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Open Roads Forum  >  Towing

 > Charging trailer battery while towing and smart charging

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opnspaces

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Posted: 12/03/19 04:05pm Link  |  Quote  |  Print  |  Notify Moderator

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?


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Lwiddis

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Posted: 12/03/19 04:35pm Link  |  Quote  |  Print  |  Notify Moderator

An adequately size solar system eliminates this issue most days.


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time2roll

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Posted: 12/03/19 05:42pm Link  |  Quote  |  Print  |  Notify Moderator

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.


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corvettekent

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Posted: 12/03/19 08:59pm Link  |  Quote  |  Print  |  Notify Moderator

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


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Posted: 12/03/19 10:58pm Link  |  Quote  |  Print  |  Notify Moderator

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


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mbopp

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Posted: 12/04/19 07:45am Link  |  Quote  |  Print  |  Notify Moderator

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


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garym114

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Posted: 12/04/19 08:26am Link  |  Quote  |  Print  |  Notify Moderator

The charge voltage the tow vehicle battery needs is measured at its battery. The second battery is not a load so the voltage is not increased just because it is there. Operating in tow-haul or turning the headlights on will increase the output voltage. You need a larger gauge wire to carry that voltage. You would still have to measure output voltage to see if the increase is enough.
I loathe the EPM system in our GMC Acadia. It doesn't ever fully charge the battery it leaves the battery at low voltages, 12.4, and lets is sit there and sulfate, reducing its capacity and preventing it to ever fully charge again. The battery goes into a death spiral.


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time2roll

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Posted: 12/04/19 09:18am Link  |  Quote  |  Print  |  Notify Moderator

The point of the DC-DC converter is such that you can ignore the voltage gyrations of the alternator and any voltage drop in the wire and get proper charging voltage on the trailer battery. You no longer care what the vehicle is doing or how it works.

opnspaces

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Posted: 12/04/19 11:25am Link  |  Quote  |  Print  |  Notify Moderator

Thanks Time2roll and GaryM, Yes I do get that a DC to DC converter should do what I need. But those seem to be hundreds of dollars. So before I consider putting down that kind of money I really want to understand why a factory setup is not longer applicable. I've read your and the other posts multiple times and something still eludes me. Please tell me if I have it correct below.

I think what I'm gathering is that the alternator will see the sag as I plug the trailer in. But it doesn't see the additional battery as a battery. So all the electronics see is an additional load as the starter battery and the trailer battery try to equalize to each other. So the alternator only bumps up the output to get the whole system back up to 13.x volts and not into any kind of useable charging mode. Or put another way, even though the trailer battery is needing a strong charge, the alternator is only putting out enough to float charge?
Thanks

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Posted: 12/04/19 11:40am Link  |  Quote  |  Print  |  Notify Moderator

Start by running a heavy dedicated charge line between the truck and trailer. It will help in trickle and maintenance charging. If you want more, later you can add a DC to DC charger off this new run line.


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