"Power On" light not working

[Delcolight]

So... Here's the million dollar question.. with 12 VDC ish negative going to positive on the converter. Would this cause a back feed into the converter or the wall wart.. or am I missing something.

[uncle_bob]

Hi

Ok, converter turns 120V shore power ( or generator power ) into 12V DC. Since they charge the batteries, it is very normal for them to have 12V on the output and nothing on the input. Typical they do not present a significant parasitic load. They will not power a wall wart.

The inverter turns 12V into 120V. It will indeed power a wall wart. They typically present a fairly sizable parasitic load.

Putting 12V negative on the 12V positive of the converter or inverter is a bad idea ( assuming the 12V positive is hooked to the negative input. In either case, this is likely to (at best) blow a fuse. At worst it will destroy the device.

So, just what's going on with the "power on" light?

Bob

[Delcolight]

After changing the old converter out of the 79 Argosy the usual hook ups were made and the lack of a lead for the shore power indicator. Upon looking at old unit it gives wire layouts.. white is 12 VDC neg. Red is positive, and black lead is 12 VAC 100ma max. So, the quest is to make the shore power work again. Further up in the posts folks have used a wall wart or small transformer to reduce 120 to 12 VDC or ac. With this set up they repowered the light to work as intended. I had a similar thought and after reading posts.. I question the way it has been carried out.. i understand the idea or rewire for a bulb. Having a circuit board makes things a bit harder... Any ideas

[uncle_bob]

Hi

Ok, the "ground" makes no difference if the "hot" is an independent feed. It's no different than a light switch. Everything stays hooked to ground / neutral / chassis / return at all times.With the switch open, no current can flow.

The feed for the light bulb is the same thing. Unless the wall wart is feeding power, you don't have a circuit. The bulb does not light.

There is the odd case of a three prong plug on a wall wart. That could be internally connected to the output of the device. You then already *have* a ground connection made before you wire anything in. Simple answer is to use a wall wart that does not do this. If it's a two prong plug, there is no ground.

Bob

[featherbedder]

I have same prob. after changing from old univolt to solid state convertor, my simple fix is pur. cheap 119 night light plug into any socket easily visable from outside will light when plugged into shore power, {no hassle no gimmicks}, positive proof of power on w/out going inside to check panel if power connected if inside loss of power you will no immediatly power is off,w/out looking at panel.

[uncle_bob]

Hi

Backing up quite a bit:

The "good" answer is to get an internal EMS and wire that up with a display panel on it. It will serve the function of "do I have shore power" *and* protect the vehicle at the same time.

Bob

[rmkrum]

Or install one of these monitors:



From Amazon. Gives lots of data for us Overkill Engineering types…

[ROBERT CROSS]

Originally Posted by rmkrum

Or install one of these monitors:

Attachment 402969

From Amazon. Gives lots of data for us Overkill Engineering types…

Or MacGyver this into an AC outlet...TETO

Bob
🇺🇸

[uncle_bob]

Hi

Or a plug in "socket tester" for < $5 .... It does use up a socket though.

Bob

[lemley]

I wanted the power light to work for several reasons. It came with the unit so a bit of “keeping it original”. I’d just bought the unit and was doing a lot of upgrades - from toilet to tires and axles. No budget for a power monitor (and less need when there are no delicate electronics to blow). And I’d gotten used to just looking through the back window while setting up to see if the LED was on. Saves steps.

I found a wiring diagram from an engineer at boondocker that showed how to hook it up. Since I have plenty of leftover wall warts from 40 years of electronics it was “free”. I hooked it up according to the schematic and it didn’t work. I gave the schematic a critical look and saw that the problem was that the cathode of the LED was connected to +12, so the anode needed to be above that. +24 was fine, so I hooked the negative from the wall wart to +12 at the converter and the positive from the wall wart to the power indicator LED wire at the converter (and thus to the anode of the LED). Works like. a champ.

I contacted the engineer at boondocker about updating the schematic. He said he’d decided not to bother. “Nobody uses it. They can just look at the microwave”.

Personally (and much of Airstream life is personal preference - there is seldom only one “right way”) I use it and like it.

[Delcolight]

Lemley.

I am right there with ya.. so my thought is as such. By hooking up wall wart that way you create a converter wires in parallel. Wouldn't the amps difference from converter to wall wart be enough to let out the magic smoke? And next idea if it the wall wart hold out would there feed back into the converter and could be a reduction in the output to the battery bank..

[uncle_bob]

Originally Posted by lemley

....... No budget for a power monitor (and less need when there are no delicate electronics to blow)....... t.

Hi

You do indeed have one very delicate piece of electronics on your trailer. The converter charger is *not* all that rugged a device. They can and do blow out ( = been there done that) due to line issues. When they do the output can go to a high voltage, 12V gear (like lights and the fridge) can and do die as a result.

The big dollar item the EMS protects is the A/C. If you go to this or that campground with low line voltage .... bad news for your compressor. Sitting in the heat and humidity for a couple weeks while a replacement is made ... even worse news

None of this is purely hypothetical / never happens sort of stuff. You can find lots of threads here about very basic electrical problems (that an EMS could catch) doing significant damage, even to an older trailer.

Bob

[lemley]

Originally Posted by Delcolight

Lemley.

I am right there with ya.. so my thought is as such. By hooking up wall wart that way you create a converter wires in parallel. Wouldn't the amps difference from converter to wall wart be enough to let out the magic smoke? And next idea if it the wall wart hold out would there feed back into the converter and could be a reduction in the output to the battery bank..

The wall wary is not in parallel. I’ll put together a schematic. Think of the wall wart as a 12v battery with the negative side hooked to the cathode of the LED and the positive hooked through a resistor to the anode. The only difference is that the wall wart provides power only when the trailer has shore power. And that’s when we want the light on. I promise. I’ve done it on two trailers. Works perfect.

Yes, the cathode is also connected to trailer +12 in the overhead, but that’s really beside the point. It’s the way airstream wired it then tucked it away.

If you want my electronics pedigree I can provide it, but it’s probably easiest just to say that I have a lot of training and experience in the design and implementation of very large scale systems. I’m not much with tubes, but from transistors forward I have a pretty deep understanding.

[lemley]

Originally Posted by uncle_bob

Hi

You do indeed have one very delicate piece of electronics on your trailer. The converter charger is *not* all that rugged a device. They can and do blow out ( = been there done that) due to line issues. When they do the output can go to a high voltage, 12V gear (like lights and the fridge) can and do die as a result.

The big dollar item the EMS protects is the A/C. If you go to this or that campground with low line voltage .... bad news for your compressor. Sitting in the heat and humidity for a couple weeks while a replacement is made ... even worse news

None of this is purely hypothetical / never happens sort of stuff. You can find lots of threads here about very basic electrical problems (that an EMS could catch) doing significant damage, even to an older trailer.

Bob

I certainly understand and agree with your point. I’ve installed lots of protection devices over the years.

In the end they are insurance. All insurance is a probability trade off. You decide how much loss you can withstand and insure above that. One of these days (hopefully sooner than later) I’ll add both the EMS and the TPMS. But right now DW says “no” to both. Until then I replace the tire when it blows out and I replace the AC when it fails.

[Delcolight]

It would be great to see that diag. Lem. Please when ya can throw it up there

[Bill M.]

I think the power on light on my older trailers was wired from the 12 DC volt positive from the battery to the un-rectified 12 volt positive AC voltage inside the converter. Current flowed through the light in response to the varying voltage difference throughout the AC cycle. No flow when the AC was not present.

[lemley]

Originally Posted by Bill M.

I think the power on light on my older trailers was wired from the 12 DC volt positive from the battery to the un-rectified 12 volt positive AC voltage inside the converter. Current flowed through the light in response to the varying voltage difference throughout the AC cycle. No flow when the AC was not present.

You are definitely right here. The LED was "powered" when the 12 (14) VAC on the converter secondary was at least .6 volts below the battery voltage.

Yes, I said below... I need to eat a bit of humble pie and correct my statement above.

The anode of the LED is connected through a resistor to trailer +12. The LED is energized when the cathode is below that. The trick is to get the cathode negative ONLY when power is applied to the trailer. That's where the wall wart comes in. AC or DC will work, but I have only DC wall warts laying around. Pics of the installation and a schematic are attached.

[Delcolight]

I just tried the set up and sadly no joy.. I have 12vdc wall wart wired as shown in above diagram. I checked voltage from wall wart 12.3 ish VDC with maybe 500 milli amp. So.. last tech question I have is what power out put are you guys using.. I have tested other wall warts say 12 volt but when measure almost 16 to 18.. and lastly I tried to enlarge the picture to read the amps on the wall wart... I thought I saw 1.1 amps... Or are my eyes getting bad

[uncle_bob]

Hi

Wall warts come in a wide range of "flavors":

1) Unregulated DC. These put out the rated voltage at the rated load. Put a light load on them and they go higher. 50% high is not at all unusual on these units.

2) Regulated DC. These *try* to put out an accurate voltage. How well they do ... who knows. 5% is not unusual on a regulated unit.

3) AC ( always unregulated). These will track the line voltage. They should be pretty close to the marked numbers.

4) Broken. Remember when that gizmo died and you kept it's wall wart? It might have been the wall wart. They can fail dead (nothing out) or they can fail in other more violent ways .....

Backing up a bit: Is the bulb ok? Is it a 12V bulb? Swapping it out for a known good 12V might be a cheap way to take that out of the picture ....

Bob

[Wazbro]

Originally Posted by uncle_bob

\Backing up a bit: Is the bulb ok? Is it a 12V bulb? Swapping it out for a known good 12V might be a cheap way to take that out of the picture ....

Bob

Doing this and only connect the wires to the wall wart and it works when you have AC to wall wart. No need for wires to anything else. Why make it so complicated?