The battery builders club

I get why mixing in the same p group is bad but hoped at battery level it might work…

I started to wonder why we don’t have a smart discharge system capable of using different cell types, use the quick burst from cell type a, and range capability of type b

Edit: love the idea of a much smaller boost pack within the battery to cope with sag better :wink:

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Don’t you just divide the resistance by the number of cells?

So, wouldn’t it be 2mohm for the 3 x 30T, and 1.8mohm for 6 x 30q?

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Why is it possible for powerwalls to use any cell mixture without dangers or problems (to some extent)?
What circuitry do they use to make that a possibility that couldn’t be applied to esk8s?

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I‘m not a power wall expert, but I think even for a power wall people check the capacity of cells and match them as as close as it’s possible in the p- groups as well as try to not mix up too much different types of cells.
And
Power walls use p-groups with idk 50-100+ cells in parallel. There it doesn’t really matter if your cell is rated for 5A or 8A or 10A+.

It’s done…



Some of the balance leads cross the copper wires. Same potential so they won’t fry. However if it gets hot enough it may melt the isolation. Noticed it too late to fix. Worst case I have to cut the package open to resolder those

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The k supply was faulty and provided power spikes that blew the k capaditers. even after proving it was a component fault on the k supply not user error he only prepared to repair the supply not the k caps.

So useing Turnigy Graphene 6Ah. Battery starts to warm up if you useing over 120 so I added a 2nd but the XT90 was getting hot still.

Only need 6-10j to weld 0.15 nickle 2% of what the unit can deliver

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Sorry to hear about your disappointing experience with the capacitor set up.

I followed some of the early threads on the K weld where it was said that 90-100 joules were enough for 0.3mm, hence why I asked.

Anyway, glad it’s all working for you now, and thanks for the useful information.

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I think 50 would be enough for .3mm the issue I’m having is the current is mainly passing thro the Nickle not threw it in to the battery and back out. I proved this by 0.3mm Nickle strip and a scalpel blade and a electrode on the top and bottom. I chose this k weld as the plan was to start useing thicker strips as the current capacity is a issue for esk8 and how our battery’s are configured flat works against it.

0.3mm is rated at 8.3a. Were 0.15 is rated for 4.3a if you use this table

Or 0.3 is rated to10-15a 0.15 is rated 4.7-7a for lengths 8-30mm long

A 3P CVT5A is rated up to 105a
AWG 10 is rated up to 55A
Unity 100A or dule VESC 6 300a
XT 90 90-120a
Diebie MS 70A
Makes the Nickle strip the weakest point by a long way.

I run my settings currently at 35a a motor 60a battery from r25 cells but I’m seeing short peaks of 60a motor 30a battery and I’m sure it’s limitation of the battery build. Was planing on doubling up the .3 mm so then when I solder the flat copper braid between each cell I could almos discharge the full 35a max rating from 1 cell down double .3mm Nickle in to the copper.

As placing the electrodes on 1 surface is not the ideal way to spot weld and with no way of placing one of the electrode on the other side with out damaging the batty iv been unable to achieve a decent weld to use .3mm and it’s not thro lack of power in the spot welder as most people claim is the limiting factor it appears my issue is stoping the curent travailing thro the Nickle and more in the battery contacts and back out. I would like to try some slotted 0.3mm strip as this should aid in that but iv not found any were I can buy that from as of yet. if any ones has some or knows were I could buy some I’m interested.

I’m trying to research a battery that is giving me issues. Can anyone tell me what this white cable dangling from my BMS is:


I think the BMS might be a BesTech D140 charge only

It’s a temperature sensor.

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Try using more pressure and a little less J
It gets the coloring from the welding away (too much heat)

Careful – VTC5A will do 25A without supplemental cooling.

Sorry to hear about the k caps thing. Ouch, sad to hear.

I’ve always just shoved the sensor out of the way - where should I be placing it?

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I normally put it ontop the closest p group.

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25 continuous
35 continuous with a thermal sensor set to 80deg from BMS
Prity hard to sustain 105a at full duty cycle on a street board for me even on a hill. Same reason I’m only using AWG10 not uping it to AWG 8 or 6

To put this in to perspective
750w is 1 BRITISH BHP (I know u US like to take parts of a engin to inflate you BHP ratings)
25a*3p in 10s is 4410w at full charged or 3885w on average

So 5.1hp fully charged or 5.8 charged

My Maytech 6355 rated to 55a vesc says one can take 50.8a the other 52.2a tested at 20deg so this will reduce when it heats up. Pulling any thing like that for any amount of time it will heat up.

Personally I think a draw of 100a is a good realistic figure to aim for on a good quality dule urethane board. It’s why the 10s 4p Q30 is the tried and tested norm that just works as thay can deliver 25a per cell were the R25 were struggling and people could see a improvement on the Q30 when thay came out.

That’s why I think the Q30 are fine in 4p but in a 3p are a limiting factor and the VTC5A in 3p are just about good enough when balancing components for a build.

This then creates the next bottle neck of the build is the cables been AWG 10. AWG8 would be a better balance but still a limiting factor AWG 6 is over kill

I can solder awg10 easily and quickly with a high power iron.
8 is a little bit tricky and risks a chance of cold solder joint if I don’t get it right as I have the dance the tip from side to side to heat both sides of the cable to a sufficient temp this as well as the insulation is wanting to loosen up from the copper cor if there’s any bend on the cable, also doesn’t fit very nicly in a xt90

I have a 12s3p vtc5a on my Tayto with hubs and I have a good sag of 5-7V when going up a slight hill. I don’t think it would be better with 30q either. If you want to ask 100A from a streetboard than I think a 3p 18650s is not the right choice anyway. It’s good for a city cruiser light weight commuter, but not if you really want to have a high performance.

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Interesting was expecting some sag as this is running them at there limit but same reason space in a commuter build is at a premium
how many amps are you drawing from the pack at the time?
What did you link the cells with how many layers on nickel/p group links made from?

All this amp draw discussion got me going. I’m building a 12s4p pack from 40t cells. Since these are high discharge cells, I would like to not have it botlenecked. This is my plan of connecting them:



So the nickel in use is rated for 40A, I think this is somewhat debatable. I’m building with battery PCB’s, going one layer of nickel on P groups, individual strips from cell to PCB and an additional strip on the top, as for series: 2x braids in 15mm. What do you think? Should I up the nickel? Is this moderately good enough?

Hi guys, i have a bit confusion about my Bestech d140. I’ve requested bms for charge only and remove all the discharge feature, but by mistake they sent me the charge and discharge bms.

My data sheet request:

What they sent me:

Here’s the look of bms they sent:

After asking for why they didn’t sent me as a requested, they come with this solution:
“can you make short circuit of the two components as the Pic I attached? The DS foot of the three FETs short circuit (QR35 and RQ34 and RQ33) , and RS2 RS1 short circuit.”

I’m goin to use this for charge only bms, can someone help me what best to do with the bms i got? 1. should i just short circuit them like they suggested? if yes, what wiring diagram should i follow.
2. Do nothing and just bypass the discharge? if yes, what wiring diagram should i follow.

Really appreciate any helps, thanks.

At 32A I have 5.5V sag.
That’s my pack

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