What could cause alternator voltage to fluctuate?

[jmz]

Hey all I have a 93 king cobra with a fresh 502 and new marine HEI distributor. (no spitfire stuff anymore)

The alternator has been rebuilt and checks out at the alternator shop showing around 14.4 volts.

When installed on my boat we have anywhere from battery voltage to around 16 volts.

Can anyone suggest what might be happening?

 

[gm280]

Re: What could cause alternator voltage to fluctuate?

Hey all I have a 93 king cobra with a fresh 502 and new marine HEI distributor. (no spitfire stuff anymore)

The alternator has been rebuilt and checks out at the alternator shop showing around 14.4 volts.

When installed on my boat we have anywhere from battery voltage to around 16 volts.

Can anyone suggest what might be happening?

Alternators vary their output in proportion to the RMPs it is turning. So if your engine is sitting at one fixed RPM level then the output should be steady also, but once you apply any speed (increase the engine RPMs) then the output will go up as well. The only other reason for varying voltage is how much current other things running off the same battery/alternator is requiring... You didn?t say whether the alternator had a voltage regulator or not. If it doesn?t have a voltage regulator then there will be more fluctuation in the voltage as well...

 

[Don S]

Re: What could cause alternator voltage to fluctuate?

Check using a DVM, not just the helm gauge. Those helm gauges are very inaccurate.

 

[jmz]

Re: What could cause alternator voltage to fluctuate?

Check using a DVM, not just the helm gauge. Those helm gauges are very inaccurate.

Got it, I am checking with a nice DVM off the back of the alternator. It is a prestolite alternator with internal regulator.

 

[Levinz11]

Re: What could cause alternator voltage to fluctuate?

Does it put out 16V for long or just hit that amount momentarily?

 

[glenn property of pam]

Re: What could cause alternator voltage to fluctuate?

measure the voltage on the sense wire if its got a dirty connection (either end) then the sense wire will be lower voltage than the battery voltage and since the alternator is being controlled by the sense wire it will try to increase until the sense wire is the correct voltage.

 

[jmz]

Re: What could cause alternator voltage to fluctuate?

It looks like it is a problem with my connection with the jumper wire between the excite and sense posts. I cant tell yet if it is due to the wire (crimped connections or gauge of the wire) or if it is the posts on the alternator that are the problem. When the voltage starts to fluctuate i can wiggle that wire around and it will stabilize. I can also induce voltage fluctuations by moving the ire around.

 

[gm280]

Re: What could cause alternator voltage to fluctuate?

It looks like it is a problem with my connection with the jumper wire between the excite and sense posts. I cant tell yet if it is due to the wire (crimped connections or gauge of the wire) or if it is the posts on the alternator that are the problem. When the voltage starts to fluctuate i can wiggle that wire around and it will stabilize. I can also induce voltage fluctuations by moving the ire around.

Seems you located your problem. Fix or change the wire and connections and all will be good...