Can I connect my alternator to my MPPT?

Drooling Piston said:

In this scenario, if the alternator is putting out 13.2V would a PWM charge controller work? They are smaller and half the price of the Renology 20amp B2B charger.

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Drooling Piston, I have a Renogy 12V-12V 20A charger and mounted it in my trailer so that it can be fed by either the power line from my truck OR the converter in the trailer if I have shore power. It works very well. Keep in mind that Maintenance Free, Deep Cycle, AGM and Lithium all take different voltages to reach full charge. That is where the DC-DC really shines. I purchased and open box from Renogy and paid ~$100.
Attached is the wiring I used.

MisterSandals said:

I installed the 30a model (there are other sizes including a hard to find 18a).

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After looking around at different DC-DC chargers, I wish they would publish what the amp draw is on the starter battery & alternator.
If the B2B is rated at 30amps, I assume that is the maximum charge rate it will put into the batteries it is charging. Is it safe to say that this same unit will draw about 25% higher amps? So I will need to size wiring & fuse, for about 40 amps?

With a 34ft trailer who’s batteries are in the rear, plus another 20ft of truck length, equaling a 55ft run of wire, probably a 2 gauge, there will be a substantial cost for the wiring.

Is 25-30% a good guide for calculating the draw?

Drooling Piston said:

I don’t know how important this really is. But I liked the sound of this “Intellegent charger” automatically switching between different stages of charging.

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Since posting this comment, I have found a newer, version of this victron orian-tr smart B2B, on Amazon in either the 18 or 30 amp model.

Victron Energy Orion-Tr Smart 12/12-Volt 18 amp 220-Watt DC-DC Charger, Isolated (Bluetooth) https://www.amazon.com/dp/B0851TPKV7/ref=cm_sw_r_cp_api_glt_fabc_M8EA1PZPCR8NAZRW8YHK

This looks like it has all the charging features and smart sensing features I want. This unit has good looking cooling fins, to dissipate it own heat. The only thing missing is a battery temp sensor.

Drooling Piston said:

Since posting this comment, I have found a newer, version of this victron orian-tr smart B2B, on Amazon in either the 18 or 30 amp model.

Victron Energy Orion-Tr Smart 12/12-Volt 18 amp 220-Watt DC-DC Charger, Isolated (Bluetooth) https://www.amazon.com/dp/B0851TPKV7/ref=cm_sw_r_cp_api_glt_fabc_M8EA1PZPCR8NAZRW8YHK

This looks like it has all the charging features and smart sensing features I want. This unit has good looking cooling fins, to dissipate it own heat. The only thing missing is a battery temp sensor.

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The Renogy 20 Amp has an optional temp sensor which I purchased.

Jasgeer said:

The Renogy 20 Amp has an optional temp sensor which I purchased.

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I actually have one that I recently purchased too but I am considering returning it because I don’t want to run the ignition wire from the truck (tow vehicle), add a plug, and another 34ft of wire to the rear of the trailer. To turn on the charger.

Why do you need to run the separate ignition wire? My truck has a relay on the power line running to the 7 pin and there is no power if the ignition is off. I just connect the power from the 7 pin to the control line when I want the truck to feed power to the DC-DC. I added a spst switch so that I can force if off if I need to. It is perfectly fine if they turn on at the same time. You might look at my wiring diagram.

The Victron Orion is fully user programmable for charge and float voltages , absorption time and total bulk charge time. The voltage thresholds for activation and deactivation are fully programmable with out of the box settings good for most situations. It can be used in charger mode or power supply mode.
There are control pins to force activation or to disable the unit.

Mike

Jasgeer said:

Why do you need to run the separate ignition wire? My truck has a relay on the power line running to the 7 pin and there is no power if the ignition is off. I just connect the power from the 7 pin to the control line when I want the truck to feed power to the DC-DC. I added a spst switch so that I can force if off if I need to. It is perfectly fine if they turn on at the same time. You might look at my wiring diagram.

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I missed that part of the wiring diagram the first time I looked at it.