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extra fuse box
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Author:  '67 Dart 270 [ Mon Sep 02, 2013 11:55 am ]
Post subject:  extra fuse box
I'd like to add some keyed accessories to my dart, i.e., another fuse box that is powered when the key is on the run position. What is the best wire to tap into? Should I just tap into the (run) wire from the ignition switch to the ballast or is there a better way?

thanks all.

BG
Author:  Reed [ Mon Sep 02, 2013 12:30 pm ]
Post subject: 
I would use the ignition circuit as a trigger for a relay that drew power directly from the battery.
Author:  nuttyprof [ Mon Sep 02, 2013 12:40 pm ]
Post subject: 
I would use the ignition circuit as a trigger for a relay that drew power directly from the battery.

x2

I'm setting up a set of 4 relays and a 3 post terminal block to run headlights (high, low separately) H.E.I. , and accy. from under the hood, all fused separately.
Author:  wjajr [ Mon Sep 02, 2013 1:33 pm ]
Post subject: 
Quote:
I would use the ignition circuit as a trigger for a relay that drew power directly from the battery.
X3

Make sure relay that you use is rated to handle total calculated amp load of new fuse panel plus a little bit more.
Author:  '67 Dart 270 [ Mon Sep 02, 2013 7:05 pm ]
Post subject:  relay
Yes, also I think the wire running from the battery should have a fuse rated to the (sum) load of the fuse box, so as not to overload the relay. Does anyone have pics of their relay wiring, I was thinking of using like 10 gauge to the relay (with inline fuse before the relay), then 10 gauge from the relay to the fuse box, then run lower gauges as appropriate to the accessories. Is 10 gauge enough? I think so, the starter relay uses like 8 gauge, but nothing else requires that kind of load.
Author:  wjajr [ Tue Sep 03, 2013 5:44 am ]
Post subject: 
You have to add up the actual amp draw of each accessory being feed from the new fuse panel, than using a table that shows ampacity by wire gage select proper gage conductor for your application. Same goes for over current protection (fuse) sizing.
Quote:
Yes, also I think the wire running from the battery should have a fuse rated to the (sum) load of the fuse box, so as not to overload the relay.
Just select a relay that can handle 120 – 140% of calculated load.

A fuse between battery and new fuse panel won’t be necessary if mounted close to battery under hood, as any of the sub circuits feed by it are individually fused so any short down line in a sub circuit will be broken.

The original wire harness in these A Bodies have several circuits that bypassed the fuse panel which are unprotected, so the factory included a fusible link between battery and fuse panel in main feed on the engine side of bulkhead connector to protect all those circuits. It is a rather crude, but effective method to manage loads and protect against dead shorts... most of the time anyway.

I would draw out a simplified schematic of new circuits, and existing circuits to insure proper fusing, conductor size, and how these new circuits integrate with existing harness. Keep it simple as this could easily be one of these projects that spiral out of control with mission creep ending with a total harness redesign that is needlessly over engineered.
Author:  64ragtop [ Tue Sep 03, 2013 7:16 am ]
Post subject: 
I added a Painless Wiring accessory fusebox. 7 new circuits, 3 always hot and 4 ignition hot. Epoxied it onto the side of the original fusebox for convenience.
#8 wire from battery to circuit breaker to new box.
I was so proud - til I noticed that the new box uses the new style fuses and the original......:roll:

OK, I'll just carry two sets of spare fuses, what the heck - it's up under the dash anyway. :oops:

BC
Author:  '67 Dart 270 [ Tue Sep 03, 2013 2:35 pm ]
Post subject:  Yes...
I noted that #8 wire on a 12v circuit will hold up to 100 amps if not too long, typically #8 is rated at 50 amps load.

See handy chart:

To choose an adequate wire gauge, determine the amp draw (amperage) that the wire circuit will carry. Then measure the distance that the wire will travel (length) including the length of the return to ground (the ground wire running to the chassis or back to a ground block or battery. Using these two numbers, Amps and length, locate the nearest gauge value in chart below. For 6 volt automotive systems typically a wire gauge 2 sizes larger than what is shown should be used.

American Wire Gauge (AWG)


Amps @
12 Volts LENGTH OF WIRE

3' 5' 7' 10' 15' 20'
0 to 1 18 18 18 18 18 18
1.5 18 18 18 18 18 18
2 18 18 18 18 18 18
3 18 18 18 18 18 18
4 18 18 18 18 18 18
5 18 18 18 18 18 18
6 18 18 18 18 18 18
7 18 18 18 18 18 18
8 18 18 18 18 18 16
10 18 18 18 18 16 16
11 18 18 18 18 16 16
12 18 18 18 18 16 16
15 18 18 18 18 14 14
18 18 18 16 16 14 14
20 18 18 16 16 14 12
22 18 18 16 14 12 12
24 18 18 16 14 12 12
30 18 16 14 12 10 10
36 16 14 14 12 10 10
40 16 14 12 12 10 10
50 16 14 12 10 10 10
100 12 12 10 10 6 6
150 10 10 8 8 4 4
200 10 8 8 6 4 4

Also, I'm replacing my fusible link with circuit breakers at the firewall. I'll engineer the new circuits for extra capacity when it's time for the headlight upgrades and whatever comes later...
Author:  '67 Dart 270 [ Tue Sep 03, 2013 2:37 pm ]
Post subject:  clearer chart, see....
http://www.offroaders.com/tech/12-volt- ... e-amps.htm
Author:  wjajr [ Tue Sep 03, 2013 3:34 pm ]
Post subject: 
Quote:
I'm replacing my fusible link with circuit breakers at the firewall.
Be advised that circuit breakers automatically reset after they cool down, and were used on headlight, wiper, and convertible top pump circuits. Having a device that resets for other loads normally fused may not be a good idea should a dead short develop.
Author:  '67 Dart 270 [ Tue Sep 03, 2013 4:34 pm ]
Post subject:  circuit breakers...
Duly noted, there are things fusible link will do that breakers won't....
Author:  '67 Dart 270 [ Tue Sep 03, 2013 4:36 pm ]
Post subject:  also...
I was planning on using manual reset breakers, so I could investigate why one opened before reengaging.
Author:  olafla [ Wed Sep 04, 2013 2:39 pm ]
Post subject: 
Instead of fusible links, I use Midi - also known as Ami - fuses, as far as I know, they are also used in modern Mopars. They are 'sloblo fuses', i.e. they react almost as a fusible link, as they can take an overload for some time before blowing, but a direct short will blow them immediatly.

http://www.bluesea.com/articles/1393

I also use an older version of this fuse block in my Aspen. Recommended.

Olaf
Author:  Danarchy [ Wed Sep 04, 2013 5:17 pm ]
Post subject: 
Oh Yeah Olaf! This thing is cool! I'm getting one of these!

Image
Author:  olafla [ Thu Sep 05, 2013 5:30 pm ]
Post subject: 
My old alternator collapsed with bad diodes, so I use a 3-wire 105Amp GM 12si alternator now. I have a BlueSea SafetyHub 100 fuse block with 3 Midi/Ami fuses and 4 ordinary blade fuses.
  • I have a 10mm² cable from the alternator to the intake post on the fuse block. The alternator sense wire is connected to the same post.
Midi/Ami fuse connections:
  • One 120A fuse for the 8mm² cable to the battery. The only other cable connected directly to the battery, is the starter cable, unfused. The emergency lights circuit is fed from the same post on the fuse block as the battery, so there is always power in that circuit even if the other fuses blow. There is also a separate fuse in that circuit.
  • One 70A fuse feeding the old main circuit, that was connected directly to the battery previously. The only large power draws in that circuit now, are the heater fan, wipers, el. seat motor (never used), and rear window defroster. Most fusible links are eliminated.
  • One 30A fuse feeding the relay for the electric radiator fan, but that may change when I rewire later.
The ordinary blade fuses:
  • One 15A fuse feeding the relay for the HEI ignition.
  • One 20A fuse feeding the relay for the driving lights.
  • One free, for the time being.
  • One free, for the time being.
This is a work in progress, my goal is to eliminate all fusible links, and have all under-hood circuits separated from those going into the original fuse box inside the car. The wires for lights and ignition from inside the car (which have almost 0.8V voltage loss), are now only activating the under-hood relays, which are fed from the fuse block. The old wiring harness is slowly being stripped of unnecessary wires, and new ones are included. The whole harness will be rewrapped when I finish the redesign.

BTW, Littelfuse has now bought Terra Power Systems, which was the company BlueSea used to promote their marine products for heavy vehicles. My BlueSea Safety Hub 100 fuse block, is listed by Terra as XT Series Power Distribution Module.

When rewiring/redesigning your car's wiring harness, remember that the alternator is the actual power source, the battery is only a temporary storage for starting current, and a buffer for the the charging current going into the wiring harness.

Olaf
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