Aaccessory power not working consistently on Bobcat 225

[Sean Brown]

Andy,

I've got an older (about 5-years) Bobcat 225 gas (onan engine) welder. Just recently I've had some problems with the accessory power not working when you start it. In other words, if there is something that presents a load to the machine when you start the engine, it won't work (no power output). Sometimes unplugging the accessory and then plugging it back in will get the thing to put power out, sometimes I have to start then engine and then plug in anything I intend to use. It's worked for years the other way, but the last week or so we've acquired this new problem. Is there an "unloader" relay or something that could be the culprit?

Any idea what might be causing this?

Thanks,

Sean

[imported_matt]

Hi Sean;
Please give me a call about this machine you are having a problem with. My phone number is 920-954-3972. We didn't use a relay in the Bobcat 225 for the ac power circuit. It sounds like a crack lug on the circuit breakers, I would check that part of the circuit. Please use all the safety precautions when working on your machine. Thank you
matt

[ROCK]

HEY SEAN........... DID YOU CALL MATT......... HE WORKS AT PORTABLE POWER AND HAS RESPONSABILITY FOR THIS MACHINE. VERY KNOWLEDGEABLE MAN HE CAN HELP PIN POINT THE PROBLEM......... I'VE WORKED WITH HIM A LOT YOUR CALL................ROCK.................. [email protected]

[Sean Brown]

Hey guys,

I'm sorry I didn't follow up on any of this yet, I've been so busy I didn't even read the forum until this weekend. I will try to call Matt this next week and get the problem figured out. Thanks for the help!

Sean

[ASKANDY]

Sounds like a flashing diode problem to me. It's not flashing the field properly when starting. The flash diode should be always in the circuit even after starting and running in case the machine should ever loose residual magnatism. If this is indeed the problem, the unit would also have weld output problems too as the stator assembly runs both aux power and weld output. The diodes sometimes don't fail they get corroded or have a loose connection.

Andy

[Sean Brown]

Andy,

I think you are on the right track. I Did call Matt about a month ago now and following that, tore into the thing to find the problem. Incidentally, Matt is a very nice guy who deserves all the good words you could lavish on him for the help he gave me in understanding how the system worked.

In any event, I went through everything, checking the fuses, diodes, capacitor, rheostats, brushes, rectifier and about everything else that was in the general area. I could not find any faults with the system. But one thing Matt had told me about, was to check the voltage at the brushes (which I did and found it to be insufficient).

As I went through it, I cleaned all the contacts as I put them back together and in the end, the voltage across the brushes was still low (on startup), but it was better. I figured I'd gotten nowhere and put the cover back on, because I had to get the thing in service again.

Low and behold it works fine now! I have no idea what it was, but it must have been as you say and just have been a bad connection. Matt suggested that might have been a problem also, so that could have been (actually must have been) the problem.

So I am very happy. This welder has been a serious workhorse for us and was more than worth the initial cost. I saw a new Bobcat 250 in the welding shop today and was really eyeing it over because I could use the extra juice. Maybe fortune will smile?

Thanks again to everyone involved.

Sean

[Karin Bayne]

Could I get a picture of the flashing diode? Can some one tell me how to check the voltage at the brushes?

[Aeronca41]

Looks like there are two threads running here. I posted pictures on your other thread. If you go to the other thread and look at the schematic diagram, you will see that the wires to the brushes are numbered 33 (the grounded one) and 24. Again, I'm not familiar with the insides of this particular machine, but the brushes should be accessible through a hole in the generator housing. See page 44. If not, you should be able to find wire 24 on one end of the fine current adjust control. Wire 33 (ground) should be one of the two wires on the big capacitor above the flashing diode, and also on the SR2 rectifier. If you can't find this stuff, post some pics of those areas in the welder and maybe we can point them out.