alternator regulator

[Mark Maulden]

Looking at upsizing my little 35a alternator. Probably to an 80a as I won't change the existing single 3/8 belt config. So, my question is why is an external regulator needed? With flooded batteries, is there a problem letting them sit a 14.4V while motoring as long as the batt plates don't experience air? Batts are 4-6Volts and 1-12 volt. No batt monitoring. Just a dumb batt switches that are managed.

 

[Stu Jackson]

Mark, try this:

http://forums.catalina.sailboatowners.com/showthread.php?t=125392

 

[Maine Sail]

Looking at upsizing my little 35a alternator. Probably to an 80a as I won't change the existing single 3/8 belt config.

There is no need to limit the alt you buy based on the belt. I actually prefer to install larger alts then derate them via an external regulator. They can then run at the belt limit all day long and barely break a sweat. If you decide to go with bigger pulleys in the future you now have an alt that can handle it.

So, my question is why is an external regulator needed?

Very often, with basic flooded batteries, it is not needed. With a true "dumb regulator" it simply charges to a predetermined voltage set point. You'll want 14.4V.

However with some alternators, Hitachi/Yanmar for example, when the alternator gets hot it self protects by lowing the voltage. The voltage regulator both regulates to a voltage but also "temp compensates"... Lowering the voltage cuts back the output and the alt runs cooler but it then charges very slowly.. If you go "dumb regulated" you DO NOT want a regulator that internally temp compensates.

With flooded batteries, is there a problem letting them sit a 14.4V while motoring as long as the batt plates don't experience air? Batts are 4-6Volts and 1-12 volt. No batt monitoring. Just a dumb batt switches that are managed.

No problem at all.


External regulators however offer many great options such as "belt manager", soft start, and alternator and battery temp sensing. One of the biggest advantages of external regulation is voltage sensing of the actual battery bank + terminal. Dumb regulators sense the alternator output itself and can't account for voltage drop. Because of this any voltage drop in the wiring, with many factory installs the voltage drop is HORRIBLE, can't be accounted for.

With an external regulator if there was 0.8A of voltage drop at say 50A of current the regulator would simply up the voltage until it saw 14.4V at the battery terminal. With a dumb regulator you'd see 13.6V at the battery and charge quite a bit slower. Voltage is pressure...

For your application with 450Ah's plus a start battery I would suggest an external regulator, especially if you go with an 80A alt.

 

[Mark Maulden]

Thanks Maine. The thought of a bigger alt and derating it did not cross my mind. I do want to get ~80a out of it and I think that would be the maximum for one 3/8 belt. You're costing me more money. I'm an EMI engineer of 36 yrs so I know the theorey. I doubt I can go to bigger pulleys as the belt goes basically around the (big) flywheel of the engine. I probably should put a bigger pulley on the alt. The current alt does seem to charge the batt to full charge but we can motor around here for hrs at times. The panel meter gets above 14V and it's accurate. But there's still about 8' of wire after that. All 4ga which is getting replaced cuz I'm also installing a 1KW windlass. Some big wire going fwd..

There is no need to limit the alt you buy based on the belt. I actually prefer to install larger alts then derate them via an external regulator. They can then run at the belt limit all day long and barely break a sweat. If you decide to go with bigger pulleys in the future you now have an alt that can handle it.




Very often, with basic flooded batteries, it is not needed. With a true "dumb regulator" it simply charges to a predetermined voltage set point. You'll want 14.4V.

However with some alternators, Hitachi/Yanmar for example, when the alternator gets hot it self protects by lowing the voltage. The voltage regulator both regulates to a voltage but also "temp compensates"... Lowering the voltage cuts back the output and the alt runs cooler but it then charges very slowly.. If you go "dumb regulated" you DO NOT want a regulator that internally temp compensates.





No problem at all.


External regulators however offer many great options such as "belt manager", soft start, and alternator and battery temp sensing. One of the biggest advantages of external regulation is voltage sensing of the actual battery bank + terminal. Dumb regulators sense the alternator output itself and can't account for voltage drop. Because of this any voltage drop in the wiring, with many factory installs the voltage drop is HORRIBLE, can't be accounted for.

With an external regulator if there was 0.8A of voltage drop at say 50A of current the regulator would simply up the voltage until it saw 14.4V at the battery terminal. With a dumb regulator you'd see 13.6V at the battery and charge quite a bit slower. Voltage is pressure...

For your application with 450Ah's plus a start battery I would suggest an external regulator, especially if you go with an 80A alt.