Lectrix again

[Yoda]

This is not my experience.

 

I can't see it can be quite this clear-cut as the above statement, as obviously it's the RPM of the alternator that really counts, and how that relates to engine RPM will clearly depend upon the relative size of both pulleys fitted.

 

Snibble identified mine as a Lucas A115 45 amp model, and to my untrained eye, comparing it to pictures in a BMC manual, it doesn't look like pulley sizes have been fiddled to make it turn faster for marine use.

 

Although I have no rev counter, I can confirm it will start to charge at little over tick-over, and exhibit as good a rate of charge with the engine running at slow speeds, as when being pushed much harder.

 

If you search previous threads, this is one of those topics the experts are firmly divided on. Some have sworn that a basic alternator, not supplemented by any external controller, will only really charge well at high engine revs. Many others have reported practical experience that contradicts this, saying that they get a fairly constant rate of charge from low revs upwards. (I think somebody quoted real measured numbers, but I can't immediately find that thread).

 

I fall into the latter of those 2 camps. I belive Moley's setup is much like mine, although he has a rather more powerful alternator, I think.

 

That is the reason I stated engine rpm as I cannot tell what the alternator rpm is, without checking the ac frequency. It is probable that the output is not fixed frequency so that would be even harder. Without measuring the pullies you cannot know what the alternator rpm charging point is. Suffice to say that at the engines maximum rpm the alternator must not exceed its max rpm and that it has to charge above engine idle rpm.

 

I would be interested to know the full specifications of the alternators used and that way you can size pullies accordingly as well as run the engine in the charging band of the alternator.

 

The best guidence is to attach a voltmeter to the output side (or where the manufactureer states) to read the output voltage, to ensure the 14.5 volt minimum.

[Yamanx]

The best guidence is to attach a voltmeter to the output side (or where the manufactureer states) to read the output voltage, to ensure the 14.5 volt minimum.

 

13.8v is the minimum required, upto 14.4v.

[bottle]

 

13.8v is the minimum required, upto 14.4v.

 

And I expect that Moleys alternator is elderly, before the newer higher voltage were available, so will be designed to give only 13.8v.

[alan_fincher]

And I expect that Moleys alternator is elderly, before the newer higher voltage were available, so will be designed to give only 13.8v.

I'm not at all sure about that.......

 

As I've said, I've a similar BMC setup to Ade, but with an almost certainly lower specced Lucas alternator. (Mine identified as 45 Amp - Ade said his recent replacement was 70 Amp, I think).

 

Mine shows no evidence of being any newr than the original engine build (197x something ?), and has definitely not been replaced since the engine was marinised 11 years ago, (same green paint over everything).

 

I know, because I measured it during the previous debate about charging losses due to inline ammeters, that mine puts out a pretty constant 14.3 volts, irrespective of the state of the batteries. (Checked on 2 different voltmeters).

 

I'd be fairly surprised if working correctly if Ade's alternator shouldn't be outputting over 14 volts, and probably closer to 14.5 volts. We need the experience of the hamster on this one, I think.

[John Orentas]

The voltage is fairly academic anyway you need to measure the current. The best way to get good reading of output is to load the system with as much as possible, headlight, water pumps, hair-drier etc. Make sure it will ballance the load, measuring the current with just a charged battery connected will tell you nothing.

 

With my 3 fully charged batteries the charge rate is no more than 4 amps but it will ballance at tick-over with every appliance I have turned on. approx 50 amps.

 

Otherwise find a flat battery and connect that on it's own but don't expect to see more than 10 or 15 amps.