From: Neon John <johngdNOSPAM@bellsouth.net> Subject: Re: New Q about Leaving converter plugged in Date: Tue, 12 Oct 1999 02:06:18 EDT Newsgroups: rec.outdoors.rv-travel Ben Franklin VI wrote: > Leaving it on is ok. Probably will last longest if left on. Inductors have > nasty trait concerning current and voltage. Switch them on and off you get > current surges and voltage spikes -- a self destructing behaviour. Yup. > The noisy transformer may have a loose lamination. There may be another piece > of sheet steel near the unit that is vibrating in sympathy with the magnetic > field of the transformer. > > For noise reduction you could try mounting the unit on rubber taking care to > keep it solidly restrained. Also build a box around it with holes for > ventilation -- check into the hospital for a few days [any malady you can > survive will do :) ] --- when you leave ask for the sponge rubber waffle > mattress pad from your bed -- use this to line the box -- the rough side goes > toward the noise. There is another solution to this problem, one that addresses the root cause - something loose and vibrating inside the transformer. This solutions assumes you're comfortable enough working inside electrical things to remove the transformer. Assuming you are, read on. Most of these noise problems originate from the mfrs getting cheap and not varnishing the finished transformer. The varnish adds insulation and it bonds all surfaces together to prevent them from vibrating. A final dip and bake costs extra and so they don't do it. You can. Locate your nearest friendly local electric motor repair shop. Take the transformer to the motor repair shop and ask them to dip it in their varnish tank. Make sure they leave it in the tank until all the bubbles quit. This usually takes 10-15 minutes. Tell them NOT to dip the leads. Normally they know not to do this (makes the insulation brittle) but just in case... If your transformer has screw terminals, coat them (and anywhere else you don't want varnish) with a heavy coating of grease. This will keep the varnish at bay. Be sure to have a cardboard box lined with a garbage bag with you. This varnish cures by baking. It will never dry without baking. It's REAL sticky when uncured. CAUTION: The baking process is fairly stinky. If you think that will cause domestic problems, let the motor shop bake the transformer. This will be a come-back-tomorrow affair since the baking takes several hours and they'll probably not want to fire off their oven for one little transformer. If you want to do it at home, simply put the transformer in the oven, put a foil pan below to catch the drippings and bake for 2-3 hours at 275-300 deg F. There will be lots of solvent odors but no smoke (unless the varnish drops on the heating element) so the odor won't linger and a vent hood will quickly pull it out. Another source of noise, sometimes significant, is nearby sheetmetal being magnetically stimulated by the leakage flux from the transformer. This is different from the acoustic stimulation Ben mentioned. Leakage flux is a sign of a poorly designed transformer. The solution to the noise is the same - dampen the sheet metal so it won't vibrate. Two methods I use are dampener sheeting and aerosol automotive undercoating. The dampening sheeting is made by 3M and is used by body men on sheet metal to make it not resonate. One of the tricks used to give car doors that nice "thunk" when you slam them. The stuff comes adhesive-backed and can be cut with ordinary scissors. Just stick it to the inside of whichever metal panel is vibrating. Available from auto parts stores that cater to body men. Undercoating does the same thing but it more inconvenient and messy. OTOH, it is available almost anywhere car accessories are sold. If you're like me and HATE the sound of buzzing appliances, you probably won't think these solutions to be TOO radical :-) Nothing less than the total absence of 60hz buzz is acceptable to me. This solution works well too for those cheap but buzzy mercury vapor security lights one can buy at Wal-Mart, etc. John -- John De Armond johngdSPAMNOT@bellsouth.net http://neonjohn.4mg.com Neon John's Custom Neon Cleveland, TN "Bendin' Glass 'n Passin' Gas" |