Sunday, November 16, 2008

Weak Point of the New Yanmar

Lets start by saying we love or new Yanmar 4JH4E. It will push our 15 ton boat at 6.5 to 7 knots in the open ocean. The repower installation done by Bill Engel of Bill's Marine/Golden State Diesel Marine is truly top shelf.

The weak point of the new engine is the voltage regulator. To be fair, this problem would be found on all engine brands that I know of. The engine came equipped with an 80 amp Hitachi alternator that is internally regulated. This is an automotive type setup. The regulator is either off or on at a set battery voltage. Marine-oriented smart regulators sense the battery voltage and temperature and usually have three settings to optimize the charging of deeply discharged house batteries.

The second weakness of this alternator is the small output post combined with a tiny wire on the wiring harness. This causes a voltage drop that cuts the alternator's ability to produce peak power.

On Maitreya and many other boats, the alternator is hooked to a battery isolator. The isolator allows the alternator to charge two batteries or banks, but keeps the batteries separate during discharge. This is meant to guard the engine battery so that is is not drained by appliances used on the boat. These appliances are only allowed to draw from the house battery. The problem is that the simple regulator can only sense the higher voltage of the two batteries. This means that the house battery might be empty and the engine battery full. The regulator sees the full battery voltage and turns off the alternator, leaving the house battery undercharged.

Additionally, the isolator uses diodes that allow electricity to only flow one direction from the charge/input post to the battery. This works well, except that the diode causes another voltage drop and produces heat reducing the alternator output that reaches the battery further.

Given these conditions, what can be done to get the house battery charged properly?

1) Increase the size of the alternator output wire from the standard 18AWG to 4AWG. The larger wire will let the alternator output current travel more easily to the isolator or battery.

2) Use the isolator to only isolate the engine battery. If we move the house wire from the house output post on the isolator to the input post of the isolator, we skip the path through the diode. This could allow the engine starter to drain the house battery. In practice, if you could not start your engine, you would probably use the the house battery to help anyway. The engine battery is still protected from the house load.

3) Use a smart or multi-stage regulator rather than the internal automotive style regulator. These are made by Balmar, Powerline, and many other manufacturers. There are two catches. First, these cost $150 to $400. Secondly, the Hitachi alternator must be modified to allow external regulation. This costs about $75 at an alternator shop.

4) One could fit an aftermarket high-output alternator that would allow external regulation and output 100 to 400 amps. These are made by Balmar, Powerline, Electrodyne and many others and cost $250 to$1000 depending on capacity. Other than the price, the catches here are that you may need a custom bracket to mount the alternator and that your tachometer may not work properly. For years, Yanmar tachometers were driven mechanically off of the engine. Starting in about 2004 some models started shipping with VDO-supplied instrument panels that have tachometers driven by alternator pulses. Accuracy of the tachometer will depend on the size of the alternator pulley ad possibly the number of internal posts contained in the alternator.

In general, I know this list works well. Maitreya's old engine had an Electrodyne 80ES alternator with a Powerline isolator and regulator. This charged the two battery banks well. We have two 12 volt starting/engine batteries (250 amp/hours) and four 6 volt house batteries wired for 12 volts (525 amp/hours).

I am currently having my alternator modified for external regulation by Barry Kessler of in San Diego. Barry builds Altra Regulators and works closely with the folks at Downwind Marine.

Electrodyne builds brushless, industrial strength, high output alternators. I learned about them from a recommendation by Steve Dashew.

1 comment:

yachtwork said...

Greetings and interesting points you make. A few thoughts-

The battery isolator is no longer in use on new boats. They have all gone to the VSR to get around the volt drop. Less heat, more charge.

The simple solution to the lack of amps is to install a second alternator from companies such as For less than a thousand dollars a Yanmar JH4 will charge at over 250 amps and provide a back up alternator. Real cool.

The idea of upgrading the wires to the original alternator is excellent and solves much of the 14 volt cap issues.

Thanks for posting.


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