Iceshark-- possible improvement over fusible links?
12-25-2002, 03:03 PM
#1
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Iceshark-- possible improvement over fusible links?
Ice,
I know you're developing a new grounding harness for our cars. I was browsing through the Real Goods catalog (thinking about a solar system for a cabin) and happened across <a href="http://www.realgoods.com/renew/shop/product.cfm?dp=1601&ts=1025168&kw=dc%20circuit%20breaker" target="_blank">this</a>
Perhaps it would be an improvement over a fusible link? If it pops, you press a button... seems handier than cutting up and resoldering a harness.
Again, I have no idea if it would work... I'm not an electrical guru. Still, I thought I'd share the find.
Thaddeus
I know you're developing a new grounding harness for our cars. I was browsing through the Real Goods catalog (thinking about a solar system for a cabin) and happened across <a href="http://www.realgoods.com/renew/shop/product.cfm?dp=1601&ts=1025168&kw=dc%20circuit%20breaker" target="_blank">this</a>
Perhaps it would be an improvement over a fusible link? If it pops, you press a button... seems handier than cutting up and resoldering a harness.
Again, I have no idea if it would work... I'm not an electrical guru. Still, I thought I'd share the find.
Thaddeus
12-25-2002, 10:56 PM
#3
Nordschleife Master
I'll look at it Thad but I don't think it will solve the basic fusing problem. Just make it easier to have a new fuse once your system had a major malfunction.
The automotive system for the starter and alternator are are a unique problem to prevent damage from a hard short, short of some sort of intellegent system that could differentiate between a hard short and major but normal current load.
Take the alternator which can and will put out something a bit over it rated capacity of 115 amps in the later 944s. So we standard fuse or circuit breaker it a bit over 115 amps, say 130. Ok, now we have a short but the alternator can't put out that much. It will start kicking say 123 amps into the short. The breaker won't trip but 130 amps is enough to start arc welding metal so there better not be anything that will catch on fire around. And if we fuse a couple amps away from rated capacity some alternators will be blowing the fuse/breaker many times a day.
On the battery side, we can solve one short problem between the battery and alternator. Fuse the run with a 150 amp fuse and this will prevent the battery from dumping many hundreds of amps, maybe over 600, into the short though we still have the problem with the alt dumping in current if the car is running as discussed above.
The last short to protect is between the battery and starter. The starter is going to draw different amounts of current depending on the particular compression of the car, oil viscosity being used, ambient temperature, etc. 400 amps in small cars is not unusual, maybe even more. OK, what fuse size do we use? This is where a circuit breaker might come in handy because you could size the allowable load down tight and just keep blowing and resetting it until your car gets out of the cold. But even this wouldn't work if your battery gets tired and can't dump the trip load on a hard short but can still dump say 300 amps.
So this is where a breaker could be some use. There are other consideration, but this reply is getting too long.
Thanks for thinking about this and pointing it out to me but I'm not sure it will help the basic problems presented by battery cables to starters and alternators. Its why the auto manufacturers don't bother to try and fuse the circuits except the high end ones that do something about preventing the battery from dumping in its whole load into the alternator under short.
The best thing is to use good, well protected cables and route them well so you don't get a short in the first place. Even this won't help in a crash when the cables get cut .... one reason many serious crashes can result in fires.
The automotive system for the starter and alternator are are a unique problem to prevent damage from a hard short, short of some sort of intellegent system that could differentiate between a hard short and major but normal current load.
Take the alternator which can and will put out something a bit over it rated capacity of 115 amps in the later 944s. So we standard fuse or circuit breaker it a bit over 115 amps, say 130. Ok, now we have a short but the alternator can't put out that much. It will start kicking say 123 amps into the short. The breaker won't trip but 130 amps is enough to start arc welding metal so there better not be anything that will catch on fire around. And if we fuse a couple amps away from rated capacity some alternators will be blowing the fuse/breaker many times a day.
On the battery side, we can solve one short problem between the battery and alternator. Fuse the run with a 150 amp fuse and this will prevent the battery from dumping many hundreds of amps, maybe over 600, into the short though we still have the problem with the alt dumping in current if the car is running as discussed above.
The last short to protect is between the battery and starter. The starter is going to draw different amounts of current depending on the particular compression of the car, oil viscosity being used, ambient temperature, etc. 400 amps in small cars is not unusual, maybe even more. OK, what fuse size do we use? This is where a circuit breaker might come in handy because you could size the allowable load down tight and just keep blowing and resetting it until your car gets out of the cold. But even this wouldn't work if your battery gets tired and can't dump the trip load on a hard short but can still dump say 300 amps.
So this is where a breaker could be some use. There are other consideration, but this reply is getting too long.
Thanks for thinking about this and pointing it out to me but I'm not sure it will help the basic problems presented by battery cables to starters and alternators. Its why the auto manufacturers don't bother to try and fuse the circuits except the high end ones that do something about preventing the battery from dumping in its whole load into the alternator under short.
The best thing is to use good, well protected cables and route them well so you don't get a short in the first place. Even this won't help in a crash when the cables get cut .... one reason many serious crashes can result in fires.
12-25-2002, 11:09 PM
#4
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Guys, I installed one of the Blue Sea circuit breakers in my Trooper when I added an auxiliary fuse block. I bought mine at a local West Marine store.
In short, these things work great. I have the breaker located near the battery in the engine compartment, and run the cable from there to my fuse block, which I located inside the cabin. This protects me against a major short in the event of an accident, etc., where the firewall might sever the cable.
The unit is basically weatherproof. One of the best side benefits is that you can trip the breaker with a push of a button so you can do electical work downstream without having to disconnect the battery, etc.
Just a comment in general... marine grade wiring is far superior to your everyday stuff. Most of the wiring, connectors and heat shrink I buy are made by Ancor, and I can't say enough about the quality and extra peace of mind it gives me.
Merry Christmas
Ron
In short, these things work great. I have the breaker located near the battery in the engine compartment, and run the cable from there to my fuse block, which I located inside the cabin. This protects me against a major short in the event of an accident, etc., where the firewall might sever the cable.
The unit is basically weatherproof. One of the best side benefits is that you can trip the breaker with a push of a button so you can do electical work downstream without having to disconnect the battery, etc.
Just a comment in general... marine grade wiring is far superior to your everyday stuff. Most of the wiring, connectors and heat shrink I buy are made by Ancor, and I can't say enough about the quality and extra peace of mind it gives me.
Merry Christmas
Ron
12-25-2002, 11:27 PM
#5
Nordschleife Master
Ron, you are fusing the rest of the car's electrical system down stream close to the battery. A very smart idea, but it is different than what we are talking about.
All the components I use are marine/military/aviation stuff, there really is no comparison to automotive wiring.
Porsche also doesn't fuse the run from battery to the fuse box on the other side of the engine bay. I'm looking at a new arrangement on that to fuse off the battery. Looking it over right now.
All the components I use are marine/military/aviation stuff, there really is no comparison to automotive wiring.
Porsche also doesn't fuse the run from battery to the fuse box on the other side of the engine bay. I'm looking at a new arrangement on that to fuse off the battery. Looking it over right now.
