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Author Topic: Voltage gauge fluctuating.  (Read 2659 times)
jeetS
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Voltage gauge fluctuating.
« on: April 19, 2011, 09:08:22 PM »

Whenever I have any accessories running my voltage gauge moves with whatever is drawing power... ie. moves up and down with the signal light or wiper relay.  Huh

problem seems to be worse with the headlights on....

Is there something wrong with my wiring somewhere?


 
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Ronmar
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Re: Voltage gauge fluctuating.
« Reply #1 on: April 20, 2011, 03:58:17 PM »

Bad ground into the instrunment panel or dash most likley.  There are also quite a few connections in line in the harness between source and gauge.  Mine does it a little also...  But with a load like headlights, there is a significant load being applied to the charging system.  A quick check is to measure at the battery and see how much of a fluctuation you see there when various loads are applied.  If the fluctuation at the battery is significant, the alternator voltage regulator may be loosing it's edge:)
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Ron

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jeetS
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Re: Voltage gauge fluctuating.
« Reply #2 on: April 20, 2011, 05:31:13 PM »

Thanks Ron I will do that. If the voltage regulator checks out should I worry about the bad ground?
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swerks
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Re: Voltage gauge fluctuating.
« Reply #3 on: April 21, 2011, 08:21:26 AM »

would a higher out put alt help these problems  Huh
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Ronmar
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Re: Voltage gauge fluctuating.
« Reply #4 on: April 21, 2011, 11:45:17 AM »

would a higher out put alt help these problems  Huh

No, I don't think so.  The largest auto alternator on the planet still only puts out 14.5VDC +\- .5V Smiley. The fluctuations are probably only being seen by the inst panel gauge due to poor connections and the way Toyota chose to route power.  The alternator is probably only fluctuating a very small ammount when you turn the headlights on.  But since the control power to energize them came from the switch in the steering colum, there is a voltage drop seen there which is where the gauge is sampling the DC buss.
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Ron

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1project2many
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Re: Voltage gauge fluctuating.
« Reply #5 on: April 21, 2011, 06:17:05 PM »

Quote
But since the control power to energize them came from the switch in the steering colum, there is a voltage drop seen there which is where the gauge is sampling the DC buss. 

Additionally the voltage regulator in the alternator lags in it's response to voltage drop.  This lag can cause a very noticeable drop on a dashboard volt gauge when a load (lights, turn signals, etc) is applied.  What's sometimes missed is the gauge creeping back up as the alternator output increases to match the load.  Newer alternators which are integrated with body or engine control systems will often increase output in response to anticipated load preventing the operator from noticing fluctuations.

And as for the higher output alternators, these units often require higher rpm than stock in order to produce full output and have longer response times when a load is applied.  More than once I've seen these alternators cause more flickering than the OE low amp units they replace.
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