Low voltage side of relays

[zz71s]

How much current does the low voltage side of a relay use?
The reason I am wondering is I am installing a eletricly boosted power brake kit and it uses a relay.
I am useing the eletric choke terminal on the carb for the 12 v source for the dual rad fans and I want to use the same 12 v source for the relay on the brake kits relay.
The 12 v source to the carb terminal comes from the fuse panel this will mean there will be 3 relays and the eletric choke on that one fuse do you all think this will be to much and I should find a new key on 12v source for the brake relay?

 

[mrvette]

I would use the choke wire to control any relay coil + side, OR use the yellow circuit off the wiper motor...

and you certainly can NOT run any heavy current device off that yellow +12 wire....you need run the fans through the control relay with a nice ~8 ga wire off the alternator stud directly, and other side of motors to ground....
I used the frame directly...

the brake relay can use the same sources, both seem fine by your description, and of course the power to run the device need come through the relay off the main alt output.....I think the fans are a bit much to run off the horn relay due to the thinner wire but I dunno about the current demands on the brake system....

:drink:

 

[zz71s]

The carb terminal is only key on 12v for the fan relays heavy side comes off the pos alt terminal.
I was thinking about using the pos stud on the starter for the heavy side of the brake kit.
How much current do relays pull?

 

[mrvette]

The carb terminal is only key on 12v for the fan relays heavy side comes off the pos alt terminal.
I was thinking about using the pos stud on the starter for the heavy side of the brake kit.
How much current do relays pull?

Relays coils pull maybe 1/2 amp at MOST.... 1/10 amp is more like it....

measure the resistance of the coil, and divide by the voltage.....so if a 120 ohm coil, divide by 12 you will draw .1 amp for the coil....nothing to worry over....

I would not wire anyting to the battery wire directly, starter or not, unless a cheep power amp for some stereo...and the main head unit power, not the switched control power....

when doing electric motor loads, best to take them off the alt out stud directly.....controls are almost an afterthought...POWER use wise....:shocking::shocking:

 

[zz71s]

I can see if the engine is running the alt could power both the fans and the brake pump but what if you just turn the key to the assessary and the fans and the pump come on can that stock wiring harness wire take the load of the pump and fans .
This is why I was thinking about using the starter stud.

 

[mrvette]

Most of the time your sensors ground one end of the relay coil, to close the main power contacts which feed the device, and should get their power from the alt stud direct, so if the +12 side of the relay coils are not fed with power, it don't matter what the sensor want to do, the relays don't close until your engine/ignition is running.....

in the acc mode the ign is dead, only radio type stuff can work....

I hate the thought of running any accessories off the battery/starter directly, because they draw power thorugh that wire coming from the battery....alt puts out only 13.8 for instance, and so battery--with that extra load maybe only see 12.3 or so for a charge voltage, battery is very unhappy....never fully charges, and if it's a short hop/commute situation instead of hour or better on the freeway, battery is ever MORE unhappy....

:suicide:

 

[zz71s]

All right you talk me into using the alt stud.
Here is the way my fans work now if the engine is hot enough the fans come on if I turn the key back one click the engine dies but the fans keep running turn the key back an other click fans stop if you where to turn the key back forward one click again the fans would come back on if the engine was hot enough.
Here is what is going to happen if I use the alt stud when I turn the key one click forward if the engine is hot enough and if the acumuator has low pressure both the fans and pump are going to come on at the same time that little wire that goes to the stock harness doesnt look very big if headlights,brake lights,fans and brake pump are all running at the same time with the key one click forward
I fear for the fusable link at the starter.

 

[mrvette]

All right you talk me into using the alt stud.
Here is the way my fans work now if the engine is hot enough the fans come on if I turn the key back one click the engine dies but the fans keep running turn the key back an other click fans stop if you where to turn the key back forward one click again the fans would come back on if the engine was hot enough.
Here is what is going to happen if I use the alt stud when I turn the key one click forward if the engine is hot enough and if the acumuator has low pressure both the fans and pump are going to come on at the same time that little wire that goes to the stock harness doesnt look very big if headlights,brake lights,fans and brake pump are all running at the same time with the key one click forward
I fear for the fusable link at the starter.

I messed up, you need take those relay COIL +12 ends and tie to the YELLOW wire of the windshield wiper or similar tie point off the fuse panel....reason is that they are disconnected when in the crank mode...and the main power is obviously disconnected from battery during crank mode....while of course ignition is live, and so would be the relays if hooked to the PINK wiring....sorry...

I take ALL heavy loads with their own 8 ga wire off the alt stud directly, not off the horn relay/power distribution point....
there is no hazard to the battery fuse link this way....

 

[zz71s]

So there is no where on the fuse panel that I can get 12v key on power and avoid turning on everything on the first click of the key.

 

[mrvette]

So there is no where on the fuse panel that I can get 12v key on power and avoid turning on everything on the first click of the key.

Yes, there is, it maybe marked 'wipers' but I forget exactly, it is fusing that yellow wire.....which when you crank the engine the ignition switch removed power from that wire, to lessen battery loading during cranking, in run position it's power restored.....

but the power of one or two relay coils is minimal as discussed....so I would find that wire back in the harness, and make a splice joint into it, and run what wanted from there.....

:bounce:

 

[TimAT]

So there is no where on the fuse panel that I can get 12v key on power and avoid turning on everything on the first click of the key.

Yes, there is, it maybe marked 'wipers' but I forget exactly, it is fusing that yellow wire.....which when you crank the engine the ignition switch removed power from that wire, to lessen battery loading during cranking, in run position it's power restored.....

but the power of one or two relay coils is minimal as discussed....so I would find that wire back in the harness, and make a splice joint into it, and run what wanted from there.....

:bounce:

There is usually a terminal in the fuse block marked "IGN" too.

 

[mrvette]

So there is no where on the fuse panel that I can get 12v key on power and avoid turning on everything on the first click of the key.

Yes, there is, it maybe marked 'wipers' but I forget exactly, it is fusing that yellow wire.....which when you crank the engine the ignition switch removed power from that wire, to lessen battery loading during cranking, in run position it's power restored.....

but the power of one or two relay coils is minimal as discussed....so I would find that wire back in the harness, and make a splice joint into it, and run what wanted from there.....

:bounce:

There is usually a terminal in the fuse block marked "IGN" too.

Correct, and that is what I thought to correct about my early posts, IF the engine is hot, and the fans triggered on by the sensors, they will draw heavy currents from the battery along with the cranking/starter....not a good thing....that yellow drops off during cranking, but comes back when running/key relaxed.....

:bounce: