Victron 12v - 24v MPPT controller, investigating the FETs. 

Hi, thanks for this info, yes rob a FET out of another board, check it and install. I.m hoping because it's not actually let the smoke out that the rest will be OK. Test with a limited current is definitely the answer, cheers

@@TheInfoworks The bench power supply is, in my opinion the second most important piece of kit to get after a multimeter if you want to repair electronics, apply power, low voltage, low current, see what happens, if voltage stays near set limit and current is low then no shorts or significant power consumption, if current goes to limit and voltage drops significantly then you have a low resistance, you can calculate that from Ohm's law, it's exactly how a multimeter works, but you get to set the limits, so it actually tells you far more than the multimeter.

I sometimes temporarily replace a blown fuse by linking an ammeter across the fuse socket to see what current is flowing under test.

@@andypdq Very much like testing a circuit with a battery and a small load rather than a multimeter, tests the ability to carry current, or pull the voltage down and show a large load or short. Interesting experiments.

@@davidbrodie5044 It's a suite of analytical tests, each one hopefully tells us something, just like the first unit blue smoke showed the problem area, cheers

Ian, I'm thinking its a product of a duff gel battery charging up rapidly, The fact that things were happening and a FET got warm is promising, cheers

Ian, yes I think they are variable buck converters, allowing current to rise until voltage drops, a balancing act. I'm thinking to replace the duff FET and see what happens, cheers

Hi, that's interesting, I'll rob some out of the duff unit and test them with a bulb and battery, cheers

Hi @Sim6699, do you have any theory as to why a seemingly well specified fet would fail?

@@ianhelsbyservices Ian, I'm thinking heat is the problem, either direct or by destroying capacitors that could maybe make it switch half on, and so get very hot, cheers

​@@ianhelsbyservicesusually to much current creating heat, which in access breaks down the material between drain and source. At first they breakdown underload but eventually short or go open circuit.

Hope so, time and experiments may reveal, cheers

Ian, yes I'm wondering about that, there must have been a path to create a dead short across the battery, there may be a diode somewhere that has blow also, or maybe the FET also acted as a diode, hmmm

Ian, where's the best place to buy FETs? cheers

​@@TheInfoworkshi Andy, they seem to be £5 each on the UK sites, clones to be had for £1 each, some say new and original. Alternative I've found is Toshiba TK100E10N £3.86 each or £3.19 each if you buy 10 on Farnell. There's also Vishay SUP70042E which seems to tick the boxes except it's surge Amp rating is only 200A (continuous 135A at 75degC), it's surge rating is much lower than the Infineon but well over the devices rated 30A charge current. They're £2 each inc VAT from Farnell if you buy 10. You'd be safe replacing them all with the higher rating unit I'd bet. Victron themselves might populate with what they have in stock and may have bias or preferable purchasing price with Infineon brand FETs

​@@TheInfoworksI usually pick a FET then shop around, end up on ebay or Aliexpress. I go off the photos to determine authenticity. Been OK so far. I had a look for FETs over 100V. Seems odd that the device is a 100v 30A charger and then use 100v FET. Perhaps the FETs are in series rather than parallel, or the FETs are ran at battery voltage as they are on the output.

@@ianhelsbyservices Ian, thanks for the info, I think as a proof of concept I will rob one out of the duff unit, cheers