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vomund avatar image
vomund asked

Should I connect trailer electrical to MPPT "load" connection"?

I am adding a 100W ground solar panel and a Victron SmartSolar MPPT 75/15 controller to my small travel trailer. I run just basic stuff off of the trailer battery, and NO inverter for 110V power. Should I connect the trailer's electrical system to the MPPT "load?" I like the idea of having the MPPT shut off the load if the battery runs too low. However, I'm wondering what happens when I connect the trailer to shore power or the trailer is being towed. During those times the battery currently gets charged by those sources. If the trailer electrical is connected to the MPPT load, can the shore or tow power travel into the "load" of the MPPT and out the "battery" connections of the MPPT and into the battery? Wondering if the MPPT is setup to allow this "reverse" flow of power.

MPPT Controllers
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kevgermany answered ·

Details are in the downloadable manual, but that's how load works.

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vomund answered ·

The distributor whom I bought the MPPT from replied with this answer...

"If you hook the trailers DC connection to the load output on the MPPT one of two (or both) things will happen. 1. It will destroy the MPPT 2. The battery will not charge. "

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kevgermany avatar image kevgermany ♦♦ commented ·
Did the distributor back this up with reasons?

Destroy the MPPT? Maybe if you try to run excessive loads

Not charge? If the load is higher than the MPPT can deliver at the time, yes, but that's no different to having the load on the battery.

If this was correct, why are switched load terminals provided?


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vomund avatar image vomund kevgermany ♦♦ commented ·
The distributor stated that if I want to use the load connection on the MPPT then I would need to locate the wiring that is powering the trailer's DC devices from the battery and separate those from the wiring that provides charging power coming in from the shore and towing connections. The distributor said that, if I do that, then I can connect the trailer's DC wiring to the load connection on the MPPT. The wiring that provides "inbound" charging currents, should go direct to the battery and avoid the MPPT.


I don't know who is right. I found the Victron documentation, regarding the "load" connection," to be pretty vague. I would think they would spell out some real world connection scenarios, like what I am facing. But they more or less just say to connect DC stuff to the load.

As I have searched the Internet on this topic, it seems somewhat common advice to not connect anything to the load. Some say if you just connect something really simple, like a single light or one simple device, then connect that to the load if you wish. Otherwise, connect all load devices direct to the battery.

I like the idea of the load connection on the MPPT, and it seems like it should be made to handle "real world" setups like mine, but right now I'm leaning toward hooking up to my battery and leaving the load connection empty.

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kevgermany answered ·

Your first paragraph is clearly correct. It's a big job. Is it worth doing?

But that doesn't explain the no charge/wreck the MPPT.

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Kevin Windrem avatar image
Kevin Windrem answered ·

I would not rely on charging current flowing in the Load Output back to the battery connection. If the load is switched by a relay things might work. If it's a solid state switch then you could do damage or it simply would not work.

Charging sources should connect to the battery so that the battery will charge even if the load output is switched off.

Separate the wiring so that charging sources go directly to the battery and loads come off the load output of the MPPT.

Also keep in mind there is a maximum current that can be supplied by the load output. Your loads must not exceed this or they need to be connected directly to the battery.

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