# Capacitor bank for pulse welder

#### rg12

Joined Jun 27, 2016
12
Hey guys,

I had someone a while back telling me he built a capacitor bank to help run a spot welder on home grid at high settings without tripping the switch and he also said that it provides "cleaner" current thus making better spot welds (although I doubt that one).
He also said that it may take a second for the caps to charge between welds which can be a bit annoying in case I want to work fast so the first question is, can I use super capacitors?

Main question is, can you guys help me figuring out which and how many caps would I need? (220v grid)
Which other components would be required?

This is the spot welder I ordered (my much weaker one is already tripping my grid when maxed:
https://www.aliexpress.com/item/1pc...492.html?spm=a2g0s.9042311.0.0.24534c4dmeTxPN

Joined Jul 18, 2013
21,594
Depends on the product you are welding, A capacitor disharge welder generally uses a charged bank of capacitors and discharged with a SCR.
As with a resistance welder, sufficient electrode pressure has to be applied before the weld takes place.
Max.

#### rg12

Joined Jun 27, 2016
12
Depends on the product you are welding, A capacitor disharge welder generally uses a charged bank of capacitors and discharged with a SCR.
As with a resistance welder, sufficient electrode pressure has to be applied before the weld takes place.
Max.
This is not a capacitor pulse welder (which exists as an off grid spot welder), this is a regular pulse welder that connects to a wall outlet and has a big transformer inside.
I want it to act like those big capacitors that car audio uses when the bass dims their headlights they connect it between the battery and the amp and it helps keep the current stable.
For me it's for not taking huge amp pulses from the grid

#### Danko

Joined Nov 22, 2017
1,005
Capacitor discharge welding
Principle of Capacitor Discharge welding (CD welding)
During CD welding the required welding energy is taken from previously charged capacitors. This energy is transferred via a thyristor and a welding transformer. Charging times are typically between 0.5 and 2 seconds; weld times between 3 and 10 milliseconds.
The capacitors are typically loaded at a voltage of 1500 V for maximum usage of them. These high charging voltages allow high turns ratios. Doing so high weld currents are achieved as well as relatively high secondary voltages.
This effect gives advantages in designing machines and fixtures. Through the short circuit like discharging of the capacitors the energy maximum is reached very quickly. The resistance maximum is reached also very quickly due the fixture and advance preparations.
This extremely fast temperature raise in the welding zone heats it up before the heat can dissolve. This prevents the heat to reach other parts of the part. Just after a few milliseconds the weld is finished without heating up the surrounding area. This effect is responsible for all advantages and possibilities of the CD welding.

Grace to the high energy density on the heated volume the efficiency factor of a CD weld is higher than 90%. So CD welding is a very economical weld application. Additionally there is a low requirement on the mains supply. The combination of both makes CD welding very attractive.

#### rg12

Joined Jun 27, 2016
12
So how is this done exactly?
and can I use super capacitors instead of regular ones to prevent the slow charging ones?

Joined Jan 15, 2015
5,667
What are supercapacitors? May help you to understand what supercapacitors are. The following comes from the link.

Characteristics
Charge time
Supercapacitors have charge and discharge times comparable to those of ordinary capacitors. It is possible to achieve high charge and discharge currents due to their low internal resistance. Batteries usually take up to several hours to reach a fully charged state – a good example is a cell phone battery, while supercapacitors can be brought to the same charge state in less than two minutes.

The idea behind capacitor discharge welding is to charge a bank of capacitors and then simply discharge them rapidly through a work piece exactly as Danko mentions in post #4. Generally this is done using a SCR (Thyristor) as Max mentions in post #2. So we make a big pile of energy stored and then rapidly, in a few milli-seconds, discharge it.

I have no idea what your reference to the grid is all about? Capacitor Discharge Welding is a DC process so a grid voltage AC is converted to DC and charges capacitors. The grid voltage has nothing to do with it. Also, before I forget, supercapacitors are generally low voltage devices. Another reason they would not be suitable for capacitor discharge welding.

Ron

#### rg12

Joined Jun 27, 2016
12
What are supercapacitors? May help you to understand what supercapacitors are. The following comes from the link.

Characteristics
Charge time
Supercapacitors have charge and discharge times comparable to those of ordinary capacitors. It is possible to achieve high charge and discharge currents due to their low internal resistance. Batteries usually take up to several hours to reach a fully charged state – a good example is a cell phone battery, while supercapacitors can be brought to the same charge state in less than two minutes.

The idea behind capacitor discharge welding is to charge a bank of capacitors and then simply discharge them rapidly through a work piece exactly as Danko mentions in post #4. Generally this is done using a SCR (Thyristor) as Max mentions in post #2. So we make a big pile of energy stored and then rapidly, in a few milli-seconds, discharge it.

I have no idea what your reference to the grid is all about? Capacitor Discharge Welding is a DC process so a grid voltage AC is converted to DC and charges capacitors. The grid voltage has nothing to do with it. Also, before I forget, supercapacitors are generally low voltage devices. Another reason they would not be suitable for capacitor discharge welding.

Ron
How come super capacitors and regular capacitors have the same charge/discharge duration if they have different internal resistance?

So is this possible to connect a power bank to an ac outlet (I know that there are AC capacitors) and have them charged for the transformer driven pulse welder to use when needed very high currents (more than the grid can handle)?

Also, will it be possible to pull an extension chord from two different outlets that are connected on two different phases and connect them in parallel to create a dual power socket or does that idea only work in theory and will end up with fire/me getting electrocuted to death?

Joined Jan 15, 2015
5,667
Also, will it be possible to pull an extension chord from two different outlets that are connected on two different phases and connect them in parallel to create a dual power socket or does that idea only work in theory and will end up with fire/me getting electrocuted to death?
Depends on the power distribution. I have no clue where you are located but here in North America in the US typical residential mains power is single phase delivered to a residence as 240 VAC 60 Hz Split Phase. The relationship of the signal is each 120 VAC side to ground is 180 degrees out of phase from the other. Residential power is single phase and not poly phase.

Once a capacitor is charged, it is charged and that is as good as it gets. The plates are saturated and there is no more room for electrons. If we charge a capacitor using AC the capacitor will charge and discharge at a rate determined by the AC line frequency. Using 60 Hz as an example between 0 and 4.166 mSec the capacitor will charge then discharge as the sine wave drops through zero at the 8.3 mS mark. It will be charged to its negative peak 4.166 mSec later. All in all over 16.66 mSec the capacitor will charge to one positive and one negative peak and be crossing zero again.

Also, will it be possible to pull an extension chord from two different outlets that are connected on two different phases and connect them in parallel to create a dual power socket or does that idea only work in theory and will end up with fire/me getting electrocuted to death?
Yes, it can be done but I would just run 240 VAC service from my entry panel rather than find two 120 volt opposing outlets to get 240 VAC. You are also starting to teeter on what could be dangerous.So we won't pursue that thinking.

Ron

#### Danko

Joined Nov 22, 2017
1,005
Use inductive ballast GEP250MLTAA4-5/2, US $29.95 on ebay. Connect it in series with your welding machine. It will limit current from grid, but allow charge capacitors very fast. Current from 240V grid will 1A, from 120V grid will 2A, only in process of capacitor bank charging (some part of second). Last edited: #### oz93666 Joined Sep 7, 2010 737 I have a feeling mains spot welding is old tech ( I could be wrong)... very complex and expensive , transformers etc ... Super capacitors have done away with all that , no high voltage , everything below 12V , you need a car battery or similar source to power it. I expect many people doing this on youtube. #### MaxHeadRoom Joined Jul 18, 2013 21,594 As I posted in another thread, resistance welding still has its place, for example in seam welding where the welding is done with circular rotating dies that constantly pulse power to create a leak proof seam. Also large projection welders where the current has to be a short rapid series of pulses. In operations where the delay in capacitor charging is unacceptable. Max. Thread Starter #### rg12 Joined Jun 27, 2016 12 Use inductive ballast GEP250MLTAA4-5/2, US$29.95 on ebay.
Connect it in series with your welding machine. It will limit current from grid, but allow charge capacitors very fast.
Current from 240V grid will 1A, from 120V grid will 2A, only in process of capacitor bank charging (some part of second).

View attachment 156458
Why do I need this ballast thing?
and can I use DC capacitors for that?
my grid is 220V, which caps would I need? I don't know how much capacity I need and I don't want to much in order to not have to wait for them to be charged so long as I work pretty fast with the machine.

#### Danko

Joined Nov 22, 2017
1,005
Why do I need this ballast thing?
and can I use DC capacitors for that?
my grid is 220V, which caps would I need? I don't know how much capacity I need and I don't want to much in order to not have to wait for them to be charged so long as I work pretty fast with the machine.
I am sorry, it was off topic.
...so the first question is, can I use super capacitors?...
Yes, you can. For example - "3000F 2.7V super capacitor for spot welding machine" - https://www.alibaba.com/product-detail/3000f-2-7v-super-capacitor-for_1618151933.html
...Main question is, can you guys help me figuring out which and how many caps would I need?...
Try one. If spot will weak, add more.
...Which other components would be required?...
It depends on someone who will design this welder for you.

Last edited:

#### DNA Robotics

Joined Jun 13, 2014
588
You may be exceeding the duty cycle on that small welder. I don't see a duty cycle rating on the new one.

The new welder has a 25 amp breaker. They don't give an input amp rating.

What amp breaker is tripping on your welder. On my breaker panel, the dryer is 30 amps, the range is 50 amps, central A/C is 60 amps and my lathe with a 10 HP motor never trips its 70 amp breaker. That is enough power to melt the wires on your little welder.

That new welder on a 30 amp circuit should be fine.

#### rg12

Joined Jun 27, 2016
12
You may be exceeding the duty cycle on that small welder. I don't see a duty cycle rating on the new one.

The new welder has a 25 amp breaker. They don't give an input amp rating.

What amp breaker is tripping on your welder. On my breaker panel, the dryer is 30 amps, the range is 50 amps, central A/C is 60 amps and my lathe with a 10 HP motor never trips its 70 amp breaker. That is enough power to melt the wires on your little welder.

That new welder on a 30 amp circuit should be fine.
I talked with a professional about it and for me to have a 30A breaker I need to replace the wires in the wall and I don't wanna go there.

#### DNA Robotics

Joined Jun 13, 2014
588
You didn't say what amp breaker is tripping.

Do you have an electric clothes dryer? You could plug your welder in there.

Do you have an electric range/oven? You could plug your welder in there.

#### rg12

Joined Jun 27, 2016
12
You didn't say what amp breaker is tripping.

Do you have an electric clothes dryer? You could plug your welder in there.

Do you have an electric range/oven? You could plug your welder in there.
It trips the 16A breaker (it's a 220v grid so I guess it's like your 30A breaker on a 120V grid)

#### DNA Robotics

Joined Jun 13, 2014
588
On my breaker panel, the dryer is 30 amps, the range is 50 amps, central A/C is 60 amps and my lathe with a 10 HP motor never trips its 70 amp breaker. That is enough power to melt the wires on your little welder.
These are all 230 volt circuits.

#### rg12

Joined Jun 27, 2016
12

#### DNA Robotics

Joined Jun 13, 2014
588
Why does the dryer need 7kw?
Because the instructions say so.

We believe in overkill.

We would rather be safe than sorry.

We don't want undersized hot wires in the wall.

Affluent Americans use a lot of power.