Rebuilding Battery Pack Of Schiller Ventilator Model GRAPHNET TS
This was brought to me with the complaint that the battery backup was not working in the ventilator and this pack was not taking the charge. As the pack was already opened and checked by the biomedical technician, I checked and confirmed that the batteries were indeed weak. In fact, I saw rust formations also in the contacts. Let us have a look at the inside of this pack and the charger control board with its various connections:
From the above pictures we can easily understand that nine batteries were connected together in series with three batteries in parallel in each set to get the 11.1V (3.7Vx3) at the same time of which increasing the power. We all know that parallel connection would give same voltage adding up the power whereas series connection would give same power but adding up the voltage.
That’s what was done in this case. There were tap wirings for the ICs and other components in the charger circuit, which can be seen in the picture given below. I have also given a manuscript of the connection diagram:
The board had a fuse that looked like a VARISTOR/MOV/CVR that can be seen in the last picture above. It also had a thermal sensor inserted into the battery pack I had to buy a battery spot welding machine for building a pack like this, which helped me to a great extent. Soldering it directly to the battery not only dries up the electrolyte reducing its life but also increases the thickness. This tool was found very handy and I could finish the job using the nickel sheets that I bought together.
The tool came with an adaptor for charging the built in battery which I used first to make the battery full. I had to do a bit of practice before I could achieve good results. The sparks when the foot switch was pressed after keeping the two probes close enough tightly on the battery terminal, were thrown around and we need to protect our hands and face. I also bought the insulation rings and isolation rounds along with the machine. You can have a look at the machine in Amazon here.
I connected the board and placed it on the battery like how it was. The pack was given without the covering as I wanted it to be tested on the machine by the biotech. He reported that the machine was working indicating the battery level and charging was also taking place, which made my mission successful.
He packed the battery like how it was before and placed it inside the compartment provided in the machine. Let us have a look at the picture of the machine working with the battery level indicator on:
The satisfaction of a different kind found its way to the collection bag!
This article was prepared for you by Parasuraman Subramanian from India. He is 76 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
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Albert van Bemmelen
February 28, 2026 at 7:41 pm
Happy to see that you had great success with the new bought spotwelder.
I say this because I had limited success with several new bought spotwelders that practically failed to make decent welded spots.
My first spotwelder from China used way too much AC power that easily could blow my main power fuse and therefore was completely useless in a home with only a 25A main powerfuse. And the 709A spotwelder probably used much more power than the max allowed 3680 Watts. Just the in-rush current alone was already blowing my 16A group fuse.
So therefore I then bought a 2.1KG Super capacitor 12V/3A digital spotwelder which supposedly could weld 0.25mm upto 0.3mm nickel strips, and even 0.1mm copper strips. But completely failed doingh what it promised and also was wasted money!
So my third spotwelder was a lithium operated Dh20 4.2V 650A max current welder that supposedly could weld 0.1 to 0.15mm nickel strips. And was designed for a current upto 1200A but also was a bad working welder. Although it still was useful for 5V backup battery because of its USB output connector.
After that a fourth and my last bought welder was an AWithZ model H1 input chargable Type-C 5V/1A completely handheld portable spot welder that outputs 4.2V at max 650A.
All these above mentioned welders are still disappointing to be honest. I hardly could weld spots that held after trying to pull loose the strips.
And if I would be sure your shown spot welder really outputs upto 1200A making sturdy spotted welds I would even consider buying a fifth welder. But I have not much confidence left in those welders that fail to do what they promise.
Parasuraman S
February 28, 2026 at 11:19 pm
Sad to hear your repeated failures in getting a useful spot welder. This one has been used by me several times and is found to be reliable and handy, especially with the foot switch. The probes should be as close as possible to make a proper and powerful arcing. Many thanks for your expert comments and sharing your experiences, dear Albert!
Albert van Bemmelen
March 1, 2026 at 5:44 pm
Just for confirmation... My first, second and if I'm not mistaken also my thirth welder, all had foot switches, but that didn't make them any better.
Thanks for sharing your good experiences with the on Amazon bought spotwelder dear Parasuraman! Glad that Amazon is also available in your big country.
Parasuraman S
March 1, 2026 at 11:43 pm
Many thanks for the clarification!
Mark J
March 1, 2026 at 4:11 am
I have never used a battery spot welding machine before. I will have to look into getting one. Good job on the repair. Thank you for sharing.
Parasuraman S
March 1, 2026 at 8:35 am
Battery spot welding is an interesting work and I enjoy it! Many thanks for your comments, dear Mark!
Mark
March 1, 2026 at 7:58 pm
Good repair with spot welder. I have just ordered mine for a project. Videos I have watched all indicate that most of the welders work as specified.
Parasuraman S
March 1, 2026 at 11:45 pm
Many thanks! I think I have to claim some commission for the sales boosting from this supplier! HA! HA!
Yogesh Panchal
March 4, 2026 at 4:12 pm
Good Job! Sir
It's good to see that "Ventilator" has come out of the ventilator.
If you want to stay in this industry, then investment is must in good tools.
Parasuraman S
March 5, 2026 at 8:31 am
Ha! Ha! Good pun and fun! Yes, we need to have a minimum investment required. But I think no one can match the class tools and facilities our Jestine Yong is providing to his students! Lucky are those who get a chance to study there! Many thanks, dear Yogesh Bai!