Warning: Those eBay transformers are not top-shelf quality
Elliot wrote:OK, so eBay is awash in transformers that are designed to convert between 220V and 110V -- up and down. 3000 Watt capacity for under 100 bucks delivered to my door.
My original plan was to use a step down transformer between the Variac and Rectifiers to:
- Halve the current thru the Variac
- Double the useful range of the Variac's dial
Here's what I learned about the 3000W transformer I bought from eBay seller unlockedcellphoneexpert:
- I think it is an autotransformer, the guts only have 3 leads (the 2nd output lead is wired around the transformer to one of the input leads). The pigtail leads seem skinny, the stranded wire measures ~Ã˜1.8mm which is a touch heavier than 14 ga. I don't know what the core is wound with.
- The 3000W rating is peak, the box recommends running it at 1/2 rating. (btw the power rating is deceiving for your application, it really hints at a current rating while in 110/220 V use... for you, a 3000W transformer is 13.6A in/27.2A out max)
- The fuse holder is crap... it ejects the fuse with the slightest jostle. (btw, it comes with a 30A fast blow fuse & 2 spares, I replaced it with a bit of Ã˜6mm copper tube and added an external breaker).
- Its heavy... ~28 lb.
The one I started to use on the playa died early. After returning home I opened it up and found one of the solder joints had come apart. The soldering quality was poor, I do not know if it failed due to vibration or overheating.
Warnings on eBay Variacs:
- The 22 lb puppies are expensive to ship! I bought a pair of V-20's for just $100 but the UPS/Mailbox Etc. shipping added another $76.
- If you buy used, be careful when you power up for the first time, I probed one of mine and found the case at 40 V.
fyi if you reconsider running off batteries.
Here's a pricey speed controller that will give you ideas:
Low-Voltage DC Motor Speed Controller 60 Maximum Amps, 36/48 VDC Input/Output
Keep your eyes peeled on eBay/Craiglist for a cheap one