In this blog, we will talk about three mobile welding pens S71A, S71B and S70BN(red shell). These pens are designed for 797 and 709 series.

We all know that there is resistance in any conductor. 
P=UI=I²R
The greater the current passing through, the more power will be lost because of the internal resistance of the spot welding pen.
So we strictly control the length of the spot welding pen according to the characteristics of each series of spot welders, and the length of welding pen is controlled at 22.4" to 24.8". The internal resistance is controlled within 2 mΩ. (For the specific power output of spot welding pens, please refer to the article " How much is the maximum power of Sunkko welders?")

Below are some questions on spot welding pens that users encountered:
1. Are the mobile pens compatible with all sunkko spot welders?
Only 797 and 709 series can be used with mobile welding pen, and the shorter style(for 788 and 737 series) mobile welding pen is not going to be produced any more.

2. How to assemble the spot welding pen?
Users just need to insert it directly; 

3. Why are the spots not reliable enough when users welding with a mobile pen? 
When you spot welding with a mobile pen, the power output at the end of the mobile pen will be reduced by 35% to 40% compared to the fixed welding head under the same setting and the same nickel thickness, so after the mobile pen is assembled, the user need to adjust the power output settings. (power of a sunkko welder)

4. What kind of mobile pen need to work together with a pedal? 
All the mobile pens need to work together with a pedal except in 709AD+ AT MODE.

5. What should I pay attention to before using mobile pen?
Before spot welding, fix the two welding pins and keep them separated. Otherwise, a short circuit will occur. Please wear gloves and glasses.

6. After a period of using, the spots are not as reliable as the spot welding pen's original status. How to solve it?
Possibilities:
(1)The welding pins are covered by a oxidation layer, the heat can not pass directly from copper welding pins to nickel sheet. In this situation, users need to polish the pins with  a grinder.
(2)The contact area between the welding pin and the nickel sheet is too large, and it needs to be polished with a  grinder to reduce the contact area.