Repairing a heavily modified charge setup. - Fiberglass RV


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Old 08-12-2013, 09:36 PM   #1
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Name: Corey
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Repairing a heavily modified charge setup.

I went out to my uhaul VT this morning and the fridge was off and the water pump wouldn't cut in.
I assumed the shore power became unplugged and the battery was dead.
It turned out that the household power breaker was tripped so I reset it and found that my battery charging voltage was only reading barely above 12V.

A little back story at this point: The original converter was ripped out by a previous owner and replaced with an automotive bench-top 10A/2A battery charger. It is set to 10A. I know that the 12A bench charger in my garage reads well over 13V while charging so it would seem that the uhaul's make-shift converter has gotten weak?

Perhaps someone with experience in this area could tell me if it is possible for a failing converter/charger to output a reduced voltage or is this a symptom of something else, such as a cooked battery?
The battery is a maintenance free car battery (not deep cycle) that came with the trailer. When connected to my garage charger, it shows 13.4 V

I'm going to get the battery tested tomorrow, but in the meantime I thought I'd share a diagram I drew of the modified charging setup. (attached) Most of it makes sense to me except for a few things:

1) shouldn't the load lead on the econocharger be the sole source of power for the distribution panel? Otherwise,

what would be the point of the Low Voltage Disconnect?

2) Why run the load wire to the "master switch, 12V only" switch? and what was the original purpose of this switch?

3) This setup does charge the batteries and i have lights, radio etc when unplugged form shore, but are there any glaring issues with it? It looks like the whole thing is contingent on that bench battery charger not overcharging the battery.
Attached Thumbnails
uhaul modified charge setup.JPG  
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Old 08-12-2013, 09:42 PM   #2
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Welcome to the Forum Carey.
There will be some experts on here shortly to help you out.
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Old 08-12-2013, 09:48 PM   #3
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Thanks Carl,
And I should probably apologize to everybody ahead of time for the roughness of that diagram
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Old 08-12-2013, 10:18 PM   #4
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This is my perception of your given diagram and my personal thought ab this set up...Again, I have no credential or formal training as professional of electrical field..1/ A battery charger 10A/2A alone is too small to play a role of a converter in a RV. 2/ The previous owner used a combination of solar/battery and battery charger as a 12VDC supply for your RV needs. In my guess, depend on how big your solar panel is, but I doubt about this kind of combination would be strong enough for RV circuitry. It might work with fan, light bulbs in RV but not with water pump or other stuffs which requires high current. Again, I guess the man used Master SW when he finds out RV needs more energy and he just flips that SW to let solar energy kicks in..I do have question ab how many watts that solar panel is rated, though....In the case of combination of different DC supplies for main panel, one should design high current diode and act as automatic switch when necessary. Otherwise, the surge current in secondary portion of that battery charger would alter the rule of it's designed work as a rectifier and cut it off from the whole circuitry. Just my quick thought. With more clearly diagram I might try to analyze it more carefully....
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Old 08-12-2013, 10:28 PM   #5
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10 amps isn't very much power. You could overwhelm a charger this size if you aren't careful. You haven't got anything else turned on do you?

You do need more than 13V to charge a battery. Anything less isn't charging. Some of the more aggressive chargers will take you up over 14v for short periods of time.
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Old 08-12-2013, 11:19 PM   #6
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Thinh: The solar panel is the stock one that came with the uhaul in 1986. The manual that I dug up on this site says it was only for trickle charging to prevent sulfation of the battery. It is wired to always provide a small amount of power to the system.
Someone posted a uhaul solar/charging diagram in the electrical documents section of this site that shows the load wire form the stock econocharger shunting unit running directly to the distribution panel. it is supposed to cut off access to battery power at 10.5V to prevent the battery from being drained too low. I tested the unit and it still works as it should. But why it was eventually wired to the master switch is beyond me. Especially given that there are 2 other alternate lines from the battery to the distribution panel. All disconnect would do is remove one of the the 3 paths from the battery to the distribution panel, which is irrelevant since the in-line "master switch" is left off all the time anyway.

Glamourpets: I was running the fridge overnight while the battery was charging. Perhaps that overwhelmed the charger and ultimately tripped the household breaker of my shore power. I measured the charging voltage at one point last year and it was 14.2V which I thought was unusually high at the time. I haven't seen it that high this season. perhaps the battery a turn for the worse over the winter and the charger has been 'working harder' ever since?
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Old 08-12-2013, 11:19 PM   #7
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It looks like it was configured originally for solar charging only, with the power inputs from the Econocharger and directly from the battery individually fused at the distribution panel. It seems that then the automotive charger was added, connected directly to the battery and also connected to the supply side of the distribution panel by a direct wire that makes that battery connection fuse pointless by bypassing it. Pull that one wire and the design makes sense to me again... if the wire sizes are adequate.
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Old 08-12-2013, 11:34 PM   #8
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Brian:
I see what you're saying about removing that wire form the charger to the distribution panel. I was considering removing one of the lines but as you say it may leave me with one line of inadequate size.
As for the solar, I hadn't considered that it may have been wired before the charger was added. In that scenario the master switch would actually serve a purpose allowing a type of "manual overide" and cutting any load on the battery. Perhaps once he realized that the solar panel provided only a trickle charge he was forced to add the battery charger?
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Old 08-12-2013, 11:36 PM   #9
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People often discuss charging voltage as if it is somehow independent of charging current; it is most certainly not. Current flows because voltage pushes it. When charging a battery, the charging voltage must overcome the battery voltage; how much more voltage than that is applied determines the current. If the battery is dead, it doesn't take as much voltage to push a given amount of current as it does to push the same current against the higher voltage of a nearly charged battery.

The automotive charger is set for 10 amps. If it is decently controlled, that means that it will apply only enough voltage to make 10 amps flow, and at the beginning that might not be very much voltage. As the battery charges, its own voltage rises, and the charger will put out higher and higher voltage. Eventually it will reach some set maximum - likely 14 volts or more - and stay there as the current then drops until the low current indicates that the battery is charged enough.

If anything is turned on during charging, it will take some of that 10 amp allowance, and the leftover may only be enough to charge the battery very slowly, and thus at very low voltage. This is one reason why 10 amps isn't very much for an RV converter/charger; however, in some situations (such as with low loads and in combination with a solar system) it may be perfectly adequate.

Some chargers have a display so you can see if this is what is happening. Even without that, I would leave the charger connected - with nothing that uses power running - and see what happens over a few hours.
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Old 08-12-2013, 11:38 PM   #10
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Quote:
Originally Posted by CoreyNL View Post
Perhaps once he realized that the solar panel provided only a trickle charge he was forced to add the battery charger?
That's what I'm thinking, yes.
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Old 08-12-2013, 11:49 PM   #11
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Quote:
Originally Posted by CoreyNL View Post
As for the solar, I hadn't considered that it may have been wired before the charger was added. In that scenario the master switch would actually serve a purpose allowing a type of "manual overide" and cutting any load on the battery.
But even with that switch open (off) everything is still powered from the battery.

Some solar chargers have a load output so they can shut off the load when the battery voltage gets too low - they "manage" the load. The connection of battery to panel defeats that feature, and thus the switch seems pointless. Re-reading the original post, I realize that you already understand this. On the other hand, if the switch were in the battery-to-panel line, not the controller-to-panel line, it would provide a bypass (when turned on) of this load management feature of the controller.
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Old 08-13-2013, 04:09 AM   #12
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...I agree with Brian ab the third branch which connects directly from battery charger to main panel/load. IMO, this set up will work normally with the Master SW stays open, but when this SW is closed in combination of full-charged battery, this directly branch will lead solar current to the charger and interfere with battery charger's function. In this particular effect, in a half cycle of sine wave from AC, the charger will not work as the role of rectifier itself and is cut off at diode bridge(like open cct) and in other half cycle of ac sine wave, the cct closed at secondary of transformer( of the charger) and acts as a reversed transformer,--->your shore power breaker will trip. IMO, either disconnect this direct branch from battery charger to panel and get rid of master SW or change the master SW position..i.e..put this manual master SW in the third direct branch from battery charger to the panel...if you want to keep that branch..Just my thought and I could be wrong. I wish I could have this set up at home to do the test....
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Old 08-13-2013, 08:41 AM   #13
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Thanks guys, this is a great help!
I'm going to just leave that master switch open while the system is in this configuration. Should I remove the connection between the charger and panel and go with a heavier gauge between the battery and panel?

I also happen to have on hand a "mean well S-150-12" power supply - 115 AC input, 12V DC output at 12.5A. Perhaps I should add this to the system to handle my lights/radio/fridge while the charger charges the battery?
Or are there units available that do both? (power accessories while intelligently charging/maintaining the battery)
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Old 08-13-2013, 08:55 AM   #14
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I agree with most of what has been said.

On my CT, the solar panel controller was wired directly to the battery with no low voltage cutoff function in the controller. The output, when I got it, was so low, it was irrelevant. (You might want to test the solar output just to know).

The converter was designed so that when it was plugged in, a relay isolated the battery from the loads and a sub-circuit in the converter provided a charge to the battery with some minimal regulation. I installed a switch so that I could shut off the battery charging when plugged in for a long time (to prevent battery overcharging).
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