Alternator not charging

[BarryL]

Hello,The alternator on my boat (1986 Newport 28) is not charging. The motor is a Universal M-18 diesel. The alternator is a Motorola 51 amp model. The belt is properly tensioned and the alternator turns easily. There is battery voltage present at the alternator, but no charging output.I have removed the alternator and bought it to a shop for testing. What options do I have if I need to replace it? It seems like marine alternators are expensive, and I have seen prices from $150 or so for a 35 amp model (seems too small) to over $500 for 75 amp models! I don't need anything special, there are only 2 batteries in the bank, I don't use much electrical power, etc. Any suggestions on how to proceed?Thanks,Barry

 

[J.B. Dyer]

Local Repair

Check around for a local alternator/starter repair shop. The basics of the marine alernator are the same as what cars/trucks use. If the parts are available, your local shop can probably rebuild yours at a reasonable cost. I had my 20 year old alternator done last year and it's working fine. Seems like the rebuild was around 120.00.

 

[p323ms]

I went to autozone

I bought a self exciting self regulating 45 amp alternator for about $40.00. It works great. I don't motor a lot but the new alternator has kept my batteries charged all summer. With a gas engine you need a spark suppressor type of alternator. To the best of my knowledge this isn't required with a diesel as there shouldn't be any fumes to ignite.

 

[Bob]

Might be the IDIOT LIGHT

Hi Barry,If the shop doesn't find anything wrong - might be the light. The light on some alternators connects bewteen the battery and the output of the alternator and when thew alternator outputs that shuts off the light. Possible the wire is not connected right or broken. If the battery voltage is 14+ when running = charge.

 

[Ed Schenck]

Tested?

You said that you took it to a shop for testing. Do you have the results? Auto electric shops around here charge about $10. to test a starter or alternator. And they will quote a price to fix them, not much magic here.I bought a 55-amp Hitachi for my Yanmar from E-Bay for about $75. Guys are always upgrading and dumping their old ones. I kept my 35-amp for a spare. But if you do not need the amps I think a repair is the way to go. Then there is no concern about the installation.

 

[Robert B. 19996]

Universal alternator

I went through the exact same thing about two years ago with my Universal engine and the 55 amp alternator. I went to NAPA auto parts and the guy looked up the part number in their Kubota tractor applications. They still make the alternator. (At least they did 2 years ago.) He ordered from Kubota, was delivered 3 days later, for about $80.00. It is the same marine grade that came with the boat. Suggestions for fixing the existing alternator are good too. Good Luck!

 

[Randy]

Same Problem

The key is good diagnostics before you do anything. Do a web search on alternators and bone up on how they work (which terminals do what, etc.), then use a voltmeter to do the testing. I assume your alternator has the regulator built in, as most original equipment ones do. Start testing at the power output terminal on the alternator and any ground - not at the battery. Then do a "field" test. If both tests fail, then at the very least the regulator diodes in the alternator are fried. Could have been from starting the engine with the battery charger on, changing the battery switch while the engine is running, or they just wore out. I had an alternator problem that I eventually traced to a broken terminal where the aternator output wire connected to the starter. Good luck.

 

[BarryL]

UPDATE

Hello,I just picked the alternator up from the shop. According to them, the regulator (external) was bad, everything else was fine. They installed a new regulator ($80.00) and I will install it this afternoon and test.I have a few questions about operation of the battery switch. According to the owner's manual, while the engine is running I can change the battery selector switch from battery 1 to ALL, and to battery 2 without damage. I know if I change to OFF while the engine is running I will damage the alternator. Does that make sense?Also, I found the wire that drives the tach was loose and not making good contact. I don't think that would damage the regulator, would it?Thanks for all the advice,Barry

 

[p323ms]

two types of selector switches

Type one has a gap where there is no load on the alternator when changing batteries!!!! It will blow your diodes!!!!!type two keeps a load on the alternator except when in the off position. My present boat has a type two and even then my wife blew the alternator by turning through the off position. I blew an alternator with a type one switch!!! The boat would only start on battery #1 but #2 needed charging. I thought that if I rapidly flipped to both that it would be alright...wrong!!! You can figure out which you have by turning on a light. Slowly go from battery one to two. If the light dims or goes off you probably have type one switch. Never turn off the switch when the motor is running. The PO of my boat had the alternator running directly to battery one so that the alternator couldn't be damaged. But I now have the alternator going to the positive pole of the selector switch so that I can charge battery #1,#2 or both. Tom

 

[tomfoolery]

zap stop

you should consider installing a zap stop which is a slow fuse to protect your alternator incase you "accidentally" turn off the battery switch . They are not very expensive, compared to rebuilding your alternator.

 

[Gord May]

Zap-Stop

A “Zap-Stop” device is actually a diode, not a “Slow Blow Fuse”. The Zap-Stop Diode is connected between the Alternator 12V output and Ground. It protects against a accidental momentary disconnection of the battery (selector switch “Off”). An “Alternator Field Disconnect” Switch is an auxiliary (pair) contact on the Battery Selector Switch. This “AFD” disconnects the Alternator’s Field coil (without which, there is no Alt’ output), when the Batt. Selector Switch is turned to “Off”. The “AFD” is only used with External Regulators, or Alternators which have accessible Field wires (an Alt’ shop can modify your internally regulated Alt’ to bring the field wires out).ALL proper Battery Selector Switches are “Make Before Break”, which allows for switching between Banks !

 

[BarryL]

Update 2

Hello,I installed the alternator on Friday. The installation went well. I had put a solar charger on the low battery when I removed the alternator, and it was charged enough to start the engine. The tach worked (a good thing) and there was 12.6V at the battery when the engine was at 900 rpm. Revving the engine to 1500rpm gave about 13V at the battery. So everything works fine.I tested the battery switch (with the engine off). When switching from battery 1 to both, and then to battery 2, the cabin lights stayed on and bright. So I must have a 'make before break' switch and I can safely switch batteries when the engine is running.Thanks again,Barry