can alternator speed be increased with pulley change?

[Tugether]

I have the 21 with Volvo. D1-30F 869645 5102161261Y

I took out the factory AC (it didn't work well) and put in a 120v AC with an inverter. The AC is fine, the inverter works perfectly. The challenge is that at idle and very low speeds the alternator can not keep up with the load so the batteries drain. The alternator has way more than enough capacity at slightly higher engine speed. I'm thinking that a slightly smaller pulley on the alternator will cause it to turn faster at lower engine speeds and then everything will be perfect. Advice, please. Is there a smaller pulley available? source? If you don't know a source can you tell me the make and model of the alternator, please? If smaller pulley on alternator is not available, how about a larger pulley on the engine? In south Florida the AC is a must and I need to get it to work at lower engine speeds. "fat people sweat a lot" I need help!

 

[NorthernFocus]

Perhaps a simpler solution is to manually control the field current on the alternator. This is an old trick used by long distance cruising blow boats to allow recharging the batteries in minimal engine idling time. It is a simple electrical mod. You simply wire a rheostat into the field circuit. By controlling field current you can force the alternator to output full capacity at idle speed. It is a good idea to install and ammeter on the alternator output if you don't already have one. Then you have a visual control point to monitor.

 

[knotflying]

I would go with NorthernFoucus' suggestion. Speeding up the RPM on the alternator may work at lower speeds, but at higher speeds I would be concerned about bearing ware. And then there is the issue of finding the proper belt size.

 

[Romakeme IV]

As stated above at high speeds the bearings can burn out. Years ago one of our Police forces had this idea to keep their batteries charged during extended periods of idling. Yes they went back to the original size pulley!

Controlling the field current will increase amp output but it also causes problems. When the alternator is "tricked" into putting out high amperage at low speeds it produces a lot of heat and its fan is not turning fast enough to eliminate this heat.

I would suggest a custom tailored alternator built to spec or a Honda invertor generator on the swim platform.

Regards, Rob

 

[NorthernFocus]

...When the alternator is "tricked" into putting out high amperage at low speeds it produces a lot of heat and its fan is not turning fast enough to eliminate this heat.

I would suggest a custom tailored alternator built to spec or a Honda invertor generator on the swim platform.

That's a good point. The subject modification is intended to be able to operate the alternator for short periods of time at high output. Having a custom alternator built to handle the load/heat would be advisable. You may still need to manipulate the field current but have the alternator built to handle the load at low speed.

 

[captstu]

If you try to increase the alternator output much beyond stock - be careful of the engine.

My last cat had twin Yanmar engines - I added two alternators (one each) to increase the total power to run an inverter and air conditioner.

It all worked fine with two exceptions.

1. The engine was seeing a load beyond its design limits - so wide open throttle would not produce maximum rated rpm - just as if I had over propped the engine. This caused the engine to add more fuel in a attempt to ret the actual rpm to the demand rpm. The extra fuel was not burned and a portion of it ended up in the engine oil. The result was premature wear on both engines - they needed a full rebuild at only 5,000 hours - cracked pistons, signs of long term over heat.

2. The second problem is heat. The air conditioner I had drew about 9 amps at 120 volts. This required about 100 amps of additional 12 volt generation. The extra heat was just to much for my engine room over the long term. I had a battery run away from heat damage and similar problems. I just could not see the cause while the damage was happening.

It was nice to have a/c without a generator. I had a 3kw inverter, 8 CG1 batteries for about 950 Amp hours of storage, and the ability to start up the air conditioner underway after a day of sailing with only the noise of the engine being used to drive into the anchorage. Once cooled down with the engines running, I could shut down the engines and the a/c ran most of the night on just the batteries.

Even with the rebuild, the whole setup cost only about $12,000 over the five years I used her in this mode. Expensive, but no more than a Diesel generator with a lot less weight and space.