18 August, 2016

Repairing a Chinese Li-ion battery charger 42V "Rait" brand

The circuit: in one UF1004 dissipating diode and a MOSFET 600V N  MDP11N60 (left)
A collegue had broken his battery charger, he told me that he had left running, hitting an explosion when going to charge his battery 20Ah scooter for the last time .
Normally when a small explosion sounds, it is that any electronic component has gone to hell, so I checked the components and at first sight there was nothing broken, not even the MOSFET had been damaged.
It is  quite simple transformer of 180 / 240VAC to 42 Vdc with 5A load capacity (although the actual output voltage 40,7V are even better for the longevity of the battery), of unknown Chinese brand that came with the battery of 20Ah Chinese acquired.

In reviewing the tracks below, we see what happened: the track that connects with the departure had not stood the peak intensity of the moment to connect to charge the battery (capacitors can deliver a significant current at the time of connection); It is that by design has 3 tracks (possibly to put resistors as a fuse in the Tinned areas) but only one was connected.

So we solve these welding points (green resistance I put a few ohms, as if he put it ) and tin reinforcing tracks :

However the test operation the fan was not working  (active fan when consumption in the output); probably at the time of the peak of the energy it was derived the poor fan, burning his HAL chip or coil. We changed for another, and is already working.

To the left. burning fan

Maybe they left it like that on purpose as a fuse, but did not realize that is too thin for minimum 200W (peak of over 300 in the likely connection) that will circulate around electricity (5A * 42V) surely to save removed the "fuse" resistance without recalculating the capacity of that track, forgetting reinforce it with tin. 
Hopefully now will last many years, because otherwise it is well chilled with 80mm fan and heat sinks (which is what really makes the difference in the duration of electronics, that and that is well dimensioned).
In the circuit shown that many welds are performed by hand:

And this is the case, where its characteristics are as follows:

"Rait Battery Technology"

Remember what we indicated on the right of the blog: Do not try to do this at home without proper knowledge and precautions; I am not responsible for the consequences of using the info of this entry.

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