Geared Alternator at Low RPM’s

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Geared Alternator at Low RPM’s

Post by MichaelPawelek » Mon Oct 25, 2021 2:56 pm

Approximately at what RPM’s does a geared alternator on a Model T start to produce electricity. Having a discussion with a T friend and he states the gearing does not spin it fast enough until engine rpm is over 1000. I have no clue….😊

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Re: Geared Alternator at Low RPM’s

Post by Mark Gregush » Mon Oct 25, 2021 3:31 pm

The generator starts producing power as soon as it starts turning. With a mechanical cutout, till it reaches sufficient output to close the points and show on the ampere meter, the current flows through the shunt to ground.
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Re: Geared Alternator at Low RPM’s

Post by MichaelPawelek » Mon Oct 25, 2021 4:01 pm

Thanks Mark. Let me rephrase. We were discussing whether a geared generator or alternator on a Model T starts producing electricity sooner at low rpm’s.


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Re: Geared Alternator at Low RPM’s

Post by TXGOAT2 » Mon Oct 25, 2021 4:42 pm

I believe the T generator turns at 600 RPM at a road speed in high gear of 10 MPH. Assuming the alternator was geared the same as the generator, and I think it would have to be, I doubt if it would do much at that speed. Alternators typically run at multiples of crankshaft speed in order to provide good output at idle. A modern vehicle idling at about 700 RPM would likley see an alternator speed around 2100 RPM or more at idle. A Model T would be doing about 30 MPH in high to obtain an alternator speed of 1800 RPM, assuming the alternator had not been rewound and that it was installed in place of the T generator and gear driven. ///// I measured the alternator RPM on an 08 Chevrolet V8: Indicated engine idle speed, 650 RPM. Indicated alternator RPM, 1850 RPM. This vehicle has a heavy duty alternator that looks larger in diameter than the once typical GM alternator. If it has a larger rotor diameter, it may give higher output at low RPM than the earlier style.


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Re: Geared Alternator at Low RPM’s

Post by speedytinc » Mon Oct 25, 2021 5:38 pm

MichaelPawelek wrote:
Mon Oct 25, 2021 4:01 pm
Thanks Mark. Let me rephrase. We were discussing whether a geared generator or alternator on a Model T starts producing electricity sooner at low rpm’s.
My experience says the common model T modified alternator does not put out enough @ typical T speeds. I cant speak to all of em.
I cant think of ANY, ANY reason to replace a stock T generator with an alternator.
I have seen a lot of sheared gear pins & burned up alt. units. They dont belong on a T.


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Re: Geared Alternator at Low RPM’s

Post by greenacres36 » Mon Oct 25, 2021 6:25 pm

I don’t know who manufactured the alternator on my car but it’s been on there a number of years and will still charge with the headlights on at just above idle speed. It is A 6 V alternator. I put a generator on it for a while but I did not like The fact that if you want to run at night the setting did not charge enough at the same setting that I felt was overcharging during the day. The alternator cures that. I will agree with most people that an alternator looks extremely out of place on the model T. I do not like the looks but I’m getting more used to it because I love the performance.

This is almost like one of those which oil is best topics. There is no way I would put an alternator or a car but I did not run at night at all but my car is a driver not a show car. Big difference in my opinion.

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Re: Geared Alternator at Low RPM’s

Post by John iaccino » Mon Oct 25, 2021 6:56 pm

I put a 12 volt gear driven alternator on one of my cars when they first were offered. After about a week, the battery died. Had the alternator checked and found out that the cut-in speed of the alternator was 1500 rpm's. With a pulley on a modern car this speed is easily obtained, but on the gear driven unit, I would have to be traveling about 25 mph to start charging. I then changed to a model T generator with a 12 volt regulator and now charge at 12 volts but at half the amperage which is fine for me.


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Re: Geared Alternator at Low RPM’s

Post by speedytinc » Mon Oct 25, 2021 7:01 pm

greenacres36 wrote:
Mon Oct 25, 2021 6:25 pm
I don’t know who manufactured the alternator on my car but it’s been on there a number of years and will still charge with the headlights on at just above idle speed. It is A 6 V alternator. I put a generator on it for a while but I did not like The fact that if you want to run at night the setting did not charge enough at the same setting that I felt was overcharging during the day. The alternator cures that. I will agree with most people that an alternator looks extremely out of place on the model T. I do not like the looks but I’m getting more used to it because I love the performance.

This is almost like one of those which oil is best topics. There is no way I would put an alternator or a car but I did not run at night at all but my car is a driver not a show car. Big difference in my opinion.
Not meaning to start a fight. Your T could be run with a net discharge for the short times you drive after dark.(assumed). I do it with no issues.
My 14 charges a 12V battery @ 3 amps @ speed from the magneto. I run serious power sucking halogen headlights. I dont drive it frequently @ night. I have done Christmas light tours for 5-6 hours @ a time. There has always been plenty of juice + to do the tours. I dont worry, but, I do have the capability to unplug 1 headlight & the mag will always run the car. My 27 is set @ 5 amps. for short, typical tours. It is wired with a generator grounding switch for those long, all day mileage runs. I still cant think of a reason for an alternator.


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Re: Geared Alternator at Low RPM’s

Post by TXGOAT2 » Mon Oct 25, 2021 8:03 pm

Most common alternators have an open frame construction to allow air flow and many have a fan as well. They are not normally attached directly to the engine block, either. I wonder if cooling is an issue when adapting an alternator to bolt in place of a T generator. Vibration from the timing gears might be a problem, too. I'd think one of the smaller alternators, such as were common on Datsuns some years ago, would be a better choice. Mount it on the left side of the engine and run it with a belt at an appropriate speed.


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Re: Geared Alternator at Low RPM’s

Post by MichaelPawelek » Mon Oct 25, 2021 8:19 pm

Though I have wired standard household electrical stuff for years anything else electrical pretty well baffles me. Having said that what happens when the internal voltage regulator goes out in a automotive system like the Model T with a alternator? Is the current totally stopped or does one have headlight/battery problems after the regulator no longer functions properly.


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Re: Geared Alternator at Low RPM’s

Post by TXGOAT2 » Mon Oct 25, 2021 8:27 pm

I think the internal regulators tend to fail totally, if they fail at all. External regulators, early style or electonic, seem to be more failure prone. Slapping the cover on the early electromechanical regulators will often get them to work again. One or more open diodes can cause low alternator performance, and a shorted diode will cause the battery to run down when parked. If you drive an old MOPAR, always carry a spare regulator, ignition resistor, and ignition module and enough tools to change them.


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Re: Geared Alternator at Low RPM’s

Post by TXGOAT2 » Mon Oct 25, 2021 8:30 pm

I'd think the alternator on a Model T would be wired through the ammeter, which would give an indication of performance. A voltmeter would be easy to add, and will give a good idea of what's going on.


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Re: Geared Alternator at Low RPM’s

Post by greenacres36 » Mon Oct 25, 2021 8:36 pm

I have to admit one thing. I have never thought about using a grounding switch. So not starting a fight made me remind this. I’ll be quite honest, after that post I just might go back out and put my generator back on. Seriously. I always hated the looks of an alternator and I just can’t believe I didn’t think of that. So I have to thank this John for that. Honestly the generator that I have I had just spent about $200 rebuilding it myself. I used it for about one day and took it back off. It’s going back on now probably. My question now is at the risk of hijacking this thread is, can you use a grounding switch while you are going down the road or do you need to have the engine off before you turn it on?

It’s funny how some things are so simple it just one’s memory and expertise.


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Re: Geared Alternator at Low RPM’s

Post by MichaelPawelek » Mon Oct 25, 2021 8:50 pm

TXGOAT2 wrote:
Mon Oct 25, 2021 8:30 pm
I'd think the alternator on a Model T would be wired through the ammeter, which would give an indication of performance. A voltmeter would be easy to add, and will give a good idea of what's going on.
Since a alternator in a Model T converts the current from AC to DC am I correct that a volt meter for that alternator should also be DC but that a voltmeter to read the magneto output should be AC?


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Re: Geared Alternator at Low RPM’s

Post by TXGOAT2 » Mon Oct 25, 2021 9:32 pm

The regulated output from the alternator will be DC, so the regular add-on type volt and ammeters sold at auto parts stores should work. An ammeter doesn't care about voltage, within reason, and a 12 volt automotive voltmeter ought to work all right on a 6 volt system. I don't see a problem using the stock Model T ammeter with an alternator, as long as the altenator output did not exceed about 20 amps. Fuses ought to be used.


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Re: Geared Alternator at Low RPM’s

Post by TXGOAT2 » Mon Oct 25, 2021 9:45 pm

I would NOT to use a grounding switch with the engine running. The grounding switch would need to be connected to the output terminal on the generator, NOT to the cut out terminal. Opening the switch to allow the generator to charge shouldn't be a problem with the engine running, but I would not close it with the engine running. An alternative to a grounding switch would be to add a switched resistor to the wire from the cutout to the ammeter. Opening the switch would insert the resistor into the circuit to limit charge rate, and closing it would allow the generator to charge normally. The resistor would be placed in series with the generator output wire. The switch would be placed in parallel with the resistor, allowing current to shunt around the resistor when the switch was closed. One or more old style ignition resistors would probably be suitable. They could be arranged in series or parallel with one another to obtain the desired effect. The type of ignition resistor I'm thinking of is a wire-wound device in a porcelain body. They are about 1.5 ohms cold, and they heat up and increase in resistance when in use. It would be better in insert them in the field circuit, instead of the output, but either will work. Some old tractors used a similar arrangement to offer a choice of charging rates.


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Re: Geared Alternator at Low RPM’s

Post by MichaelPawelek » Mon Oct 25, 2021 9:59 pm

TXGOAT2 wrote:
Mon Oct 25, 2021 9:32 pm
The regulated output from the alternator will be DC, so the regular add-on type volt and ammeters sold at auto parts stores should work. An ammeter doesn't care about voltage, within reason, and a 12 volt automotive voltmeter ought to work all right on a 6 volt system. I don't see a problem using the stock Model T ammeter with an alternator, as long as the altenator output did not exceed about 20 amps. Fuses ought to be used.
My question was more geared as to whether one uses a different type volt meter on their dash to read current from the alternator or from the magneto. The vendors sell a cool meter pictured below to read the magneto but since the face states “AC” can I assume this same type could not read the DC coming off the alternator?

Image

PS-If I did this I would use separated meters. I know to never allow DC battery voltage to go to the magneto.


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Re: Geared Alternator at Low RPM’s

Post by TXGOAT2 » Mon Oct 25, 2021 10:16 pm

It's somewhat confusing. What is called the magneto on a Model T is actually an alternator, and it puts out unregulated AC current only. Modern alternators also make AC current, but they include an electronic rectifier set to change the AC to DC and most now in use have an electronic regulator circuit to control voltage and current. The magneto meter for Model T use will not work * correctly on the rectified DC output from a modern alternator, but you can still add one to your T, just be sure to connect it to the magneto as per instructions, and not to a generator or modern alternator.
Last edited by TXGOAT2 on Tue Oct 26, 2021 3:26 am, edited 1 time in total.


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Re: Geared Alternator at Low RPM’s

Post by TXGOAT2 » Mon Oct 25, 2021 10:40 pm

I believe that typical automotive DC generators also produce AC current. The armature windings are connected to the commutator bars in such a way that the windings that are connected to the brushes at any given instant are putting out current at the nominal polarity. In other words, the commutator and brushes not only collect the current from the armature, but function as an automatic switch to allow only the windings of the correct electrical polarity at any instant to be connected to the output terminal. The commutator and brushes function as a mechanical rectifier, and the result is a series of overlapping electrical impulses having the same polarity at the output terminal. This pulsating DC current works fine for the general automotive electrical system, but it has to be filtered before it can be used in a car radio. This is accomplished by special circuity in the power supply section of the radio itself.

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Re: Geared Alternator at Low RPM’s

Post by Mark Gregush » Tue Oct 26, 2021 12:26 am

MichaelPawelek wrote:
Mon Oct 25, 2021 4:01 pm
Thanks Mark. Let me rephrase. We were discussing whether a geared generator or alternator on a Model T starts producing electricity sooner at low rpm’s.
How did I completely miss read that? (that is a rhetorical question) Sorry I could have sworn I read generators, but think when I saw geared my mind filled in generator completely ignoring alternator.
I know the voices aren't real but damn they have some good ideas! :shock:

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Re: Geared Alternator at Low RPM’s

Post by TXGOAT2 » Tue Oct 26, 2021 3:24 am

You made a significant point nonetheless. I have put a couple of GM style internal regulated alternators on an 856 Farmall tractor. They did not work very well or very long. I blame that on low running speed and too much dust.


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Re: Geared Alternator at Low RPM’s

Post by speedytinc » Tue Oct 26, 2021 9:21 am

greenacres36 wrote:
Mon Oct 25, 2021 8:36 pm
I have to admit one thing. I have never thought about using a grounding switch. So not starting a fight made me remind this. I’ll be quite honest, after that post I just might go back out and put my generator back on. Seriously. I always hated the looks of an alternator and I just can’t believe I didn’t think of that. So I have to thank this John for that. Honestly the generator that I have I had just spent about $200 rebuilding it myself. I used it for about one day and took it back off. It’s going back on now probably. My question now is at the risk of hijacking this thread is, can you use a grounding switch while you are going down the road or do you need to have the engine off before you turn it on?

It’s funny how some things are so simple it just one’s memory and expertise.
Turn it on or off @ will. I didnt mention that next to the switch is an idiot light tied to the ignition switch. When the generator is working, its off. Like cars from the 60's. If during a drive, the light comes on or the ammeter isnt showing a charge, hit the switch to ground the generator to keep it from possibly burning out from a defective/failed cutout.

The grounding switch goes to the generator output terminal, not the cutout output terminal.


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Re: Geared Alternator at Low RPM’s

Post by speedytinc » Tue Oct 26, 2021 9:28 am

MichaelPawelek wrote:
Mon Oct 25, 2021 9:59 pm
TXGOAT2 wrote:
Mon Oct 25, 2021 9:32 pm
The regulated output from the alternator will be DC, so the regular add-on type volt and ammeters sold at auto parts stores should work. An ammeter doesn't care about voltage, within reason, and a 12 volt automotive voltmeter ought to work all right on a 6 volt system. I don't see a problem using the stock Model T ammeter with an alternator, as long as the altenator output did not exceed about 20 amps. Fuses ought to be used.
My question was more geared as to whether one uses a different type volt meter on their dash to read current from the alternator or from the magneto. The vendors sell a cool meter pictured below to read the magneto but since the face states “AC” can I assume this same type could not read the DC coming off the alternator?

Image

PS-If I did this I would use separated meters. I know to never allow DC battery voltage to go to the magneto.
Yes 2 different meters. The alt is putting out DC. The T ammeter can be used. The AC meter is only for reading magneto output.


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Re: Geared Alternator at Low RPM’s

Post by TXGOAT2 » Tue Oct 26, 2021 9:50 am

The pilot light, or idiot light, on a grounding switch hookup is a great idea. If switching the ground in while the generator in operation works, thats fine. I would think there is a risk that the cutout points might stick, which would be a train wreck. A fuse in the ground lead would prevent any serious problem, and a backup diode in the feed wire would provide additional protection.


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Re: Geared Alternator at Low RPM’s

Post by speedytinc » Tue Oct 26, 2021 10:33 am

TXGOAT2 wrote:
Tue Oct 26, 2021 9:50 am
The pilot light, or idiot light, on a grounding switch hookup is a great idea. If switching the ground in while the generator in operation works, thats fine. I would think there is a risk that the cutout points might stick, which would be a train wreck. A fuse in the ground lead would prevent any serious problem, and a backup diode in the feed wire would provide additional protection.
You may have a point here. The common cutout failure that will kill a generator is the "open" while running. If the cutout points stick during a run, no harm, untill low RPM & not running. Now a fuse in the line between the battery & cutout terminal prevents the smoke from leaving the wiring.


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Re: Geared Alternator at Low RPM’s

Post by TXGOAT2 » Tue Oct 26, 2021 10:43 am

Normally, the cutout points would open with a very low voltage/current differential across them as the engine slowed down and generator output faded to battery voltage. Using the ground switch with the generator at higher speeds would cause the cutout points to open with considerable voltage/current across them, which might cause excessive arcing. It might be best to avoid closing the grounding switch unless the engine was running at a low speed, in which case the cutout would probably already be open, or if not, it would open with only a low voltage/current differential across the points. The grounding switch itself would also be protected from opening or closing under a high load, which would probably extend its life.


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Re: Geared Alternator at Low RPM’s

Post by speedytinc » Tue Oct 26, 2021 11:15 am

I see your point on the cutout points. Slowing motor RPM's wouldnt hurt.
As far as switching load. Is battery voltage @ 4-6 amps max output. (Highest RPM's) significant enough to worry about?
The toggle switch is rated @ 110 & 15 or 20 amps.


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Re: Geared Alternator at Low RPM’s

Post by TXGOAT2 » Tue Oct 26, 2021 1:26 pm

I'd be more worried about the cutout than the switch, but the switch will last longer when operated at lower current.

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Re: Geared Alternator at Low RPM’s

Post by dykker5502 » Wed Oct 27, 2021 6:27 pm

Generally both a generator and a alternator starts charging at around the same RPMs which is around 1000 RPMs.
The reason why alternators can charge at idle is because yu can put pulleys on so that they run twice asfast as the engine. The alternators construction does that it can handle much higher RPMs than the generator, so in modern cars they can handle 15 - 20.000 RPMs when engine is doing max revs and you have that 2:1 gearing.
Putting an alternator on a T with the normal model T generator gear does not give you that advantage of charging at idle. It will be the samr aswith a generator but of course when driving at cruising speed you may get much more power out of the alternator than with the T generator.
I do believe there are vendors that do an alternator with a planetary gear in front which give the 2:1 gearing so that you can have the full benefits of an alternator. But they are expensive.
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Re: Geared Alternator at Low RPM’s

Post by Cordes_jeff » Thu Oct 28, 2021 2:41 pm

I have a geared alternator on a TT truck. I have to Rev it up to engage it. Once engaged it will keep the lights bright at a low idle. Way more output than a generator at idle. I putt putt through neighborhoods looking at Christmas lights every year with bright lights on 6 volt.


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Re: Geared Alternator at Low RPM’s

Post by speedytinc » Thu Oct 28, 2021 3:46 pm

Cordes_jeff wrote:
Thu Oct 28, 2021 2:41 pm
I have a geared alternator on a TT truck. I have to Rev it up to engage it. Once engaged it will keep the lights bright at a low idle. Way more output than a generator at idle. I putt putt through neighborhoods looking at Christmas lights every year with bright lights on 6 volt.
Thats an interesting observation. I would ask what your generator output was set @. One could easily set a generator to max output & get 12+ amps @ low rpms. More than necessary for good lighting+. The situation gets more dodgy as you speed it up & throw 20 amps for a while, untill that unknown magic moment you discover the generator got too hot. Generator output settings are for best compromise charging. Day/night, frequent starting, etc output NEEDS vary wildly.

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