One of the coarse sights commonly seen onboard boats these days is a row of wall to wall batteries displayed by a proud owner who boasts; "Power?... No problems mate, there's sufficient amps here to supply the national grid of a small African Nation!" However, as we all know, there ain't no such thing as a free lunch and upon enquiring "How do you payment up this lot?" the write back is a knowing smile accompanied by the giveaway phrase, "I all the time run the machine for a couple of hours every day, that's heaps!"
Fine, except for a couple of things. The automotive alternator (usually one of about 35 amp hour rating) is the most widely used source of on board charging devices, along with the poor old 'taken for granted' el cheapo battery charger that seems to be permanently associated to the 240 volt dockside association when the boat is in port, which is commonly permanently in a state of twenty four hour meltdown.
[Regulated High Voltage Power Supply]
The real qoute is that in the majority of most onboard charging setups the systems are incorrectly rated for the installed battery capacity and the net corollary is the inability of the charging systems to adequately get the batteries to payment properly. The corollary of that is wasted money each year and in many cases a severe risk of overheating cables, stressed circuits and the risk of onboard fires. A shortened battery life is par for the course and that leads to the blame being allocated to the innocent party, the battery.
Inadequate charging problems are especially relevant for outboard powered craft that at best yield tiny charging rates for the gear found aboard. Houseboats are typical cases of this syndrome.
The alternator is usually a very reliable law when it comes to battery charging duties but it is very leading to realise they have several limitations when it comes to onboard use. True, they payment batteries reasonably well on a 'day to day' basis but it is petite realised that a diesel machine that is used for battery charging duties can suffer damage by way of glazed cylinder bores when the machine is run with petite or no load. Enter 'Mr Big Bill' following close behind. The maximum run time should not exceed an hour in the morning and one at night. However, if one hundred amps have been consumed and the total input is 70 amps (35 amps x 2 hours) we have a short fall. It is vital that full and allowable charging to 100% capability is maintained otherwise the missing 20% will equal battery damage straight through undercharging. Therefore, it is vital to match 'battery charging input' to 'required amps discharge' usage to profess the status quo. This is known as 'battery load matching'.
Here's a couple of points to bear in mind. When a battery is discharged fast during use, the less the real amp hour capacity is. Excess discharging for the battery extraction rate during use (usually 10 to 20 amps per hour) can give up to 20% less amp hours available. On the other hand, too slow a extraction rate can give you much better figures. issue is, that batteries that extraction too gradually can be very hard to payment if allowed to drop below 50% capacity and issue occurs when 'charge up time' comes around.
So you see, the battery charge/discharge scenario is a bit of a high wire act requiring at best, exquisite equilibrium and systems matching each other perfectly. So what do we look for in alternator outputs? Well, the ample payment rate is dependant on a few things. Battery condition, voltage regulation, engine/pulley ratio speeds. Ideally a battery will require 120% transfer by the alternator to bring it ultimately up to 100% payment value. The 'lost' 20% is due to losses incurred within the battery itself due to condition and internal resistances during the charge-up time.
If an alternator doesn't seem to fully payment a battery there's no earthly use in rushing out and replacing the alternator with a heavy 130 amp job hoping you'll nuke it into submission. Battery charging rates are 'self limiting' and assuredly the best way to do it is at a firm but steady rate with the input voltages monitored by 'smart charging circuits'. That is becoming much more coarse aboard boats today with sophisticated onboard systems requiring constant vigilance and monitoring.
However, back to alternator requirements. spoton matching and maintenance is celebrated to perform the true life of a shipboard alternator. All drives must be correctly aligned and no misalignment of pulleys can be tolerated. They must be of the same width and no abrasion or twisting allowed. Premature belt failure will arise if this is neglected. Drive belt tension is to be maintained. Slipping belts can overheat causing failure and incorrect output. 10mm is the norm. petite known is that the 'under tensioned' belt will also cause belt overheating, stretching, slippage with lack of electrical output.
On the other hand too tight a belt can be a disaster. Bearings will fail due to side loads and belt wear. Large output systems will also need dual belts due to higher corporeal load ratings.
Engine speeds must match the 'cut in' speeds of the regulators and also it must be checked that the maximum machine speed does not exceed the maximum speed of the alternator itself otherwise premature failure can occur.
Alternator Maintenance
What can we do? On the face of it, it assuredly doesn't seem like much can be done but surprise, surprise there's a lot more than you first realise! It's a sad fact that 'preventative maintenance' on an alternator usually consists only of unbolting it when it burns out! Here's a few sensible alternatives to stretch a couple more years out of it!
Check The Belts
Ø Clean
Ø Not twisted
Ø Cuts, dings, nicks or stretch marks
Ø Tension 10 mm not too tight
Wiring Connections (Check Monthly)
Ø Clean
Ø Undamaged
Ø Stiff
Ø Not corroded
Ø Tighten connections properly
Ø Cracked, burnt or frayed
Pulleys
Ø Undamaged
Ø Nicks, powdered rubber, too tight
Ø Loose
Brushes
Every 100 hours remove the alternator and turn the rotor. Listen for any 'rough running' bearings. Check the brushes and get the whole shebang taken to a maritime electrical engineer. Get the following done:
Ø Check the alternator for spoton output
Ø Renew bearings and brushes
Ø Check the diodes!
Further Problems
Many onboard charging problems come about because accepted 'automotive' alternators are used to do the job that is beyond their capabilities. On a vehicle the alternator's job is to replace a relatively small amount of discharged power within a short space of time. When this job is done the alternator concentrates on supplying the vehicles power requirements. On a boat this law invariably runs short as the alternator is required to supply and profess virtually a 24 hour demand, especially in a 'live aboard' arrangement. The batteries are only expensed for one or two hours daily, at best.
The alternator usually supplies a high first payment rate that 'tapers off' during charging and the corollary is usually an 'under expensed battery' about 30% short of its required charge. The write back to this is a fully regulated 'smart electronics' law that can equilibrium and manage differing battery types. Onboard, there can typically be input variables from solar panels, generators, alternators, wind speed gennys and battery chargers. This lot requires razor precision management, juggling lots of electrical balls in the air.
However, for the moment, with many craft, the real underground of sufficient charging is matched input/output voltages, sensible battery matching and a decent maritime alternator that is built for the job and conditions. A decent maritime alternator will probably be 80 amp output, ignition protected (preventing accidental ignition of perilous vapours) decent totally enclosed bearings, encapsulated wiring and corrosion unyielding fittings.
All this luxury don't come cheap but, by golly, you'll be taking the first step in procuring a decent charging law that will punch some life into your much maligned batteries. Matched to a decent maintenance agenda your benefits will all the time be a greater trust in your electrical law and eventually, dollars rattling around in your pockets.
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