OT - Voltage Drop In Trailer Wiring

I'm reading a voltage drop in my trailer wiring and wondering if it's normal.

Here's what I've found:

Flat four plug from vehicle reads 12.5V from ground pin to tail light pin without the trailer plugged in.

Flat four plug from vehicle drops to 10.5V from ground pin to tail light pin when the trailer is plugged in.

Light fixtures on trailer read 9.5V from when testing both "socket ground to socket hot" and "ground-screw-into-frame at rear of trailer to socket hot".

Resistance between trailer's flat four ground wire attached to trailer tongue and the ground at the sockets and the ground-screw-into-frame at rear of trailer reads about 2.5 ohms.

The side marker lights have no ground wire, using the self tapping screws that hold the markers to the trailer shell as the ground. The rear lights use a ground wire, with the ground provided by a pigtail to a self tapping screw into the trailer frame.

What would cause a 2 volt drop right at the plug when the trailer is plugged in and then another 1 volt drop at the fixtures?

Thanks!

Reply to
DerbyDad03
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I would start by giving the plug a good cleaning. Without a load except for the meter, there will not be any noticable voltage drop at all. In a 12 volt system, it only takes a small ammount of resistance to have a large voltage drop.

If the lights only pull 1 amp and you have only 1 ohm of resistance, you will loose 1 volt. You mention 2.5 ohms, If you zeroed out all the resistance of the meter, that is where you are loosing most of the voltage. Going back to that 1 amp load, (which is probably not as much as you have) that 2.5 ohms will drop 2.5 volts under the load of the lights.

I would make sure that the wires going from the battery or switch to the plug are good and tight with no corrosion on them. Then clean both plug and socket and make sure the ground wires are tight and don't have any corrosion under them.

The wires should be put on with lugs, but if the wire is just wrapped around the screws, that would be a good place to start.

Reply to
Ralph Mowery

I had all sorts of troubles with a friends trailer used for ministeries........

I finally traced all the troubles to a poor ground on the tow vehicle....

Reply to
bob haller

That's for sure. IDK how many lights he has, but just 12 watts worth of lights would be 1 amp, giving him that 2.5 volt drop. On the other hand, if he has voltage drops without any loads on at all, then he must have some partial short somewhere.

Reply to
trader4

[snip]

Ralph provided a pretty good answer, so there is no need to repeat what he already stated.

I will add, however, that I noticed a sizeable drop on my 5-way to 4-way adaptor, which I ascribed to a typical voltage drop due to semiconductor(s) (diode and/or transistor) in the adaptor.

The way I dealt with this was to ditch the incandescent bulbs that I previously had on the trailer for LED units, which have no problem lighting up nice and bright, despite the lower voltages (the incandescent bulbs were really dim, and I didn't feel safe driving with them in such a condition).

Jon

Reply to
Jon Danniken

Hi, Remeber Ohm's law? Use it.

Reply to
Tony Hwang

Hi, Typical Si junction voltage drop in semiconductor is ~0.2 Volts.

Reply to
Tony Hwang

Since I'm running flat four to flat four, there are no electronics involved in my situation.

The LED route is where I'm headed which is why I was checking out the wiring, just making sure everything was OK. I'm looking at LED replacement that will plug into my existing bulb socket.

This 1157 replacement bulb says it will run at 7.5 - 14 V

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The marker units say they'll run at 9 - 16 V

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However this complete unit, which plugs into the 1157 socket, doesn't list a voltage range.

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I'm guessing the complete unit will be brighter than just the bulb, and I'm guessing it'll run at the 9.5 V I have at those fixtures, but I'll have to call the vendor to find out for sure.

I'm assuming that LED's have one brightness. In other words, any voltage above the minimum produces the maximum brightness, correct?

Reply to
DerbyDad03

Hi, LED's another benefit is it is fractional second faster coming upto full brightness. In panic braking situation it can mean a difference for avoiding the accident. LED is either on or off voltage is applied.

Reply to
Tony Hwang

The 2 volt drop at the plug indicates undesized wiring in the tow vehicle or poor connections. I'd bet on a combination of the two. The scotchlock connectors used by most installers are CRAP and make a high resistance connection - and most cars are wired barely heavy enough to handle the OEM lighting load.

As for the extra drop to the lamps on the tailer, most likely ground issues - 2.5 ohms on a 12 volt 36 watt tail lamp circuit (3 amps)will cause a voltage drop of 7.5 volts, so if you DO have a 2.5 ohm resistance in the ground the trailer has to be getting part of it's ground through the ball hitch.. I'd take a set of good booster cables from a good clean spot on the trailer frame to a good clean spot on the tow vehicle frame and see what it does for your voltage at the bulb.

Reply to
clare

No; you can make an LED barely come on, or you can run it with too much current and it will get brighter than specified. Too much current and you burn it out (heat death), in an amount of time that depends on the excess amount of current. There is a threshold for them to begin to come on at all though, at which point they are still dim, while an incandescent has an infinite amount of dimness (down to zero).

There do exist current-limiting circuits for LEDs; I have one in my headlamp that keeps the LED at a constant state until the battery drops down below the threshold needed to maintain the illumination level.

As far as taillight assemblies go, my experience is that the unit I got works great at the 9.5VDC that I got from my original converter (the new one puts out 11.3VDC). I'm sure it would be brighter if I fed it 12VDC, but it put out more than enough light at 9.5VDC, and far more than incandescents at that voltage (which were barely discernable), which is why I switched.

Jon

Reply to
Jon Danniken

Not technically. The more current through a LED the more light - but good LED LAMPS use driver circuits that control the current. This makes your assumption relatively close to true - for quality lamps (but those are not terribly common on the market - you pay your money and you take your chances.

Reply to
clare

2.5 ohms is a lot when you're talking about 12V systems; V=IR so if you are pulling an amp or more (extremely possible, unless you are using LED lighting on your trailer) that's a 2.5 volt drop right there. Time to break out the deoxit, abrasive of choice, and some grease...

if the trailer is steel you might want to just go ahead and run a ground wire connecting all the ground points together.

nate

Reply to
Nate Nagel

Better ones that have a proper driver, yes. Don't use LED replacement "bulbs" instead use dedicated LED lighting assemblies. The latter are far superior in every way, are likely available as sealed units (in case you are talking about a boat trailer where the lights may be submerged when launching) aren't significantly more expensive, and are fully legal for road use.

This or something similar should work well

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Peterson, Grote, etc. are also good brands to look at - whatever your local boat supply, truck parts store, etc. has in stock. Any of those manufacturers should have a selection of surface mount, flush (snap in gasket) round, flush oval, whatever you need.

nate

Reply to
Nate Nagel

I think he said it is aluminum - and tying all the clearance lights together would be a major job..

Reply to
clare

I can't use the type of tail lights that you linked to. My tail lights are built into the rear doors, which is why I provided the link to this fixture...

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It replaces my current lens and plugs into the 1157 bulb socket. Unfortunately, it's one of the few LED products on that website that doesn't list the operating voltage range. I'll be giving them a call soon to find out.

As a side note, the kit you linked to includes those Quick Splice connectors. Those belong in the same container as back stab receptacles - the trash container.

Reply to
DerbyDad03

My entire post was part of your response and is part of this one.

I'm not sure what made you think I said it was aluminum.

Reply to
DerbyDad03

oh yeah, if you're going to splice, use proper solder and heat shrink, or else proper plug in connectors... I just ASSumed that nobody actually used those things.

can you post a pic of your current taillights? I bet there is a drop in LED full fixture replacement available unless they're real odd, which is really the best way to go... they'll last you another decade at least.

nate

Reply to
Nate Nagel

...snip...

...Snip ...

There's a link to a pic included below.

Follow this 4-step logical progression and tell me if you think it makes sense. Obviously a call to Bargman should clarify everything. I plan to call them on Monday.

1 - The part number on my fixture is 30-84-022, which tells me it's an 84 series fixture.

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2 - I found an RV forum where a poster said he replaced his 30-84-022 with a 47-86-101 LED fixture and that it was an exact fit. I've looked at the Bargman site and it looks like the 47-86-101 should work, but mine is an 84 series, so I'm not sure.

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3 - The replacement part listing for the 47-86-101 shows just the LED lens with a part number of 47-84-420. Note the "84". This is just the LED lens with bare wires.

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4 - Bargman also makes a "upgrade" LED lens with an 1157 plug that fits the existing socket in my 30-84-022. The part number is 42-84-410.

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My conclusion:

If the replacement LED lens (47-84-420) for the full replacement LED fixture (47-86-101) is nothing more than the upgrade LED lens (42-84-410) without the 1157 plug, it would be a waste of time for me to replace the entire fixture and have to wire it in. As long as the socket is in good shape, why shouldn't I just buy the upgrade LED lens? Two screws, a "bulb twist" and I'm done.

Am I'm missing anything in that thought process?

Thanks.

Reply to
DerbyDad03

I would buy ONE and just try it......

Although if the trailer is older I would just rewire it, add dedicated grou nd wires to not only the trailer but the tow vehicle, with proper soldered wires and heat shrink tubing.....

like i said if the traier is older sometimes its best to start over...

the side marker lights arent as likely to have wiring troubles since most o f the wiring is up high away from rain water and deicing chemicals.... but still replace them with Leds. Look at this as a one day interesting project . while your at it fix anything else thats broke or failing like hinges and locks, and check the underside and roof for rust, and check the ires if th ey are old replace them and repack the wheel bearings.... while checking th e trailer jack and restraint chain/////

a few years ago a tree chipper trailer came loose and killed 3 or 4 people. ..

maintence is key to safe operations I found one trailer with flakey lights where much of the wiring was rotting away. undoubtedly from salt water exposure

Reply to
bob haller

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