alternator question?

[betayv]

hello guys 1987 searay 5.7 engine, got the boat about 3 months, new starter, and today I installed a new alternator, the old one was rusty and noise, the new one is a one cable type alternator, has a 55 amp, I installed a 75 amp, I have the same reading on the volt gauge in the dash? 11, how can I check if is the gauge or a cable somewhere, please advice. thanks

 

[NHGuy]

Clean up all your contacts.

 

[Silvertip]

Verify voltage reading with a hand held multitester (also called a volt-ohm-milliameter) available for $10 - $75 (depending on the degree of fancy) in the electrical dept of any home improvement store.

 

[Bt Doctur]

the alt is connected to the battery at the starter lug. you have a battery cable, the alt feed and the boats main power . sometines there is a 90A fuse in a square
plastic square. Verify you have battery voltage and the orange output lug at the rear of the alt.

 

[betayv]

clean all my contacts?, what contacts, and how I verify the voltage?.

 

[Bt Doctur]

"contacts" meaning where the wires connect. you use a voltmeter to test voltages. you can use a panel light also. if it lights you have voltage.

 

[betayv]

bt doctor thanks, contacts are clean, in the alternator, how I can test the gauge in the dash?.

 

[jayhanig]

I'm not sure I understand the question. You've changed to a higher amperage alternator but that merely provides more amps; not more volts. You say you have a voltage gauge in your dash. It's going to read volts; not amps. At idle with all the accessories off, you ought to be somewhere between 13.8 and 14.3 volts. Ideally turning on accessories shouldn't change the voltage but it normally will drop it maybe 0.1 volts with a healthy alternator.

You can go to Harbor Freight and get a perfectly good digital VOM for $5 when they go on sale. For that price you should keep one in the glove box of every vehicle you own including your boat. They are handy things to have around.

 

[Bt Doctur]

before you test any gauge you need to know the voltage leaving the battery with the engine off, and with the engine running, and with the alt connected to the system and putting out voltage.
Eg: measure the battery , measure the output post at the alt(they should match) , start the engine and measure the voltage again, it must be higher than the static voltage you measured with the engine off.
Now compare to the dash gauge. If they don't match, connect your voltmeter directly to the dash gage and measure the voltage..If the voltmeter reads the battery voltage with the engine running and the dash gauge does not, the dash gauge is incorrect.

 

[Fishermark]

...You've changed to a higher amperage alternator but that merely provides more amps; not more volts. ....

^ Yep. If you are thinking you will get a different reading because you have a higher amp output alternator, then no. The voltage reading will be the same as before. (Assuming your old alternator was working).

 

[betayv]

thanks guys for all your help with this I will find out and will post results, and I understand amps from volts, the old alternator was bad, the bearing was noise.

 

[fishrdan]

the old alternator was bad, the bearing was noise.

The alternator could have been working just fine, even though it was growlin/howlin from a bad bearing. (I've swapped alternator front bearings before, cheap and easy fix...)

I agree with the other comments, time to start troubleshooting with a voltmeter

 

[betayv]

hi guys update on the alternator issue, the alternator have a positive cable and a negative cable I start the engine and used the voltmeter and is showing only 12v, I did what bt dctor said measure the battery with the engine off read 12.24v, I found out something the positive cable from the alternator is a orange cable and was disconnected at the starter lug, I put the cable at the starter lug and I have the same voltage on the battery with the engine off 12.23v at the alternator output 12.23v, start the engine same thing 12v coming on the back of the alternator, another thing I found out like I said I just got the boat and I bought the same kind of alternator that was installed on the boat one wire alternator, now in the same harness is the alternator is two cut cables here is what I have there one black cable connected to the ground of the alternator, another orange connected to the positive lug of alternator was disconnected on the starter lug I connected already and the two cut cables is a red one and a purple cable, what are this two cables for?, please advice as I understand I will said the new alternator is bad because even with the engine running If I measure the volt on the ground and positive lug should have more of 12v.

 

[fishrdan]

Did you blip the throttle after starting, to get the alternator to "cut-in"?

The alternator won't start charging until the engine RPM is raised up to around 1200-1500RPM, then it will continue to charge even if idling.

Having the alternator disconnected from the battery, could have damaged it...... Run the alt down to an auto parts shop and have them test it.

 

[Bt Doctur]

Originally the motor came with the 3 wire alt Orange, black ,red, purple ,your new 1 wire only uses 2 black and orange.per fishrdan the rpm need s to get to 1000-1500 for a second to turn on the alt.

 

[betayv]

ok guys update on the alternator issue I replaced the alternator for another one, the brand new alternator was a defective unit, I used the voltmeter with engine off, and with engine running and I getting 13.5-14.0. by the way the gauge is dead is not moving. thanks guys for your help.