Marine engines are usually fitted with an alternator and regulator that was designed for use on a car. For automotive use this is fine because most drivers are running their engines the whole time with a fully charged battery. The alternator and regulator is designed to keep a fully charged battery topped up. Few drivers stop and park up overnight and leave the lights on. Therefore, the batteries in a car are seldom ever run down. This changes with camper vans and boats but the alternators and regulators provided as standard are not suited to these requirements. Problems arise because the standard charging system cannot properly charge a fully or partially discharged battery.

If you cruise a lot with a standard Yanmar 1gm 10 with 35 amp Hitachi alternator and you run your batteries down on a regular basis you will destroy your batteries. Personally, I have bought 5 new lead acid batteries for my boat in the six years I've owned her. I added a solar panel a few years back and this has really helped because the intelligent regulator is able to fully charge the batteries and keep them topped up. However, having a purpose built alternator and regulator package is the best solution when energy demands are high.

Only recently have engine manufacturers woken up to this problem and started delivering engines with proper charging systems built in. Volvo have moved in this direction with the D1 and Beta are now providing engines with Balmar charging systems as standard. Yanmar, as usual are slow to catch on.

So what are the options?

There are two directions one can go in. Firstly one can buy an intelligent regulator and use it with your existing alternator. This is the cheapest solution. These regulators are available from companies such as Adverc, Sterling, and Driftgate with Adverc being the most specialised. I have heard good reports about some of these products and also some pretty poor ones. If I were to chose this route I would go for the Adverc. However, the 35 amp alternator that comes with a Yanmar 1gm 10 is a little small if you want faster battery charging so you might have to upgrade this anyway. If you are going to upgrade the alternator, why not buy one built for the job?

The drawback of the 3rd party regulator route is that the alternator must be taken apart and re-wired. The manufacturers such as Adverc are usually slow to point this out and although it should be fairly simple it's not always easy to get the alternator casing apart. The other possible problem is that the alternator, not being designed for heavy use, is now required to work much harder and wears out more quickly. Adverc claim that the alternator will last longer being intelligently regulated and this may well be the case but there is some doubt in my mind since I've heard stories of alternators being blown out by external regulators.

The other option is to buy a purpose built alternator and regulator package. The only supplier I know of is Balmar who provide a range of supposedly Yanmar ready alternator/management packages. The problem is that there is no package ideal for the 1gm 10. These packages are designed for the bigger 2 cylinder Yanmar engines. However, if you are prepared to work for it you can install a 70 amp Balmar alternator and regulator on your 1gm 10. You will need to move a fuel pipe which is in the way when you fit the bigger Balmar and you will need to make a spacer to get the pulley in the right place. I also recommend two modifications.

Firstly you should fit the pulley from the old Yanmar alternator onto the Balmar because the Balmar pulley is very small and the engine would otherwise be required to work under heavy load at idle revs.

Secondly, the 1gm 10 does not have enough power to drive the alternator at max output and to push the boat at the same time. If you need power urgently after a night at anchor when your batteries are low you must have an option to cut or reduce alternator output. There are various ways to achieve this with Balmar regulators. In my case I fitted a toggle switch in the alternator temperature sensor wire which cuts the output by 50% when required.

Buy Balmar alternator packages for Yanmar engines by clicking the image here!