Alternator Output

[Vasco]

Originally Posted by SaltiNeil

Hello Sailing Dog, you seem to be very knowledgeable regarding this subject so I would like to ask you a question.

I have a 35 amp alternator on my Yanmar diesel engine. I am trying to calculate approximate amp output at idle or low speeds so I can figure how long to run my engine while on a mooring to replace the day's usage.

The max engine rpm is 3200 so I assume the max alternator output would be near 35 amps at 3200 rpm. But is there a formula for calculating output at 500, 1000 or 1500 rpms?

I have meters that tell me how many amp hours have been used so I am just looking to figure approximately how long I need to run the engine to replace the day's use.

Thanks so much for your time

Neil

Salti,

It really depends on the size of your battery bank and your daily usage. Having said that, if you have a fridge and your daily usage is about 100 amps (this is a low figure) you will have to run that stock alternator with the built in regulator all day to make up your 100 amps. Within an hour of running your alternator will cut back to well under 10 amps. To keep a battery bank up with a few hours motoring you really need a high output alternator and an external smart regulator.

[sailingdog]

Actually, there are a few that would be far better at answering this question than me... There are a lot of variables to answering this, since it depends on things like the sheave size ratio, the alternator design, the idling RPM, etc...

You haven't given enough information for anyone to take even a WAG stab at this... the make and model of the alternator would be a good starting point, as would the regulator make and model,.

Originally Posted by SaltiNeil

Hello Sailing Dog, you seem to be very knowledgeable regarding this subject so I would like to ask you a question.

I have a 35 amp alternator on my Yanmar diesel engine. I am trying to calculate approximate amp output at idle or low speeds so I can figure how long to run my engine while on a mooring to replace the day's usage.

The max engine rpm is 3200 so I assume the max alternator output would be near 35 amps at 3200 rpm. But is there a formula for calculating output at 500, 1000 or 1500 rpms?

I have meters that tell me how many amp hours have been used so I am just looking to figure approximately how long I need to run the engine to replace the day's use.

Thanks so much for your time

Neil

[Uglydave]

Neil
Do your meters not tell you how many amp hours you are putting back into the batteries?
I only use solar to charge my batteries but the controller has a readout for a/h in and out

[roline]

I have a 2GM20 that had a 35amp alternator that went south. Replaced it with a 50 amp alternator and a Zap Stop Diode. I added a new electrical panel with an amp meter that is hooked up to monitor current to and from the battery. It will display the charge current from the alternator, or when the engine is not running, consumption. The 50 amp alternator will put out close to 45 amps to a 1/2 depleated 200AmpHR AGM battery bank when the engine is at 1900 RPM. As the batteries recover the current drops. When both banks are charged the voltage is around 14.1, 14.2 volts and the alternator puts out 2 to 5 amps. This is about right for both AGM and Wetcells. When motoring, the normal RPM's are in the 2,900 range, close to hull speed.