Dear Mr itsmoked
Mr Mr edison123
Info 1. Oh, ooh, see Muthu, I was correct about bigger contactors being higher ACx for lower loads. bigsmile.
A1. Agreed, most AC3 contactors can be de-rated to AC4, by [lowering the current rating] by say about half (approx) in order to [maintain the same durability] (number of operating cycles).
Info 2. As for cost difference for DC it doesn't matter, pay for it! They're superior because they can control the coil current better and that results in less heat generated in the contactor. Also, a little grunge in a contactor won't burn up the contactor if it has a DC coil involved whereas it can quickly toast a contactor with an AC coil. Having a weee bit of hysteresis in the contactor because of the AC/DC aspect can also prevent chatter which will quickly obliterate the contacts in a large contactor. Oh, and DC coils can hold in better in a bumpy environment like on a ship.
A2. a)In general, modern contactors (e.g. A-series) with (standard ac coil) [do not] encountered any problems for marine applications. This is evident that these contactors are certified by major marine classification societies.
b) if you have a {strong} dc control supply at 110Vdc or higher, fine; but avoid using 12Vdc or 24Vdc operation from a step-down control transformer and a rectifier! Unless directly from the close-by battery.
c) avoid designing the [dc control source] yourself by using a "small" local step-down control transformer and a rectifier including smoothing capacitors. The ac coil pulling-in surge is [very heavy] that causes huge voltage dip and the small control MCBs to trip, if it is not properly selected with the correct current rating and [tripping type] (characteristic).
d) use AF-series would circumvent the problems, if any at all.
Che Kuan Yau (Singapore)