Kweld spot welder

How-Tos & Esk8 mechanics
#101

So 3s battry = 11.1v - 6.3v (kweld needs at 1500a)= 4.8v

So as stated above you 4.8v over voltage will alow 4.8*0.67=3.216Mohm reactance inside the battry /3= 1.072Mohm per S to stay in the optimum range of the Kweld

In the video each cell had a internal resistance of 6-44Mohm well above the recommended 1.072Mohm per a cell in a 3s configuration

2 options to rectify this higher voltage or lower internal resistance

Say you used a 3s6p each cell is 6Mohm resistance (best battry internal resistance I saw in the video if I used the 44Mohm it will be way worse)

1s 6p (1/6Mohm battry resitance)*6Series=1Mohm
1/1=1Mohm battry resistance in the parallel group.

3s6p 1(parallel Group battry Mohm resistance)*3(number of series)=3

So a 3s6p should work if you got only the most healthiest 6milly ohm cells and no bad ones. To put this in to prespective a 30q has a 20mohm internal resistance so each cell is aprox 3*30q in capacity and discharge.

Unless I’m screwing some thing up the 1000a burst rating is well over estimated and is closer to 250a burst rating

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#102

A customer has tried these without any luck, less than 1000 when paralleling 3 of them. If a seller has to shout out his advertistment in capital letters like that one, then this is already enough for me to skip it entirely.

The order numbers don’t count like this. I’m using Wordpress/Woocommerce, and it seems that they even increment when someone creates a shopping basked which he then discards. Real numbers are approaching 2000.

Can’t tell with regards to duties, but you’ll certainly have to pay VAT as you aren’t buying from one of your country fellows, and effectively make a net purchase from me.

was just rereading this and noticed a mistake. Correct wording would be “for every volt above 6.3V that the battery has, it needs to have >>>>0.67<<<< milliOhm of internal resistance”

4 Likes
#103

That would explain my confusion of 1.5v been 1ohm and 1 battry ohm was as much as 1v befor not making sense in you post above I will correct My post above in case any one reads it later and uses it to calculate

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#104

Just out of interest I wondered what size pack you would need to run the welder of 30Q Maths below (let me know if I made a mistake so were typed it on my phone)

Working on Optimal Kweld power requirement 6.3v-30V at 1500a

For every V over 6.3 we can have 0.67mohm Battry internal resistance.

Or for every 1ohm battery internal resitance we need another 1.5V

30Q has a
internal resistance of 20mohm
Average voltage 3.7V

So working on a 3s20p

No. of Series * Average Voltage
3*3.7=11.1v

Battry Pack Avrage Voltage - Kweld Min Required Voltage
11.1-6.3=4.8 exsees voltage

Exsees Voltage * Allowed Battery Internal Resistance = Maximum Battery resistance
4.8*0.67=3.024

Maximum Battery resistance/Series count
3.024/3=1.008

(1/cell internal resistance)*P Group=
1/Answer=Battery P Group internal resistance
(1/20)*20=1
1/1=1

So a Q30 3S20P (60 cells) pack is a optimal solution

————————————————-
What if we go fo a high voltage option up to 30V the max voltage of the Kweld

No. of Series * Average Voltage
8*3.7=29.6V

Battry Pack Avrage Voltage - Kweld Min Required Voltage
29.6-6.3=23.3 exsees voltage

Exsees Voltage * Allowed Battery Internal Resistance = Maximum Battery resistance
23.3*0.67=15.611

Maximum Battery resistance/Series count
15.611/8=1.951 battery P Group Internal Resitance

(1/cell internal resistance)P Group=
1/Answer=Battery P Group internal resistance
(1/201)*11=0.55
1/0.55=20

So in theory a Q30 8S11P (88cells) the smallest P count pack you could use with out exceeding the Max voltage of the Unit staying at the optimal 1500A

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#105

Plus it uses much better mosfets and only 20% of their capacity

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#106

I think that @thisguyhere tried to make a 25r spot welding battery 3s20p and it just couldnt give the current fast enough

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#107

yeh absolutely. I am looking for a car battery seems the lipo overheat easily. What would you reccomend to look for? I will just buy it locally.
I know the caps will work better but tjey are out of stock.

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#108

I bought a 45 ah650CCA Yasua battery if I remember right and it couldnt give enough current, maybe it was because of my cables but Im not sure

I would reccomend you to get a 4Ah red graphene for 30-40$ and weld really slowly untill kcaps are in stock

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#109

Well I do not need to weld right now. I will then wait and think about it. I really thought the car battery works out better :sweat_smile:

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#110

If you are going big amps I recommend using as150 to connect everything, I killed some nanotech lipos with a big pull using xt90 plugs in series/parallel.

Ordered some grahenes to replace

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#111

that I bought it already :blush:

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#112

I would say green is better than red and higher capacity

#113

I guess @Acido wanted to give an alternative to save some money to invest in the Kcaps later on. Just my guess.

Green is better for sure but 2p costs like the Kcaps

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#114

Not saving money if it dosent meet the min spec

Red is rated to 90C burst
Green is Rated to 150C Burst

4ah*90 = 475A Burst

K weld absolut min 800A
Recommended 1500a

It just not poky enougth in its own

4-5AH Green I thing is about the bare min I would recommend

Dule 6Ah 3s Green keeps me at the optimum 1500a for most of the battry life as a good spec (12ah*150c=1800a burst in real life it averages 1600a burst)

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#115

Shorted and not shorted is totally different

Trust me one is enougu as I burned through at least red ones and 4 green ones both 4 and 5ah work well

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#116

KCapps deliver 1200A and are out of stock due to been in the middle of a redesign for a over volt protection as a safety thing to stop the exsploding. Think @Acido is running Dule Kcapp that should be able to deliver around 1700a

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#117

I talked with the creator about this, and at the time a bms was going to be put before the kcap as a standalone device, but maybe the idea has changed

#118

He was doing both developing a external board for people who have then kcapp all ready as a free upgrade and including it in the new design when I talked to him was a while ago tho

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#119

Am I crazy to run 2 of these in parallel @tatus1969

I’m aware they will run out of usable charge quickly, but presumably enough to weld a parallel pack of 6x18650 at a time?

https://hobbyking.com/en_us/graphene-1600mah-4s-75c-square-pack.html

Should I get a third in parallel?

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#120

Is not the useable charge that’s the bottle neck it’s the total short circuit amps it can deliver. If you hold down the peddle it will tell you the total amps delivered in how long of a time.

Longer it takes to deliver the current the more it heats the Battry up. the point is to deliver a high ampage in as short about of time as possible