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Old 02-22-2020, 12:08 PM   #1
jwaldrich
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Default 6 V Positive Ground

On a 6 volt positive ground flat head V8, and if everything is working correctly, can I remove the negative cable from the battery while the car is running and expect the car to continue to run on the generator?
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Old 02-22-2020, 01:51 PM   #2
Kurt in NJ
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Default Re: 6 V Positive Ground

it depends ----on a 3 brush with cutout at idle --no , ig engine running fast enough to charge and battery cable removed the voltage can go over 40 volts and if kept that way long enough smoke starts to come out of wires, points,coil can burn up, and any light bulbs that are on will burn out ----ending when the fried generator finishes itself off


on a 2 brush with regulator that engine is running fast enough to be charging it will keep running, but it won't like it and the regulator has to work overtime to keep control ---
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Old 02-22-2020, 02:00 PM   #3
jwaldrich
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Default Re: 6 V Positive Ground

Quote:
Originally Posted by Kurt in NJ View Post
it depends ----on a 3 brush with cutout at idle --no , ig engine running fast enough to charge and battery cable removed the voltage can go over 40 volts and if kept that way long enough smoke starts to come out of wires, points,coil can burn up, and any light bulbs that are on will burn out ----ending when the fried generator finishes itself off


on a 2 brush with regulator that engine is running fast enough to be charging it will keep running, but it won't like it and the regulator has to work overtime to keep control ---
Kinda funny how many answers start with "It depends".

You've answered my question and thanks! I always thought it would keep running even at an idle but this isn't the first time I've been wrong.
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Old 02-22-2020, 05:34 PM   #4
Jack E/NJ
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Default Re: 6 V Positive Ground

Are you gonna try it? Then tell us what happens? 8^) Jack E/NJ
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Old 02-22-2020, 07:13 PM   #5
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Default Re: 6 V Positive Ground

Alternators will do a better job of carrying the load when the battery is cut out but I wouldn't recommend anyone do it for more than a few seconds. As was mentioned, the old 3-brush generators depend on the battery to set voltage output. With no battery, the output will definitely go off scale high.

Ford updated stuff pretty regularly but the 2-brush didn't start to show up until the late 30s. We actually answer a lot of questions with that term at the beginning due to updates and variations in Fords production over the years. A specific year and model would lead to less use but not always. Ford changed things mid year in a lot of cases.
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Old 02-23-2020, 10:54 AM   #6
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Default Re: 6 V Positive Ground

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The question that comes to me is WHY do you want to do that? I am trying hard to think of a reason to do this. I am very curious as to what this accomplishes. Like "if I drain the oil out of a running engine, will it keep running?"
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Old 02-23-2020, 11:52 AM   #7
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Default Re: 6 V Positive Ground

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Originally Posted by deuce_roadster View Post
The question that comes to me is WHY do you want to do that? I am trying hard to think of a reason to do this. I am very curious as to what this accomplishes. Like "if I drain the oil out of a running engine, will it keep running?"
It was one of my methods of testing as to whether or not the generator was working. I have now installed a "used" generator with the same results when I disconnected the neg battery cable (positive ground).

The gauge on the dash indicates the installed generator is working but I was surprised to find that the car died when disconnecting the battery. I thought it would run.

Seems to me "somewhere" in my history I have done this before and the car continued to run but that must have been with an alternator.
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Old 02-23-2020, 12:03 PM   #8
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Default Re: 6 V Positive Ground

I have done this when having a boat battery problem. Back the boat into the water, take the battery out of the car but leave it running. Install the battery in the boat and offload it. Then go park the car and turn it off. This is with an alternator, not a generator.
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Old 02-23-2020, 12:35 PM   #9
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Default Re: 6 V Positive Ground

Disconnecting the battery when running an alternator gives you voltage spikes up to 120v...for very short periods mS since the alternator stator is a big inductor(coil).
If you have any electronics in the car like fuel injection i wouldnīt try my luck.
Most cars with electronics has voltage clamps keeping it under 40v above that voltage regulators of ECUīs fry fast....but they take so much then you can toast them to.
Bulbs or a fan motors etc donīt care about it since itīs for a blink...but solidstate is fragile if unlucky.
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Old 02-23-2020, 12:43 PM   #10
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Default Re: 6 V Positive Ground

Well, I hate to be in this position! But here goes, I have disconnected batteries with the engine running may times and never seen an issue. Just lucky I guess. And I'm the one that doesn't like people saying "will I never had a problem", LOL. Next time I'm around that situation I'll have to throw a voltmeter on the system.

Here is an interesting video, but it's just something off the internet, so don't mean much. I'll have to do my own testing.

https://www.bing.com/videos/search?q...88E4&FORM=VIRE

Last edited by JSeery; 02-23-2020 at 12:58 PM.
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Old 02-23-2020, 01:11 PM   #11
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Default Re: 6 V Positive Ground

Voltmeter is way to slow to show mS voltage spikes...you need an oscilloscope for it.
Worst is actually when you disconnect...you get what is called a load dump in geek language.
And Murres law says Murphy was a damn optimist...so anything will happen if i try it...lol
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Old 02-23-2020, 01:45 PM   #12
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Default Re: 6 V Positive Ground

Quote:
Originally Posted by flatheadmurre View Post
Voltmeter is way to slow to show mS voltage spikes...you need an oscilloscope for it.
Worst is actually when you disconnect...you get what is called a load dump in geek language.
And Murres law says Murphy was a damn optimist...so anything will happen if i try it...lol
Interesting, thanks for the info.
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Old 02-23-2020, 07:08 PM   #13
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Default Re: 6 V Positive Ground

I had customers that would check their alternator output this way on the helicopters. The alternator is a 70-amp 24-volt unit with a 70-amp ampere meter. There is nothing in the aircraft that will pull near half of 70 amps so they couldn't tell if it was working by the amp meter unless the cut of the battery switch.

They finally started putting a low voltage warning light in the panel that fed off the alternator control unit. At least this way a person can tell if the system is working. A volt meter would have likely been a better choice than an amp meter for gauging alternator output.
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Old 02-23-2020, 10:47 PM   #14
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Unhappy Re: 6 V Positive Ground

If you have a FUN PROJECTS voltage regulator, disconnecting the battery will fry it.
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Old 02-23-2020, 10:54 PM   #15
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Default Re: 6 V Positive Ground

If you are trying to determine if your generator is working, disconnect the generator and hook it up directly to the 6 volt battery. If it turns, its working. Then determine the polarity, adjust the brushes, hook up the cutout.
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Old 02-24-2020, 11:53 AM   #16
jwaldrich
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Smile Re: 6 V Positive Ground

Quote:
Originally Posted by fourfords View Post
If you are trying to determine if your generator is working, disconnect the generator and hook it up directly to the 6 volt battery. If it turns, its working. Then determine the polarity, adjust the brushes, hook up the cutout.
I'm "cheating" here. This issue is on my 1940 LaSalle but I figured the theory and tests would all work the same. There is no cutout on this generator.

I AM a fan of the Fun Projects cut outs and have them on all three of my T's. My Model A came with an alternator so I haven't screwed with that since it is working just fine.

So many cars and so little time...
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