not charging

[satelliteman]

I have a 1998 Forest River w/454 on a p-30 Alternator that has checked out good. But not charging the system. Have checked wires and all connections for ohms and voltage coming from and to where it goes. But still no charge. If you unhook the battery it will die. Where do I go next?

[jyrostng]

Some Isolators require a voltage from the ignition switch and on that line there is a low amp fuse. Look for that fuse if it's that type isolator.

[JamesJudasPries]

Measure voltage on the post of isolator that alternator wire came from. Should be 13-14.5 volts to frame with motor on. Chances are connections are bad. If I were you I would replace the diode isolator with a solenoid type, especially if it is original from 1998. You can tell if you have one like others mentioned: heat sink= diode isolator, can shape with posts = mechanical solenoid. The voltage loss from the diode ones are brutal. At idle rpm you probably are draining the batteries. I don't know why these are installed since they are both more expensive and don't work very well at all.

[wa8yxm]

There are often protective deices in the alternator lead, (Fuses/fusable link/Circuit breaker)

I would start with a charged battery (use external charger if you need to)
and then check for voltage at the BIG terminal on the alternator. if it is there hook a 100 watt 12 volt "Trouble light" to said terminal (And ground) put the other clip on the alternator housing, not the engine, not another ground, the alternator housing) bright light is good.

If you don't find voltage then back up the leads towards the battery until you do.

Problem is between voltage (or light) and dark

NOTE: THe reason for connecting the light between the alternator's big terminal and the alternator's housing... I've had a case were the alternator did nto ground properly.. The solution was to remove one mounting bolt, add a "Star" type lock washer (many teeth) and replace.

On a `1998 I do not think this next paragraph will apply but I've seen it on older vehicles.. FIVE TIMES (one was even mine)

Back in the days when the fan belt was a 'V' Belt instead of the modern Serpentine belts... Loose belt (on mine it was actually the wrong belt) lets the alternator pully slip

As I said. Have seen FIVE times.. Well 4+1 The 1 the belt was not just loose.. This was a brand new sticker in the window car and the belt was.. NOT,, Period. it was MIA, Factory never installed it.

[satelliteman]

thanks for what you have added for now. Both battery and house is not charging. I have voltage out of the alternator and all the way to the asolator that is where I get lost

[jyrostng]

which system is not charging? there are two, one for the house, one for the engine starting

[crasster]

Check ALL connections, especially the negative ground. Remove it and clean it. Also make sure when the vehicle is on that the battery reads 13.4V or higher.

[eHoefler]

There is 2 fusible links at the starter solenoid, chances are you have one bad.

[allbrandauto]

for one disconnecting battery while engine is running is the worst thing you can do if alt. was working right it would lead to blowing out other electrical componits start engine and cheak voltage out big wire on alt should be between 13.5 and 14.2 volts if not turn engine off cheak volts at big wire should be 12 if ok cheak cheak the smaller wire one should have 12 volts with key off another one should have 12 volts with key on

[Matt_Colie]

Sat,

If it stops when you disconnect the battery, then (as you noted) the battery is not the problem. What is the problem is the alternator or its connections.

You said you ohmed things out. I will assume you have some kind of meter. So, Let's do the whole diagnostic starting at the top.
As said, the battery is not the problem, but it should be 12.6 if fully charged and at 12.0 is about done. If we are in that range lets go on.
Start the main engine. Now, find the post on the back of the alternator. Measure voltage there. There may be a cover that you have to get past. Measure both the post and the cable terminal. They should be the same. (If not, clean the connection.)

=>If it is the same as the battery, the alternator is toast.
=>If it is way higher than the battery, there is a bad connection.

Keep moving down the alternator output cable until you find where the voltage changes some amount. If it is a connection, Fix that. If that does not change things, keep going down the cable.

There are two different means to attach alternators to RV systems.
One is beast called an isolator that is a large heat sink with three (or more) terminals. If you find one of these, again measure voltages. Usually the alternator is in the middle and the house banks is on one end and the main engine start is on the other. If it is working right, the alternator post should be highest voltage and the other two no more than 0.7V less. If it is different than that, you problem is close by. Each of those terminals goes off to a battery.
The other method is called a charging contactor or combiner and it looks like a Ford solenoid. The engine power is on one side and the house is on the other. When the engine is running, both posts should be the same.
There is some strangeness that can happen with these, so if you have not found the problem by now, come back here with what you do find and I will make suggestions for other tests.

Matt

[satelliteman]

Just not getting the power to the system

[satelliteman]

with good battery power it will start and run. Till I unhook the battery, then it dies

[satelliteman]

have tried a new battery

[satelliteman]

have changed the battery to two different ones and no change

[donn0128]

Take the battery out and put it on a charger. Fully charge and take it to a battery shop of local auto parts store and have it load tested. Probably ypu will find battery is toast.