Spot welder - change out transformer for car battery

[Jonnytub]

Hi guys,

New here and after getting some excellent advice here recently I wanted to ask the boffins a theoretical technical question. I recently borrowed a spot welder from a mate who bought it on ebay for the same reason, making our own batteries. He could only get it to run at work as the current draw is too much for normal house circuits, he failed (or forgot) to mention this when he dropped it off.

It’s a cheapo Sunko 788h which I had a little dig around being curious. I have limited experience with electronics but do have good soldering skills having worked in a factory as a youngster tinning and soldering capacitors and transistors on a production line and I had a thought.

I’ve already given up on the idea of putting my own pack together and have been talking to Jimmy at Insat to arrange for him to make the battery using my own sammy 30q cells and then I got wondering whether the transformer in this machine which I presume is what’s causing the huge initial current pull and subsequent breaker trip to happen could be replaced with a car battery, i.e. keep the main circuits powered from mains but the actual weld current supplied from the battery, my battery will still be going to Jimmy but was wondering whether this is even possible, maybe even to use on future projects.

I’m only asking as really butthurt over not being able to make my own pack so once that’s sorted maybe a future project.

Thanks

Jonny

 

[mountainsport]

Hi guys,

New here and after getting some excellent advice here recently I wanted to ask the boffins a theoretical technical question. I recently borrowed a spot welder from a mate who bought it on ebay for the same reason, making our own batteries. He could only get it to run at work as the current draw is too much for normal house circuits, he failed (or forgot) to mention this when he dropped it off.

It’s a cheapo Sunko 788h which I had a little dig around being curious. I have limited experience with electronics but do have good soldering skills having worked in a factory as a youngster tinning and soldering capacitors and transistors on a production line and I had a thought.

I’ve already given up on the idea of putting my own pack together and have been talking to Jimmy at Insat to arrange for him to make the battery using my own sammy 30q cells and then I got wondering whether the transformer in this machine which I presume is what’s causing the huge initial current pull and subsequent breaker trip to happen could be replaced with a car battery, i.e. keep the main circuits powered from mains but the actual weld current supplied from the battery, my battery will still be going to Jimmy but was wondering whether this is even possible, maybe even to use on future projects.

I’m only asking as really butthurt over not being able to make my own pack so once that’s sorted maybe a future project.

Thanks

Jonny

Good stuff!

MS.

 

[cyclebuddy]

I wouldn't suggest for a moment you do this unless you know what you're doing, but it's quite possible to run a 30A mains supply from your consumer unit using 6mm sq T&E (cooker) cable, or a 45A supply using 10mm sq (10kw shower cable). I run 4 x 500kva toroidal transformers for my hi-fi this way, which each appear physically far bigger than the one transformer in this device.

My worry with doing that with this welder is that the internal wiring feeding the transformer primary looks very inadequate for carrying that amount of current to me - even if it is only surge/inrush while the windings saturate.

Your other issue may be the RCD tripping (if you have a fairly newish consumer unit)?

 

[Nealh]

Although I don't have one I believe they require 80 or 100a power supply from 240v, though some are dual and 110v.
Most house supplies will not be up to it let alone a dc power supply.
However on a much smaller scale the very mini Boss spot welder (palm size) about $85 delivered only requires a 12v lipo or other 12v dc supply and is very capable.
If you use the search part of the forum you will see mine and a link to the ES thread which is very good.

 

[Deleted member 4366]

I have one of those welders, and it works perfectly on the normal 13A supply.

When it comes to welding, either use slotted nickel strip or use a Dremmel and disc cutter to plunge slots into the nickel strips so that there is a gap between where the electrodes land. That forces the current downwards instead of letying it take the easier direct path between the electrodes. You can then weld with much less power.

 

[Jonnytub]

Hi guys,

Sorry for not replying sooner, took too much on lately.

Anyhow, i did a little socket hopping this morning whilst all the appliances were either in standby or not being used and voila, what i believe to be the first socket in the run from the consumer powered it up no problem so project battery is back on!

Thanks for the ideas and advice!

 

[awol]

Anyhow, i did a little socket hopping this morning whilst all the appliances were either in standby or not being used and voila, what i believe to be the first socket in the run from the consumer powered it up no problem so project battery is back on!

Could the power trip off from maybe using another high power device like a kettle/tumbledryer at the same time as trying to spot weld with one of these?

 

[Jonnytub]

Yes, as tested when I tried to make a cuppa with the kettle and tried to turn it on using the same circuit, it tripped, turned the kettle off and fine. Happy days. It's a greedy box so I'm going to make sure for initial switch on it's the only running device, after that, no problem.

 

[Jonnytub]

Sorry, the actual welding isn't what causes the trip, it's the initial inrush current to the transformer as far as I can tell.

 

[Deleted member 4366]

The power is really low. It's not like an industrial welder!

 

[Danidl]

Although I don't have one I believe they require 80 or 100a power supply from 240v, though some are dual and 110v.
Most house supplies will not be up to it let alone a dc power supply.
However on a much smaller scale the very mini Boss spot welder (palm size) about $85 delivered only requires a 12v lipo or other 12v dc supply and is very capable.
If you use the search part of the forum you will see mine and a link to the ES thread which is very good.

No way do they require that level of current..on the input The 80 amp would be available at the output terminals at say 3 to 4 volts.and into the welding rods. It might assist if the op posted a picture of the faceplate .giving it's power requirements.

 

[Danidl]

Sorry, the actual welding isn't what causes the trip, it's the initial inrush current to the transformer as far as I can tell.

If it's tripping a circuit breaker, then it is inrush current, and you need to replace the CB with a slo blog type.
Alternatively you need to put some thing in the line.. traditionally a thermistor would be used. But .a car bulb would act very effectively as well. After the power on switch connect one those incidental lights 12 watt jobs in series between the trafo and the switch. Then if the trafo is switched on at the wrong instance in the phase, the inrush current is reduced by the added resistance of the gulf. The power rating will suggest the amperage of the bulb...so look at the faceplate.
What is actually happening is that when the trafo was switched off last time, the iron in the core of the trafo was magnetised in a specific direction. If the current flows in the same direction, the inductance of the coil in the trafo is negligible, as the core is already saturated and the inrush is limited only by the resistance of the wire, after a cycle, proper performance is restored and the inductance does the right amount of lagging. ..but if the trip has tripped! That is why these trafos sometimes trip and sometimes don't.

 

[Jonnytub]

Just to clear a few things here up guys:

This is a new build so wiring is current regs.

A picture of the faceplate is meaningless given that this is a chinese box.

This box is notorius for tripping breakers due to inrush current.

9 times out of ten it will switch on fine using the first socket from the cb on the kitchen circuit, otherwise a quick trip to the fuse box is required.

I’ve watched every single english speaking youtube video on this welder and I can say that build quality is much better than the original ones, this particular box is 20 weeks old, soldering points are now mostly machine performed with hand soldering jobs on the_ pcb not being bad but they are chinese.

It’s still a crap chinese box but it’s welds are good and I haven’t blown a fuse in it yet despite being supplied with 3.

Most of the parts in this thing are recycled or repurposed from other machines, I’m sure I’d have a different opinion had I not gotten this to work but all in all, inrush current with UK typical circuits is the downfall of this particular box.

 

[Deleted member 4366]

No way do they require that level of current..on the input The 80 amp would be available at the output terminals at say 3 to 4 volts.and into the welding rods. It might assist if the op posted a picture of the faceplate .giving it's power requirements.

15A at 220v input. 50A to 800A output.

 

[Danidl]

Just to clear a few things here up guys:

This is a new build so wiring is current regs.

A picture of the faceplate is meaningless given that this is a chinese box.

This box is notorius for tripping breakers due to inrush current.

9 times out of ten it will switch on fine using the first socket from the cb on the kitchen circuit, otherwise a quick trip to the fuse box is required.

I’ve watched every single english speaking youtube video on this welder and I can say that build quality is much better than the original ones, this particular box is 20 weeks old, soldering points are now mostly machine performed with hand soldering jobs on the_ pcb not being bad but they are chinese.

It’s still a crap chinese box but it’s welds are good and I haven’t blown a fuse in it yet despite being supplied with 3.

Most of the parts in this thing are recycled or repurposed from other machines, I’m sure I’d have a different opinion had I not gotten this to work but all in all, inrush current with UK typical circuits is the downfall of this particular box.

Its fuse won't blow as it takes a while for the fuse wire to heat up to melting point. And by that time the trafo has stabilized. The CB can trip because the large current has mechanically accelerated the armature in the circuit breaker with the initial impulse. there are other CBs which have built in dashpots and so slow down the response to a momentary overload. On the basis of d8vh figures, perhaps a car headlamp bulb would be more suited... As the resistance element. Eg. A car bulb designed for 55w at 12 volt will have a hot resistance of 3 ohms and a cold resistance of about 1/2 ohm.