Opening a new thread from Link about newer vehicles and their smart charging systems so as not to derail that thread.Basically I'm just looking for a better understanding of the newer charging systems. In the other thread it was posted that "Some time around 2000-2005 ALL cras and light trucks start using "smart charging systems". Various manufacturers do it differently and even the same manufacturer have made changes since they first started. These smart charging system put out the MINIMUM voltage to keep the starting battery charged, typically between 13.2V and 13.8V (about 2-5 minutes after the engine has started). This is NOT ENOUGH VOLTAGE TO CHARGE A HOUSE LEAD ACID BATTERY BANK ! Installing heavier wire will NOT improve this !!What you need is a DC-DC battery charger."I can understand the statement about the smart charging just keeping the starting battery up as they typically don't use much to start the engine. But what about when the trailer with a battery at 12.3 volts is hooked up? Wouldn't that cause the alternator to come out of maintenance mode and start trying to charge the batteries? I mean if not then why would the manufacturers even bother to equip a high amperage battery?

An adequately size solar system eliminates this issue most days.

The alternator simply holds the voltage at the level determined by the computer. And yes the program does not always hold a high voltage as it did in the old days.No. Connecting an additional load does not alter the alternator charging profile. That second battery is just another load same as turning on the headlights or air conditioner.You can connect that battery at 12.3 volts very close to the start battery and you will get a decent charge going. The nature of lead-acid will have the charge level tapering off quickly as the alternator just holds the 13.x volts.Now connect with the OEM #14 wire 25' back to the trailer and the voltage will drop causing the tapering off to be even worse.Enter the DC/DC charger and that voltage drop back to the battery can sag down to 11 volts and yet you will still have full 14.5 volts on the trailer battery. Still takes 2 to 4+ hours for a charge.

About 200 watts of solar on the roof of your trailer will keep your batteries charged when traveling down the road.

corvettekent wrote:About 200 watts of solar on the roof of your trailer will keep your batteries charged when traveling down the road.This^^.Rob

I heard, but can't confirm, that GM trucks raise the system voltage when the tow-haul is engaged.

Charging trailer battery while towing and smart charging

24 Replies

sayoung
Explorer
Dec 21, 2019
ivbinconned wrote:
You are pulling with a Suburban so what I do is not an option for you how ever I will describe what I do for the benefit of all.
I use a “20amp Smart Charger around the farm year round and we have a 2000 Yamaha gen/inverter.
I fished an extension cord from the 4 - 6 volt batteries to the fifth wheel hitch. I set the gen on eco in The back of the truck, plugin the charger and clamp to the batteries.
If we use the furnace all night while boon docking on the road the house batteries get charged properly as we cruse down the highway.
A heavy gaged wire from your truck battery to trailer batteries may take out your alternator.

I added a 2nd 50amp plug at the front of our 5er along with a transfer switch/surge protection . I just use this to run the AC when we have our pooches with us & need to stop for a while. We don't boondock so was never concerned about high current charging wile traveling
2112
Explorer II
Dec 21, 2019
pianotuna wrote:
opnspaces wrote:
Yes I do get that a DC to DC converter should do what I need. But those seem to be hundreds of dollars.
Thanks

Here is one that does up to 15 amps for about $30 bucks.

https://www.amazon.com/Numerical-Regulator-10V-120V-Converter-Adjustable/dp/B01GFVI6R6/ref=sr_1_3?keywords=12+volt+dc+to+dc+converter+adjustable&qid=1575607837&sr=8-3
This is the one I use
https://www.amazon.com/Voltage-Converter-DROK-Regulator-Transformer/dp/B076TTBKFG/ref=sr_1_19?crid=1W730TNW56RP9&keywords=drok+voltage+regulator&qid=1576918618&sprefix=Drok%2Caps%2C1001&sr=8-19
rvshrinker
Explorer III
Dec 21, 2019
Second Chance wrote:
corvettekent wrote:
About 200 watts of solar on the roof of your trailer will keep your batteries charged when traveling down the road.

This^^.

Rob

Everywhere? Are you sure?

Today my 40 panel 12 kWp HOME solar system generated a grand total of 3.47 kWh. It’s like that a lot in this part of the country, this time of year.
ivbinconned
Explorer II
Dec 15, 2019
You are pulling with a Suburban so what I do is not an option for you how ever I will describe what I do for the benefit of all.
I use a “20amp Smart Charger around the farm year round and we have a 2000 Yamaha gen/inverter.
I fished an extension cord from the 4 - 6 volt batteries to the fifth wheel hitch. I set the gen on eco in The back of the truck, plugin the charger and clamp to the batteries.
If we use the furnace all night while boon docking on the road the house batteries get charged properly as we cruse down the highway.
A heavy gaged wire from your truck battery to trailer batteries may take out your alternator.
pianotuna
Nomad III
Dec 06, 2019
opnspaces wrote:
Yes I do get that a DC to DC converter should do what I need. But those seem to be hundreds of dollars.
Thanks

Here is one that does up to 15 amps for about $30 bucks.

https://www.amazon.com/Numerical-Regulator-10V-120V-Converter-Adjustable/dp/B01GFVI6R6/ref=sr_1_3?keywords=12+volt+dc+to+dc+converter+adjustable&qid=1575607837&sr=8-3
time2roll
Nomad
Dec 06, 2019
A DC clamp-on ammeter will tell the real story.
opnspaces
Navigator II
Dec 05, 2019
Thanks everyone. I'm hopefully going camping (boondocking) soon with a slightly newer tow vehicle, 2001 Suburban. I plan to take a few voltage checks while there. I'm really curious to see if I get any significant charging while driving.
theoldwizard1
Explorer II
Dec 04, 2019
Bedlam wrote:
I run a 2 gauge dedicated run between my truck and trailer and use Anderson connectors for the link at the receiver.

How about some "real world" feed back !

Next time you are hitched up, check the battery voltage at the truck battery and then the battery voltage at the trailer battery.

For best results for this test, the trailer battery should be at least 10% discharged.
time2roll
Nomad
Dec 04, 2019
opnspaces wrote:
Thinking about wiring gauge and voltage drop, do I then have to mount the dc to dc charger at the back of the Suburban so it's close to the trailer? Or can I mount it up front and run a 12 or 10 gauge wire back to the plug? If I mount the charger in the back, do I need to run a 12 or 10 gauge wire to feed it? I think oldwizard kind of answered that but I want to be sure.
Assuming you get the 20 amp you will mount it on the trailer close to the battery. No other modifications needed.
ependydad
Explorer
Dec 04, 2019
opnspaces wrote:
Thinking about wiring gauge and voltage drop, do I then have to mount the dc to dc charger at the back of the Suburban so it's close to the trailer? Or can I mount it up front and run a 12 or 10 gauge wire back to the plug? If I mount the charger in the back, do I need to run a 12 or 10 gauge wire to feed it? I think oldwizard kind of answered that but I want to be sure.

The one installation that I've seen of this, the DC-to-DC converter was installed in the camper near the batteries.

btw, thank you for asking this. I'm learning a lot!