Alternators

[merle&louise]

Can anyone tell me how to check to see if my alternator is working? I'm not sure what size it is (no markings that I can read). The engine is a 1999~ series 60 DDEC.

I had a tech check it and what he did was to put a volt meter on it first to test the battery. Then he put an amp meter clamp around the red cable as I ran the engine; it read 20 amps. He said that the alternator was working properly.

My volt meter on the dash shows 12V when driving @ 65 mph, but when I start the generator it will run up to 13.5+. Why?

[Lee Bornstein]

Tuga:

If I understand your question correctly, Voltmeter/Ammeter test on Alternator shows 20A. This means battery/batteries are nearly charged and Alternator load is 12v X 20a = 240 Watts (not that much).

Not familiar with the setup on your Newell but I'll tell you about my Liberty. The big alternator on my 97 Prevost (Detroit 60) is rated at 270A output or 12 X 270 = 3240 Watts that charges my House Batteries and runs the huge DC motors required for my Prevost Over the Road Heat/AC system. If I have a 20A load... that's less than 10% of the total capacity of the alternator.

I also have a 24V alternator used for charging Engine Staring Batteries.
On my Dashboard I have three (3) meters used to monitor the electrical system.
One meter shows both Battery Voltage and Amperage on the Engine Starting System. (Typically 26 -27 Volts)
Another meter shows both Battery Voltage and Amperage on the House Battery System.
The third gauge is a Volt Meter showing voltage on the Diesel Generator Starting Battery. If the Generator is running, this shows about 13.4 Volts.

Could it be you're looking at the Diesel Generator Starting Battery Voltage when you refer to 13.5+ Volts?

Hope this sheds some light on your situation..

Lee

[MangoMike]

Tuga / Lee,

I could be wrong here but...

It's my understanding, from messin' w/ restaurant stuff, that a clamp meter displaying amps only shows what is being drawn from the system not total charging capacity.

One of the brains needs to step in here.

Mike

[garyde]

Yes Mike that is correct. Lee was saying there was not much amperage flowing to the batteries because they were full. Current (Amperage) flows at the rate of demand. Gary

[Jon Wehrenberg]

Maybe I'm being simplistic, but I check alternator output by verifying output voltage is around 27 volts. The easiest place for me to check it is at the bus battery bank.

If the voltage is less than that the alternator is not doing its job.

As was expressed earlier, the amperage is only an indicator of how depleted the batteries are or how big the load is on the batteries.

The alternator output is going to be higher than the nominal battery voltage because it is just like the situation when you try to fill the bus tires. You can eventually fill a tire to 110 PSI if the compressor only maintains 110 PSI, but it will take forever, so you use a compressor that can maintain a higher pressure, such as 140 PSI.

Think of batteries as a tire and the voltage as pressure. If you want to top off batteries that need 25.6 volts you need an input voltage of some value greater than that such as 27 volts. Amperage would be akin to the volume of air, so as the batteries are loaded or are depleted, you want to deliver more volume so you do not go into a discharge condition.

[Lee Bornstein]

The original questiob posted by Tuga was:

"My volt meter on the dash shows 12V when driving @ 65 mph, but when I start the generator it will run up to 13.5+. Why?"

Answer: The Volt Meter on the dash he's referring to is the one that monitors Generator Starting Battery Voltage. It will show 12V when Generator is off and 13.5V when generator is running and alternator on generator is charging.

Would you all agree with me on this?

Lee Bornstein BSEE, MSEE, POG, AKC and more.

[MangoMike]

Lee,
Not that I want to speak for TUGA, but we all love to spew forth.

I still thinks he's referring to the voltage on the house batteries that should be charging by the engine/house alternator as he's motoring down the road, but doesn't. But will charge when he fires up the generator then will charge the house batteries via the inverter/charger combo.

Mike

[Lee Bornstein]

Guess we'll have to wait for Tuga to come back with more detail.

Can't wait .... I'm ready to spew forth now!

Lee

[merle&louise]

Lee & Mike:

The volt meter on my dash shows voltage of the engine/generator batteries.

The Link 2000 next to my microwave shows the voltage of the house batteries; bank 1 & bank 2. I THINK that the alternator will charge the house batteries AFTER it charges the engine/generator batteries. The problem is the alternator is not charging the engine batteries; therefore, it can not charge the house batteries.

I do not have a meter on my dash that shows house battery voltage.

The volt meter on my dash reads 12 v when the generator is not running.
It kicks up to 13.5 as soon as I start the generator. This would indicate to me that the alternator is not charging the engine/generator batteries.
A CHECK ENGINE light comes on and off when the voltage of the engine/generator batteries drops to about 11 volts.

When I start the generator; no more CHECK ENGINE light.

My knowledge in this area is limited, so please bear with me.

[Jon Wehrenberg]

Now it is getting clearer. What you have to do Tuga is determine why your engine driven alternator is not charging. These coaches are all different even among converters so every coach has to be examined based on its equipment. My bus has a single alternator that charges the house and the bus. Mango has a coach also by Liberty, but he has a house alternator and a bus alternator.

It sounds like you have a single alternator for both the house and bus. It could be a failed alternator, a bad or broken belt, a failed voltage regulator, or something as simple as a broken field wire if you have an external regulator.

If you are uncomfortable playing with this type of a problem just get a shop that is good at dealing with alternators and regulators. They will know in a few minutes where the problem exists.

Before you spend any money you may just want to check for broken wires or terminals at the alternator or regulator. Make sure the belts are OK, and if you want to go a little further without running the engine, just make sure there is continuity between the field wire at the regulator, and where it attaches to the alternator.

If you want to determine if it is an alternator problem or regulator problem, jump from the 12V positive (such as at a battery) to the field terminal on the regulator. Have your voltmeter hooked up to the alternator output. and the engine running. If the alternator is OK the voltage will go way past 12 volts because now it is unregulated, and the problem is the regulator. You want to be prepared to pull the jumper off right away so you do not do any over voltage damage.

If there is no output charging voltage from the alternator, the problem lies with the alternator. They can be rebuilt and usually the cost is pretty cheap compared to the cost of a new one.