i tested the amps coming off my alternator this morning at idle right after starting it and it was only 5 amps. is that normal?

voltage was ~14.5 between alt and neg post of both batteries.

 

Your volt reading is good....alternator is working.
The Amp reading is going to vary with load. I'm not sure what the lowest reading can be...everything electrical off.
How did you measure the Amp's? Most volt meters will not measure the Amperage the alternator is capable of.

 

Cuda

That test has to be invalid.
How was it tested?

Bill

 

i've got a fluke T5-600 meter that has a u-shaped jaw which slips over wires and measures the current. i think it goes up to 100 amps. so you are right i bet i couldn't' measure the top end output. thanks for the input!

 

some of those meters are for AC only. and will give an erroneous reading when trying to measure DC amps.

 

I beleve it takes 35-45 seconds for the Alt. to kick in after start up too so make sure you wait that long.

 

dirk- i'll have to look at the meter. it switches automatically between ac and dc on voltage readings, so i would assume it would do the same for amps but i really have no clue.

can al alternator kick out the correct voltage at too low of a current? if i am getting the 14.5 volts should i bother looking more deeply?

-e

ps- i have been having starting problems that a jump start seems to fix. brand spankin' new batteries

 

Has the starter been load tested?

Bill

 

whats the problem ?
maybe i mssed that.
alt. is only going to produce amp as the are used.
worried about the alt.? light?
spinning slow ?
what madvan said.

 

That's partially true. I used to think that too untill I worked on a dual Alt system.

Single Alt systems: If the PCM sees too much voltage, it turns the GPR
off, not the Alt, for short durations. You can see this happen on the volt
meter in the dash, it pulses high and low if you rev the engine with the
GPR energized because the alternator is supplying too much voltage. The
pulsing happens too when the GP's heating is near the end of its
cycle....up to 2 minutes.

Dual Alt systems: The PCM controls the lower Alt and turns it OFF as
long as the GP's are ON. The PCM still monitors Voltage and shuts the GPR
off if it gets too high.

 

A lot of people make the mistake of thinking that but it's actualy the glow plugs circuit cutting out. The wait to start light is not directly connected to the glow plug circuit. It tells you when it should be warm enough to start, and goes out. The glow plugs are still on and stay on for a bit, when the volt gauge suddenly rises 30 some seconds after the truck is started it is because the glow plugs just shut off.

 

Sorry Jim, I posted after reading his post but before reading yours

 

I had a similar problem a year or so ago, truck wouldn't start after sitting for over 10hrs. Turned out the stock remote door lock/unlock module was faulty and had a slight draw that was draining my batts as it sat.

If you have a crewcab, might be something to look at......

 

check the voltage at the batteries with the truck idling with all electrical stuff on (blower, lights, blinkers, wipers....) and see if it still maintains 14v. if it is, then you can assume its pushing enough amps. the batteries could have failed, and are not taking the available amps from the alternator, or there could be corroded connections restricting amperage.

 

Well, I dont know the specifics on the charging of out trucks but since we work on DC power systems for off grid homes, I can provide some insight.

First, the Fluke T5-600 is not designed for measuring DC current as a clamp on. Checked the specs and measures AC current only. The obvious clue is the sine wave mark next to the A setting on the meter.

There are DC clamp on meters that we commonly use. To measure the output of just the alternator with a clamp on, you need to be on the wire right at the alternator that goes to the battery. This will give you the alt output. If you measured on the main cable at the battery, you would get a net amp reading. Since DC can go either direction, the reading at the main battery cable is amps from alt minus amps of loads.

You can measure standby draw off of a battery. In off grid homes, we call these phantom loads. Things that draw power when not really on. If you have something drawing on your batteries when not in use, your batteries will be less than optimum for starting. We encounter this with backup generators on our systems. Since backup gens have an engine control for auto start, some have a continual draw on the gen battery. A 14 mA draw will drain a battery in a 2-3 month period. To measure a draw when the truck is off, disconnect one battery. Using an inline DC current ammeter (inline is more accurate for small measurements) measure the remaining battery between the loose + battery cable and the + battery post. Ideally, there should be a zero reading. If you have a draw here, start pulling fuses until your reading goes to zero. When you pull the fuse that drops your reading, this is the circuit that has a problem.

If there is no standby draw AND your batteries are good, it sounds like you could have a bad connection. DC requires good clean tight connections. I have seen bad connections get so hot they would burn your hand.

One last word. DO NOT think you can measure the current off of a battery with an inline meter by putting the red lead on the + battery post and the black lead on the - battery post. If you have ever dropped a wrench across the battery terminals and practiced DC welding, you are doing the same thing with the meter. Best case scenario is that you will blow the meter fuse.

I have learned a lot on this site about diesels, so I try to return the favor if you hit something I have background in.

Ron Stauffer
Montrose CO