Balmar 912-100

This alternator has a significant whine at around 2250 Engine RPM when loaded, 50 RPM above or below and the noise goes away, unload the alternator and the noise goes away. It does not appear to be belt slippage.

I find that with a Gates Green Stripe XL 1/2 Inch V-Belt I can pull 80 Amps from this alternator without any difficulty. Only as the belt ages will I find the occasional squealing as the RPM is increased rapidly. Recently (2004) Gates has started producing their "Fleet Runner" line which is a long life belt series for various applications. This technology is available in the 1/2 Inch belt family as the Gates Green Stripe HD. Botany Bay uses a 9405 series Green Stripe. A 9403 series is slightly shorter and requires dismounting the alternator to install and the 9412 series is too long. I will see if the HD series makes any difference in my application.

The low RPM output of this alternator is amazing, I routinely see 65 amps output at 1000 RPM fast idle. I would definitely select this alternator above the 150 Amp version due to superior low RPM performance and I have found that pulling more than 80 amps at cruising RPM will result in a slow but significant increase in engine temperature. It is important to have the ability to restrict alternator output significantly when powering into heavy seas or with a dirty bottom, the alternator load is significant.

I am seriously considering changing to a serpentine belt system or two v-belts to alleviate issues with belt tension and ability to handle the load. This alternator can easily produce 95 amps but a single belt would have to be tensioned excessively to prevent slippage at 95 amps.

The recent coolant circulation pump failure provided the opportunity to consider options to upgrade the belt system on Botany Bay. Two upgrade paths were examined: 1) Foley Marine has the bolt up second sheave for the power take off (PTO) of the Perkins 4-107 at a cost of about $200, they have to have a double sheave for the water pump manufactured and have only done so for a 4-108 water pump, luckily it will directly replace the 4-107 water pump (the diameter of the shaft is different the bolt pattern is the same), a new water pump and double sheave is $500, the double sheave for the Balmar alternator is another $50 for a total parts cost of $750. 2) S&W Diesel in Wilmington CA replaces all three of the sheaves with a custom 1" wide serpentine belt (no tensioner required for a simple system) at a cost of $135 for the crankshaft sheave, $115 for the water pump sheave, and $37 for the alternator sheave. The water pump would have to be replaced with a 4-108 water pump to match the diameter of the available water pump sheave (4-108s are far more common engines) for a total cost of $287 excluding a new 4-108 water pump at $105 for a total cost of $392.

However, I had previously purchased a spare 4-107 water pump (without any sheave) which cannot be used with any of the above upgrades and the total increase in alternator performance would be approximately 20 amps at the start of the charging cycle. The cost to have the old sheave pressed off the old water pump and onto the new water pump is $25. 

So, faced with the choice of $750 to upgrade to double v-belts (retaining a basically stock configuration), $392 to convert to a serpentine belt in a basically custom configuration, or $25 to continue running the alternator tuned back 20% and remain in a purely stock configuration I opted for the $25 solution. This setup has been very reliable over the years (Installed in 1993), is easy to maintain, and did not seem to cause excessive wear on the water pump (31 years is a long time for a water pump to go).

I have often considered one of the 200+ amp large frame alternators with a 165 amp fast idle charging capability but I am torn between that and one of the small diesel engines coupled to a large alternator to provide completely redundant charging capability.

The Balmar website has a nice description of this alternator (cached)

Balmar 912-100 Alternator