I purchased this as a battery charger for a remote cabin used in winter. I went with the 55 amp unit because the battery bank could not accept a charge much faster than 55 amp, and the generator on site was only a 1KW unit, with very poor AC voltage and frequency regulation. And, the 55 amp unit seemed to be the most "amps for the buck." This charger accepts the poor quality AC of a 39 year old generator just fine. In the many years it's been used, it has worked perfectly. It goes in to current limit at full output when the batteries are flat, but after 30 minutes when the voltage comes up to 14.2, it starts to taper down the amps. It's serious about 55 amps. I use 4 gage wire, and it does warm up the cable. The variable speed fan is quiet. It's a well engineered product.
If the input voltage is too low, it just puts out less amps.
It will even operate just fine off inverter power.
It worked so well at the camp site, I put a set of large alligator clamps on it, and use it as a normal daily use battery charger, and as an off season battery maintainer. My Kill-A-Watt indicates that the DLS-55 tapers all the way down to only drawing 9 watts AC with a fully charged battery connected and 8 watts AC under no load.
I was so impressed by IOTA's product, that I purchased several other DLS chargers/power supplies (24 volt) to power DC power systems for wireless communications sites.