VR technical question

So I'm trying something on a 12v VR.
Friend that is helping me is asking what
the max field current would be. Since I'm
here, I had no idea what the value would
be. While I'm asking, what would a 6V VR
have for Max field current?

Thanks.

(quoted from post at 20:54:59 05/02/20) So I'm trying something on a 12v VR.
Friend that is helping me is asking what
the max field current would be. Since I'm
here, I had no idea what the value would
be. While I'm asking, what would a 6V VR
have for Max field current?

Thanks.

Click to expand...

That's a pretty VAGUE question as you didn't tell us what you are playing with, or even the make and capacity of the charging system, but, what the heck, I'll play!

To start with, here's some DEERE 4010 and 4020 generator specifications:

What is it about Virtual Reality you are having problems with???

Couldn't one measure the field resistance? Then use Ohm's Law to determine the maximum field current?

Pat, your question "what the max field current would be" might be available if you had the specs for the exact Generator and Voltage Regulator you're using. I don't have any specs or data from which to find any of that but can give you some basic information. Field current is a function of the generators field winding resistance and the Voltage Regulators control.

The VR acts similar to a pulse controller as it, versus a manual Low/High fixed charge control light switch system which uses a fixed value resistance, switches/chatters the field current versus it being a constant value. Obviously, the absolute Max field current would be I = V/R if you know the Gennys total field winding resistance. IE at 12 Volts with 4 total ohms of field winding resistance the field current would be 12/4 or 3 amps. EXAMPLE ONLY NOT INTENDED AS ACCURATE It would take a quality ohm meter to measure the relatively low field resistance, but hey that's a start, give it a try !!!!

That being said and remember there are tons of different Generators and Voltage Regulators and I have no specs or data to answer your question, I have seen or read data where the field current might be less then one up to 3 or more amps. That can be true on a 6 or a 12 volt system.

The max current would be a number that yields the most magnetic field strength WHICH HOWEVER allows the heat to be dissipated and the windings not to overheat.

SORRY I CANT TELL YOU THE MAX FIELD CURRENT. Maybe if someone has you Generator and VR data they may be able to find it. Adjusting the VR is a bit tricky and technical (requiring accurate meters) and again you need the exact specs, I don't get into that over the net, I think Professor Jim or Bob have at times posted some Delco literature pages covering that but again it has to be for your system.

Sorry best I have to offer absent any data whatsoever. See if you can find some Delco literature, its out there

John T

The older Motor?s truck manuals have a lot of data and test
procedures for VRs.

Not impossible to measure, but difficult to calculate from ohm measurements. Generators in operation (I will use a Delco "A" circuit 2 brush example) have the voltage applied to the source at the Armature terminal. For the field circuit is going to be 7.2 volts. This is the operating, charging voltage of the output into a battery being charged at the generators max output. The current through the field windings will be considered to be directly to ground. (full fielded) the magnetic fields produced in the fields interact reactively to the current generated in the armature (Back EMF) this loads the field with a dynamic increase in current, that varies with speed, and the efficiency of the generator (magnetic coupling between the rotating and fixed components). So rather than get all scientific and radically complex. just put a good amp meter on the field wire and measure it under some variable conditions. Jim

Yo Jim, great answer "So rather than get all scientific and radically complex. just put a good amp meter on the field wire and measure it under some variable conditions."

MUCH easier then trying to find all the data and its the real world and varying conditions (condition of battery and RPM and VR settings etc etc etc) that determines the actual answer.

John T

Also helps to know. What system you are working on.

I have been assisted in my thinking by you. I also had an extreme teacher at Vincennes University Automotive Technology Program that discussed how things worked, and how things get complicated beyond the simple look they often have. He was the master mechanic for a Indy 500 race car for 5 years in the mid 50s (the Offenhauser years) we used Sun scopes to look at the wave forms of a variety of charging and regulating systems under a wide variety of setups both bench, and in vehicle. Invaluable. Jim

When I proudly attended VU (Pre engineering) in the sixties my Math Professor Alan Bradfield was also the Varsity Basketball Coach, bet you don't hear of that nowadays lol Similar I have learned a thing or two in my advanced age from you, we rarely disagree lol

John T

> So rather than get all scientific and radically complex. just put a good amp meter on the field wire and measure it under some variable conditions. Jim

I assumed the OP didn't have a working charging system to measure. (He didn't share what his end goal is, which is a common problem with questions posted here.) I agree, if he has a running system then directly measuring the field current is the best way to go. But if he doesn't, measuring the field resistance will give him the maximum current (what he asked for), but of course the current under normal conditions will be much less.

Attended F-68 all of 69 and S-70 Fantastic. Then to ISU for Industrial Arts W/manufacturing Technology emphasis. Jim

(quoted from post at 01:48:14 05/03/20)

(quoted from post at 20:54:59 05/02/20) So I'm trying something on a 12v VR.
Friend that is helping me is asking what
the max field current would be. Since I'm
here, I had no idea what the value would
be. While I'm asking, what would a 6V VR
have for Max field current?

Thanks.

Click to expand...

That's a pretty VAGUE question as you didn't tell us what you are playing with, or even the make and capacity of the charging system, but, what the heck, I'll play!

To start with, here's some DEERE 4010 and 4020 generator specifications:

Click to expand...

ore out's Deere numbers are good typical numbers! Seen similar range for generators in size from 15 amp output up to 50 amp output.
Some want to make everything complex?

"Some want to make everything complex? "

FWIW I agree, do like Jim says and stick a meter on it will provide a quick easy answer...??.He would have to find the exact spec sheets for his Genny and VR to get an idea of the max field current and actual conditions may change that grrrrrrrr lol

John T

Ok, so sounded like an easy question to me, but a I was wrong.

Correct, I have the VR off the tractor since it doesn't work at all. If it was on, then I would probably be able to measure. It's off a JD. Say a 620, or something older than that.

End game is to make it work again, but trying to redo the guts with an electrical guru, but he had questions I couldn't answer. However in seeing the 4020 results down below, so I'm pretty sure anything older would have less due to not being as advanced.

> However in seeing the 4020 results down below, so I'm pretty sure anything older would have less due to not being as advanced.

Actually, no. Those values were for 12 and 24 volt generators, but you have a six volt generator. Note that the field current of the 12 volt generator is double that of the 24 volt unit.

Making a VR for the tractor is a great idea. All reliable electronics have a reserve capacity to assure reliability, and circuit protection at some fraction of that to reduce smoke. So make the regulator capable of 8 to 10 amp control of field circuit ground. (what the generator needs to have the field energized) then fuse it for 5 amps. Jim

(quoted from post at 03:19:18 05/04/20) > However in seeing the 4020 results down below, so I'm pretty sure anything older would have less due to not being as advanced.

Actually, no. Those values were for 12 and 24 volt generators, but you have a six volt generator. Note that the field current of the 12 volt generator is double that of the 24 volt unit.

Click to expand...

"but you have a six volt generator."

In the thread-starter post the O.P. wrote "So I'm trying something on a 12v VR. Friend that is helping me is asking what the max field current would be."

He followed up by writing "While I'm asking, what would a 6V VR have for Max field current?"

> In the thread-starter post the O.P. wrote "So I'm
trying something on a 12v VR. Friend that is helping me
is asking what the max field current would be."

> He followed up by writing "While I'm asking, what
would a 6V VR have for Max field current?"

Yes he did. It's quite the mystery what he has and what
he's trying to do with it. I was speculating that he's
trying to get a 12 volt regulator to work with a 6 volt
generator. But who knows?