Dual Alternators

[rarebear.nm]

Many assumptions to made made. Typically shore power will recharge batteries in 24-48 hours to 100%. This depends on the output of your converter (maybe an inverter/converter), size of your battery bank the SoC (Sate of Charge) plus how much 12 volt power you use while connected to shore power. While on shore power the converter provides 12 volt power up to the output capacity of the converter. If more 12 volt power is required the batteries are used to make up the difference. Considering what you bought I doubt if there'd be any problem at all.

Yes, the generator will recharge the batteries, given enough time. When I used a geny for that purpose and my batteries would be down to about 86% in the morning, with 460 AHr battery bank and 115 watt of converter output it would take about 3-4 hours of generator time to get back to about 98%. That last couple of percent of recharge can take a long time.

Since I installed a good sized solar system, 1050 watts, I turned off the breakers to the converters and use solar for 100% of my 12 volt recharge needs. I reach 100% every day even in cloudy weather, etc.

[RoadEyePie]

I'm trying to think before I ask this question, but I'm coming up blank. How do you check the battery bank to determine that it's at X%.

[rarebear.nm]

A few options exists.
1. Simple is to have a battery monitor like a Trimetric 2030, other good brands too. It will tell you percent what the battery banks SoC is. Quick and easy from inside the RV.

2. Take 12 volt system voltage. There are tables similar to this and they will give a reasonable take
Battery voltage state of charge table
State of Charge Sealed or Flooded Lead Acid battery voltage Gel battery voltage

Lead-acid Gel
100% 12.70+ 12.85+
75% 12.40 12.65
50% 12.20 12.35
25% 12.00 12.00

I think other types (AGM, Li-ion) have different voltage/SoC level. A Li-ion can be discharged much more deeply with no harm.

3. Measure Specific Gravity for every battery cell, get a good SG gauge

4. Use a volt meter and measure the voltage of each battery cell. This is one of the best ways to determine if you have a bad battery or a bad cell in the bank.

Look at:

https://www.youtube.com/watch?v=_8qgZoovWHI

Hope this helps.

[tuffr2]

I use my, what I call my amp meter or wire tester. It does, however not give you a % of charge but will give you the amps. I look for 12.x is good enough.

Set the amp meter to 12v.

[rarebear.nm]

Originally Posted by tuffr2

I use my, what I call my amp meter or wire tester. It does, however not give you a % of charge but will give you the amps. I look for 12.x is good enough.

Set the amp meter to 12v.

I think in this case you are setting your meter to DC voltage to get a reading of 12.x. You state you set it to 12v.

Many multimeters can measure amperage, but most can are rated only for up to 10 amps. You might have a clamp type meter that can measure well above 10 amps. But you are correct that a multimeter has no way of measuring % charge. Amperage is measured in series with a load, not parallel to it.

[CharlesinGA]

Originally Posted by Yosemite77

I’ve thought about doing this. Does anyone know what electrical equipment would be needed besides heavier cable? Given that it’s a long run back to the trailer, what gauge cable and would it even be worth it?

Originally Posted by Yosemite77

Thanks! Another question - What would be needed to keep the trailer from draining the truck batteries should I forget to disconnect the trailer?

4 gauge to 2 gauge welding cable run from front to rear, an Anderson 200 amp connector

https://www.amazon.com/HYCLAT-Batter...cal+connectors

Link is for another brand, but identical looking. Anderson is the best, they make the connectors in different sizes, amperages, and cable sizes. This would be mounted on the rear of the vehicle. These are known as manlift battery connectors, forklift battery connectors, etc.

Also would be a battery isolation device such as this, mounted under the hood, which only closes after the vehicle battery system reaches a certain voltage (indicating to the unit that the vehicles batteries have reached a full recharge after a start). With the vehicle shut off, this opens and prevents current flow either direction. Also has a circuit that can be connected to a toggle or momentary switch to force the relay to close for using either the trailer batteries for jump starting the vehicle or a set of jumper cables, winch, etc that could be plugged into the connector at the rear bumper.

https://powerwerx.com/battery-separa...CABEgI30_D_BwE

The supply directly off the vehicle battery to the isolation device also would need to be fused. Blue Sea and others make very good quality fuse holders with covers for this, use a fuse rated to the size cable you install.

Charles

[CharlesinGA]

Dual alternators with their own internal regulators will not parallel perfectly. The regulators will be slightly different settings and one alternator will always do most of the work, especially when the system is at or near its peak voltage.

Many modern alternator systems have the vehicle's computer controlling the alternator, thus no internal regulators, and the computer will act as one regulator controlling both alternators, in which case they will pretty much parallel each other.

This is much the same issue that multi engine aircraft have faced for years. The ones with two independent alternators always had one that did most of the work, while systems with a single regulator (the Beechcraft Baron comes to mind) always had the two alternators working together. There is a second regulator and the pilot can choose which one to use with a selector switch, but only one regulator at a time works to control both alternators.

Charles

[twinboat]

Originally Posted by CharlesinGA

4 gauge to 2 gauge welding cable run from front to rear, an Anderson 200 amp connector

https://www.amazon.com/HYCLAT-Batter...cal+connectors

Link is for another brand, but identical looking. Anderson is the best, they make the connectors in different sizes, amperages, and cable sizes. This would be mounted on the rear of the vehicle. These are known as manlift battery connectors, forklift battery connectors, etc.

Also would be a battery isolation device such as this, mounted under the hood, which only closes after the vehicle battery system reaches a certain voltage (indicating to the unit that the vehicles batteries have reached a full recharge after a start). With the vehicle shut off, this opens and prevents current flow either direction. Also has a circuit that can be connected to a toggle or momentary switch to force the relay to close for using either the trailer batteries for jump starting the vehicle or a set of jumper cables, winch, etc that could be plugged into the connector at the rear bumper.

https://powerwerx.com/battery-separa...CABEgI30_D_BwE

The supply directly off the vehicle battery to the isolation device also would need to be fused. Blue Sea and others make very good quality fuse holders with covers for this, use a fuse rated to the size cable you install.

Charles

Here is another battery combiner website with lots of info.
Check out the FAQ section.

https://www.yandina.com/

[tuffr2]

What you guys are saying makes sense with my experience. There really is not much current going back to the trailer. You can not recharge the battery with the truck very quickly and using the truck to recharge the battery is not a good idea

I know my truck with 2 batteries and 2 alternators still would not put much of a charge back to the battery on the trailer.

[Yosemite77]

I’m undecided on what I’ll do, but in any case I appreciate the responses to my questions.