Home Forums General Discussion Technical Questions MRVF Transistor fault

having an intermittent Transistor fault on an mrvf car. the mechanics have already swapped out all the transistor units, all the control boards, the backplane rack that the boards plug into. the ribbon cable that connects the transistor boards to the backplane board. I went out there a couple of weeks ago, and the car would fault every run, probably ran it 20 times . i removed the connector on two of the boards that connect the flyback diodes to check if they were ok, all was good, so i tried to run it again, and it ran fine. it has run for two weeks now, and started again on friday with the transistor faults. the mechanic has reseated the connectors again, but this time it faults continuously. any ideas,

hey scott. from what you have said it sounds like it could be developing a high resistance in the flyback diodes(not sure what these are)area under load. might be an idea to swap them out to another lift or resolder or replace them clean.

What's the motor waveform look like on a scope?

(When the problem is occuring)

those things are sketchy all the time. Its usually a battery problem but if their all good who knows . I've seen transistor faults from loose tach couplings to brake not picking fully because the aluminum doughnut inside the brake is worn out. Powersupply crowbaring or you need to zero out the boards if you have the updated version.

some batteries have good voltage but wont pass enough current. have any of the battery monitors tripped? how old are the batteries? word of advice dont let the boss buy you anything less than all 16 batteries. buy good interstate batteries they last 3-5 yrs or for 2x the cost you can get gel cells that last more than 10 years. i have a MRVF job running on 13 yr old batteries that is a testament to gel cell technology.

i second the gell cell's , all of my mrvf's have them and all are 8-12years old

thanks for the info guys, the batteries are old, they don't have any monitors on them, the route guy has monitored the voltage and said it was fine, but if it can't supply the current like green pants indicates, maybe the transistor shuts off when it should be on. I think i will have them replace the batteries, they are definitely old, and it could not make the performance any worse. thanks again guys. Hey vic, I work for a company that makes a couple million dollars profit a year, they can't afford a scope, that would bring there profit down to 1,998,000 dollars, unacceptable to the bean counters. hey uppo, I was not sure what a flyback diode was either, just saw it in the mrvf literature. do a google search for more info, but basically it is diode that is connected to a circuit to keep the large voltage that appears when a current is suddenly removed from the circuit from damaging components in the circuit. you see these sometimes across relay contacts, to keep the contacts from arcing when opening with hi current still flowing. you also see them in relay coil , brake coil circuits,etc. they keep the collapsing magnetic field voltage/current in the coil circuit, not allowing it to stray to other circuits. thats how i see it anyway.

Yep.. and on old style tube TV sets.

If replacing batteries replace them all. Besides the mariginal ones still make great batteries for deer feeder timers.

I've always wondered about a piece of equipment where the tips are bigger than the manual.

one otis tip: if you advertise to elevator guys in town you are changing mrvf batteries just get them to carry the ones they want down from the machine room. usually cuts your job in half.

We are going to replace all 16 batteries. Not sure if this will solve the problem, but while testing, the voltage was dropping to 175 VDC. On a good car it would stay above 195 or so, also i noticed that the meter would sometimes go up to 250 VDC. on the good car while the car was regenerating. the car that is having the problem, never went above 210 volts. Hopfully this will take care of the problem, if not, on to the drawing board. Green pants, you are right, i just mentioned the replacement to one mechanic, and by the end of the week a few more chimed in to collect old batteries for there trailers. only problem, they want me to deliver them. what has the world come to? ha ha. will keep you posted as to the outcome. personally i am crossing my fingers, but still have a bad feeling in my gut.

batteries are def your problem if your voltage is that low. make sure your charger is working after you change your batteries. change them, turn everything on and let them charge until the amps drop on the charger before you run it.

Did anyone resolve this problem? I have one that will not run due to a TFLT fault on the Inverter control board. We have installed all née gel cell batteries and rebuilt all of the transistor packs. Any ideas?