Do you use your alternator to charge your travel trailer batteries?

[Varago]

I do like Keymastr's idea about "1000 watt inverter generator" that is so KISS.

Dave

[Lstyles]

Thanks for the input. I am planning on a nice solar set up on the trailer and was just wondering if one could also take advantage of the “lost” electricity that the alternator is producing like they do on the RVs. 10gauge is not going to produce much charge compared with solar set up so not sure it worth doing it. Will also likely have a small generator on board for times when solar can’t keep up (and AC).

[twinboat]

When I bought my last tow vehicle, back in 86, I ordered it with a tow package.
It came with a higher amp alternator, among other things.

If that wasn't for charging another battery what was it for ?

By design, motor home alternators charge house batteries all of the time.

A charge line is not going to wear out your alternator.

[ScoobyDoo]

Going off topic.
If I did any dry (Why is no power hook-up called dry? Better to call it "Dark") I think I wound mount a fair sized battery on the TV, and a smaller battery on the trailer. Then rig a power cord so when the TV is on site, that battery would power the trailer. When out in TV, the smaller battery could power it. If nobody home, it shouldn't use much power, so that battery should last. While driving the main bank would get some charge...

[Persistent]

Charging a TT (travel trailer) battery from a TV( tow vehicle) alternator is severely limited. It could take 10 to 20 hours of driving to charge a lead/acid battery. Why is that? It is all explainable using the principals of physics.
I am going to round things off and approximate values to make the math simpler. The actual values will vary. A 230 volt 30 amp home electric dryer circuit has much in common with a 115 volt 30 amp TT shore power system and a 12 volt 30 amp converter/charger often found in TT’s. They all involve 30 amps of electric current. One might use 10 gage electric wire, plugs, sockets, and connectors for all three.
The effect on devices consuming the power delivered in these circuits is substantially different. National wiring codes are set to provide no more than 1.5 volts of loss in wire runs of 50 feet. A 1.5 volt line loss due to resistance in copper wire and various connectors is the same for all these systems, but the effect is not. A 230 volt system looses 1.5/230 * 100% or .65% of its power. A 115 volt system looses 1.5/1150 * 100% or 1.3%. A 12 volt system looses 12.5%. A 2.5 volt charging system looses 1.5/2.5 * 100% or 60%.
You can see that a 2.5 volt charging system is severely affected. You may not see what a 2.5 volt charging system has to do with TT’s. 2.5 volts is what is available to charge a 12 volt lead/acid battery. An alternator may provide 14.5 volts charge voltage. A discharged 12 volt battery is say, 12 volts. The difference available to drive charge into the battery is 2.5 volts. The line loss in a 50 foot run of 10 gage wire with all of its connections is still the same 1.5 volts. That leaves 1 volt to drive charge into the battery. As the battery charges, the battery voltage increases causing a further decline in amps flowing.
Further, a TV alternator has more to run than just charging the TT battery. All the TV electrical systems consume current. The remaining capacity of the alternator will further limit the charging current. Of course a “bigger” alternator has more reserve capacity to charge the TT battery.
Granted, the details of the physics are much more complicated than shown above. However, the results will be about the same. Tow vehicle charging of a TT’s batteries is possible, but severely limited. Larger wire, connectors, and alternator help, but the distance, and number of connections in the circuit are going to limit.

[AnotherMike]

Originally Posted by Persistent

A discharged 12 volt battery is say, 12 volts. The difference available to drive charge into the battery is 2.5 volts.

I copied the image below from a ham radio web page several years ago...

Note that if there is a electrical load in the trailer while the tow vehicle is connected that the battery charge ability will be limited... that the voltage drop caused by the current to feed that load will lower the voltage at the trailer, and therefore limit the ability to charge past that voltage.

[theoldwizard]

There IS some good information in this thread, but there is also a lot of "old wives tails" and simply WRONG information !

First, around 2000, every manufacturer started developing "smart charging" systems. The idea being, to recharge the battery "just enough" to replenish the energy removed from the battery that starting the engine used. While the engine was running, "maintain" the battery state of charge. This means that even though the voltage delivered to starting battery, immediately after starting the vehicle, might be as high as 14V, it will drop to 12.8V-13.0V within a few minutes. To put energy into ANY lead acid battery take >13.2V !

THESE GOALS ARE TOTALLY INCOMPATIBLE WITH RECHARGING A HOUSE BATTERY, ESPECIALLY A "DEEP CYCLE" HOUSE BATTERY !

The +12V line at your trailer connector is useless for recharging your house battery. It will maintain a fully charged battery, even if you have an inverter running a refrigerator, so that is good.

Originally Posted by RobE

They suggest using ... a DC to DC charger for newer vehicles. These protect the tow vehicle battery and provide charging to the trailer batteries.

If your goal is to recharge your house battery during your next drive, then you absolutely MUST use a DC-DC battery charger. This type of charger actually boosts the voltage delivered to the house battery to replenish the consumed energy and then it does a proper "multi-stage" charging.

REDARC is one manufacturer. CTEK is another. There may be others.


Understand these chargers have limitations and so does the wiring in you vehicle ! If you spent the night dry camping, watching videos and recharging cell phones and laptop, you probably will NOT recharge the house battery bank in a couple of hours of driving. 6 or 8 hours ... MAYBE. If you are going to dry camp again, fire up the generator, pull in your regular charger and top of the house batteries properly !

[PKI]

Using a vehicle alternator is a poor method of RV battery charging. Not a bad option in an emergency, but solar, suitcase solar, fuel cell, generator, or conservation are all better plans.

There is the potential of an integrated vehicle RV battery system where the storage, charging and regenerative capability is all balanced for best power use, but that's not what is being discussed here. Some day soon, it will be.

[Soppy]

Using the vehicle alternator while traveling is a good way to charge your TT battery. You should add a DC-DC charger to be more effective. The DC -DC charger will compensate for the voltage drop in the truck/trailer wiring and will increase the voltage to properly charge the battery a lot quicker. If you are parked , a small generator is your best bet.

[Lstyles]

Thanks for all the info. Things are as I suspected....limited. Can you tell me if these DC - DC chargers will work with a lithium battery? When I looked at them they seem to be focused on pb batteries.

[Cliffy]

OK a reality check- It really pays to test a system before you postulate on how it works. I did just that. 2006 F-150 with a 2019 TT.
I have a battery monitor hooked up to the TT batteries ( 2 6 volt GC batteries).

After a night dry camping I can see as high as 14 amps going into the battery just from the trucks wiring. It usually starts off at about 14.1 volts and then drops to the high 13 volt range. After 4 or 5 hours of running I see 13.4 to 13.6 volts and amps at 1 or 2 going into the battery telling me the battery is getting topped off. I have even checked the monitor readings with a clamp on meter on the battery positive lead at the battery. A double check.

I can recharge to about 90% or higher on my driving trip to the next destination.

When I plug in ground power I see again maybe 2 or 3 amps in in the mid 13 volt range (by my Xantrex 40 charger) telling me again my battery is about full just from driving. If it wasn't I'd be seeing 14.4 volts and 30 amps or more from the Xantrex.

SO, by actually testing the system I have determined that it is possible to recharge while driving. Test your system before you invest in other technology. A good battery monitor is worth its weight in gold.

[theoldwizard]

Originally Posted by Cliffy

OK a reality check- It really pays to test a system before you postulate on how it works. I did just that. 2006 F-150 with a 2019 TT.

Originally Posted by Cliffy

After a night dry camping I can see as high as 14 amps going into the battery just from the trucks wiring. It usually starts off at about 14.1 volts and then drops to the high 13 volt range. After 4 or 5 hours of running I see 13.4 to 13.6 volts and amps at 1 or 2 going into the battery telling me the battery is getting topped off.

Good choice of words !

I suspect the voltages you are seeing at the house battery are a bit higher than on newer F150s.

Originally Posted by Cliffy

I can recharge to about 90% or higher on my driving trip to the next destination.

Point being, it is NOT a 100% "proper" recharge !

Originally Posted by Cliffy

SO, by actually testing the system I have determined that it is possible to recharge while driving. Test your system before you invest in other technology. A good battery monitor is worth its weight in gold.

I still think you would achieve BETTER results using a DC-DC battery charger. Following up with a GOOD charger is important !

[theoldwizard]

Originally Posted by Soppy

Using the vehicle alternator while traveling is a good way to charge your TT battery. You should add a DC-DC charger to be more effective. The DC -DC charger will compensate for the voltage drop in the truck/trailer wiring and will increase the voltage to properly charge the battery a lot quicker.

Well said ! Plus, a good like any good charger, it will do a proper multi-stage recharge !

Originally Posted by Soppy

If you are parked , a small generator is your best bet.

Hooked of course to your house battery charger. The 12V outlet on all small generators is NOT meant for battery charging !

[Persistent]

Originally Posted by Cliffy

OK a reality check- It really pays to test a system before you postulate on how it works. I did just that. 2006 F-150 with a 2019 TT.
I have a battery monitor hooked up to the TT batteries ( 2 6 volt GC batteries).

After a night dry camping I can see as high as 14 amps going into the battery just from the trucks wiring. It usually starts off at about 14.1 volts and then drops to the high 13 volt range. After 4 or 5 hours of running I see 13.4 to 13.6 volts and amps at 1 or 2 going into the battery telling me the battery is getting topped off. I have even checked the monitor readings with a clamp on meter on the battery positive lead at the battery. A double check.

I can recharge to about 90% or higher on my driving trip to the next destination.

When I plug in ground power I see again maybe 2 or 3 amps in in the mid 13 volt range (by my Xantrex 40 charger) telling me again my battery is about full just from driving. If it wasn't I'd be seeing 14.4 volts and 30 amps or more from the Xantrex.

SO, by actually testing the system I have determined that it is possible to recharge while driving. Test your system before you invest in other technology. A good battery monitor is worth its weight in gold.

Cliffy,
I agree, nothing like making good measurement before making conclusions. I have an alternate conclusion about the TV charging while you drive. It is not necessarily correct, but it is a good alternate.
“… a night dry camping I can see as high as 14 amps going into the battery just from the trucks wiring. It usually starts off at about 14.1 volts …”
This could be because the truck battery is low after starting the engine. The alternator detects this and goes into fast charge mode bringing the charge voltage at the alternator up to 14.6 to 15 volts. 14 amps into the TT batteries is substantial. This means your truck and TT wiring are excellent.
When the truck battery reaches the last charge stage, the alternator switches to 13.6 volts to avoid producing large amounts of hydrogen gas. The TT batteries are too far away with too much resistance in the wiring to stop that change and even though not fully charged show in the 13 volt range.
A battery charge using 13.6 volts can take many hours to fully charge. Possibly 18 hours from full discharge to full charge. If you drive 4 to 6 hours you may have partially charged batteries when you shut down the engine. One way to check this is to disconnect the batteries and let them set for 2 to 4 hours. You can then use that voltage to look up in a battery static voltage chart what the actual charge percentage is.
I can’t come up with an alternate explanation for: “… When I plug in ground power I see again maybe 2 or 3 amps in in the mid 13 volt range …”. That seems to indicate charging is indeed in the last phase. It can still take a long time to go from 70% to 100%. 70% is easily enough to get through the night or even a couple of days of dry camping. (I assume the Xantrex is a high quality micro processor controlled fast charger.)