The Problem

The Cat320 has been built with a variety of engines but they all have inadequate charging systems. Unless you motor for hours each day, the combination of a small (55amp) alternator and an internal automobile-type regulator will not replace the amp-hours used daily to power the refrigerator and other 12 volt hogs that we want to tie into our electrical systems.


Submitted By John Langford – “Sabbatical2” #172


While consumption will vary, the average cruiser can easily use 50-60 amp-hours over a 24 hour period. Even under ideal circumstances, the solar panel option sold by Catalina will not add much more than 6-10amps hours per day. When facing a deeply discharged battery, the internal regulator that came with the alternator on the Perkins 30 produces about 18 amps at the outset and after about 5 minutes tapers down to under 10 amps. With this regime, if you don’t plug in almost every night or motor instead of sailing most of each day, your batteries will soon be flat. The sailing cruiser, therefore, either has to improve the charging capacity of the engine or plug into shore power at least every couple of days.


The Solution:

Unless you want to try a wind generator or cover your boat with solar panels, you have two upgrade choices:

(1) to improve regulation by replacing the internal regulator with an external one designed to make the existing 55 amp alternator work hard enough to bring back deeply discharged, deep-cycle batteries;

(2) to fit a new, more powerful alternator and a new external regulator. Please note that a more powerful alternator always requires the addition of a new external regulator.


Let’s look at both options.

(1) Replacing the internal regulator

If you want to try improving regulation first before investing in a more powerful alternator, one route is to install a device like Cruising Equipment’s Amp Hour Plus Two Monitor and External Regulator. The monitor isn’t essential, but it is one of the great toys of all time, allowing you to keep track of all current flows in and out of both batteries. The key piece of gear is the smart three step, external regulator which forces your alternator to earn its keep. In the case of the Perkins 30, for example, the external regulator makes the Lucas alternator produce up to 40 amps per hour in the early stages of recharging then slowly taper down the charge in steps as the battery “fills up”. I use up about 50 amp-hours per day when cruising. I can effectively refill the battery in an hour and a half with the new external regulator and the standard Lucas alternator.


If you have the Heart Interface inverter/charger option with the Link 2000 monitor and inverter control, then it is possible to upgrade to the Link 2000R which provides “smart” external regulation. Although H.I. Technical Support, indicates that the software in earlier inverters (serial numbers below about 1000) doesn’t fully support the functions available in the L2000R, the manufacturer will send at no cost (apparently) a new microprocessor chip along with Technical Support Bulletin 009-2/16/96, Rev 1, which explains how to install it.


Please note that it is possible to replace the internal regulator without adding any monitoring equipment or even interfacing directly to whatever monitoring equipment you might have. Cruising Equipment and others sell “smart” three step external regulators on their own.


If you choose an external regulator (with monitoring capacity, or as an add on to your inverter/monitor package, or as a stand-alone item), MAKE SURE that it gives you the capacity to control the maximum amps that the alternator will be asked to produce. If not, it may ask too much of a 55 amp alternator which probably shouldn’t try to produce more than 40-45 amps for any sustained period of time. Also, if you don’t have the Lucas alternator then check to see if your alternator is robust enough to work harder for a longer period of time. The Lucas is a real marine alternator, but not all 55 amp alternators are as robust, apparently.


Whatever option you choose, you may want to get a marine-auto electrical shop to remove the internal regulator from the alternator and lead a field wire out of the alternator. This is a $30 job which you can do yourself following advice in the “12 volt bible” but can lead to confusion about the distinction between a “P” and “N” field lead.


A good location for mounting the external regulator is in the engine compartment just aft of the coolant reservoir (which can be moved forward an inch or two to give you more room). The heat in the engine compartment is apparently not a problem, but the external regulators are electronic toys and they don’t like to be exposed to salt water.


(2) Replacing the existing alternator and its internal regulator

This option involves purchasing a higher power alternator from a manufacturer such as Balmar or Powerline. The alternator will probably be rated about 75amps. For this alternator you will need a smart, three stage, external regulator of the type described above.


Before opting for a new larger alternator and external regulator package, be sure that you have room for it in the engine compartment, that it can be attached to the engine without a lot of welding of the alternator case and/or a new bracket, and that it doesn’t require you to alter all your pulleys to accommodate a wider belt size. Such extras will substantially increase the cost of the change-over.


Some Final Notes.

One change that can be made in concert with the above or on its own is to reduce the size of the alternator pulley. For $15 I had an auto-marine electrical shop fit a 2″ pulley to replace the existing 2 1/2″ pulley. This forces the alternator to work harder at lower engine rpms which is good. It did not require fitting a different belt. Unfortunately, it has also affected the adjustment of the tachometer which reads off of the alternator. This can be adjusted but I haven’t got round to doing it yet. One thing that is a nuisance on the Perkins engine is that as you can’t manipulate the adjustment nut on the bracket when the alternator is bolted to the block. So it’s a bit of a trial and error process to make the adjustment for the new pulley. I have been advised not to put on a pulley less than 2″ in diameter.


Another change worth making is to upgrade one or both of the batteries that come with the boat originally. The Exide Commercial 4D is not really a deep-cycle battery and has very limited effective capacity. As soon as my house battery shows signs of slowing down, I am going to replace it with the best 200 amp deep cycle 4D that will fit into the available space (Jim Krogness has already moved to an Exide Marine deep cycle replacement). Then I can count on that battery having 70 amp-hours of real capacity (following the general rule that a 200 amp battery should have about 70 usable amp-hours because the last 15% of used amp-hours are very hard to replenish and you don’t want to discharge your battery below 50% of its rated capacity).


Some 320ers have added a third battery to make sure that they always have cranking power to start the engine. My sense is that if you improve the charging capacity of the engine, a third battery will not be necessary.


John Langford
Victoria, British Columbia
Canada, “Sabbatical2”