# Dh Did It, Reversed The Battery And Hosed The 40 A, Now A Question



## NH Campin' Fam (May 13, 2007)

My dh has joined the ranks of the very elite group who have reversed the battery and blown the 40a's in the converter panel.

My question is this: we replaced the 40 a fuse but also happened to notice that there is a red light at the top of the column of blue 15 A fuses? Not sure if it was on before. It sits next to the number 1 position which is an empty slot and on our legend doesn't even have a designated function. The rest of the numbers are labeled as "stereo, bath, etc" and have a 15 a fuse next to them. So, what is the significance of the red light? Does it mean that I should insert a 15 a fuse into this empty slot just to satisfy the light?

Thanks in advance for your input. Heading out this weekend for our first trip of the season! Whoo hoo!!


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## CamperAndy (Aug 26, 2004)

The red LED indicates the slot is open. If there are no wires then you do not need a fuse.

You also need to check the radio as the in line fuse to it may have blown when the battery was reversed.


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## NH Campin' Fam (May 13, 2007)

Thanks, will do!


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## egregg57 (Feb 13, 2006)

Welcome to the ranks!! I did the same thing...and I deal with electricity all of the time. The fuses did it's job. Hopefully you're all set. Where about in NH are you? Are coming to the Spring Rally?

Eric


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## W4DRR (May 17, 2005)

CamperAndy said:


> The red LED indicates the slot is open. If there are no wires then you do not need a fuse.
> 
> You also need to check the radio as the in line fuse to it may have blown when the battery was reversed.


The red LED will light if the fuse is blown or missing _AND_ there is some kind of load connected to that circuit. With no load, the LED can not light, regardless of the fuse.

Bob


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## usmc03 (Jun 6, 2006)

I just re-installed my batteries and may have done this myself as my radio is not working either when everything else does. Question: What should the black wire be hooked to and what one should the ground (white) one be hooked to?

Thanks
Lance


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## W4DRR (May 17, 2005)

usmc03 said:


> I just re-installed my batteries and may have done this myself as my radio is not working either when everything else does. Question: What should the black wire be hooked to and what one should the ground (white) one be hooked to?
> 
> Thanks
> Lance


At the battery, the Black wire is Positive, and the White wire is Negative.
The radio has it's own separate fuse. It always blows when the battery is connected backward.

Bob


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## usmc03 (Jun 6, 2006)

W4DRR said:


> I just re-installed my batteries and may have done this myself as my radio is not working either when everything else does. Question: What should the black wire be hooked to and what one should the ground (white) one be hooked to?
> 
> Thanks
> Lance


At the battery, the Black wire is Positive, and the White wire is Negative.
The radio has it's own separate fuse. It always blows when the battery is connected backward.

Bob
[/quote]
Thanks,
I will have to take a trip by the storage lot and check to see if that is how it is now. I also think I hooked the two of them together correctly, postive to positive and negative to negative.


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## CamperAndy (Aug 26, 2004)

W4DRR said:


> The red LED indicates the slot is open. If there are no wires then you do not need a fuse.
> 
> You also need to check the radio as the in line fuse to it may have blown when the battery was reversed.


The red LED will light if the fuse is blown or missing _AND_ there is some kind of load connected to that circuit. With no load, the LED can not light, regardless of the fuse.

Bob
[/quote]

Not true in this case. The LEDs in the WFCO converters have voltage detection upstream and down stream of the fuse and light when those voltages are not equal. No load device is required for this to function. Requiring a load device for the LED to operate would indicate the LED is a load carrying device and that is the last thing LEDs do very well is carry any kind of amperage.


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## W4DRR (May 17, 2005)

CamperAndy said:


> The red LED indicates the slot is open. If there are no wires then you do not need a fuse.
> 
> You also need to check the radio as the in line fuse to it may have blown when the battery was reversed.


The red LED will light if the fuse is blown or missing _AND_ there is some kind of load connected to that circuit. With no load, the LED can not light, regardless of the fuse.

Bob
[/quote]

Not true in this case. The LEDs in the WFCO converters have voltage detection upstream and down stream of the fuse and light when those voltages are not equal. No load device is required for this to function. Requiring a load device for the LED to operate would indicate the LED is a load carrying device and that is the last thing LEDs do very well is carry any kind of amperage.
[/quote]

Traditionally, in the past, the LED (or neon indicator for AC) was in parallel with the fuse. It would have a series current limit resistor. If the fuse was intact, virtually all the current would pass through the fuse. If the fuse was blown, the current path would be through the indicator light. Of course, the current would only be a few milliamps by virtue of the current limit resistor. Without a current path downstream, the indicator would not light, such as the case of an open circuit.
Now if WFCO put some kind of active sensing circuit on the fuses, it could work as you describe, but in this day and age of "get the cost out", why would they do that, instead of just the traditional parallel LED? Especially given the fact those WFCO converters/chargers don't strike me as being "high end". I can tell you one thing, they didn't spend much time or money quieting them down, RF-wise. I doubt they could pass an FCC Part 15 certification test.

Bob


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## W4DRR (May 17, 2005)

I just consulted the WFCO manual. Here is what it says with regard to the DC fuses:

"Each 12VDC circuit of the WFCO ULTRA Distribution panel is provided with a LED indicator light. Should the fuse "blow" or an open be caused the LED will light up indicating which circuit is open and which fuse needs to be replaced."

The only "open" condition it detects is the fuse being open, not the downstream circuit, as it only says to replace the fuse. No mention of troubleshooting an open circuit. I think the WFCO manual suffers from poor Chinese to English translation that plagues most products from China.

I still stand by my original statement, that if a fuse is missing, and the LED is lit, there has to be something connected to that particular circuit. If the circuit was truly disconnected, then the LED will not light.

Bob


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## CamperAndy (Aug 26, 2004)

Well I am on the road today but will see what I can do to test the LED/fuse function when I get home. Updates to follow tomorrow.


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## 3LEES (Feb 18, 2006)

W4DRR said:


> The red LED indicates the slot is open. If there are no wires then you do not need a fuse.
> 
> You also need to check the radio as the in line fuse to it may have blown when the battery was reversed.


The red LED will light if the fuse is blown or missing _AND_ there is some kind of load connected to that circuit. With no load, the LED can not light, regardless of the fuse.

Bob
[/quote]

To confirm Bob's analysis:

I have a couple of open slots (slots without fuses) in my fuse box. None of them has a lit LED.

On the other hand, if I remove a fuse or blow a fuse (done that a few times), the red LED lights.

My assumption is:

Just like a 120V panel, there are open slots in my 12v panel. In a 120v panel, you must install a circuit breaker on the bus bar in a open slot and hook up your source wire to that breaker. Then hook up the associated neutral wire to the neutral bar in order to have a completed circuit.

The same is true for 12V. You have to hook up a source wire to the back of the fuse slot and hook the ground wire to ground to make a circuit.
If the 12v slot is not needed, why would the factory hook a wire to that slot? Therefore, no load is present, and the LED is not lit.

It also make logical sense. Dealers all over the country would be fielding questions about why a LED light in their fuse panel was lit. And since the LED DOES light when the fuse is blown or missing, it is a good way to troubleshoot a 12v problem.

Dan


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## Nathan (Jan 2, 2007)

usmc03 said:


> Thanks,
> I will have to take a trip by the storage lot and check to see if that is how it is now. I also think I hooked the two of them together correctly, postive to positive and negative to negative.


They are both 12V batteries?








If so, then yes, you did.


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## CamperAndy (Aug 26, 2004)

Well I am home and will investigate tonight if I can and tomorrow for sure but the assumption that the LED only lights with a completed circuit down stream of the fuse panel is not valid.

Picture this. You have a light circuit connected to the fuse panel. You blow the fuse because you hooked a disco ball to the light switch. Since you know you over did the circuit you turn the light switch off and go to the fuse panel to check the LED to indicate the blown fuse. Well since you turned off the switch there is NO load down stream of the fuse to complete the path for the LED. This would not be very helpful in a dark trailer.

On Edit - Assumptions are bad, as it appears I have made one.

Threads like this are good for several reasons one of which is to make you really look close at your fuse panel. I have 9 fuses but only 7 are labeled and none of them match the 9 wires. So tomorrow I will be chasing and labeling fuses.

Now to the meat of the question. Even though it appears to have a comparator circuit (with a transistor and several fuses) on each fuse it does not look to work that way (consistently). I pulled all my fuses and had 4 LEDs out of 9 light up. It looks like there are plenty of parasitic loads. The blown fuse detectors will not work on switched circuits. The transistor needs a least a micro amp or two of current flow to switch and turn on the LED. I will need to look and see if there is a grounding wire missing.

I can now see a mod where I add some meg ohm resistors to each of the fuse branches to have a continuous path to ground so the LED's will work even on the switched circuits.


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## W4DRR (May 17, 2005)

If they use transistors, then it is essentially the same circuit, only with more sensitivity. Instead of the LED in parallel with the fuse, the base-emitter junction is across the fuse, with a fairly large resistor in series with the base to limit current. Then the LED is connected from the collector to ground, with a current limit resistor to set the LED current to an appropriate level. This would have to be a PNP transistor for this to work, by the way. But this circuit would still require something connected to provide the current path to turn on the transistor. Now I suppose, high value resistors could be added to ground on the output side, so it could sense switched circuits, as you mentioned doing. The down side of this would be a steady current draw, lighting LED's indicating an open circuit on something that isn't even used. Not necessarily good for dry camping, where every milliamp counts.

Bob


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