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Alternator power to trailer

Rick Schleicher
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Rick Schleicher Enthusiast

Rick Schleicher

Posted
Posted

Hello all

 

2021 2500 HD Gas, towing a 30' TT with 2 - lead acid batteries

 

Trailer has a 160W solor panel on the roof  and between the solar and the truck, the TT batteries continue to loose charge throughout a travel day due to the 12v refrigerator (mainly) and a few other parasitic draws that can't be turned off.

 

When driving, I notice the truck volt meter generally sits right at ~12v, the trailer batteries do not show as being charged. When the volt meter shows closer to 14v, then the trailer batteries show as charging. The higher charging voltage isn't enough to overcome the 12v refer draw.

 

A few questions

* Is my truck battery weak so the alternator is spending more time trying to keep it changed before sending power to the trailer?

* Is the BMS bad and not switching when the truck battery is charged?

* Is it possible to install a second battery in the truck and wire it to provide more consistent power to the trailer while sill getting charged from the alternator? (I'm grasping here)

 

As we know, draining lead acid batteries effectively kills them and on long travel days, they are quite low

 

I'm also considering adding another solar panel to the trailer however that only helps to partially solve the issue

 

Thoughts?

Rick

Another JR Senior Enthusiast

Another JR

Posted
Posted

The behavior you are seeing is the result of the voltage loss between the alternator and the trailer battery and the output characteristics of your vehicle’s “smart alternator” system. These two in combination with the trailer loads result in insufficient voltage at your trailer battery for charging except when your alternator is putting out high voltage to recharge the truck battery for a period after engine start.
 

Ideally, what you would want to do to to solve this is 1) run larger positive and negative wires from the truck battery fuse block and a large ground stud in the engine compartment, respectively, to the trailer battery compartment, and 2) install a DC to DC converter/charger in the trailer battery compartment or very near to to it. A popular and versatile 30 amp DC to DC converter/charger is the Victron Orion Smart 12/12-30. Renogy makes a 40 amp converter but the ability to tailor the battery charging is more limited than the Victron.

 

6 awg wires from the truck are sufficient for the Victron because of its more sophisticated engine running detection logic. You probably would need at least 4 awg with the Renogy.
 

One good thing about installing such a charger is you will be all set for a lithium battery conversion in the future, at least with respect to charging from the truck. I have one of those Victron chargers in my truck camper along with a solar setup.  It works very well and can be monitored and controlled from a smart phone. 

64BAwagon Senior Enthusiast

64BAwagon

Posted
Posted

On previous trucks I have run a new wire to feed the 12v+ at the trailer plug. The OEM wire is very thin ( I believe around an 18ga) and is very limited in capacity. I have run 12 or 10ga to the back of the truck. You can connect it via a fused line on the posts on the battery or use a 30A relay switched to ignition only if you chose. The relay would require you adding a tap to a fuse thats on only with ignition and connecting that tothe 85 terminal on the relay, 30 goes to your power source, 86 to ground and 87 to your new wire to the rear. 

GMCustomerService Senior Enthusiast

GMCustomerService

Posted
Posted
On 11/12/2022 at 11:12 AM, Rick Schleicher said:

Hello all

 

2021 2500 HD Gas, towing a 30' TT with 2 - lead acid batteries

 

Trailer has a 160W solor panel on the roof  and between the solar and the truck, the TT batteries continue to loose charge throughout a travel day due to the 12v refrigerator (mainly) and a few other parasitic draws that can't be turned off.

 

When driving, I notice the truck volt meter generally sits right at ~12v, the trailer batteries do not show as being charged. When the volt meter shows closer to 14v, then the trailer batteries show as charging. The higher charging voltage isn't enough to overcome the 12v refer draw.

 

A few questions

* Is my truck battery weak so the alternator is spending more time trying to keep it changed before sending power to the trailer?

* Is the BMS bad and not switching when the truck battery is charged?

* Is it possible to install a second battery in the truck and wire it to provide more consistent power to the trailer while sill getting charged from the alternator? (I'm grasping here)

 

As we know, draining lead acid batteries effectively kills them and on long travel days, they are quite low

 

I'm also considering adding another solar panel to the trailer however that only helps to partially solve the issue

 

Thoughts?

Rick

This is certainly not what we like to hear, Rick Schleicher.  Please know, customer satisfaction is extremely important to us. Our team would be more than happy to take a closer look into the concerns with your 2021 2500 HD. To do so, please send an email to [email protected] with ATTN: Rick Schleicher/GM Trucks in the subject line.

Please include your contact information, VIN, a brief description of your concern, and the name of your preferred dealership. We look forward to hearing from you. To learn more about GM’s privacy policy, please visit https://www.gm.com/privacy-statement.html.
 
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  • 3 weeks later...
Jettech1 Senior Enthusiast

Jettech1

Posted
Posted
On 11/12/2022 at 11:12 AM, Rick Schleicher said:

Hello all

 

2021 2500 HD Gas, towing a 30' TT with 2 - lead acid batteries

 

Trailer has a 160W solor panel on the roof  and between the solar and the truck, the TT batteries continue to loose charge throughout a travel day due to the 12v refrigerator (mainly) and a few other parasitic draws that can't be turned off.

 

When driving, I notice the truck volt meter generally sits right at ~12v, the trailer batteries do not show as being charged. When the volt meter shows closer to 14v, then the trailer batteries show as charging. The higher charging voltage isn't enough to overcome the 12v refer draw.

 

A few questions

* Is my truck battery weak so the alternator is spending more time trying to keep it changed before sending power to the trailer?

* Is the BMS bad and not switching when the truck battery is charged?

* Is it possible to install a second battery in the truck and wire it to provide more consistent power to the trailer while sill getting charged from the alternator? (I'm grasping here)

 

As we know, draining lead acid batteries effectively kills them and on long travel days, they are quite low

 

I'm also considering adding another solar panel to the trailer however that only helps to partially solve the issue

 

Thoughts?

Rick

We tow our Grand Design Imagine with our 2022 custom gasser and we have never had a problem, even with the 12v fridge running.  We also have a 165W solar panel on our camper but when plugged into the truck, never a problem.  So I think you might have a problem with your 7 pin connector.  Might be time to get out the old trusty digital VOM meter and start troubleshooting your loss of power to your camper.

  • Like 1
  • 2 weeks later...
ExYukon Enthusiast

ExYukon

Posted
Posted

I'm not familiar with HD trucks, but I know that on the 1500 SUVs and pickups, GM increases the alternator voltage when you turn on tow/haul mode.  The voltage algorithm is complicated, taking into account things like estimated battery state of charge and what accessories are turned on, but tow/haul does increase voltage over what you would get otherwise.

 

Do you use tow/haul with your TT?

 

Does anyone know if the HD trucks increase voltage for tow/haul?

  • Like 1
  • 1 month later...
Jettech1 Senior Enthusiast

Jettech1

Posted
Posted
On 12/17/2022 at 7:13 PM, ExYukon said:

I'm not familiar with HD trucks, but I know that on the 1500 SUVs and pickups, GM increases the alternator voltage when you turn on tow/haul mode.  The voltage algorithm is complicated, taking into account things like estimated battery state of charge and what accessories are turned on, but tow/haul does increase voltage over what you would get otherwise.

 

Do you use tow/haul with your TT?

 

Does anyone know if the HD trucks increase voltage for tow/haul?

I have no idea concerning the HD increased voltage when in tow/haul mode, nor did I know that the 1500's do.  The gauge stays right at 14v and never moves.  Interesting.  We've never had a problem with our HD keeping up with our TT voltage needs when towing.  The 12 volt fridge works amazing and always stays cold, the TT battery holds a charge, no problems at all.

  • Like 1
Another JR Senior Enthusiast

Another JR

Posted
Posted

When I first responded to this in November I didn’t catch that the OP said that the truck voltage gage was at 12 volts at times while the truck is running. I don’t think that’s normal. Also, if the truck electrical system really is at that low a voltage, the charge control relay in the trailer likely is open circuit because that is an “engine not running” voltage level.

 

i would put a voltmeter on the battery when the truck is running and the truck gage says only 12 volts. If your meter confirms that, then the dealer should look at it. There may be an issue with the truck. 

  • Like 1
Jettech1 Senior Enthusiast

Jettech1

Posted
Posted
7 minutes ago, Another JR said:

When I first responded to this in November I didn’t catch that the OP said that the truck voltage gage was at 12 volts at times while the truck is running. I don’t think that’s normal. Also, if the truck electrical system really is at that low a voltage, the charge control relay in the trailer likely is open circuit because that is an “engine not running” voltage level.

 

i would put a voltmeter on the battery when the truck is running and the truck gage says only 12 volts. If your meter confirms that, then the dealer should look at it. There may be an issue with the truck. 

I think I missed that too.  12v output from any vehicle is not a good thing.

RnA2021 Enthusiast

RnA2021

Posted
Posted

We have a 2021 2500 gasser.  We have 2, 100 amp lithium batteries in our trailer.  We also have a 190 watt solar panel.  Last fall, camping in a forested area, and cool weather, we drew our lithium batteries down to about 60 percent of capacity.  When we connected truck to head home, the alternator was putting out over 20 amps (I have a battery monitor).  So, the factory alternator with stock wiring should take care of your battery needs.

 

Rick B

  • Like 1
Jettech1 Senior Enthusiast

Jettech1

Posted
Posted
1 hour ago, RnA2021 said:

We have a 2021 2500 gasser.  We have 2, 100 amp lithium batteries in our trailer.  We also have a 190 watt solar panel.  Last fall, camping in a forested area, and cool weather, we drew our lithium batteries down to about 60 percent of capacity.  When we connected truck to head home, the alternator was putting out over 20 amps (I have a battery monitor).  So, the factory alternator with stock wiring should take care of your battery needs.

 

Rick B

I've been wanting to change my one standard battery over to 2 lithiums.  Our solar panel is only 165W but keeps the battery charged when in storage.  What brand did you go with concerning the batteries?

Another JR Senior Enthusiast

Another JR

Posted
Posted
1 hour ago, RnA2021 said:

We have a 2021 2500 gasser.  We have 2, 100 amp lithium batteries in our trailer.  We also have a 190 watt solar panel.  Last fall, camping in a forested area, and cool weather, we drew our lithium batteries down to about 60 percent of capacity.  When we connected truck to head home, the alternator was putting out over 20 amps (I have a battery monitor).  So, the factory alternator with stock wiring should take care of your battery needs.

 

Rick B

Agreed. A base alternator on these trucks that is operating properly has sufficient excess capacity to deliver at least 30 amps of trailer battery charging when the engine is at or above about 1200 rpms. I have the gas engine with the optional 220 amp alternator, and it will deliver 35 amps to my dc to dc charger for my camper lithium batteries at idle immediately after engine start. That’s with 6 awg positive and negative wires end to to end.  I imagine my alternator could deliver 60 amps or more for charging, but my dc to dc converter is a 30 amp output and draws max 35 amps from the truck. 
 

The truck has 10 awg wire for its charging circuit via the 7 pin connector. That wire can carry at least 30 amps without excessive wire heating, but the voltage drop will be high. I’m guessing to get 20 amps charging rate into your lithium batteries you have a dc to dc converter charger to deal with the voltage drop?  If so, does it cycle on and off due to the voltage drop or remain stable?

Another JR Senior Enthusiast

Another JR

Posted
Posted
15 minutes ago, Jettech1 said:

I've been wanting to change my one standard battery over to 2 lithiums.  Our solar panel is only 165W but keeps the battery charged when in storage.  What brand did you go with concerning the batteries?

I know you directed this at RnA, but I’ll chime in. I have 203 ah of LiFePO4 battery, a Victron 30 amp dc to dc converter, a Victron 30 amp mppt solar charger and 400 watts of panels, and a Victron battery monitor. I would have bought Battleborn batteries if I could have made two of them fit in my battery compartment, but it was not a good space or shape for that. They use cylindrical cells and have an excellent case and BMS. I ended up buying a 203 ah battery from BigBattery.com. They use prismatic cells like most of the other manufacturers. They had a good teardown review from Will Prowse on youtube, and the form factor and feature were perfect for my physical installation.  Two years in it is working well. 

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