Just a couple of weeks ago, after the repaired Eagnas Plus 8000 Electronic Tension Head had gone back to the client, another came in – this time it had been opened, with case screws removed and no gripper head. I took the case off and found this.
Obviously, one of the problems of having an inline load cell – that is, a load cell that is connected in line with the pulling force, in this case the chain – requires that the fasteners that connect the load cell should not come apart. In the previous tension head, the bolt that connected the chain to the load cell had come off – however, in this case, the bolt that connected the load cell to the carriage failed, which meant that the wires to the load cell, the yellow one – had been pulled off.
Usually, this means getting a new load cell as it might be difficult or near impossible to repair. Another thing is that getting an equivalent load cell could be difficult if the manufacturer is unwilling to provide spare parts – which is the case in this situation.
On the bright side, I realized that one of my digital luggage scales that I use to check the tension heads might use a similar load cell – and it seems to be the case.
I opened my luggage scale and sure enough, the load cell is the same size – but is it similar enough? The wiring color is different, green, white, red & black instead of yellow, white, red & black. The notation on the circuit board indicates that green is +excitation, and black is -excitation, hence white is +signal, and finally red is -signal.
I found a site that showed some load cell wiring colors – Load Cell Wire Colors which shows that this is a common wiring arrangement, so that is good to confirm.
Now the broken load cell has yellow – probably instead of green. The load cell strain gauges are covered in a soft silicone sealant for protection, and I could scrape it off and have a look at the strain gauge and see if I could perhaps reconnect the yellow wire.
It looks like I can reconnect the yellow wire as it had broken off on the solder pad. If I reconnect the yellow wire, I then need to work out where the other wires should go to – three wires to connect to three other wires – what could go wrong? Ok – the yellow wire is still connected to a yellow wire, so the other wires on the connector are red, black and green – so presumably, red to red, black to black and green to white would be an obvious first try.
Anyway, I don’t have to rush on this repair because the client came back to me saying that the other one I had repaired had started smoking and his customer no longer wants them both, so now I can wait until the other tension head comes back eventually and check the wiring colors. In the meantime, I might order a similar load cell from aliexpress.
[P.S. When the smoke leaves a machine, it generally stops working, until we can repair it to put the smoke back in.]