Minnie 2201DS. Battery Charging

skypilot · 07-01-2020, 09:27 PM

Pulled into campground tonight, tongue jack slow, checked battery lights inside coach and only had one light showing. After plugging in shore power, batteries began to charge. It was connected ok to my 2014 ram pickup. Did not charge today from truck. I don’t know if the truck has fuse that can blow that has something to do with charging while driving. Looking for thoughts on this. Trailer has two batteries, 2018 trailer

Goodspike · 07-01-2020, 09:46 PM

For some GM trucks you need to be either in tow/haul mode or have headlights on. That causes the alternator to run at a higher voltage, which is necessary to charge remote batteries.

On my truck without tow/haul on the voltage can get down to 12.4, which is not going to charge anything. It will increase going downhills, so apparently part of this is fuel economy related.

Anyway, read your truck's manual to see if Ram has something similar, or if you have a voltage readout on your truck's display, monitor it to see what keeps it over 14 volts. My truck will often stay over 14 for the first 20 or 30 miles, longer if I haven't driven it for a while.

Finally, there is one of the connections that is responsible for the charging, so if you have a voltage meter check it out. It's entirely possible it's a fuse.

pmglidden · 07-02-2020, 09:17 PM

There’s a good book that I think every rv owner should have.

“Managing 12 volt”

In this book he states that in modern vehicles alternators are not appropriate for charging batteries. The premise is that the computer uses the charge state of the cars battery to determine output.

You can force the system to put out a bit more through turning on the headlights, or using tow/haul in some vehicles, but it will never truly be the amount necessary to charge a battery

Goodspike · 07-02-2020, 09:25 PM

Quote:

Originally Posted by pmglidden

You can force the system to put out a bit more through turning on the headlights, or using tow/haul in some vehicles, but it will never truly be the amount necessary to charge a battery

First, not sure if you intended to post a link, but there was no link.

I think that would be entirely dependent on the size of the alternator, although those are probably getting smaller too for fuel efficiency. If it's putting out over 14 volts it will be charging a normal battery at whatever amperage the thing puts out, less current vehicle demands.

Absent some full size trucks that offer the option of a second alternator, I'm not sure any allow the option of a larger alternator as they did in the past.

pmglidden · 07-02-2020, 09:33 PM

Here’s the amazon page to the book. I check it out from the local library

Managing 12 Volts: How to Upgrade, Operate, and Troubleshoot 12 Volt Electrical Systems https://www.amazon.com/dp/0964738627..._2AQ.EbZRFWDNF

Micro1808 · 07-03-2020, 08:58 AM

While the truck does supply some charge through the 7-wire plug, the main job of the alternator is to charge and maintain the battery on the truck, not the trailer.

Assuming the trailer batteries are lead acid, they need different stages to charge (bulk, absorption, float) to reach full capacity. The truck does not have the ability to do this, nor can it figure out what state of charge you have in multiple trailer batteries. It can, and does, do this for your truck battery, but that's it.

Your best bet is to start off with a full charge on your trailer batteries, and not rely on the truck to bring them back to a charged state, especially if they are fully depleted.

Goodspike · 07-03-2020, 09:02 AM

I really wish my trailer had a 12 volt cigarette style outlet so I could easily plug in a digital voltmeter and monitor voltage. That would be useful for other purposes too, such as phone chargers. Seems really cheap that Winnebago doesn't do that anymore, but they are hardly alone.

Bigbird65 · 07-03-2020, 09:33 AM

Get a voltmeter and see if there is 12 volts between pins 1 and 4 on your RAM. 12 volts is always there on my 2017 RAM 1500. There is also a diagram on the trailer connector door. If you have voltage there put the voltmeter on the RV battery terminals and see if the voltage goes up when you start the truck.

Goodspike · 07-03-2020, 10:12 AM

Quote:

Originally Posted by Bigbird65

I think those pin placements are correct, but the colors may vary by vehicle. Also I think the center on GMs and many others is for backup lights.

pmglidden · 07-03-2020, 10:18 AM

Once the battery on the vehicle is charged, the alternator won’t put out full output. As was stated above the alternators job is not to charge the rv battery.

The vehicle has nothing to determine charge state on a trailer battery and it just doesn’t apply charge with the goal of charging your trailer battery.

Bigbird65 · 07-03-2020, 10:26 AM

Quote:

Originally Posted by Goodspike

I think those pin placements are correct, but the colors may vary by vehicle. Also I think the center on GMs and many others is for backup lights.

On the RAM also, the center pin is indicated as backup lights.

DavidM · 07-03-2020, 10:30 AM

Newer TVs are a PITA when trying to charge trailer batteries while towing. As noted the tow/haul switch or headlights being on helps. One solution is to install a B2B charger to help boost the current to the trailer batteries.

Renogy makes a 20A unit that would be suitable for existing TV wiring that costs $116. See https://www.amazon.com/Renogy-Batter...a-728968810259

My 2013 Nissan Pathfinder which has a fixed 13.8 V alternator output will charge my trailer battery at 3 amps if nearly full, 7 amps if 10% discharged and 15+ amps if 50% discharged. It never gets much over 15 amps due to the voltage drop in the TV wiring limiting the current that is supplied.

David

Bigbird65 · 07-03-2020, 10:49 AM

Quote:

Originally Posted by pmglidden

Once the battery on the vehicle is charged, the alternator won’t put out full output. As was stated above the alternators job is not to charge the rv battery.

The vehicle has nothing to determine charge state on a trailer battery and it just doesn’t apply charge with the goal of charging your trailer battery.

Sorry but I respectfully disagree with you. The 12 volt pin on the RV connector is in parallel with the truck battery. The alternator charges the trailer battery along with the truck battery so that the trailer battery is ready for use when you get to your camping site. Anyone agree?

Goodspike · 07-03-2020, 02:49 PM

Quote:

Originally Posted by Bigbird65

Sorry but I respectfully disagree with you. The 12 volt pin on the RV connector is in parallel with the truck battery. The alternator charges the trailer battery along with the truck battery so that the trailer battery is ready for use when you get to your camping site. Anyone agree?

I do. And so does GM. From my manual.

Quote:

To help charge a remote (non-vehicle) battery, press the Tow/Haul Mode button on the center stack. If the trailer is too light for Tow/Haul Mode, turn on the headlamps to help charge the battery.

The tow vehicle battery may have a better connection to charge, particularly given it's closer, but the remote battery should charge.

Also, that alternators cut back when the battery is charged is relatively new. They used to just put out 14+ volts pretty much constantly.

Morich · 07-03-2020, 08:26 PM

Quote:

Originally Posted by Bigbird65

Sorry but I respectfully disagree with you. The 12 volt pin on the RV connector is in parallel with the truck battery. The alternator charges the trailer battery along with the truck battery so that the trailer battery is ready for use when you get to your camping site. Anyone agree?

I totally agree!
When we connect two batteries together they become one battery string, not two batteries. If the alternator is charging the start battery of the vehicle and the trailer battery is connected to that start battery, current will flow to the trailer. It will be somewhat slower to charge two batteries than one but that is normal and expected.
When we start the engine on a motorhome both the coach and start batteries are charged from the alternator.
The only difference in having a trailer battery in the string versus two batteries side by side is the distance between the two and the wiring size.
We often read that it is not good to replace only one battery in anything as the new battery voltage will be pulled down to whatever level the old will hold. Given time and the truck engine not running, the discharged trailer battery will pull the truck battery down and both will have low voltage. Can we agree that if we leave the truck and trailer batteries connected and leave a bunch of lights on in the trailer, both go dead?
So if current flows out of the truck to the trailer to let the battery voltage go down, why would it not flow out to let the voltage go up?

There might be some concern on charging a battery that is fully down as the wiring in the trailer connection is not very large and it could overheat or blow a fuse if too much current flows.
I would favor starting with a fully charged trailer battery as the trip would not have enough time to fully charge one but for just putting some back, I have no trouble with using the center pin.

Bigbird65 · 07-04-2020, 07:21 AM

Good write up Morich. I always start out with a fully charged battery and have never had a battery problem in the two Winnebago Minnies that I have owned. I was hoping to hear back from skypilot.

Morich · 07-04-2020, 08:27 AM

Sometimes we let things become too complex in our thinking and part of that is due to what I call marketing. There is a definite tendency for sales to make things sound far more exciting and elaborate than they are actually built.
Sensing the "state of charge" is an example. When we see something doing this we need to look at what it is actually doing and then we can get better use of the information.
When we hear of an alternator "sensing" the state of charge of the battery, does that mean it take a reading of the specific gravity of each cell and then converts that info to the information it gives us? Not likely, more likely it senses the voltage at the positive and negative posts and tells us nothing more than what the surface charge is at that moment.
That's why we get the reports worried about the battery being bad because we see the "state of charge" being 100%, so we turn off charging and when we get home a few hours later the charge has gone way down! State of charge and voltage are not the same---except in marketing terms.
Recharging batteries on fishing boats on the trip home is pretty commonly done but most do finish it off with a charger once there as they don't get a full charge in the short trip of a few hours.

Goodspike · 07-04-2020, 08:42 AM

Quote:

Originally Posted by Morich

Recharging batteries on fishing boats on the trip home is pretty commonly done but most do finish it off with a charger once there as they don't get a full charge in the short trip of a few hours.

I think that is the other part of the problem. People expect the recharge to occur too quickly. And they don't stop to think that the more battery capacity they have the longer it will take.

I've never done the math to figure out how many amps of charging power it would take to recharge two 50% depleted batteries in 5 hours (the length of many day travels). Anyone care to take that on?

RDP · 07-04-2020, 07:41 PM

A good multi-meter is your friend. Check the voltage if the battery before plugging into the tow vehicle, then check the voltage when connected and motor is running, if it is higher, then you are charging.

Goodspike · 07-05-2020, 08:14 AM

Quote:

Originally Posted by RDP

A good multi-meter is your friend. Check the voltage if the battery before plugging into the tow vehicle, then check the voltage when connected and motor is running, if it is higher, then you are charging.

Generally a good idea, but you'd need to check the tow vehicle too to make sure it was in a condition where the alternator was charging the battery (that it has a higher voltage when you test).