Voltage Regulators

The regulator L terminal is indeed hot all the time. Otherwise lights and igntion would not work with the engine stopped exactly as you note. Consequently when the generator is charging, current drawn from the L terminal DOES pass through the cutout points.

I suspect rather the regulator is arranged so current drawn from the L bypasses the current sense coil on the voltage regulator relay. Ie. the VR's current limiting function senses only charging current supplied to the BAT terminal, not the total generator output.

If time permits I'll open up a 4 terminal regulator tonite and see if that's indeed the case.

They sure are a great bunch of traditional folks there and I plan to return, but after ten years thought it good to take a short break.

God Bless and best wishes for you and all at the GOG I will miss them all but its warmer down here lol

PS According to some literature I read somewhere, the 4 terminal VR system was reported to provide more precise regulation and lessen the chances of overcharge versus the later 3 terminal (NO L terminal) VR's which Deere used on later model tractors.

John T

Hey John T - see what you're missing down there in sunny Florida?!!

...Bob M

It would be pretty tough to come up with a SIMPLE design that would keep the "L" terminal "hot" at all times AND bypass the lighting current around the current sensing coil.

Also, since the current limiting function of the regulator is typically set to what the generator can safely handle BYPASSING the lighting current around the current regulator could cause the generator to overheat and burn up if there was a large non-lighting load AND a large lighting load.

Therefore, I don't think they are set up so the lighting load bypasses the current relay coil.

HOWEVER, I will defer to what you discover upon your regulator inspection!

The L terminal connects to the HIGH (input) side of the current sense coil. Thus the L terminal is hot at all times.

Note that under this arrangement with the engine stopped current flows “backward” thru the current sense coil when there’s a load on the L. This backward flow however affects nothing since the generator is stopped.

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Bob -

I agree - to a point anyway - with your 2nd statement: It does not make sense to bypass lighting current around the sense coil and risk overloading the generator from excessive load current.

But a 3 brush generator is by design inherently self-limiting for current output. Ie. the setting of the 3rd brush determines the maximum current the generator can supply, even under dead short conditions. (Theoretically anyway…I’ve not tested this for obvious reasons!)

I cannot however think of any possible advantage WHY a 4 terminal VR is wired like this.

Voltage regulated yes; but current regulated no.

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>So, you are saying regulators with the "L" terminal are only used on 3-brush generators?

Don’t know that for sure. My 2-brush generator experience is limited to Oliver tractors and IHC/GMC/Mack trucks from the late 50’s/early 60’s. (All had 3 terminal VR’s)

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>I didn't realize that, but that would seem to make sense as there would be no current limiting of the lighting current and a 2-brush generator COULD easily charge itself "to death".

Indeed it could!

OTOH back in the day there were no electrical loads beyond the factory work lights. Accessory loads like heater blowers, wipers, sound systems, etc. were still in the future. Further, supplemental lighting beyond the factory-supplied lights had yet come into vogue. So the risk of an overloading a 2-brush generator thru the L terminal may have been too small to worry about.

Only after the shortcomings of 4 terminal regulators mentioned by Pete 23 were recognized - also probably more than a few overloaded generators burned up by their owners - was the design changed to 100% generator current regulation.

PS we still gotta look into giving a Seminar at Red Power, I was asked about it here at Florida Flywheelers by the IHC folks here

John T

The 4-terminal setup effectively removes the load wiring between the VR's BAT terminal and the ammeter. This takes load current and it's associated voltage loss out of that piece of wiring (actual wire length/voltage drop depends on the VR's location).

This results slightly less voltage drop between the ungrounded battery terminal and the VR when the lights are burning. Ie. the VR senses voltage at the battery a bit more accurately and thus does a better job of charge control when the lights are on.

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We're contemplating a visit to Red Power this year. A joint sparky seminar there might be kinda fun - unless we get lightning/rain/wind like you did at the Canandaigua Expo that is!

...Bob M