Does Univolt need battery to run 12 volt fixtures?

[Airboutique]

Clarification please. My 12 volt "fixtures" only work when I have a battery hooked up to the univolt. According to an electrician, the univolt doesn't need a battery if it is connected to the main power source. I can hear the univolt running when I have the breaker on but it will not power anything 12 volt.

Thanks for any input!

[Bill M.]

That is interesting. On my 1988 Excella I can run the 12 volt stuff without a battery. I do not like to do it because the battery serves to flatten out the spikes and make the voltage more uniform. But I did run it for a week or so last year before I realized I had not hooked the batteries back up. I disconnect them over the summer since we leave the trailer plugged in to run a dehumidifier.

Not sure what the battery isolator switch does. Have you checked to see what position it is in? Are you saying the 12 volt system works fine with a battery (charges) but no voltage withoot a battery?

[rhudson12]

It almost sounds like it might not be switching from Battery power back to 120V. When you have the battery out have you tried checking the cables from the univolt with a meter?

[HowieE]

Test for voltage on the output terminals of the univolt while the batteries are disconnected. If you have voltage at that point and no lights will work the univolt may not connected to the circuits. Look at the battery terminals to see if the connection was made at the terminals and is open when the batteries are disconnected. If there is no voltage the univolt be designed to shut off when there is no battery load sensed.

As mentioned incorrectly above there is no connection between the 12 volt and 120 volt systems. I would also look for another electrician.

[rhudson12]

I'm sorry. I think I didn't explain myself well. The 120V supplies the power for the 12 Volt output from the univolt. It most likely goes through a transformer, bridge, and rectifier to produce the 12 volts. So it is connected to the circuitry for the 12v. My point was that when the 120v is connected, the battery is connected to a charging circuit that probably outputs something low, like 2Amps. When the 120V is disconnected, the univolt has to switch over to allow the battery to supply the voltage through the univolt to the 12 volt circuitry. If the switch is bad, that would only allow the battery to supply 12 volts. By removing the cables from the battery and testing with a meter while plugged into 120V, you can see if the univolt charging circuit is switching and supplying 12v to battery for charge. Just my two cents.

[HowieE]

Check this site for more info.

http://www.tompatterson.com/VAC/disc....php?936805560

[Leadvox]

I have a 1973 tradewind. My univolt was doing the same thing, but it was also not charging the battery. When I took off the univolt cover it all made sense. There was a leakage and total corrosion of the converter.

It is really an easy fix to swap out the univolt for an upgraded 12v converter. I bought the boondocker from bestconverters.com and a new 12v distribution panel. It took about an hour to remove the univolt and install the boondocker. I have yet secure everything and tidy it up, but I had my 12v running smoothly in no time. If you have your manual, all the wires should be listed but even that is easy to figure out without it.

A couple benefits: The weight-the univlot is crazy heavy compared to the new technology. Better battery maintenance-the new converter is better at charging batteries. Sound-the new converters are quite a bit quieter.

Good luck!

[TG Twinkie]

The Univolt does not "switch over" it is on continuously as long as there is 120 volt power to it. It is wired in parallel with the battery and the 12 volt fuse panel.
If you don't have lights without the battery but the battery is charging (which I doubt) you probably have a wiring problem, connection problem or maybe a blown fuse.
The Univolt will provide power without the battery but it is not regulated well and the power could vary from 13 to 15 volts.

[ijustlee]

When my Univolt did that it was because one of the capacitors went bad. Watch out, 500V on those capacitors! The Univolts are tough but awful noisy, the Capacitors and the fuse panels are what usually quits on them. After replacing a bad capacitor twice I removed the Univolt and replaced it with a solid state power supply, much quieter but easy to kill with generator power malfunction. I kept the fuse panel from the Univolt so I could have the Amp meter function in the control center and it was still in good shape.

[GR8DANE]

Go fishing, use univolt as anchor, unplug first.

[A W Warn]

Originally Posted by Airboutique

Clarification please. My 12 volt "fixtures" only work when I have a battery hooked up to the univolt. According to an electrician, the univolt doesn't need a battery if it is connected to the main power source. I can hear the univolt running when I have the breaker on but it will not power anything 12 volt.

Thanks for any input!

Isn't there an external fuse on the converter?

I know that those older units are supposed to only be run with a battery connected or they might be damaged. What brand/manufacturer do you have?

[Leadvox]

Originally Posted by GR8DANE

Go fishing, use univolt as anchor, unplug first.

Be careful it doesn't sink your boat.

[ijustlee]

Yes. A W Warn, In my '73 I think there is a 50 Amp fuse in the black - wire that connects to the Univolt. It may go to the - battery terminal but I can't remember. Worth checking all fuses for sure. An old blue Univolt will run the lights and furnace without a battery and shouldn't hurt anything. They will overcharge a battery and I believe Airstream was paid by a battery manufacturer to install these Univolts so they were guaranteed repeat battery sales!

[Jacob D]

One of the best things to happen to my '67 Overlander was when the original Univolt quit working. I replaced it connection for connection with an Intellipower 9100 converter by Progressive Dynamics which so far has been flawless. it uses less power itself and takes up less space. When it failed in warranty, PD replaced it at no charge with an upgraded model. I've never tried to operate w/o a battery. The main function of the battery when on shore power is to act as a buffer to eliminate spikes and dips in voltage.

[rhudson12]

TG Twinkie. I'm sorry. I did state "When the 120V is disconnected". It is then that the circuitry "connects" the battery to the 12V battery. My owners manuals from '70, '71, and '72 all state the "Whenever possible, use the automatic built in charger of the Univolt System for charging. the charging circuit automatically controls the current, reducing it as the battery increases in charge." It also warns against a quick charge. This indicates to me that there is a separate charging circuit for the battery and it does not connect in parallel straight to the 12V distribution. The converter is capable of outputting 30A or more and this would be bad for the battery. It also would not be able to control the current to the battery unless it is a separate charging circuit. I don't know if designs prior to 1970 would be different. I know it shows me as a new member, but I have had an EE degree for over 20 years. I just thought I could help with a little insight. After reading the other responses, I think replacing with a new converter/charger is a would be a good option.

[TG Twinkie]

There are only 2 wires that connect the Univolt to the 12 volt system in your coach. The + and -. The Univolt is connected to the + and - buss on the fuse panel. There is NO. Switching device in the Univolt!
The battery connects to the same + and - buss. As does the charge line from the TV. The + and - buss is connected to each of the fuse holders one the "line" side. Each branch circuit is protected by it's own fuse. Some coaches have a large fuse (30 amp) in both the positive and negative leads of the battery.
The Univolt doesn't know the difference between your battery and any other 12 volt device in your coach. It does not differentiate. It is only a power source rated at about 30 amps on the output.
Since the 12 volt devices seem to work when you have battery power the aforementioned fuses are probably good.
The internal resistance of the battery is what limits the charge current. There is no kind of intelligence in a Univolt. Thus the reason these units tend to cook batteries.
Since you are a EE the use of a multi meter should be second nature to you. Trouble shooting this system only requires a basic understanding of the system.
What voltage output do you get from the Univolt when it is powered?
What voltage are you getting when the Univolt is not powered.
If you disconnect the battery from the system and the Univolt will not power the lights etc in your coach there is a problem.
You could use a battery charger to confirm this. Leave the Univolt unplugged, connect the battery charge to the + and - terminals on the fuse panel and see what happens. It won't be necessary to have the battery in the circuit. The charger should light up everything in your coach.
I think you are reading too much into what the owners manual states. In short it says the Univolt charges the battery. Don't leave it plugged in when you are not using the coach because it WILL cook the battery.

Here is a basic coach wiring schematic.

http://s1166.photobucket.com/user/do...iring.jpg.html