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Farmall & IHC Tractors Discussion Forum
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measuring voltage

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Farm130

09-17-2007 21:15:08




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Where is the best place to measure the voltage being generated by the genny as it charges the battery while the tractor is running? I have I 130 with a VR.




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John T

09-18-2007 07:13:40




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 Re: measuring voltage in reply to Farm130, 09-17-2007 21:15:08  
Farm, Any open unloaded output voltage reading taken direct from a genny dont really tell you all that much which is why I agree 100% with Bob n Hugh below. Its the voltage the genny can supply when coupled up to a load that counts. If a charging system is working properly, battery voltage should rise from 6.3 to 6.5 to around 7 on a 6 volt battery and twice that on a 12 volt. Once the gennys output voltage rises higher then the batterys, the cutout relay should close in whch case (notwithstandign voltage drops) the battery voltage n the gennys would be near the same.

John T

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Hugh MacKay

09-18-2007 03:20:30




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 Re: measuring voltage in reply to Farm130, 09-17-2007 21:15:08  
Farm130: I always check voltage at the battery, however I don't think it matters where you attach the volt meter. It's more a case of engine running or not running. When the engine is stopped, you know you have battery voltage, and with engine running if that voltage is not 1-2 volts higher you very likely have charging problems. If the engine running voltage is lower than non running you know you've got charging problems.

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Bob

09-17-2007 23:55:43




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 Re: measuring voltage in reply to Farm130, 09-17-2007 21:15:08  
Well, what's REALLY important is the voltage AT THE BATTERY. You want to keep it fully-charged, and not overcharge it, so voltage at the battery has to be held within a pretty close range.

That's why many newer systems with alternators often have a "voltage sense" lead that runs back to the (+) battery cable, to provide "feedback" to the regulator as to the actual voltage at the battery.

On a system with wire of adequate size, and CLEAN, BRIGHT, and TIGHT connections, the voltage measured at the output of the generator or alternator will be only a small fraction of a Volt higher than the voltage measured across the battery terminals.

So, if you meaure at both places, and see a LARGE voltage drop, it's time to clean up and repair the charging circuit.

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Farm130

09-18-2007 07:11:54




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 Re: measuring voltage in reply to Bob, 09-17-2007 23:55:43  
Bob - How do I measure the voltage at the generator?



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Bob

09-18-2007 07:43:21




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 Re: measuring voltage in reply to Farm130, 09-18-2007 07:11:54  
From the "A" terminal on the generator to chassis ground.



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