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Author Topic: on-off-on "light switch"  (Read 5177 times)

Steve-White

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Re: on-off-on "light switch"
« Reply #10 on: February 25, 2023, 03:06:19 PM »

What I'm looking at with either the SPDT or DPDT are ON-OFF-ON toggles.  The SPDT appears exactly what I need.  Though, for a DPDT toggle, I would need to connect (using a jumper wire) the "2" load to the "1" load, in order to route the power from the second 12V service to the LED light.  Is "cross-connecting" of wires an acceptable practice?

Follow up question:  would there be any issues with having 2 x 12V batteries (independent of each other) sharing a common " - ", when one of those batteries is powering the LED light?   

That's exactly my point between single and double pole.  Without knowing the exact characteristics of the sources, you would do best with double pole and switch BOTH the ground and hot sides.  No jumpers needed.

WRT your question - is it separate batteries that won't be connected to a charging circuit then yes.  If charging is involved I wouldn't do it without seeing schematics of the charging system(s).
« Last Edit: February 25, 2023, 03:26:01 PM by Steve-White »
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Bob Faulkner

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Re: on-off-on "light switch"
« Reply #11 on: February 25, 2023, 04:31:00 PM »

That's exactly my point between single and double pole.  Without knowing the exact characteristics of the sources, you would do best with double pole and switch BOTH the ground and hot sides.  No jumpers needed.

WRT your question - is it separate batteries that won't be connected to a charging circuit then yes.  If charging is involved I wouldn't do it without seeing schematics of the charging system(s).
Good point about the charging circuits.  One 12V battery will NOT be on any charging circuit.  The other battery will be on a charging circuit (but may not be charging all the time); this battery is in the cargo van (the engine battery), and would only be providing power (through the 7-way trailer connecting power cable) if the first battery (the non-charging battery) is depleted.  Our night time load-outs can take a few hours, and I don't like running lighting off the cargo-van battery for that long... which is why I installed a "dedicated" battery in the trailer to run the lighting.  But, if that battery runs out during a load-out, I would be able to switch to the van battery "at the flick of a switch".

The LED lights in the trailer were originally being powered by the van (via the 7-way trailer connector).  It's been like that for years, but is now being powered by a stand-alone 12V battery inside the trailer. 

I like the idea of having separate 12V power sources for the lights, but it looks like when connecting all the " - " together, this may introduce other issues.  Maybe I'm not fully understanding the electrical paths within a DPDT switch.  I'm learning about it from the Internet, but I haven't been able to find something that is specific for my need.

The previous suggestion from Art looks exactly right for my situation; but the connecting together of " - " I wasn't too sure about. 

My backup plan would be just to have another 12V battery available to replace the one in the van.  If a DPDT or SPDT toggle would work, I would rather opt for that solution.

Thanks.




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Steve-White

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Re: on-off-on "light switch"
« Reply #12 on: February 25, 2023, 04:43:22 PM »

Pretty simple stuff Bob.  Just be sure it's all fused.  Lots of stories from the racing community on trailer fires with the ignition source being a battery.

With a backup battery that's not connected to the vehicle electrical system a SPDT will work fine.  Just connect the negative to the vehicle ground which will be the frame which is where the negative of the lights will end up being tied to somewhere in the circuit.

Inline fuse on the positive side of the battery is highly advised.
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Jim Thorn

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Re: on-off-on "light switch"
« Reply #13 on: February 25, 2023, 11:08:30 PM »

Bob,

  The wiring diagrams you linked to may be a little confusing, because they show a commercial electrician how to wire two selectable loads to a single power source, and you're looking for two selectable power sources to a single load.  To an electrician, "L1" means incoming powerline #1, not "Load #1", so the labeling may be confusing, too.
 I've linked a diagram for using that DPDT switch for your situation.  Unless the cost of that switch is prohibitive, I would use DPDT for its sheer conceptual simplicity (and no splice required), but if you go with SPDT as others have mentioned, the link has a diagram for that, too.

Switch sketch

I hope this is helpful.

Jim Thorn

Thanks again for the switch link!

My project is to supply power (12V) to a single strip of LED lights.  But, the power would be originating from 2 separate sources.  At any given time, the LED lights would receive their power from only 1 electrical source at a time.  Therefore, if one source of power is unavailable, I could switch (using the on-off-on switch) to the other power source for the same set of LED lights.  Also, I could power-off the LED lights by keeping the switch in the middle position.

I downloaded a Leviton "schematic" covering double pole switches.
https://www.leviton.com/en/docs/PK-93107-10-02-0D-W.pdf

On page #1 of the document (it's only 2 pages) under Figure #3, this looks like what I need... however, the schematic shows two loads, but I only need one.  From the schematics, looks like Circuit A can only power "load 1" and Circuit B can only power "load 2".

Question: Can the "load 2" be wired into "load 1" so that circuit "B" can power "load 1" when the switch is moved from Circuit A to Circuit B? 

Should I be looking at a completely different solution?

Bottom line...I'm trying to come up with a way to have a redundant power source for a single set of LED lights in my trailer.

Thanks.
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Steve-White

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Re: on-off-on "light switch"
« Reply #14 on: February 25, 2023, 11:34:50 PM »

Try this one.  There are 3 negatives on one side of the switch and 3 positives on the other side.
« Last Edit: February 25, 2023, 11:42:32 PM by Steve-White »
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Bob Faulkner

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Re: on-off-on "light switch"
« Reply #15 on: February 26, 2023, 12:40:01 PM »

Thank you for all the great info!

Pretty simple stuff Bob.  Just be sure it's all fused.  Lots of stories from the racing community on trailer fires with the ignition source being a battery.

With a backup battery that's not connected to the vehicle electrical system a SPDT will work fine.  Just connect the negative to the vehicle ground which will be the frame which is where the negative of the lights will end up being tied to somewhere in the circuit.

Inline fuse on the positive side of the battery is highly advised.
Thanks.  Yes, will be adding an inline fuse before calling it "done". 

Bob,

  The wiring diagrams you linked to may be a little confusing, because they show a commercial electrician how to wire two selectable loads to a single power source, and you're looking for two selectable power sources to a single load.  To an electrician, "L1" means incoming powerline #1, not "Load #1", so the labeling may be confusing, too.
 I've linked a diagram for using that DPDT switch for your situation.  Unless the cost of that switch is prohibitive, I would use DPDT for its sheer conceptual simplicity (and no splice required), but if you go with SPDT as others have mentioned, the link has a diagram for that, too.

Switch sketch

I hope this is helpful.

Jim Thorn

Exactly!!  I was looking for two power sources for a single load.  This is why I have found it confusing to understand how something (seemingly) simple could end up a confused mess (confusing for me).  All the info I've been able to find (prior to this original posting), appeared to point to using the switches in a particular manner, which was not how I needed a switch to be used.

Thank you for the explanation and image.

Try this one.  There are 3 negatives on one side of the switch and 3 positives on the other side.
Thank you for the image.  This is how I envisioned a DPDT switch to work with my setup, but couldn't prove it!

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Patrick Tracy

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Re: on-off-on "light switch"
« Reply #16 on: February 26, 2023, 02:20:04 PM »

Craig Hauber

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Re: on-off-on "light switch"
« Reply #17 on: February 26, 2023, 03:01:01 PM »

Thank you for all the great info!
Thanks.  Yes, will be adding an inline fuse before calling it "done". 
Exactly!!  I was looking for two power sources for a single load.  This is why I have found it confusing to understand how something (seemingly) simple could end up a confused mess (confusing for me).  All the info I've been able to find (prior to this original posting), appeared to point to using the switches in a particular manner, which was not how I needed a switch to be used.

Thank you for the explanation and image.
Thank you for the image.  This is how I envisioned a DPDT switch to work with my setup, but couldn't prove it!
I wouldn't be looking at 120VAC switches for building electrical.  I've been told they aren't the best for DC and contacts are designed assuming a zero-crossing every 1/60th a second.  I would look instead at automotive and RV type equipment.

I also think you may be overthinking this.  Honestly, how long are your load-outs?  I've run the LED work lights I installed in my trailer for over 12 hours straight on a basic riding mower battery -and still didn't see the end of it because I turned it off before the battery ran out!.  I can imagine I would be able to get an easy 4 hours off just a tiny UPS type gel-cell.  Before testing this I ran trailer lights long enough to think "Oh crap!" before dashing to the cab to start engine -and have never had any issues or even hesitancy in cranking.  (and it's an early-80's 7.3 Diesel so it definitely draws some juice)

Now that being said, I also have a big sine-wave inverter for power tools and possibly running PA gear (haven't had to use it for that yet but it's been used to fire-up and test a rig before main generator plant arrived) either way it runs my air compressor, DeWalt contractor saw or the compound miter just fine.  But it would drain even a big battery in short time.
I use a motorhome battery isolator under the hood to allow charging a second battery from the alternator but no draw-down of the main starter battery when engine isn't running  There's a second deep-cycle RV type "house" battery under the hood that runs the inverter and 12v feed to the trailer (pin-4 on the 7-round).  My interior lighting is just the typical plastic RV ceiling lights but with LED bayonet type (dome light) bulbs instead of the original stock incandescents.  Some of those have extra circuitry in them to not confuse modern vehicle (CANbus) lighting controllers so they draw significantly more current, but I got mine from a friend who is obsessed with off-grid solar and intended for minimal power draw.  there's a switch on the face of each one so I don't have to use all 8 lights if I don't need.  Master switch by back door that turns them all off if you forgot after loadeing and can't reach the front ones.  And they are all just the normal accessory toggle type switches you can buy at NAPA.
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Craig Hauber
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Bob Faulkner

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Re: on-off-on "light switch"
« Reply #18 on: February 26, 2023, 03:53:42 PM »

How about this? Just tie 2 to 4 and 6 to 8 on the output.

https://www.amazon.com/VictorsHome-Changeover-Positions-Terminals-Universal/dp/B07MZ739CS/

This is a great design.  Though, I would be back to tying terminals together.

I wouldn't be looking at 120VAC switches for building electrical.  I've been told they aren't the best for DC and contacts are designed assuming a zero-crossing every 1/60th a second.  I would look instead at automotive and RV type equipment.

I also think you may be overthinking this.  Honestly, how long are your load-outs?  I've run the LED work lights I installed in my trailer for over 12 hours straight on a basic riding mower battery -and still didn't see the end of it because I turned it off before the battery ran out!.  I can imagine I would be able to get an easy 4 hours off just a tiny UPS type gel-cell.  Before testing this I ran trailer lights long enough to think "Oh crap!" before dashing to the cab to start engine -and have never had any issues or even hesitancy in cranking.  (and it's an early-80's 7.3 Diesel so it definitely draws some juice)

Now that being said, I also have a big sine-wave inverter for power tools and possibly running PA gear (haven't had to use it for that yet but it's been used to fire-up and test a rig before main generator plant arrived) either way it runs my air compressor, DeWalt contractor saw or the compound miter just fine.  But it would drain even a big battery in short time.
I use a motorhome battery isolator under the hood to allow charging a second battery from the alternator but no draw-down of the main starter battery when engine isn't running  There's a second deep-cycle RV type "house" battery under the hood that runs the inverter and 12v feed to the trailer (pin-4 on the 7-round).  My interior lighting is just the typical plastic RV ceiling lights but with LED bayonet type (dome light) bulbs instead of the original stock incandescents.  Some of those have extra circuitry in them to not confuse modern vehicle (CANbus) lighting controllers so they draw significantly more current, but I got mine from a friend who is obsessed with off-grid solar and intended for minimal power draw.  there's a switch on the face of each one so I don't have to use all 8 lights if I don't need.  Master switch by back door that turns them all off if you forgot after loadeing and can't reach the front ones.  And they are all just the normal accessory toggle type switches you can buy at NAPA.
I've used AC electrical things with DC for many years, no issues.  My trailer currently has a USA standard AC light switch in for the LED lights.  I installed this about 8 years ago to replace the factory 5-watt incandescent mood-light that came with it; have had no issues.  You are right, I am probably overthinking this whole project (I have a tendency to over-engineer things).  Over the years, I have found household electrical things to be a lot more "heavy duty" than automotive things.

Some of our load-outs can take 3 hours; and I do not want to have to worry about loss of battery power.  In my years of doing this, I've been stuck twice due to running the vehicle battery down too far to start the engine (plenty of power to light a few lights, but not enough to start).  Since then, I do what I can to ensure no issues.

Sounds like you have a decent setup! 

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Steve-White

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Re: on-off-on "light switch"
« Reply #19 on: February 26, 2023, 04:12:22 PM »

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ProSoundWeb Community

Re: on-off-on "light switch"
« Reply #19 on: February 26, 2023, 04:12:22 PM »


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