[Solarsail]

Sounds good. I believe the 2 kWh capacity is on the anemic side, and you should increase that to over 3 kWh for a motorcycle.

Note that 48V/3.6V = 13.33s. So 12s (12 in series) which is what the BMS says is too low. Either choose 13s or 14s, depending on what BMS you can find that meets your power requirement. You may be able to get away with 75A. And if you build two packs in parallel, then each of the two BMS needs only be 35A.

48V motor controllers can handle up to 65V in most cases, so I would recommend 14s which maxes at 4.2 x 14 = 58.8V. Or you may want to altogether go to 96V (27s) by connecting the two packs in series instead of parallel with a 96V motor/controller. In which case current draw will be 30A to 50A. Efficiency improves with higher voltage.

The charger is only 200W and will take forever to charge. I would recommend a 1200W charger and a 1 kW 36V or 48V power supply. The charger can be installed in the cycle. Here is an adjustable charger:

https://www.ebay.com/itm/1200W-DC-D...162690?hash=item4b1f914a82:g:HccAAOSwjIRZkT9L

 

[Functional Artist]

Sounds good. I believe the 2 kWh capacity is on the anemic side, and you should increase that to over 3 kWh for a motorcycle.

Note that 48V/3.6V = 13.33s. So 12s (12 in series) which is what the BMS says is too low. Either choose 13s or 14s, depending on what BMS you can find that meets your power requirement. You may be able to get away with 75A. And if you build two packs in parallel, then each of the two BMS needs only be 35A.

48V motor controllers can handle up to 65V in most cases, so I would recommend 14s which maxes at 4.2 x 14 = 58.8V. Or you may want to altogether go to 96V (27s) by connecting the two packs in series instead of parallel with a 96V motor/controller. In which case current draw will be 30A to 50A. Efficiency improves with higher voltage.

The charger is only 200W and will take forever to charge. I would recommend a 1200W charger and a 1 kW 36V or 48V power supply. The charger can be installed in the cycle. Here is an adjustable charger:

https://www.ebay.com/itm/1200W-DC-D...162690?hash=item4b1f914a82:g:HccAAOSwjIRZkT9L

Thanks for the reply

I am learning as I go so, small steps are best

I started off running the bike @ 36V then moved up to 48V.

(I believe the (4) 12V 35AH SLA's (80 lbs.) I have currently are ~1kW)

So, the plan is to start off ~1kWh, & next move up to 2kWh, then later I can go bigger.

By using a 2kWh section of a Volt battery(45 lbs.), I should have nearly twice the power capacity while only carrying half the weight.

* These Volt battery packs seem to address many issues associated with larger DIY lithium battery packs.
...they are professionally assembled (no DIY welds or resistance issues)
...mounted in a sturdy frame
...easy to control heating &/or cooling (if necessary/depending on climate)


Now, the BMS, from my research

A 2kWh section of a Volt battery is
...12 cells in series (12S)

* that's why I linked the 12S BMS

They have an average of 3.7V per cell x 12 cells = 44.4V
...the average SAFE use voltage range seems to be 3V - 4.2V
...under 3V will damage the cell & over 4.2V can overheat/cause fire
(3V x 12 cells = 36V - 4.2V x 12 cells = 50.4V)

*that's why I linked the 50.4V charger
...I agree, it will take a while to charge
...I don't need quick charging, overnight (8 to 10 hrs.) is fine
...I think the main concern is to match the 50.4 top charge rating for these batteries


The speed controller on my bike is a KDZ72550 (input voltage 24V - 72V)

I ran @ 36V 35AH for a while, so going to a 44.4V 45AH Volt battery (40V - 50V) is still an upgrade & should be fine (for now)


**So, going with a 2kWh (12 cell) section of Volt battery & wanting a 100A discharge current, is this an adequate choice of BMS to protect this battery?

 

[brian_]

So, the plan is to start off ~1kW, & next move up to 2kW, then later I can go bigger.
By using a 2kW section of a Volt battery(45 lbs.), I should have nearly twice the power capacity...

A kilowatt (kW) is a measure of power. A kilowatt-hour (kWh) is a measure of energy. In the section quoted above you use only power units and refer to "power capacity", but you are discussing energy, not power.

I suspect that you know the difference, but if you are sloppy and show power units when talking about energy, it just causes confusion.

 

[Functional Artist]

A kilowatt (kW) is a measure of power. A kilowatt-hour (kWh) is a measure of energy. In the section quoted above you use only power units and refer to "power capacity", but you are discussing energy, not power.

I suspect that you know the difference, but if you are sloppy and show power units when talking about energy, it just causes confusion.

As I said, "Learning as I go"

So, it should be: "So, the plan is to start off ~1kWh, & next move up to 2kWh, then later I can go bigger."

Thanks for the clarification

 

[Solarsail]

OK, now it makes more sense to me.

If I have gotten it right, each Volt cell is 15.4Ah and there are 3 in parallel, hence your configuration is 12s3p, for 3x 15.4 = 46.2Ah. 1C acceleration (46.2A) is normal, while 2C would require 92.4A, which requires fatter cables. A 12s3p would be 36*3.6*15.4 = 2 kWh. So I am not sure how you will build the 1 kWh pack in particular that you are using a volt 12s3p module and it would be tough to break it apart?

If you were to build the powerpack from scratch using new 3.5Ah 18650 cells (LG or Samsung), which are the densest form of storage, A 2kW pack would weigh only 14 lbs not including the packaging and cables. The volume could be as little as 3 liters.

The charger that I linked can do any number of cells in series: 10s, 12s, 14s, even 20s. It is adjustable by the pots that are on the board. There is another charger on eBay that has a digital display and you can set the CCCV voltage and current by buttons - but I have not used this and do not know if it is entirely suitable.
https://www.ebay.com/itm/900W-DC-DC...760187&hash=item28143be280:g:MW8AAOSws4JW69fZ

Good charging would be at 0.5C, or 46.2*0.5 = 23.1A. So you would adjust the charger to 12 x 4.15V x 23.1A or 49.8V and 1.15kW. And you can charge in 2 hours. I have chosen 4.15 instead of 4.2V to increase the life of the cells. Of course GM was charging to something like 3.9V, with a conservative 35% unused buffer (top and bottom) for the Volt cells. Other auto manufacturers use 5% unused buffer.

At 100A discharge, you are draining at 100A/46.2Ah = 2.16C which is not unusual. Depending on the chemistry and manufacturer of an 18650 cell, 2C and 3C can be just fine. With nano-LFP type cells, you can do 20C! Panasonic recommends 1.5C continuous discharge and 30 second peak discharge at 2C. Tesla discharges at 15C during top acceleration Ludicrous mode, and that is supposed to be OK. At 2.16C you should be safe, as long as you do not do that often and keep it below 30 seconds. However, the Volt prismatic battery may be quite different from an 18650, so I am not sure. The BMS board seems to be the right one for this purpose. It is a pricey board, so it may be of good quality. This BMS does not have temperature monitoring, but that should not be an issue for your bike at 0.5C/2C charge/discharge, and adequate ventilation would do.

You may also want to take a look at http://www.diyelectriccar.com/forums/showthread.php/18650-13s10p-project-48v-x-34ah-188618.html

 

[brian_]

...
If I have gotten it right, each Volt cell is 15.4Ah and there are 3 in parallel...

... So I am not sure how you will build the 1 kWh pack in particular that you are using a volt 12s3p module and it would be tough to break it apart?

Any of the Volt battery experts, please correct me if I am mistaken...

As with most production EVs, the parallel connection in the Volt pack is at the lowest level. That means that 3 (Gen 1) or 2 (Gen 2) cells are connected in parallel, then those sets are connected in series (96S in total). The series chain is broken up into modules with different numbers of cells (and thus different module voltages) as determined by packaging requirements:

• Gen 1:
  • 18 or 36 cells,
  • so 6 or 12 in series
  • or 22.5 or 45 volts (nominal)
  • in 9 modules
  • 56 Wh per cell, 167 Wh per group of 3 cells, so 1 kWh @ 22.5 V or 2 kWh @ 45 V per module
• Gen 2:
  • 24 or 32 cells,
  • so 12 or 16 in series
  • or 45 or 60 volts (nominal)
  • in 7 modules
  • 94 Wh per cell, 188 Wh per group of 2 cells, so 2.25 kWh @ 45 V or 3.0 kWh @ 45 V per module

Nominal voltages are based on GM's spec of 360 volts nominal for 96 cells in series.

The only 12s3p combination is the larger module size in the first generation Volt. If the idea is to use the larger Gen 1 modules, then they are indeed 12s and 2 kWh. Another 1 kWh can't be connected in parallel, as it would the smaller Gen 1 modules, which are 6s (and so half the voltage). Even if breaking down modules to the cell level and re-stacking, the logical combinations which would still be 45 V (nominal) would be one-third or two-thirds of the large module (12s1p or 12s2p combinations)... not half.

 

[Functional Artist]

The BMS board seems to be the right one for this purpose. It is a pricey board, so it may be of good quality. The BMS does not have temperture monitoring, but that should not be an issue for your bike at 0.5C/2C charge/discharge, and adequate ventilation would do.

Working on understanding the connection of this BMS unit

https://www.ebay.com/itm/222353573658

It seems, to (properly) connect this BMS to a 2kWh section of a Chevy Volt battery.

First,

...you have to connect the (B-) to the negative (-) pole of the battery pack (0 Volts)

...then start taking voltage readings from the orange OEM (original equipment manufacturer) 12 wire pigtail that plugs in to the battery pack
(to find the end (wire #1) that shows a 3.7V reading)

...this first wire (between cells 1 & 2) with a 3.7V reading connects to balancer port #1)

...the second wire (between cells 2 & 3) with a 7.4V reading connects to balancer port #2

...the third wire (between cells 3 & 4) with a 11.1V reading connects to balancer port #3

...the fourth wire (between cells 4 & 5) with a 14.8V reading connects to balancer port #4

...the fifth wire (between cells 5 & 6) with a 18.5V reading connects to balancer port #5

...the sixth wire (between cells 6 & 7) with a 22.2V reading connects to balancer port #6

...the seventh wire (between cells 7 & 8) with a 25.9V reading connects to balancer port #7

...the eight wire (between cells 8 & 9) with a 29.6V reading connects to balancer port #8

...the ninth wire (between cells 9 & 10) with a 33.3V reading connects to balancer port #9

...the tenth wire (between cells 10 & 11) with a 37V reading connects to balancer port #10

...the eleventh wire (between cells 11 & 12) with a 40.8V connects to balancer port #11

...& the twelfth wire connects to the positive (+) pole of the battery pack & it should read 44.4V

That all seems simple & straight forward enough

I am confused by

this part that says: (see below)
...(B-) is positive (+) pole for both charging & discharging
...(P-) is negative (-) pole for both charging & discharging


1, The charging port and the discharge port of the board are the same Positive port. “B-“ for negative Pole of the battery pack, “P-“ is negative pole for both discharging and charging.

2, “B-“, “P-“ welding pad are through-hole port, hole diameter of 3.5 mm; You could use solder iron to weld the wires through the hole port, Every charging port for battery are the DC needle seat forms output.

3, First connect the “B-“ to the battery pack, then re-check with the battery voltages, then connect the 12 wires onto the batteries, Do not connect in wrong ordering, or it will burn out the board.

If you made wrong connection and reverse the board that will cause smoke, please check with every wire to be sure you are doing correct connection.

check all the wires voltage with orderly, start from B- , and see if it increasing from 3.6V, like:
( wires / voltage )
1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12
3.7V - 7.4V - 11.1V - 14.8V - 18V - 22V - 24V - 29.6V - 33V - 36V - 40V - 44V


Check every voltage on the wire step by step before plug in the connector. Check every wire and see if the orderly are correct. Because if any of the wire get a wrong order, it will get burnt. Smoke shows board already get burnt for protecting the battery being damaged by wrong connection, For DIY assembling. Please make sure you are capable to do the assembling before ordering! If you dont know how to do the connection, DONT ORDER IT!

So, trying to understand this (correctly)

How can (B-) (battery negative (-) as far as I know) be the positive (+) for charging & discharging?

...& how can (P+) be the negative (-) for charging & discharging?

 

[Solarsail]

"...(B-) is positive (+) pole for both charging & discharging" -- It does not say this anywhere. Rather it says "“B-“ for negative Pole of the battery pack" - which is correct.

"how can (P+) be the negative (-) for charging & discharging?" -- It does not say this. It says "“P-“ is negative pole for both discharging and charging." - which is correct.

The motor controller (fat) cables will be in parallel with the charger (thin) cables.
The positive of both will go to the battery postive.
The negative of both will go to the board P- terminal.
The B- of the board will go to the battery negative with a fat cable.

So no - the motor/charger negative do not go to the battery pack but to the P- on the BMS board. The 100A (negative) current goes through the board and three of the mosfets will be in series with the motor. (The 3 mosfets are parallel to each other.) If for any reason the current has to be cut, the three mosfets turn off just like a mechanical relay, and cut off the power to the motor/controller. The other three mosfets will be in series with the charge current and can cut off charging if necessary.

The diagram is correct.

 

[Functional Artist]

"...(B-) is positive (+) pole for both charging & discharging" -- It does not say this anywhere. Rather it says "“B-“ for negative Pole of the battery pack" - which is correct.

"how can (P+) be the negative (-) for charging & discharging?" -- It does not say this. It says "“P-“ is negative pole for both discharging and charging." - which is correct.

The motor controller (fat) cables will be in parallel with the charger (thin) cables.
The positive of both will go to the battery postive.
The negative of both will go to the board P- terminal.
The B- of the board will go to the battery negative with a fat cable.

So no - the motor/charger negative do not go to the battery pack but to the P- on the BMS board. The 100A (negative) current goes through the board and three of the mosfets will be in series with the motor. (The 3 mosfets are parallel to each other.) If for any reason the current has to be cut, the three mosfets turn off just like a mechanical relay, and cut off the power to the motor/controller. The other three mosfets will be in series with the charge current and can cut off charging if necessary.

The diagram is correct.

I guess the way they had it written confused me.

The charging port and the discharge port of the board are the same Positive port. “B-“ for negative Pole of the battery pack, “P-“ is negative pole for both discharging and charging.

It would of been clear if it was spread out like:

...The charging port and the discharge port of the board are the same Positive port.

...“B-“ for negative Pole of the battery pack,

... “P-“ is negative pole for both discharging and charging.


OK, thanks much clearer

So,
...the (fat) 4g. (discharge) positive (+) battery cable coming from the speed controller, along with the (thin) 10g.(charging) positive (+) wire both connect to the positive post of the battery pack

...the (fat) 4g. (discharge) negative (-) battery cable & the (thin) 10g. (charging) negative (-) wire both connect to the 10g. wire on the BMS

Thanks for clarifying

 

[Solarsail]

...the (fat) 4g. (discharge) positive (+) battery cable coming from the speed controller, along with the (thin) 10g.(charging) positive (+) wire both connect to the positive post of the battery pack

...the (fat) 4g. (discharge) negative (-) battery cable & the (thin) 10g. (charging) negative (-) wire both connect to the 10g. wire on the BMS

First paragraph is correct. But not second paragraph.

1) Battery negative 4g. connects to B- on the BMS (4g. black). Nothing else connected here.
2) Speed controller negative 4g. connects to P- on the BMS (4g. yellow). ('P' stands for Power and not positive. P- is negative and almost same as the B-, only the mosfets acting as a switch are between P- the load, and B- the battery, ready to cut off battery from motor/charger. The BMS switch is on the negative line, not the positive line.)
3) Charger negative 10g. connects to P- on the BMS (4g. yellow). Therefore the charger (CH) and speed controller (SC) are in parallel (+ to + and - to -).

Therefore:
Battery+ connects to SC+ and CH+ and also line #12 of BMS.
Battery- connects only to BMS B-
BMS P- connects to SC- and CH-

The diagram is accurate.

 

[Functional Artist]

Very helpful & clearly explained.

I understand now.

https://www.youtube.com/watch?v=W98lwFeFC8w

What is the proper size wire/cable for the

...battery negative (-) connecting to the BMS (B-) port?

...& the (P-) port connecting to the (B-) of the speed controller?


Is some kind of a monitor or led read-out required?

or

...when hooked up properly, this BMS just does it's thing?


Thank you for your patience

You have been of tremendous help.

 

[dain254]

I use the 2kwh blocks for my electric dirt bike - I don't carry the charger OR BMS on the bike, I simply balance charge the packs with one of the cheap chinese balancers that plugs straight into the port on top of the block and a 50.4V 17A charger, all hard wired to the charger. This helps me keep weight down and I just monitor the voltage and when I get down to around 38V I stop.

I pull 500A occasionally, if you aren't doing at least 300A @48V I can't imagine your motorcycle would be any fun to ride! You don't have to worry about over working these batteries, just over discharging them! Your SLA's will have significant Peukert gain as compared to the lithium (meaning you get out exactly what you've put in VS lead acid you get less out the faster you drain it)... so in reality a 2kwh block will give you 4x the range of the SLA's.

 

[Functional Artist]

I use the 2kwh blocks for my electric dirt bike - I don't carry the charger OR BMS on the bike, I simply balance charge the packs with one of the cheap chinese balancers that plugs straight into the port on top of the block and a 50.4V 17A charger, all hard wired to the charger. This helps me keep weight down and I just monitor the voltage and when I get down to around 38V I stop.

I pull 500A occasionally, if you aren't doing at least 300A @48V I can't imagine your motorcycle would be any fun to ride! You don't have to worry about over working these batteries, just over discharging them! Your SLA's will have significant Peukert gain as compared to the lithium (meaning you get out exactly what you've put in VS lead acid you get less out the faster you drain it)... so in reality a 2kwh block will give you 4x the range of the SLA's.

Thanks for the reply, lots of good info

How long have you been using them?

Can you send me a link to the balancer & charger that you use.

...& to your bike, I'd like to check it out.

 

[Solarsail]

Lol - nice video. Yes, it is correct.

You can see the gauges from the chart here - http://www.cerrowire.com/ampacity-charts

Of course it also depends on the length of the cable, because the loss (but not cable capacity) depends on the length. So even if the cable capacity is adequate, you may want to go to a larger gauge if the length is long, in order not to lose too much power.

Let's say you are designing for 100A. Note that in normal cruising you will probably be only around 20A.

Battery- to BMS B- 100A or 2g. copper - 4g. can also do because you will occasionally be running at 100A for short periods only.
BMS P- to SC- same as above.
Battery+ to SC+ same as above. Fuse and Contactor same.
Motor + and - same as above.
Everything else can be 18 gauge. If charger is 900W, then 12 gauge.
Monitoring wires can be 24 to 28 AWG.

The BMS will protect and balance the cells. But you need to know how the pack is performing and where the bad cells (if any) are - the BMS will not tell you this. One 100V digital display to check pack voltage combined with one 100A ammeter to check the current ($10). The ammeter (shunt) will be connected inline to the fat Battery- to BMS B- line. Note that this will not show both the charging and discharging currents. Just one of them (unless you install a 2p2t switch). And the display power should be connected to the + of the 4th battery (and not the 12th battery). https://www.ebay.com/itm/DC-100V-0-...hash=item2846c0e76f:m:m-qA_YuutCaGZZIY6P7he-g

You should also have a 10V digital display to check each of the cell group (group means cells in parallel). To check the voltage for each group, you need a 2p13t rotary switch. I can only find a 2p11t. So you need another switch like a 3p4t which will allow you to see the 12th cell, and also cut off the power so that the battery does not get drained empty when stored for weeks. You will need one of each of these:
https://www.ebay.com/itm/Red-DC-0-1...404746&hash=item1c7196cb3f:g:~G4AAOxy039TOl4e
https://www.ebay.com/itm/Band-Chann...998507&hash=item2823a2ca19:g:TS4AAOSwXeJYGp2R
https://www.ebay.com/itm/3P4T-3-Pol...934475?hash=item3d5094ce4b:g:hk4AAOSwrRlZoNp9

NOTE: A lithium ion cell that is drained under 1.0 volt is only good for the trash can.

The 3p4t switch will show cell #12, cells #1 to #11, or be off. When off, it will also cut power to the ammeter. When showing cells #1 to #11, it is connected to the 2p11t rotary switch which you can then select which of the 11 cells to view.

Finally, if you wish to get 200A or 300A momentarily out of your pack, then you need a contactor to short the BMS B- and P- terminals. This will allow over 100A to be delivered to the controller. You can have a push button drive the contactor, so when you press the button you can accelerate beyond 100A. Sort of like a ludicrous mode. You will also have to upgrade all the 4g. cables to a 4/0 cable.

 

[dain254]

Here is a link to my build on another forum I frequent:

http://www.minibuggy.net/forum/projects-progress/22487-yz400a-electric-dirt-bike-build.html

Originally in the build I use a pair of 1kwh packs that I balance charge with 2 hobby chargers - took 24hrs to charge. Later I switched to the BMS and higher amperage charger.

 

[dain254]

I really can't disagree with anything SolarSail is telling you, but I will say that it is WAY over the top. If you want to monitor voltage, grab a couple "cell medics" from hobby king. If you are monitoring voltage all the time, you can even ditch the BMS all together and use the cell medics. They are cheap but they do work. The Volt modules have a nice port on top, and it is easy to find connectors to interface with it - then just wire a couple 6S plugs to plug into the cell medics. Anything more than 12S you wouldn't want to use this method.

https://hobbyking.com/en_us/hobbykingtm-battery-medic-system-2s-6s.html

Charging/discharging slowly will help keep you in balance, and you can use the cell medic to balance the pack out when you decide the voltages are no longer close enough for you to feel good about them. This is the BARE MINIMUM you should do to run a lithium battery. I'd also recommend not charging to the full 50.4V (4.2V/cell), order a charger and specify your cutoff voltage at like 48 or 49V. This gives you a little room for when you have some cells peaking sooner than others - you want to avoid charging them higher than 4.2V/cell.

 

[Functional Artist]

Lol - nice video. Yes, it is correct.

You can see the gauges from the chart here - http://www.cerrowire.com/ampacity-charts

Of course it also depends on the length of the cable, because the loss (but not cable capacity) depends on the length. So even if the cable capacity is adequate, you may want to go to a larger gauge if the length is long, in order not to lose too much power.

Let's say you are designing for 100A. Note that in normal cruising you will probably be only around 20A.

Battery- to BMS B- 100A or 2g. copper - 4g. can also do because you will occasionally be running at 100A for short periods only.
BMS P- to SC- same as above.
Battery+ to SC+ same as above. Fuse and Contactor same.
Motor + and - same as above.
Everything else can be 18 gauge. If charger is 900W, then 12 gauge.
Monitoring wires can be 24 to 28 AWG.

The BMS will protect and balance the cells. But you need to know how the pack is performing and where the bad cells (if any) are - the BMS will not tell you this. One 100V digital display to check pack voltage combined with one 100A ammeter to check the current ($10). The ammeter (shunt) will be connected inline to the fat Battery- to BMS B- line. Note that this will not show both the charging and discharging currents. Just one of them (unless you install a 2p2t switch). And the display power should be connected to the + of the 4th battery (and not the 12th battery). https://www.ebay.com/itm/DC-100V-0-...hash=item2846c0e76f:m:m-qA_YuutCaGZZIY6P7he-g

You should also have a 10V digital display to check each of the cell group (group means cells in parallel). To check the voltage for each group, you need a 2p13t rotary switch. I can only find a 2p11t. So you need another switch like a 3p4t which will allow you to see the 12th cell, and also cut off the power so that the battery does not get drained empty when stored for weeks. You will need one of each of these:
https://www.ebay.com/itm/Red-DC-0-1...404746&hash=item1c7196cb3f:g:~G4AAOxy039TOl4e
https://www.ebay.com/itm/Band-Chann...998507&hash=item2823a2ca19:g:TS4AAOSwXeJYGp2R
https://www.ebay.com/itm/3P4T-3-Pol...934475?hash=item3d5094ce4b:g:hk4AAOSwrRlZoNp9

NOTE: A lithium ion cell that is drained under 1.0 volt is only good for the trash can.

The 3p4t switch will show cell #12, cells #1 to #11, or be off. When off, it will also cut power to the ammeter. When showing cells #1 to #11, it is connected to the 2p11t rotary switch which you can then select which of the 11 cells to view.

Finally, if you wish to get 200A or 300A momentarily out of your pack, then you need a contactor to short the BMS B- and P- terminals. This will allow over 100A to be delivered to the controller. You can have a push button drive the contactor, so when you press the button you can accelerate beyond 100A. Sort of like a ludicrous mode. You will also have to upgrade all the 4g. cables to a 4/0 cable.

Wow! That's great, lots of good info & clearly explained.

I am OK with most everything
...except running the motor off/thru that little BMS
...is it necessary? (is seems like the only benefit would be over-discharge protection)

...& a bunch of switches/dials complicates things

I have used an amp/volt meter like the one you linked
...it would be a good (but, simple) addition to the bike
...it will help me monitor current & voltage levels


Hypothetically (just an idea) -- (what if we split the baby?)

* Mount the BMS on a 2kWh section of a Volt battery
...pretty much as described earlier

But, only run the charger thru it

...& leaving the propulsion system connected as is

BMS:

The main functions: Over-charged, Over-discharged protection, short circuit protection, over-current protection, with Balancing function.

I believe this set up would provide:

...over-charged protection (while charging only)

...BUT, NO over-discharged protection (would have to be monitored & controlled by user)

...short circuit protection (while charging only)

...over-current protection (shouldn't be an issue)

...& the balancing function would (always) be working

Sound plausible?

 

[Solarsail]

Thanks dian254 for the pointer to the cell medic. I think it is a useful device for monitoring and even balancing, but I would still recommend having a BMS, for protection and automatic balancing. Two cell medics together can replace the voltage monitoring that I described using rotary switches (but not the current monitoring or the 12s pack voltage monitoring). I would probably have used the medic myself, but my pack is 14s, so I would need 3 of them, and the module does not have the room to install three medics permanently in the module.

I think the protection for a 2kWh pack is required, so a BMS is required. If you leave anything on and forget about it, overtime it can kill your whole battery pack. And it will stop the cells from being abused both on charge and discharge. Chargers are not always reliable, and there are examples where the charger has exceeded its set voltage. In which case the BMS will protect the cells. Adding a BMS is not a big hassle, and if it were not for the 100A, a 12s 35A BMS would cost only $20. I can see that dian254 requiring 300A will have a hard time finding a BMS. If you don't run the motor through the BMS, then a 35A BMS would do, and it will protect the pack from devices that steal the power. But you will have to monitor the voltage manually when running on empty. In any case, you may want to install a switch or contactor across B- and P- on the BMS so that if you run out of juice one mile away from home, you can still limp home and immediately charge.

And yes, do not charge to 4.2V. I believe the Leaf charges to 4.125V. You only lose about 3% of the range.

BMS does the following:
Overcharge protection - important and necessary as chargers can malfunction, or if cells go wildly out of balance, and you have forgotten to balance.
Overdischarge protection - important, especially when there are power stealers, or while driving you forget to look at the pack voltage. Also if one cell is weak, you can still use bike with peace of mind.
Over current protection - important as during acceleration or hill climbing at high speeds, you may fail to watch the ammeter.
Short circuit protection - good to have this, and comes handy. A fuse can do the job more or less.
Balancing - can be done manually via cell medic - I don't believe cell medic can do it automatically. But good to have peace of mind.
Temperature monitoring - important for 100A driving, or ultra fast charging. A must if pack is powering a plane or in a confined space. If a cell catches fire, it can jump to the next cell. Not necessary for a 2kWh bike, IMO. Some BMS monitor temp.

So I would recommend the BMS, especially if you one day decide to increase to 4kWh.
You can use two cell medics to view 2x 6 voltages at once, but note it will only give you total voltage for 6 cells only, and you have to add the two to get the total 12 cell voltage.

 

[Functional Artist]

I really can't disagree with anything SolarSail is telling you, but I will say that it is WAY over the top. If you want to monitor voltage, grab a couple "cell medics" from hobby king. If you are monitoring voltage all the time, you can even ditch the BMS all together and use the cell medics. They are cheap but they do work. The Volt modules have a nice port on top, and it is easy to find connectors to interface with it - then just wire a couple 6S plugs to plug into the cell medics. Anything more than 12S you wouldn't want to use this method.

https://hobbyking.com/en_us/hobbykingtm-battery-medic-system-2s-6s.html

Charging/discharging slowly will help keep you in balance, and you can use the cell medic to balance the pack out when you decide the voltages are no longer close enough for you to feel good about them. This is the BARE MINIMUM you should do to run a lithium battery. I'd also recommend not charging to the full 50.4V (4.2V/cell), order a charger and specify your cutoff voltage at like 48 or 49V. This gives you a little room for when you have some cells peaking sooner than others - you want to avoid charging them higher than 4.2V/cell.

Very Kool bike!

I checked it out several times while I was doing research to build my bike.

I appreciate your advise

Trying to find a "SAFE" middle option

Not "bare bones" but, not "premium" either


It seems that the (2) MOST IMPORTANT issues that NEED to be addressed are:

Maintaining cell balance
...that's where the BMS balancer comes in

& Over charging
...that's where a charger with a preset cut-off voltage of 49V comes in.

So, I think I can go with this this BMS https://www.ebay.com/itm/221274094989
It is a 48V 30A 12S BMS for ~$45.00/delivered
(SolarSail is right, A 100A unit not necessary just for charging)

It can be mounted on the battery & left connected
...The 11 balance wires will be connected to the balance plug on the battery
...the 12th wire on the balance plug connects to the battery pack positive (+) pole
...a 16g. wire connects from the battery pack negative (-) pole to the BMS (B-) pole
...a 16g. wire connects the BMS (P-) pole to the negative (-) side of the battery charger connector plug
...& another (red) 16g. wire connects the positive (+) side of the battery charger connector plug
...the 4g. cables from battery pack to motor/speed controller are still connected as per the instruction manual

* I don't think "over current" should be an issue in this situation

The other critical issue is "under-voltage" which MUST be dealt with by the user manually or

...maybe by the speed controller, I am not sure if the low-voltage cut-off is programmable on Kelly Controllers

...or maybe by the contactor

What is the low-voltage cut-off of a 48V solenoid contactor?

Recently I upgraded from 36V to 48V this is the contactor I have:
http://kellycontroller.com/main-contactor-kzj-48vdc-coils-400amps-p-1154.html

Anyways, thanks again