Converters / univolts 101

[59er]

Can someone please give me a brief overview of 12v converters?

is there a difference in the old type univolt 'buzz boxes' and newer units?

[RUSSELL]

Yes there are. The biggest is silence.
Charging when battery require the charge and not boiling out your battery. The new units have a trikle charge modes that slow down the charge when the demant is not there. I replaced miny with a 25 amp battery chargers that swiches down to trickle charge.
Regards russell in hot Tucson Az.

[Poprivet]

The univolt is basically a battery charger, It converts 110 A/C to 12 volt DC. The DC capcity varies from 20 to 50 Amps DC. When allowing for IR losses, the A/C amps will run 3+ to 8 amps.

The univolt chargers are basically a step down transformer with several rectifiers to produce the DV voltage. They are noisy and inefficent. Some moderen electronics do not like the univolts DC as it may have ripple. The new units are solid state. New technolgy makes them more efficent and less noisy.

As a battery charges, it increaes its internal resistance and draws less current. Older chargers cause the battery to gas as the extra energy is converted to breaking down the water in the battery to H2 (hydogen) and O2 (oxygen). In submarines, we used this process to make O2 for breathing during extended patrols submerged. H2 can explode so it's important to use a charger that will not overcharge the batteries. It is also important to make sure your battery compartment is well vented to the outside. The new solid state chargers are a great upgrade - worth the money. And they are easy to exchange but if you are not familar with basic electrical theory, you should get some assistance.

[mikeandbecky]

I've read several posts in the past about ditching the old Univolt converter, but instead of replacing it with another unit, some people have replaced them with one of the newer style 3-stage battery chargers( float, trickle, etc.). Why wouldn't this work as long as it maintains your batteries without boiling them?
Does anyone have any experience with this subject?

Thanks.

[mello mike]

Lot's of Airstreamers do exactly this. I did. The UNIVOLT systems in the older coaches are outdated. It's best to replace it with a newer, three-stage, unit.

[Buttercup]

The 3 stage units not only charge the battery without boiling them over but also maintain the battery by equalizing the batteries which help prevent sulfer buildup on the plates. They really pamper your batteries compared to a univolt. And they ARE quiet!

[Airstream25]

So when did Airstream switch from the old/bad to the new/OK?

Originally Posted by mello mike

Lot's of Airstreamers do exactly this. I did. The UNIVOLT systems in the older coaches are outdated. It's best to replace it with a newer, three-stage, unit.

[68 Overlander]

Originally Posted by Airstream25

So when did Airstream switch from the old/bad to the new/OK?

They haven't yet in my opinion. Airstream's DC power supply of choice is the Parallax. A fine converter but not desirable by most (including me) as a charger for your batteries. The 7455 deck mount and the 7355 power centers found in Airstreams will not drop back to less than 13.8 volts, ever. This will cause your lead acid batteries to use a lot more water in the warmer months and require extra discipline to check the electrolyte (water) level on a more regular basis. If you forget and dry up just one cell one time, the battery will lose it's ability to hold a charge and never be the same. Lead acid battery electrolyte begins to gas at 70 degrees at 13.8 volts. Parallax is fully aware of this and for that reason developed the 4455 with temperature compensation (TempAssure).
This technology measures the battery ambient temperature and adjusts the output voltage automatically to prevent the excessive gassing. In the summer months, it might drop as far back as 12.9 volts. That is really what it takes in 110+ temps found in the desert climates. Also, it's important to note that the temperature in the battery compartment can be significantly higher than the outside temperature.
Conversely, in the winter months, it will increase the voltage to as high as 14.4 volts to maintain a full charge on the batteries. I even wish it were a little higher but the theory is to prevent damage to the other DC control boards and that is a valid point since they don't know what brand X can withstand over time.
The 7300 and 7400 series converters are not available with temperature compensation (yet). In fact, if they were even 3-stage like the WFCO or the Inteli-Power, it would provide a much better charging profile than just 13.8 volts.
If I were purchasing a new Airstream today, that would be my chief complaint on the survey card (assuming they wanted to listen) is why in the world they don't use a multi-stage converter/charger? Actually to be fair, they do install the WFCO 8900 series on some of the Base Camps and I only know that because I looked at them this summer but none of the "regular" Airstreams I saw had anything except the 7300 series.
Some people believe there is circuitry in the processor that causes the unit to stop charging when the battery is full. This is just not true. The battery's internal resistance is the only factor that prevents current from entering the battery. The voltage is still "pushing" constantly and this is why modern 3-stage units drop the voltage back to 13.2 in the storage mode to ease the pressure in the event a cell weakens, thus preventing overcharging and/or water loss.