There is no reason to have to put them period. Extra protection is well...... to each his own. MOV's are not the greatest, but certainly won"t hurt Kevin B.S.E.E.
--- On Mon, 6/7/10, Jeff DePolo <j...@broadsci.com> wrote: From: Jeff DePolo <j...@broadsci.com> Subject: RE: [Repeater-Builder] MOVs for power supply primary To: Repeater-Builder@yahoogroups.com Date: Monday, June 7, 2010, 11:54 PM > Hello to group, > Is putting a MOV from hot to ground, neutral to ground, on > the primary of the transformer of the power supply a good idea.. > I have a ICE surge suppressor on in front as well but thought > I would put more inside the supply for back up. I'm not that big of a fan of MOV's, but if you really feel the need to add them across the transformer primary, as long the input to the power supply is properly fused, whatever floats your boat. > Also, are the MOVs that radio shack sell any good. Rated at > 130VAC. Any body used them... I'm not sure that there's anything that Radio Shack sells any more that's any good, is there? Seriously, I'd buy > Last question: when MOVs fail or take a surge do they fail in > a shorted condition taking out the fuse till the MOV can be > replaced, or do they blow or fail open leaving the supply working. My experience that small MOV's fail in one of two ways. Either they fail shorted, quite often with no outward visible signs, or they fail open catastrophically as a zillion pieces of shrapnel that can cause damage to nearby components, wiring, people, livestock, etc.. Another downside to MOV's is that after they've successfully quenched an over-voltage event of any significant energy, their clamping voltage changes. So, you may end up with less and less protection over time. Good surge arrestors/TVSS's are expensive, and like most things in life, you get what you pay for. If your site has a good surge arrestor at the service entrance, you really shouldn't need anything extra. --- Jeff WN3A
