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Old 03-04-2015, 10:16 AM   #1
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Replacing univolt with solar panel system-newbie needs help

I have a 1970 Safari Double Special and I'm going to try doing a solar conversion this spring. I have a 250w panel by grape solar and I'm getting a mppt charger to charge three 35ah solar batteries. Putting together the solar system is not a problem for me but I am not sure how to integrate it into the existing rv electrical system. I'm assuming I'm removing the old univolt system but I'm not sure how to wire my batteries to the trailer without the univolt.
Any ideas?
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Old 03-04-2015, 07:35 PM   #2
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Replacing the Univolt

Keithgregg,
There is quite a bit of information on replacing Univolt systems in these threads but finding it concisely presented is another thing.
I am not familiar with solar systems (I still think pluto is a planet, for example), but I have recently replaced a Univolt in a 1965 Globetrotter and so I think I may be able to help a bit.

I'm going to assume you know how to mount the panels and run wires and such from you system and what you have coming out of that system is a positive + and a negative - wire that need to integrate with the AS.

The old univolts convert the 110v from shore power to the 12v needed to power the three (or more) 12v circuits. These circuits power some of the lights, the furnace fan, the water pump and ceiling fans. The univolt also charges the AS battery(ies) so you can still have these fixtures while disconnected from shore power.

My understanding is that the Univolts varied somewhat and that earlier ones in the 1960's had a univolt and a separate distribution/fuse panel. Later ones, perhaps yours since its a 70, will have a distribution panel inside the univolt. Look at this thread and it's probably what you have.

http://www.airforums.com/forums/f449...ich-60130.html

Now... Is your Univolt working? That is, is it both running the 12v systems when you are attached to shore power AND charging the battery? If it is working and doing both of these tasks you may not need to replace the univolt at all. If this is the case, I'm probably at the end of my help to you. I'm sure it would just involve running a wire (properly fused/breakerd) from the solar to the univolt but I'm not sure exactly how).

IF your univolt is NOT working or you just want a more reliable charging source, then there are several models of converters out there. I went with the progressive dynamics
Progressive Dynamics
others use the Powermax Boondocker
Powermax Boondocker Converters

So if you get one of these converters, you now need a separate fuse box to deliver power from the converter/battery/solar panels to the 12v circuits. Here is a fusebox that will do the trick.
https://bestconverter.3dcartstores.c...l#.VPexYmPnFX8
12V RV Fuse Box

The key thing to remember when installing this box is that the three DC positive inputs on the fuse panel don't care what the source is coming in, so this is where you connect your battery, your converter and your solar panel.

I am attaching a revised version of a diagram for this fusebox. I think it illustrates what goes where a bit better.

I'm sure I've missed something but hopefully others will chime in and clarify.
Best
Jitney
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Old 03-04-2015, 08:12 PM   #3
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Ok so if I got it right
If my univolt is GOOD I just hook my solar charge controller to the batteries.

If the univolt is BAD I get a new converter and fuse panel and hook the solar charge controller to the batteries.

Does the univolt also supply 110ac to the trailer? Does it still supply 110v when off grid?

Thanks for all the info!
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Old 03-04-2015, 10:18 PM   #4
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In either case I'd replace the univolt with a more modern battery charger. Univolts cook batteries if you use them for any length of time. We lost a perfectly good set of batteries to an OEM charger in our 2007. The replacement is awaiting time for me to install it. In the meantime our solar system is the only thing allowed to charge batteries...the use/store switch stays on store.


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Old 03-04-2015, 11:33 PM   #5
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Thanks for the heads up!
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Old 03-05-2015, 06:42 AM   #6
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Originally Posted by keithgregg View Post
Ok so if I got it right
If my univolt is GOOD I just hook my solar charge controller to the batteries.

If the univolt is BAD I get a new converter and fuse panel and hook the solar charge controller to the batteries.

Does the univolt also supply 110ac to the trailer? Does it still supply 110v when off grid?

Thanks for all the info!
For 120VAC power while off-grid, you will need an INverter. However, your choice of 3 X 35 amp/hour batteries will be a severe limiting factor for the amount of amperage and operational time that any inverter will provide you. You have a total battery capacity of 105 amp/hours, of which you have 50% useable, or 50 amp/hours.

250 watts of solar (if regulated thru a good quality solar charge controller) will keep your batteries well charged under many conditions. I don't know of many folks that can get by with only 100 amp/hours of battery capacity though.

If you are not going to be on-grid power very often, you can probably get by with a smaller converter....say 45 amps....but DUMP THE UNIVOLT!!!!! With the modern switch-mode converters available, there is no reason to jeopardize your batteries with a relic that never worked properly even when new. (just my humble opinion....of course!)
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Old 03-05-2015, 08:10 AM   #7
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Thanks lewster. I was thinking it would be best to replace the 45 year old univolt system.
I was thinking that 105ah was be a bit low on battery. It is what I currently have leftover from a small solar system I used to have. It will be enough until I am done working on her. Then I was planning on getting a couple of 100ah batteries or maybe four 6volt golf cart batteries.

This may sound stupid but, if I'm adding 250w solar and 200ah of battery, would it be feasible to add a Battery Tender instead of a new converter?
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Old 03-05-2015, 08:54 AM   #8
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For maintenance, sure. Your solar should take care of the battery charging. I would look at the BatteryMinder 12248 unit. Excellent and it has temperature compensation!


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Old 03-05-2015, 09:36 AM   #9
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Ok so if I got it right

Does the univolt also supply 110ac to the trailer? Does it still supply 110v when off grid?

Thanks for all the info!
This part of your question was not answered in the followups but maybe you realized that the answer is "no".
Univolt converts shore power 110v to 12v for both circuits and battery charging ONLY when connected to shore power.
Unplug from the house/30amp connection and you are on battery alone.
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Old 03-05-2015, 11:10 AM   #10
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Thanks jitneybead. I wasn't sure if there was also an inverter function or if it supplied 110v there the trailer while plugged in. So what supplies power to the 110v outlet in the kitchen area of my trailer?
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Old 03-05-2015, 11:24 AM   #11
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On option is to keep existing univolt if it is working but put it on separate circuit or switch. You could use solar for battery maintenance 99 percent of time but turn univolt on for short periods of bulk charging if needed when solar not keeping up. Don't want to use it regularly or it will fry batteries. Cost of a smart charging converter upgrade is around $ 200 so may not be worth the hassle of manual operation of univolt.
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Old 03-05-2015, 01:32 PM   #12
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Thanks jitneybead. I wasn't sure if there was also an inverter function or if it supplied 110v there the trailer while plugged in. So what supplies power to the 110v outlet in the kitchen area of my trailer?
Your kitchen outlet is powered by your shore power cord. It will only work when the trailer is plugged into the grid, ot into a generator.

If you want to power that outlet from your batteries when boondocking, you will need an inverter as well as a new converter. It's possible to get one unit that will do it all - charge batteries, run DC devices, and provide 120VAC from the batteries - and it will do it automatically. I'm familiar with the boating market, where we call those units "inverter/chargers," and Lewster will be a good source for what's available in the RV market.
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Old 03-05-2015, 02:45 PM   #13
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On option is to keep existing univolt if it is working but put it on separate circuit or switch. You could use solar for battery maintenance 99 percent of time but turn univolt on for short periods of bulk charging if needed when solar not keeping up. Don't want to use it regularly or it will fry batteries. Cost of a smart charging converter upgrade is around $ 200 so may not be worth the hassle of manual operation of univolt.
I agree 100%. Thats what I've done and it works great. I monitor my battery levels with a Trimetric and when I need some extra help, I flip on the breaker that powers the univolt. It's easy to remember to turn it off because the dang thing hums like crazy!!!
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Old 03-05-2015, 05:00 PM   #14
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If I can cheap out and not replace it, trust me I will.
I have plenty of other reasons I can throw money at her.
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