Is this possible to get over 100v?

E

ebike11

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Hi guys
I have an em3ev 20s10p samsung 25r pack with only 10 cycles on it
I bought it recently. However id like more voltage and there is a local seller of 25R cells here that builds packs
Could I simply add 4S or 6S to the 20S since the cells are pretty much new? Is 4S10P or 6S10P possible? The 2 packs would have separate BMS units though. Thanks!!
 
Possible but not as straightforward as parallel sub-packs.

Personally I'd just get the pack made that you want in the first place.

Modular 7S or 8S subpacks would make more sense, easy to use cheap hobby gear for charging and maintenance

Then get a 28S BMS for per-cell LVD functions only, 4 subpacks x7 in series

Note that once you get past 90V or so, the FETs and other electronics get lots rarer and more expensive

most cheap Chinese stuff is built with fake or substandard components will burn on you

better to pay for good Euro gear, BMSs cost more than most are willing to pay for the whole pack.

If you are an electronics DIY geek could maybe get away with constant replacing / upgrading, if you don't put a high value on your time.
 
john61ct said:
Possible but not as straightforward as parallel sub-packs.

Personally I'd just get the pack made that you want in the first place.

Modular 7S or 8S subpacks would make more sense, easy to use cheap hobby gear for charging and maintenance

Then get a 28S BMS for per-cell LVD functions only, 4 subpacks x7 in series

Note that once you get past 90V or so, the FETs and other electronics get lots rarer and more expensive

most cheap Chinese stuff is built with fake or substandard components will burn on you

better to pay for good Euro gear, BMSs cost more than most are willing to pay for the whole pack.

If you are an electronics DIY geek could maybe get away with constant replacing / upgrading, if you don't put a high value on your time.
Click to expand...

Thanks for your advice!
Well im just trying to increase my 20s10p voltage. Im happy with 20s and its 84v fully charged. The pack is almost new so i cant go the 6s or 7s lipo route yet.
I thought since my pack cells are fairly new and if i added a 4s or 6s of new 25r cells to my 20s pack then it might be doable. The 20s pack already has its own bms and the 4s or 6s pack would also have its own bms. Then wire in series
 
Finding someone to decompose the packs and rebuild them for you to work that way will be difficult.

As I said, the biggest challenge will be figuring out what sort of BMS you can find that can handle being wired in series at such high voltage like that.

By the time you're done IMO easier to just get the welder and supplies and learn how to do it yourself, put together the 24/26S pack you actually want, with a BMS designed to handle such high voltages.


 
One big large pack is the easiest to manage. 2 equal packs in series is the next way to go when you start going 20s plus 4S and bms's gets more complicated the more complicated the more prone to mistakes. it would be easier not running a BMS but then again you would have to be a human being a mess and handle all of the responsibilities.
Now you turn your ebike into a battery hobby.
 
spinningmagnets said:
Add 4S in series as a second pack. When charging, charge it separately with an RC charger...just a thought.
Click to expand...

I was just thinking like this. Wouldnt it be the easiest way? I dont want to tear apart my 20s pack or weld more cells together.. I dont mind having 2 different chargers for 2 packs. 4s10p on a smaller charger
 
j bjork said:
It would probably work, if the bms can handle the extra voltage.
24s seems to be the wrong way to go from what I understand. Too high for most controllers (with 100v components), and unnecessary low for most higher voltage controllers.
Click to expand...
.

Hi thanks
Hmmm so if the 4S pack had its own bms and the 20S already has its own bms...i would still need to make sure the both bms units can handle 100V ??
The controller i have is rated to handle 120V so i think the caps are over 150V
 
ebike11 said:
Hmmm so if the 4S pack had its own bms and the 20S already has its own bms...i would still need to make sure the both bms units can handle 100V ?
Click to expand...
Yes

With parallel not, but serial all the current, at that pack level voltage, flows through each cell/group.

Such an expensive BMS required, you only want to have to buy one.

Nothing to do with your controller.

Are you sure you really "need" to increase your top speed that much? If not then what do you think going so crazy-high voltage is going to buy you?
 
john61ct said:
ebike11 said:
Hmmm so if the 4S pack had its own bms and the 20S already has its own bms...i would still need to make sure the both bms units can handle 100V ?
Click to expand...
Yes

With parallel not, but serial all the current, at that pack level voltage, flows through each cell/group.

Such an expensive BMS required, you only want to have to buy one.

Nothing to do with your controller.

Are you sure you really "need" to increase your top speed that much? If not then what do you think going so crazy-high voltage is going to buy you?
Click to expand...

Yeah i dont really need to but its the common theme of always wanting more speed lol
 
For more speed you can use field weakening or/and higher gearing.
For more power go more A or more V (and gear down if you need more torque)
More volt will give more power (but only at higher rpm than the peak are now) and higher rpm.

Higher voltage will give more power and a wider power band.
 
ebike11 said:
j bjork said:
It would probably work, if the bms can handle the extra voltage.
24s seems to be the wrong way to go from what I understand. Too high for most controllers (with 100v components), and unnecessary low for most higher voltage controllers.
Click to expand...
.

Hi thanks
Hmmm so if the 4S pack had its own bms and the 20S already has its own bms...i would still need to make sure the both bms units can handle 100V ??
The controller i have is rated to handle 120V so i think the caps are over 150V
Click to expand...

I'm no expert here but I dont think this is correct. The BMS should only care about the batteries it is attached to. So a BMS on the 4s only thinks its passing a max 16.8v through it.

Voltage is potential difference between Any 2 points So why would either BMS care what the rest of the string is doing?

I could maybe see it being a problem if the mosfets in the 4s bms were not rated to handle the voltage of the 20s bms when they are open but even then I think thats unlikely.

I think you would be fine running 2 bms packs in serial. Please correct me if this is wrong.
 
j bjork said:
For more speed you can use field weakening or/and higher gearing.
For more power go more A or more V (and gear down if you need more torque)
More volt will give more power (but only at higher rpm than the peak are now) and higher rpm.

Higher voltage will give more power and a wider power band.
Click to expand...

Has anyone used 100 setting for field weakening on a qs205? I wasnt sure if i should go so high so its at 50 at the moment
 
100 what? %? A?
It may depend on the controller, but I guess 100% is full speed. When you go over 100% you go in to field weakening.
If it is A, yes.. I think I have 200A on my nucular.
500pA, 3-400bA (I dont remember) I think 150% speed (dosent really matter, the controller limits when bemf gets too high) And I think 200A field weakening. This is on my qs 205 50h 4t, there are a lot of qs 205:s, not all are the same.

Maybe you should take a step back and learn how to use the things you have first, before you hurt/kill yourself with more dangerous voltages.
 
j bjork said:
For more speed you can use field weakening or/and higher gearing.
For more power go more A or more V (and gear down if you need more torque)
More volt will give more power (but only at higher rpm than the peak are now) and higher rpm.

Higher voltage will give more power and a wider power band.
Click to expand...

I think I should make something clear, you will sure get more speed with higher voltages and the same gearing.
But if you cant feed the motor more amps, you can also use higher voltages to get more power. If you gear down you can have the same top speed, but more torque on the wheel.
 
j bjork said:
100 what? %? A?
It may depend on the controller, but I guess 100% is full speed. When you go over 100% you go in to field weakening.
Click to expand...

Sorry..i meant when you go into the Sabvoton controller phone app..you can see field weakening and it is set at "0" from the factory but can be increased up to 100 and higher. I have it at 50 at the moment.
So im not sure if "0" field weakening means the motor is already at 100% full speed and starting at "1" goes into field weakening OR if i set the field weakening to "100" means the motor is at regular top speed and anything over that goes into field weakening??
 
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