Trials Motorcycle - 1st Build. Qs-motor +Votol

[gbeals]

I had to step away from my project for a bit, but I'm back now and looking to finish this bad boy up. Hopeful I can get some help along the way; I'm super new to electric vehicles, but not from building/fabricating. I had posted a while back and the help I received gave me a enough confidence to dive in and do a build.

The Bike:
2003 Gas Gas TXT Pro - Not easy to come by living in Hawaii. The bike is pretty sweet; only problem is.... How can I enjoy nature with all that noise and smoke? Enter this fine Forum. This was my last trip to the woods yesterday. The engine is coming out!

The Components:
3KW QS Motor with the 150 Votol Controller was what I landed with after many nights of research. I plan on doing a primary drive to get me close to 300 ft. lbs of torque (Similar to production Trials bike like Electric Motion), with a top speed of 40 mph.

So I have the bike, the motor, controller, speedo, and throttle that came with the kit I purchased from QS Motor. (Who was super easy and helpful to work with) I'm not super fond of the throttle as it has a key in it, and not super fond of the speedo unless it has some electrical monitoring as I don't care about speed in the trail. (I'm up to trade or sell if anyone wants them.)

What's left?
Battery, primary gear, wiring for bench test and install. Yes, not as easy some brackets and fitting, and chain, etc.. That is what I'm more comfortable with.

QUESTIONS:
Battery - What is the suggested recommendation for my application and components? I can't quite seem to wrap my head around this; but in all honesty I haven't dove in fully just yet.
I see in some diagrams a battery goes to a contactor and then to a converter - then to the controller - is this the ONLY way?
I also see some diagrams with battery goes direct to B+/- on controller - is this the ideal path?

Bench Test - I'd like to figure out the wiring. I have the diagram and it looks pretty straight forward.
I'll need B+/-, U,V,W, Hall Connector then E-Lock as bare min. wires - Is that right?

Monitoring - I'm sure I can download an app to my phone for bench testing - any recommendations on apps? But for longer term monitoring of battery, volts, amps, etc.. Are there products you folks would recommend?

Thanks in advance for looking and/or helping with any of the questions I have. I'm pretty excited to get this bike built; its been rattling around in my mind for a while now. Last few hurdles and I'll be on the electric path!
I'm sure I'll need to hook up the USB to the computer and controller first to do some basic settings? Or will it work out of the box?
Motor is for 72v. Can I use my 40v Trimmer battery temporarily to test movement? Or is this a bad idea?

 

[rynhardt]

Nice! I used a 2001 Gas Gas TXT Pro frame for my build - very similar.

https://endless-sphere.com/forums/viewtopic.php?f=10&t=102413

Battery:
LiPo packs were the easiest to source where I live, up to about 20AH. Use 2x 6S for 48V, 3x 6S for 72V.
A 1 kWh pack should you give between 1 and 3 hours riding time, depending on how many hills you're climbing.
2 x 6S20Ah = 48V x 20Ah = 0.96 kWh
3 x 6S14Ah = 72V x 14Ah = 1.008 kWh
i.e. if you're using higher voltage, you can use smaller Ah for the same total energy.

Contactor:
The contactor is just a big relay. You could also use just a really beefy SPST switch (e.g. simple on/off switch: Single Pole Single Throw), but these are hard to come by with high current ratings (say 200A+). There's no other easy way to just connect your controller to the battery, unless you're physically plugging/unplugging the battery leads.

Pre-charge resistor:
Now when you first connect your controller to the battery (using contactor/switch or plugging in leads), the capacitors in the controller need to charge up, and they draw an awful lot of current in a very small period of time (micro/nano seconds). This generally manifests itself as a large spark, which is both scary and not necessarily good for your equipment.
To prevent this, and to allow the capacitors to charge slower, say over a period of a full second, a pre-charge resistor is usually wired to bypass the contactor.
The circuit feeding this pre-charge resistor is normally a key switch (or any other low current latching switch, like a magnetic cutout switch on a lanyard, which I'm using).
Some controllers then have a contactor circuit which they use to switch the contactor on once the caps are charged, which then prevents any sparking.

So, here's what typically happens (say a 48V system).
1. You switch on the key switch, which sends 48V (in a direct voltage system) to the pre-charge resistor (say 220 ohm 5W), which draws say 100mA (i.e. low current).
2. The controller capacitors start charging, and as soon as they hit 48V the controller sends 48V to the contactor coil, which draws say 100mA (still low curent).
3. The contactor switches the main 200A circuit onto the contactor and now you're ready to roll.

Convertor:
Depending on your controller/contactor/other accessories, you may need to convert your battery 72V/48V down to 12V/5V.

 

[skeetab5780]

Sub'd this is going to be sweet! GL

 

[SlowCo]

I'll be following this build. Good luck and update regularly :wink:

 

[gbeals]

HA - Thanks Gents!

rynhardt - I read your build thread from beginning to end months back deciding if I should build a trials bike. Apparently I liked your thread. :thumb:

Solved a bunch of my issues this evening already with.. YES that is right! The search button! Phone call with a dude in California helped a bunch as well.

Votol Controller:
Main colored wires from the motor (Green, Yellow, Blue) were very well marked. The L2 Hall Connector (Lowest connector in the photo) also only had one place to go, so that was a pretty easy snap.

The L3 port however (Top right of photo) is for an an Alarm; being a dirt bike I don't plan on using this. I'm still not certain if I can leave this fully disconnected? I see there is 1 of 2 e-locks wires and the Pre-Charge (Hat tip rynhardt). I do have the e-lock from the main connector L1 connected however.

Which brings me to the much more complicated L1 Port. For now I only needed to figure out the throttle which was pretty straight forward until the throttle had two extra wires (Blue, Yellow) I found a a diagram showing the Blue went to e-lock (there is a key on this throttle)?? and Yellow went to +Power. Oddly enough E-lock also goes to +Power. So in my mind both Yellow and Blue connect to the e-lock and then over to Power. Seem legit? (I'm still researching this) Hooked my trimmer (40v) battery up to see if things were working; Apparently I'm low and need a charge. But worked, so moving on.

Lastly for the evening I hooked up the USB which was the only port I didn't have to take a part and rebuild as everything was bunched together for a different application than mine; which was expected

Tomorrow I'll install the software to my laptop, remove the lock (Read that tid-bit here at Endless-Sphere) and then try to find or figure out the motor settings in the software. Which I think a thread on this board can help me there as well.

 

[DanGT86]

Nice! Looking forward to watching this one.

 

[macribs]

Sub'd. Cool project, I will keep coming back.

 

[rynhardt]

dunno if it's just me, but your picture links are broken..

 

[gbeals]

dunno if it's just me, but your picture links are broken..

It's me... However I have fixed the image links. I'm a designer of sorts, and documenting my journey on the web so maybe others will find use in it.

It has some videos I like that motivate me in this project. A timeline of events I've taken to get this far, and some design ideas I'm working on related to the project "Quite-rides". Maybe it will evolve into something, or maybe it will be a way for me to document and review one day when i'm old and short on memory.

A T-shirt design I'm working on, but will remove the .com - I'm going for more of a generic anyone can use type of design for E-Motos. I use a CNC to make block prints and then print out small run t-shirts for my personal use; and give to friends.
www.quiet-rides.com

NOTE: Although my blog says it sells stuff it is for placement only; I am not an approved vendor to resell on this board and the site is NOT accepting orders of any kind; I hope this is OK to post the link.

 

[macribs]

Quickly checked out that vid on your site. Epic riding. And no noise 8)

 

[gbeals]

Hooked up the Votol to the 40v battery. Got a lot of help from some folks on this site and to no luck. I continue to get a low volt fault even when setting the limiter lower than 40v. I'm not good with electronics so it's a guessing game at this point.

I did however hook up the USB to the votol and got the computer to connect. It shows the volt reading for a second, then goes to zero with the fault.

I've decided to purchase a proper battery and skip the guess work. Only problem is I haven't the slightest idea on how many batteries I can fit in there. I think I may get a smaller battery to begin, and then use it on a smaller project later. Something like a 20ah to start.

I'm quite visual so I decided to make a Blueprint, to wrap my mind around the battery ordeal. Not the specs mind you, but the space.

Back to the battery specs. I've started my research but it is quite confusing. I'll continue but what I find confusing is when someone says the battery is for a 2kw motor or a 3kw motor. Well mine is a 3kw but can see 24kw bursts (not that I need that). Then how much amps can be used; BMS limiters - Oh My... I get the fact the the more batteries will produce more power and more distance. Just not sure what I need as I'm not building a normal ebike. Then there are those who toss out a generic 20sp10 - but that doesn't tell me much. Of course I can google that, and it tell me a format; but now how many peak amps, etc.. Noob territory for me; I wish there was a formula -My motor + My controller = Need for this battery. But everyone power needs are different. I get it. I'll figure it out one day. I'm very open to any link of battery suggestions to get me started, I don't think I want to build one myself.

Provided this as a starting point: 3 x 6S14Ah = 72V x 14Ah = 1.008 kWh
What determines the amp output? Is that the controller? I set it to say max 80am, and it can use up to 80amps? I need a battery that can produce 80amps? Is that controlled by the BMS?
Sony VTC4 was also mentioned to me as they produce high amp output.
Lot of questions. Sorry.

I'm not concerned with speed (top speed should be 40mph), but do want torque. So VOLTS and AMPS if I'm thinking correct.?.?
Specs on my motor:
qs 3000w 138 70h mid drive
rated: 3000w
Max Power 5900w
Matx Torque:56N.m (I'll add primary drive for around 300 ft lbs torque -Ideally)
peak current 120a 72v
Max peak phase current 450a

I'll keep digging around and see how to put it all together. The problem is I find a lot of mis-information and get stuck in a loop.

 

[gbeals]

Not one to fail, I kept reading.... Found a different version of the software I was using and it took care of my low voltage fault and now the motor will run on my 40v battery.

 

[DanGT86]

I've decided to purchase a proper battery and skip the guess work. Only problem is I haven't the slightest idea on how many batteries I can fit in there. I think I may get a smaller battery to begin, and then use it on a smaller project later. Something like a 20ah to start.

Back to the battery specs. I've started my research but it is quite confusing. I'll continue but what I find confusing is when someone says the battery is for a 2kw motor or a 3kw motor. Well mine is a 3kw but can see 24kw bursts (not that I need that). Then how much amps can be used; BMS limiters - Oh My... I get the fact the the more batteries will produce more power and more distance. Just not sure what I need as I'm not building a normal ebike. Then there are those who toss out a generic 20sp10 - but that doesn't tell me much. Of course I can google that, and it tell me a format; but now how many peak amps, etc.. Noob territory for me; I wish there was a formula -My motor + My controller = Need for this battery. But everyone power needs are different. I get it. I'll figure it out one day. I'm very open to any link of battery suggestions to get me started, I don't think I want to build one myself.

Provided this as a starting point: 3 x 6S14Ah = 72V x 14Ah = 1.008 kWh
What determines the amp output? Is that the controller? I set it to say max 80am, and it can use up to 80amps? I need a battery that can produce 80amps? Is that controlled by the BMS?
Sony VTC4 was also mentioned to me as they produce high amp output.
Lot of questions. Sorry.

If you want a small battery with enough power to test your concept then RC lipo batteries are probably the way to go. Lots of power density there meaning that a small capacity pack (Ah) can produce large bursts of power.

Batteries are not "for a 2kw or 3kw motor". What you are running into is retailers generalizing to sell to the public that does not care to understand the details of batteries. I don't mean that in a bad way. You sound interested in quickly becoming an advanced user rather than a plug and play type of user.

The most basic way I can explain it is this. A motor will try and take whatever power a controller can provide. A controller will try and draw as much power as you let it from your batteries. Batteries will try to give out as much power as you ask them too. So your task as a builder is to first figure out how much power you need. Most people estimate way too much in this dept. My 7kw full suspension bike was perfectly willing to kill me on technical single track at a motorcycle offroad park and I found myself dialing it down to 4kw.

So lets say you intend to build a 16 hp trials bike. You pick a QS 3kw motor. That's a good choice. Now you need a controller. The Votol will probably do it. With a 20s pack of Li-ion cells you have about 74v average. 16hp is 12kw. 12,000w/74v=162amps. So you need a battery pack that can supply bursts of 162amps. Lets say you pick the suggested sony VTC6 cells. They are rated for 15Amp continuous discharge. That is a power dense cell because an only 3ah cell is discharging at 5x its AH rating. That is known as 5C. If you wanted to be on the safe side and only stress them that hard you would need about 10 cells in parallel to achieve the 150-160 amps we calculated earlier. So you would have to build a pack of 20 series groups of 10 cells in parallel. That is 200 cells. At 46 grams each you are looking at 20lbs of battery weight. You would have 74v X 3ah X 10cells = 2.22 Kwh of battery. For perspective a 27hp zero FX dirt bike weighs 250lbs and would go about 25-30 miles of city riding with a 2.2Kwh pack.

So if you look at those numbers and think "Its a trials bike. I don't want a 20lb battery" well then you are going to need a more power dense cell than a VTC6. Or you need to use less VTC6 cells and just abuse them harder than 5c discharge rate. The more current (Amps) you draw from a cell the faster it wears out. Cells will kill themselves trying to provide any level of current you ask them too. So if you find a great deal on a certain cell and want to kill them in a short time that's totally up to you. Its always a give and take relationship based on how often you want to build packs and how affordable the cells are.

RC lipo cells are super power dense and are a cheap way to try out a powerful build. You could buy $400 worth of cells and make 10-12kw with them to try out your setup. They can also burn your house down.

Sorry if that adds to your confusion. Hopefully a breakdown example with some real numbers helps you grasp the greater concepts a little better.

Long story short regarding current:

• Motor will only take what the controller can give out

• Controller will give out whatever you ask it too up to its max rating

• Batteries will attempt to supply whatever the controller asks for

 

[gbeals]

So lets say you intend to build a 16 hp trials bike. You pick a QS 3kw motor. That's a good choice. Now you need a controller. The Votol will probably do it. With a 20s pack of Li-ion cells you have about 74v average. 16hp is 12kw. 12,000w/74v=162amps. So you need a battery pack that can supply bursts of 162amps. Lets say you pick the suggested sony VTC6 cells. They are rated for 15Amp continuous discharge. That is a power dense cell because an only 3ah cell is discharging at 5x its AH rating. That is known as 5C. If you wanted to be on the safe side and only stress them that hard you would need about 10 cells in parallel to achieve the 150-160 amps we calculated earlier. So you would have to build a pack of 20 series groups of 10 cells in parallel. That is 200 cells. At 46 grams each you are looking at 20lbs of battery weight. You would have 74v X 3ah X 10cells = 2.22 Kwh of battery.

THIS iS AWESOME! Everything you wrote has made things so much clearer to me. This is making sense! You have pretty much provided me with the formula(s) I was missing. How does this translate to torque? I NOW get 12kw = 16hp. My motor is rated for 40 ft. lbs of torque (56nm) at 3000RPm (I think). My bike has a current 1:4.5 gearing (10t/42t); I was thinking of running a primary drive to get up to 1:8 to make torque like the Electric Motion Trials bike; however it would seem that is SUPER overkill perhaps? I see many folks go direct from motor to wheel. I'll have an 18" dirt bike wheel. Am I correct to assume, with that gearing and motor I should be 4.5 x 40 ft. lb of torque yielding me 180 ft. lbs of torque? Not really concerned with speed, but figure with that size tire and gearing I'd be around 40ish mph?

Here is a pic of what I'm going after (I think); not sure if I should go direct drive; but this seems to have enough power for sure. Notice it is direct drive, with a pretty small battery, that you can stack two on. I perhaps can go up to a 50T in the back and have more than enough torque?

My 7kw full suspension bike was perfectly willing to kill me on technical single track at a motorcycle offroad park and I found myself dialing it down to 4kw.

After reading this I should mention this is a concern of mine as well. I've ridden a Electric Trials motion bike which is a full blown race machine! I probably don't need that. That is a 12kw beast with a massive gear reduction as well. If I went with half of that and ran 80amps (I see most with my motor going between 80-120amps); I'd assume I'd be at 6kw producing half the power? I of course would rather have the ability to "turn it up" later so what if I went with a Battery like VTC5a that has closer to 30a output (Is that right? I see various number for sony continuous amps). I'd need less? If I wanted a 100 battery pack with twice the amps - would I be at the same power output but half the Hours of use? I'm trying to have the 120-160amp possibility but with around 100 batteries - then a BMS that is rated for that size amp.

All super helpful information you have provided; I've read it numerous times and each time I get new take aways.

 

[gbeals]

Perhaps something like this with no primary gear. Goal is NOT Trials crazy leaps, but trail riding through the jungle. Wonder if I'd have enough Torque with no primary. 10 Teeth up in the back to 52T would give me 1:5 ratio.

Inspiration video : This bike has peak 12kw but only 20ft. lbs torque, no primary drive. This is the style of riding I'll be doing. Nothing too crazy. (NOTE: Video riding starts at 30secs.)
[youtube]AFKT19UuXwM[/youtube]

 

[SlowCo]

Perhaps something like this with no primary gear. Goal is NOT Trials crazy leaps, but trail riding through the jungle.

You will need more of a 1:8 reduction. Read the last few posts of j bjork and look at the size of the rear sprocket you'll need to have made:https://endless-sphere.com/forums/viewtopic.php?f=12&t=103800&start=125

 

[Xtr6]

If you go for no reduction then you need at least 450 Amp. for youre controller. I have build severall trail bikes, but al with a second stage reduction. A sevcon gen 4 size 4 is the one to have if you go for 1 reduction and at least 1:10 reduction. This is mine gas gas with 2 stage reduction one belt and one chain.

 

[gbeals]

Perhaps something like this with no primary gear. Goal is NOT Trials crazy leaps, but trail riding through the jungle.

You will need more of a 1:8 reduction. Read the last few posts of j bjork and look at the size of the rear sprocket you'll need to have made:https://endless-sphere.com/forums/viewtopic.php?f=12&t=103800&start=125

I just read the post - Gear reduction it is. Thanks. I have the 428 10t sprocket already, I'll start looking at go kart websites for the pieces I'll need.

 

[gbeals]

If you go for no reduction then you need at least 450 Amp. for youre controller. I have build severall trail bikes, but al with a second stage reduction. A sevcon gen 4 size 4 is the one to have if you go for 1 reduction and at least 1:10 reduction. This is mine gas gas with 2 stage reduction one belt and one chain. probleem eta2.jpg

That is Excellent, thanks for the photo - Looks like I'll go that path.

Seems you have a bearing in the steel mounting plate, a "broken" shaft , probably to another plate and bearing on the other side? Any photos? I have a 428 gear I believe that came with my motor, so I'll most likely use that then to my standard cycle chain size. Should I up the primary chain size or will that be enough you think?

Any details on that battery you have on the photo of your bike? Awesome by the way.

 

[rynhardt]

I think a reduction stage is definitely a good idea. It opens up more options in terms of gearing, chain and sprocket selection and placement.
With my build I was lazy and went direct drive with a 10T sprocket front and 121T sprocket rear. The bigger sprocket is more exposed and supposedly more prone to damage but I haven't had any issues with it yet.

For the battery pack, perhaps consider making it easily replaceable. That way you can start off with a 20Ah pack now, and later add another pack you can swap out?

I used LiPO packs without any BMS, just low cell voltage monitors. Mounted them in a metal enclosure and just used a good balance charger to keep them in shape.

More power is always welcome, but you can get surprisingly far with good line choices. I finished another regional comp yesterday with my bike (clubman class), which has a 1.5kW (cont) PMDC motor and go up to 6kw (max). That's 130A @ 48V.

With your setup you should have enough power and several options regarding gearing/sprockets.

 

[DanGT86]

THIS iS AWESOME! Everything you wrote has made things so much clearer to me. This is making sense! You have pretty much provided me with the formula(s) I was missing. How does this translate to torque? I NOW get 12kw = 16hp. My motor is rated for 40 ft. lbs of torque (56nm) at 3000RPm (I think). My bike has a current 1:4.5 gearing (10t/42t); I was thinking of running a primary drive to get up to 1:8 to make torque like the Electric Motion Trials bike; however it would seem that is SUPER overkill perhaps? I see many folks go direct from motor to wheel. I'll have an 18" dirt bike wheel. Am I correct to assume, with that gearing and motor I should be 4.5 x 40 ft. lb of torque yielding me 180 ft. lbs of torque? Not really concerned with speed, but figure with that size tire and gearing I'd be around 40ish mph?

Here is a pic of what I'm going after (I think); not sure if I should go direct drive; but this seems to have enough power for sure. Notice it is direct drive, with a pretty small battery, that you can stack two on. I perhaps can go up to a 50T in the back and have more than enough torque?

After reading this I should mention this is a concern of mine as well. I've ridden a Electric Trials motion bike which is a full blown race machine! I probably don't need that. That is a 12kw beast with a massive gear reduction as well. If I went with half of that and ran 80amps (I see most with my motor going between 80-120amps); I'd assume I'd be at 6kw producing half the power? I of course would rather have the ability to "turn it up" later so what if I went with a Battery like VTC5a that has closer to 30a output (Is that right? I see various number for sony continuous amps). I'd need less? If I wanted a 100 battery pack with twice the amps - would I be at the same power output but half the Hours of use? I'm trying to have the 120-160amp possibility but with around 100 batteries - then a BMS that is rated for that size amp.

As for how the numbers translate to torque, the torque per amp numbers of that motor are probably posted somewhere. That is a know value for a given motor. So if you know the current you are feeding it you don't have to guess. You can also back figure it by HP and RPM. Just from experience with motor bikes and Ebikes I would safely say that if you have 12kw electric motor geared for only 40mph then your torque is going to be way more than enough.

Direct drive vs multi stage gearing is a tough choice. On a true trials bike for true trials riding you really don't want a giant vulnerable sprocket on the wheel. Additionally the size and position of the motor sprocket and rear sprocket with respect to the suspension have an effect on the suspension action under throttle. So Ideally you would want keep the same sprocket positions and sizes as the stock bike. The downsides to doing the reduction in stages is that every stage kills some efficiency, adds weight, and adds noise. So you need to decide for yourself whats worth it and whats not. If you do a primary reduction before the final drive to the rear then you can easily buy off the shelf sprockets for your bike. If you have free or cheap access to a machine shop to make sprockets for yourself then maybe that changes things and you can just go single stage and bash giant sprockets all the time.

Your assumption about using half the pack and getting half of the current and capacity is generally correct but not entirely realistic. There isn't a hard limit on battery current draw. Your VTC6 or VTC5 might be just fine at 30 amp peaks but 30amps from an 18650 seems optimistic in my opinion. I believe you would surely be at the low end of cycle life doing that to them. You could build 2 small packs and run one or both depending on range you need but its always going to be easier on a cell to share the load with as many other cells as possible. So a simple glance at the numbers seems like half the pack would give you the same power but half the range. In actuality half the pack would provide less than half the range because they are less efficient when you are torturing them. They also wear out way faster because of all the heat from high amp discharges. This is why there are so many different types of cells on the market. Some are energy dense but don't like high current. Others are power dense but don't have as much capacity per unit weight. The VTC cells are on the power dense side but even still I would ask around to see people are really pulling 30Amps from them with good results.

 

[j bjork]

You have got a lot of good suggestions already, but I thought I might be able to give some too.
I think you want to go pretty low in gearing, so I think 2 stage is a good idea.
On my dirtbike I had 7:1 at first, it wasent that peppy then. It wouldent wheelie just by giving throttle, and if was going up a hill where I had to start really slow it didnt pick up much speed.

With 8:1 it was a big difference. It wheelies and rips up the hills. Now, your bike will probably be half the weight of mine. So it will probably need a lot less power. The controller is rather capable, I run it with 500 phase amps and 300 battery amps.
I only use sport mode, where it is more aggressive on the throttle and I have max settings on throttle rise and decline.

At first after I changed gearing I thought it got too aggressive, and thought about tuning down the controller a little. But I got used to it very fast :wink:
My point is, you may think you don't need low gearing and high power. But chances are you may want it after a while..
You can just tune the controller softer to start with, then all you have to do is change settings if/when you want more power.

A trials bike is supposed to be able to climb a wall, right?

About batteries, I think 20-22s is where you should be.

20s can be convenient, for example you can build it like 2 10s batteries series connected with an automatic fuse between.
Then you can just turn off the fuse and charge like 2 10s packs with an iCharger 4010duo for example, without having to disconnect anything. Like I do on my "stealth bomber"

21s is the highest you can go and still charge to 4,2v/cell without going over the controllers max voltage.

22s you can probably not charge much over 4,1v/cell, but it is good for the batteries. Probably a little less weight effective than 21s
You get a little higher voltage span with a little higher nominal voltage, meaning a little higher power.

Amps give torque, voltage rpm. So a higher voltage means you keep full torque up to a higher rpm =more power.

I think rc lipo is a good idea on a bike like this, voltage sag is not just lost battery life and heat. It is also lost power.
With tough cells you can build a 20Ah pack that have no problem delivering 300A

 

[gbeals]

Gear reduction around 8:1 is my chosen path. I'm looking at websites for the parts needed to build the reverse jackshaft. Seems pretty straight forward. I'll post up my chosen parts once I've made my decision.

LIPO - That seems pretty interesting. I like this idea. I'm kind of scared to build a battery, so this R/C Battery choice may be an easier more digestible path for me at this stage in my knowledge. Seems there are plenty of options from HobbyKing for example.

Now for my ignorance (but learning a lot from reading and re-reading all these posted -thanks). Now 20s as was 22s was mentioned; build it like 2 10s packs - J bjork - do you have details on how you do this with your stealth? Are we talking about wiring up 3 of these bad boys up to get 72v?

Just for clarity, we are talking about something like this right? If i use the 12C number, it would seem I can pull 240amps from something like this. Run 3 in series keeps me at 240 amps get me around 75v. Set the controller at 120-140amps I have a safety factor included. Rynhardt You mentioned 14ah, these at 20 seem similar to what you had mentioned. I'd run just shy of twice your amps so I'd imagine quite less ride time.

Specs:
Minimum Capacity: 20000mAh
Cell Count: 6 / 22.2V
Constant Discharge: 12C
Peak Discharge (10sec): 24C
Pack Weight: 2630g
Pack Size: 203 x 93 x 70mm
Charge Plug: JST-XH
Discharge Plug: XT90

It was a nice day in Oahu the other day. Not too hot with a nice mist in the air. My bud and I took advantage and hit the trails with two of the gas bikes.

 

[j bjork]

The pack you posted is not what you want to draw high currents from.
You should look at packs with maybe 40c rating or so, the higher the better (and the more expensive)
They will probably be about 5Ah, so you would have to paralell a few.

Well, you get two 5s bricks (or one 4s and one 6s)and series connect them. Then you have one 10s. Make another one so you have two.
Then connect the negative wire on one of them to the controllers negative, and the positive to the automatic fuse. Then you connect the negative on the other pack to the other connection on the fuse, and the positive on that pack to the positive on the controller.

That is the principle at least, if you want to see how I did it it is easiest to look in my build thread.

 

[rynhardt]

It's been mentioned above but I'll recap with what I know about LiPo's (sorry, this turned out to be a long post):

You can charge a LiPo cell up to 4.2V, but you don't have to. Charging only up to 4.1V per cell will extend your battery lifetime.
You can discharge to around 3.3V/3.2V/3.0V per cell depending on who's advice you choose to take :lol:
Nominal is 3.7V, which is approx 10% below max and 10% above min.

A BMS (battery management system), which monitors each cell's voltage, will most likely disconnect the battery if any of the cell voltages drop below say 3.3V. You may then have the option to reset the BMS and limp home.

An LVA (low voltage alarm), which also monitors each cell's voltage, will simply make a loud beeping noise once any cell drops below say 3.3v (this is normally settable). It won't disconnect the battery/cell like a BMS.

I chose to go the LVA route because it's cheap.
But, an advantage is it won't cut the power when you need it most. Now my experience has been that the LVA really only beeps when you require a fair amount of power, i.e. full throttle, and the cells are on the low side already. Having the power cut when you really need it can be a problem, like getting stuck halfway up a staircase

My personal opinion is I'd rather draw the cell below 3.3V for a short while than have the power cut, even though it may not be great for the cell. The cell normally recovers to above 3.3V again if you don't draw any power for a few seconds - if this is the case then I'm not too concerned I damaged the cell.

Now for 72V (nominal), it means the battery voltage can range from approx 65V (discharged) to approx 80V (fully charged) if you're using Lead Acid chemistry, which seems to be a generally accepted benchmark. Alternatively you can use a 10% variance up or down, so 72V/1.1 = 65V, and 72V*1.1 = 79V.

So, using x LiPo cells in series, i.e. xS: discharged V, nominal V, recommended usable V, max V
18S: (3.2V*18) = 57.6V, (3.7V*18=66.6V), (4.1V*18) = 73.8V, (4.2V*18) = 75.6V.
20S: (3.2V*20) = 64.0V, (3.7V*20=74.0V), (4.1V*20) = 82.0V, (4.2V*20) = 84.0V.

LiPo packs are usually packaged in 4S,5S & 6S varieties, with 6S being the most common for large Ah packs.
Depending on what may be available in your area, you could either go
18S = 3 x 6S, or
20S = 4 x 5S, or
20S = 5 x 4S, or
20S = 2 x 6S + 2 x 4S

As long as the mAh and C ratings are the same, you can combine as many xS packs as needed in series. In fact, a 6S pack is just 6 cells wired and packaged in series, and the same cells are used in a 4S pack, just using 4 cells and not 6.

For example, a 22000mAh 6S 25C Lipo pack contains 6 cells, each of which is 22Ah. The continuous discharge rate is 25C * 22Ah = 550A, and max amps may be up to 1100A (depending on manufacturer).

Whether you go 18S or 20S is going to be determined by your controller's max voltage and low voltage cutoff. The motor won't care much apart from the top speed you may lose out by going to a slightly lower voltage.

Lastly, you'll need to invest in a good balance charger, which may be somewhat expensive.