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philb 09-14-16 10:30 PM

Jelly Jar surge protector
Several posts lately have mentioned using mov's for surge and lightning protection on mains voltage.
I thought I'd post my version that's been in use for a while.
The jelly jar is used because it's cheap, it has excellent insulation properties and mov's can have meltdowns when subjected to high amps and voltages.

I put the mov's on half of a 50 cent 5x7 mm board from ebay. The board will hold 2 rows of four mov's.
The wires are 10 awg because I had some short pieces of USE-2 wire after rewiring my solar panels for a lower voltage. 12 AWG THHN wire is my usual choice. The mov legs are wrapped around the 10 awg wire and then soldered. The manufacturer suggest using a heat sink between the mov and the soldering. Apparently excessive heat will destroy them. Imagine that!

The photos show one side of both rows soldered together to a common green taped ground wire. The other two wires can go to a hot wire and neutral for 120 volt circuits. For 240 volt split phase, the wires both go to hot.

The metal lid is drilled and fitted with a 1/2 inch emt screw connection. Then I fill it with silicon. The metal ring and lid
are painted for outdoor use.
I like to use 150 volt RMS version on mains voltage and 84 volts DC version for my 65 volt solar panels.

Keep in mind this device is not UL listed. Insurance companies might frown on them. I don't know. I'd rather explain this to them than explain how one of my building burned.

philb 09-14-16 10:33 PM

There are TMOV'S out to help prevent thermal run away. I dont see that as a problem when they're enclosed in a glass jar.

The white sheet also details how to install a led to tell when the tmov needs replacing.

philb 09-14-16 10:47 PM

3 Attachment(s)
I'll try the photos again.

NiHaoMike 09-15-16 10:24 AM

I would also add some 10-40uF or so motor run caps from the hot(s) to neutral to suppress small surges without wearing out the MOVs. And also a choke upstream of the protector and load although that might not be practical for high current loads.

philb 09-15-16 12:15 PM

Yes, I agree with you NiHaoMike. There are several items that can be added to the basic circuit that are environment specific.

My normal fair is MAINS – FUSE – INDUCTOR – MOV's – LOAD. The inductor is usually 2 or 3 strands of the electrical wire wound in a 12 inch circle and put in a metal box. The ends of the loops make a 90 degree bend when entering and exiting the box. It's a good idea to get the 90's to touch the box. Lightning does not like to conduct through tight turns. That's not much of an inductor, but it usually gives the fuse time to blow.

The entire jelly jar surge protection cost me $12.00 with all new parts mostly from Ebay. I would be hesitant to add run caps because of cost. If I had a low power factor, I'd be first in line for them. Just from here. If you happen to have them on hand or have a cheap source, it's worth the effort.

The mov's do need to be changed out periodically. The 150 volt mov's I used are V150LA10CP. They are rated for 10 surges at 3KA and 80 surges at 750A.

philb 02-12-17 07:44 PM

1 Attachment(s)
The jelly jar surge protector I posted did its job. The electronics and major appliances are fine. I can't say the same for protector though.

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