Explode-O-Matic Todd Charger
Posted: Thu May 07, 2009 4:29 pm
I mentioned at the end of the Lester thread that the charger for my Electrak tractor had turned itself into an improvised incendiary device, leaving me with fewer options for charging the tractor's battery pack.
Today was a wet and blustery one, so I stayed indoors and began the operation of repairing the Todd charger. Once I had it open, the sight was not a pretty one:
This is a high frequency switching supply with three modules, one master and two slaves. The input of the modules is rectified line voltage, about 164 volts DC. The output of each module is 12 volts nominal, three modules wired in series for 36 volts to charge the tractor.
Problem is that one little stressed component can cause the master module to fry dramatically, setting up a chain reaction that takes out the slaves in a spectacular display of fireworks. This charger had caught fire once before, but not nearly as badly. This time, I was faced with some heavy duty rebuilding. The burned components you see are the tip of the iceberg, there is much more damage to smaller components on the underside of the high frequency transformers, burned resistors, diodes, integrated circuits, etc.
Fortunately, I am a resourceful pack rat, and had a spare charger on the shelf out in the storage locker:
It was something that someone had given me back when I was still repairing these things for money. I plugged it in one time to test it, but got nothing for my efforts. Turns out that it needed only two resistors replaced, all of the active components were OK. This made my job much easier, if I don't have to replace IC's and MOSFET's, I don't have to recalibrate and align the PWM section to keep the current at a safe level.
What I ended up doing was swapping over the modules from the spare charger to the old heat sink assembly. The spare charger had some corrosion on the underside of the heat sink that had seized the steel screws tapped into it, I ended up breaking off the heads of all of them on one side of the charger. No matter, I had enough parts to make one functional charger with a bag of mostly burned stuff left over for "next time".
Tomorrow is supposed to be nice, so I hope to spend some time putting in a 2.4GHz microwave link to the neighbors house to pick up on some high speed internet, they have a satellite IP link and don't use it all up every month, so I may be able to listen to streaming audio again soon.
Today was a wet and blustery one, so I stayed indoors and began the operation of repairing the Todd charger. Once I had it open, the sight was not a pretty one:
This is a high frequency switching supply with three modules, one master and two slaves. The input of the modules is rectified line voltage, about 164 volts DC. The output of each module is 12 volts nominal, three modules wired in series for 36 volts to charge the tractor.
Problem is that one little stressed component can cause the master module to fry dramatically, setting up a chain reaction that takes out the slaves in a spectacular display of fireworks. This charger had caught fire once before, but not nearly as badly. This time, I was faced with some heavy duty rebuilding. The burned components you see are the tip of the iceberg, there is much more damage to smaller components on the underside of the high frequency transformers, burned resistors, diodes, integrated circuits, etc.
Fortunately, I am a resourceful pack rat, and had a spare charger on the shelf out in the storage locker:
It was something that someone had given me back when I was still repairing these things for money. I plugged it in one time to test it, but got nothing for my efforts. Turns out that it needed only two resistors replaced, all of the active components were OK. This made my job much easier, if I don't have to replace IC's and MOSFET's, I don't have to recalibrate and align the PWM section to keep the current at a safe level.
What I ended up doing was swapping over the modules from the spare charger to the old heat sink assembly. The spare charger had some corrosion on the underside of the heat sink that had seized the steel screws tapped into it, I ended up breaking off the heads of all of them on one side of the charger. No matter, I had enough parts to make one functional charger with a bag of mostly burned stuff left over for "next time".
Tomorrow is supposed to be nice, so I hope to spend some time putting in a 2.4GHz microwave link to the neighbors house to pick up on some high speed internet, they have a satellite IP link and don't use it all up every month, so I may be able to listen to streaming audio again soon.