After lots of readings about batteries, cells, BMS… on this forum and in order to build my own battery for my LouBoard, I have some questions to ask to you.
I’ve chosen Sony VTC6 batteries because they have high capacity, higher maximum discharge current than my previous battery pack and I can buy them from a local supplier. Sony VTC6 have followed characteristics :
Maximum discharge current : 15 A (without temperature control) / 30 A (with temperature control)
Capacity : 3,12 Ah I will organize them as a 10s configuration.
I have a charger which is 42 V and 2A continuous.
Thus, I need to choose the right BMS. I will take one from Bestech. Here’s my question : I’ve understood that in most cases, BMS are used for charging and not for discharging; So should I consider the Maximal continuous discharging current when I select a BMS? If yes, does it need to be at 30 A or higher (as the maximum discharging current of VTC6 is 30 A)? Do you have a specific Bestech model to recommend? They have so many models :o
Also, most BMS have a Maximal continuous charging current around 6 A or 8 A. Does it mean that I could buy a new charger which will provide more current (my current one is only 2 A) ?
Hiya! Welcome aboard.
The discharge of the BMS can be safely ignored as long as you bypass the discharge port when connecting your ESC(s). There are plenty of awesome diagrams that lovely folks here have made for how to do that. Just be careful that your ESC(s) doesn’t draw more than the maximum rated current for your battery or things might start to get a little toasty in there. That maximum current will depend on your parallel configuration, so choose that wisely.
Most lithium cells shouldn’t be charged at any more than 1C - for 3000mAh cells, 1C is 3 amps.
So, again depending on your parallel config, your max charging current will be some multiple of 3.
Thank you very much
I’ve seen those diagrams to bypass the discharge so yeah I could do that !
Previously I had a 10s battery with Samsung 22P cells with maximum current of 10 A.
If now I switch to a 10s battery with Sony VTC6 cells with maximum current of 30 A, does it mean I’m gonna need to make some modifications in the ESC to increase the maximum current allowed?
If I don’t make these modifications, do I have the risk to not fully use the Sony VTC6 because the current stays under 10 A?
Also, I don’t really need what will be my maximum current discharge because I don’t know what’s the motor in my LouBoard. Maybe I never exceed 10 A…
You definitely exceed 10A when braking / accelerating / going up a hill
Most likely yes. I highly doubt your ESC determines the max amps it can draw by looking at battery voltage sag or something. Most people on this forum use ESCs based on the open source VESC design, which allows us to program them with a tool off a computer or phone. With a 10s battery, you can probably find a cheap, used vesc from someone on this forum
I think your the one I was helping in the other forum. 30A cells, specifically Samsung 30Q on my upgraded Lou battery is a night and day difference. Get yourself a bestech 10a d239. The VESC that they send is absolute shit anyways. The standard double (or single) escs on most of these sites (even Amazon I believe) will work for what you need. Comes with a remote and to push start switch.
As I exceed 10 A when braking / accelerating… and my cells can go up to 30 A, if I use a BMS for charge only, the only thing that matters when choosing a 10S Bestech BMS is its size right? I don’t need to take care of its maximum discharge current, am I right?
I can take a cheap one like this one for example : https://www.litechpower.com/product-detail/HCX-D503V1LI10S15A_07.html
Yeeees that’s me ! I decided to go for your solution to re-build the LouBoard.
I’ve chosen VTC6 because they are easy to find for me. Are you sure that Samsung 30Q are 30 A, I’ve seen in the datasheet that they are 15 A ? That’s why I didn’t pick them.
You took the Bestech D239 because you use it for charge only right?
Short answer: Yes. Discharge characteristics don’t matter if you’re not using the BMS for discharge
Long answer: You might not want to do that. Here’s why:
The general consensus on this forum is that you don’t want to use your BMS for discharge, because
Those BMSes are larger
If they fail, you might lose power, or even worse, your ESC won’t be able to store the braking energy, and fry itself.
However, that’s because most people are using vescs. We program them to not over-discharge the battery which could harm it. Since you are not using a vesc, I don’t know if your ESC has undervoltage protection like this. Furthermore, BMSes meant for discharge will often have an e-switch, which is a safe way to turn your board on and off. Without this feature, you need either an anti-spark loop key, or an anti-spark switch.
Anyway,
Your diagrams look correct to me
I really don’t know why Samsung advertises the 30Q as being 15A, because tests have shown that it is one of the best cells out there for 20A discharge. 30A is way too much, I think @Chase just made a typo and meant 20A.
The Sony VTC6 are also rated for 30A if you stop the discharge before they get hot. In the real world, their power + capacity characteristics are very similar to the 30Q. The VTC6 are a bit better, but after a dozen or so cycles, the 30Q outlast them. I recommend just buying the ones that are cheapest at any given time.
What’s the goal of an e-switch or an antispark switch ?
As VTC6 are 30 A max, my BMS need to be a bit more like 35 A right?
In fact, I’d like to determine what’s gonna be my maximum current discharge : I understand that cells have limits (like 30 A) but I guess that this maximum current is defined by the motor. Maybe the motor will never require more than 20 A, thus I can take a BMS that is 20-25 A. How can I determine this maximum current? Just by looking on the characteristics of the motor?
The first few sentences in its description say “E-Switch integrated” lol
To turn your ESC on or off by cutting off power. The capacitors on ESCs cause big sparks to fly if you just connect them without one or the other. It’s important to turn off power in case
you don’t want your battery to drain below a dangerous threshold
you want to restart your ESC after programming it
ESC starts acting up or smth. and you just want to turn your board off to be safe
Depends how you configure your ESC, but yes, if you are drawing close to the limits, the BMS might toggle its over current protection and switch off, which is bad. Btw, are you building just a 10s1p battery? That’s pretty small, but ok.
Depends on riding style / what your ESC supports / motor kv and gearing. Unless you’re a very light guy and like going slow, I can guarantee you’ll want more than just 20A
@rusins is right I meant 20A. They say 15 but it’s widely accepted that they do 20A continuous
Id just bypass the bms and not overthink it. You’ll be fine. Unfortunately it may be difficult to get anything more than 20A in there because anything past 1p will be too big and the higher current cells may be too fat
Understood ! I’m wondering how this is currently done in my LouBoard. When I check the wiring, I don’t think that there is a antispark switch or loop. I guess that the BMS is used for discharging also and so there is an e-switch. Do you confirm @Chase?
Well, the LouBoard is quite small and there is no space for more than 10s1p. Also, I’ve only one motor so I think it should be enough for city rides as I do.
I ride as fast as I can, in the city and I’m light. Previously, on my LouBoard, there were Samsung cells with 10 A max : it was nice riding. So I guess that with 20 A or 30 A cells, that’s gonna be even better @Chase, do you have the characteristics of the motor for the LouBoard 1.0 ?
Also, on your custom LouBoard, did you add an anti-spark switch or loop ? As you’re using BMS for charge only.
So you have a non programmable esc already with a push start switch already integrated. If you were to unplug the XT30 from the current battery/esc connection and then back you will see a tiny little spark, but that’s just how these cheap little single hub escs work.
Your right, you will not be getting over 1p no matter what you try, it’s just too tight in there. I wouldn’t add a switch personally. If you get the switch option for the bms you’ll end up having to discharge through it and add a big flip switch on the sleek board. And you’ll still face the board cut offs if you try to brake on a full battery or bursts above the discharge limit on that bms. Just bypass it and use a cheap vesc like this one that has push start capability and is non-programmable.
I’m very aware of everything your getting into, been modifying my Lou since I got it and I use it far more than any other board.
Double check that this one has push start if you pull the led switch off
An expensive BMS to do discharge + charge which has an e-switch.
A cheaper BMS to charge only with an anti-spark loop key.
Am I right? If yes, I will go for the 2nd solution.
To implement this solution, I need to connect the anti-spark loop between the + side of my battery and the + side of my ESC, right?
For the BMS, as I use it for charge only, I can take this one from Bestech ?
It is even cheaper than the D239 that you recommended.
I’ve checked the ESC you sent. It seems that its current is 12 A, quite low no ?
Also, please explain to me : why should I change my current ESC? I understand that yours broke down, but mine seems to work and I don’t see lots of difference compare to the one you sent?
Last thing : this all project to modify my LouBoard is due to some issues I have when riding it. Sometimes I can ride for 20 min, sometimes just 5 min, and it stops instantly. When I explained that issue in the esk8builders forum, people told me that the issue was the BMS and not the ESC. Now that I understand electronics a bitter better, it would mean that my BMS is used for discharge also and it cuts off the battery, is it right?
Thank you very much for all your helps. I was quite a noob in the field but I better understand thanks to you @rusins@Chase
If that one said 12 A discharge then it’s not the one I’m thinking of. The esc you have now is fine but you should double check it’s max discharge rate as well. You can get an eswitch as option even on cheap bms like the one I recommended you, you would just have to run discharge through that and it’s just another issue that can arise with cutouts. Just bypass it and avoid the big flip switch.
If you chose to use the esc you have, you don’t need an anti spark or a loop key, or flip switch bms. It has a switch built into the esc, that’s how you push your board and it turns on (unless it’s different with the single hub models since I have the dual). The same with the one I sent a link of and the ones similar, they have an led switch built in and most have the push to start option if you unplug the led.
I run mine on the 30Q 1p pack with two hubs and it performs really well. If you weren’t so space limited on the single hub lou insides I’d say add another hub motor as well.
How can I know the maximum discharge rate of the current ESC? As it’s a cheap one, it must be 12 A like all cheap ESC no? Could it be the reason why my board stops instantly after 5 min riding? Instead of an issue with the discharge of the BMS?
Okey ! Why everyone on this forum is speaking about anti spark so? Because they are using VESC and there is no switch built in it? Thus they need this anti-spark.
No, that just sounds like a hard voltage cut-off. I.e., battery is too low, ESC refuses to work so that it doesn’t damage the battery. Nothing to do with max discharge really.
I guess the cheaper ESCs don’t have powerful capacitors, so there might not be that big of a current rush to even kill anything, so they can get away with cheap switches. Or maybe they die as well after a while, I’m not sure. It’s probably fine though
Okey ! But it does that even when my battery is fully charged… Does it mean that my BMS doesn’t charge properly the cells?
Right
On this cheap ESC, there is a ON/OFF button. But it has the possibility to start when pushing the skateboard, I don’t need to instal that button right?
