To Fuse or not to Fuse

Post by **david58** » Mon Dec 11, 2006 9:05 pm

What parts of the electrical system is it ok not to fuse? Example the Battery to Starter is'nt fused.

Post by **Marc** » Tue Dec 12, 2006 6:05 am

Ideally all circuits should have fuses or circuit-breakers, but automotive cranking and charging systems almost never do and that doesn't seem to be a problem.
VW didn't get around to providing fuse protection for the dashboard warning lights until ~1971; dashboard illumination lamps and even the early-headlamp front parking lights were seldom fused. The only thing that keeps a short in one of these areas from causing a major problem is the use of "sacrificial" small (0.5 square-millimeter) wires which fry before any upstream damage happens.

fortyeye · Post by **fortyeye** » Tue Dec 12, 2006 9:20 am

I'm with Marc. Everything should be fused. One thing to keep in mind. If you use circuit breakers ... ok, but not on any device that has electronics in it. Circuit breakers have a trip time that will allow overcurrent surges to damage your electronics before they trip. Always use fast-blo type fuses on these circuits.

Ol'fogasaurus · Post by **Ol'fogasaurus** » Tue Dec 12, 2006 11:01 am

I agree with using the fast blow fuses.

I run circuit breakers on my off-road buggy. I also run a master circuit breaker. I run both hot and switched circuits that are bussed in the circuit breaker box. The C/B radio is fused off a (swiitched) circuit breaker controlled circuit that has other things on it.

Circuit breakers are not always the best way to go but they have gotten me back to camp when a wire shorted. (I was able to disconnect the offending wire then was able to get back to camp to fix it. This same part,l the licence plate light, had failed me several time so I finally removed it.) I use disconnects on certain components that could be prone to causing problems so I can easily remove them allowing me to keep other things that are on that circuit usable. The disconnects also allows me to remove items when I need to (removing the rear engine cage for example). My mast light, back up light, front aux headlights, licence plate light all have disconnects on them as well as some others electrical components. I also index connectors where two or more disconnects are close enough together so I don't get them confused.

I have also played with the idea of a fusable link but have not done it yet nor am I sure I will.

Lee

takotruckin · Post by **takotruckin** » Tue Dec 12, 2006 12:47 pm

so say you were mounting your battery up front, and you want to run two fuse/circuit breaker panels, one in front, on in the rear. would you use some sort of circuit breaker from the battery to rear panel, and from the battery to the starter?

Ol'fogasaurus · Post by **Ol'fogasaurus** » Tue Dec 12, 2006 3:05 pm

so say you were mounting your battery up front, and you want to run two fuse/circuit breaker panels, one in front, on in the rear. would you use some sort of circuit breaker from the battery to rear panel, and from the battery to the starter?

With the battery up front, I would run a heavy cable back, say a 00 or a 000. The longer the distance the heavier the cable. I would also run a negative cable, the same gage, back and ground it to a starter or engine bolt first, then run a heavy ground cable to the chassis. I do not trust chassis grounds unless I can guarentee the welding is good and not contaminated. If it is a glass buggy on a modified pan, even more reason not to trust old metal and someone elses' welds (glass is not electrically friendly... an insulator). I would run a battery shut-off swithch on the ground leg too.

I think you would want only one fuse/circuit breaker panel but you could run two it you wanted. Just double the trouble though. Come off the starter on that one.

My opinion. Lee

fortyeye · Post by **fortyeye** » Tue Dec 12, 2006 3:45 pm

I'm with Lee on this one. Had to dig up some of my old current/wire size/wire length calculators. Absolute minimum would be single 0. Double 0 (wire size 00) would be preferred. Run power and return (ground) front to back. The key is to choose the correct breaker. Located some Bosch figures on starter draw. Nominal (light to no load) is 90amps. Max is 170amps. I'd breaker your front to back circuit at 125-150amps. Well within the current capacity of your power wire and probably enough to allow for starter draw fluxuations. The important thing ... this is safe. Always size your wire at least 25% (when measuring current capacity) above your protection device (breaker). Under size wiring will act as a fuse (what's that I smell?) and could very well cause a major fire. Once you have your main wiring to the back of the car and the starter is taken care of ... you can create a power buss and tap for your fuse panel. This tap should be fused (inline) and your individual loads can be protected within the panel. Breakers are ok for your main power leads. I prefer fuses at the panel and/or anything beyond the mains.

Ol'fogasaurus · Post by **Ol'fogasaurus** » Tue Dec 12, 2006 6:19 pm

By-the-way, 000 gauge is basically leads from an Arc welder. This is what we used to use when the battery was mounted in the rear of a drag car. Does this heavy of wire make a difference in performance, a big YES! Is this over kill in a VW ...

maybe.

FYI. Lee

takotruckin · Post by **takotruckin** » Tue Dec 12, 2006 6:48 pm

overkill is nothing for me, i run a V6. i want to run two panels, one for forward lights gauges etc, then another small one for the engine, fuel pump, etc.

Ol'fogasaurus · Post by **Ol'fogasaurus** » Tue Dec 12, 2006 7:12 pm

I am interested in your logic on this because, right now, I don't understand why you want two panels. Could you run two panels... of course you can. Could you run two master fuses or circuit breakers, one for each panel... yes, I am sure you could. You just need to match them (total amperage draw) to your charging system.

I have a glass buggy that I have a V-6 sitting by for it but I haven't seen a need for the second box forward yet. You can split up a single box if you want that but I see no reason why a single box in the back can't be done.

Is this an off-road machine?

I haven't figured hou how to post pictures yet so look for an email from me soon.[/img]

Ol'fogasaurus · Post by **Ol'fogasaurus** » Tue Dec 12, 2006 7:13 pm

I am interested in your logic on this because, right now, I don't understand why you want two panels. Could you run two panels... of course you can. Could you run two master fuses or circuit breakers, one for each panel... yes, I am sure you could. You just need to match them (total amperage draw) to your charging system.

I have a glass buggy that I have a V-6 sitting by for it but I haven't seen a need for the second box forward yet. You can split up a single box if you want that but I see no reason why a single box in the back can't be done.

Is this an off-road machine?

I haven't figured hou how to post pictures yet so look for an email from me soon.

Ol'fogasaurus · Post by **Ol'fogasaurus** » Tue Dec 12, 2006 7:17 pm

takotruckin, please email me so I can send some pictures. Lee

takotruckin · Post by **takotruckin** » Tue Dec 12, 2006 7:42 pm

you can email pics to [email protected]

yes, its an off road car. i want a seperate box up front to simplify the wires running from the front to rear of the car. the engine is injected, and totally computer controlled, and it has an "integrated relay control module" that i would like to simplify into just a couple relays.

Ol'fogasaurus · Post by **Ol'fogasaurus** » Tue Dec 12, 2006 10:26 pm

"integrated relay control module"

Ok, now that makes more sense. If you want to add the second box for that it should be no problem. The picture I was going to send you may have helped, maybe not. I use a six circuit breaker box that is divided by using a buss across each system circuit. In my case it was a switched circuit and a hot circuit but it would be the same using it for two different circuits.

If you do run two circuts, then each of them should (I believe in them) contain a master circuit breaker or fuse. With the FI then a fast burn fuse would be a good idea just to protect the module.

I think I would still not put lights in the same circuit that your electronics. The reason is just in case there is a full, or intermittent short in your lights your car would still run and you are less likely to mess up the module. You still want to be able to get back to camp.

The group of people with one of the guys we ride with were able to get another guy back to camp, using their lights, after his lights failed. He was wired to allow his engine to run with everything else out.

By-the-way, if it seems I am too detailed, it is because of my job of amost 34 years. We had to be "cause and effect" and redundant in the systems we designed (I am not an electrician).

Lee

Post by **david58** » Wed Dec 13, 2006 5:46 am

Ol'fogasaurus wrote: I haven't figured hou how to post pictures yet so look for an email from me soon.[/img]

Here is your pic