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Old 07-25-2004, 10:02 PM   #1
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Question why would the univolt boil the batteries dry

I keep reading that the univolt will boil your battery dry yet the manual that I have for our 67 says that the univolt has a 100% shut off and that it is impossible to overcharge?

David
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Old 07-25-2004, 11:16 PM   #2
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Most of the batteries that were boiled dry by a Charger needed replacement to begin with. Unless, of course, the Univolt is defective.
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Old 07-25-2004, 11:35 PM   #3
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There is a separate unit that protects the battery that can be purchased if you are worried about that. I think its called Charge Guard or something simular. You install it between your battery charger and your battery and it cuts the charge off when the battery is up to 100%. I think you can get it from most RV stores.
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Old 07-26-2004, 08:36 AM   #4
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Quote:
Originally Posted by uwe
Most of the batteries that were boiled dry by a Charger needed replacement to begin with. Unless, of course, the Univolt is defective.
Which can happen after 37 years. I believe they use a set of electrolytic capacitors to regulate output. These will dry out after 20 years or so.

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Old 07-26-2004, 12:09 PM   #5
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Quote:
Originally Posted by silver 67
I keep reading that the univolt will boil your battery dry yet the manual that I have for our 67 says that the univolt has a 100% shut off and that it is impossible to overcharge?
The word boil is a little dramatic for what is actually happening.

A battery is charged by applying a DC voltage to the battery that is higher than the voltage the battery currently has. The higher the voltage difference, the greater the charge rate will be. I believe a fully charged battery will read 12.9 vdc on a volt meter.

Charging a battery is an electro-chemical reaction. As the battery charges, tiny bubbles of hydrogen gas & water vapor form on the plates, and eventually bubble off. These bubbles eventually escape from even sealed batteries. The higher the charge voltage, the more bubbles that are formed. It is this bubbling that is commonly referred to as boiling although it does not occur the same way as water boiling in a tea kettle.

My '67 owner's manual says the exact same thing yours does. I will give Airstream the benefit of the doubt, and assume that some Univolts had a circuit breaker which would trip to effect "100% shutoff". A Univolt has no "smarts" to it. It could care less if your battery is boiling, simmering, or even there. It's job is to supply roughly 13.5 vdc with as much current as it can muster. I put it that way because, the voltage will drop as the load on the Univolt increases. If you are actively camping and have a bunch of lights & fan motors going, the voltage difference between the battery & the Univolt will be small. In fact, the battery may even help the Univolt out if you have A LOT of stuff on.

But, with no lights or anything but the Univolt on, the battery is subjected to the maximum voltage the Univolt can deliver. It will attempt to charge. After a while, the water will bubble off.

Additionally, Univolts do not regulate the voltage they deliver. They were designed to output one single voltage with as much current as possible available. In fact, a Univolt is amazingly simple: A big transformer to step down the voltage, diodes to convert AC to DC, and capacitors to tune the circuit.

If you plan to keep your Univolt, it is important to be mindful of how long the battery is connected when the Univolt is on.

Tom
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Old 07-26-2004, 08:23 PM   #6
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Talking Univolt,

Hi all,
My univolt boiled my batterys . The surprise was when I was leaving for a trip and had no brakes on the trailer. Twoo hundret dollars latter I had 2 new batterys. I replaced it with a 20 amp battery charger which cost less than 75 dollars. IT has bein doing well. The battery charger has automatic shut down so it does not over charge.
By the way does anyone know how to take the control pannel of so I can replace a burn out bulb.
Thanks to all , Russ
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Old 07-26-2004, 10:23 PM   #7
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Quote:
Originally Posted by RUSSELL
Hi all,
My univolt boiled my batterys . The surprise was when I was leaving for a trip and had no brakes on the trailer. Twoo hundret dollars latter I had 2 new batterys. I replaced it with a 20 amp battery charger which cost less than 75 dollars. IT has bein doing well. The battery charger has automatic shut down so it does not over charge.
By the way does anyone know how to take the control pannel of so I can replace a burn out bulb.
Thanks to all , Russ
I was going to suggest that, but figured I hear a bunch of people telling me not to replace it with a battery charger.
There are a lot of good quality battery chargers out today that will not overcharge the battery.
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Old 07-26-2004, 10:55 PM   #8
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You not only need a good battery charger but also a good battery maintainer if you really want to keep your battery in top shape.

One of the better choices is the intelli-power with charge-wizard. Some of the better inverters designed for continuous duty alternative power systems will also have good chargers and maintainers, too.

The maintainer is a good idea if you let your rig sit unused for a month or more because batteries tend to discharge when left idle. A good maintainer will take steps to reduce sulfation as well as keeping the charge topped off.
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Old 07-06-2005, 09:37 PM   #9
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The Univolt is old, very old technology. It is ineficant, hot, noise and puts out DC current with a little AC mixed in. I recently replaced it with a new IOTA with a bult in IQ Smart battery charger. It works great! Quiet cool and verry clean DC. I just can't figure out what to do with the Battery Check light wire. So I caped it off and put in a volt meter, I like meters better than idoit lamps anyhow, it all works great! Griff

P.S. Spelling is not my thing, besides why can't we have alternate spelling!
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Old 07-06-2005, 10:04 PM   #10
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univolt charging

I took my univolt to work to clean/test it. With a slightly discharged battery it started at 13.8 v at the battery posts and I had a ammeter clamped around the charage wire. I let it "cook for about 3 hrs and the voltage dropped to 13.6 and stayed steady when I hooked up my load of the bathroom vent fan. Although my battery has never boiled, I would not recommend leaving the system on long term with out any use, i.e. lights on, fans etc. It was not intended to "mantain" long term. Also of note, when camping, I do notice mine gets 'quieter' after a few hours.
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Old 07-08-2005, 04:14 AM   #11
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In fact, a Univolt is amazingly simple: A big transformer to step down the voltage, diodes to convert AC to DC, and capacitors to tune the circuit.
Tom, what model is your Univolt? The ones I have seen so far have a series voltage regulator board and no capacitors in the output of the regulator. When working properly they will not overcharge a battery.
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Old 07-08-2005, 04:20 AM   #12
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Don't know the model, but it is original equipment for 1967. There is no regulator circuit.

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