13.5V adapter across car battery

Here is what I wish to do.
Solar panel (17V /1A max) --> 45 Ah lead acid battery <-- 13.5V /3A max adapter
In theory, solar panel will float charge the battery and when mains is on adapter will maintain the float voltage. Load is around 2 Amp and I don't intend to use it for more than 1 hour at most. Is this a safe setup?
Thanks in advance.

To make that work, you have to put a diode in series with each source of recharge. That will keep them from fighting each other.

Someone else will be along in a little while to tell you why you don't need a diode for the solar panel.

What sort of battery is it? Flooded or sealed gel cell?

The battery will overcharge if left connected to 17V@1A or too long, if it's a gel cell.

13.5V from the adaptor isn't enough to float charge the battery.

Forgot to mention solar panel is connected with charge controller as well. And battery is good old lead acid wet type. When it is sunny, the 20 Watt solar charger will keep on charging the battery. If the battery is fully charged, its voltage is 13.8 V. At that time the AC adapter which provides 13.5 V hooked in parallel should not cause problem (me thinks).

And when I am using the computer (that needs 12V, 2A but can safely work until voltage goes up to 14V) it will get the power from AC adapter (if mains is ON) via battery as a bank. When the power goes out, computer will get at the most 13V (which slowly drops depending on how long I use). I found that after 1 hour usage, the battery voltage drops down to 12.6 V.

13.5 V adapter is meant only as a way to not let the battery voltage drop below 13.5 V when mains is ON. That way solar charger wouldn't take too long to replenish battery charge.

Regarding diode, doesn't solar panel already have one built-in? And what if I use lower capacity panel (let's say 5 W) without charge controller?

Thanks.

Specifications from one manufacturer calls for a float voltage of 2.25 volts per cell. Since a 12 volt car battery has 6 cells, the float voltage should be 13.5 volts. That voltage can be maintained indefinitely without risk of damage to the battery.

Yes, you can use a smaller solar panel as long as the output voltage remains between 10.5 volts and 13.5 volts. 1.75 volts per cell (10.5v) is the recommended minimum discharge point. Anything lower and you risk damaging the battery permanently. Anything below 13.5v won’t fully charge the battery. This finally takes me to the answer about the 5w panel. If the load is less than 5 watts, it will work. The charge rate will be the difference between the panel output and the power used by the load (assuming the mains charging system is off line at the time).

Thanks for the replies. Only thing I was concerned was connecting 13.5V adapter to battery may be risky. I guess it is not. If the battery voltage is less than 13.5V, the adapter will pump current to raise the voltage just up-to 13.5V. And solar panel will float charge the battery. But what if the battery voltage is more than 13.5V during sunlight and mains ON? Will the imbalance of voltage between battery and adapter cause problem?

By the way adapter is SMPS/laptop type and not the regular transformer type. Thanks folks.

A lead acid battery won’t put out a higher voltage unless you add cells. The charger, however, could. It is at that point that battery temperature and out gassing becomes a concern. I suggest you get the specification sheet for the specific battery you intend to use and make sure your set up stays within that battery’s operating range.