Weather Station - 12V Battery - Solar Panel : Help needed

Thread Starter


Joined May 9, 2016
I am trying to improve the setup of a remote weather station that I am responsible for.

It is a Onset U30 data logger. The factory supplies a small 4-volt (10Ahr) sealed battery that has trouble maintaining the unit during the winter. I want to upgrade the system to use a 12-V deep cycle marine battery.

The Onset technician says that their U30 needs 3.5 volts to operate, 4-5 volts optimally, and can tolerate up to 8 volts input. It sips power and can run quite a long time on just a battery.

I found a unit that looks like this in one of our labs.

It behaves strangely though. When I hook it up to a 12V supply on the solar terminals, the battery terminals show a few millivolts less, but theload terminals show no voltage. Stranger if I meter the negative battery terminal to the positive load terminal I get 12V, and if I meter the negative battery terminal and the negative load terminal I get 9V. If I meter the two load terminals I get 0.1V.

I also got something similar to one of these.

But the manufacturer says it needs _exactly 12V_ all the time to work. Would not discuss <12V or >12V with me.

So. I'm looking for another solution.

I want to supply between 4-6 DC Volts to the weather station.
I want to use a 12 V deep cycle
I want to charge the battery with the solar panel. The one I have I think is 12V... output varies between 10 and 14 or so I think.

A weather resistant would be desirable, but the electronics are contained in a weather-proof box.

A better made solar controller may be all I need, but given the one I found and that seeming to be such a prevalent model I don't know what to shop for.

I could consider getting a different battery, but we have lots of these marine batteries lying around unused... so it would be good to at least try to use one of these.


Joined Sep 9, 2010
If it can work in car, that 5V adapter will be fine off your battery. If you have doubts, there are many other options off e-bay. Just look for a DC-DC converter that meets you specs.

I'm not sure I understand what you need for your panel and charge controller. You want a panel with an open circuit (no load) voltage of at least about 18V and even 24V would be OK. You may not need anything but a blocking diode to prevent reverse current. But we need more details about your panel to be sure.


Joined Apr 24, 2011
Your Amazon seller is a stock clerk not an electrical technician. If he were he would have read the very first spec on that thing is the input voltage range of 8 to 23 volts.

NO power supply needs an *exact* voltage of anything. Everything has a tollerance.

However, you may be better served using a 6volt battery and ditching the buck converter, which while very efficient is not really going to "sip" power.

Back up, get a handle on your needs before you design a solution. How much does your station really "sip"? Is that continuous? How much sun do you get in the winter? Maybe the battery is just fine but you need a larget solar cell to charge it on a short sunny day?