Off Grid Truck Camper

[Mikerodrig27]

I'm going to quote myself here:

So one port for each of the batteries that are in parallel

(1998 Dodge Ram 2500 with a 24v Cummins Diesel) so there are two batteries ran in parallel to start the truck.

The starting batteries are parallel 12v

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Yes the batteries are in parallel. I understand that the alternator won't be putting 136amps out at all times. That would probably cause the batteries to boil over which would not be a good method of charging. You still need to size the isolator up to the max capacity of the alternator right?

I have been reading about relay type isolators. They look as though they are easier to wire into the truck. Is there any downfall to these?

[Naptown]

The relay type don't work as well

[Sunking]

Sorry, not 136 amps.

More likley it's 136 amps at some ridiculous RPM (4000 and up ).

Don't be silly, alternators are not generators that needs a specific RPM to deliver full power. Just about all alternators are geared and designed to deliver full power at idle.

[Sunking]

Yes the batteries are in parallel. I understand that the alternator won't be putting 136amps out at all times. That would probably cause the batteries to boil over which would not be a good method of charging. You still need to size the isolator up to the max capacity of the alternator right?

Yes they have to be sized to take in the full capacity from the alternator, and then distribute the power to individual ports.

I have been reading about relay type isolators. They look as though they are easier to wire into the truck. Is there any downfall to these?

A few disadvantages.

1. The contacts will burn up at some point.

2. Main disadvantage is there is no way to isolate batteries and to charge at the appropriate voltage. The electronic isolators have switches in them to designate each output port battery type. For example you truck batteries are AGM Starting/Lighting/Ignition, have a different voltage charge requirement than deep cycle flooded lead acid batteries do. Mechanical isolators have no controls what so ever, it treats all the batteries the same, and voltage control is done by the vehicle alternator regulator designed for a SLI battery. The electronic isolator takes the voltage regulator out of the alternator and is replaced with its internal regulator.

[OregonSolar]

Don't be silly, alternators are not generators that needs a specific RPM to deliver full power. Just about all alternators are geared and designed to deliver full power at idle.

Generators have both their amps AND volts go up and down with the RPM's Alternators produce steady voltage at variable amps.

Alternators also have a ratio set up so that they will never exceed their maximum RPM's, for that kind of truck most likely no more than 5000, when the engine is running at redline, for that diesel I'd say about 2800-3000 RPM So at idle you only get about 2000 RPM alternator speed. So what, about 1/2 power or so?.

Any alternator geared to produce max power or thereabouts at the engine's idle will be dangerously close to over speeding or actually past the safe limits when the engine is actually revved up for any period of time, such as taking a cross country haul with a big camper on the back.

Tell me if you see a flaw in my logic.

EDIT: Here's a snapshot of the performance testing for one of the dual alternators in my Ford 550.
UGGvQoF.jpg
The belt gearing on it is 2:1. At idle (800 RPM) the alternator is running at 1600 RPM, generating 46 Amps of current, at a steady 13.2 volts. At the engine's redline (3000 RPM) the alternator is running at it's maximum safe speed, 6000 RPM, producing max 120 amps of current still at 13.2 volts.

[Sunking]

Generators have both their amps AND volts go up and down with the RPM's

Incorrect. Only the frequency changes. Amps are not determined by RPM. Amps is a product of voltage and resistance. Amps = Volts / Resistance. If you vary the frequency (RPM) of a generator only the frequency changes.

Alternators produce steady voltage at variable amps.

Incorrect, alternators are generators with a rectifier and voltage regulator to change the AC power to DC

Look at it like this. How much current does a 12 volt battery deliver?

You cannot answer the question because you do not know what the load resistance is. All that you can say to be a true statement is 0 amps or more.

There is some truth that Alternator RPM does effect maximum amp output. Very high output alternators of 250 amps and up are made to operate at maximum efficiency at higher RPM's But these are not what OEM's use. The OEM's manufacture alternators to operate at maximum output at idle and above. The high output alternators are made for things like a DC generator where the engine runs at a specific RPM. For example on a smaller scale many of your portable generators you find at box stores will also be equipped with a DC battery charger in addition to the normal AC generator. Engine RPM is set at 2400 to 3600 RPM for gas units.

Almost all OEM's use a 6 pole alternator which is a 3-phase generator for their low end model. With the shaft turning at 1200 RPM is 60 Hz 3-phase AC power maximum output. The higher the RPM goes, amp capacity goes down.

[OregonSolar]

That is not how they work. If you have a fixed voltage, the output current will be between 0 amps and full rated amps. Current is determined by load resistance and maximum capacity of the source.

Look at it like this. How much current does a 12 volt battery deliver?

You cannot answer the question because you do not know what the load resistance is. All that you can say to be a true statement is 0 amps or more.

I am talking about the alternator's CAPACITY, not it's direct load. Spinning at 1600 RPM, the alternator example I gave you has a CAPACITY to produce 46 amps. It CAN produce that much, but not like it is at any given moment.

I do know something about this, you know.

[Sunking]

I am talking about the alternator's CAPACITY, not it's direct load. Spinning at 1600 RPM, the alternator example I gave you has a CAPACITY to produce 46 amps. It CAN produce that much, but not like it is at any given moment.

I do know something about this, you know.

Alternators capacity is virtually the same at any RPM above threshold and below saturation . Any 6 pole alternator can supply the same current it can at 1200 RPM (600 engine RPM) as it can at 9600 RPM (4800 engine RPM). In fact they supply less as RPM increases due to magnetic saturation in the stator winding cores. The higher in frequency (RPM) the more saturated the core becomes and the impedance rises which means lower current.

Alternators are designed to work in a narrow range of frequencies. An 8 cylinder engines idles at roughly 600 to 700 RPM and cruises 2500 to 2800 RPM. The alternator is geared as such to produce maximum power from idle up to cruise rpm. Idle i sthe most crucial where the greatest demand is placed just after starting the engine to recover with all accessories turned on.

The OP has a diesel Dodge Ram. It idles at 500 RPM and Red Lines at 3000 RPM. It cruises at 1500 to 1800 RPM. I have one tricked out with a lot of electrical gear like a 6-ton winch that are huge power hogs and when running the engine is idling.

[OregonSolar]

Alternators capacity is virtually the same at any RPM above threshold and below saturation . Any 6 pole alternator can supply the same current it can at 1200 RPM (600 engine RPM) as it can at 9600 RPM (4800 engine RPM). In fact they supply less as RPM increases due to magnetic saturation in the stator winding cores. The higher in frequency (RPM) the more saturated the core becomes and the impedance rises which means lower current.

Alternators are designed to work in a narrow range of frequencies. An 8 cylinder engines idles at roughly 600 to 700 RPM and cruises 2500 to 2800 RPM. The alternator is geared as such to produce maximum power from idle up to cruise rpm. Idle i sthe most crucial where the greatest demand is placed just after starting the engine to recover with all accessories turned on.

The OP has a diesel Dodge Ram. It idles at 500 RPM and Red Lines at 3000 RPM. It cruises at 1500 to 1800 RPM. I have one tricked out with a lot of electrical gear like a 6-ton winch that are huge power hogs and when running the engine is idling.

Then how do you explain that performance chart I put in? Guess I didn't know as much as I thought I did.

[Sunking]

Then how do you explain that performance chart I put in? Guess I didn't know as much as I thought I did.

I cannot because I do not know the test criteria. I do not know how they turned a voltage source into a current source for the test. Alternators, batteries and rectifiers are voltage sources unlike solar panels which are current sources.

What really throws me off is a voltage source when you apply an increasing load on it, the voltage will start to sag or go down due to the internal resistance of the source. Your test result indicates a steady 13.2 volts which does not make sense to me.

Don't feel bad, none of us know as much as we think we do.

[OregonSolar]

I cannot because I do not know the test criteria. I do not know how they turned a voltage source into a current source for the test. Alternators, batteries and rectifiers are voltage sources unlike solar panels which are current sources.

What really throws me off is a voltage source when you apply an increasing load on it, the voltage will start to sag or go down due to the internal resistance of the source. Your test result indicates a steady 13.2 volts which does not make sense to me.

Don't feel bad, none of us know as much as we think we do.

Yes, well keep in mind that the truck has dual alternators. So even if I put a 2000 watt inverter in the truck (which I am planning to do since it's my work truck), both alternators together can easily handle the maximum load. The capacity of any single alternator is not off much concern. Heck, I even stick welded with it one time.

But I don't know how else the manufacturer tested it. So I can't say for certain what the voltage does under load. But here's a theory: Maybe the stated amperage is how much amperage can be supplied at 13.2 volts before the voltage begins to drop off?

Now it's just getting off-topic.