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Jeff,
Looked thru all my extra stuff but no fuse or fuse holder for your beacon.
Sorry.
Mark

It's not clear to me how fuses can cause "shorting out" since they're in series with the circuit, or other electrical problems. The referenced article states:


That's been my experience -- I've used standard 1/4" diameter fuses in several positions in my airplane for more than a decade and 2000 hours of flying without any electrical or other problems. The author of the article shows a fuseholder type which might allow the smaller fuse to go deeper into the holder which would cause a problem, but it wasn't apparent to me if that was the case. When I put a 1/4 inch fuse into the holders in my 150G, I have to push to compress a spring, so I know that there's good contact at both ends of the fuse. The only potential problem I can see is if the current is close to the fuse rating, the fuse might blow at a slightly lower current since the heat might not be conducted away quite as well from the smaller caps of the 1/4 inch fuse than the larger one. But none of the fuses in my plane are running anywhere near their rated currents because the avionics and lights have been replaced by units requiring much less current.

I'd appreciate any explanation of exactly how a 1/4 inch fuse causes "electrical problems" or from anyone who has experienced such a problem that was definitely caused by using a 1/4 inch fuse in their 150.

Roy

I checked mine yesterday and all but one are AGC or SFE fuses. There is one AGS fuse. They all appear to be ok.

I am interested in this as well, Roy. I could not understand how what was being described would occur.

I can't answer Roy's question, but I'll relate my experience with flashlights. I have a few flashlights that use the non-rechargeable AA alkaline batteries, or the equivalent rechargeable NiMH type. The size of the AA alkaline batteries is very well standardized, while the diameter of the (cheaply made) NiMH batteries vary depending on the manufacturers. When I put an NiMH battery that's slightly smaller than an AA alkaline battery into the flashlight, it moves laterally a bit and causes the light to flicker. The flickering indicates an unsteady supply of power as the battery top and bottom surfaces move across the contacts/springs of the flashlight. If the same unsteady supply of power occurs when using a 1/4" AGC fuse in a 9/32" AGS fuse holder, it COULD have an effect on the longevity of the fuse. That's just my theory. I'm not an EE nor electrician.

Hung makes a good point. The problem he describes depends on the spring force holding the battery in place, the weight of the battery, and the metals used on the battery and flashlight contacts. All batteries I've seen use nickel plated contacts as do all the small fuses, although there might be some really cheap batteries that don't. Inexpensive flashlights might use any metal for the contacts -- the best ones use gold plating and other good ones use nickel. I've never had this problem with quality flashlights and NiMH batteries. (I highly recommend Eneloop brand NiMH batteries.)

Electrical contacts are a science in themselves. Basically, you need to have metal-to-metal contact, so the pressure has to be enough to break through any oxide layer and form a gas-free seal area. If the gas-free seal is broken by vibration or other movement, the contact area can oxidize (extremely quickly if one or both materials are something like tin), causing poor contact. This is actually much more of a problem with low current low voltage (so-called "dry") contacts than others. When higher voltages and currents are involved, tiny hot spots can form that burn their way through the surface contamination.

If these problems occur with a fuse, you'd see blinking lights, static-like motion related radio noise, or other intermittent problems. In cases of high currents, you might see signs of heating at the fuseholder terminals or arcing or burning at the fuse terminals, and a fuse might fail prematurely due to the extra heat. But relatively high currents, nickel plating, adequate spring pressure, and light weight all help maintain the contact integrity and seem, in my airplane at least, to be enough to prevent problems.

Roy

Hi Mark - Thanks for checking!!

I think I might resort to using an AGC fuse for the time being, until I find a better option or upgrade to C/B's.