Univolt 45 amp converter to a 30 amp converter

[scooterbug76]

Are we asking for problems if we change out our Univolt 45 amp converter to a 30 amp converter? By the way, we would be doing this on a 69 Overlander Land Yaucht.

[Globie64]

Why not just get a new 45amp converter rather than a 30?

[scooterbug76]

Well we have a 30 amp that was given to us for free.

[RickDavis]

I doubt it would make any difference, except posibly a little slower charge if hooked to a dead battery. The normal 12 volt load, lights furnace, pump etc won't approach 30 amps.
If I already had the unit I would use it

[Kevin245]

Free is good. 30 Amps should work. I would use it.

[scooterbug76]

The 30 amp is hooked up temporarily. It does have a little buzzing sound...is that normal?

[TG Twinkie]

Is it another Univolt? If so it will hum. Because it doesn't know the words.LOL
If not a Univolt. What is it?

[ddruker]

Some of them buzz. Not generally a problem. As to 45 Amp vs. 30 Amp - it's unlikely you will put more than a 30 Amp 12V load on your trailer - that's 360 watts - so the only impact you are likely to see is slower battery charging...

[Wazbro]

As others have said 30 amp should not be a problem, even if you draw more then 30 amp, if you have a battery it doesn't matter. It will only be a problem if you exceed the converters capacity enough to drain the battery.

A little secret most people exceed their converters capacity. After all on these converters the capacity is 0 amps when they are not getting 120V.

I went through 1 season with a 10 amp battery charger and since it hummed I hooked it to a timer so that it shutoff at night and came on in the morning since 10 amps was way more then I needed on average.

[ddruker]

Wazbro is right - that was stupid of me to imply that you can't also draw from your battery while your converter is turned on.

[TG Twinkie]

I don't think you draw from your battery while the converter is connected to shore power. The reason I say that is. All of the 12 volt devices will work without the battery if you are plugged into shore power.
I remove the battery when my trailer is stored. It is connected to shore power and all DC systems work just fine.

[Wazbro]

Originally Posted by TG Twinkie

I don't think you draw from your battery while the converter is connected to shore power. The reason I say that is. All of the 12 volt devices will work without the battery if you are plugged into shore power.
I remove the battery when my trailer is stored. It is connected to shore power and all DC systems work just fine.

I don't believe it's 100% true that you do or don't draw 12V from the battery when your plugged in. If you plugged in and have your battery connected (more so for older converters) the battery acts as a buffer to stabilize the voltage, slight draw from battery to absorb a surge when something first comes on till the converter increases output and if the load goes above the output of the converter for a sort time.

[ddruker]

Think of it this way -

That 30 amp converter will put out roughly 360 watts (30 amps * 12 volts) of power - for as long as it is plugged in to line voltage.

Your battery is connected in parallel to the converter. It can put out many more watts than 360 at any instant - but only until it is depleted.

The two of them work together to provide power to your 12V system. You can run your 12V devices on the converter alone if you disconnect the battery, or the battery alone if you disconnect your converter, or both if they are both connected. The inverter will also charge the battery while both are connected and the inverter is plugged into AC power.

For giggles, say you connected 500 watts worth of devices to your 12V system and turned them all on. Your converter could power the first 360 watts worth of load. You battery would provide additional power for the remaining 140 watts - and it would keep doing this until it was depleted. Once you turned off enough devices to reduce the load back to below 360 watts, your converter would have enough surplus capacity to start charging your battery again.

Make sense?

[TG Twinkie]

I don't think so. If the converter reaches it's max capacity or exceeds it. It will shut down on overload. Or fail all together.

[Globie64]

Aren't they fused to avoid overload? Thanks for the in depth explanations, trying to understand the Airstream electrical system, charging/12/120v, makes my head hurt.

[TG Twinkie]

If you have a Progressive Dynamics converter for example. There are fuses (2) which are there to protect the unit if it is connected with the wrong polarity. Not to protect it from an overload. The large fuses in your fuse panel are there for the protection of the wire between the converter and the fuse panel.
Back in the last century, there were battery chargers that were literally small welding machines. These devices would literally destroy themselves if shorted for an excessive period of time. With the advent of intelligent design of the modern charging equipment. These devices will protect themselves by limiting the output current. The less expensive devices just "crowbar" shut down the output until the overload is removed. Others simply limit the current that is available.
This is the reason I always recommend using a modern battery charger when troubleshooting the 12 volt DC systems on a trailer. Instead of using a battery. I don't recommend do this in any way. But if you were to connect a wire across the + and - terminals of a battery. The wire would turn red hot and melt instantaneously or worse yet, the battery may explode. You can do a lot of damage to the wiring in the trailer by using a battery that is not wired thru the correct protective device, either a fuse or 12 volt circuit breaker.
Probably more than you wanted or needed to know.