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Another voltage question.

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SS from MI

09-22-2004 05:37:44




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My volt meter goes crazy (with engine running)when I check voltage on the battery. I thought it was interfence, but it doesnt happen when I check generator (7.2 volts)arm to gnd. So I think my voltmeter is ok. I have been informed to buy new regulator and I will. But, I am curious. I also get this crazy reading when I check bat. on VR to gnd with engine running. If I disconnect bat. wire from VR and check bat. wire to gnd it still makes my volt meter go crazy with engine running. Why is that?

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SS from Mi

09-23-2004 05:06:23




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 Re: Another voltage question. in reply to SS from MI , 09-22-2004 05:37:44  
Thank you all for your help. I used an analog meter and found 6.x volts on battery with engine running. The digital meter was giving me grief. Again Thanks



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Bob

09-22-2004 19:49:59




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 Re: Another voltage question. in reply to SS from MI , 09-22-2004 05:37:44  
You guys sound like a bunch of politicians obscuring the issue!!!

#1. If the battery is staying up, there's no need to worry!

#2. If there IS a problem, use an analog voltmeter to troubleshoot the problem!!!



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bobby16781

09-22-2004 19:19:59




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 Re: Another voltage question. in reply to SS from MI , 09-22-2004 05:37:44  
Remember - - - positive ground - - - and yes probably picking up ignition discharge
also you might check all ground connections, when you test from arm to ground and doesnt go wild,but it does when you go from batt hot to ground. check all connections on volt regulator test for voltage at the arm terminal. dont know if you realize it but the field connection is the control circuit for regulator. if you ground the field terminal, it will cause the generator to charge wide open. do not leave connected very long or it could eventually burn out the generator, but you can check to see if it is the volt reg or something else. temporarily ground field then check your battery terminals, like before and see if it is still showing wild readings. if it is not, then it is your regulator.
if it is, then it is something else.
one other test. if it is the ignition, while you are holding the test leads to the battery, have someone shut off the ignition while you are watching the tester. as the key is turned off, see if for a moment if it tests true. while the engine is still turning but with ignition off.
you will only have a half second to check. if you are quick. if it straightens out in that split second. then it is ignition noise.

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Dell (WA)

09-22-2004 07:34:04




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 Re: Another voltage question. in reply to SS from MI , 09-22-2004 05:37:44  
SS..... ...I told you that your Digital Voltmeter leads were acting like an antenna and picking up sparkies from your ignition while the motor is running. I told you that Marconi's first radio transmitter was a spark-gap. And the difference between a radio sparkgap and sparkplug gap is???.....NOT MUCH.

Your posting is still consistant with failed Voltage Regulator.

All this other meter stuff is technical stuff to confuse you.

You might find it interesting to use a real AM transistor radio (the cheaper the better), tuned to NO STATION, and go sniffing around your sparkie wires. Bettcha radio goes nuttz too....rattat.tat.tat.tat...ignition noise.

You might even find that your sparkie wires are leaking sparkies. You doubt? When it is very dark tonite, go out and start yer tractor up and watch for blue sparkies dancing on your old dried out and cracked ignition insulation. Replace with new coppercore sparkplug wiring kit ($10 cheap), cut to fit. Don't use modern anti-radio static carboncore sparkplug wiring.

When I replaced my sparkie wires 10 yrs ago, I used a hot-rod sparkie wire kit for Pontiac V-8 because it had molded right-angle sparkie boots and modern silicone insulation to keep the sparkies from leaking out..... ...Dell the self-appointed sparkie-meister

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souNdguy

09-22-2004 05:45:34




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 Re: Another voltage question. in reply to SS from MI , 09-22-2004 05:37:44  
Even with your genny and vr disconnected.. your points ignition system is still placing a pulsed inductive load on the battery.

If your ammeter shows a charge, it is charging. Make your voltage checks with that digital vom ( digital right? ) with the system off.. or get a 4.99 - 9.99 auto store cheapy analog meter.. they don't whack out like the little digital ones.

Save your 40$ on the VR unless you know it has a charge problem.

report back what you find.

Soundguy

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MikeT

09-22-2004 11:52:45




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 Re: Another voltage question. in reply to souNdguy, 09-22-2004 05:45:34  
Hey SouNdguy -

I was suprised to find that an alternator is producing 3 phase AC internally. After it goes through the 3 phase rectifier bridge and the internal capacitor, it is a pretty good flat DC voltage. DC generators not the same. Lotsa noise coming off the communtator segments.

Somebody posted a schematic of an alternator here a few days ago. First time I'd ever looked at one.



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souNdguy

09-22-2004 11:59:25




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 Re: Another voltage question. in reply to MikeT , 09-22-2004 11:52:45  
Think of the waveform of a sine wave. The dc gen chops the bottom and flips it to the top by switching 'magic' with the way the arm/com segments are layed out. that givces you a look like a bunch of MMMMM M's together. The diode trio is way more efficient.. more humps to lay out together in the same time frame. that gives you less 'bumpy' dc. Add a battery and it is flat. Lots of the noise from the genny is the mechanical comutator and the flop of the wave.. diodes in the alt take care of it much neater.

Course.. the dc genny was a great idea / design to produce dc power from an otherwise ac source...

Soundguy

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MikeT

09-22-2004 13:22:45




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 Re: Another voltage question. in reply to souNdguy, 09-22-2004 11:59:25  
Eons ago, I used to make and sell golf cart battery chargers in my spare time. They were large units with 12 drops running to 12 carts. Three large fan cooled transormers inside hooked in a Y-Delta 3-phase arrangement. Off the delta it fed into a large bank of 6 diodes with homongous heat sinks. Each unit could pump out, continuously, 30 amps to each of the 12 cart.

Made lots of money doing that till the cart manufacturers started selling individual chargers with each cart. They upped the cart prices by $300 and provided no option for NOT getting their chargers. After that I started selling 'gas guages' for electric golf carts. Sold several 1000 of those to country clubs. Those two moon light jobs put two kids through college!

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souNdguy

09-22-2004 16:44:49




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 Re: Another voltage question. in reply to MikeT , 09-22-2004 13:22:45  
It's great when you can make a hobby pay.

Soundguy



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TXBLU

09-22-2004 06:15:54




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 Re: Another voltage question. in reply to souNdguy, 09-22-2004 05:45:34  
Or put a 5 cent .01uf 50 volt or so capacitor (condenser) across the leads at the meter. (Radio Shack) The cap shorts the spikes but allows the dc to be read by the meter.

Mark



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Bryan(OH)

09-22-2004 18:34:06




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 Re: Another voltage question. in reply to TXBLU, 09-22-2004 06:15:54  
Man, I thought 8N owners were dumb old hillbilly's like myself. You guys are pretty impressive. My RadioShack digital VOM doesn't seem to have any noise problems when I use it on my N. I'm not sure what model it is but it wasn't too expensive when I bought it 10 or so years ago.



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souNdguy

09-22-2004 06:26:47




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 Re: Another voltage question. in reply to TXBLU, 09-22-2004 06:15:54  
Good point. A reverse polarity diode would be a good / additional choice too. It will help with back emf.

I usually don't suggest the semi-hi tech answers for these common problems. I get so many funny looks when asked about ceramic disc caps.. and diodes.. etc... usually by the same people who want to know what vom stands for...

Soundguy



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txblu

09-22-2004 06:27:34




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 Re: Another voltage question. in reply to souNdguy, 09-22-2004 06:26:47  
I was waiting for you to respond. Grin.

Mark



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