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| Electrical Plan Review [message #64111] |
Fri, 13 November 2009 07:23  |
petemosss
Messages: 221
Registered: August 2008
Location: Jacksonville, Florida
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Just trying to finish rewiring things and adding new devices. What needs a relay?
Any additional tidbits on correct wiring would be appreciated.
Air comp
vacuum pump JC4
fuel pump main
fuel pump aux
electric wiper motor
H4 headlights
rear docking lights
thanks!
Pete
74 Canyon Lands 26' "Emery"
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| Re: Electrical Plan Review [message #64124 is a reply to message #64121] |
Fri, 13 November 2009 09:19  |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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Your Air compressor and vacuum pump could share a relay. I don't think that they would be both drawing current at the same time.
H4 headlights should use their own relay, improving the light output with heavier gauge wire (and shorter runs).
Fuel pumps could share, unless you are worried about a failure, bringing the fuel delivery system down.
Electric Wiper motor on it own.
Rear Docking Lights? What is meant here? Back up lights? Rear projecting beams (I've thought of these.)?
Relays are cheap and move the load from the switches to the relay. Most automotive types will handle 30 amps @ 12v. You will need to check on the amount of current the H4 lights draw.
I'm sure that one of our professional E.E.'s will add to your knowledge base. Ken?
Tom Phipps
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: Electrical Plan Review [message #64157 is a reply to message #64111] |
Fri, 13 November 2009 13:29 |
Chr$
Messages: 2690
Registered: January 2004
Location: Scottsdale, AZ
Karma: 1
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The Ground switching is something I design into Automated machinery as well. Much cheaper (and safer) to run 100 ground wires through a machine tool than 100 24VDC lines that need to be fuse protected. It amazes me that it is not done in automotive products from the factory.
-Chr$: Perpetual SmartAss
Scottsdale, AZ
77 Ex-Kingsley 455 SOLD!
2010 Nomad 24 Ft TT 390W PV W/MPPT, EV4010 and custom cargo door.
Photosite: Chrisc GMC:"It has Begun" TT: "The Other Woman"
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| Re: [GMCnet] Electrical Plan Review [message #64165 is a reply to message #64157] |
Fri, 13 November 2009 15:07 |
jayrabe
Messages: 509
Registered: June 2009
Location: Portland, OR
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Interesting concept. So you run a hot wire to the hot side of the relay, but then how do you wire the load (pump, lights, whatever)? Do you (like your relay wiring) run a hot line direct to your load, and have the relay switching the load ground, or do you run hot to the relay contacts to switch the hot to the load, with the load ground connected presumably to the frame?
But I am even more curious about your comment re fuse protection. Don't you still want fuses in all the hot legs whether they are switched or not?
J
> To: gmclist@temp.gmcnet.org
> From: cchoffataz@yahoo.com
> Date: Fri, 13 Nov 2009 13:29:03 -0600
> Subject: Re: [GMCnet] Electrical Plan Review
>
>
>
> The Ground switching is something I design into Automated machinery as well. Much cheaper (and safer) to run 100 ground wires through a machine tool than 100 24VDC lines that need to be fuse protected. It amazes me that it is not done in automotive products from the factory.
> --
> -Chr$: Perpetual SmartAss
> 77 Ex-Kingsley 455: The Engineer's Motorhome
> Scottsdale, AZ
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| Re: Electrical Plan Review [message #64181 is a reply to message #64111] |
Fri, 13 November 2009 18:28 |
Jim Wagner
Messages: 339
Registered: February 2004
Location: Brook Park, Oh
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I use a 4 lug 30 amp relay. The lugs are marked 30, 85, 86, and 87. Power across 85 and 86 will close the relay. That connects 30 and 87. I wire the relay by connecting a fused 12 volt power source to lug 87 then a jumper from 87 to 85. Then run a wire from 86 through a n/o switch to ground. When the switch is made it closes the relay putting 12 volts to lug 30 that is connected to whatever you want to opperate.
JWID
Jim Wagner
Brook Park, oh
Interesting concept. So you run a hot wire to the hot side of the relay, but then how do you wire the load (pump, lights, whatever)? Do you (like your relay wiring) run a hot line direct to your load, and have the relay switching the load ground, or do you run hot to the relay contacts to switch the hot to the load, with the load ground connected presumably to the frame?
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| Re: [GMCnet] Electrical Plan Review [message #64200 is a reply to message #64181] |
Fri, 13 November 2009 21:32 |
jayrabe
Messages: 509
Registered: June 2009
Location: Portland, OR
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OK, so your relay is switching the hot leg to the accessory. Would there be any situation when it would be an advantage to switch (still via relay) the accessory's ground leg?
J
> To: gmclist@temp.gmcnet.org
> From: slwjmw@sbcglobal.net
> Date: Fri, 13 Nov 2009 18:28:07 -0600
> Subject: Re: [GMCnet] Electrical Plan Review
>
>
>
> I use a 4 lug 30 amp relay. The lugs are marked 30, 85, 86, and 87. Power across 85 and 86 will close the relay. That connects 30 and 87. I wire the relay by connecting a fused 12 volt power source to lug 87 then a jumper from 87 to 85. Then run a wire from 86 through a n/o switch to ground. When the switch is made it closes the relay putting 12 volts to lug 30 that is connected to whatever you want to opperate.
> JWID
> Jim Wagner
> Brook Park, oh
>
>
>
> Interesting concept. So you run a hot wire to the hot side of the relay, but then how do you wire the load (pump, lights, whatever)? Do you (like your relay wiring) run a hot line direct to your load, and have the relay switching the load ground, or do you run hot to the relay contacts to switch the hot to the load, with the load ground connected presumably to the frame?
>
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| Re: [GMCnet] Electrical Plan Review [message #64226 is a reply to message #64217] |
Sat, 14 November 2009 08:18 |
Gary Casey
Messages: 448
Registered: September 2009
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I agree with Jim, but there are a number of considerations to take into account. First, the primary purpose of a fuse or circuit breaker (CB) is to wires, not the appliance. The fuse should be sized so that the wire protected will not overheat before the fuse opens. If the relay is placed on the "high side" of the appliance the fuse can be placed upstream of the relay and protect both the power wire and the wire to the switch. This assumes that the high side of the relay coil is wired in parallel to the power and that the wire to the switch is large enough. With the relay coil only drawing half an amp it might be tempting to use a #24 wire or something, but then it wouldn't be protected by the fuse, which might be rated at 20 amps. Somewhere I have a chart that lists the required wire gage for a given current level and length of run. Example: You might want to use a 16-gage wire to power a remote 20-amp appliance and protect it with a 30-amp fuse
or CB to avoid nuisance trips(I'm making these numbers up - don't take them as gospel!). According to the chart you might need an 18 gage wire to be protected by a 30-amp CB. don't use a 20-gage wire to go to the switch. There could a partial short in the switch circuit that would burn up the 20-gage wire before the CB opens. Not a good thing. But most people would say that putting the switch on the low side of the relay coil will use the relay coil as the current limiter, avoiding the need to protect that wire. True for a short to ground that occurs in the switch or the wire. But what happens if the short is at the relay? Either the coil itself or the wire might short to the power lead. Then you have an overcurrent condition when you turn on the switch and the fuse won't protect the wire.
Putting the appliance on the high side might be convenient if it is to be turned on by a number of switches in different locations, eliminating the need to run power to each of the switches. All the wires could then be protected by one fuse or CB on the high side of the appliance. However, if you want to use a relay(s) to do the switching you have to run power to each of the relay locations. That would take more wiring and each of those wires would have to be protected. I think it is very unlikely that putting the appliance on the high side of the switch would be appropriate, although the dome light of a typical car is an example of a logical application. As Jim said, there is no reason it can't be done, and done safely. .
In ground vehicles the worst that can usually happen is the vehicle burns to the ground. In aircraft the result can be (and has been) much worse. In the various aircraft forums there are endless discussions about the best way to wire and protect the systems. Rightfully so - it is not a simple question. A short to ground or power (or an open circuit) anywhere in the vehicle of any wire or appliance should result in either no function or a blown fuse or CB. Difficult, but not impossible. On the trip home with my new '73 the + post of the engine battery shorted to the hold-down bracket, which conducted to the body. The way the current found its way back was by a small-gage wire, apparently OEM that went back to the negative post. Burned the insulation off the wire before I got things disconnected. Fortunately, the wire was away from combustibles so nothing else caught on fire. Bad design, or maybe someone left off a wire somewhere along the way.
Haven't yet got into that part of the renovation.
Sorry about the long post. Hope it is useful to somebody.
Gary
Jay,
There isn't any I can think of but it can easily be done if needed.
Jim Wagner
Brook Park, oh
OK, so your relay is switching the hot leg to the accessory. Would there be any situation when it would be an advantage to switch (still via relay) the accessory's ground leg?
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| Re: Electrical Plan Review [message #64227 is a reply to message #64111] |
Sat, 14 November 2009 08:28 |
petemosss
Messages: 221
Registered: August 2008
Location: Jacksonville, Florida
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Ground switching this way = Fire Prevention 2010
Thanks all! This might just be the greatest safety improvement yet.
I have 2 new additional fuse blocks up front (ign. sw./ unsw.) and one new in rear closet so the fusible factor is in.
Has anyone used ORRINCO relays? I can get them for about $4 with a wired socket.
Pete
74 Canyon Lands 26' "Emery"
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| Re: Electrical Plan Review [message #64254 is a reply to message #64111] |
Sat, 14 November 2009 15:59 |
Jim Wagner
Messages: 339
Registered: February 2004
Location: Brook Park, Oh
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Dan,
Those are old photos. The Perko batt. switch has been replaced with latching remote opperated solenoids and the isolator update is on my to do list.
Is your bug painted yet?
Jim Wagner
Brook Park, oh
Dog Gone it Jim, you and Ken Henderson always showing us up with your neat wiring. Why can't you keep a few stragglers there so I don't look so bad? I see you still have an isolator though. I am ahead of you there, ha.
Dan
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