Anyone replaced the diodes or rebuilt their Alternator?

[jrowan]

Hello, We were out sailing on this fine day on the Chesapeake when I noticed that our Universal diesel was a lil' hard to restart at the end of the day, due to low battery power. I beleive that the batteries are not more than a few years old - two set in parallel wiring. The diesel should have charged them, but they are only reading 12.3 volts without charge, and only 12.8 under power. I believe that they should be charging at more like 13.2 or more volts under power from the alternator charge. I suspect that my original unit may have bad diodes, since it is so easy for them to blow out if the house switch is turned off under power. Anyone replaced their own diodes, and/or where did y'all take your alternator to be rebuilt? A new marine alternator is really expensive, so I hope I can have one rebuilt for less than $200. Although I do recall that the origianl Amp meter can reduce battery capacity greatly due to the inefficiency of the long length of wiring to engine panel gauge.:neutral:

 

[shipwreck66]

No matter what conditions, your batteries are only reliable for about 3-4 years. Before you start messing with diodes it sounds like it's time to replace, I did mine 2 months ago and all problems disappeared. Chesapeake is a cold areain the winter, hard on batteries, even on maintainers.

 

[DanM]

J,

I'm one of many that struggled with weak starts with the stock Catalina wiring and you're describing just what happened to me when I first got my '85. Maine Sail even uses our vintage C30 as the way NOT to wire a starting circuit!

Voltage isn't a great indicator of state of charge, at least in the way that we usually check it so it's difficult to tell what's going on exactly just based on voltage alone. I'd recommend Nigel Calders "Boat Owners Mechanical and Electrical Manual" if you don't already own it for some of the best troubleshooting advice I've ever seen.

My guess would be that your boat is wired just like my boat was, with #4 SAE wire to the starter and for the ground wire. This wire is woefully undersized. It probably worked fine fresh out of the factory but add in 30 years of corrosion and we're lucky it even turns over. Maine Sail has recommended replacing it with 1/0 AWG and reports that the engine turns over as though there is a new starter installed. I paralleled my original #4 SAE wires (both positive and negative) with new #4 AWG marine wire and the difference in starts was significant. I should have just replaced with 1/0 AWG but I didn't know it then and it's "on my list" still.

An alternator shop could quickly check out your alternator for you but if you can bring the batteries up to full charge and then put a meter on the alternator output you can see what it's really putting out. In my case (Universal M18, Motorola 35a alternator) my alternator is putting out 14.0vdc. 14.4vdc would be even better, but that's a whole other topic.

I have eliminated the run to the cockpit ammeter and ran a #6 AWG wire directly from the alternator to the starter/battery positive cable to eliminate all that voltage drop out to the cockpit and back for better battery charging.

I would definately suspect the wiring prior to spending any money on alternator parts or batteries. If corrosion and undersized wire isn't your problem right now it will be eventually and really it's the simplest of places to start. I wasted so much time fiddling with other things until I rewired (and cleaned contacts and checked connections of course) that I should have just started with the rewiring and saved myself a few years of frustration thinking I had starting/charging problems.

I got 7 years out of my last batteries but I'm in a warm climate but I sort of baby them. Your cold winters combined with not bringing them up to full charge if (which you wouldn't be doing if you're only getting 12.8v to them) could certainly kill them much quicker, but I'm no cold weather battery expert so that's just speculation on my part.

I like genuinedealz.com or gregsmarinewiresupply.com for great wire prices and they will even properly install the lugs for you so that they are secure and not a source of additional resistance.

If I were to start over I'd run 1/0 AWG with proper lugs for both positive and negative sides of the starting circuit. Then I'd change the alternator output to elimiate the run to the cockpit with short #6 AWG wire to the starter. Then I'd have the batteries load tested and brought up to charge with shore power if possible before reinstalling them. At that point you could start the engine and check alternator voltage and you'd really know just where you are. Less than 14vdc at your alternator at this point then would lead me to further investigation of the alternator.

Hope this helps in some way, I look forward to seeing what you end up figuring out with your boat!

 

[Stu Jackson]

Dan summarized it quite well.

See see alternate alternator sources: http://c34.org/bbs/index.php/topic,5686.15.html

 

[Old Skool Neil]

Getting back to marine alternators and their cost, it's true they can cost a pretty penny but depending on your needs or preference, they needn't be all that expensive.

For example, I replaced my working, stock Motorola 35A alternator with a brand new Delco 10Si 100A single wire, fully marine ignition protected alternator that cost approximately $75. I was skeptical at first over the price and the single wire concept but it has proven to be a real performer with excellent output at low RPM. The only modification I've made to it was an AC tap for the tachometer.

 

[foolproof]

Neil:

I too replaced my old Hitachi alternator with a single wire marine 45A marine alternator, though I paid a bit more than $75 (but not much).

Tell me more about to AC pickup for the tach. I replaced the engine panel and now have a tach, but I'm not sure how to power it. Please elaborate!

Mike

 

[Old Skool Neil]

Big hijack (sorry)

There are basically three types of signals by which tachometers function: mechanical drive, ignition coil for gassers and alternator AC tap. Note that a tachometer is manufactured for a particular type of sensing.

I recently bought an alternator type tach on eBay and had a tap installed in my alternator by a local shop ($20).


Due to pulley ratios, the tach has to be calibrated after installation. I used a non-contact optical tachometer tool to do mine. There's a calibration screw on the back of the tach.
http://www.harborfreight.com/digital-photo-sensor-tachometer-66632.html

 

[jrowan]

Thanks for the input. I had a feeling that the ampmeter wiring connections and excessive cable length to the engine panel may be causing the voltage drop. Although when I first start the engine in the morning, after the glow plus have been run, it will fire up immediatley, without hesitation. The batteries are topped of with shore power connected to a 3 stage automatic charger, so they have plenty of charge initially.
I only run my GPS & sounder during sail time, so that shouldn't be much power draw.
I suspect that the problem may be in the wiring. I have been planning on taking out the ampeter anyway. The shortened length of cable should definitely help. My old Yanmar didn't have any gauges, & it was probably better off without 'em!

 

[DanM]

J,

I've found I can live without my cockpit ammeter just fine too!

I would suggest though that if you've got those #4 SAE positive and negative cables between your engine and battery though that that will be the biggest problem with weak starts. Changing the alternator output wiring was one of the last things I did on my boat and although it certainly makes some difference in the ability to charge the batteries somewhat quicker, it was the battery cables that solved my starting problems.

Good luck with the upgrades and let us know how it goes!

DanM.