buv18a transistor sub

[petehall347]

i am looking for buv18a transistor sub or genuine replacements . the sub said to work is bux20 . one was replaced with bux39 and worked for some time .
transistors are on motor control board in still r70-16 forklift truck which is diesel electric . there are pics of same board here if needed . https://www.elektroda.com/rtvforum/t...html#gallery-9
also looking for zener bzv47c39

[petehall347]

just to note have been looking on the net and it looks like the BUX39 might be original . not sure which one is shorted yet i need to do some desoldering first .

[petehall347]

ok its just one blown buv18a so looking for genuine replacement or substitute if anyone can help please .

[redwire]

BUV18 250W 120V 50A (90A pk) fast switch fT 8MHz.
BUV19 250W 160V 50A (70A pk) fast switch fT 8MHz 1.5usec. Like a BUV20 (BUV21G is available), 2N6277 is faster.
BUX39 is 120W 120V 30A.

It's in the big TO-3 league rated P_D 250W, I don't see much for offerings, certainly not in the 50A league.
How many volts there? Is this for the field winding of the generator? or the motor?
The construction is weird, upside down TO-3 on the heatsink? It's not so great as far as power electronics, I don't see snubbers/bus capacitors anywhere and 50A from the traces/wire looks a bit optimistic. Is the stud-mount diode a zener, to protect the transistor?
I'm saying buy many of them lol.

[petehall347]

BUV18 250W 120V 50A (90A pk) fast switch fT 8MHz.
BUV19 250W 160V 50A (70A pk) fast switch fT 8MHz 1.5usec. Like a BUV20 (BUV21G is available), 2N6277 is faster.
BUX39 is 120W 120V 30A.

It's in the big TO-3 league rated P_D 250W, I don't see much for offerings, certainly not in the 50A league.
How many volts there? Is this for the field winding of the generator? or the motor?
The construction is weird, upside down TO-3 on the heatsink? It's not so great as far as power electronics, I don't see snubbers/bus capacitors anywhere and 50A from the traces/wire looks a bit optimistic. Is the stud-mount diode a zener, to protect the transistor?
I'm saying buy many of them lol.

not quite sure how it all works until i see the wiring diagrams that the customer has on pdf . from the forums it says blown transistors and resistors means motor fault . have placed an offer on a job lot of t03 transistors including 20 bux20 . just waiting on a counter offer . is buv same thing ?

[petehall347]

looks like i am now the owner of 36 transistors . got them for less than the price of 2 .

[petehall347]

I'm saying buy many of them lol.

thinking 20 plenty enough .

[redwire]

I think a 50A transistor will surely have a double-die inside. BUX22 die shots
You can hacksaw the top off the failed part and peek inside.

I would make sure the base-drive circuit is not damaged. I think the 22R carbon resistors go to the base. The control board looks all analog and many trimpots.
What I've seen with forklift drivers is they are basically maniacs and trash the machine - brakes, full throttle, brakes etc. check out the tires and see if they are scuffed bad.

[petehall347]

it only gets used once a month and short term at that . brakes dont even work . it had burned a resistor . am replacing with 1/2 watt metal film up off the board a bit so it dont burn as bad next time .

[redwire]

Just check whatever is on the other end of the resistor. If the power transistor shorted C-B it would cook the base-drive resistor and also overload the TO-220 driver transistor, see if it survived.

[petehall347]

shorted normal way c to e .. well definitely case to one pin . just assumed c to e . will check to make sure . went over other transistors and diodes quickly looking for shorts and didn't see any . the 100 ohm resistor is intact .i guess that's the base stopper

[petehall347]

i haven't studied it enough but quick look is transistors are wired emitter follower or darlington but these 2 are not paired . what i need to find is what caused the overload . wires are too thin to drive a motor directly unless i am not understanding it properly so wondering if they just excite the generator . i will be looking at commutators of both if easy accessible . if all good there then i am thinking insulation breakdown in windings and that will make it scrap . i could just try it with having plenty of transistors on the way but the owner might not like having fix the board twice . its something i want to avoid anyway if possible .. something blew it up .. its to me like replacing a blown fuse and expecting it to be fine .

[petehall347]

https://www.elektroda.com/rtvforum/topic3077152.html

Check if burned resistors are visible on the plate to which the motor is connected. If so, then the motor transistors went down. Transistors are difficult to get, currently the only replacement available is BUX20. Burned resistors also need to be replaced (22 Ohm). Unfortunately, burned transistors testify that the motor is already out of order (damaged winding insulation or burnt commutator), if you replace only the transistors without repairing the motor, the problem will recur after a while.

[redwire]

The 22Ω carbon resistors are too high value for base-drive, 50A power transistors need amps of base current, they have low beta. I can't see where the resistor connects.
You can see four power transistors make up an H-bridge. The other two power transistors look to be in parallel (1,2) it might be for motor braking. The stud mount diodes look like zeners across C-E.

Some designs of power electronics are not that great - not so reliable so they overspec parts to make up for it.
I would inspect the commutator and brushes/slip ring if you can, they might be a problem.
Posting pic of board from the .pl site:

[petehall347]

the odd pair of t03 are the ones in question especially the buv18a . those 2 are in series with b and e . they are not installed the same way round but 180 degrees to each other .

[petehall347]

owner said it was driving then he smelt burning and it went slower and slower . when i checked it it tried to drive but just didn't get enough juice to the motor .
am still waiting on the service manual .he has found it so i need to go over there and copy files to sd card to get back to my pc .

[petehall347]

pics of other side of the board here . you can see collectors go together as plates are connected to collectors , no insulation under transistors .
https://allegro.pl/oferta/plyta-jazd...30-13409534527

[petehall347]

redwire have sent you the manual in a message

[redwire]

I looked at the block diagram pdf pg 70/251, attached a snippet.

The 4 power transistors make an H-bridge that drives the generator field winding. The generator output goes directly to the motor. Weird but not really - for reverse, they flip polarity to the generator field winding."R" and "V" are the two H-bridge command signals from the main u200 board. Not sure if any PWM is done, it's fwd/rev direction only my guess.

The 2 power transistors in parallel are for the motor's field winding, downstream of the safety relay. Again, control board u200 outputs something to drive the transistors for the motor's field. So PWM (for speed) control likely be done here.

There is analog PID speed/sag control and quite a bit of logic and braking control as well. I wonder if you can test it with the wheels safely lifted up off the ground.

If it was one of the H-bridge transistors that cooked, then I would check the cross-connected drivers. One driver turns on two power transistors X in the bridge, so a blown tranny might affect both totem poles.
Whatever smoked I wonder what it was. The blown H-bridge can arm wrestle with itself and burn up. So deffo check all involved.

[petehall347]

H Bridge looks ok its one of the other 2 that shorted along with the 22 ohm resistor burning up . looks like these 2 deal with controlling the shunt coil in the drive motor .
as for lifting it up i would have to commandeer another forklift for that from down the road . .
as for the burning smell it might have been the resistor but that is under the rear cover .makes me wonder if the smell was from the motor , i will be looking at the motor after fixing the board so will see then . i reckon i can use my pat tester to check insulation . well that's if its working as i have never tried it and had it a few years now .