my vehicle is a Dodge be 3500 ram van camper conversion 5.9L. It has the normal starter battery and the cabin/camper batteries. The output from the alternator runs through a battery isolator and charges both the starter and the cabin battery as needed. My concern is that when I measure the amperage from the alternator, The reading fluctuates rapidly and significantly. From about 2 A to 17 A and everything in between. The voltage is consistent at approximately 14.1 V. The starter battery is close to full charge but the camper/cabin battery is low and should be taking a significant charge. When plugged into shore power, the cabin battery is charging at about 35 A through a 45 amp converter.
Questions. What is going on here? Why isn’t the cabin battery charging off of the van alternator as I would expect and why is the amperage from the
alternator fluctuating so much?
thanks in advance for any thoughts. Lk

 

Who did the conversion ? Did they use a split charge diode / VSR or just a bog standard ignition relay. ?

 

Thanks for responding. The van conversion is a Roadtrek. They’ve been building camper vans for over 30 years. There are tens of thousands of them on the road
i’m not sure about the diode or VSR. I replaced the original battery isolator a few years ago. The current set up is:
alternator pos to isolator pos in - iso pos in to starter battery pos. Iso pos aux to cabin battery.
Starter battery pos to relay block. Relay block to starter and everywhere else.
im mainly trying to figure out if the alternator needs replacing. Seems odd that the voltage output is good and steady. The starter battery stays charged, but neither the starter or cabin battery appear to be getting a steady current input.
thanks again in advance for any help. Tom

 

I've had a couple of Road Trek's myself so that's a good start. Most RT's have a split charge diode / isolator. Dodge have 3 terminals and Chevies have 4. Easy to check. Leave the alternator connected to whichever terminal it's on at the isolator. Disconnect the house or van battery from the isolator and then connect it directly to the same terminal as the alternator. Make sure it's secure. Start it up and check the amps on the battery you have reconnected to the alternator. If they are now steady then either the isolator is bad or you have a bad connection. If there is no difference then try connecting the other battery to the same terminal. If that makes no difference then post back and I'll give you some other pointers on what to check and how.. Mik

 

Also what year is it.

 

Cool Mik,
its a 97. I did what you suggested and attached Cabin battery to the alternator terminal on the isolator. When I first started the van, the output was steady. About 14 amps into the starter battery and only 8 Amps into the cabin battery.
14.2 volts. After warming up and increasing the RPMs the output got more and more unsteady. The starter battery wavered between 12 and 15 amps. The cabin battery from 1 to 13 amps. I don’t know what to make of it. When plugged into shore power, the cabin battery was taking a steady 35 amps. All connections are tight.
I did notice that the tensioner pulley was chirping quite a bit but it was still performing it’s job. I can’t imagine it would have an effect on the alternator.
thanks. Tom

 

Hi Tom. We need to establish a few things here as those numbers don't make sense. Ohm's law and all that.....
How are you measuring the amperage charge ?
Is the voltage remaining steady at 14.2 ?
A slipping serpentine belt or a dragging idler / tensioner pulley will definitely alter the readings.
Most of the faults with charging affect volts and amps at the same time. Make sure when you are testing that all of the gear in the van is turned off, especially the fridge. Also make sure that the dash panel dimmer switch ( headlights) is turned fully anticlockwise.. Mik

 

I am using a Clamp meter. I am totally off grid where I live and have a solar system with battery bank etc and I use it constantly to monitor what is going on with the system. Also the solar system on the van.
The voltage was fairly consistent. Dropping to about 14.15v from 14.2v when warmed up.
I didn’t sense any slippage or significant drag when observing the belt. That doesn’t mean that it definitely isn’t happening. I am going to replace the pulley regardless.
Everything in the van was off and the head light switch turned all the way to the left - counterclockwise.
I agree that it’s odd that the current is messed up but the voltage okay.
thank you for your brain work in trying to figure it out.

 

Sorry for the delay. Work has a tendency to get in the way of having a chat. I'm glad to hear you have knowledge of DC systems and on that point you said you have a Solar panel on the roof. You need to disconnect that to get and accurate reading on you clamp meter. The 2 separate charging sources ( Solar / Engine) will fight with each other and will give spurious readings. This could explain consistent Volts dc but varying Amps dc. If you have already tried this then apologies, but it seems like a likely cause. Also please measure the Amps out put at the alternator and the volts. Clamp meters although good do not like dealing with fast fluctuating values on DC as they have a built in delay. Analogue is better..

 

Hi Mik,
It rained all Day on Monday so nothing happened. When I went to check on Tuesday I realized I had left all three connections on the same input side of the isolator.It appeared That the low cabin battery drained the starter battery some.Before doing anything else, I started the engine. The amperage measured proximately 32 A into the starter battery and 8 to 9 A to the cabin battery. The output stayed steady within one amp or so even after the van was warmed up and I increased RPMs.I then connected the cabin battery to the auxiliary output connection on the isolator as it normally should be. All of the readings stayed the same. I turned on head lamps and heater in the van and the input into the starter battery went up to approximately 66-68 A and the input to the cabin battery stayed in the 8 to 9 amp range. (4.25 volts)
So basically it’s working as it should and nothing has changed. I will check again today and see if it is the same.
I don’t get it. I wouldn’t be surprised if the issue came back. From previous experiences with my van, It seems like the electrical system is possessed.
as for the solar system interfering, it doesn’t seem like it should, but my understanding of electrical interactions is limited. The panels feed into the charge controller and is hooked directly to the battery. It has been cloudy and the van parked under a tree so any solar input while I’ve been testing has been near zero. The set up for my home is the same. Panels to controller to battery bank. A 12 V charger connected to a generator when there has been multiple days of cloudy weather and the battery bank is low. The two have always worked in harmony.
I have ordered a belt tensioner pulley and will be replacing that as soon as I get it. At least I’ll be able to eliminate that as a cause of the problem.
thanks, Tom