lithium4750 Posted July 14, 2009 Share Posted July 14, 2009 I have a SBC in my 260Z and have been driving it for awhile now. I've noticed that it blows the fuses every now and then from the alternator to the battery. They are 30amp fuses and I thought that should be high enough but maybe I'm wrong. I was driving it the other day and all at once the car shuts down. I get out and immediately check the fuse... it's blown. I replace it and try to start the car but nothing happens. Turns out I blew the fusible link on the firewall for the ignition. I replace that and everything is back to normal. The alternator charges fine and has never blown a fusible think other than that one time. I've got an exciter wire coming from the #2 prong of the alternator to the BAT terminal but no wire from the #1 to an idiot light in the car. Does anybody know what's going wrong? Quote Link to comment Share on other sites More sharing options...
rytherwr Posted July 15, 2009 Share Posted July 15, 2009 You should not have a fuse in the charging line from the alternator to the battery. If you do, it must be at least 10% larger than the amperage your alternator is rated for. I.e., if you have a 60 amp alternator, then it stands to reason if you are putting out full amperage and you only have a 30 amp fuse or a 40 amp fusible link, you will blow them every time. Again, you shouldn't have a fuse between the alternator and the battery, you should have a fuse or fusible link between the battery and the rest of your wiring harness. Wayne Quote Link to comment Share on other sites More sharing options...
lithium4750 Posted July 15, 2009 Author Share Posted July 15, 2009 Thanks for the info. That's really weird to me because I'm not a very electrically inclined person and had someone do the wiring on my car. It seems weird the pros would put a fuse in line between the alternator and the battery. And the fusible link that blew was the stock one put there by Datsun, and even then it wasn't the battery it was the ignition one right next to it. Quote Link to comment Share on other sites More sharing options...
rytherwr Posted July 19, 2009 Share Posted July 19, 2009 Think of what the fuse is trying to protect....most modern alternators have an internal voltage regulator so there is little chance of overcharging the battery...you are trying to protect from a short in the rest of your wiring harness from the battery throughout your vehicle. Electrical theory doesn't stop you from putting a fuse in line between the altnernator and battery. It is not common practice, but if you do, it must be at least 10% higher amp rating than the alternator. Do you know what amperage your alternator output is? I run a single wire 200 amp alternator with a 00 gauge (the size of your battery ground wire) wire from the alternator directly to the battery and don't have any problems at all. Wayne Quote Link to comment Share on other sites More sharing options...
deja Posted July 19, 2009 Share Posted July 19, 2009 Quote Link to comment Share on other sites More sharing options...
beebeecivic Posted July 19, 2009 Share Posted July 19, 2009 Are you sure you have the correct amperage on the fusible link? Quote Link to comment Share on other sites More sharing options...
lithium4750 Posted July 20, 2009 Author Share Posted July 20, 2009 As I said before I didn't do the wiring but have gotten better at it since getting it done. I will go through it and explain it more in detail tomorrow and maybe even draw and scan a diagram. I will also check the alternator and see what output it is but it is a reman from Autozone, uses an exciter wire. I'm not sure if the wire coming from the alternator is going straight to the battery or to the starter but it definitely has a fuse in between it and wherever it goes. I'm sure the fuses I'm putting in it are way under the rating of the alternator but the highest I can get in these size blade fuses are 40 amp. I will have everything specific answered tomorrow for sure and maybe even some visual for you guys to look at. I just need to get it figured out before I try and drive it 3 hours to school in Statesboro. The engine runs like a top but this problem is making the whole thing kinda sketchy. Thanks for all the help so far guys! Quote Link to comment Share on other sites More sharing options...
lithium4750 Posted July 20, 2009 Author Share Posted July 20, 2009 Ok so I followed the wire today and it seems to be going back through the harness to the fusible link box (BAT (green) IGN (black) style) then back to the battery somehow. That all seems as it should be to me and how the Datsun one was run also. I'm guessing I will be ok just to get some 10 to 12 gauge wire and replace all the wire and fuse holder with it back tot he original white and red wire? And I'm pretty sure it's something like a 90 amp alternator because I didn't pay anymore to get a higher amperage one. Quote Link to comment Share on other sites More sharing options...
rsicard Posted July 21, 2009 Share Posted July 21, 2009 Lithium4750: There is a lot of misinformation out there. In higher current applications there should be adequate circuit protection. If the alternator were to internally short with an unprotected circuit to the batter and undersized cable between the battery and alternator, then said wire cable would heat up red burn off the insulation and likely start a FIRE under the hood. Best to put an appropriate easy to get at FUSE in series in this cable about the same amperage as the alternator is capable of supplying. Typically the most amount of current from the alternator to the battery flows just after the car is started to replenish the energy drained from the battery. Typically a smaller FUSE can be put in line to FEED the remainder of circuits within the vehicle as they DO NOT draw as much current as battery charging current. The automotive manufacturers always come VERY CLOSE on the wire gauge size for the battery charging circuit. It is always better to go with a larger wire gauge size in this charging circuit. Quote Link to comment Share on other sites More sharing options...
Careless Posted July 21, 2009 Share Posted July 21, 2009 Weird, I have a fuse that is 70 amp rated on my charge line going to the battery with my 110amp alternator. Never did get it to go to full amperage, I guess. Quote Link to comment Share on other sites More sharing options...
rytherwr Posted July 21, 2009 Share Posted July 21, 2009 Careless, charging system is load-dependent, so if you aren't drawing over 70 amps with your starter and all your accessories on, then no worries...if you draw more, you will blow the fuse. Again, nothing says you can't run a fuse, it just needs to be large enough and the charging wire needs to be big enough to handle it, typically 12 or 10 gauge minimum. Quote Link to comment Share on other sites More sharing options...
Careless Posted July 21, 2009 Share Posted July 21, 2009 Careless, charging system is load-dependent, so if you aren't drawing over 70 amps with your starter and all your accessories on, then no worries...if you draw more, you will blow the fuse. Again, nothing says you can't run a fuse, it just needs to be large enough and the charging wire needs to be big enough to handle it, typically 12 or 10 gauge minimum. I believe I split the load using two wires and only one has a fuse. I really need to check it, since the motor is out of the car. Quote Link to comment Share on other sites More sharing options...
rsicard Posted July 21, 2009 Share Posted July 21, 2009 Gentlemen: The starter draws its large amount of energy from the battery to start the gasoline engine. During the start cycle the alternator is not rotating fast enough to contribute any energy to the situation. Once the gasoline engine has started, the alternator replenishes the energy used in starting back to the battery. With a 110 ampere alternator with a 70 ampere fusing, the energy from the alternator back to the battery did not exceed the 70 ampere figure. Immediately after the start the alternator current to the battery is at peak and tapers off till the battery is charged. It is the amplitude and amount of time of the peak current that MAY blow the 70 ampere fuse. Additionally, the alternator is excited by a small amount of current from the battery to produce a large amount of current back to the battery. The alternator is not spinning very fast after start and therefore not supplying FULL amperage but only a PORTION of its rated amperage until such time as the gasoline engine is revved up and the alternator supplies much more current/amperage back to the battery. Hope that this is a good explanation. Quote Link to comment Share on other sites More sharing options...
hoov100 Posted July 22, 2009 Share Posted July 22, 2009 "as the gasoline engine is revved up and the alternator supplies much more current/amperage back to the battery." i coulda swore the voltage regulator regulates voltage? Quote Link to comment Share on other sites More sharing options...
rsicard Posted July 22, 2009 Share Posted July 22, 2009 What is the voltage value regulated in a normal charging system? Quote Link to comment Share on other sites More sharing options...
hoov100 Posted July 22, 2009 Share Posted July 22, 2009 What is the voltage value regulated in a normal charging system? i thought it was regulated to 13.6/14v's? Quote Link to comment Share on other sites More sharing options...
Careless Posted July 24, 2009 Share Posted July 24, 2009 i thought it was regulated to 13.6/14v's? usually it's written that 14.4v its standard alternator charge when developing products for automotive applications that run on a 12volt system. My Quest 110 amp runs 14.26v, rock solid from idle to 6000 rpm. Quote Link to comment Share on other sites More sharing options...
lithium4750 Posted August 5, 2009 Author Share Posted August 5, 2009 So from the info I've gotten from these posts and the experience I've had driving my car I've come to this conclusion. The alternator is only going to put the amount of voltage or amperage back into the battery that it needs. So before I rebuilt my carb it took alot more to start the car which in turn took more energy from the battery, therefore putting more energy through the wires and fuses to recharge the battery and not to mention the radio or lights which blew the fuses and so on. I have rebuilt the carb since then and it takes alot less energy to start the car since it turns on with the first turn of the key pretty much every time. So less energy taken from the battery to start the car means less energy coming from the alternator to replenish that which was lost. You will only put out as much as you can use? Quote Link to comment Share on other sites More sharing options...
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