Repop Ammeter Junk

[alexiskai]

I was interested in Fun Projects's specification of a 25A fuse, because I used to have a 20A fuse in my coupe, and after a couple of blown fuses I moved to a 30A fuse and it's been good since then. But I'd be interested to know if going to the 30A is putting the ammeter at risk of damage, especially since we now know that good ammeters are hard to come by.

[rotorwrench]

Circuit protection is for the conductor wire. Wire will get hot in a pair of seconds if there is ever a direct short to ground. With a fuel tank in the cowl, that can spell disaster. A lot of cars burned down back in that era due to the lack of adequate protection.

Each size of American Wire Gauge (AWG) electrical wire is rated for a certain number of amps of current flow. The fuses are sized to protect each AWG size. If you use a larger fuse the the factor of protection is nil. A wire will burn just as fast as a fuse if the rating isn't spot on. I use a chart in The FAA Advisory Circular AC43.13-1B to get the correct fuse or circuit breaker to build a circuit. The ACs are available on the FAA web site.

[alexiskai]

It does say the ratings are for "wire bundles of 15 or more wires," and " a wire run individually in the open air may possibly be protected by the circuit breaker of the next higher rating." But it's a good rule of thumb.

[ryanheacox]

Originally Posted by alexiskai

I was interested in Fun Projects's specification of a 25A fuse, because I used to have a 20A fuse in my coupe, and after a couple of blown fuses I moved to a 30A fuse and it's been good since then. But I'd be interested to know if going to the 30A is putting the ammeter at risk of damage, especially since we now know that good ammeters are hard to come by.

Interesting, do you have any accessories in your coupe? I use a 20A fuse and have only ever blown it with a direct short.





It would seem that if you want to protect the ammeter you should match the fuse to the scale of the meter. 20A meter, 20A fuse.

[alexiskai]

Alternator and halogen headlights, that's it. I did have an experience, when I was setting up the horn, where I wired it wrong and when I hooked up the battery, the ammeter pegged at 20A. I disconnected the battery right away and fixed it. So I guess if I didn't blow anything up that time, a 25A or 30A fuse is OK. But if we're setting rules of thumb, it sounds like 20A is better.

[rotorwrench]

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This is one of the bad things about having one circuit in a car and no circuit protection. Separate circuits came along a few years after the model A era but it wasn't till the 49 models till they actually started to set up a proper fuse block with separate fuses and even then they still had a few short stop circuit breakers in there. Model A vehicles generally only had one or two accessories available like the windshield wiper and cowl lights so they didn't worry about it much.

Someone mentioned the Fun Projects model T ammeter before. I've noticed that a lot of the stuff John Regan used to carry regularly is listed as back ordered. He made a lot of stuff for the model Ts but he only had the 25 & earlier ammeter made. I think the 26 & 27 T had the same type ammeter as the model A. I know John sold Fun Projects to Birdhaven but I wonder where they were having that stuff manufactured if it's on back order. John was still helping them out but it's hard to say what's going on with that now.

[alexiskai]

I ordered the Fun Projects 6V voltage regulator back in April 2018 and I was probably one of the last people to get one, I think it's been "backordered" ever since.