying to get maximum output from the batteries during one race, we gave up. Not without trying several times though.

Good luck!

[slappy76]

How's your project coming along? I'm very interested in your build for this as I am very distrusting of capacity claims by lesser name Chinese makes. I'm planning on getting the TG F3 from Banggood.com as a beater to mess with before I lay down cash on a Nine bot or something similar.

Check out this link. I picked up (20) 18650 from thsee from this guy last year for 25 bucks. I think they were a little over 2ah each. I suppose you could try putting together 32 of these . I use them in my cheapie CREE lights no prob.

 http://budgetlightforum.com/node/34088#node-34088

I was thinking I could 3d print a 18650 battery case like this. Anyone good at CAD? Chime in.

http://www.thingiverse.com/thing:331394

Thoughts? 

-Tony in Brooklyn

[OleTC]

Hi Tony,

Slowly evolving. I have build the footpedal to activate the spotwelder by now and am facing that the spotwelder must have a solidstate relay and a 555 IC based timer Circuit.  That can be done.

Also will need a mechanical stable arrangement of the electrodes to make good, reliable welds. So they must be attached to a hinged rod.

Actually I believe, I will settle for the 2900 mAh Panasonic 18650PF cells, since they are constructed for eVehicles. There's another thread mentioning their max. allowed discharge current of up to 10 Amperes. That will give a pack of 174 Wh capacity.

I  had a bad case of the flu but I will get there.

Regs

 

[Jay Barnett]

Ive bought a generic BMS board from aliexpress and have 32 18650s to put together a kickass battery pack, but im looking for some diy instuctions or video of how to put it all together. Anyone know hoe its done. I have multimeter, solder and various parts needed. cheers.

[OleTC]

Bin a while.....won't bore anyone, explaining why. Here's the update:

I found a R/C equipment shop just 4 km away, who had the XT-60 plug and the-other-type. So for discharging I soldered it with 2,5 squaremillimeter wire, that is rated 16 Ampere continous current. For charging 0,75 squaremillimeter wire, rated 6 Ampere continous current.

BMS board with wires

And thanks to esaj and his description of his build of batterypacks for the Firewheel, I choose cells, same type. That is LG DBMH1 18650.

I have tested all of them for capacity and they all test above specs (nominal capacity 3200 mAh and minimum 3100 mAh) and very close. All within 1,5% from the average. Tested with an Opus CT-3100 2.2 charger. Discharge with half an Ampere from full charge down to a voltage of 2,9 Volts, gave the following results (mAh) for the 16 cells:

3377
3351
3340
3280
3334
3318
3327
3317
3323
3341
3319
3337
3362
3347
3314
3335

Now these cells must have tabs spotwelded  and I'm still in the process of Building a DIY spotwelder. I'm progressing slowly but surely and I'm now pretty sure, I will reach goal and be able to do strong and secure welds, without wrecking the cells or ruin the capacity. Cross my fingers.

Am a couple of weeks away from my first test-welding but have build ver. 1.1 of the control-circuit, as well as the footpedal for activating the welder. Works well and activates the transformer primary circuit via a solid state relay as long as the time-constant is adjusted to via a potmeter.

With version 2.0, I should be able to weld consistently with warm-up of 50 ms and welds of 250 ms duration. Am using 2 pcs of 555 chips and a reed relay for timing, etc.

Will update later.

 

In the meantime, can any one point me to where I can purchase the light blue heatwrap that is around the batterypacks?

And to where I can purchase the insulation - like sticky glued cardboard - that is used on the end of the welded cells on the BMS? There's 2 different sorts, one with holes in it below the tabs and one without holes, on top of the tabs.

Thank You in advance.

 

Oh and by the way - anyone who knows if the cells in a pack are attached with hotmelt to the BMS-board?

[OleTC]

Cutting edge Danish hi-tech:

Warning

Admit it. No other county comes near Danish escalator-technology with sensors, warning waiting passengers not to just jump-enter the escalator but with open doors let it ventilate the air first.

 

 

 

Disclaimer:

The phrase "I fart" could be Danish for "In motion".

[cg]

@OleTC, you know, to view those pictures you upload, you need to have a yahoo account...

I am quite interested in the pictures, are there any way you could share them without requiring login?

[robca]

Yep, requires login... imgur, Google drive, Microsoft OneDrive, Dropbox... all great alternatives  

[OleTC]

My bad. They're public now.

[OleTC]

First weld. Actually 2 welds, attaching a nickel strip to a worn out AAA size battery.

I just completed my first test-weld. Or first and first, first-ish, that is. First a Little fiddling with a burned out strip and and the welding parameters.

But here it is. Believe I will go on with the parameters for welding, that I've used here. Those are 50 ms warmup weld, which in combination with a pressure of approx. 4 Newton on each electrode, brings the parts together. Then a pause of 4 seconds and the actual weld-pulse of approx. 125 ms.

Electrodes have a surface of 1,5 x 1,5 mm and are 2 mm apart. And thats more or less it.

Nickel strip removed again

Then I removed the strip Again with a pair of pliers. Sits really well and the metal is torn apart in the spots where the weld is.

The strip does not get hot in any way. Not that I immediately put a finger directly on the weld but just a few seconds after, everything was cool to the touch.

Really promising. I have all parts now for completing my battery-pack and feel very comfortable about going on.

If You see something I haven't noticed on the welds, pls. let me know.

 

Oh yeah, and regarding the spotwelder, I must say it was one of the bigger challenges I've given myself, to build it. It is what I would describe as a working mockup and not ready for industrial, serial production. But it Works, mate!

I know quite a few out there are considering Building one themselves and if You're up for it, give it a go. You should know that You're on Your own. Since the build and handling is including an Electronic control-part, a not unsofisticated mechanical construction, as well as lethal voltages and currents, this is not a total beginners job and I will not be the one who is blamed for anyones calamities. So You can not rely on my advice on anything. This is also based on the facts, that I have used, so to speak only recycled parts, and if You don't have similar parts, my advice could be wrong. 

Again - know that You're on Your own, if You try!!!

[OleTC]

I worked through the Whole day. Has welded the cells, soldered them in place on the board, completely with insulating gaskets, and all, plus heat shrink wrap and it Works!

Took a night ride which would normally have drained the old pack completely but there's still good power in the pack. Tomorrow I'll check the actual range of the new pack.

It gives more torque as well. Probably due to lower inner resistance than the old worn out packet. I've been driving up hills at good speed, which I would normally crawl.

Crazy that it took me months to build  the welder. But now I can assemble a packet in a few hours time. If I'll ever need that Again.

[OleTC]

I ran the batterypack empty and Endomondo said 9,33 km. I would probably have gone 5,5 km on the old pack on a chilly day like today.

In addition I have kept an average speed of 11,7 km/h going with nearly constant beeping, which sets in at 12 km/h. Actually I wanted to go faster most of the time, which I usually don't want to with the old pack. I also mostly end up on an average speed of 9,5 km/h on the old pack.

In conclusion, I believe the distance is what I could expect. With economy driving and omitting hilly terrain, I believe I could reach more than 11 km distance, with my 110 kg bodyweight.

So a dual-pack with > 340 Wh capacity would be what I really want for comfort, torque and confidence. Never the less, I feel like upgrading to a 16" Wheel with stronger engine.

King Song upcoming 16", Firewheel and IPS Lhotz are the more obvious candidates.

Will probably wait for spring and follow Development from the sideline.

Happy riding out there.

EDIT:

"It took exactly 30 minute to recharge the old pack. The new pack takes 68 minutes.

And if anyone are interested in prices - the overall cost for parts have been very close to 100 Euro. Coincidentally I seem to have used exact same BMS-board and cells, that 1Rad Werkstatt use for their packs. Apparently same heat-shrink tubing as well. So maybe I'm close to the quality they provide, which would make for a nice saving, over buying a board. "

 

[Maxime]

Just for information, I bought a TG F3 from Banggood China, rather far. I have also bought a Charge Doctor from Hobby16, and tested my battery along the charge from 0 (cut off by the wheel) to full. My Batt is sold for 264 Wh, and I measured 284 ! Max V is 67,4 v which is quite good. I run since 3 months with no problem, except a fall in the beginning after which I shunted it. and Max V seems absolutely constant as far as now. So, I am very happy of it except I would like to go a bit faster on solid roads, but no so much faster, now I know the result when you fall all of a sudden...

So Chinese products are not so bad and deceptive...

[OleTC]

An update on my home-assembled 192 Wh batterypacket that now lives inside my generic 14" X3-clone.

I just rode 9,14 km today in relatively cold weather. My weight is 116 kg. Average speed for the trip was 10,2 km/h. I believe I could have gone a half to a full kilometer longer, before the Wheel had shut down. The meter was Down to 1 out of 4 bars but the Wheel was absolutely rideable.
The LG-cells appear to be genuine good quality-cells, which just confirms the overall sentiment about them in the Communities that use these cells.