Keeps your auxiliary battery charged from your battery pack this 12 volt charger uses AC or DC power. See hook up suggestions below.

There are lots of ways to hook up the IOTA. Much of your set up will depend
on how you use the car. Many people leave the AC/DC to DC converter ON all
of the time. They put a fuse one it and if they want to turn it OFF they
can just pull the fuse out... (like if they go on vacation).. The fuse is on
the AC side and should be 5 or 10 Amps.

Some people have the DC to DC converter hooked up so it ONLY comes ON when the main contactor is ON. The advantages to this is that the DC to DC only runs when the car is running so it won't run the battery pack down if the car is stored or sitting idle for a long time. The DC to DC converter if left on uses 2 1/2 to 5 Ah a Day and can overcharge your Aux. 12V battery with out a sophisticated cut off.

There are two (2) settings on the IOTA, A Low and a High. And the Low
setting is designed to be left ON all the time.

Also, does the IOTA require any relay/contactor to engage and charge the
accessory battery smoothly?

You do not need a contactor or relay on the 12V side. But, on the INPUT HIGH VOLTAGE side you could have a relay that turns it ON when the key switch comes on. Or have a manual switch that you can turn OFF and ON as you like. The current is usually less than 2Amps on the Input side, but it is DC so you want a good switch if that is what you are using. You can get a double Pull and wire the two in series, to get a little more ARC breaking space