Jeep Enthusiast Forums banner

Relay Wiring Question - AUX Fuse Block

2193 15
Hey JF,

I posted a week ago asking about mounting locations for an AUX fuse block and, after figuring that out, I have some wiring questions. I am planning on making the fuse block IGN-powered, so that none of my accessories run with the Jeep turned off and drain the battery. I will probably just use a relay with the switching signal being a ACC power line that already exists in the Jeep (ie: cigar lighter).

Does this diagram look right?

Could I just use a 12V-100A 5-pin relay?

Any other input would be awesome. Thank you.

Attachments

1 - 16 of 16 Posts

·
Premium Member
Joined
·
10,374 Posts
You don't need both the 100a fuse and 100a circuit breaker. Only one overload device needed, and closer to the battery the better.

Also, 100a is probably more than needed, the 100a is probably more than relay is rated. It's probably only rated at 40 or 60 amp.

Your diagram is ok otherwise.
 

·
Registered
Joined
·
242 Posts
Discussion Starter · #4 ·
You don't need both the 100a fuse and 100a circuit breaker. Only one overload device needed, and closer to the battery the better.

Also, 100a is probably more than needed, the 100a is probably more than relay is rated. It's probably only rated at 40 or 60 amp.

Your diagram is ok otherwise.

@2jhanna, always chiming in to help. I appreciate all your feedback recently. So, the reason I want a 100A fuse / relay / breaker is because the fuse block is rated at 100A max. If I have all six accessories on, I want to make sure I am okay. The reason I put both in is to protect the relay with a fuse and the fuse block with a breaker. Could I get away with just protecting the fuse block?

Here is the relay I found: https://www.amazon.com/SupportTM-Automotive-Truck-Alarm-Relay/dp/B01MPYARO4/ref=redir_mobile_desktop?_encoding=UTF8&dpID=61RMJuBLJFL&dpPl=1&psc=1&refRID=S1MXMJGRVX11N912586M&ref_=pd_aw_sim_sbs_263_3&tag=pda0ea-20

Aside from those things (protection), does the wiring look right? I am no expert at wiring, so I wanted to double check that.
 

·
Premium Member
Joined
·
10,374 Posts
While I can't think of a reason why two of the same size current overload devices in the same circuit, in series, helps, I also can't think of a reason why it would hurt. The important thing is to have one as close to the power source, the battery in this case, as possible.

What size wire gauge do you plan to use for the 100a feed, and remember that the distance plays a factor. Meaning that long runs may require a step up in wire size.

Lastly, a 5 pack of 100a relays for less than $14. Continious duty ???? At least you'll have some spares.
 

·
Registered
Joined
·
242 Posts
Discussion Starter · #6 ·
While I can't think of a reason why two of the same size current overload devices in the same circuit, in series, helps, I also can't think of a reason why it would hurt. The important thing is to have one as close to the power source, the battery in this case, as possible.
I will just put a breaker in front of the relay, between it and the battery. That makes sense, the more I think about it. No need for redundancy.

What size wire gauge do you plan to use for the 100a feed, and remember that the distance plays a factor. Meaning that long runs may require a step up in wire size.
My battery runs 4 AWG cable. I would probably run those cables to the breaker in and then a 10 AWG cable out of the breaker, to be able to use common female disconnect wire connectors on the relay. Then, probably continue with 10 AWG cable from the relay to AUX fuse block. The "trigger" wire will probably just be the same 18 AWG wire as the cigar lighter hot wire. Please see the new diagram.

Lastly, a 5 pack of 100a relays for less than $14. Continious duty ???? At least you'll have some spares.
That was my philosophy behind the five pack... Haha. Best deal I can find on Amazon and I do most of my shopping there because Prime.
 

Attachments

·
Registered
Joined
·
886 Posts
It's fine that your relay and fuse block can handle 100A, but your devices will never add up even close to that. They normally operate at a much lower amperage than what they're fused for. This allows some room for an occasional spike.

Putting 4g before the fuse adds no protection. Once you add the 10g in series, it becomes the weakest link.
My suggestion would be to put a 70A fuse (or use a ckt.brkr.) in the 100A fuse holder. This will then become the weakest link and protect the 10g wire. If that fuse ever blows, without tripping one of the ckt. fuses, then you'll know you need bigger wire.

If every connection isn't perfect, the heat generated from the resistance (at 90A) could melt something apart before the 100A fuse ever blows. If you're truly expecting 100A, you should wire it for 200A.
 

·
Registered
Joined
·
242 Posts
Discussion Starter · #10 ·
It's fine that your relay and fuse block can handle 100A, but your devices will never add up even close to that. They normally operate at a much lower amperage than what they're fused for. This allows some room for an occasional spike.

Putting 4g before the fuse adds no protection. Once you add the 10g in series, it becomes the weakest link.
My suggestion would be to put a 70A fuse (or use a ckt.brkr.) in the 100A fuse holder. This will then become the weakest link and protect the 10g wire. If that fuse ever blows, without tripping one of the ckt. fuses, then you'll know you need bigger wire.

If every connection isn't perfect, the heat generated from the resistance (at 90A) could melt something apart before the 100A fuse blows. If you're truly expecting 100A, you should wire it for 200A.
Thank you for your comment, @1longcj. Each accessory I add will probably be a maximum of 10 A draw (2 seat heaters @ 10 A max ea, 1 USB power adapter @ 4.2 A, and a couple of other goodies down the road). Therefore, with a 6-fuse block, I will only reach a max of 55-60 Amps. So, in theory, I could buy a 60 A breaker and keep the 4 GA & 10 GA wires as they are pictured in the 2nd diagram?

Bussmann 60A Breaker: https://www.amazon.com/Bussmann-CB185-60-High-Amp-Breaker/dp/B001PYL4UA?tag=pda0ea-20

Also, does my diagram wiring make sense in general? Will it work for the application I wish to use it for?

Thank you!
 

·
Registered
Joined
·
226 Posts
I would make a few changes to your plans. If this circuit is primarily to be used only for items inside the passenger compartment then I would run either 6 or 8 gauge wire from the battery to fuse/breaker then the same gauge to the block. That way if you exceed a 70amp draw (highly unlikely) you still have a measure of safety with the wire not melting. Look for welding cable of the proper size since it tends to be more flexible. Also do not forget to use a grommet where the wire penetrates the firewall. I would not use those relays, you are better off using a contactor or at least a relay that uses ring terminals for the high current power wires, instead of spade terminals. The last change I would make is in the trigger branch for the contactor/relay, I would use a normally open oil pressure switch in the ground side of the contactor/relay. That way the circuit is only active while the engine is running, otherwise it could be energized with the key on but engine off, which could lead to a drained battery. It also takes those circuits offline while starting the jeep and allows more current to go to the starter.
 

·
Registered
Joined
·
242 Posts
Discussion Starter · #14 ·
@Kalten, I like your suggestion about the ring terminal relay. I did not realize those were available. Could you show me what you are talking about?

I already have a lot of 4GA and 10GA wire leftover laying around. Do you feel it absolutely necessary to run 6GA or 8GA instead? I am no electrical expert, but I do not foresee any issues with running 10GA, based on the table in 2jhanna's post and the fact that I will not be running anywhere near 7 feet of cable.

Could you explain what you mean about the oil pressure switch in a little more detail (actual execution)? Does it mean even if the hot side is "hot" (ie: the ignition is in ACC mode or on), that the circuit will not be live until there is oil pressure (ie: the engine is on)? I get the concept, but you kind of lost me on that one. Where do I tap into the pressure switch? Again, no expert on this stuff. Still trying to learn, through little projects like this one.
 

·
Registered
Joined
·
226 Posts
I'll do the best I can from my phone... do an amazon search for a 100a 12v relay and you will see on the first page one that will accept ring terminals. As for the wire gauge better in most cases to go larger than what you need rather than smaller. You could get by with 4ga or even 10ga if you run multiple wires in a single terminal (four minimum) but you would still be better off in my opinion if you ran the welding cable since it will not preload your terminals and cause them fail down the road. Not saying using 4ga will but the possibility exists unless you can form it to where you need it to be so that when it's resting on the lug without a nut it's not trying to twist or spring off. For the oil pressure switch again look at amazon for a normally open oil pressure switch. They can be had in various trigger pressures but 10-30 psi would be more than enough. Obtain a t-fitting and place it near your oil pressure sending unit. (Someone may know a better location) For wiring the contactor/relay run the positive wire from the same lug point the battery is attaching to and just wrap it around to the positive of the solenoid, in your diagram it would be a wire from 30 to 85. Take the ground side (86) and place one wire from the solenoid to the oil pressure switch and another wire from the opposite side of the oil pressure switch to ground. That also means you don't need to run any additional wires into the passenger compartment other than the feed to the block. If you have more questions I'll try to answer from a computer so I can provide links.

https://www.amazon.com/WinnerEco-Tr...qid=1519388525&sr=8-5&keywords=100a+relay+12v
http://www.rockauto.com/en/moreinfo.php?pk=97401 can find on amazon but this link lists the operating range.
 
1 - 16 of 16 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top