I will be using a Renogy 20 amp MPPT 12v solar charge controller to charge the battery and to power the radios at the same time. I was wondering if this Renogy charge controller gives out regulated DC output?
I looked at their webpage and the only 20 amp MPPT controller I could find looked like they intended for the load to be connected directly to the battery. The battery should regulate your voltage just fine.
My concern with this design is that there's no low voltage disconnect to protect the battery in this setup. Leaving a radio on and over discharging a gel cell will quickly destroy the battery. If you are using one of the fancy batteries, it may have a low voltage disconnect built in.
The systems I've worked with have the load connection as part of the solar controller, and that handles the battery protection side.
Is it safe to connect the radios directly to Renogy charger? I also have Astron BB-30M module but i think it requires a regulated DC input. Another question would be, is it safe to directly connect the Astron BB module to the Renogy charge controller?
No, like I said, the design appears that they want the load connected to the battery. You shouldn't need the battery backup module as that's part of the role of the controller.
My aim is to have solar power during the day and automatically switch the load to the battery during night or cloudy conditions. This is because the scanner will be on 24 hours.
I would appreciate your advice.
Yeah, I think your panel size is way too small. A solar panel rated at 25 watts is only going to give you the full 25 watts in full sun. You'll only get full sun for a short part of the day. That 25 watts from the panel will need to recharge the battery. At the same time, your scanner is going to be sucking some of that power. Probably a few watts at least, depending on the scanner. That means that the battery may never get fully charged and eventually the battery will not be able to keep up. Remember that you not only need to power the scanner, but have enough power available to fully recharge the battery. Battery needs to be sized to support the load all night long, plus support it when the solar panel is unable to generate enough to power the radio and recharge the battery. This design requires some careful calculations. I've been through this at work where someone tossed together a solar system at work to power a remote network access node. They panels were not big enough to power all the equipment during the day -and- fully recharge the battery. They couldn't understand why the system kept crashing every night. They kept adding more and more batteries, but they never had enough panel output to keep them charged.
Think of the battery as a gas tank, and the solar panel as the gas station.
Your gas tank might give you 400 miles range when full. But if the gas station never fills the tank up all the way, you won't be able to keep driving 400 miles. Eventually you burn up all the gas in the tank (battery) and if you don't fill it all the way (solar panel), it's just going to leave you stranded on the side of the road.
I've been doing the solar powered radio site thing at some of my remote work locations for about 10 years and it really takes some careful design. Before you purchase any hardware, you really need to reconsider your panel size and battery size.
