Improved Toad Wiring Efficiency - I Hope

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Just Lou

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Dec 25, 2005
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I have my TOAD Signals and Lights wired using the "added bulb" technique.  I have never been satisfied with the significant lack of brightness of these lights. 

My theory is that all the small wires, and many connections, required to get voltage from the front of the coach (battery compartment) to the lights in the rear of the TOAD, simply results in too much voltage drop.

I have designed the circuits in the attached photo (not yet wired/constructed) to help alleviate the problem.  I intend to use a fairly large gauge wire to tap 12V from the generator start battery connection (located at the rear of the coach) to power the TOAD lights through the relay contacts.  My hope is to deliver a higher voltage to the lights.

Unanswered questions;
  • will the existing signals from the FLASHER power the relay coils without adversely affecting the operation of the existing coach signal lights?
  • Will I need to add diodes across the rely coils?
  • Will this even work?
What do you think?
 

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I have a similar problem, but I decided to go a different route.  I plan to switch the light bulbs to LED.  They will draw much less current and therefore much less voltage drop.  I just need to find the right LED replacements that will handle the voltage variations.
 
Tom, I considered that approach, but since I'm already working with an apparent large voltage drop, and a cloudy taillight lens, I think just the additional voltage will do the trick.  I have enough used parts lying around to build a prototype for testing.  It doesn't have to be pretty, it just has to work.
 
I have to agree with Tom.  With 1/10th of the current draw compared to an incandescent bulb (typically 300 ma vs 3 amps) the wiring voltage loss will decrease a like amount.  On board voltage regulation used in automobile LEDs pushes line loss further into insignificance - a bulb that is rated for 7-14 volts meets spec with socket voltages as low as 7 volts.

And it's plug and play - no need to run an extra wire from the battery or rely on relay contacts.

Do a Google search for dual intensity LED replacements.  I didn't find any dual intensity LEDs on our board sponsor's site, but here's an interesting one from another vendor.
 
Lou, having worked extensively with relays, solenoids etc...  I would recommend going with diodes across the relay coils.  Depending on the size of the coils a pretty hefty voltage spike may be generated when the field collapses. Could interfere with the blinker circuitry upstream.  Just my thoughts.
 
All you have to do is decide if you want the week's worth of recreation making all this work or would rather spend a few bucks for LEDs. ;D
 
Have you measured the voltage at the toad to verify that there really is a voltage loss.
 
Jeff said:
All you have to do is decide if you want the week's worth of recreation making all this work or would rather spend a few bucks for LEDs. ;D

Hells Bells, I never even thought about there being an LED that I could just plug into the socket that I installed for the extra bulb.  What's that old saying about not seeing the forest for the trees? ??? :-[

You know that other old saying;  "If the only tool you have is a hammer, every problem becomes a nail." :-\
 
carson said:
Lou, having worked extensively with relays, solenoids etc...  I would recommend going with diodes across the relay coils.  Depending on the size of the coils a pretty hefty voltage spike may be generated when the field collapses. Could interfere with the blinker circuitry upstream.  Just my thoughts.

Thanks Carson, I suspected that might be the case.  I don't want to cause more problems than I solve. 
 
Hi Ho:  Assuming that it is about 15 feet from the battery to the lights and for the moment ignoring contact and switch loss:  for #18 AWG wire the voltage drop is about 0.07 volts round trip, for #22 AWG it is .16 volts.  Guessing how many milliohms are in the contacts is really just a guess since the condition of the contacts is probably the determining factor.  Before I would spend time with relays, my first thought would be to measure the voltage at the light bulb.  For 0.1 to 0.2 volts I think the gain would be inconsequential.

I do like the LED idea since there are very bright LED replacement bulbs available these days.
 
In my case, motorhome battery to toad tail lights equals 55 feet and three connections.  It's the MH battery that is driving the MH signal lights plus the added load of the toad lights.  I was simply trying to devise a way to power the lights from the toad's own battery. 

I have already proven, to MY satisfaction, that a bulb driven by the toad's own battery blinks brighter than the currently added bulb, being driven along with all the existing coach bulbs, from the coach battery some 55' away.

If using relays is such a poor idea, I wonder why FORD put these in place on some F53s? (see attached) 
 

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Just Lou said:
In my case, motorhome battery to toad tail lights equals 55 feet and three connections.  It's the MH battery that is driving the MH signal lights plus the added load of the toad lights.  I was simply trying to devise a way to power the lights from the toad's own battery. 

I have already proven, to MY satisfaction, that a bulb driven by the toad's own battery blinks brighter than the currently added bulb, being driven along with all the existing coach bulbs, from the coach battery some 55' away.

If using relays is such a poor idea, I wonder why FORD put these in place on some F53s? (see attached)

Lou,

Hate to tell you this but Winnebago used your relay idea on some of their DPs. Found this out while wiring a friends new Winnebago for a toad. So yes, your idea works well but you can't patent it.  (relay-solenoid/parkey-margarin) GRIN

Richard
TDY Starkville, MS
 
[quote author=rls7201]
Hate to tell you this but Winnebago used your relay idea on some of their DPs. Found this out while wiring a friends new Winnebago for a toad. So yes, your idea works well but you can't patent it.  (relay-solenoid/parkey-margarin) GRIN
Richard
TDY Starkville, MS
[/quote]

Hey Rich,  I see you and Michele are still east of the Mississippi.  Hope you are having a great time.  You need to be working your way home if you are going to be ready for your Alaska trip.

LOL - I wasn't planning to patent the relay solution, just confident that I wasn't too far off base.  I will admit, however, that if the low current LED's were available back when my F53 was built, the relays might not even have been considered.

I'm too busy watching the shortened, but hectic, hockey season to put the contraption together.

BTW - that nasty chilly weather that you brought to NC with you, is still hanging around.  I think it legaly has to leave by Thursday, since that's the first day of spring.
 
One of the things I find interesting.... When I had a towed behind my motor home the towed had a wire for Turn/stop lights (Right and left) For Tail/license plate lights and a ground.. all the same size,  It also had a battery charge line for the electric aux brake system..  But no additional weight on the ground wire.

The first thing I will do if I go with another electric brake system (As opposed to the Ready brake I'm considering) is upgrade that ground to 10ga.
 
Lou,

That hefty spike that carson suggested is a possibility but a diode is certainly not the answer and would only inhibit proper operation of the relay. What is needed to control the spike from the collapsing field is a series RC network. Some times called a snubber. See the link below for information on how to construct a RC network for your application, if you feel it's necessary.

http://www.filmcapacitors.com/rcnetworks

Richard
 
rls7201 said:
Lou,

That hefty spike that carson suggested is a possibility but a diode is certainly not the answer and would only inhibit proper operation of the relay. What is needed to control the spike from the collapsing field is a series RC network. Some times called a snubber. See the link below for information on how to construct a RC network for your application, if you feel it's necessary.

http://www.filmcapacitors.com/rcnetworks

Richard
Interesting.  Our military aircraft equipment had a diode across all 28 vdc relays.  Seemed to work for that okay for that application and a solenoid should be not any different.
 
I've always used a diode across DC relay coils, too.  Since the voltage transient generated by a collapsing magnetic field is the opposite polarity from the voltage that generated the field, a reversed polarity diode across the coil seems like a simple and effective fix - an open circuit to the incoming voltage that operates a coil, a short to the reverse polarity spike.
 
The RC network described is to protect the relay contacts.  The diode is to protect the circuit feeding the relay coil.  Two different applications.
 
Ned said:
The RC network described is to protect the relay contacts.  The diode is to protect the circuit feeding the relay coil.  Two different applications.

Thank you Ned, My point exactly. The relay contacts being protected are the turn signal flasher contacts.

Richard
 
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