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Old 11-22-2017, 08:03 AM   #1
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1973 27' Overlander
Lexington , Kentucky
Join Date: Nov 2017
Posts: 1
Univolt Replacement

I know there are several post concerning this topic, but I thought it was worth documenting this entire process or at least my understanding of it in cause someone wanted a more collective and thorough instructions.

Overview:
The Univolt in my 73 Airstream International is loud and is only able to charge batteries at a single rate. Because it's not a multistage charger it won't maintain batteries very well. I am going to switch out the Univolt with a converter/charger and upgrade the battery capacity at the same time.

Required Components:
Converter Charger
Fuse Box
50 AMP Battery Fuse
6AWG Wire
misc wire nuts, screws, connectors

What I used:
PowerMax PM3-55
VANJING 100A Color LCD Digital Voltmeter Ammeter
Battery Disconnect
Blue Sea Systems ST Blade ATO/ATC Fuse Block
50 AMP Fuse Block
Shunt from inside the Univolt/DC panel
2x 6v Gulf Cart Batteries in Series


Process:
Removing the Univolt was surprisingly difficult. in my model it was located beneath/beside the bathtub in the rear bath. The DC load center was on the face of the univolt, and was accessible though one of the side hatches, but the unit itself is screwed down on each corner and the screws spin freely. In order to remove the unit i had to remove the rear bed and part of the bath. Fortunately I'm remodeling the bath soon so this wasn't a big deal. But i literally had to chop the screws off with a sawza blade to remove the univolt.

The univolt is big and heavy, for my purposes i will be using the location where it was to store an additional battery but the location of how one connects it all back together is irrelevant to me.
My unvolt housed the DC load panel and this was the most difficult thing to figure out. I searched this forum several times and eventually found some help here:
http://www.airforums.com/forums/f37/...ck-135473.html
But this was only part of the process, the rest wasn't documented straight out. The DC load panel as you can see in the attached images is split into two sides (kinda) the top half houses all the positive leads and the battery/power from the tow vehicle. The bottom half has the shunt and is (kinda again) the negative bus, and a light to illustrate the univolt is powered on.

Connecting the new converter charger to the new DC fuse panel will mean that you run a minimum 6AWG wire from the converter charger to the positive lead on the DC panel and then to the battery. The negative lead will go from the negative side of the inverter charger to the negative pole on the DC panel and to the battery. I put a 50amp battery fuse on that line between the battery and the panel, you can put a battery fuse on both the positive and the negative sides, but I only did one. My converter charger has fuses built in, so it's not required to put one on at the converter charger.

At the fuse panel you will connect the old wires in the following fashion:
Blue (car battery+) should connect to a 40 AMP fuse on the positive side
SKT 1 (purple), 2(yellow), 3(Pink), 4(Brown) each gets their own 20AMP fuse
The grey wire (indicator light) gets a 6 amp fuse. The white wire is the return to the Airstream and tow vehicle, and needs to connect to one of the negitive pins on the DC load panel.

The red wire that was connected under the blue wire is going to the new batteries, and has a dedicated fuse outside the DC fuse box (in my design).

I incorporated a few more elements to get it working how I'd like. First, I kept the shunt from inside the univolt. The shunt is used to send a signal to the gauges up front for the battery gauge. I put it in line with the Negative side of the new converter charger and batteries. it's wired just like it was while inside the univault. with the grey wire on the sliding pin, the red wire on the fixed pin, the negative feed from the inverter charger on the large pin in the back (it was out of sight), the battery connection on the pin with the black wire in the image and the white wire (- negative to airstream) connects to the negative bus on the DC panel and that connects to where the white wire was on the shunt.

I also incorporated a new power meter to get a better reading. The classic shunt is cool to have but the new one measures so much more, and has a wireless face I can use to read the information from anywhere.

A battery cut off switch, to make accessing and working on the batteries easier.

If I'm mistaken on any of this, please let me know in the comments, I haven't put it back together yet, but this is my plan to do so.

I do have a few questions though, mostly due to the tow vehicle. Is a Terminal Battery Isolator required on the Blue wire? if so, i'll probably connect it up near the 7 way access panel and not here in the battery compartment. and what would be used to signal the Terminal Battery Isolator?




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Old 11-22-2017, 08:15 AM   #2
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1974 Argosy 26
Morrill , Nebraska
Join Date: Nov 2009
Posts: 6,008
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I believe you will find that the fuses in your new converter are only there to protect from reverse polarity protection.
Most new converters "crowbar" (shut down) if there is an overload.
The new batteries should be located close together.
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Old 11-11-2020, 06:37 AM   #3
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1983 31' Excella
1983 31' Airstream310
Jax , Florida
Join Date: Dec 2018
Posts: 8
Could it be that simple.

So there may be a difference between MH and trailer BUT, it
Seams to me that the univolt could be removed and replaced with a modern charger/inverter. Just unplug the old and plug in the new? If that works then adding a solar charging system should be very simple. The 12 volt distribution could even be left unchanged The MH is a 1983 300.
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