Will LiTime's 40A DC-DC charger work from a small trailer's 7-pin plug?

Why the setting matters

The question comes up with small trailers like a T@B charged from a Jeep: lithium battery in the trailer, factory 7-pin from the tow vehicle, and a DC-DC charger in between. The charger draws more current from its input than it puts out, so its input demand is set by its output setting. LiTime's 12V 40A DC-DC charger lets you select 20A or 40A charging current.

The 20A mode for a 7-pin feed

A factory 7-pin charge circuit is a long run of modest wire with its own fuse in the tow vehicle. Asking it for 40A of charge, plus the converter's own losses, is more than that circuit was built to carry. Setting the LiTime charger to 20A keeps the demand down while still doing what a 7-pin alone cannot: charging the lithium battery to its proper voltage with a proper profile. LiTime's charger runs a 2-step CC/CV profile for LiFePO4 and a 3-stage profile for lead-acid.

When to use the 40A mode

Use 40A only with a dedicated feed: heavy cable from the tow vehicle battery, fused at both ends, to an Anderson-style connector at the hitch. The 6 AWG Anderson-to-lug cable on this page is the trailer-side lead for that kind of setup.

Fusing

Put a fuse or breaker on the charger's input and output close to each battery. A 50A DC breaker suits a 40A charger.

Other things the LiTime charger does

• Wakes a lithium battery after its BMS has shut it off.
• Isolated input and output, so the two systems do not interfere.
• A cooling fan for sustained high current.
• The output can run DC loads as well as charge the battery.

The trailer battery LiTime pairs most often with this is a 100Ah, which LiTime recommends charging at 20A anyway, so the 20A setting is a good fit.