Albin Delta #19 – 'Fine'

Howto install a Sterling ‘alternator to battery charger’ on a Yanmar Y3M20

I want share some knowledge about installing a ‚Sterling Power‘ alternator to battery charger. This not an official manual. It is no approved by Sterling or Yanmar. It is just my personal experience, which resulted in a working installation.

This description covers this setup:

- Sterling Power 'Alternator to battery charger' - Model 12V, 130Amp
- Yanmar 3YM20 from 2003
- Service battery: 110 AH, gel type
- Starter battery: 70 AH, AGM type


DSC00150My motivation

I spend quite some time to design the core energy storage and a correct charging of all batteries. Beside many other things I did for optimization at the consumer side, the engine alternator is still an important and solid source to generator electric energy. Unfortunately its specific relation of current and  electric tension is totally inefficient for modern AGM or gel type batteries.

Sterling Power is currently the only vendor,  which offers a simple to install charger for existing engine installations. All other vendors I found, do offer special alternators or electronics for the existing alternators, which require a reassembly of the existing alternators.

So far, I was convinced and ordered the device.

The device

Having received the charger from ship chandler, it look compact and solid. I my case, it is the 130 Amp model, as the specification of Yanmar tell, that the standard alternator, can produce up to 125 Amp for charging.

It is important to find a place, where it is a close a possible to the engine and batteries, to keep any cable length as short a possible.
The dimensioning of high load cables is a topic by its own. Please read the manual from Sterling carefully and do a proper sized cabling with well connected cable end links.  Besides the electric load, these cables are heavily stressed by mechanic vibrations! Incorrect cabling is a perfect source of fire! I my case, the charger is cabled with 16 sqmm cables.

Crimp tool for big sized wires

Crimp tool for big sized wires

A second aspect is, to assure a proper ventilation. The combination of these two, can be tricky because typically is will get warm close to the engine.

Having found this place below the aft cabin bunks, separated by a wall to the engine compartment, I started to install the cables.

The design of the device housing for cable connections if not very smart. You have to remove the side covers and fit the cable through a small hole. All sensor cable connections are even more difficult to reach. Compared to my shore power charger from Philippi, this is not very service friendly.
Very negative: The recommended wire size for the sensor cables (0.5 sqmm), will not fit into the terminal block at the circuit board, if you use wire end caps. 🙁

The installation process

The basic installation is simple. Chose the battery type by turning the selector wheel: I selected type 3, which is a compromise for sealed lead acid batteries, because I have a gel type for service and an AGM type for start. The Sterling documentation gave no indication, how to deal with such installations, it is only focused one type of batteries. This setting was at least the recommend setting for my shore power charger with mixed battery types.

Than I:

  • Connected plus to start battery positive
  • Connected plus to service battery positive
  • Connected ground to common ground
  • Connected alternator B+ to charger input

Charger installation

At this point I stopped, because the charger came to life, even though the engine was not running. So I disconnected the charger input.

Analyzing this, I found on the wiring diagram at the Yanmar manual, a connection between alternator B+ and the starter (pls. refer Yanmar wiring diagram – connection between item 32 and 35). This is ok for a standard installation but with this charger, you have to assure, that only the alternator is providing energy to the charger.

verbindung zum LAdegrät_seitenansicht

cable routing to charger

So I disconnected the original Yanmar B+ cable and mounted the connection from the charger to the alternator directly. Make sure, that you isolate the original cable well after disconnecting or cut off the loose socket. The engine body is connected to common ground and the disconnected cable will cause shorts, if not isolated!

Ok, everything looks fine, no energy while the engine does not run.

Now it was time to start the engine and check the input into the charger. Engine runs – no power.


alternator sockets

The reason is found in the design of the alternator, which is typical for most modern alternators. To generator electric power, its need a small starting load of electric power, to build up a magnetic field.

The solution is a special feature of the charger. There is an ‚ignition feed‘ connection option. You have to connect this, to the starting switch at the starting position. Means: If the starter will get energy, the sensor detects this and will lead energy to the alternator for app. 2 seconds. Once the alternator is producing energy, it will not need this power any longer.

Tested – everything works!

From here you can update the installation with temperature sensors, to improve the loading of the batteries and avoid overheating at the alternator.

Current imperfections of my installation:

  • I have not installed any circuit breakers at loading cables.
  • I have not installed the temperature sensors.

In short, you can work along this checklist:

  1. Mount the charger at a good place
  2. Disconnect batteries or switch off main switch for service and start.
  3. Connect loading terminals to start positive and service positive.
  4. Connect of ground (black cable) of the charger to common ground.
  5. Disconnect B+ socket at alternator to the charger loading cable
  6. Connect charger loading cable B+ to charger input
  7. Turn main switch for service and start on – check whether charger is without power. This is the correct state!
  8. Connect ignition sensor from terminal to engine start switch
  9. Start the engine. Check if charger is on – Indicator LED will be on (pls. refer Sterling manual for state descriptions)
  10. Measure load input or check electric tension at your electric meter. Should be >13V if system works.
  11. done – Attach temperature sensors if desired.
Important resources:
Please refer directly to these documents. I am not allowed to publish any content from those on my website.


  1. Pingback: Looks like a boat again – Albin Delta #19 – 'Fine'

  2. Markku

    Hi, nice description, how does it deliver, it it as described

    1. sehret (Post author)

      Hi Markku,
      no complaints at all, it just works! The batteries do charge quicker and show no overloading at all. I can really recommend it.


      1. Markku

        Hi Stephan do you remember some charge figures before and after installation

  3. sehret (Post author)

    Hi Markku,
    what kind of figures do mean? I can see now, that I have now the same final loading voltage of 13,8 V like with the shore power charging unit. Both are configured for the AGM I/O loading curve. Before it was definitely over 14V.
    It is a bit difficult to tell, as I only have a precise insight into these data since I did that Installation as a whole. Before I only had a Voltmeter, which was not very precise.
    Cheers Stephan


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