IGN Light: When should it be on?

[ggzilla]

So I went out to my garage, where I have a 411 alternator and a 510 ext. 35A and a 720 I/R 35A. Put a longer bolt through your 411 bottom mount, with some washers or spacer. It will be perfectly aligned by the existing engine-side mount. The wiring connector needs modification, but now you can use modern parts instead of that antique 25A alternator.

[KFunk740]

Ahhh well I ordered a 411 alt from 'Click On Auto Parts' Online, so I'll wait and see if it shows up. First day of moving, battery is starting to get drained a bit, but holding up well. About to make 3rd trip. Yoinked the battery from one of my other cars and put it in back of truck as backup.

[KFunk740]

OK, moving is about done. Re-charging was annoying, but it worked. As expected, 'Click On Auto Parts' refunded my money when they figured out they didn't actually have what their website says. So yeah, 411-style alternators are near impossible to find new/rebuilt. Found a local rebuilder, haven't called him yet. Think I may just go the Autozone route to get one fast, of the later style (now that ggzilla has verified its easy). Might be using truck as primary transportation for a bit, so I just need it done. Might take my original alternator to the rebuilder eventually to get it done as a backup.

 

Thanks for the help with the test fit, ggzilla

[KFunk740]

OK, I got a 620 alternator from Autozone. I don't mind having the external regulator. Haven't hooked it up yet because I didn't have a bolt that was both thin and long, so gotta pick one up at store. New alt has two wires going to a plug, a yellow one and a white with black stripe. Old alt has 4 wires coming from its plug. Do I just connect the yellow and white/black wire to the similar ones on the old plug, and tape off the rest?

[ggzilla]

Dunno about a 620 alternator. Those take an external regulator and are wire differently than a 411 alternator.

[KFunk740]

Ahhh poop, I thought it was the same as the 510 alt and all others. Looks pretty much the same except for the wires.

[datsunaholic]

620 alternator 73-77 is the same as a 510 alt. 78-79 is different because it's internally regulated, but the wire connectors LOOK but do not function the same. The 510 alt only has the 2-wire plug.

[ggzilla]

Did you get a 620 35-amp alternator? that's the one that fits the bracket and fan belt. The 620's 50/60-amp unit are larger and need new belt and bracket.

 

Next, does it have LS connector on back, or FN connector?

[ggzilla]

Here's the three basic types of Datsun alternators:

 

Early type, FN type and LS type

FN type can be metal/plastic (as shown) or all-metal. Look for the FN or LS markings.

 

The first (25A) is a small diameter unit. The other two types come in small or large diameter (small vs large require different fan belts and brackets). Small is 35A and large is 50A or 60A.

[KFunk740]

I bought one that looks like the early FN type, the center one you pictured, and I'm trying to use it to replace one that looks like the one on the left with the 4-spade connector . It has a yellow lead and a white/black lead. My 4-spade connector has a yellow lead, a white/black, a white, and a black.

 

The new FN alt bolted in there fine with the addition of several washers/spacers and a new long bolt. Now I just need to figure out what to do with the white wire. I tried just connecting the yellow and white/black, and started it, and it went straight to 16 or 17V and I shut it off. I haven't made heads nor tails of the wiring diagrams yet, and not sure exactly what to do with that white wire. It must control the VR somehow.

[KFunk740]

OK, trying to figure out the wiring diagrams.... it looks like the white wire *may* just be a normal 12V wire for when the ignition is on. It seems to come originally from the ignition switch, and goes to three different fuses (clock, radio, etc.). Perhaps it is needed to 'activate' the VR, but was dropped in later years. Why go thru alt, when key on is fine? I can't seem to find where I saw that mentioned in an old thread, but there was something like that. I'm wondering if I run the white wire to a normal 12V ignition on source, maybe it'll make the VR go... or something like that.

[KFunk740]

Actually, I see on some cars it goes from the VR to positive post on the starter, which connects to positive post on battery ('72 510). On the '74 620 it goes to the white-red of the alternator, and thru a fusible link on the battery, and to a black-yellow wire that goes to ignition switch. Maybe if I try one of those, I'll have some luck.

[banzai510(hainz)]

rockauto has a 4 blade one,for 68 510

[ggzilla]

Glad to hear the 3-ear alternator WILL mount to a 2-ear bracket.

 

To wire up the FN type:

* 12 IGN from regulator goes to the STEM of the T

* Yellow wire goes HEAD of the T

Also confirm the regulator has 12V HOT and Black wire is grounded. You might have to jump the other two wires in the 4-wire connector to A and E.

 

Of course you also need the large A/BAT wire and the large E (earth ground) wire.

[ggzilla]

Btw, to be clear, if you use an FN-type alternator, you need an external voltage regulator. I have no idea if the early voltage regulator is compatible. But if it is the above wiring should work.

 

It is much easier to make the LS-type work (1980 Datsun 720 35A unit, same mounting as the 35A FN-type). It has a built-in regulator and only two wires to worry about. You unplug any existing regulator, and just connect IGN and the CHG lamp wires.

[KFunk740]

OK, I believe I have it connected as you say. But..... I still have around 12.5V max. Even if I bypass the VR as shown in diagrams for those with IRs (unplug VR, jump white to yellow, and jump white/black to white/red).

 

However, if I disconnect the white wire (12V hot connected to A/BAT), the voltage jumps to 16V+. So, the alt is capable of putting out 16V, until I connect it to the white wire that should have 12V, which brings it down to 12V. I tried connecting it direct to battery too, same result. Actually, the idle speed even goes way up when I connect it. Disconnect it, and the idle goes way down. I figure that's because there's a bigger load on the engine if it's trying to crank out 16V.

 

So, then I'd suspect the VR being a problem, but if I leave the alt all connected properly, and bypass VR, I only get 12V max. Which is back where I started, exactly. Alt not putting out 14V. I don't think the alt was ever the problem, and probably not the VR. Could there be something else in the system that can drop my voltage, or tell the VR to over-regulate?

 

I'm going to try a Nissan IR alternator that my dad had laying around (from a Pulsar I think), 50 or 60A, but the measurements appear to match my old alt. But, I don't know if even that will solve it.

 

I'm gonna try contacting the guy that did much of the work and re-wiring on my truck to see if he has any ideas.

[KFunk740]

OK, so in backwards land, in which I might live... I bet the VR is not only necessary for limiting voltage, but also increasing alternator output to 14.5V. It probably uses that white wire to sense and/or modulate the output of alternator (must just be tapped in somewhere else in later years, other than the white wire).

So, it's likely not a passive regulator, it's an active one. In just the same way that when I disconnected and reconnected the wire, it can just tweak the voltage up or down to produce the same result.

 

So, I'm callin Autozone again for one... hooray for 1 year warranty.

[ggzilla]

You MUST use the external Voltage Regulator with an FN-type alternator. If you hot-wire an FN alternator, you get unregulated output (16+ volts), which will ruin the battery after a short while.

 

The 720 alternator costs less than a voltage regulator, and has a built-in VR.

[KFunk740]

You MUST use the external Voltage Regulator with an FN-type alternator. If you hot-wire an FN alternator, you get unregulated output (16+ volts), which will ruin the battery after a short while.

 

The 720 alternator costs less than a voltage regulator, and has a built-in VR.

 

Yes of course, I've only disconnected it briefly for testing purposes.

 

But in addition to downregulating voltage, it appears to me that it also upregulates voltage from 12V by increasing the load on the alternator.

 

I'm getting a new VR under warranty from autozone, but now that I know their VRs are crap (2nd one thats taken a dump), I might search for a better source or just go IR.

[datsunaholic]

It doesn't uprate the output. It simply starts/stops (and sometimes meters) the current going into the field terminal on the alternator. With no current to the field, the alternator doesn't have any output at all. Once the field is started the alternator will start producing. Its output current is dictated by load and RPM. The voltage is dictated by the field, sent via the regulator. Regulators are set to a "safe" area for a fully charged battery, which is around 14.3-14.5V. Once it hits that level, the regulator cuts off curent to the field, which causes the field to collapse and the alternator stops producing output. Of course, as soon as that happens the battery naturally drops (it's not instantaneous) to its steady-state voltage of around 12.0-12.6V. Because that's less than the threshold of the regulator, it restarts the field. This happens faster than you can see, but on an oscilloscope you can see the transition. The more current draw of the car's electrical system, the faster it would force the battery down to its steady-state voltage, so the regulator is pretty much ALWAYS providing a field, but not so much as to overcharge the battery.

 

An unregulated alternator can produce upwards of 30V. It has no limit except the amount of CURRENT it can provide and the ability of the parts to stay together. They are rated at a particular current at a particular RPM. The reason they can provide such high voltages is because they are designed to be able to provide a significant percentage of their rated output at idle, and anywhere in the operating range of the engine. Actual output is dictated by LOAD, the regulator simply ensures the voltage doesn't go over a preset amount.

[KFunk740]

It doesn't uprate the output. It simply starts/stops (and sometimes meters) the current going into the field terminal on the alternator. With no current to the field, the alternator doesn't have any output at all. Once the field is started the alternator will start producing. Its output current is dictated by load and RPM. The voltage is dictated by the field, sent via the regulator. Regulators are set to a "safe" area for a fully charged battery, which is around 14.3-14.5V. Once it hits that level, the regulator cuts off curent to the field, which causes the field to collapse and the alternator stops producing output. Of course, as soon as that happens the battery naturally drops (it's not instantaneous) to its steady-state voltage of around 12.0-12.6V. Because that's less than the threshold of the regulator, it restarts the field. This happens faster than you can see, but on an oscilloscope you can see the transition. The more current draw of the car's electrical system, the faster it would force the battery down to its steady-state voltage, so the regulator is pretty much ALWAYS providing a field, but not so much as to overcharge the battery.

 

An unregulated alternator can produce upwards of 30V. It has no limit except the amount of CURRENT it can provide and the ability of the parts to stay together. They are rated at a particular current at a particular RPM. The reason they can provide such high voltages is because they are designed to be able to provide a significant percentage of their rated output at idle, and anywhere in the operating range of the engine. Actual output is dictated by LOAD, the regulator simply ensures the voltage doesn't go over a preset amount.

 

OK, thanks for putting it into words way better than myself. So, I guess instead of failing to 'upregulate,' I should say that I suspect that my VR is not putting out sufficient current to the field terminal on the alternator, for unknown reasons.

[KFunk740]

Seems to be working OK with new VR (replaced under warrranty), with white wire connected to positive on back of alt, black hooked to ground, etc. Voltage up to a steady 13.8V at least, not sure why it won't go above that. I'll double-check tonight. At leats it's charging some, and the IGN light is out.

I think the Duralast VRs from Autozone are just crap. I need to find a new source (but I figure others come from same manufacturer), or just go IR.

 

In any case, yes the external VR does appear to be responsible for increasing alternator output to proper levels....

[ggzilla]

Actually, the voltage regulator LIMITS the alternator voltage output, keeps it below about 15.5 volts, depending on temperature. The Datsun service manual explains it.

 

Have you verfied that your alternator will go above 16 volts?

[KFunk740]

Actually, the voltage regulator LIMITS the alternator voltage output, keeps it below about 15.5 volts, depending on temperature. The Datsun service manual explains it.

 

Have you verfied that your alternator will go above 16 volts?

 

Yes, it will go sky high if I disconnect the white wire from it....

 

Simply thinking that it only limits the voltage was our mistake from the beginning.... It's also responsible for stimulating the field current of the alternator, which INCREASES voltage to 14V, where it should stay.

[datsunaholic]

Well, it's all semantics. With no field current the alternator has an output of zero. Once field current is applied the alternator will be excited and will produce as much voltage as the windings can handle for a given RPM and load. The regulator moderates the field to keep the output voltage below a set value. It does attempt to start the field whenever the output is below a certain range, but beyond generating the field it cannot increase the output of the alternator. The field is self-sustaining. If you were to overload (or under-drive) the alternator to get its output to below 10V, removing the regulator would have no effect. Reducing the load or increasing the RPM would cause the voltage to go up, even with no regulator. But once the field collapses, yes, it needs the regulator to re-excite it. It isn't increasing output as much as switching it on.