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alternator / fusible link

PostPost by: rdssdi » Wed Jul 13, 2011 1:53 am

Has anyone added a fusible link into the alternator wire?

I have used 8 ga wire and I believe that a 12 ga fusible link wire will protect the 8 ga wire. Any suggestions as to the length of the link? I have a 55 or 60 amp alternator.

Any reason not to add it?

i was also thinking of adding a 275 amp mega fuse into the battery + cable. Any insight into this?

thanks

Bob
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PostPost by: Higs » Wed Jul 13, 2011 7:23 am

I'm not sure of the benefit of the fusible link. The alternator cannot put more current into the circuit than its rating and as long as the 8ga wire is capable of taking 60amps (I think it is but over this side of the pond we use metric sizes) then the link will add no further protection.

The only benefit of fusing this wire would be to protect it against it being shorted out (by the alternator or a wire defect) and the battery putting out more than 60 amps through it. The better way to protect the car from this would be to put a 60-80 amp circuit breaker in the circuit that goes from the solenoid to the alternator/car electrics (and close to the solenoid). This would protect the car from any short in the circuits after that. 60-80 amps because this is roughly the max current drain with all circuits on and the car not started (a slightly strange scenario).

Of course, individual circuits should also have their own correctly rated fuses - but that has been discussed many times before.

Hope this helps.

Richard
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PostPost by: rdssdi » Wed Jul 13, 2011 11:37 am

On modern cars one reason why there are "maxi" fuses and fusible links is to break the current flow in the event of an accident and a wire or wires are now grounded. A battery cable directly shorted could prove to be very dangerous.

I concur about the alternator. I plan on using a fusible link on the wire that feeds the fuse panel (from solenoid or in the case of a starter with solenoid from the starter terminal).

That leaves the question of a Mega fuse (275amp) for the battery + cable. Some starter motors under severe conditions could draw up to 425 amps but that is probably large starters on diesel engines and other large power plants.

I am also adding a remote latching relay to disconnect the battery. I have grown tired of opening the boot to turn the battery off. This latching relay can handle very high amperage loads, only uses power when switching modes and is sealed. I am thinking of offering it to the auto after market. I will see how it works once all is up and running.

Bob
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PostPost by: Galwaylotus » Wed Jul 13, 2011 8:53 pm

If you want to have a fuse in that circuit, why not just install an in-line fuse? No messy smoke from the wire insulation and you can be pretty accurate with the rating! :wink:
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PostPost by: stugilmour » Thu Jul 14, 2011 4:09 am

rdssdi wrote:...I plan on using a fusible link on the wire that feeds the fuse panel (from solenoid or in the case of a starter with solenoid from the starter terminal)...

...I am also adding a remote latching relay to disconnect the battery. I have grown tired of opening the boot to turn the battery off. This latching relay can handle very high amperage loads, only uses power when switching modes and is sealed. I am thinking of offering it to the auto after market. I will see how it works once all is up and running.

Bob


Plus 1 to Bob; I installed a fusible link as he did at the main loom power supply to protect the loom. This was recommended in the instructions that came with my after market loom.

I also installed a latching relay device similar to Bob's idea at the +ve battery terminal. Mine has the trade name "Battery Brain". I was Googling recently as I wanted to report on this product to the list, but their US web site seems to have vanished, so not sure of current availability. If you Google Battery Brain you can probably find some remnant articles describing/reviewing their product line, and perhaps a new site. I did find this one in the UK though:

http://www.batterybrain.co.uk/

My model (Battery Brain Gold with Remote Controls, Type III if I recall correctly) even has a remote control key fob to operate the latching relay. It is equipped with a secondary connection for 'Green - Hot in run & start, fused' that senses if the ignition is on, preventing disconnection of the battery to prevent alternator damage. It is also equipped with electronics to disconnect the battery when the standing battery voltage drops to a pre-set critical level, preventing one from being left in a no-start situation. Note these last two features are both present, but you have to choose one or the other when connecting the devise.

Good product line, with models for motor homes and marine use. Don't know if they had patents in place or whatever, but thought you might find this info helpful if you are looking at product development. I recommend the product if anyone wants a battery disconnect that is reliable and easy to install and use. No more disassembly of my boot floor to do minor electrical service work! :). Was able to install in the Plus 2 without interference with the boot floor panels.
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PostPost by: rdssdi » Thu Jul 14, 2011 11:31 am

I searched for a latching relay with enough capacity . Some of the units that look like starter solenoids, in my opinion, were not adequate. Further some of these also drew power continuously to keep the relay closed.

My unit is not made for automotive use and would need a minor change if offered to auto aftermarket.

I am mulling over the situation.

bob
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PostPost by: bob_rich » Thu Jul 14, 2011 4:04 pm

Hi Bob

On my rebuild of my +2 I will be putting fusing in series with the alternator. On my seven, to the entire electrics of the car except 4 the starter motor, I used two 30A fuses in parallel and this seem to work OK. Like you I wanted to protect the fault of the alternator rectifiers going short and overheating the alternator-battery lead.

Fusing the starter motor could be a problem as say a 500A fuse could add to the voltage voltage drop in a low voltage circuit and this might effect starting.

Hope this helps

best of luck

Bob
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PostPost by: rdssdi » Thu Jul 14, 2011 6:18 pm

I have given thought to a fusible link or fuse in the alternator output and have decided against it.

I am considering a fuse (Mega 275 amp) on the + cable but I find the comment about the fuse adding to voltage drop.

Of course each circuit will be fused as well as a fusible link on the wire supplying current to the fuse box. I am also powering the headlamp circuits from the + terminal of the battery shut off relay. Going through two 12 ga wires, fused, each going to a relay(hi and low beams) then to power the lights. That way the current the dip and main headlamp switches have to handle is minimal as they only energize the relay coils. The relays have one "input" terminal and two "output" terminals fed through twin contacts.

It is challenging but fun.

Bob
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PostPost by: rdssdi » Fri Jul 15, 2011 9:42 pm

I should proof read.

I meant :"I find the comment about the fuse adding to voltage drop interesting." Would it cause a voltage drop as the fuse conductor cross section is less than that of the 1/0 battery cable?

I am considering a 275 amp maxi fuse. I know a starter motor can draw more than that but I doubt that a starter for a 4 cyl engine will exceed 275 amps. Or could it?

As of now I have the battery cables made up without the 275 amp Mega fuse. I have all the crimping tools and lugs and shrink tube so i could change it anytime.

Bob
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PostPost by: bob_rich » Sat Jul 16, 2011 5:32 pm

Hi Bob

As far as I am am aware starter motors are very rarely fused. They take such a high current that allowing for the wire drop and the battery performance the fuse may not actually fail given a serious overload. I am guessing but I suspect that if the starter takes 250A then the battery and wiring would possibly not deliver more that say 500A to 600A or so ( especially when cold) so the fuse may not blow at all. Most fuses do not have a simple pass or fail current it usually a current / time characteristic. In many circuits the prospective current with a load short is way above the operating current by a large factor but with a starter motor this is probably not the case. Be interesting to see what others think. And to get full details of the fuses.

My feeling is that given a motor shorting and the starter solenoid sticking on would collapse the voltage and all the electrics would drop out and best bet would be an easy to reach battery isolator switch should this happen.

Hope this helps

Like 2 C what others think

Bob
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PostPost by: rdssdi » Sat Jul 16, 2011 11:28 pm

Many years ago I left engineering school. I only attended for two years. My understanding of electrical theory is basic and fading. I opted for the wholesale liquor and wine business. Quite a change. But profitable and fun.

Anyway, it is my understanding that the fusible link or a fuse in the + cable (assuming - ground) is to protect from fire or an exploding battery in the event of an accident and a direct short.

I believe that Ford years ago used a large fusible link.

Bob
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