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Need advice on custom battery


Harishmirror

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Hello Everyone,

I am in the process of building a custom battery for my skateboard. I am confused with which battery to choose.

The motor is 450W brush less and the controller stays 48v, current = 20A . Based on the available space, I derived at 13S5P layout. I have chosen LG MJ1  or LG HG2  for this build. I am not sure which one to go with, 

1) MJ1 is 3500mAH so I get 18Ah with the 13S5P layout. But max continuous discharge is only 10A per cell

2) HG2 is rated at 3000mAh puts out 20A continuous discharge per cell and the end result is a 15Ah output in 13S5P layout

Can someone point me in the right direction on which 18650 battery will better suit my motor and controller? 

I would love the 18Ah setup but not sure with 10A continuous discharge per cell will suffice the motor draw.

The current battery is 13S2P at 278.4Wh\5.8Ah

 

 

 

 

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It is very depending on what are your priority of either you want more range or peak power.

The formula for calculation is Watt=Volt x Amp so for your case max discharge power for MJ1 is 48volt x 10amp=480watt while for HG2 is 48volt x 20amp=960watt. If your ride is mostly flat then the MJ1 is suitable & it has more range. If your ride is mostly hilly & you like speeding then HG2 but less range. 

Best is that you ask this question at esk8 forum, since then my esk8 has been retired & collecting dust now :lol: Having said that, they do have better experience on this as many DIYers has done this already, here not many can advice you, they just use the cells that comes with the EUC & it lasts minimum 2-3 years before they are replaced & many opt for the exact same factory pack battery replacement.

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@yuwengThanks for your response.

I though each series carried the max discharge power of an individual cell, so the max output adds up, when connected in parallel.

I am doing 13S5P which makes the continuous discharge for MJ1 at 10A X 5P = 50A and the HG2 will be 20A X 5P = 100A

Isn't that correct?

If it is correct then my setup with MJ1 will be 18Ah at 48v X 50Amp = 2400Watt - Maximum output?

If that is the case then my motor is 450W and Controller draws 20A

Please advice

 

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52 minutes ago, Harishmirror said:

@yuwengThanks for your response.

I though each series carried the max discharge power of an individual cell, so the max output adds up, when connected in parallel.

Exactly.

Quote

I am doing 13S5P which makes the continuous discharge for MJ1 at 10A X 5P = 50A and the HG2 will be 20A X 5P = 100A

Isn't that correct?

Yes.

Quote

If it is correct then my setup with MJ1 will be 18Ah at 48v X 50Amp = 2400Watt - Maximum output?

Maximum continous output.

Maximum peak output will be higher.

And the 48V are just nominal ("average") voltage...

Quote

If that is the case then my motor is 450W and Controller draws 20A

The motor power should be something like continous power the motor can take. Noone know how the designers work with this value. If they use it at all or use double of it, since it is nicely air cooled and not operated fir hours... So this value can, if at all just be used to estimate a magnitude but not for calculations.

How you come to 20A? With 48V this would be 920W... (Don't confuse motor current with battery current)

Quote

Please advice

Your "problem" are the "marketed values".

Datasheet capacity of this cells is only valid for some very low in the datasheet specified values (somewhere around 0.2C).

This capacity is also only reached when discharged downto 2.5V. Your board will most probably only use the cells downto some 3-3.3V?

Could easily be, that the HG2 has more usable capacity as the MJ1!

You would need to know the "current draw" profile of your board when and how you drive it and then look at li ion web sites like dampfakkus.de for the different discharge graphs...

Most likely you'll come to some result like for nice panorama rides with constant (maybe also high) speed riding the mj1 will offer more range, for start/stop/high acceleration/going up hills the hg2 could be the better choice...

If one assumed this 450W motor number as some average power usage that'll be ~10A average current draw. So 2A per cell.

From my gut feeling average values could be even below (if this is not some high speed high performance board and you are a neck braking crazy driver...)

So mj1 could be your choice? Especially from my experiences with EUCs (which motor power numbers are marketed there and how much batteries are burdened) mj1 should "win"...

Dig a bit around to get some solid data and look into the discharge graphs for some scenarios - or just take mj1 (or flip a coun if you're unsure) and use your spare time for riding... 

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@ChriullThanks for the knowledge and dampfakkus.de was very helpful.

No into speed and board isn't build for that as well, so I think I must stick to the MJ1 or even better the Sanyo GA ones.

Also need your advice on BMS for the given setup,  a 20A BMS should suffice?

Once again, the charger is 2A, Motor 450W and controller draws 20A

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15 minutes ago, Harishmirror said:

a 20A BMS should suffice?

Bms amperage should be a short circuit protection far away from possible peak currents. For euc's thats extremely important - for skateboards it should not be the worst idea, too?

I'd tend to some ~70-80A board.

18 minutes ago, Harishmirror said:

Once again, the charger is 2A, Motor 450W and controller draws 20A

Pfff... That's no numbers i'd take to serious - dif further, you got a link before to a forum specialized to skateboards. You should get better infos there.

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The bms max current should be greater than the required peak currents, not merely continuous.

In EUCs there is no current protection and they work fine. I guess it would only help if the control board or motor gets short circuited.

On a 2000w EUC the smaller battery packs supply at least 40A continuously. If you really do only draw 1000w continuously then 20A or more would be along the same line.

You can pick any cell and get the pack over 20A in a 5p configuration. The high amp cells have the benefit of staying cool and having less voltage drop under load. High density MJ1/GA or the newer 21700 cells would be more than adequate for your application which has the added benefit of bringing you great range aswell as decent performance.

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If you have 450W motor and you plan to connecet 5 Cell in parallel you don't need to use high current 18650, cause most of producents says that max continues current on normal 18650 is 2C, on 3500mah will be 7A if you have 5 parallel it will be 35A continues current,  your motor takes 10A propably 20A in peak, but if you wat to use high current 18650 dont take too expensive 10A will be enough. BMS with Ballancer is thing that you must have with current cut off about 40A, don't look for 13S BMS cause most of them are "from - to" so take BMS 16S and connect 13S. BMS with load and charge parallel gives you oportunity to charge when you use your skateboard, you can make another battery pack in backpack, use dc-dc convertert to set constant current and you have much more distance. If you connect 5P battery charge with 2A charger will be too long, you can use 5A charger it will be 1A on cell, for MJ1 0.68A is standard charge and 1,7A is rapid, so 1A per cell will be best option, don't buy charger just DIY it's simple, ONE server redundant power supply, ONE DC-DC converter with CC-CV to setup current and voltage.

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8 minutes ago, evil696 said:

for MJ1 0.68A is standard charge and 1,7A is rapid

That's interesting!

LG has "severly" downgraded charging specifications for the MJ1 cell.

But the datasheet from 2018-07-25 i found with this specifications (standard charge 680 mA and rapid charge 1700 mA) is from Ansmann and not from LG....

In the least "official" MJ1 datasheet (i found) from LG from 2014-08-22 there was still

Standard Charge: Conctant current 0.5C (1700 mA)

Max Charge Current: 1C (3400mA)

...

You have a link to an official LG datasheet specifying this new, lower numbers?

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No i just take first PDF.

Max charging current is dependent on temperature.

I will not try to charge 18650 with 1C.

 

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9 hours ago, evil696 said:

If you have 450W motor and you plan to connecet 5 Cell in parallel you don't need to use high current 18650, cause most of producents says that max continues current on normal 18650 is 2C, on 3500mah will be 7A if you have 5 parallel it will be 35A continues current,  your motor takes 10A propably 20A in peak, but if you wat to use high current 18650 dont take too expensive 10A will be enough. BMS with Ballancer is thing that you must have with current cut off about 40A, don't look for 13S BMS cause most of them are "from - to" so take BMS 16S and connect 13S. BMS with load and charge parallel gives you oportunity to charge when you use your skateboard, you can make another battery pack in backpack, use dc-dc convertert to set constant current and you have much more distance. If you connect 5P battery charge with 2A charger will be too long, you can use 5A charger it will be 1A on cell, for MJ1 0.68A is standard charge and 1,7A is rapid, so 1A per cell will be best option, don't buy charger just DIY it's simple, ONE server redundant power supply, ONE DC-DC converter with CC-CV to setup current and voltage.

Yes the battery cell vendor mentioned 1 to 1.5A to be the ideal charge range for the MJ1 or GA. So I must get a 16S BMS @ 40A and use a 5A charger? and the charger must be balanced?

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If you connect BMS with ballancer you don't need to balance cells when charging, balancer in bms do the job when charging is done (i didn't see any 13s charger with ballancer and if you find any it wont be cheap).

https://www.aliexpress.com/item/33023638541.html?spm=a2g0o.productlist.0.0.745cfdaaihelHG&algo_pvid=83ba773a-1ed8-4423-8fc7-e7f063f629ec&algo_expid=83ba773a-1ed8-4423-8fc7-e7f063f629ec-19&btsid=0b0a0ad815881933040573461e47a7&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

This is best BMS i used it's cheap, have ballancer and same connections for charge/discharge 16S 45A.

To make a charger just buy DC-DC bostup converter like this or any compatible with your parameters.

https://www.aliexpress.com/item/4000232811203.html?spm=a2g0o.productlist.0.0.704a418czrOCoU&algo_pvid=438a3721-f98c-4520-99cb-2372432944ad&algo_expid=438a3721-f98c-4520-99cb-2372432944ad-12&btsid=0ab6fa7b15881968510084633e6ea6&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

or

https://www.aliexpress.com/item/4000122349939.html?spm=a2g0o.productlist.0.0.704a418czrOCoU&s=p&ad_pvid=202004291447311606870342286370001397498_3&algo_pvid=438a3721-f98c-4520-99cb-2372432944ad&algo_expid=438a3721-f98c-4520-99cb-2372432944ad-2&btsid=0ab6fa7b15881968510084633e6ea6&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

I hope you know how to set CC CV on converter. Connect server PSU like this dps-700gb a or any you want (just look for popular PSU cause you get pinout easly to start PSU).

This link tell you much more about PSU.

https://www.xsimulator.net/community/threads/2dof-to-3dof-diy-seat-mover.5271/page-2

The main problem is input voltage on converter, used server PSU is cheap but have only 12V and it gives you 240W output on converter 240 / 48 = 5A but nothing more so it doesn't matter if you use 400W or 700W PSU.

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  • 4 weeks later...

I think the key issue here is your weight and whether that 450W motor will be able keep the pedals stable IF it is able to draw enough power from the battery pack. What voltage is the motor? If you oversupply power to it of course it will be better...

I ride an MCM5 67V with 48 x Sanyo 20700B 4250mha, 20A discharge rate and it does make a different, from raw acceleration and pedal stability. I tried to run it with a single 32 cell pack and it was average, it was not enough to cope with the 900W? 1200W? MCM's motor being pushed hard.

Regardless of what they say if your cell count is small, your amp discharge rate is really going matter...

Don't forget also to look at your BMS wether it is inline during discharge as it may limit AMPs and make the whole exercise futile. You ideally only want the BMS for charging, or have BMS with high AMP discharge (but those cost money).

Also look at Sony VTC batteries, they have the biggest range of high discharge batteries out there....  VTC5x and VTC6x   (x = a/b/c etc)

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