Toyota Coaster

[wazza21]

Just fitted a new 24volt alternator to my 1986 toyota coaster bus.I noticed that the terminal voltage at idle was 25volts. I figured that this should be around 27.5 volts so I adjusted the idle speed to suit. Have I done the right thing?

[Brian R.]

I would set the idle to spec and live with whatever voltage you get. 25 volts won't discharge your battery.

[wazza21]

Thanks very much Brian R. for your prompt reply but why? An auto sparky showed me once how to test if my alternator was working correctly. Firstly he checked the battery voltage with the vehicle turned off and read 25volts then he started the vehicle and read 27.8 volts. which he said was the correct charge voltage. I asked the question only because the vehicle is now idleing faster which makes starting real easy but what problems can I expect to arise from this if any? thank you.

[wazza21]

Thank you so much for your prompt reply Lindamarks321.However does anybody know for sure?

[Brian R.]

It is not clear. I have no experience with your car. Sorry. I use idle spec religiously.

[fourwd1]

An alt puts out more current at higher rpms than low rpms. When the current drain is higher than the alt can produce, the output voltage drops also. So a higher rpm lets the alt put out more current, which keeps the voltage higher. Ideally you want at least 1.3V higher than the battery voltage to charge the battery. SO a 24V battery should have an alt supplying at least 25.8V to charge properly at idle rpms.