Another alternator question

[Kerry13709]

I took my suspect alternator off my Perkins Prima 50 to have it bench tested. It is not putting out at all. The tech said it was a Lucus, and only about 40-50 amp. I have two 4d gel cells in my house bank, and he said an alternator was not designed to charge this much battery. (400 amp plus starter battery) I know there are lots of you sailers out there who cruise to places where you have to depend on the alternator to bring the batteries back up. Is therea an alternator I can replace my current one with that will do the job? If a lot bigger, in the 100 plus amp class, do the wires that go to the starter and to the battery need to be up-sized?

 

[abe]

Look up Balmar for larger alt/regulator...

40-50 amp alt too small for 400amphrs. Balmar has bigger alt/plus smart regulators. Also consider a honda2000 generator. It will provide about 75amps plus you can also use it to heat up your water heater and other ac stuff.abe

 

[jviss]

Please!

No air cooled, deck mounted generators in the anchorage! I've used my air horn to counter this. Seriously, I was enjoying a sunset in Mattituck Inlet last year and someone came in, dropped the hook and then fired up a transom mounted air cooled generator, distrubing EVERYONE'S evening - it was going like the hammers of hell! Hamilton Ferris sells good, high output alternators at reasonable prices, along with regulators, etc. They also carry wind and solar stuff.

 

[Ray]

Balmar is one of many ways to go.

We had a Balmar 100 amp on our 38. It is about as large an alternator that you can run with a single fan belt. If you already have two then you're in fine shape there. The new alt must also have a similar bolt pattern or some modifications are required and this is not so easy. Alignment of the belts is very critical along with all the pulleys being of the same angle, depth and size. Some expertise very helpful. And lastly, your voltage regulator invertor/charger must match in output. Call in the experts on this. It might be time to have your alt rebuilt and a solor or wind gererater added to supply the extra output. We have 400 watts of solar and a Air-X wind gen and the system very, very seldomly needs the engine run to meet high power demands.Ray

 

[Fred Ficarra]

Kerry, tell the tech thanks. Then find another.

A simple rebuild will probably get it going. By simple I mean a set of brushes. While they're in there have the bearing replaced. If it worked for you before then that's all you need. If you do it yourself, $5.00 will fix it.

 

[Gord May]

wire size

A 100 Amp Alternator should be wired (to batteries) with a minimum wire size of #6 AWG copper, depending upon circuit length (Alt to Batt’s and back). For instance, a round trip circuit length of about 12 feet (6' each way) would suggest #4 AWG wiring, and longer ccts would require even larger yet.A 50 A alternator may have been wired /w as small as #10 AWG.Wire Size Chart (pg. 1):http://cruisersforum.com/photopost//showphoto.php?photo=1321Wire Size Chart (pg. 2):http://www.cruisersforum.com/photopost//showphoto.php?photo=1322“Ohm’s Law & Boats”http://cruisersforum.com/showthread.php?s=&threadid=372

 

[Bill Roosa]

Get a new stator winding

If you look around on the net you can find a bolt in replacement for you alternator stator windings. Those are the wires that fit around the outside of the rotating rotor in the alternator case. By just changing the stator you change the output of the alternator. I did this on my auto in about 1.5 hours and went from a 30 amp to a 100 amp output. Don't go over 100 amps without adding another belt however. If you are a good electrician you can just change your existing stator from a "delta wound" to a "Y wound" configuration and get a 75% increase in output. This will require that the alternator pullys get changed to make it turn over faster however.

 

[newly anonymous]

disagreeing with Fred

Your mechanic was right. A rebilt Lucas 40-amp alternator is going to take hours upon hours to charge a set of 4-Ds. By the time it gets even close to an 80% charge, it will be running so hot you'll be lucky to be getting 8 amps out of it.Go with the Balmar. You'll never have to worry about running the refer at anchor again.

 

[jviss]

One step further.

John is right, and I also disagree with Fred. A rebuild is not going to make the alternator have higher capacity. That battery bank calls for an alternator in the 100 Amp neighborhood. Figure that flooded batteries have an acceptance rate of about 25% of their capacity.

 

[Mick]

Alternator

The main problem with keeping the original is the regulater. It is probably internal, and not really reccomended for 'Gel Cells' as the out put is not of the proper voltage for charging gels. If you only have a single belt you are limited to around a 100 amp unit. Get an alternator with an external regulater. These are 3 stage, and can be set for the type of battery being charged. They also come in dual models that can charge 2 different batteries.

 

[Fred Ficarra]

Oops,

I didn't notice his bank size. Yep, get a bigger alternator. But first see if you can install a larger stator. With a Lucas I'm not optimistic. But still, if it worked for YOU, before,,,,, Nah, replace it. It's a Lucas.

 

[jviss]

Lucas...

...Prince of Darkness.Fred, if you get to maximum excitation, i.e., a saturated field, you've hit the maximum output of the alternator, regardless of how big the stator is. At that point additional load will make the alternator output voltage drop. So, you won't melt the stator, but you won;t get any more output, either. Better to size up the whole alternator.

 

[ruedi ross]

Lucas...

Do you know why the british drink warm beer??They all have Lucas refrigerators.

 

[Fred Ficarra]

JVISS

True, but like the guys pointed out below, a larger stator puts out more juice before it's 'saturated'.  So, is Lucas still in business?

 

[jviss]

Don't know...

...if Lucas is still around, but they did the electrics on my Land Rovers, adn I curse them daily for that.Fred, it's the rotor, the electromagnet that saturates, and therefor limits the current output of the stator - which is perhaps what you're saying. So, yes, with a larger stator you can get ot the limit of the rotor withoug melting hte stator. Any more current output will reuqire a bigger rotor (field) magnet.

 

[Fred Ficarra]

But bigger electromagnets are not done. It's the

stator that's swapped. The magnetic field capacity isn't modified for increased output. Only the stator.

 

[jviss]

O.K.

Fred, I give up. First, I can't even understand what you mean in the last message. Imagine this - size the stator up to "Big Alice" size, and leave the rotor size alone. How much power do you think you can get out of that thing?Once you saturate the field, meaning you're at the limit of the strength of the magnetic field, it doesn't matter how big the stator gets, you're not getting any more current out of it.

 

[Bill Roosa]

Jviss. It is a more turns of wire thing

A higher output stator will have more turns of larger diameter wire. Since you know that magnetic fields can't "get used up" the regular rotor field is now cutting more wires and that means more EMF (electromotive Force). The amount of toqure on the rotor is an issue when you "Big Alice" the stator however. I saw one just shear of the shaft as the back EMF acting on the rotor was just too much for the little guy. Made a big mess of the housing when it broke too.

 

[jviss]

Agreed that it's a turns thing,

I understand the principle Bill, thanks. I think you actually have it backwards, though. For induction machines, the stator current would go down with increased stator turns, for constant rotor current and rotor turns. Higher output alternators have larger wire, often square in cross section, along with heavier rotors.

 

[Capn Dave]

Don't bother rebuilding

That Lucas alternator, You can count on anything Lucas makes not to work. Just ask anyone that has a British made car with a Lucas electrical system. It's just a matter of a short time until something breaks.If the gel cell batteries were installed with the internal regulator, you might as well throw them away. They are toast or so close to it, you will not have power when you really really need it. It is part of my three o'clock in the morning therory. Just start all over with a new alternator and a set of batteries. Throw away the gels and get lead acid T-105's or if you have lots O boat bucks go with AGM type. With the T-105 you will not need a special regulator. You can even get by with a regular alternator with AGM types. It just cost boat bucks.Fair WindsCap'n DaveFair WindsCap'n Dave