relays and offroad lights

[RootBreaker]

I know for lights you divide the watts by 12v so for my example..
100w x 4 = 400w / 12v = 33.33(repeating)
so I can run 2 20a relays which will only run @ 16.67a so 20a relays are fine
BUT
why cant one run 1 x 40a relay on all 4 lights? I need to figure this out as I have 4 lights on front bumper and 5 on roll-bar...

would you use more relays or go bigger relays? so for front bumper I can either have 2 relays and smaller gauge wire or 1 larger relay and thicker gauge wire?

 

[sreidmx]

I know for lights you divide the watts by 12v so for my example..
100w x 4 = 400w / 12v = 33.33(repeating)
so I can run 2 20a relays which will only run @ 16.67a so 20a relays are fine
BUT
why cant one run 1 x 40a relay on all 4 lights? I need to figure this out as I have 4 lights on front bumper and 5 on roll-bar...

would you use more relays or go bigger relays? so for front bumper I can either have 2 relays and smaller gauge wire or 1 larger relay and thicker gauge wire?

I would run dual relays personally, finding a good 40a relay might be hard and if it goes out you prob won’t find one in a parts house. One thing you could do is get a windstar fan relay, they’re 70a! But you’ll need the special plug for them because the terminal is huge.

 

[RootBreaker]

I would run dual relays personally, finding a good 40a relay might be hard and if it goes out you prob won’t find one in a parts house. One thing you could do is get a windstar fan relay, they’re 70a! But you’ll need the special plug for them because the terminal is huge.

ok that explains why people go with the 20a's thx!

interesting on the windstar fan relay... I have the windstar fans but didn't get the relays as I'm planning on using the Volvo setup but then realize that is for a 2 speed fan.
I could use one of those relays on circuit 2 and kick both fans off... didn't know they were 70a.. so ill be heading back to the u pull it (when it isn't 2F out!!!!)

 

[sreidmx]

ok that explains why people go with the 20a's thx!

interesting on the windstar fan relay... I have the windstar fans but didn't get the relays as I'm planning on using the Volvo setup but then realize that is for a 2 speed fan.
I could use one of those relays on circuit 2 and kick both fans off... didn't know they were 70a.. so ill be heading back to the u pull it (when it isn't 2F out!!!!)

Right on!

 

[diesel4me]

You could use one metal cased "continuous duty" solenoid ,those can handle a lot of amps,some are used in dual battery isolator setups,and emergency beacons on wreckers and other vehicles..just don't mount it on anything plastic or where the heat it may generate could pose a problem..

 

[sreidmx]

You could use one metal cased "continuous duty" solenoid ,those can handle a lot of amps,some are used in dual battery isolator setups,and emergency beacons on wreckers and other vehicles..just don't mount it on anything plastic or where the heat it may generate could pose a problem..View attachment 254374

I had one of those 100a versions powering all my electrics on my blazer when it was running. Trying to prevent a huge voltage drop to the distributor. Youll need big wire though. At least look it up on an ampacity chart to figure out what you’ll need. Prob 12ga or 10

 

[RootBreaker]

so ive had many parts just sitting around... and one of them was the Pontiac trans sport 140v alt upgrade. I tried it once but didn't get it to work so ditched it. Guess I need to revisit that first and get that done before continuing as the electric fan upgrade and offroad lights WILL tax the 1978 factory alternator... what 63A? LOL

 

[Blue85]

Another reason to split the lights between relays is redundancy. If something fails, you only lose half of them. Sometimes it also lets you run a more standard wire gauge (that you have on-hand) and avoid things like 1x 8AWG spliced to 4x 12AWG.

Yes, a stock 70's alternator won't be up to Windstar fans + off-road lights. You could run 2 of them, though...

 

[Hosalabad]

so ive had many parts just sitting around... and one of them was the Pontiac trans sport 140v alt upgrade. I tried it once but didn't get it to work so ditched it. Guess I need to revisit that first and get that done before continuing as the electric fan upgrade and offroad lights WILL tax the 1978 factory alternator... what 63A? LOL

Yeah Windstar fans murdered my factory alt. I wound up with a Spectre bracket for the CS144 alt, had to add dual pulley for the v-belts too.

https://www.summitracing.com/parts/spe-42263

 

[RootBreaker]

Yeah Windstar fans murdered my factory alt. I wound up with a Spectre bracket for the CS144 alt, had to add dual pulley for the v-belts too.

https://www.summitracing.com/parts/spe-42263

ive got a CS144 pontia trans sport alternator, regular pigtail and also the wiring harness with resister but never installed. well tried but ran into issues and bailed on it. I have to get back to this once the weather gets a bit better...

can you elaborate on when you put the alt in, what else you needed to do?

 

[Hosalabad]

Once I had the bracket where I could get enough tension it was as easy as bolting it on, connecting the pigtail adapter to the original wire and running a new hot from the Alternator output to the battery.

I used this for the double pulley. https://www.summitracing.com/parts/SUM-G3949B

Going around the alternator, water pump and crank pulley netted me a 50" belt.

I had to play with alternator spacing to clear the head and valve cover , there are spacers on the lower bolt, and the point on the water pump where the Spectre bracket attaches.


Pics at post 39 and 63 note it using 50" belts, I had posted 55, before this edit.

https://ck5.com/forums/threads/fitech-efi-installation.329654

 

[RootBreaker]

Once I had the bracket where I could get enough tension it was as easy as bolting it on, connecting the pigtail adapter to the original wire and running a new hot from the Alternator output to the battery.

I used this for the double pulley. https://www.summitracing.com/parts/SUM-G3949B

Going around the alternator, water pump and crank pulley netted me a 55" belt.

I had to play with alternator spacing to clear the head and valve cover , there are spacers on the lower bolt, and the point on the water pump where the Spectre bracket attaches.

gotcha. ive been all over the web now reading up about this. and im reading that you do not want the wire to go from alt to battery but from alt to junction block where original goes which is the horn relay... so that maybe a different vehicle but they say running the wire from alt to battery will over charge the battery... how long have you been running that way?

 

[1-ton]

You could use one metal cased "continuous duty" solenoid ,those can handle a lot of amps,some are used in dual battery isolator setups,and emergency beacons on wreckers and other vehicles..just don't mount it on anything plastic or where the heat it may generate could pose a problem..View attachment 254374

That is the set-up I used on my off road lights

 

[Hosalabad]

gotcha. ive been all over the web now reading up about this. and im reading that you do not want the wire to go from alt to battery but from alt to junction block where original goes which is the horn relay... so that maybe a different vehicle but they say running the wire from alt to battery will over charge the battery... how long have you been running that way?

So far since July. I wonder when my horn quit working though, haha.