Noobie planning an Electric bike with >30 mph

[macribs]

mac,

18650 li-ion cells may be another battery option to consider

- Safer than lipo
- Cheaper than lifepo4
- Can be configured in any form or shape
- With 700 cycles they are less enduring than lifepo4, but after at least 3 years of continuous use I would probably want to switch to the then next generation of batteries anyway. So the longevity of lifepo4 may not be an advantage after all.

I've been looking into 18650 as well. As I never spot welded batteries before I am not sure if I will make it without causing death to the whole pack
But yes there have been significant improvements on these. Sony VTC5 for instance. I think also Samsung and Panasonic have either fresh releases of new ones or they are just to be released. So yes I might reconsider and do 18650, but as of now I try to learn most about each chemistry and battery type available.

It is so hard to make decisions because any and all choices made will come into play with other choices taken down the road. So I have kind of been going about to learn enough about each part to make educated decisions that will not give problems in other areas before I commit and start ordering. But this means it will be a lsow start to gather the needed know how first hand.

Oh well hopefully the result will be parts that matches well and not box upon box with leftover parts I could not use.

 

[chriss]

Still having troubles with battery / controller configurations.

For illustrative purposes I found an example of a 48V frame battery ready to purchase.
The setup is 13s4p of 3.7V 2900mAH li-ion cells for 48V voltage and 11.6 AH. So far so good.

Now, my problem is the continuous current and how to ensure that a controller would fit well with the chosen battery.
This battery has a stated continuous current of 10A, so should a controller also have 10A to be in balance? Or should the continuous current from the battery be higher for safety reasons? Or am I missing something entirely?

 

[windtrader]

the controller needs to be sized to the max amps it will be passing along to the motor. The way to do this is to look at the battery amps, in this case, 11.6amps and multiply by the C rating you will be pushing the battery. If this battery is rated 1C then you can sized the controller for about 11.6*1c = 11.6amps. So a 15 amp controller would work.

The battery you chose is not a desirable battery due to two main factors. The chemistry does not allow many cycles or recharges. 300 is pretty low. The other factor is continuous and max C ratings. You want to use a battery with higher ratings.

Continuous ratings of 10C and max of 15-20C would be much better. You would then plan to run the battery between 50%-100% of the continuous rating. Here is another example. Say the battery pack is rated 15 amps and continuous rating of 5C and max of 10c. A controller of about 60 amps would be acceptable as long as you limited exceeding 60amps as anything over this is going to stress and easily make it fail.

For noobies, it is better to obtain a pack that is prebuilt. DIY battery right requires spot welder and quite a bit more knowledge to wire properly and balance and manage. Prebuilt packs plug and play and you need to primarily monitor and charge and discharge properly.

 

[macribs]

I am struggling too with the batteries. Some places we can see C rating other sites not so much.

Here is a lifepo4 pack claimed to have 30C rate. Yet it does not say so in the specs.

And this Lipo has lower C rate of 15.

So the Lifepo4 has double the C rate and will deliver double the current over the lipo?

These are from the site of crazymotor, from his battery thread.


Those lifepo4's seems to be a good choice. What do you think?

 

[windtrader]

The EXB3610LFP, like all Lithium Ion type of batteries all have several C ratings. Using this as an example states the nominal capacity as 10 amps. 1C = 10 amps. The "working" current rating of 15 amps is 1.5C. It represents the rate at which the battery can be drawn down with no harm to battery life or structure. The "rate discharge" is 20 amps or 2C. This represents the rate at which one can draw the battery for a few minutes before becoming stressed and heating up. The "overload" rating of 50 amps is 5C. It is the rate at which you can run for several seconds before starting to heat up/ melt/ fail.

Basically, this is a crap and poor performing battery for a high performance ebike. The continuous C rating to power the system is less than 2C, very low. Low C means you can run longer but you can not expect run at higher power if the same battery had higher C ratings.

So the Lifepo4 has double the C rate and will deliver double the current over the lipo?

LiPo typically have pretty high C ratings. LiFePo4 tend to have lower C ratings but certainly in a suitable range.

Those lifepo4's seems to be a good choice. What do you think?
As mentioned before LiPo offers the highest performance of the two. Lightest weight per output and higher C ratings. LiFePo4 weight more, cost more but are far more stable and offer a good balance of performance, safety, and cost for most daily driver bikes. If you plan on just going balls out at the track the LiPo is the choice. If you plan on commuting daily and want fewer worry about fire go with the LiFePo4.

 

[chriss]

windtrader
Thanks for your notes. I think this helped me understanding this subject better. But let me take the specs for the lipo battery that mac has posted for clarification. Following your argumentation ("like all Lithium Ion type of batteries all have several C ratings. Using this as an example states the nominal capacity as 10 amps. 1C = 10 amps) that lipo battery has a:

- capacity of 20AH, so 1C = 20amps
- working current of 2.5C
- rate discharge of 5C

Then, an appropriate controller should have 2.5*20 = 50A to 5*20 = 100A. That is a wide range! Should the working current / continuous current or the rate discharge / max current be used to select the controller? Intuitively, I would go with the higher settings, but after a second thought there is something odd in the setup. With 48V the controller may draw 100A*48V = 4800w at peak times! And you mentioned in a response to my earlier repsonse to my post that you were looking for 10C-20C ratings in a battery.

 

[windtrader]

The peak ratings have no practical use in design or operation as it indicates you are destroying the battery. You would set max thresholds much lower to cut discharge from the battery.

The key value is the continuous rate as this implies the battery can supply power safely and without cutting short the life of the battery.

 

[chriss]

The key value is the continuous rate as this implies the battery can supply power safely and without cutting short the life of the battery.

OK, many thanks.

Here is one more question: Does the continuous discharge (rated in C) multiplies when two cells are put in parallel?

I'm looking at standard 18650 li-ion cells. 3.7V, 2600mAH. Now a single cell is usually said to have a discharge current of 0.2C which seems pretty low. If I compare that to the values named in recent posts, this value must logically multiply to just reach 1C, let alone the 10c some find desirable.

Say I wanted to build a 48V 20AH battery pack.
With a 13s 1p setup I have 2.6AH and 0.2C continuous discharge.
With a 13s 5p setup I have 13AH and 1C continuous discharge.
With a 13s 8p setup I have 20.8AH and 1.6C continuous discharge.

If 1C equals 20amps, then 1.6C equals 32amps. So a 30amps controller seems appropriate.
To continue this thought:
With a 13s 10p setup I have 26AH and 2C continuous discharge and a 40amps controller would be appropriate.

So, increasing the capacity linearly increases the continuous discharge and, hence, requires a stronger controller.

Please, someone tell me this is correct

 

[windtrader]

Of single cell is 2600maH, 1 2600 or 2.6 aH. As far as I know a battery is not rated below 1c nominal. In parallel overall pack rating is single cell times number of cells in parallel.

 

[chriss]

This is what I was looking at just off alibaba. But I also see 18650 cells with 1c continuous discharge. Makes no sense to me. These type of cells are supposed to be standardized. :?

 

[chriss]

OK, I'm really confused about battery management systems here.

There seem to be different types and layers of "protection". What do I really need to "just" charge by batteries safely? Are all these complementary or do they replace each other?

- At the individual cell level there are protected / unprotected cells (PCB protected circuit board)
- Combining cells to a battery pack may or may not include the installation of a BMS module
- And when connecting different battery packs to a battery unit a balancer would take care of equal voltage distribution across the cells.

So do I just need a balancer and go with unprotected cells?

 

[underdog]

OK, I'm really confused about battery management systems here.

There seem to be different types and layers of "protection". What do I really need to "just" charge by batteries safely? Are all these complementary or do they replace each other?

- At the individual cell level there are protected / unprotected cells (PCB protected circuit board)
- Combining cells to a battery pack may or may not include the installation of a BMS module
- And when connecting different battery packs to a battery unit a balancer would take care of equal voltage distribution across the cells.

So do I just need a balancer and go with unprotected cells?

NO... That is a by my experience a bad idea, no mather how carefull you are. Go for a desent BMS system, and a bulk-charger. Problem with balance charging, is that you are running unprotected when driving. While doing this I have killed 10% of my cells over a 30-day period (I only run up to 60 amps). Your real problem comes at the end of your charge, when driving. Cells are never 100% identical, and some are going to sag more than others. So these already "bad" cells are destined to dipp to low, and get f*-ed pretty fast if you are accelerating at low state of charge. Some are going to say that this can avoided by running "RC-style" low voltage buzzers or other similar solutions. Wellm true as it might be, your quest for making a simple setup just got even more complicated to use and charge. Go BMS! It is money very well spent.

What you want, as a minimum is:
* individual cell low and high voltage protection.
* overcharge protection
* over-discharge protection
* balancing function (bleed-type is ok)

 

[windtrader]

The best option is to get a complete battery pack at first. There are many ways to build your own battery pack the wrong way. And charging is critical too. There is very little tolerance for errors with batteries and mistakes can be expensive and dangerous. Read the pinned thread on burning houses or some stories of some very badly burned hands.

A quality well built battery pack is not cheap but brings much comfort, more ride time, and few headaches. Many do design and build their own packs but there is a lot to it.

 

[macribs]

@underdog and @windtrader both good replies and useful for me as well.

I am still back and forth about what chemistry to choose. One day Lifepo4 seems like the way to go and the next day Lico from hobbyking.

So to try to come to a conclusion on what is the right choice for me I have some Q's for you guys regarding charging and discharging.
Lico gives most current but are harder to keep alive and to charge correctly. But if I used a BMS it seems like many of my worries about Lico's could be removed.
Will a good quality BMS monitor the charging and discharging of batteries within safe limits when I do bulk charge? I would hate to charge each cell in a pack on its own. That seems like too much hassle. If I bring the bike inside where I can monitor the charging, will bulk charging be safe enough when using BMS and a bulk charger?

Those A123 pouches seems relatively light weight and easy to stack. And I see many uses them. Does the extra weight of A123 compared to Lico really matter for real world use? I mean it seems they discharge fast enough to be used in various builds here on ES. With high output motors and speeds well past 40 mph. If I get like 2 x 36 v or 2 x 48 v packs will they pack enough punch and add extra safety to justify extra weight? And will a field weakening controller in any way help for use with a A123 pouch pack?

There are so many things to consider, and all of the choices made will inflict on the rest of the chain of components and how they will perform.
Maybe a pre build bike is not such a bad idea after all

 

[999zip999]

Look at a Prodeco a good bike for the price. A plug and play go ride bike. With 2yr. warranty. Then you will have an ebike you can go out and ride. At the same time understanding your new ebike. Then keep on reading.

 

[windtrader]

More than just a fancy name. TURNIGY nano-tech lithium polymer batteries are built with an LiCo nano-technology substrate complex greatly improving power transfer making the oxidation/reduction reaction more efficient, this helps electrons pass more freely from anode to cathode with less internal impedance.

Lico? I was not sure if that was a typo as it was a new one to me. So basically a LiPo battery.

LiPo vs LiFeO4. You know the pluses and minuses by now. Backing up from this decision is make or buy. There are vendors producing great quality LiFeO4 packs, ready to plug in and go. There are few if any vendors selling ready to LiPo packs for ebikes.

Make this decision first. Even with HK packs you still need to wire them together and package them and other decisions around charging connections and such. And this takes time to think through and get right. This is the precise scenario where the risks and hazards show their ugly side. If anything you would want to charge your batteries OUTSIDE in a fire free zone.

A123 is a top tier battery name. Humm.. still shooting for a 72-100V beast first time out eh? Need to do more research and create some serious design plans, then go over it and over it until you get all the bugs worked out. If you do this diligently and competently you may very well reconsider the performance objectives downward. You just don't want to make mistakes on such an expensive build. And you WILL make mistakes. Build something 1k-1.5K and learn then decide where to go from there. Anything in the 72-100v range done right looks like the pretty exotic builds you see here. Either you have a lot of money to pay for a well engineered unit or you have a lot expertise if you DIY but still have cash stuffed in your pockets; there is no way to build a safe high performance ebike on change or shortage of gray mass.

Lastly, if you must build your battery pack look at the headways. They are designed to be connected via a system of connectors without doing any welding or wiring. They offer formed plastic holders to make a variety of pack sizes. To me, this is actually in the range of a DIYer without having to start buying spot welders and such.

 

[windtrader]

Look at a Prodeco a good bike for the price. A plug and play go ride bike. With warranty.

There are plenty of ways to DIY an ebike with minimal hassles. Pick up a spoke hub motor kit all included (EDIT: Minus battery) and just grab a six pack and an afternoon and a donor bike and you will be on your way. All other options, even mid drive kits have far more "Oh shi..., now what?" moments.

http://www.yescomusa.com/Electric_Bicycle_Engine/
There are several excellent threads written in great deal on these holding up really well on daily commutes adding to many thousands of miles.

 

[macribs]

Look at a Prodeco a good bike for the price. A plug and play go ride bike. With warranty.

Nah I rather drive an ICE car to work.
Can't see the good price either, when you take into account they are all stiff tails.


Maybe it is time to bite the bullet and shell out the big cash for a hi power full suspension e-bike.

 

[999zip999]

My reason is a 2yr. warranty and how many ebay batteries last 2yrs. ?
I guess the cheapest is the 300usd. Kit shipped and the 500usd. calibike battery both L.A. base. Or a sunthing battery.
So 900Usd. Plus a 80-100usd donor bike.

 

[windtrader]

Being able to obtain these locally is a huge plus. Shipping is a joke at standard UPS ground rates. Plus as resident buying from a Ca based company we have substantial consumer laws on our side. You can get batteries elsewhere but the running gear is hard to beat at that price given the really good experiences being reported.

Per the OP title, the 48V 1000w unit I suspect might just register 30mph too.

 

[underdog]

You want one of the 50V packs from here: http://em3ev.com/store/index.php?route=product/category&path=35
Paul will sort you out. Good priced top quality packs! Go for the 20R-cell-packs if you want stupid-power 8)

 

[windtrader]

Agree EM3EV is a very solid choice of vendor and product. Many mentions of folks happy with his batteries. I rode with them for a few days and they were fine, no comment over the long term.

 

[chriss]

Look at a Prodeco a good bike for the price. A plug and play go ride bike. With 2yr. warranty. Then you will have an ebike you can go out and ride. At the same time understanding your new ebike. Then keep on reading.

But there is nothing to learn from a "plug and play" bike. I want to make my hands dirty, just not burn them, :wink:

 

[chriss]

Lastly, if you must build your battery pack look at the headways. They are designed to be connected via a system of connectors without doing any welding or wiring. They offer formed plastic holders to make a variety of pack sizes. To me, this is actually in the range of a DIYer without having to start buying spot welders and such.

You can do the same with 18650 cell brackets and metal strips, don't you?

Google image search
http://tinyurl.com/qaa8nk9

 

[molybdenum]

Interesting thread; I've been following this awhile.

Lastly, if you must build your battery pack look at the headways. They are designed to be connected via a system of connectors without doing any welding or wiring. They offer formed plastic holders to make a variety of pack sizes. To me, this is actually in the range of a DIYer without having to start buying spot welders and such.

You can do the same with 18650 cell brackets and metal strips, don't you?

Google image search
http://tinyurl.com/qaa8nk9

You still need to spot weld the 18650s. The Headways screw together.