Xyster's X5

[patrick_mahoney]

That is a much neater soldering job than I did on my, Xyster. Very cleanly done. I'm impressed. Soldering sideways is also much smarter than how I did mine. If I was going to do mine again (which I am definitely not), I would copy your method. It's safer and better than the rather goofy way that I soldered my 12s8p pack.

I did 12AWG on the power wiring and 18AWG x 2 for the charging wires.

[xyster]

You really are not running ANY kind of protection with your battery pack?

There's a main 40-amp fuse, there's the controller's 35-amp current limit, there's the voltmeter and ammeter on the handlebars, there's the DVM I take with me on long rides with which I can check any of the now 20 individual subpacks via their respective charging port. In other words, I'm the BMS...now go ahead, crack a joke

The only "meltdown" was when you allowed the voltage to drop below the safety zone and it burned out about 25% of your batteries. (as you were riding?)

2 cells ruptured, the heat from overdischarge (these cells tank fast below 3.7V resting!) also killed (or tripped the PTC) on two dozen others -- about 10% of my pack at that time. I reconfigured and resoldered the entire pack, going from 19s12p to 16s15p. Since then I've added 4s15p more batteries.

Did the fire occur in such a way that you could smell it or feel the heat as you road?

There was no fire, just heat and some smoke. I could tell something was wrong because the voltage as read by the meter on my handlebars was drooping far more than normal. According to reports on rcgroups.com, lithium cobalt fires are almost never caused by overdischarge, but by charging at too high of a voltage, charging as the wrong type of battery, physical damage like when wrecking an RC airplane, and defective manufacture like with the recalled Sony's. This fit with my experience where there was no fire.

Do you use any protection in your charging or are you simply dividing things up into small units and then praying each one is okay?

What protection would I use? Each subpack is charged individually by a single cell 1.5 amp charger -- which is a very low charge rate. Each and every single cell is balanced with every charge this way. The chargers themselves only have one voltage setting: 4.2V. It seems virtually impossible to overcharge the batteries because as 4.2V is approached, the current trickles down to zilch.

[xyster]

It's safer and better than the rather goofy way that I soldered my 12s8p pack.

Ah, perhaps, but my bike looks goofier for sure!

And the award for most prolific overuse of duct tape goes to...envelope please....Xyster!

And the award for most individual lithium cells on a bicycle goes to....Xyster again!

And finally folks, the one we've all been waiting for....And the EV Academy Award for ugliest small vehicle in the world goes to...the Producer of the new hit show Ugly EV.... Xyster!

It's a clean sweep!!! rah rah cheer cheer....


Next up tomorrow: hookin' up and ridin'

[RatoN]

...

What protection would I use? Each subpack is charged individually by a single cell 1.5 amp charger -- which is a very low charge rate. Each and every single cell is balanced with every charge this way. The chargers themselves only have one voltage setting: 4.2V. It seems virtually impossible to overcharge the batteries because as 4.2V is approached, the current trickles down to zilch.

Sorry Xyster, but that is very confusing to me. I have a big interest in Lithium pack charging...

1. You charge your pack(s) with a SINGLE CELL charger? How could this be, since many 4.2v constitute more volts, there for the charger will detect LOTS more volts, and not even begin to charge.

2. Your pack(s) don't have a charge-discharge electronic board, so how do you know when the batt pack has reched it's discharge limits?

[fechter]

If that thing bursts into flames, look what gets roasted.
Got Nomex underwear?
I didn't see any PTC's. Was that a previous pack? Those work like a fuse, but suck at high currents.

They do make much more stylish duct tape. I use black.
I used to have a roll of camoflage duct tape, great for that "military grade" look.

[xyster]

1. You charge your pack(s) with a SINGLE CELL charger? How could this be, since many 4.2v constitute more volts, there for the charger will detect LOTS more volts, and not even begin to charge.

See the 20 single-cell chargers in the picture below? Each one gets simultaneously (well close) connected to each jack on the bike for charging. Each jack on the pack goes to one, and only one, parallel "subpack" of 15 cells, in well, parallel. Each of the subpacks is strung together in series. As you might surmise, there's 20 jacks on the bike.

2. Your pack(s) don't have a charge-discharge electronic board, so how do you know when the batt pack has reched it's discharge limits?

The light on each charger changes from red to green, and the charger stops charging (well, I think it stops charging) Anyway, the end charge from 4.15 V to 4.2 V goes quite slow, so I let it charge overnight and disconnect them all at the same time when all the lights turn green. Most of the time, the light actually turns at about 4.15V, so I'm only charging to 95%, which is fine with me as the pack should last much longer that way (see the tesla motors site blog for more on this...link is somewhere here I think).

[xyster]

If that thing bursts into flames, look what gets roasted.
Got Nomex underwear?

If the entire pack bursts in flames, a roasted weenie will be the least of my worries.

I didn't see any PTC's. Was that a previous pack? Those work like a fuse, but suck at high currents.

The PTC's inside the cells. Which is another point in re the BMS, safe. A BMS won't stop a cell fire caused by damage internally or mismanufacture.

See link for battery specs:
http://www.all-battery.com/index.asp?Pa ... rodID=1643
Internal Impedance: less or equal to 180 milliohm (with PTC)

See link for charger specs:
http://www.batteryspace.com/index.asp?P ... rodID=1231

They do make much more stylish duct tape. I use black.
I used to have a roll of camoflage duct tape, great for that "military grade" look.

I see you speak fluent "cool" too A regular Fonzarelli on a scooter [/i]

[xyster]

As seen in the top frame, I connected the new 2 subpacks in series with the rest of the batteries. Then turned it on, and.... it works!
The whole pack is 60% charged, and the voltmeter reads about 7.5 volts more than before! Now on the voltmeter I'm going to have re-mark the "e" for empty again....

Well friends, it's time to go pedal the pavement. Gonna have to take it easy, no hard testing yet because of that broken spoke....

[safe]

Your total disregard for the conventions of "safety" is having an effect. Rather than me being worried about Lithium batteries the lack of fear you demonstrate tends to make me also want to "risk it" and build a pack without all the PCB's and crap that makes the things overly expensive and complicated.

Do me a favor and create a new "technical thread" and just walk through category, by category all the areas that you need to watch out for and also what is "overhyped" as a fear. (when you are done with your ride of course)

If charging is the danger area, then also talk about that.

Try to pretend you are a college professor teaching a class on "Risk taking Battery Packs and how they are Cool".

Make it theoretical and not about your specific hardware...

[RatoN]

Ok, brainstorming here…

What about, a dum-charger? (Dum= no automatic cut off, no lights, just DC current).

One that would mimic a fully charged battery. One that would give constant 4.2v from the beginning, until you unplug it, like a fully charged battery that never runs out of juice. Would it charge the other batteries, therefore the whole pack?

Because, if one battery has more juice than the others in a pack, it will give its juice to the others, right? Then all batteries in the pack have equal amounts.

[xyster]

Just got back from a short test ride. Worked as expected. The box does not hit my thighs, though it might if I keep biking and buildup big huge quads

I'll get some hard comparison data as far as acceleration, and speed@amps after I get that spoke fixed and charge the pack fully.

Your total disregard for the conventions of "safety" is having an effect. Rather than me being worried about Lithium batteries the lack of fear you demonstrate tends to make me also want to "risk it" and build a pack without all the PCB's and crap that makes the things overly expensive and complicated.

I have great regard for the conventions of safety, but I've done enough study I think of lithium batteries to better appreciate what constitutes end-user protecting tech, and what constitutes vendor protecting tech (from lawsuits by non-diligent users). Patrick Mahoney has a pack of the same cells configured 12s8p and doesn't use a BMS either. His fancy RC charger balances the subpacks of parallel-wired cells during charge as I do with cheaper, multiple chargers.

Do me a favor and create a new "technical thread" and just walk through category, by category all the areas that you need to watch out for and also what is "overhyped" as a fear. (when you are done with your ride of course)

Do me a favor and read up and study about lithium batteries like I did, then as you have specific questions, post them to the tech thread and I'd be happy to give my 2 cents along with everyone else.

What about, a dum-charger? (Dum= no automatic cut off, no lights, just DC current).

One that would mimic a fully charged battery. One that would give constant 4.2v from the beginning, until you unplug it, like a fully charged battery that never runs out of juice.

That's basically what my batteryspace chargers are. Plug'em in and with a DVM they measure about 4.2v (range 4.15 - 4.2). Fechter would know more, but since each puts out no more than 4.2v, I don't think it can overcharge lithium batteries -- the current slows to zero as the battery voltages approaches the charger voltage (there is no electromotive force when the voltages are equal to shove in any more amps).

Would it charge the other batteries, therefore the whole pack?

If you wanted to charge the whole pack with one charger, then your charger would have to 4.2v times however many llithium cells in series you have. In my case that'd be 84 volts. But the problem there is each subpack in series will not balance with the other subpacks in series (though the cells within each subpack, because they're wired in parallel with each other, will balance each other within a subpack) so you'll end up with one subpack at a significantly lower voltage then the others, and while total voltage will look OK on a voltmeter measuring the entire pack's voltage, one or more subpacks (of cells wired in parallel) will begin to overdischarge.

Because, if one battery has more juice than the others in a pack, it will give its juice to the others, right?

For lithium and lead-acid in parallel, yes. For nicad/nimh, the situation is more complicated. But lithium and lead and every other chemistry I'm aware of will not balance in series, that's why those powercheq devices for lead batteries are popular, and why lithium RC chargers have battery balancing functions, and why good BMS's also balance batteries in series during discharge.

Balancing during discharge is slightly better, but much more expensive and/or complicated to wire. Balancing during charging as I do is good enough for me because the difference at the end of a ride between subpack's voltage is very small, like 0.02 volts or less, and gets equalized whenever I recharge.

[/quote]

[knoxie]

Yo

That bike needs a wash!! check your shock absorber on the rear ha ha, does it move?

Cheers

Knoxie

[xyster]

That bike needs a wash!! check your shock absorber on the rear ha ha, does it move?

I don't know about you, Mr. City Slicker, Mr. upstanding tea-sipping wig-wearing English gent and all that, but I live smack in the middle of mud country, and I love it here! I practically bathe in the stuff

And yes, the shock absorber usually moves. To loosen it up, I just ride through a deep puddle or two.

[xyster]

I want to know how the batteries are charged,one by one ? no BMS contol it when the batteries charged

As shown in the picture below, the batteries are simultaneously charged by 20, single-cell chargers, each connected to a single, 4v subpack of 15 cells in parallel. There is 20 of these 15-cell subpacks in series for 80 volts total (at 4 volts charge).
There is no BMS as it's normally thought of. The total current is limited by the controller to about 1C (35 amps). I watch the batteries' voltage with a voltmeter on the handlebars. Each of the cells has a PTC fuse inside.

[D-Man]

Questions :

So when you pull the batterys off the charger, how many volts does a cell read when resting?

Also, what should the cut-off voltage be per cell from your experience?

[xyster]

Questions : So when you pull the batterys off the charger, how many volts does a cell read when resting?

If I let them charge as far as they will, 4.15v - 4.20v. I often stop them at 4.0-4.1v so they'll live longer. Higher voltages, even within the limits, make lithium-cobalt cells oxidize and degrade faster.

Also, what should the cut-off voltage be per cell from your experience?

For 100% state-of-charge: 4.20 volts
For 95% state-of-charge and longer lifetime: 4.15 volts (this is the level tesla motors says they charge their lithium 18650s to):

http://www.teslamotors.com/blog1/?p=39
"Cycle Life
For Li-ion cells, manufacturers define cycle life as the number of full discharge-charge cycles that it takes to reduce a cell’s capacity to some fraction of its original state. (A common threshold used in the laptop industry is 80 percent.) Note that the cell is generally not completely dead at the end of these cycles. It has a significant number of useful cycles left, just at a lower capacity.
There are several factors that affect Li-ion cycle life. Some are physical and are built into the cells at the time of manufacture and so they can’t be changed. Not all cells are created equal, and we have worked very hard to find the best cells on the market that offer an exceptional combination of cycle life and energy density from a top-tier Japanese manufacturer.
The other factors affecting cycle life are tied to how the cell is used. In particular:
1. Avoiding very high and very low states of charge. Voltages over 4.15V/cell (about 95 percent state of charge [SOC]) and voltages below 3.00V/cell (about 2 percent SOC) cause more stress on the insides of the cell (both physical and electrical).

2. Avoiding very high charge rates. Charging faster than about C/2 (two hour charge) can reduce the cell’s life.

3. Avoiding charging at temperatures below 0° C. (Our design heats the pack before charging at cold temperatures.)

4. Avoiding very high discharge rates. (Our pack has been designed such that even at maximum discharge rate, the current required from each cell is not excessive.)"

In multicell packs without individual cell BMSs I would not run a lithium cobalt cell below 3.65 - 3.7 volts. There's almost no usable charge left at that point, and the cells tank so fast from there down below their 2.75 dead-forever level, that it is not worth the risk, IMO. And the heat generated by overdischarge is hot enough to melt solder and rupture the cell's interior! Like these here:


Are you planning a lithium pack, D-man?

[D-Man]

So let me get this straight. You charge them up to like 4.15-4.20 volts. You take the charger off and it stays at that voltage? A Sla for example charges to like 14.4 but then when you take the charger off, it sags to 13.04 resting. I was just trying to figure out how to get the most voltage out of a 55 volt controller if a person builds his own pack.

[xyster]

You charge them up to like 4.15-4.20 volts. You take the charger off and it stays at that voltage?

Yes. There's 20, 33ah subpacks in series. Each subpack is charged to 4.15-4.2v as a single big cell by it's own charger. And the voltage stays there. So pack voltage after full charge is always between 83 and 84 volts -- and it's exactly the same 12 hours later. Lithium has a very low self-discharge rate, and no noticeably post-charge sag.

A Sla for example charges to like 14.4 but then when you take the charger off, it sags to 13.04 resting.

I was just noticing that on my scooter.

I was just trying to figure out how to get the most voltage out of a 55 volt controller if a person builds his own pack.

If 55v is it's absolute max, then you could build a 13s lithium pack (13 x 4.20 = 54.6 volts). 48 volt lithium packs sold commercially are usually 13 cells in series.

[xyster]

<p align="center">Process Pictorial</p>

1) Bought a bike I liked.

2) Added a schwinn speedo and cheap plastic mirrors.

3) Built a battery box that was too tall to be stable or allow easy mounting/dismounting.

{more next page}

[xyster]

4) added voltmeter and ammeter

5) started work on a new box

6) got the batteries, chargers, wires, ports, etc, and went to work assembling a 19s12p pack of 2.2 ah 18650s.

7) added XLR plugs to the chargers.

[xyster]

8 ) Put the batteries in the box.

9) Put the box on the bike.

10) Got a 72V 35 A controller and mounted it midframe.

11) Put 6 10w 12v MR11 halogens in pvc couplers and mounted those to the handlebars

[xyster]

12) Installed the rear 5304 hubmotor with a 3 speed freewheel, maxxis hookworms with kevlar lining and thick downhill tubes. Oh oh! No room for a rear disk brake. Oh well, rear brake only accounts for 30% of stopping power anyway

13) Tested the batteries and lights

14) Prepared for first ride! Took it down to LBS where the nice owner attached the rear brake lever to a front v-type, so I have two front brakes.

[xyster]

15) Major design flaws evident on first ride: too few batteries in parallel to supply 35 amps, blew up a couple by overdischarging; bike unstable at speeds over 30mph because of too much weight on the rear -- almost bought it while riding in traffic at 30mph. So I scrapped that rear box; pulled the batteries out and began to resolder the 19s12p pack as a 15s15p pack. Figured I could add more batteries later too get back the lost voltage.

16) Built new midframe box above controller for holding 4s15p, and a new rear box for holding 10s15p, and started a little box for the remaining single subpack

[xyster]

17) found a scrap kickstand, bolted it to a metal tie attached to the frame.

18 ) To protect from weather, wrapped boxes in duct tape and nylon attached with velcro.

19) Got myself a full face helmet and hit the road again! Returned rented videos.

[xyster]

20) To block spray, added a front fender created from a metal tie wrapped with duct tape. Changed a couple broken spokes.

All's well with the bike, but I'm missing that extra 16 volts! So bought 30 more batteries and stuffed 2s15p of 'em in a box. Attached box on the rear rack in front of the big one.

21) Oh no! That extra weight was the straw that broke my back rack.