Alternator Issue

[turbolicious]

Hey Guys, I would like to fist say this is a great forum for supra info, I am a new Owner of a 1987 supra comp with 700H, run like a charm, 351W. I am in Quebec Canada so boat usally dont stay in the water all year long, , i will post picture soon, I have did original decail and I am working on my custom tower.... Mine will be KILLER :)

Anyway My alternator his new, previus owner change it!, The voltage when I am running is 14V, When I idle for 3-4 minute, the voltage drop to 9-10V, as soon as I give gas it come back up to 14V, I have a new baterie all conection and power cable are new. coult it not charge at low RPM?

Do you guys think the alternator was not properlly rebuit, or meabe the guys pu a car alternator??

Thanks Simon

[Salty87]

hi simon, welcome to the site

there's no telling what a previous owner is capable of.

your alternator doesn't sound too unusual. my alternator doesn't put out much until i'm over 1200 rpm and then it's close to 14v.

you can get it bench tested if you think it's not working right. any auto electric shop can test it and repair it. they can tell you if it's marine or not too.

[turbolicious]

Ok thanks, it just seam like the boat should run on the alternator, does your boat run funny when this accures? mine seam like it would like to stall but it dosent

Is the gage hook up on the alternator, to get that much variation in volt or it's on the batterie?

thanks for the advise

[Salty87]

it wants to stall below a certain rpms?

you can't tell on my boat when the alternator kicks in unless you use a voltmeter.

[michael hunter]

Turbo
Welcome to the forum. What RPM is your engine running when the voltage drops?
Are you using the dash gauge or a separate volt meter at the battery?
Did the previous owner put a marine alt on? Is it the original brand alt?
Can you take some pictures of your alt ? While you have the camera out take some
of the boat to. We love pictures here.

[turbolicious]

It running at about 600-700 idle!!! I am using the original gage, I had it out today and it seam to work fine, only When the radio is running for a long time relaxing on the water with the motor stoped- the light (AMP come on! but boat start and run strong

I will take picture of the alternator and the boat as well

[comeoninracing]

how many wires connectto the alt? if there is only the main one on the back of the alt, thats called a one wire alt and are very know for not charging at low rpm's

[87SunSportMikeyD]

Hey turbo. My alt just went out. The boat ran fine with the alt removed and did not die as long as I had my two batteries charged (took them out at the end of the day to charge). So if it is dying it's prolly not the alt. But if your batteries aren't getting 14v while you are driving there could be an issue there.

[turbolicious]

how many wires connectto the alt? if there is only the main one on the back of the alt, thats called a one wire alt and are very know for not charging at low rpm's

Yes it;s only one wire I am taking picture tonight

[turbolicious]

comeoninracing :

I Did not have my camera with me, i have look closelly and my alternator is a watson Marine Aprouve ALT! There is 2 conection in the back( to the black Seal box)

One of the Pin have a Yellow wire conected to a Green Wire on the main harness in the engine, That wire was cut by the previus Owner, i have a modified rotor with coil ( To remove the original point in the cap)I dont know why it got cut, but I assume for a reason???
I belive when running the boat only uses the ALT and not the batterie, it shows low voltage but baterie at 13.5 using a voltmeter... I am confused!!!!

The boat run good, but as soon as I let the fuel down to pick up a rider, the light and buzzer come on as Low Voltage.

Can you pleases advise me, if you really required a picture i will get one..

Thanks

[87SunSportMikeyD]

Turbo - I'm not an expert but from what I have heard the alt does not put out as much charging power unless the rpm's are running higher. At idle it is charging, just not as much.

Make sure your battery cable connections are very clean and very TIGHT - tighten them with a socket set as tight as you can without breaking. Make sure your battery cables aren't too old. If they crackle when you flex them they are no good.

The low power warning light/audible buzzer still come on in my boat if I am idling and I have lots of things running, ie stereo, motor, two blowers, fat sac Simer pump. It goes away when I turn things off or increase the RPMs.

I have heard there is a way to turn down the sensitivity on the buzzer/dash light but I have not found it myself.

[saltare inverts]

There is a control brain for warning lights etc. under the dash. You can change setting on it. Mine is mounted way up high above ignition switch. Easy to miss.

[turbolicious]

ok thanks Guys, i will try to adjust the alarm

i was mostly wonderring Why that green wire got cut?

I will look at calbe again but the all seam really new, i think previus owner was also tring to fix tht problem by changing theses parts randomelly

[87SunSportMikeyD]

Well your older alternator was probably a three-wire model. The new models are usually a one-wire model although you can get a three wire still. Not much difference really. See this link.

http://www.db-starter-alternator.com/Alternators/Marine/

Here is my recent thread about alts
https://forum.supraboats.com/showthread.php?t=4171&highlight=alternator

Here's a quote from Ron at DB electrical about three-wire versus one-wire alts. He is very helpful and I would not hesitate to call him if you wish. In fact this may be your issue right here. Maybe your one-wire alt is causing the light/audible alarm to go off.

"Yeah I should've just called them a long time ago lol. Ron at DB says either alt will work fine. But if you have a volt guage AND a light, you want the three wire to make both work. He said if you do get the one wire, the light will stay on all the time, so you should just disconnect it. But the guage will work fine. So there we go, getting the three wire. Thanks all!!!!!"