Adding High Output alternator to a Westerbeke 7.6 BTD?

[ttmott]

The biggest concern I'd have is based upon your genset engine is sized to efficiently drive the generator and when the generator is under full load the engine is also running at full load. After looking at efficiencies on alternators (friction and heat losses) you would be looking at more energy requirement to drive the additional alternator at 100 amps than to add a 20 amp 120VAC load on the existing generator. So as your genset is already running at close to maximum duty cycle as you say, I can't see where adding a less efficient form of electrical generation on the engine gains anything at all. What am I missing?

 

[dtfeld]

Based on the power output curve of the engine posted above, I’m not at the max engine output. The engine produces 9.1kw at 1800 rpm. Full AC load would be 7.6kw leaving 1.5kw to run at full load. Realistically, I’m only loading up to about 6.5 kw on the AC side, so I only have about .7 kw spare capacity on the AC side. Cant run a 100A charger as I don’t have the AC headroom.

If I’m at 6.5 Kw max engine load, I have 2.4kw headroom on the engine output (9.1kw-6.5kw). This leaves enough power to drive about 200A DC or about the output of a 250A HO alternator, but more realistically, a 170A version.

Given my 24 hr power budget, it gets be a full charge in less than 2 hours run time. Using AC sources, I’m at 3.5-4 hrs.

 

[km1125]

Based on the power output curve of the engine posted above, I’m not at the max engine output. The engine produces 9.1kw at 1800 rpm. Full AC load would be 7.6kw leaving 1.5kw to run at full load. Realistically, I’m only loading up to about 6.5 kw on the AC side, so I only have about .7 kw spare capacity on the AC side. Cant run a 100A charger as I don’t have the AC headroom.

If I’m at 6.5 Kw max engine load, I have 2.4kw headroom on the engine output (9.1kw-6.5kw). This leaves enough power to drive about 200A DC or about the output of a 250A HO alternator, but more realistically, a 170A version.

Given my 24 hr power budget, it gets be a full charge in less than 2 hours run time. Using AC sources, I’m at 3.5-4 hrs.

What about the efficiency of the AC alternator? It may have 9.1kW of mechanical power going into it, but only produce up to 7.6kW of electrical power due to the losses in the alternator itself, right? Maybe there is a bit of extra power, but it wouldn't be the total of 1.5kW, it would be 1.5kW minus what is lost in the conversion. Does it lose 10%? 15%?? I dunno, but it's not 0%.

 

[dtfeld]

Yes there are losses. Probably some that are constant like bearing friction and fan blowing over the windings. Some variable losses, as the unit produces more power to meet load, it produces more heat.

The biggest issue is finding the right information.