Fusible link or not?

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Kent mosby

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I am going to install a relay to power a fused distribution block to power things like the line-lock, the efi, distributor, ignition box. Since I can put appropriate fuses for each item, would be beneficial or detrimental to put a fusible link in the line to power the relay.

If so, would you place it before the relay or after the relay but before the distribution block?

Lastly, what size link is appropriate for that use?

Thanks for the help, this is like the one I have.






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I can't answer directly but maybe can help you solve the dilema.
Fusible links came into use mostly to protect against the battery being accidently grounded.
This usually took just one link in a traditional wiring strategy.
Fusible Links in Charging Systems with Ammeter

When portions of the power circuit needed larger wires, then two or more fusible links were used. A large one to protect the larger wires, and then a second one to protect the smaller wires. Chrysler didn't seem to worry about protecting 18 gage wires with fusible links. They probably figured they turn to smoke in an instant if shorted to ground.

So whether another link may be needed in your layout depends on the wiring layout. My personal view is to use a layout that minimizes the number of the fusible links. Each link or fuse is resistance to higher current flows, and every junction is a potential resistance area. (When they are in the battery charge line, they usually have plenty of time to cool off in between charging. )

If you want to convert to fuses, the approach here seems reasonable. It's based on the changes made by Chrysler to the 1980s front wheel drive cars.
Electrical Issues - MiniMopar Resources
 
Personally I would fuse it before the relay. You have to search around there are many options for fuses. I bought a pair of Jeep (used ebay) underhood relay centers. These were configured in such a way that you can tear two of them apart and use modules out of both to re-configure one more the way you want. This gave me more than enough fuse positions for main power distro

A fuse link is far better than nothing.
 
IMHO a fusable link is a slow blow fuse or slow cir breaker., It can be exposed to a lot more current then rated but for a very short time without blowing or tripping
 
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JMO,

Get a Maxi fuse holder and fuse the line for that fuse panel in total, then have each sub-system fused for their requirements. That way the overall is protected and each subsystem is as well. I wouldn't use a fusible link on that item.

I have some maxi holders/fuses here that are 6Ga wire IIRC. If you have an idea regarding draw from the components, sizing it is not tough.
 
Some off the cuff real world info on circuit breakers. Certain models of our power chairs use 2 - 70A breakers in different main circuits. That is, 140A total. The motors are only fed with no10 wire, but in a dead stall with the joystick firewalled, they can pull OVER 200 (100+A per motor) that is right TWO HUNDRED amps for maybe 15 seconds AND NOT BLOW THE BREAKER

To put that in perspective, that's about 110A per no10 wire. Your typical home electric water heater is often fed off a 30A breaker with no10 wire

Everytime I build a drive module, I test it on a "test chair." I've stalled those hundreds of times and never popped a breaker or burned up wiring or a motor. I am amazed every time I do this!!!! Typical stall for me is about 215-220A forward and maybe 205 in reverse.

The point is a breaker may not be quick enough to prevent "burn down" especially if it's oversize
 
WOW. I have a 30 amp fuse in the line from the starter relay positive post. (should I go directly from the battery post?) to the relay. Then each circuit has individual fuses. I have not placed fuses there yet.
 
Kent mosby said:
(should I go directly from the battery post?)
Click to expand...
Not usually. A fair amount of power needs to go through the relay to the starter when starting.
Where is the alternator output connected?
 
I agree, depending how everything is wired, doubt 30 is anywhere near big enough.
 
Mattax said:
Not usually. A fair amount of power needs to go through the relay to the starter when starting.
Where is the alternator output connected?
Click to expand...
Presently I am running the 60 amp denso alternator through the normal route through the amp gauge. After I get it running, (a couple weeks), I will bypass the Amp gauge as MAD Electrical explains. I just made enough changes to confuse mere mortals. If we are still quarantined and I cannot go to the track, I may do it earlier. This motor was broken in on a run stand with a carb and regular fuel pump. Many new puzzle pieces.

The 30 amp is just for the distribution block from the starter relay. Not from the battery to the starter relay. Do I need a fuse between the battery and the starter relay. I have never seen that.
 
Not a fan of the Mad approach. Put your wire around in and bypass the ammeter. If the bulkhead is in good shape, you are done. No need to run the wiring they way it's suggested.

No on the fuse between starter relay and battery.
 
Kent mosby said:
Presently I am running the 60 amp denso alternator through the normal route through the amp gauge. After I get it running, (a couple weeks), I will bypass the Amp gauge as MAD Electrical explains. I just made enough changes to confuse mere mortals. If we are still quarantined and I cannot go to the track, I may do it earlier. This motor was broken in on a run stand with a carb and regular fuel pump. Many new puzzle pieces.

The 30 amp is just for the distribution block from the starter relay. Not from the battery to the starter relay. Do I need a fuse between the battery and the starter relay. I have never seen that.
Click to expand...
OK I'll assume then this is not a 1976, and probably not a 74 or 75. Although those aere still basically 'normal' wiring strategies unless optioned otherwise.

So here's my suggestions.
1. Don't follow the MAD diagram. (It's a crappy way to do fusible links and a makes a very long rout for power to the main splice. )
2. Do connect the alternator output more directly with the new fuse/distribution box.
3. Decide if you really want a relay to power the new distribution panel. Because it seems to me each of those items probably gets its own relay. Yes? Certainly Line lock gets powered up seperate from the others. If so, then the relays come after the fuses.

This is basic scheme your car came with.
Starter relay is on the fender or the firewall.
Fusible link is after the relay.
upload_2020-3-31_22-38-41.png


Just dealing with protecting the new alternator feed and the new fuse box, it makes most sense to me to use a junction post block. It can be off of the batter or the starter relay. I don't think that matters. This way there can be a maxifuse or link between the post and the battery.
upload_2020-3-31_23-18-32.png


As far as an ammeter goes. It doesn't make much sense keeping it if this is the routing. So you could take it out and also run the feeds through a grommet.
Whether you want to take the feeds off the bulkhead depends on the condition and how much power is still going inside.

Maybe the maximum solution in terms of protection and minimizing resistance going inside would be to have one 16 ga fusible link off of the junction block and then going through a grommet.

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Thanks @Mattax for the thorough explanation. I will work on this after getting it running. That seems straightforward enough. The alternator that I am using is internally regulated. These are the field wires that are being used. Pigtail harness for Denso 210-0106 alternators | AR Engineering One wire is the feed from ignition and the other is the 12v sense wire. I have them both hooked up to the distribution panel. Should I take the sense wire and connect it elsewhere? Directly to the battery? Seems to me that it is sensing the same voltage , or close to it on the panel.
 
Kent mosby said:
Should I take the sense wire and connect it elsewhere? Directly to the battery? Seems to me that it is sensing the same voltage , or close to it on the panel.
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The voltage while running will only be the same if there was no resistance to flow. If the panel is connected near the battery, that would provide the tightest regulation of the battery charging and those items on the new fuse panel.

If you set it up off the alternator as Redfish describes he did for his relay panel, then run the sense wire to a junction electrically closer to the battery or at least closer to the key switch.

I'm not familiar with Denso wiring details. If the alternator has an internal field connection (as the GM alternators with internal regulators do) then ignition connection may need a resistor in it. On the Delco alternators, if there is no resistor the internal field supply will feed the ignition when the key is turned off. Engine keeps running.

Other than that, connecting the new box to the alternator output is a simple solution.
 
What I don't understand is how the new fuse panel works.
Does it have relays in it? Then it would make sense to me?
If it doesn't, then the ignition wire can't be hooked to it.
 
Very nice looking unit.
But I don't think this initial or trial setup will work. The battery will drain.
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Not sure what you're trying to accomplish in phase 1. I f its just to see if the Denso works, I'd skip the fuseblock and attach the Sense and Field(switch) wires to the Ignition feeds (J2 & J2B). J2A still feeds your existing ignition. If the engine doesn't shut off when the key is turned off, then the issue is the one I mentioned earlier. I just don't know about that.
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If phase 2 is EFI, then need to figure out how they will be turned on and off. Also the electric draw of the EFI unit and the fuel pumps. If there will be one relay from the key switch, then that relay will have to be capable of continuously carrying a relatively high current. If its a relay after each fuse, that's easier for me to understand.
 
There is a relay that powers the distribution block. It is not hot all the time. The power comes from the leads from what was the ballast resistor. So it will be active during cranking and also during run but not during keyed off. So that should not drain the battery, Correct? I may need another block and relays for those that need to be powered during accessory only, Lights, etc.
 
Kent mosby said:
There is a relay that powers the distribution block. It is not hot all the time. The power comes from the leads from what was the ballast resistor. So it will be active during cranking and also during run but not during keyed off. So that should not drain the battery, Correct? I may need another block and relays for those that need to be powered during accessory only, Lights, etc.
Click to expand...
Correct.
That relay may need to be a heavy duty unit. More precisely one that can carry current for multiple circuits.
 
Check the field crurrent draw on the Denso. My guess is its 5-7 amps max but dont really know.
So that's in the capability of a typical automotive relay.
Its the fuel pumps and the EFI that will probably add a lot more. Rob (Crackedback) has posted info on HD relays he's used for cuttoff switch systems with battery in the trunk.

If I understand correctly this would be your phase 1 test.
upload_2020-4-1_12-14-45.png



Another way is to run a new alternator output wire to the relay. Then IMO no fusible link is needed before the relay.
For the new wire use at least a 12 gage TXL wire or Marine wire. 10 or 8 ga GXL would be better if this is more than just quick check of concept.
upload_2020-4-1_12-21-30.png

One side benefit of this arrangement is the ammeter still shows battery charging/discharging.
Connecting the ammeter through a bulkhead grommet for the battery charging would take more load off the original alternator output line.
upload_2020-4-1_12-36-43.png


That's a bit more work, but if you're going to drive around for a while like this, then its prob worth it, or wire it like Crackedback said. That is, have a direct connection from the alternator to the battery (with a fusible link or fuse). But if you do that, wire in a voltmeter so you at least have a means to monitor the system as the ammeter will no longer show charging.
 
That is perfect. How many amps rating for the relay by the distribution block? I am not sure what I have but I can change it easily.
 
Kent mosby said:
How many amps rating for the relay by the distribution block?
Click to expand...
That's what you need to tell us! LOL.

When you know the power the items need, then you can figure out the wire sizes and relay requirements.
 
There are smaller tyco/bosch relays than the CD units that can switch to 100 amps. They aren't the 8 dollar units, but will do the job. If you come up with a total amp draw, add 10-15% to it and you will have a decent sized relay to support your fuse block.
 
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