kWeld - "Next level" DIY battery spot welder

Batteries, Chargers, and Battery Management Systems.
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flippy   100 MW

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Re: kWeld - "Next level" DIY battery spot welder

Post by flippy » May 20 2021 7:34am

no, there is no advantage in adding a lipo.

and mains is still prefferd. its provides the most stable supply. lipos degrade, have different outputs depending on SoC and the list goes on. supercaps are nice and stable.
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Andy_L   100 µW

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Re: kWeld - "Next level" DIY battery spot welder

Post by Andy_L » May 20 2021 5:52pm

Damn Boris/Brexit, UK reseller is out of stock and doesnt have the KCap, case or spare electrodes I was going to order so thought I would go order direct and face the import duty but sadly no option for UK and found the reason in an old post from a few months ago. :( :pancake:

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Re: kWeld - "Next level" DIY battery spot welder

Post by Maximum_RnB » May 21 2021 5:04am

I think I may have bought the last kWeld from the UK supplier as they're now out of stock. I emailed them about other stuff and they apparently have stock held-up in customs.

Brexit is not quite living-up to all those promises that were made, is it? Having said that, I ordered some stuff from NKON a while back and despite all the dire warnings about delays etc. it arrived in under a week with no extra charges.

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flippy   100 MW

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Re: kWeld - "Next level" DIY battery spot welder

Post by flippy » May 21 2021 6:07am

Maximum_RnB wrote:
May 21 2021 5:04am
Brexit is not quite living-up to all those promises that were made, is it?
who could see that coming?
The bitterness of low quality remains long after the sweetness of low price is forgotten

Andy_L   100 µW

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Re: kWeld - "Next level" DIY battery spot welder

Post by Andy_L » May 21 2021 7:07am

Thanks, I will message then and see if they are expecting any kcaps in as well.

Also got a big order on the way from nkon. Enough cells for 2x 14s4p packs plus spares, skyrc mc3000 as I wanted a decent cell charger and tape, cell caps etc etc. Although I did think I should have got the vp4 dragon to charge a 3s lipo for the welder.. Oh well a cheap dedicated lipo charger is only £22. Shame nkon don't resell the kweld!

Other option is ask a friend in Europe if I can send to them and then they ship it on. Got a motor from pswpower in Germany in about 4 days.

Eraser-1   100 µW

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Re: kWeld - "Next level" DIY battery spot welder

Post by Eraser-1 » May 27 2021 12:35am

I have bought now the kWeld with kCap and I have found a interesting detail.

My kCap has the revision 6 and is now equipped with SkelCap SCA0300 ultra capacitors instead of the Maxwell caps.
The datasheets states that they have a little bit less capacitance (300F instead of 310F), but more rated voltage (2,85V instead of 2,70V), a lower ESR (1,00mR/1,60mR instead of 2,2mR) and a higher short circuit current (3000A instead of 1200A).

From my understanding, now I can charge these caps to a voltage of 8,55V instead of 8,1V and with the lower ESR this new kCap module should deliver more current than the older version. Although I don't think I can change the voltage limit to which the caps will be charged, because very likely it is set in the electronics of the kcap-board. My thinking is, that the electronics will just cut the input voltage from the caps when they are charged and reconnect it when they are partly discharged.

So what I still don't know is, what is the difference when connecting i.e. 14V input voltage instead of i.e. 9V to the kCap?
Is it possible to change the voltage of the caps by just increasing the input voltage? (which would be not good with 14V input voltage).

Thanks
Wolfgang

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flippy   100 MW

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Re: kWeld - "Next level" DIY battery spot welder

Post by flippy » May 27 2021 12:45am

the board only balances, it does not cut power.
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Eraser-1   100 µW

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Re: kWeld - "Next level" DIY battery spot welder

Post by Eraser-1 » May 27 2021 4:01am

OK thanks for the answer.

This would mean, that you can adjust the voltage level of the caps with adjusting the input voltage of the kcap.

The question then would be, why is it written, that the input voltage is from 8V up to 14V? 14V would be far too much, so there must be any kind of safety feature...

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flippy   100 MW

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Re: kWeld - "Next level" DIY battery spot welder

Post by flippy » May 27 2021 5:23am

you CAN input more, it just kills the caps faster. they also get VERY hot of you do.
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spinningmagnets   100 GW

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Re: kWeld - "Next level" DIY battery spot welder

Post by spinningmagnets » May 27 2021 7:20am

The device measures the energy passing through in joules. If you use more volts, it must limit the amps, and it is the amps that causes the heat that results in the welding.

It was originally designed to use a car battery, which is readily available everywhere, and capable of the high amp-pulse that works well. A fully charged car battery is typically 13V.

Early in the process, customers wondered if super-capacitors could be used instead of a car battery, and in spite of the cost, many buyers wanted them as an option. Its not just the cost of the supr-cap board, you must also have a power supply that can recharge them rapidly using a lower voltage (*3V-8V?).

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spinningmagnets   100 GW

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Re: kWeld - "Next level" DIY battery spot welder

Post by spinningmagnets » May 27 2021 7:20am

The device measures the energy passing through in joules. If you use more volts, it must limit the amps, and it is the amps that causes the heat that results in the welding.

It was originally designed to use a car battery, which is readily available everywhere, and capable of the high amp-pulse that works well. A fully charged car battery is typically 13V.

Early in the process, customers wondered if super-capacitors could be used instead of a car battery, and in spite of the cost, many buyers wanted them as an option. Its not just the cost of the super-cap board, you must also have a power supply that can recharge them rapidly using a lower voltage (*3V-8V?).

Eraser-1   100 µW

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Re: kWeld - "Next level" DIY battery spot welder

Post by Eraser-1 » May 27 2021 7:37am

I have checked the manual of the kCap again and there is written:

-) Any current limited lead acid battery charger with 13.8V output voltage

-) Output voltage is automatically kept in 8.0V – 8.3V range (power supply disconnect)

So, it looks like it is that way what I thought with cutting the supply from the caps, because otherwise I don't think the manufacturer would write to charge the kCap with 13.8V as possibility. Also the output voltage (cap voltage) is automatically kept in the range, that would mean no change of the cap voltage with different input voltages.
The remaining question now would be if the cap voltage range on the revision 6 board with the new caps is also increased.

Yeah the kWeld is using Joules, but the Amps don't have to decrease with a higher voltage to get the same amount of Joules into the welding spot. If the Amps and Voltage increase, the pulse duration of the kWeld will decrease. The kWeld itself can't regulate the Amps, only the time. The increased input voltage on the kWeld would just help to get more Amps through the circuit with its resistances.

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flippy   100 MW

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Re: kWeld - "Next level" DIY battery spot welder

Post by flippy » May 27 2021 8:06am

the new kcap simply cuts the power of the incoming charger. but there is no useful reason to rely on the protection system of the board to prevent destruction. there is zero reason to buy a higher voltage source, it only adds inefficinety and cost.
The bitterness of low quality remains long after the sweetness of low price is forgotten

Eraser-1   100 µW

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Re: kWeld - "Next level" DIY battery spot welder

Post by Eraser-1 » May 27 2021 1:39pm

Thanks for the answer, I will definetely take a power source with around the 8V and not 13.8V or such things. I just wondered and be interested in the function and what the changes on the new version r6 are (if only the caps are changed to different ones or if also some changes were made on the electronic side).

john61ct   100 GW

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Re: kWeld - "Next level" DIY battery spot welder

Post by john61ct » May 27 2021 2:37pm

So let's say a Hobby charger designed for 2S li-ion, can charge from the pack-level power pair only, no balance lead connected

or you rig a pigtail harness adapter to spoof its need for 3 wires

Assume one port only.

What is the minimum wattage / amps output required

to feed the kcaps fast enough,

to never need to pause and wait while welding a big pack?

FMA PL8, Junsi iCharger 4010 for example, are those overkill?

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flippy   100 MW

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Re: kWeld - "Next level" DIY battery spot welder

Post by flippy » May 27 2021 3:39pm

smart chargers dont work. you need dumb stuff.

a HRP-600-7.5 would give you recharge times faster then you can physically move. i use a 300 and that can keep up with my welding speed just fine.
The bitterness of low quality remains long after the sweetness of low price is forgotten

john61ct   100 GW

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Re: kWeld - "Next level" DIY battery spot welder

Post by john61ct » May 27 2021 6:52pm

Plenty of good chargers have a "power supply mode".

But good to know a little 300W unit's good enough.

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spinningmagnets   100 GW

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Re: kWeld - "Next level" DIY battery spot welder

Post by spinningmagnets » May 28 2021 1:02pm

"I use a 300 and that can keep up with my welding speed just fine"

Link?

Eraser-1   100 µW

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Re: kWeld - "Next level" DIY battery spot welder

Post by Eraser-1 » May 28 2021 1:24pm

This was a Meanwell 7.5V, 40A, 300W.
Just google. I think a few posts back there is the exact description.


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Re: kWeld - "Next level" DIY battery spot welder

Post by hamid120 » Jun 11 2021 11:48am

Hello guys. Upgrading the cable from 8 awg to 6 awg, what length should i set the kweld on setting?
The totalt length is 1.5m.but the kweld is programed as 8 awg I assume.?

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Re: kWeld - "Next level" DIY battery spot welder

Post by Eraser-1 » Jun 14 2021 10:03am

The length has nothing to do with the diameter. The length is still the same when you upgrade your cables to AWG6. This is because of the inductive kickback.

Jatem   100 mW

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Re: kWeld - "Next level" DIY battery spot welder

Post by Jatem » Jul 07 2021 1:48am

Has anyone tried using a 7.5V stepdown converter to run a bank of super capacitors, such as item 1005001700167238 from aliexpr with 30A?
I'm debating whether to get a k power supply. I already have a 500w hp psu I could use. The k power supply would be less expensive than a meanwell hrp-450-7.5 or 300-7.5. But a 7.5v step down would be very inexpensive.

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multifrag   100 W

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Re: kWeld - "Next level" DIY battery spot welder

Post by multifrag » Jul 07 2021 8:02am

Jatem wrote:
Jul 07 2021 1:48am
Has anyone tried using a 7.5V stepdown converter to run a bank of super capacitors, such as item 1005001700167238 from aliexpr with 30A?
I'm debating whether to get a k power supply. I already have a 500w hp psu I could use. The k power supply would be less expensive than a meanwell hrp-450-7.5 or 300-7.5. But a 7.5v step down would be very inexpensive.
I have been using murata rbq-8.2/45 step down converter and in talking to Frank. Step down converter have two problems.
1. Inrush current and 0V
2. Having to bypass hiccup protection

To combat these problems I start by limiting my current with lab bench psu for couple seconds and replacing some resistors two turn off protection. The only reason why I wanted to go with a step down route is having bench psu available.

Jatem   100 mW

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Re: kWeld - "Next level" DIY battery spot welder

Post by Jatem » Jul 09 2021 1:38am

Ksupply seems a good option. Is it a good idea to add an ideal diode in front of the ksupply, to protect it from inductive kickback if I'm using a diy capacitor bank?

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