CONSTRUCT AN AC OVERVOLTAGE PROTECTOR
By Dink Stockert, WA5LNL1
This AC Over-Voltage Protector [OVP] is designed to protect your repeater from spikes and over-voltage [lightning] coming in from your AC utilities. The OVP is good for 15 to 20 amps at 120 VAC. The OVP box is equivalent to a PolyPhaserŠ power line protector [pldo-120us20a: about $350].
Construction inside a metal box is best. A #6 solid copper wire should attach to the box to earth ground to make it work! The OVP is made to hang on the wall, then feed your repeater cabinet. Use a copper (Cu) lug, remove the paint under the lug and apply a layer of NoaloxŠ anti-oxidant joint compound under the lug. Please see the photos for construction details.
Inside your repeater cabinet you should have another power strip (maybe an Iso-barŠ) with OVP. Always have more than one protector in series. All wiring should be done with #12 copper. The AC cord should be a minimum # 12 gauge. The main coils are wired on 1/2"dia. PVC pipe x 8 1/4" long with 2" screws to hold off the coil forms. Wind 59 turns of #12 Cu and leave extra wire at each end for hookup. Use the 130vac 23mm size MOVS. Mount (2) MOVS* per leg [H to N, N to G, H to G] and (3) MOVS on the output of the EMI filter.
The EMI filter needs to have a [bare] #12 cu. wire soldered from its metallic case to ground. Fusing at 15A would be better than 20A if you do not need the extra power. Making coils [5 to 7 turns, 1/4" diameter] with left over wire between hookups never hurts. Lightning gets dizzy in the coils and quits!
Total costs =$52.50 +\ - your junk box parts
*MOVS wear out with time and even faster with only minor spikes. So if you are using an OVP that is 5 years old and not blown up; change the MOVS.
TranszorbsŠ do not wear out and clamp voltages accurately with no over shoot.
If youÕve got the bucks, you can substitute a General Semiconductors TranszorbŠ [#587b151, 15A, which will blow a 15A fuse (and not blow up)
1. 1 Pull-Box, 10"x10"x4", Hubbell SC101004, [Lowe's]
2. 1 2-socket, surface-mount steel electrical box [Lowe's]
3. 1 Steel outlet cover [Lowe's]
4. 1 Dual 20A AC outlet, gray color – commercial grade [Lowe's]
5. 1 AC cord +plug #12 gauge (Buy an extension cord and cut the outlet off).
6. 1 15A/20A ceramic 3AG fuse + fuse holder [Hosfelt, 31-774, 342014A]
7. 1 EMI filter, 20A [Hosfelt 927-188]
8. 2 Capacitor, .01uF @ 1.6Kv [Digikey 495-1372-ND]
9. 1 17 in. PVC, 1/2" [Lowe's]
10. 2 Ground lugs for #6Cu. [Lowe's]
11. 1 AC wire clamp [Lowe's]
12. 1 1/2" steel nipple and 2 nuts to secure outlet box [Lowe's]
13. 1 Yellow wire nut [Lowe's]
14. 4 RF Chokes, ~ 0.12 mH; 7 turns #12 insulated solid copper house wire, wound on ¼Ó drill. (L1, L5 black wire, L2, L6 white wire)
14. 2 RF Chokes: ~ 10.24 mH2; 59 turns #12 insulated solid copper house wire, wound on 13/16Ó o.d. white PVC. (L3 back wire, L4 white wire). 22 feet of wire required for each coil.
15. 22 ft. white #12 Cu solid wire [Lowe's]
16. 9 MOVS :130vac/150vac, quarter size,23mm [Hosfelt V150LA20B]
17. Optional General Semiconductor Industries TranszorbŠ # 587b151 (15A), or 587b201(20A) [Arrow]
Figure 1. An AC Overvoltage Protector
Hosfelt; Electronics, Inc. www.hosfelt.com
Arrow Electronics, Inc. www.arrow.com
Digikey, Inc. www.digikey.com
1 Consultant, Intertie, Inc.
2 Inductance values nominal, calculated as air core inductor, using formula, page 6.22, ARRL Handbook 2001. American Radio Relay League, Newington, CT 06111. Permeability of PVC pipe was not considered.
© Copyright November 10, 2004, Intertie, Incorporated. All rights reserved
Revised: 02/12/10 by KC5PIY, Webmaster. Copyright 2003 by Intertie, Inc. All Rights Reserved No use of these symbols or phrases is allowed without the express written permission of Intertie, Inc.