B7800 IC Regulator smoking, literally smoking

[curlesw]

After mowing with the B7800 today for about 2 hours, the IC regulator started smoking...and I mean a LOT! For a little background.

A couple of months ago I attempted to jump the tractor and reversed the cables. The tractor would not start, I checked all safety switches, they are good, replaced the ECM and ignition switch to not avail...the tractor still would not start. I bypassed with ignition switch to start the tractor and it has run great until today.

Back to today, I ended up disconnecting the IC regulator to finish mowing without any apparent issues. So now I have a couple of questions:

1) Any idea on why the IC regulator would overheat so much that it was start smoking? Maybe it's defected due to the cable swap and now overheating due to extended use. Should I replace it?

2) I know the IC regulator is required, so what are the issues with operating the tractor with the IC regulator disconnected. In looking at the electrical diagram, I would assume the dynamo is not working and hence the battery not charging. I checked the battery voltage with the engine running and it was a little above 12V, not the normal 14v+ with a normal alternator. Dynamos are new to me so I'm learning here. What else am I missing?

I would greatly appreciate your thoughts and ideas.

Thanks in advance.

Wayne C.
B7800

 

[boz1989]

Have you checked all the fuses? I kinda remember reading about someone doing the same thing and blowing a fuse. He found and replaced the fuse, and it started. This might fix all the issues.

Sent from my LGMP260 using Tapatalk

 

[North Idaho Wolfman]

Get a new regulator.

When you reversed the cables you fried the diodes.

Fix everything that's defective at once or your going to keep having issues.

 

[curlesw]

Have you checked all the fuses? I kinda remember reading about someone doing the same thing and blowing a fuse. He found and replaced the fuse, and it started. This might fix all the issues.

Sent from my LGMP260 using Tapatalk

Thank you, I did check them and replaced the one at the starter, all fuses are good.

 

[curlesw]

Get a new regulator.

When you reversed the cables you fried the diodes.

Fix everything that's defective at once or your going to keep having issues.

Fried the diodes! When checking the electrical diagram that was the one item I could not find...so I assume they are internal to the regulator?

Agree, that's the best place to start.

Thanks!

 

[lugbolt]

when the generator is running (engine turning it via belt) it is putting out 20-60v AC. You know that the battery is DC voltage not AC so it has to be both regulated down to around 12-15v and also rectified from AC voltage to DC voltage in order for the generator to charge the battery.

The regulator is just that, it regulates voltage-but it also rectifies the AC output from the generator to DC so that it will charge the battery.

It does this via a set of diodes and transistors among other things.

A diode allows current to flow in one direction only. When subjected to a high current reverse polarity, they can actually fail which is what I suspect you are having an issue with.

When that diode pack fails it fails to properly rectify and sometimes regulate the current output from the AC generator; which causes the IC reg/rec to overheat. It runs warm anyway, which is why it has fins on it, but with the rectifier diode "bridge" fried, it will either send generator current to nowhere OR (more commonly) it will send it directly to ground, which causes an internal short circuit inside the reg/rec which causes it to run really hot; potentially resulting in fire if the conditions are correct.

Replace it ASAP.

 

[BruceP]

...
A diode allows current to flow in one direction only. When subjected to a high current reverse polarity, they can actually fail which is what I suspect you are having an issue with.
...

Speaking as an electrical engineer - Most of what you said is correct. Damage to the rectifier/regulator is the likely issue...but not for the reasons you describe.

Just for clarity, it is nearly impossible to pass ANY current reverse-polarity thru a diode. (let alone 'high' current) This is because a diode does not conduct current in the reverse-direction.

Passing high current in the FORWARD direction thru a diode is a sure way to fry it. I will not get into the technical reasons how reverse-connection of jumper cables can do this to a bridge rectifier.

If I was asked to resolve this issue, I would attempt to rebuild the rectifier/regulator.... diodes cost less than a dollar each and there are four of them in the bridge. It is trivial to test the diodes with a meter. (most meters have a "diode test" setting which makes it even easier)

 

[curlesw]

All, thank you for the information, I will be offering a new regulator tonight.

What is extremely frustrating is that I talked with 2-3 techs at the local Kubota service shop and not one of them mentioned checking the regulator or that the diodes might have been damaged, they were all focused on the darn safety switches.

yes when I posted what occurred the other day and explained things, boom, first thing was to look into the regulator. I can't help but being VERY discouraged with the techs. I mean, it seems very straightforward, should have they at least gone down this path first?

Thanks for everything, will report back when I install the new regulator.

Wayne C.

 

[curlesw]

I finally got around to getting the regulator out and yep, looks like this is the culprit.

Will order one today and get it installed, hopefully this fixes my issue.

Wayne

 

[Dave_eng]

Speaking as an electrical engineer - Most of what you said is correct. Damage to the rectifier/regulator is the likely issue...but not for the reasons you describe.

Just for clarity, it is nearly impossible to pass ANY current reverse-polarity thru a diode. (let alone 'high' current) This is because a diode does not conduct current in the reverse-direction.

Passing high current in the FORWARD direction thru a diode is a sure way to fry it. I will not get into the technical reasons how reverse-connection of jumper cables can do this to a bridge rectifier.

If I was asked to resolve this issue, I would attempt to rebuild the rectifier/regulator.... diodes cost less than a dollar each and there are four of them in the bridge. It is trivial to test the diodes with a meter. (most meters have a "diode test" setting which makes it even easier)

I offer the attached from a JD 2210 WSM not to disagree but only to show how other manufacturers see the issue of reversed battery polarity with their models which have simple dynamos.

JD incorporates a number of "SAFETY RELAYS" along with diodes within their wiring harness. The purpose of the safety relays is to prevent the simple act of connecting a battery backwards from doing serious damage. Note at the very bottom of the page JD's comments re diode failure.

While I am a Kubota guy at heart, JD's WSM's and design do impress me!

Dave

 

[lugbolt]

I have seen diodes pass through in both directions. They were failed or defective, dunno which. They were in a wire harness that came from a mower (kubota) that had an issue that was not easily sorted, so Kubota paid us to replace the harness and they requested the harness back. A couple weeks later I was at their training center and the harness was brought to us by one of the engineers as a training aid, said find out what's wrong with it. Failed diode is what we found. Pass-through in both directions per DVOM test.

 

[Ohio Kubota]

Hi. I'm having exactly the same problem. I have a B2910 (essentially the same tractor) where the regulator started smoking and actually had small flames before I could get it put out. The visible damage on mine is mostly where the wires exit the housing. I too had recent problems where the battery wasn't charging and I wonder if this is the cause or due to something that I've done.

There are 2 wires coming out of the dynamo. They aren't marked and they both run to quick-disconnects a few inches away that lead up to the voltage regulator. Could hooking these leads from the dynamo cause the regulator to burn up?

Am I right in assuming that the dynamo couldn't be putting out TOO MUCH voltage for the regulator to handle? There's no way a dynamo could go bad and put out too MUCH voltage, is there? That would suggest that it's more efficient than normal.

I'm very mechanical, and thought I was pretty good with electricity, but figuring out what's going on with this AC to DC rectifier system and the 2 leads from the dynamo has me confused.

Did you resolve your problem by just replacing the regulator? If so, how many hours have you run it since the repair? Thanks in advance for any help or ideas.

 

[Ohio Kubota]

Just to clarify -- the smoke (which was considerable) and the damage that I refer to was limited to the voltage regulator and the wiring pigtail coming out of it. The modular plug was not damaged, but the regulator housing and internal electronics were certainly hot enough to melt components and wiring insulation. Thanks.

 

[Dave_eng]

Hi. I'm having exactly the same problem. I have a B2910 (essentially the same tractor) where the regulator started smoking and actually had small flames before I could get it put out. The visible damage on mine is mostly where the wires exit the housing. I too had recent problems where the battery wasn't charging and I wonder if this is the cause or due to something that I've done.

There are 2 wires coming out of the dynamo. They aren't marked and they both run to quick-disconnects a few inches away that lead up to the voltage regulator. Could hooking these leads from the dynamo cause the regulator to burn up?

Am I right in assuming that the dynamo couldn't be putting out TOO MUCH voltage for the regulator to handle? There's no way a dynamo could go bad and put out too MUCH voltage, is there? That would suggest that it's more efficient than normal.

I'm very mechanical, and thought I was pretty good with electricity, but figuring out what's going on with this AC to DC rectifier system and the 2 leads from the dynamo has me confused.

Did you resolve your problem by just replacing the regulator? If so, how many hours have you run it since the repair? Thanks in advance for any help or ideas.

The dynamo is very limited in its output and actually is never regulated in the way traditional alternator is.

The dynamo's output just varies with engine speed and nothing else.

The rectifier decides if the battery could use some or all of the dynamo's output. The output that is not needed is turned into heat. Hence the aluminum finned case for the rectifier.

It is rare for dynamos to fail.

Often owners damage the rectifier when boosting the tractor.

In any event, your rectifier has failed and you need a new one.

You could test the dynamo as well but only if you have a multimeter which measuring alternating current voltage.

The smoking rectifier is happening as the power stored in the battery is discharging into the rectifier because of failed internal diodes in the rectifier.

Dave

 

[Ohio Kubota]

Thanks, Dave! I still have one question.

The dynamo has two wires coming out of it. They're both the same color. They connect using a could of quick-connects to two wires (same color and same connectors) that run up to the firewall and into the dash panel. None of the wires are marked. I'M NOT SURE THAT I HAVEN'T SWITCHED THOSE 2 LEADS coming from the dynamo when I was disconnecting things and trying to trouble-shoot. I can't see anyway to determine which one goes where.

Does it matter? Given that the dynamo is creating AC, does it matter which wire goes to which lead?

I appreciate the reassurance to replace the regulator and it's obviously fried. I'm just a little concerned that I'll fry the new one if these dynamo leads are connected wrong.

Thanks for the quick response and explanation on that last posting! Jim

 

[Dave_eng]

Thanks, Dave! I still have one question.

The dynamo has two wires coming out of it. They're both the same color. They connect using a could of quick-connects to two wires (same color and same connectors) that run up to the firewall and into the dash panel. None of the wires are marked. I'M NOT SURE THAT I HAVEN'T SWITCHED THOSE 2 LEADS coming from the dynamo when I was disconnecting things and trying to trouble-shoot. I can't see anyway to determine which one goes where.

Does it matter? Given that the dynamo is creating AC, does it matter which wire goes to which lead?

I appreciate the reassurance to replace the regulator and it's obviously fried. I'm just a little concerned that I'll fry the new one if these dynamo leads are connected wrong.

Thanks for the quick response and explanation on that last posting! Jim

The dynamo leads are interchangeable. It does not matter how they are connected. One clue is that they are both the same color.

Dave

 

[Ohio Kubota]

Great!! Thanks again! I'd seen confusing references to dynamo leads on various fix-it web sites. I'll quit worrying about that and get the voltage regulator replaced.

Once again, MUCH appreciated! Jim

 

[Henro]

Just a couple of added points for what they are worth.

I also have a B2910 and if I remember correctly when I bought it I upgraded to the heavy duty, I believe 40 amp, alternator. I don't recall the Kubota term, it might have been alternator (But they might have called it a dynamo for all I know).

I believe the standard unit on the B2910 was a dynamo, or generator, that produced DC voltage. Dynamo generally refers to a device that generates DC voltage, as compared to an alternator which produces AC voltage, and must be rectified into DC voltage, if used in a DC application.

As Dave said, since the wires on your device are not color coded, it is likely a device (alternator) producing AC voltage. It is also likely it is a 40 amp unit, like I think I upgraded to. (upgraded my BX on purchase too, and think both were 40 amp upgrades).

None of this matters much, but I thought the difference in terminology might be of interest.

 

[Dave_eng]

Kubota was a little loose with the terminology in its very early days translating to English... generator, dynamo, alternator... they did not choose but used the terms interchangeably.

Any true alternator on a Kubota has more than two wires. Almost all Kubota dynamo's have only two wires.

Kubota dynamo's have never produced Direct Current as to do so would require a commutator and brushes.... i.e. be a generator.

More trivia

Dave

 

[Ohio Kubota]

Thanks, Henro. Mine is definitely a dynamo -- not an alternator. Wish it were an alternator with internal voltage regulator because I think they're more reliable and simpler overall. However, I followed another thread and looked up a few of the parts needed to convert and it looks like that would be well over $400 if I could find the parts.

I'll be thrilled to spend the $100 and get this back together if it runs for another trouble-free 18 years. I can't believe how much work this little tractor has done. It's probably the best single tool / piece of equipment I've ever bought. (Bought it 2 years old used, with 200 hours on it in 2004.)

Thanks for your input and help. Jim