Re: 175 amp alternator on SM-burned up battery bank.

ronpische <andrew@...>

Hi Alan

I will be very interested to hear what you get back from Leece Neville and your own experiences when you start to modify the alternator - I will wait on this before I do anything I think.

Unfortunately there are times that one has no choice but to motor and all the better if we can use the motoring most efficiently also in terms of battery recharging / management.



--- In amelyachtowners@..., "alan_leslie_elyes_sm2k" <divanz620@...> wrote:

Hi Andrew,

The reason you need to keep the belts tight is that shortly after start up the alt is putting out max current..these alts are 175A...which at 24 V = 4.2kW = 5.6Hp..that's quite a lot of power !!

I don't know anything about Sterling regs, but looking at their instructions they appear a little simplistic, although verbose at the the same time.
I'm not so sure about their rewiring descriptions for N alts.

The big difference between P alts and N alts is that in N alts there are field diodes (aka diode trio) that supply current to the internal voltage reg.
ALL external regs are P-type so N alts need to be internally rewired to deal with this, which as far as I can work out, involves removing the diode trio and then grounding one side of the rotor (field) and connecting the other side of the rotor (field) to the field connection at the external reg...

BUT I'm awaiting confirmation of that from a techo at Leece Neville, before I start to tear down the alternator.

But in essence, yes we need a proper external 3 stage reg to deal with this, and my only thoughts as to why Amel didn't do this is are
1. They didn't understand it
2. They didn't anticipate Amels motoring for days

--- In amelyachtowners@..., "ronpische" <andrew@> wrote:

I am very interested in this as I fitted one to my last boat - it involved some modifications to the alternator and I had to be more vigilant about keeping the belt very tight, but it ran without fault for the 8 years that we had our last boat. I installed a regulator from sterling power see . Although the instructions that come with it would not win any design prizes, they were very informative about the setup and also how to modify the alternator also they work for both N-type and P-Type alternator regulators.
I was surprised in some ways that a similar regulator is not fitted to the Amel SM - but had also wondered if there was a good reason why not? Anyway I think I plan to install one sometime soon.

Ronpische SM 472

--- In amelyachtowners@..., "alan_leslie_elyes_sm2k" <divanz620@> wrote:

There is an internal regulator..there has to be othere wise you wouldn't get a constant voltage.
This is how internally regulated alternators work...they run at (in our case) 28 odd volts all the time...the current falls off as the batts get charged....problem with that is that over a long running time (like we motored 54 hours from Noumea to Port Vila last week) it stays at 28 odd volts and this will lead to the batteries gassing..i.e. boiling off electrolyte...too much of this will eventually kill VRLA batteries (like AGM or sealed calcium etc).

What we need is to modify the alternator to remove the internal regulator...which is not so easy on these Leece Neville / Prestolite alternators as they are N-type, (which means the reg is on the negative side) and wire an external 3 stage reg. External regs are nearly ALL P-Type.
I'm having some discussion now with a tech from Leece Neville about how to do this.

There's nothing wrong with the Balmar external regs...but my choice would be Next Step from AmplePower...they make a number of different types, but the scenario for most (including Balmar) is :

1. Reg off when engine starts so no load on the alternator.
2. After 30 secs, reg gently loads up the alternator until its at either full output, or the max the battery bank will accept.
3. This "full" output current continues until the voltage reaches the absorption voltage (preset) say 28.8 Volts for a 24v bank.
4. the reg slowly backs off the field drive to the alternator to maintain the voltage at the absorption level
5. After a preset time or when current has reached a preset percentage (say 5-10%) of the banks Ah capacity, the reg switches to float...approx. 26.6 V

This ensures that the house batteries are properly charged and prevents gassing.

This is the way the Doplhin chargers work, much better to charge the batts with the genset than the engine in it's standard configuration.

When I get all this figured out with this peculiar N-reg Leece Neville alternator, I'll post the details so everyone can do it.

I don't like the idea of the batteries sitting at 28.8V for's not good for them !


--- In amelyachtowners@..., Sailorman <kimberlite@> wrote:

I had my alternator checked at a very excellent alternator shop and the
owner showed me what happens as it runs. There is no internal regulation.
However he said as the battery becomes more charged the resistance of the
bank increases and the alternator puts out less and less amps . It has a
constant output of about 28.5 volts. He said the Balmar smart regulator is a
waste of money -and he sells them.

I had no problems with this alternator with my first set of batteries for 4
years. I only changed the batteries after a lightning strike.

My current burned out battery bank must have been caused by the charger. I
will test it when I get my new batteries next week.

Fair Winds


Amel Super Maramu #376 Kimberlite


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