Power to the Sailor

[Guest]

My Bavaria 34 has 2x130AH Auxiliary batteries and a 65AH starter battery. The Alternator is 55Amp. I have a Sterling 4 phase 20A charger.

As long as I can get to a marina every 3 or so days I have enough electrical power to run the fridge, lights etc. But past this in hot weather I run out of power.

I understand that the engine alternator regulator can be bridged to provide its max output but unmodified the output falls rapidly as the charge regime is based on a car batterys requirements (falling rapidly to c.10A).

I know the regulator is required to prevent overcharge but this would not be a problem with the battery capacity I have.

I would like to be able to fit a simple switch that would maintain the charge at 55A while the engine is running.

Does anyone know how this is done?

Many thanks

 

[jfkal]

Not so. An unregulated alternator has also a high voltage output boiling off your battery water. If your alternator is the internal regulated "car-type" you can retrofit a smart regulator i.e from Sterling. This will rectify your problem and set you back about 150 USD.

Good luck

 

[billmacfarlane]

You need an intelligent regulator to charge your batteries to full capacity such as an Adverc. Have a look at the following web site: http://www.adverc.co.uk.

 

[steve_cronin]

Some years ago....

... there was an article in PBO on this very subject. In the spirit of that magazine's then "Practical" approach to sailing and spending as little money as possible whilst doing so, they published details of how to manually regulate the output of an alternator. Or see the more recent - "Alternator - converting to manual boost" (Eric Millett Feb 1999 p.66) available in reprint from PBO

You first need to understand how an alternator functions:-

Unlike an old DC generator the windings in which the current (AC & 3phase) is induced are the stationary ones (stator) and the magnetic FIELD is in the moving part (rotor or armature). This rotating electromagnet is energised via the brushes which have proved to be the most unreliable parts of alternators over the years (although regulators & rectifiers- to convert the AC to DC- come close behind). The voltage applied to the rotor is varied depending upon the load drawn by lights, fridge etc by a transistor switch (the regulator) plus a small margin for charging (typically <5amps). In other words the regulation is to balance the output to the current draw WHILST THE ENGINE IS RUNNING. This is OK for road vehicles where there is little if any (these days with parking without lights widespread) use of electrical loads whilst the engine is not running.

Now this is not how we sailors use our electrical power resources but unfortunately marine engines come equipped as standard with a car type alternator. What we need is a system which allows long periods of battery drain whilst sailing and when moored up and then allows a rapid re-charge up to the maximum voltage of 14.25 volts which a lead acid 12v battery will take. Now the "car type " regulator apart from only being sensitive to load only maintains 13.8 volts, the optimum voltage in a car system (you will note that many car accessories such as radios & aux. lights are rated at this voltage). This does not take advantage of the true full capacity of the battery and only charges to about 87% of it.

So we need something which will turn the alternator into a battery charger like your excellent Sterling mains charger (but why does he still use such fiddly imperial thread -BA? - terminals and why do they need to be so close together!)

Now that historical article in PBO showed how to throw away the standard regulator and replace it with a simple variable resistor (wire wound rheostat) to enable you to manually vary the voltage going to the rotor windings and therefore the output of the alternator like cars of the 1930's with their third brush generators). This did of course require constant monitoring of both voltmeter & ammeter but was cheap & simple therfore perceived to be reliable (Hmmmmn!)

Times have moved on and the Sterling & Adverc controllers do it for you and must be considered superior. I would get the Sterling if I were you and talk to the man himself who is a keen boater (albiet motor yachtsman!) about an elegant system incorporating both units on your Bavaria. Our Bavaria (a 42) is in Greece and the fridge demand is constant making this sort of set-up essential. However we cannot change the regulator yet as the engine is still under warranty & Volvo mightn't like it. We had this system on our last boat and all worked very well and was totally reliable! You may need a terminal "M" fitted to your alternator but his will only cost you a fiver or so.

Steve Cronin

<P ID="edit"><FONT SIZE=-1>Edited by steve_cronin on Mon Oct 1 10:56:28 2001 (server time).</FONT></P>

 

[jollyjacktar]

All the advice is good.

I understand your plight and have read the comments so far. All good stuff. Basically you can install switches to pass the voltage regulator which is in series in the field coils circuit switch in replacement resistance. This being either a heavy duty rheostat [25 amp, 3 ohms] which is very difficult to find nowadays or replace it with switched fixed resistors in series , 3 of them of about 1.2 ohms 20 watt or use 3 switched resistors in parallel of 4 ohms and 20 watt. By manually manipulating the switches to each of the resistors you can control the field current and hence the charge current. You will need an ammeter in the charging circuit and need to keep a good bit of attention to the condition of charge of your batteries and not to overheat them or boil them dry.

If you understand the electronics this can be done quite easily and safely. I have even heard of this being worked for years on end with a high degree of satisfactory pereformance if the right care is taken. I read an article somewhere [PBO] I think of an emergency repair being done in some foreign parts, where spares were not readily available along these lines. The resistance used were suitably rated 12v light globes [providing a visual display at the same time] seems it was so reliable that the owner did not bother to replace the faulty voltage regultor when he had the opportunity and 15 or so years later all was still OK.

If all this is a bit too technical and confusing, then the best idea is to use the propriatary items mentioned in the other threads. Unless you are capable of doing this yourself, these commercial options may be the most economical in the long run.

Good luck.

 

[Guest]

Lots of jolly good replies below, but before wielding the toolbox, you should try and add up your load requirements to see what size of batteries and alternator you actually need (or how much you need to cut back on usage!).

1. Add up roughly how many amp.hrs you use every day (try using an ammeter for different configurations, or use the various specs). I bet it is over a 100 amp.hrs (only 4 amps for 24 hrs!). Then think about how many hours you are likely or willing to run the engine - if this is less than 4 hours a day with your alternator, you are in trouble without another power source.

2. Batteries have a limit to how much charge they can take at reasonable input voltages (lets say 14.4V max with a smart charger). Your 260 amp.hr bank can only be charged at a max of about 40 amps at 3/4 charge and 75 amps at half charge. A "standard" 14.0V alternator is about 20% less. The advantage of a smart charger is they force batteries to take maximum charge until they reach the higher voltage, and then drop to a lower voltage after so long to avoid boiling them. This is very good, but it does not compensate for a completely undersized system. So the first step is to have a big enough alternator. 55 amp (which is the max rating) is only likely to charge at about 30 amps when you take off the boat load. If you run a fridge all the time, you probably need a 80-100 amp alternator (the best type being the dual output version from the likes of Balmar - no external diodes).

As an aside, if you have external diodes now to split between the house and starter battery, but the sensor wire is not attached to the bank directly, you are completely stuffed! - check the voltage on the battery with a digital meter when running - if it is not nearly 14.0V a very quick fix is to attach the sensor wire to the house bank positive somehow (not always possible unfortunately with some alternators). If it is something like 13.5V you can run the engine until the cows come home without much effect.

3. You should not plan to drop below half charge a lot as this will greatly reduce the life expectancy of the cells. So that means you should not draw much more than 100 amp.hr between charges. This may mean running the engine several times a day. To go for several days without much engine running will require a bigger bank (say 400 amp.hr).

If all this sounds heavy (maybe literally), then a large wind generator may seem like the answer if your winds are reliable (ie often over 10 knots). It's something you can take off when you don't need it. If you sail a lot, then maybe a towed water generator would be the ticket (I really like this idea myself).

 

[jfkal]

Was evaluating the Adverc. Seems quite good. But their sales people did not bother to respond, so I bought a Sterling