Will running electric tail lights and cowl lights affect engine performance on mag?

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Model T Ford Forum: Forum 2017: Will running electric tail lights and cowl lights affect engine performance on mag?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Robert Brough on Friday, February 03, 2017 - 08:20 pm:

I know it depends a little on the engine rpm's, but my car runs fine on magneto right now. My son is helping converting oil lamps to electric on the tail lights and brake lights and the cowl lights in addition to the already electric headlights.
If I have all the lights on and running the car on magneto, will I have enough amps and volts to insure good coil firing?

ps I've also got a spotlight on this thing.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Menzies on Friday, February 03, 2017 - 08:29 pm:

I don't know for sure but I would use a battery for the lights and charge it from an external source. I would suggest leave the magneto out of the circuit.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dan Treace, North FL on Friday, February 03, 2017 - 08:34 pm:

That magneto when running a road speed will put out 30v AC.

A typical 12v tail lamp bulb won't last long.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Robert Brough on Saturday, February 04, 2017 - 10:02 am:

I'm leaving everything 6v. Got a 6v battery in it and the generator seems to keep it charged. All my bulbs are 6v two filament bulbs. The tail lights sockets are wired so that I have tail lights as well as a brighter brake light in both.
The cowl lights are being wired up this weekend and we will see if one filament will be enough or if we want to have a dim and bright option. The owl light mounted on the machine gun uses a special 6v bulb and is wired to a separate switch on the dash and will only be used sparingly.

So what I'm hearing is run the T on mag during the day, but if I light everything up, keep it on battery.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Corey Walker, Brownsboro TX on Saturday, February 04, 2017 - 10:16 am:

I've never had one with a battery or generator but it seems like the switch would be made so that when you switch it for the engine to run on mag the lights would still be connected to the battery to work?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dan Treace, North FL on Saturday, February 04, 2017 - 10:23 am:

Yes, run on mag. You can use storage battery to start.

Are you using a Ford ignition switch ('19-'25)?
The switch for the keyed ignition is placed on BAT to start the T, the turn the key to MAG to run.

A std. Ford switch will also have a lever to turn on the lamps, OFF, ON and Dim, the tail lamps are wired to those same switch terminals too.




Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Strange - Hillsboro, MO on Saturday, February 04, 2017 - 10:35 am:

If it were me, I'd wire it so that the magneto just runs the coils (when the switch is in the magneto position) and everything else runs off the battery.

With the switch in Bat, the magneto is disconnected and the battery runs everything (including the coils). :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Robert Brough on Saturday, February 04, 2017 - 11:40 am:

I do have the key switch as shown above. Separate operation for bat and mag to run the car and separate switch to run the lights off dim bright.
I guess what I'm hearing now is that if I can isolate the lights to battery, and run the engine on mag, to do so. If not, then run the car on battery when running lights and on mag when not running lights.

Can we get a consensus?

Is the concern on the lights on mag a voltage draw issue and affecting the coil supply? Or is it a bulb fluctuation issue due to the mag putting out different voltage based on rpm?


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Zibell, Huntsville, AL on Saturday, February 04, 2017 - 11:53 am:

Robert, The battery and magneto circuits are separate. Car should run best on Magneto so keep running on that no matter if lights are on or not. Search the forum for one of Ron Patterson's schematics and you will see what I mean. As to having enough juice, the Generator can output about 20 amps, that will sustain 120 watts. So if you install a Fun Projects voltage regulator and set it up according to the instructions you should be OK. To determine load, take the wattage of each bulb and add it up. Don't exceed 120 watts and you should be fine. Any surplus wattage will charge the battery. Wattage = volts X amps


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Saturday, February 04, 2017 - 01:06 pm:

What John said. He has come up with the perfect answer. Nothing above specifies the year, but I assume this is a 1919 or later car. Here's the diagram.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Menzies on Saturday, February 04, 2017 - 02:12 pm:

I think I understand the issue, I assume you have a battery and generator. The ignition switch is just that, mag or battery. The main lighting switch is what you are using it has 7 terminals, two battery terminals, one high beam, one low beam, one tail light and mag and coil. The tail light terminal is common to high and low beam. If head lights are on the tail light will always be on, therefore you can connect your accessory lighting to the tail light circuit. Running on mag or battery will have no effect on the lighting circuits


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chris Barker, Somerset, England on Saturday, February 04, 2017 - 03:59 pm:

John, and hence Steve are right. EXCEPT that you don't want to take more than 10A (maybe 12A) from your generator. At 6v that is 60W (maybe 72W) Your cowl and tail lights should be 5W each, so that's 20W. 6v headlamp bulbs could be 36W each, and you won't see much if they are less. So that's 92W total.
Brake lights are 18W or 21W each (and IMHO a very good idea), but they are only on briefly.
If you set the generator to 10A and draw 92W which is 15A, you will take 5A out of the battery. However, assuming it's fairly well charged when you set out, you will get tired, or the sun will rise before the battery goes down. And even then, the magneto will still be keeping the engine running.
You could switch cowl lights off when headlamps are on, but that only saves 1.8A.
Unless you do a lot of night driving, I would set the generator to 10A and stop worrying.
If you want a better solution, you need to use LED bulbs which take just 10% to 20% of the power consumed by old tungsten bulbs. You can buy ready-made 'bulbs' or you can get your soldering iron out and go and buy individual LEDs and whatever resistors are needed to drop the voltage to about 2v


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chris Barker, Somerset, England on Saturday, February 04, 2017 - 04:01 pm:

going back to your 10:02 post - no; always use magneto once the engine is running. Keep the 6v DC system for your lights. The mag will run the engine until the fuel runs out.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Robert Brough on Saturday, February 04, 2017 - 05:38 pm:

Yes to all. My son walked me through the electrical system and, yes, running the car on mag does not affect the lighting circuit. All lights work off the battery. So only possible negative affect for running all 6 lamps and brake lights off the battery is if the generator cannot keep up with the draw.

So mag to run and lights off battery. I noticed today that my car starts easier off the battery when hand cranking than it does off the mag. Presume I'm just not generating enough flywheel speed for the mags to provide the initial spark. Or my amps coming off the mag is too low at slow speed. But the car runs great on mag or bat at idle and faster.

So, off for a fun run.

Thanks to all.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jeff Humble on Sunday, February 05, 2017 - 10:01 pm:

Robert, to hand crank on mag you need to advance the spark lever a couple of notches and hand crank with a 1/4 turn pull just like cranking on bat., no increased cranking speed or longer pull needed.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Robert Brough on Sunday, February 05, 2017 - 10:35 pm:

Well, we spent the afternoon adjusting and taking all the play out of the throttle and timing likage. Set the timer rod per the instructions. Start right up on bat.
Just haven't been able to get it to fire up on mag. Harder to turn, hence harder to keep speed of the crank up.
Once we start it up on bat and set the timing and mixture and idle so that it runs very smooth at low idle, we turn it over to mag and it starts to chug at low idle and we can't find a good timing setting.
So our game plan now is to always start it on bat, let it warm up and when we accerlate to put it in gear, switch over to mag for the drive. We'll see how it idles at our first few stops.

Could be our coils like the bat juice better than the mag juice.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Sunday, February 05, 2017 - 10:50 pm:

A lot of Model T's will run on MAG but need a battery to get started because their magnets aren't at full strength. This is why Henry, even though he didn't supply a battery with the car until the starter era, made it possible to use one.


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