alt not charging till you rev it
 

I have a goofy charging question. The alternator does not charge when you start the boat until you rev it boat slightly (to about 1750 rpm). The it is like the charge circuit gets engerized and it functions fine. (until the engine is shut off, then same deal). Only reason I even care is that the elect. fuel pump (carb Volvo Penta SBC) is energized by either the starter or the alternator. So if you start it and just let it idle it will run the crab dry. Is the alt bad? I can't imagine it came like this from factory. (it is a 99 and has been like this since I bought the boat about 18 months ago.

Re: alt not charging till you rev it
 

Take it to an electrical shop and have them test it on the bench. Sounds like the stator is going bad. or could be one of the diodes is acting up.

Re: alt not charging till you rev it
 

I had 2 Mercs that did the same thing...replaced them...trouble gone... case closed :D

Re: alt not charging till you rev it
 

If you have a delco marine alternator it will act like that if you have the large pully.If you use the small pully you will burn bearings out prematurely if you run high rpm.The delco is a popular swap for many applications such as marine or jap cars.The conversion kits for cars usually come with larger pulleys.My local alternator shop swaped my mando (OEM MERC) for a Delco and it kept burning out prematurely.He was insistent upon using the small pulley so it would charge at idle.I did some basic math and the bearing was not rated for the RPM it was seeing at high engine speeds.I showed my alternator guy the bearing spec and he told me the SKF bearing book was incorrect and the bearings he was using were better.He told me the belt was slipping due to loose tension.In actuality the belt was, but it was so tight you could bounce a dime 10 feet in the air of it.The only reason I brought up the bearing issue was because there is a lot of second rate korean crap out there.I hate it when you you can't talk sense to people(over speed bearing=burn out).Any how I got a larger pulley elsewhere and installed it and no more slippage or burnt bearings with normal belt tension.The down side is the alternator acts as yours does.Not a big deal in a performance boat.

Re: alt not charging till you rev it
 

And last, but not least, measure the voltage right at the battery. There may be a voltage drop in the circuit going to the gauge. (I had a similar problem and found a bad crimp on a terminal). Another reason could be a bad battery.

Re: alt not charging till you rev it
 

you one of two problems.

1. As mentioned obove, you have a one wire alternator that needs to hit a certain RPM before it will self excite.

2. You have a stock type alternator that the exciter wire is not activating the alternator. Most alternators will self excite if you spin them fast enough.

Remedy:

1. Take your one wire alternator to a electrical shop and have it converted to a externally excited version. The you will have to run an exciter wire to it.

2. Find the problem with your existing exciter wiring and fix it.

Steve H

Re: alt not charging till you rev it
 

The alternator is a " Mando and it is not a 1 wire deal, it has like 5. I went to a local alternator/starter guy today at lunchtime and asked him about the issue and heis advice was to bring him the boat and he will "trick wire it" to make it charge. Yuck. I am not doing that, I don't like the idea of messing with it like that. I am pretty anal about stuff and want to fix it correctly. I have a factory manual and I will see how good the wiring schematic is and try to troubleshoot the wiring. Steve, I take it the exciter circuit is the one with an "E" on the back. :-)

Re: alt not charging till you rev it
 

If it's a Mando you should just buy a new one.
$125.00 for the 65 AMP unit.

Re: alt not charging till you rev it
 

I repeat, and I have Mando's, check the voltage at the battery before diggin deeper. I replaced voltage regulators at 65 a pop and didnt need them.

Re: alt not charging till you rev it
 

Formula, I have dual batteries and the voltage seems about same everywhere, so I assume all connections are happy. You replaced them for allow voltage that didn't really exists? It defiantly does not charge and the dash gage is close to the measure at battery with digital voltmeter.
I got a electrical factory manual yesterday and it said to measure the voltage at the EXE terminal (I assume excite circuit) with key on and engine not running and it should be less than a 1.0 volt different than battery. Mine was about 2.5 so I thought Erika I found it, bad connection in sense line (like Steve said)/. Cleaned every connection I could find in the circuit and when I rechecked it was about 0.9 volts delta. Less than the manual said. Same issue, no charge until you rev it once then will idle at 600 rpm and charge all day. Then I jumped the excite wire and gave it the same voltage from the battery.....same deal, no charge until you rev it once. Where can you get a Mando for $125? I will repalce it if I think that will fix it but hate to start throwing parts at it.

Re: alt not charging till you rev it
 

Ive got a brand new one you can try. Let me get the numbers. If it works out for you, great. Ill see what I have in it.

Re: alt not charging till you rev it
 

Merc # 817119-2 55A Vendor # AC155603 Mando. It has v-belt pulley. Ill bet your 99 has a serpentine belt. Oh well. If this wont help ya check ebay or boatfix.com

Re: alt not charging till you rev it
 

You only need three terminals to make it work correctly. The upper right is the main out put terminal "B". That is were the big hot wire goes. The lower right is the battery sense wire "S". This is what the alternator uses to sense battery voltage. It can be hot all the time. The terminal to the left of the "S" term is the exciter wire. on this particular alternator it is marked "EXC". I suppose it could be marked with an "E" as well. This wire should be power on when the engine is running and off when the engine is off.

Steve H

Re: alt not charging till you rev it
 

Yup that is exactly like mine Steve. Mando 65 amp. I have a solid 12 volts at all three and still same goofy no charge until it self energizes. I have a ground used and a feed for the 12volt electric choke element. So that being said do you think there is something wrong in the regulator making it do this?

Formula31, I have a v belt as well. (Volvo Penta used v belts later than mercruiser). You wanna sell it just let mer troubleshoot with it? Either one would be a benefit to me.

Re: alt not charging till you rev it
 

Either way. I bought it as a spare but your welcome to troubleshoot with it and if it works and you wanna keep it, Ill sell it. Let me dig a little and see what I paid for it. Was cheap. rogue2800 *hotmail.com