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.