Voltage Regulators

Someone posted that a four terminal voltage regulator with an L or Load terminal has the advantage of not having the Load current go through the contact points of the cutout relay. The pictures I have show the BAT and L trrminals internally connected with both being supplied by the points in the cutout. Is the L terminal hot with the tractor off like the BAT terminal? I would think it would have to be or the lights would not come on with the tractor stopped. Please comment.

Tom -

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.

BobM,

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!

Bob M,
Thank you so much for your reply. I am preparing to teach some classes at Gathering of the Green in Davenport Iowa next week and am trying to prepare for all possible questions. Thanks again!

OK men – I discovered a 4 terminal regulator off my Super H in the toolbox on my truck this noon. So I opened it up for peek inside during my lunch (I’m at work…). Here’s the deal:

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.

So, apparently the current-sensing coil IS bypassed by the current drawn by the lighting load, which is drawn just AFTER the cutout points but BEFORE the current-sensing coil.

INTERESTING!

So the cutout contacts DO carry the lighting load supplied by the generator, but that current is apparently unregulated.

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

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".

GREAT discussion and "fact-finding mission"!

So...in other words...you plan to teach something you don't actually know.

You got her figured out except that this same system was indeed used on shunt wound two brush generators like 560's and the latest replacement new generators for the 400's etc were also shunt wound two brush. The combination current, voltage regulator would not allow a high rate of current and still control voltage so they took a route around this by using the load terminal system whereas accesseries could operate and still provide current to recharge the battery. The later tractors like 706 went to the three unit regulator with seperate current controls and worked much better.

>So the cutout contacts DO carry the lighting load supplied by the generator, but that current is apparently unregulated.

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.

Best wishes at GOG, you will have fun Im sure. I gave the Coil Ignition and Charging Systems and Wico Magneto Seminars there at EVERY GOG the past 10 years but declined the same this year because Im in Florida and didnt wnat to return to colddddddd Indiana in Mid March,,,,,

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

Bob, I dont have any VR's here in Florida or internal diagrams butttttttttttt I read they provided more precise regulation and reduced the chances of overcharging versus the later 3 terminal (NO L) VR's Seems the gennys output could somehow feed the loads directly (to reduce battery discharge) and only sent that charging current up to the battery (via the cutout) that was absolutely necessary... SOMETHING LIKE THAT I just dont have much info down here.

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

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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.

Click to expand...

This agrees with what I said in my Sept-Oct Red Power article. I think the advantages, such as they were, for this design have been pretty well covered by the other responses. The 3-brush generator is protected because of the self limiting behavior. The current limiting of the regulator is to protect the battery.

Sounds right John.

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