Who knows alternators? Looking for authoritative info about turning it ON or OFF

[MetroMPG]

I haven't done any alternator-optional driving this winter for a couple of reasons:

- electrical loads are higher in the winter
- battery capacity is lower (due to cold)
- roadside belt swapping in the freezing cold is unappealing

In the winter I'd like to be able to leave the alternator belted, but have the option of deactivating it.

I've already looked, and didn't find a fuse I could simply pull out.

Does anyone have some authority on the subject of alternators? If I find the field wire, is it as simple as adding a switch?

Most importantly, are there implications on alternator life with switching the field in and out while it's spinning merrily away?

[MetroMPG]

The question also has potential application to the ForkenSwift. Some EVers use "switchable" alternators as a basic form of regen, typically driving it off the tailshaft of the motor to recharge the house battery.

Apparently you can also mod a standard 12v alternator's voltage regulator to put out much higher voltages, so you can use it to feed juice to the traction pack.

[skewbe]

Originally Posted by MetroMPG

...

Does anyone have some authority on the subject of alternators? If I find the field wire, is it as simple as adding a switch? ...

Yes, if it has a seperate field wire (some are internal). I'll look at mine...

[skewbe]

It's looking like it is internal. Still you could put a switch in line with one of the brushes if you felt like taking it out and running some leads out of it.

[JanGeo]

With any luck you may have a remote voltage sense to monitoring the voltage at the battery that you could play with but generally the regulator is built into the alternator. The only problem with disconnecting the brush is that the drive circuit may go a little crazy trying to drive the field (which is disconnected) harder and burn something out in the process (remote chance however) or may spike pretty hard when you turn it back on.

I still think the best way to do it is to add a separate battery to charge the car battery above the voltage that the alternator regulates to and keep the car battery fully charge and essentially "off line" and run on a second battery powered charger / supply.

Actually you could isolate all the battery loads to the second battery except for the alternator and starter motor and even kick in the alternator to the second battery when slowing down / braking using the brake light to switch the alternator output to the second battery to charge it. . . . This actually sounds like a pretty good idea using a deep cycle battery that could be grid charged etc. and it would not require high current output for the starter motor since the original battery would be doing that.

[Randy]

Originally Posted by JanGeo

Actually you could isolate all the battery loads to the second battery except for the alternator and starter motor and even kick in the alternator to the second battery when slowing down / braking using the brake light to switch the alternator output to the second battery to charge it.

Be careful with this idea: alternators have fairly dumb control circuits. They don't limit current and will happily burn up the alternator/boil off the battery trying to charge a dead battery. You can limit current by having a smaller charge wire to the battery, e.g. 20 feet of 12 gauge wire.

I don't think you'll have any electrical problems putting a switch on the field. It's not unusual to go all the way on, and the switch would take any turn-off voltage spike.

I think the biggest problem is the fan. They're sized for high draw at idle, and no doubt draw a lot of air at speed. You do need some air, but it could be a lot smaller as long as you turn it off at idle (assuming you idle at all...).

[JanGeo]

The field voltage is supplied from the inner diodes of the alternator so if you connect it to a low voltage run down battery it loads the output down and the voltage available to the field as well so it limits the output that way and it can only generate so much current anyway unless you really start spinning it really fast and that takes more power and belt load and would probably cause slipping of the belt at some point. Another option is to Diode isolate the two batteries at the alternator so when it is connected the second lower voltage battery only charges from the alternator and when disconnected the other diode to the primary battery conducts the alternator output if it needs charging. Ideally if you have room under the hood near the original battery to install a second one would be perfect and make it easy to move the power leads.

[skewbe]

Hey Jan, I'm not sure what problem you are solving by adding another battery.

re: field interrupted problems, I've had several alternators where I ran the brushes down to less than nothing. I Replaced the brushes and was back on the road.

[Coyote X]

you can just add a switch and shut the alternator off. leave the output hooked up like normal. with the power not going to the voltage regulator it will just spin without trouble. I have done this to hook up an ac delco alternator to stuff and it is fine. The alternator is not hurt by spinning without power. When you turn it off it will probably take about 20 seconds for it to quit putting out power but that is not that big of a deal. There should be a wire that gets 12V when the key is in the on position and that is the wire that energizes it. Trace it back under the dash where it would be easy to hook a switch to it and you are done Just post where the wire is and what color it is so us lazy people can do it the easy way.

You can take the regulator out and use an old chrysler external regulator if you want and mess with it slightly to get the alternator to put out any voltage you want up to around 70volts. I have ran straight 12 volts to the brushes and used an alternator as a stick welder before. They work great as a cheap welder. The windings at full load at 12 volts on the brushes pulls around 4 amps through the windings depending on the size of the alternator so it can burn up if you weld with 100% duty cycle.

I will be adding a switch to my alternator soon to disable it eventually but it has not been much of a priority since it was really cold and messy outside.

[JanGeo]

Second battery - Simple you leave the alternator alone connected to the standard "starter" battery because most are pretty much sealed units that can't be modified - the regulator is built into it and connected physically to the internal diode assembly. Take one apart and you will see what I mean. But you run the rest of the car off the second battery that you allow to run down and then charge it when you want to. This results in virtually no alternator load connected to the original "starter" battery except for replacing starting motor energy which you need for EOC restarts. And you run off the second battery for all the other running loads until you need to recharge it. You always keep the starter battery topped off on charge to make it last and you can beat the second battery knowing that you always have reserve power in the original that you can switch back in when needed and is already there for starting. Who wants to get stuck with a dead battery in the winter?

[JanGeo]

Some of the old alternators ran the regulator off the ignition - usually the ones with the external voltage regulator. These are great for modifying. The newer ones are all built into the alternator and after taking one apart late last year I realized how hard they are to modify plus they rely on the residual magnetic field in the rotor to energize the field windings enough to produce enough power to power itself up which if left spinning and disabled may not work as the magnetic field disapates.

The startup spike from mechanically switching the field on and off could result in alternator spikes to the battery which if not properly absorbed would end up spiking the entire electrical system of your car. Remember you could be working with a 90 amp alternator or greater - one weak connection and a current spike will produce a voltage spike. It would depend upon the feedback responce time of the regulator and the RPM that it is spinning at the time that you switch it.

[skewbe]

Metrompg, if you want to instantly enable/disable your alternator, interrupt the field with a switch.

The brushes power the field so any wire (internally in the alternator) that leads to the brushes is a good candidate for a switch. Preferrably NOT the one connected directly to the carbon brush.

I don't think it will fry itself, and you won't have to wait 20 seconds (some alternators never fully unload once excited) or experiment with external regulators. It's the same "circuit" mod as the kill switch, only instead of the ignition coil it is the field coil.

I would suggest as cheap insurance from being stranded that you leave a scangauge readout on volts however, or check it often, at least initially. You already know how to manage a vehicle without an alternator if it stops charging for any reason.

[skewbe]

And like randy mentions, the fan is going to make noticeable resistance at speed.

Sounds like AC clutch time again if you want to avoid that little penalty (interuupt the torque input instead of the field)

[Ron22]

Not sure if this helps but I have a 1986 CRX HF and I am told that the alternator already has this feature.
It shuts down the field on aacceleration. I have never verified this.

[MetroMPG]

Originally Posted by Ron22

Not sure if this helps but I have a 1986 CRX HF and I am told that the alternator already has this feature.
It shuts down the field on aacceleration. I have never verified this.

Yes, I've read this about the VX also.

[MetroMPG]

Originally Posted by skewbe

And like randy mentions, the fan is going to make noticeable resistance at speed.

True. That's why I'm mainly interested in doing this as a winter-only mod. In the summer, I'll probably go back to unbelting it for local driving to avoid the fan losses. There are losses with an electric clutch too, which is why I'd avoid it as well.

Originally Posted by JanGeo

I still think the best way to do it is to add a separate battery to charge the car battery above the voltage that the alternator regulates

This is similar to a response I got from someone on the EVDL: find the voltage sensing wire and feed it 14v to fool the voltage regulator into shutting down alternator output. Though he wasn't suggesting using the 14v source to actually charge the car's battery - just as an input voltage to switch the alt off, then switch to the car's actual battery voltage to resume normal alternator function.

But I want to keep it simple. I want to avoid having to bring a second battery along (even if it's just a small alkaline pack that gets me to 14v).

Originally Posted by Coyote X

you can just add a switch and shut the alternator off. [...] There should be a wire that gets 12V when the key is in the on position and that is the wire that energizes it.

That sounds like the simplest approach, if I can figure out which wire it is and trace it back (or just splice it near the alt and run wires into the cabin).

If for some reason this isn't an option, then skewbe's idea of putting the switch inline with one of the brushes is the next idea. (I was surprised that the alternator even HAS brushes - I thought it was AC. Here I go revealing more of my electric ignorance! )

I can avoid potential problems of voltage spikes by NOT flipping the switch when the engine is running. Do that only when it's off.

[JanGeo]

Yes there are brushes in the alternator but on the low current rotor field side - the brushes are contacting slip rings instead of a series of segmented contacts like in a DC generator or DC motor. There are no gaps on the contact surfaces to cause wear. Varying the voltage to the brushs feeding the rotor winding provides the variable magnetic field in the rotor to regulate the output voltage as the demand and the speed of rotation varies.

[MetroMPG]

So when people talk about a "brushless DC motor", or a typical AC motor, they are not actually brushless - it's just that the brushes are on a slip ring rather than commutator?

[jwxr7]

So when people talk about a "brushless DC motor", or a typical AC motor, they are not actually brushless - it's just that the brushes are on a slip ring rather than commutator?

There are no brushes or slip rings in a typical brushless DC motor. For most brushless DC motors we make where I work, the motor drive circuitry controls phases in the stator windings and the rotors are typically permanent magnets.
Most AC motors are induction with no brushes, some are universal motors (vacuum cleaner) and they have brushes, but can work on DC or AC. There are some AC motors that use brushes and slip rings too. There are so many types of AC and DC motors that you can find all different combinations of things.

[skewbe]

Originally Posted by jwxr7

There are no brushes or slip rings in a typical brushless DC motor. For most brushless DC motors we make where I work, the motor drive circuitry controls phases in the stator windings and the rotors are typically permanent magnets.
Most AC motors are induction with no brushes, some are universal motors (vacuum cleaner) and they have brushes, but can work on DC or AC. There are some AC motors that use brushes and slip rings too. There are so many types of AC and DC motors that you can find all different combinations of things.

The main difference is your alternator uses electromagnets where a brushless motor uses permanent magnets (on the moving part).

[jwxr7]

In the winter I'd like to be able to leave the alternator belted, but have the option of deactivating it.

I agree that this is a mod that could be a promising alternative to unbelting .

you can just add a switch and shut the alternator off. leave the output hooked up like normal. with the power not going to the voltage regulator it will just spin without trouble.

This is pretty much what I was thinking of trying too .

[jwxr7]

Originally Posted by skewbe
And like randy mentions, the fan is going to make noticeable resistance at speed.

Are you guys talking about the fan integral to cooling the alternator? It may not be an issue in my case. I'll have to look closer to mine, but it doesn't have an external fan like the delco ones I'm used to seeing. Maybe internal, I'll see.

[Brock]

It's weird you can't find the alternator fuse or wire. In the van it's a simple large 80 amp bladed fuse. On the wagon it is a larger 120amp bolted in place. I just keep a 10mm socket in the car and pop off the alternator lead and throw a vinyl glove over the lead. I have thought about adding a 40amp 12v contactor in line with the fuse, but never got around to it.

[JanGeo]

In the old days they didn't use fuses - my Geo was wired directly to the battery and the xB has the fuse . . . I think it does anyway. The thing to be careful with is that some Fuel Injection systems will not operate below a certain voltage so if you run the battery down a little and try to start further dropping the voltage the injectors may not fire.

The alternator fan is usually a stamped metal blade bolted under the pulley and could be removed in the winter.

Brushless DC motors without permanent magnets use an iron core that becomes magnetized by the electronically controlled rotating stator field. I believe a 40 pole rotor is used in the Tesler motor. (I think there were errors in the write up on it where they said it had a 4 pole motor.) Not having permanent magnets means that it can slip if loaded enough and it also can be started with any applied phase initially - it does however limit the ability to regen but it freewheels really well compared to the cogging action of a Permanent Magnet Rotor motor.

[MetroMPG]

Of course, being winter, I'm not going to be doing anything about this until the weather warms up... and then I don't need to do it (can just take off the belt ).

Sort of like when you have bad shingles on the roof: you can't do it when it's raining, and when it's sunny, you don't need to do it.

[MetroMPG]

Brock: I was surprised too. I know I looked last year, and didn't find the fuse (doesn't mean it's not there though).

JanGeo: the suzukiclones seem to keep right on running even with system voltage (under operating load) well below 12v. I mistakenly ran it so low that the starter wouldn't work, but I was still able to clutch start it and drive home to put it on the charger.

[Coyote X]

http://swift.crime.one.pl/pliki/schematy/ has wiring diagrams. ~ page 24 for the charging circuit

It looks like the black/blue wire coming off the ignition switch is the wire that turns the alternator on and off. So probably just splice a switch into it and you are set. I will do this to my car some weekend when I have time and see if it really helps much. Taking the belt off would probably be the best but there might not be much difference in turning it off and taking the belt off. a 65 amp alternator at full load can kill a 12hp Briggs and Stratton motor so it will make a difference in a 50hp car I'm sure

[MetroMPG]

Cool, thanks.

It also shows: no fuse in the alternator circuit

[MetroMPG]

You sure you don't want to aim for the blk/whi wire at C7? Isn't the blk/blu at C1 also the main ignition circuit?

[jwxr7]

It's weird you can't find the alternator fuse or wire. In the van it's a simple large 80 amp bladed fuse. On the wagon it is a larger 120amp bolted in place.

that sounds like the alternator output. The field enable wire should be alote less current. That way you shouldn't need a contactor, a switch should handle the field current.