For the past 8 months or so, I've been using PTC fuses in combination with TVS diodes to protect my modern equipment running off my PW transformers and have had great success. I initially used PTCs with a 3 amp hold voltage (6 amp trip). Recently, I added some cars to my consists that have increased the "load"......a 3520 searchlight car and a smoking tank car.....and the fuses got hot and tripped after a few minutes of running. I made some new ones up with 4 amp hold (8 amp trip) and all was good. But I'm wondering what the upper safe limit is with this type of fuse. These fuses are attached to a PW ZW.
Sidebar...... I use a normal fuse box for these. I take an old blown fuse and break the glass and use a piece of wooden dowel as substitute for the glass. I bend the leads of the fuse and push the metal caps of the old fuse over the dowel and the ends of the leads (and put of touch of solder on the lead and cap). My "wooden fuses" then fit nicely in the fuse box.
Roger
I believe the circuit breaker in a PW ZW is 10 amps, so your resettable fuses can go to that limit. They probably would trip faster than the built-in circuit breaker.
Larry
Larry,
But will a PTC with a 10 amp trip level be fast enough to protect circuit boards?
I may be wrong, but I think the ZW breaker is 15 amp
The modern electronics in trains need protection from excessive voltage, not current; and your TVSs are already doing that. Once they begin drawing abnormal current, they are already damaged. Overcurrent protection for the individual ZW outputs is desirable, to prevent the severe damage to transformer and wiring that is possible if those outputs get connected together.
The ZW circuit breaker is rated at 15 amperes.
Bob Nelson
Hi Bob,
Good to see you pop up here......I was hoping for that. You may recall you gave me assistance in my efforts to eliminate solenoid buzz in my 1122 switches with your capacitor system. Still working GREAT!
Anyway, what would you recommend for my PTC fuses? What would be a safe upper end?
Thanks!
-Roger
Tripping at 15 amperes would protect the transformer.
Bob,
So, my PTC fuses are only protecting the transformer and my TVS diodes are protecting the modern circuit boards. Correct me please if that's wrong. Would it be better then to use PTC around 10 amp trip so they trip faster than the ZW breaker?
I stand corrected on the rating of the ZW circuit breaker. The question is: will a 15 amp PTC trip faster than the 15 amp circuit breaker?
Whether the PTC devices will trip faster or slower, I don't know. But there should be no need to trip faster than the ZW's circuit breaker. The only advantage I can see to using smaller overcurrent devices (of whatever kind) on the individual circuits is to allow use of smaller wire (16 AWG instead of 14 AWG if protected at 10 amperes, 18 AWG if protected at 7 amperes, 20 AWG at 5 amperes). However, such smaller wire, although safe if protected at its ampacity, may cause voltage-drop problems while 14 AWG or larger would not.
Ok.....I'm going to try bigger than the 4 hold amperage in the ones I'm using....just so my trains don't stop because of load in the consist. But a wire question........all my wires out to my tracks from the ZW are 18 gauge. Would you suggest I rewire that with 14? Thanks
The wire should be big enough to carry the greatest current that the overcurrent protection will allow. That's 15 amperes and 14 AWG for the ZW. However, if you protect individual circuits at a lower current, then smaller wire rated for that current is safe. You should protect 18 AWG at 7 amperes or less.
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