Power Converter Weirdness

[Bystickel]

Hi, everybody. I have a 1960 Safari that was redone by some bandits about 15 years ago.I've only been around it 3 years, and it's having some electrical gremlins, in the form of some blown fuses (including the 12v power to the hitch from the car( Audi Q7 TDI)), a battery that isn't charging on drives, and a possible draw.

I started diagnosing today. First off, my battery is only at 10.6V. Hopefully it will recover after more charging, but 10.6V is my starting voltage for this:

The first thing that puzzled me was finding 9.1V at the positive for the refrigerator, where I had disconnected both the 12V and 120V. Why would it be 1.5V lower than at the battery? I went back to the panel (Atwood aps-5530), and pulled all of the fuses. (Shore power was not connected, breakers all off).

The battery side of the fuse block reads 10.6V
The downstream side of the fuse block reads 9.1V.
How is the other side of the fuse block receiving any voltage with the fuses removed? And why would it be lower?

I suspected a short and some back-feeding of the circuit, so I disconnected all the negative wires from the ground block on the back. Same.

I'm going to check more tomorrow and try to get solid notes on what I find. Any help is greatly appreciated.

[Bystickel]

It may be some sort of feature that illuminates an LED to indicate which fuse blows. tiny resistors seem to drop the voltage by 1.5V.

Even with the fuses pulled, the lower voltage can be measured downstream at the accessories, although the current available must be miniscule, because even though 10.5V would run a fan, the fans don't run on the 9.5V coming through the fuse block.

[richard5933]

I'm guessing you have either a bad cable between your battery bank and the fuse block or a dirty/corroded/weak connection on one end or the other.

Doesn't take much corrosion to cause a voltage drop, and this can be on the fuse block terminal where the cable connects, on the battery, or inside the cable itself. I've seen cables which looked good on the outside, but one good tug on the cable and it pulled out of the battery terminal connector due to internal corrosion.

This would also be a possible cause of your poor charging performance.

Another possibility here are the ground connections - all of them, including from the fuse block to the chassis, battery bank to the chassis, etc. If you don't have a good ground circuit you won't have proper voltage or proper charging.

[uncle_bob]

Hi

The simple way to figure out if it's some sort of back feed is to disconnect the battery. If the voltage is still there with no battery then yes, you have another source of "12V" running around. If you have 9.1V with both 120V shore power disconnected and the battery out, then there's another battery somewhere ( or you have solar).

How old is your battery ( or batteries) If they are 5+ years old and at 10.x volts, it's time to consider replacing them. You don't have to go nuts on the replacements if you don't run off grid much. About $150 at Costco most weeks will get you some deep cycle RV batteries. You may never have heard of the brand before, but the price is right

With the battery disconnected and shore power plugged in, your converter / charger should put out > 13V. If it reads less than that at the converter output terminals, put that on the shopping list as well. 15+ year old converter chargers are into the "time to replace" region ....

Bob

[Bystickel]

Thanks for the thoughtful replies!

The voltage is great with shore power plugged in. The battery is low from sitting, and possibly not fully charged by the car after the last trip.

For some reason we've had a few blown fuses in the car, the one that provides charging to the trailer. I wondered if it was due to a depleted battery 'demanding' too much current from the car's charging system. We tend to stay in primitive spots and can get run down between driving.

There's nothing in between the car and the trailer battery to limit current. Should there be?

I'm going to have to hunt around to see if I can find the battery-to-chassis ground. There may not be one. I know that there's a good, no-resistance connection between the battery and shell, and that there's a new ground between the shell and frame... just not sure how the battery negative is grounded (the trailer has + and - leads from the hitch plug all the way to the battery. The only grounding may be from some small negative wires coming from some lights at the front of the trailer. I'll have to check this right away)

[richard5933]

The battery negatives on my trailer both go to a negative bus bar. From that negative bus bar there is a 6ga grounding conductor which goes to a grounding block on the frame. It's the same place I grounded the various devices in the trailer like the converter, solar charge controller, etc.

If you have a weak ground connection it's unlikely that your batteries can charge fully from all sources, and equally unlikely that all your electric circuits are seeing full voltage.

Here's a photo of how I tackled the grounding. Maybe it will give you some ideas for getting your grounding figured out.

[Bystickel]

Thank you for that image.

With the Atwood, the way it was wired, all of the negatives go back to either the DC or AC bus bar right on the unit. big + and - wires connect the unit and battery.

The only circuits that I know are ground to the body/frame are the exterior lights.

It would have been simpler if the original re-wirer of the trailer had used the chassis as ground.

[uncle_bob]

Originally Posted by Bystickel

T....

For some reason we've had a few blown fuses in the car, the one that provides charging to the trailer. I wondered if it was due to a depleted battery 'demanding' too much current from the car's charging system. We tend to stay in primitive spots and can get run down between driving.

.....)

Hi

A lot would depend on the fuse. If it's multiple different fuses then there are problems other than the battery. If it's the same fuse again and again, then the manual should tell you what that fuse does. Yes, the description may be a bit hard to decode ... sorry about that.

Next up: is it a 5A fuse or a 40A fuse? Either way, is that the correct fuse for that location? A "normal" power wire on a 7 pin should be fused up around 30A. I was sitting at a dealer earlier in the week while a tech explained to another customer that his problems came from a 10A fuse running to the 7 pin ..... stuff happens.

Any time your normal lead acid battery goes below 12.0V you are headed into "danger" territory. Down around 10V you are into "lots of damage" range. The longer the battery sits at low voltage, the worse it is on the battery. If you are out and about, the "stop using" point (at 75F) is 12V. If it's cold (like 32F) that point could be up around 12.6V.

If the battery is at 12V (or even at 11.5V) the alternator in your car will not put 30A into it. The wires simply aren't heavy enough to do that. There is to much drop / the alternator voltage is ( or should be ) to low. 6 to 10A is not unusual for a charge current under good conditions. If you have a pair of batteries at 10V it will take roughly 28 hours of full speed driving to get them fully charged.

The more practical way to get a battery back to charge is to plug into shore power for a day and let the converter / charger do it's thing. It puts a lot more current into the battery than the 7 pin can. This of course assumes the converter charger is healthy ....

Fun !!

Bob

[jquinn]

make sure that the 7 pin wiring order from the trailer matches the 7 pin wiring connector on th tow vehicle. my 65 caravel had the charge wire and the ground in a different order than my newly installed hitch connector