Remove.IT – failed bulging lithium battery from Mio C520 GPS

Last night, we went for a drive into the city as my wife wanted to visit a couple of friends from China. My car had been parked outside in the sun and my GPS mount had come off the windscreen. As I was remounting the GPS, I found that the GPS was bulging where the battery is situated – not a good sign, as it means that the battery is failing and could explode any minute.

Ok – maybe not necessarily, but it is possible – it didn’t explode on the way to the city and it didn’t explode on the way home, so after getting home, I took the GPS back into the house with me. It was a Mio C520 GPS which was bought in December 2007 before our family holiday driving down to Melbourne for the new year. I had replaced the battery in June 2009 after its capacity went very low, like a few minutes.


Mio C520 with original battery

This is the original battery.


Mio C520 with failing, bulging battery

This is what it looks like now. Lithium battery can swell up, due to increase in gas pressure – which can happen due to over charging or due to internal failure. Most reputable lithium batteries come with an overcharge protection circuit – the problem is that over time, and due to heat, that this protection circuit may fail to be effective and the end result is a battery that starts to swell up like a balloon that can eventually pop with disastrous results.

Normally there is no metallic lithium in these batteries, however during overcharging, the metallic lithium may accumulate on the anode faster than it can be dissipated – and can anyone remember high school chemistry where the teacher cuts off a piece of lithium metal and drops it into a pan of water? If not, I will remind you – lithium reacts intensely with water, forming lithium hydroxide and hydrogen gas – the result means a bright flame if the amount of lithium is small – that is why you don’t want to puncture the battery – even though you can feel that it is like a balloon, there is a reason why it is sealed to avoid ingress of humidity, i.e. water in air.


Battery from Mio C520

Ok – after removing the battery, this is what it looks like – before I put it somewhere safe in my garage.

What should I do? Order a replacement battery or get a new GPS? This battery lasted more than 6 years, whereas the original battery only lasted 1.5 years. This Mio C520 GPS does not have upgradeable maps, so there are places in Western Sydney that I cannot navigate to because it doesn’t have the street maps. The cheapest replacement battery I can get is from Netherlands for $15 or from China for $18. There are a number of GPS’s like Garmin, TomTom and Navman available with free lifetime maps for under $200, so question is new battery or new toy?



Review.IT – Eagnas Plus 8000 Electronic Tension Head

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.


Broken load cell

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.


Digital luggage scale – cover removed

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.


Load cell

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.]