There was a post on here a few days ago about cheap & dodgy clippers by an engineer & he'd looked at them & basically found that each time you use them, you're at a very real risk of electrocuting you and/or your horse.....
I'm not saying it is these clippers but the clippers mentioned on the previous thread were cheap & from E-bay.
At 30w you would be lucky to give a dog a full clip!
I would also be very careful of buying cheap clippers on ebat, as stated above. You might like to PM The Engineer to find out exactly which clippers are dangerous.
Invest and spend money on decent clippers in my opinion. We once clipped horses (many years ago) with some borrowed dog type clippers. It not only took ages but they just didn't do very well at all and blunted quickly. I have some liveryman ones for mine and we clip them, twice each in the winter generally and once in the summer generally. They are a nice weight and seem to last very well. They are mid range price and do very well for the couple of horses we have to clip. If you have a load of horses to regularly clip though you may need some real toughies!
I used the Moser dog clippers for years for one or two horses. It was all I could afford at the time. They do take a lot longer to do a clip and I wasnt doing fullclips. But they are ok. I now have liveryman and would say it takes about half the time!