How slow is it? Is there a mod you can do to make it charge quicker?I was watching a video where some ppl that like to boondock said the alternator doesn't charge the batteries on your RV very quickly. Is this correct?

The problem is mostly that it's a long way from the alternator to the batteries and the vehicle manufacturers use wire that is too small for this circuit. It's often something like #14 or so. It really needs to be more like #6 or larger to get good current flow. People who really want to set things up well for this will run a heavy charge line from the battery tot he rear of the tow vehicle with something like #2 welding cable. Then, you use connectors meant for a lift gate trailer or perhaps some Anderson Powerpole style connectors rated for 100A. Of course this require the matching connector and more #2 cable on the trailer to the batteries.The other problem is that in the ever present race to improve vehicle MPG many modern vehicles actually lower the alternator's output voltage when the vehicle is just "cruising down the road". Usually turning on the headlights or putting the transmission into tow/haul mode will raise the charge voltage back up.

It is pretty much a trickle charge, if the vehicle is set up to do it. Alternators are usually sized to supply the demand the vehicle will be needing. You would have to have a much larger amperage alternator or install a second alternator if you have room for it in order to put a dent in charging the house batteries.

Smart Boondockers use solar and backup with a generator.

Some have used a DC to DC converter in the trailer charge line to increase the voltage high enough so that charging is better. If you do, be sure to include a way to power the trailer breakaway switch - DC to DC converters are one way devices...

Thats not to say that it is useless . A good 6 or 8 hour drive will bring my batts back up . Sitting at idle waiting for a battery to recharge , ya better bring your lunch !

Tow vehicle charging RV batteries | Good Sam Community

37 Replies

time2roll
Nomad
Dec 05, 2020
Single alternator has plenty of amps. The trick is getting the proper voltage on the battery that needs charging. A DC-DC charger will work excellent for this purpose. Still takes 3 to 5 hours to get a flooded battery from low on charge to 95%+.

https://www.renogy.com/12v-dc-to-dc-on-board-battery-charger/

Also consider some solar. This works all day with no effort. Works in motion or stationary. Does need sun of course. 200 to 400 watts works well for most people. Even if it does not provide all the power solar will significantly reduce generator or alternator run time.
jdc1
Explorer II
Dec 05, 2020
Dual alternator. Best you could ever do. Some super duties come equipped that way.
pianotuna
Nomad III
Dec 05, 2020
dc to DC voltage boosting may be the best way to improve charging.
theoldwizard1
Explorer II
Dec 05, 2020
Seon wrote:
As a backup I carry a 12v charger powered by a 2K generator.

The 12VDC output on most of today's generators does a poor job of recharging a lead acid battery. You are better off plugging in a AC battery charger.
theoldwizard1
Explorer II
Dec 05, 2020
old idaho guy wrote:
If you are trying to charge your battery while camping, use jumper cables from battery to battery

A DC-DC charger will do it faster because of what I just described.
theoldwizard1
Explorer II
Dec 05, 2020
blaczero wrote:
How slow is it? Is there a mod you can do to make it charge quicker?

The real issue is how large is your battery bank and how depleted is it (what is its "state of charge" SOC ?)

Sometime around 2000, the entire auto industry switched to "smart charging". Smart charging is when the PCM controls the output voltage to the alternator to limit the voltage to "just enough" to replenish the battery after a start and not left the voltage go so low as to discharge the starting battery.

This means that about 5-10 minutes after starting you vehicle the output of the alternator is about 13.2V-13.4V and there is not much you can do about that !

So if your RV battery is at the end of 25' of wire (actually double that because you have a ground connection) you will be darn lucky to get 13.0V, probably less. You can NOT charge a lead acid battery on that little voltage. USING HUGE WIRING FROM THE VEHICLE BATTERY TO THE RV BATTERY DOES NOT SOLVE THIS PROBLEM !

The only solution is a DC-DC battery charger mounted close to the RV battery. Most can accept voltages as low as 10V-11V and boost them up to the proper voltage (>14V) to charge a battery.
Seon
Explorer II
Dec 05, 2020
I bought from Amazon a 20watt solar panel charger/maintainer connected to battery #1 while the trailer powers off #2 battery then next day switch to #1 battery and transfer the solar connectors to #2 battery to charge.
As a backup I carry a 12v charger powered by a 2K generator.

Works for me.
Lwiddis
Explorer II
Dec 04, 2020
What’s for lunch, wanderingbob?
old_idaho_guy
Explorer
Dec 04, 2020
If you are trying to charge your battery while camping, use jumper cables from battery to battery
deltabravo
Nomad
Dec 04, 2020
blaczero wrote:
Is there a mod you can do to make it charge quicker?

Bigger cables on a dedicated charge line.

This is how I did it

My truck has dual alternators

Forum Discussion

Tow vehicle charging RV batteries

37 Replies

About Travel Trailer Group

Related Content

Battery isolator charge vehicle battery on shore power

Battery Charging

Charging a towed vehicle's battery

chassis battery charge ?

Charging House Batteries