Wednesday, December 19, 2007

Charging System Test - Heavy Duty 12 Volt System

A charging system test is a very basic operation with the right tools. Pictured is a Leece Neville 160 Amp Alternator which works very hard to keep the three 900 CCA [Cold Cranking Amps] bus batteries charged. Thomas School buses have a large demand with extra lights, electric motors and the engine air intake heater. The diesel engine in this case is a Cummins ISC Electronically controlled unit.



You're probably wondering what the heck is that device hooked up to the batteries? That's my tool of choice, a 'SUN' VAT 33 [Volt Amp Tester]. This model has been around for decades and still very reliable, our shop does have a digital tester but I like this one for doing a quick check on the charging system. The reason I'm testing the charging system is because of an unusually low voltmeter & ammeter reading.




The main leads are hooked up to the positive and negative battery terminals while the amps pickup is clamped around the positive cable to read alternator ouput back into the batteries. The engine must be running at high idle [approx. 1200 rpm]

The black control knob I'm turning puts a load on the batteries which should kick in the alternator to charge very close to maximum. Once I bring down the system voltage to 12V the alternator should normally put out a full charge of approx. 160 amps.

The test revealed the alternator is only putting out 80 amps maximum which will not keep up to the demands of a fully operational school bus & must be repaired or replaced.

This is a fast and easy way to do a charging system test on a 12 Volt Heavy Duty charging system.

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11 comments :

Alex said...

Sorry about this but i cant quite figure out how to post my own question so I hope you dont mind me piggy backing your spotlight for the time being.....I am searching the net but as you have probably gathered i still have a bit to learn on surfing. I need advise on my Landini Tractor 85 HP perkins engine. It has an electric fuel pump...no lift pump...and it has a bosch injector pump. The problem I am having is that diesel has found its way into the oil. I have looked at a few things but i am now racking my brains....please can someone give me some advice or somewhere to look on the net. Many Thanks

Alex

John Whelan said...

Hello Alex,
There is a strong possibilty that you're losing fuel through the front seal of the Bosch injection pump. This will cause oil dilution & of course an increase in the oil level in the crankcase. It is probably a rotary model fastened with three retainers. Fuel dilution from a bad injector would be another cause but the white smoke out the tail pipe and excessive fuel knock would be very obvious.

Alex said...

Hi John,

Thank you so much. There is lip seal on the front there. Would it hold its form if the diesel had passed through it???There is no clear sign of the seal being damaged but i think it is the only answer...had injectors tested and they are atomising perfectly at 300psi. Thanks once again ...i think i might be aswell to change the seal anyhow in case its walls are weak. Thanks John....Does this mean I am now a blogger????hahaha

John Whelan said...

If the seal is weak it would allow fuel to pass from injection pump pressure. This is the most likely problem as there is no other possibility I can think of..
Yes, you are officially a Certified Blogger!
Congrats,

Cedric said...

Hi John, I am a first year school bus driver, and i was wonder which school buses still use glow plugs. If i am not mistaken, cat engines do not use them, but are there any others? I drive a 2007 Thomas Saf-T-Liner c2, and i think it has them also

John Whelan said...

Hi Cedric,
The School Buses of today are using air intake heaters. Caterpillar, Cummins and Mercedes Diesel Engines all use intake heaters that are specially programmed to operate only at specific temperatures.

michael Peake said...

For John Whelan: I found your blog site while looking for a operating manual for my Sun VAT-33. I presume you still have yours and might be able to e-mail me a copy. Right now the needle goes all the way to max as soon as I hook it up-the load control is off and all settings are off or zero. Obviously I don't know what I'm doing wrong. Much obliged,

Michael Peake

michaelpeake@gmail.com

Jeffery said...

Thank You John for being so helpful.
I just got a 1991 International School bus, with a 466 engine. It is running, but was being used for misc. parts. I got ignition switch working, put all fuses back into fusebox, hooked up fuel shut off plunger, hooked up starter solenoid. WOW, starting and stopping with keyswitch..... sweet. Alternator is not charging... simple circuit, i am thinking.. got your big pos, and neg terms on back, with the two wire connector going into the side of the alternator. what should i have on those two small wires, and do you haver a electrical circuit diagram, and do you recommend any book for me to get, and what about the bus controls, would that be from Thomas. that's a lot to ask, but mainly to get it charging would be a good start. Much Mahalos (thanks), from Big Island Hawaii. The bus will be my first shelter on 3 acres I just got here. Aloha Bradduh!! Jeff Moore

Jeffery said...

Wow, John I don't know if my post made it, so here goes again, shorter version..

How can I troubleshoot a non charging alternator with my Fluke DMM, on a 1991 International school bus, with a 466 engine?

many thanx

Jeffery

J. E. Whelan said...
This comment has been removed by the author.
J. E. Whelan said...

You can hook up the fluke to the battery and load up the electrical system. Turn everything on, heaters, lights etc on high idle. Monitor the battery voltage and check amperage with the fluke pickup on the charge wire to the battery.