What's the R connection for on a Yanmar / Hitachi alternator?

[prv]

I'm looking at the circuit diagram in the Yanmar workshop manual (page 12-20). Most of it I understand, but I cannot figure out the purpose of the R terminal.

The basic setup I carried in my head was much like this: http://www.tb-training.co.uk/images/altcct.gif , where the lamp wire provides the initial current to energise the coil. So at first, I thought that R was just a minor enhancement to this, duplicating the lamp circuit with a resistor (mounted inside the regulator casing for practicality) so that the alternator would still work if the lamp blew or was removed.

Then I noticed that BAT is connected to R inside the alternator. This implies two things - firstly that a cable from R is unnecessary, as the R terminal (and hence the coil) will always be energised whenever the battery isolator is connected (which is undesirable anyway), and secondly that the "ignition switch" (engine electric power only, not starting) is being completely bypassed by the cable from switch to BAT to R to the other side of the switch.

Either I'm missing something fundamental or the circuit diagram in Yanmar's own manual is just wrong.

Pete

 

[VicS]

You don't say what engine or what manual you are looking at or where it is to be found but IIRC Tb training only covers positive regulation. The Hitachi alternator is however negative regulated.

Maybe this diagram of the regulator and internal wiring of the alternator which I found in one of the Yanmar manuals for the YM series will help.

 

[Eygthene]

Yanmar Hitachi alternator

My workshop manual shows more detail of the internals with some notes on how the regulator works.

 

[earlybird]

The alternator diagram in the Yanmar GM manual does show the "B" terminal internally connected to the "R" terminal, then to the regulator. Initial exitation of the alternator would therefore seem to be independent of the lamp, whose only function is to confirm that a charging voltage is present
edit :- All as in post above!!

 

[Eygthene]

There are one or two mistakes on the diagram in my manual - one is that the capacitor connected between Bat and E has got mixed up in the reproduction with the chained lines outlining the AC Generator unit (note how it is shown differently in the diagram Vic has found). Another is that the three dots, indicating connections are missing in the output commutation diode bridge. (Note that these are even worse in the bridge in Vic's diagram)

The draftsman or printer has been inconsistent in applying the standards to the indication of lines crossing (not connected) and lines crossing (and connected) - he has drifted between the two standards. Therefore, I suspect that the dot on the line between R and R1 is a misprint also. I think there is not a connection between Bat and R at all. If there were, the charge lamp would be on even though the ignition switch was off.

If that dot were correct, with the ignition switch off, but the main battery switch on, current would flow from the battery, via Bat to R, then through the lamp and the Rotor coil and the Darlington pair Tr1 (conducting because of base current through R4) back to the battery via E. We know the charging lamp does not light unless the ignition switch is on, so the dot indicating connection between Bat and R must be a mistake as well, it should be shown as a "bridge" where these lines cross.

 

[earlybird]

[QUOTE

We know the charging lamp does not light unless the ignition switch is on, so the dot indicating connection between Bat and R must be a mistake as well, it should be shown as a "bridge" where these lines cross.[/QUOTE]

Agreed, that didn't occurred to me,. However, the answer to the OP still seems to stand, that the "R" terminal is to provide excitation current, independently of the lamp.

 

[misterg]

However, the answer to the OP still seems to stand, that the "R" terminal is to provide excitation current, independently of the lamp.

It's the voltage sense feedback to the regulator. <<Deleted>>

Andy

 

[Eygthene]

I suspect that the value of R1 would be too high to pass sufficient excitation current in the absence of the charge lamp.

 

[prv]

The diagram I'm looking at is the same one Eygthene posted - thanks.

Sounds like my second hypothesis is correct then - the diagram is wrong as printed and there is no connection between BAT and R, that wire being only for the smoothing capacitor between BAT and E. Makes sense. If R is indeed for excitation current then everything is cleared up, but then Andy reckons it's actually for battery-sensed regulation. In that case, should it not be connected directly to the battery (or at least battery isolator) rather than the charge lamp still inside the engine loom?

Pete

 

[prv]

I suspect that the value of R1 would be too high to pass sufficient excitation current in the absence of the charge lamp.

What is the value of R1? It's not stated on the diagram. If R is for excitation then some resistance is needed or the lamp would never light. It doesn't need to let much power through, because as soon as the alternator is generating anything at all it supplies itself independent of R. Indeed Tony Brooks is of the opinion that an alternator at sufficient revs will usually get going without any external exciter current, presumably due to some residual magnetism stimulating the first few milliamps to kickstart things.

Pete

 

[misterg]

Actually, I think there is a mistake in the diagram in post #3 (Hi John!) - there shouldn't be a connection between 'B' and 'R' because there would be a permanent drain on the battery (my post above edited). I think the suggestion that the capacitor is connected between B and E (without a connection to 'R') is correct.

'R' is the voltage sense feedback, though.

Andy

 

[Eygthene]

MisterG has supplied the answer. The R terminal is the voltage sensing connection to the regulator. It can either be connected internally to Bat for machine sensing or externally to the battery for external sensing, but it should not be connected to both at the same time, as it is shown on the diagram that I found. If you examine the diagram that VicS found you will see that it is not connected to Bat - though there is a misleading chain-dotted line outlining the Alternator unit that might be mistaken for a connection.

This diagram shows that the Hitachi regulator on the Yanmar engine is an externally sensed connection. As Pete says, ideally this terminal would be connected as close to the battery + as possible. In any case it should be connected via a connection which, because it carries a very small current, experiences a minimal voltage drop from the battery terminal. Unless you add other circuits to the output from the ignition switch, the connection shown would not have a significant voltage drop, once the charge lamp has gone out.

Indeed if you had a split charging diode, you could instead connect this R terminal to the battery side of the diode (on the chosen battery) and the alternator would overcome the voltage drop across the diode and provide its full regulated output voltage at the battery terminal.

 

[prv]

MisterG has supplied the answer. The R terminal is the voltage sensing connection to the regulator. It can either be connected internally to Bat for machine sensing or externally to the battery for external sensing

In isolation that makes sense (R for Regulator and all). But the wiring loom diagram a few pages back in your manual (12-2) reveals that the connection to R is a lot further from the batteries than an internal bridge to BAT would be - hardly the superior accuracy that battery sensing is meant to provide over machine sensing.

Pete

 

[misterg]

In isolation that makes sense (R for Regulator and all). But the wiring loom diagram a few pages back in your manual (12-2) reveals that the connection to R is a lot further from the batteries than an internal bridge to BAT would be - hardly the superior accuracy that battery sensing is meant to provide over machine sensing.

Pete

I haven't seen the circuit diagram, but a connection to a very lightly loaded circuit (such as the feed to the charge lamp when the alternator is charging) will give a much more accurate measurement of actual battery voltage than the 'B' terminal at the alternator. The latter can't allow for the voltage drop in the cable between the alternator and the batteries which would, of course, vary with charging current (which is the rationale for battery sensed regulation).

As a slight aside, wiring it in this way would also appear to give automatic compensation for diode splitters in the charging circuit - something that hadn't occurred to me in the past.

Whatever, it works

Andy

 

[VicS]

Ok then if it helps to clarify things here is the diagram i posted earlier edited to remove confusing bits of case outline and the connections added within the diode assembly.

I think this should be correct.

 

[prv]

a connection to a very lightly loaded circuit (such as the feed to the charge lamp when the alternator is charging) will give a much more accurate measurement of actual battery voltage than the 'B' terminal at the alternator. The latter can't allow for the voltage drop in the cable between the alternator and the batteries

But the way the Yanmar loom is wired, there is much more cable between the R terminal and batteries than between the B terminal and batteries.

One route is from the battery, via the isolator, to a terminal on the starter motor, and from that same terminal to B on the alternator. Then, perhaps, through the internal bridge. Quite a short route, big cables, few joints.

The other route is from the battery, through the isolator, to the starter motor, from the same terminal to a fuse holder, to a fuse, to a loom connector, to up to six metres of narrow cable to the control panel, to another loom connector, to the key switch, back to the loom connector, back down the six metres of cable, loom connector again, to the R terminal.

Which of these seems more closely related to what's going on in the batteries?

Whatever, it works

I guess it does. But I like to know how stuff works, especially when it's relatively low-tech like this.

Pete

 

[misterg]

But the way the Yanmar loom is wired, there is much more cable between the R terminal and batteries than between the B terminal and batteries.

Not disputing that, but the alternator will be trying to push 20+ amps down the cable between the B terminal and the batteries which will make the voltage at the 'B' terminal higher than the voltage at the battery terminal.

One route ... Quite a short route, big cables, few joints.

The other route ...

Which of these seems more closely related to what's going on in the batteries?

If the alternator's charging, and you're interested in knowing what the voltage at the battery is, then it's the second route. If the alternator isn't charging then there's nothing to choose between them. You only get voltage drop when there's a current flowing. There's next to no current flowing through your second route, so even though it's torturous, it reflects the battery voltage better than using the 'B' terminal.

HTH

Andy

 

[prv]

Not disputing that, but the alternator will be trying to push 20+ amps down the cable between the B terminal and the batteries which will make the voltage at the 'B' terminal higher than the voltage at the battery terminal.

If the alternator's charging, and you're interested in knowing what the voltage at the battery is, then it's the second route. If the alternator isn't charging then there's nothing to choose between them. You only get voltage drop when there's a current flowing. There's next to no current flowing through your second route, so even though it's torturous, it reflects the battery voltage better than using the 'B' terminal.

Ah ha! It's starting to make sense now. Thankyou.

What little electrical/electronic experience I have has been all digital, in that everything is treated as being either at V+ or gnd. I'm not used to thinking about these kinds of effects.

An illuminating thread.

Cheers,

Pete

 

[Goudurix]

another Yanmar Hitachi alternator question

I stumbled into this old but very interesting thread.

I have had trouble with premature death of a 2x90Ah AGM house bank and I suspect the Hitachi alternator on my Yanmar 44 HP diesel (same alternator as above).

I think I have a conflicting situation:

- I removed the diode splitter and have the alternator (B en E connections) charge the 180 Ah AGM house bank directly
- I have a Balmar Duo charge unit that funnels a charge to the (flooded wet-cell) cranking battery which remains in operation after 7+ years of service
- but the alternator is wired to the cranking battery via the standard wiring harness which means that R is sensing cranking battery voltage and not house bank voltage.

I think this is causing a problem on long motoring journeys (it happens sometimes) with occasional 14.4 or 14.6 Volt out of the alternator.

I might wire R (sensing voltage) directly to battery+ of the house bank...but htne I would have - when differntial voltage - a possibly high current running through the 50 Ohm resistor between R and L in the darlington...probably leading to failure?

Question: to have a correct wiring and regulation sensing the house bank voltage, should I switch a relay with the contact key switch (which is harnessed to the cranking battery) and switch house bank + voltage to R and the 12V for the charging lamp (yanmar engine panel) via this relay?
In this way seperating completely the house bank and crnaking battery + voltages?

Hopefully anyone of previous posters is interested to reply?

Thanks,

Jan
37ft Jeanneau sloop "Goudurix"

 

[Goudurix]

Pushing this thread up the list again - hoping to get an answer from expert readers.

Jan