Question About Battery Bank Backup

[azprospector]

In a gid down situation where you will be running your radios off a 12V deep cycle battery bank, is it better to connect your radios directly to the battery bank or run their power supply through an inverter. In other words, which would pull less power from your batteries?

 

[mmckenna]

If the radios will run directly off 12 volts DC, it's much more efficient to do that.

An inverter will take that 12 volts, step it up to 110 volts, chop it up into AC, send it to the power supply, which will convert it back to 12 volts DC and send it to your radio.
If you do that, you'll notice the inverter gets warm. That heat is wasted energy. You'll also notice the 12 volt power supply gets warm, again, wasted energy.
Each time you change the voltage, you are wasting energy out as heat. That heat conversion is just wasted energy. Avoid it if at all possible.

 

[azprospector]

That's what I was thinking, Thanks

 

[prcguy]

Run the radios direct from the battery if they are 12V radios. I like to isolate the battery during normal times by placing a 120V coil relay between the power supply and battery with the power supply side in line when the 120V relay is energized. During normal time the relay routes the power supply to the radios and a separate charger tops off the battery. When AC power fails the 120V relay switches the radios to the battery automatically.

You don't want the battery connected to the radios during normal times as any charger will get confused and can overcharge the battery or otherwise shorten its life.

 

[TXFitz]

Run the radios direct from the battery if they are 12V radios. I like to isolate the battery during normal times by placing a 120V coil relay between the power supply and battery with the power supply side in line when the 120V relay is energized. During normal time the relay routes the power supply to the radios and a separate charger tops off the battery. When AC power fails the 120V relay switches the radios to the battery automatically.

You don't want the battery connected to the radios during normal times as any charger will get confused and can overcharge the battery or otherwise shorten its life.

I have learned a great deal from al the experience on here. Thanks PRCGUY.

 

[azprospector]

Thanks for the information

 

[MUTNAV]

Run the radios direct from the battery if they are 12V radios. I like to isolate the battery during normal times by placing a 120V coil relay between the power supply and battery with the power supply side in line when the 120V relay is energized. During normal time the relay routes the power supply to the radios and a separate charger tops off the battery. When AC power fails the 120V relay switches the radios to the battery automatically.

You don't want the battery connected to the radios during normal times as any charger will get confused and can overcharge the battery or otherwise shorten its life.

Can you expand a little on the charger getting confused please?

Thanks
Joel

 

[prcguy]

I used to run several repeater sites and built battery backup for my repeaters which ran on 12VDC. I had various brands of 100AH deep cycle lead acid batteries and various brands of chargers always connected to the batteries. The battery and power supply were isolated by a relay that ran off 120 VAC, so when there was AC power the relay routed power supply 12VDC to the repeaters. When AC failed the relay switched over to the battery to power the repeaters and the battery charger goes off due to lack of AC power.

When AC power is back the relay switched the 12VDC power supply back in line and disconnects the battery and the battery charger starts charging again off AC power. This is also good for the charger as nothing is connected to the battery when charging which can confuse the charger and cause it to overcharge the battery.

The relay was a 2 pole double throw 20 or 30amp rated job with dual contacts wired in parallel for higher current handling. The relay was plug in with an octal base for easy replacement and the base was mounted to a 2RU rack panel. Total current for the repeaters was less than 10 amps and charge current was probably 10A max.

Is that enough info?

Can you expand a little on the charger getting confused please?

Thanks
Joel

 

[MUTNAV]

yup... Thanks

Joel

 

[mastr]

...You don't want the battery connected to the radios during normal times as any charger will get confused and can overcharge the battery or otherwise shorten its life.

FWIW, chargers are available that are specifically designed to allow continuous connection of equipment to the served battery without degradation. Telephone companies and professional radio systems have done exactly that for years. But you will not find them at the local auto parts/RV store, and they are priced accordingly.

 

[MUTNAV]

I was thinking more along the lines of a car charger that would automatically switch to a trickle charge mode after the bulk charge was done, I'm guessing it may be a matter of sizing the trickle charge current of the charger to the battery bank capacity of such a system (so the trickle charge current is right for the constant loss of a deep cycle lead acid battery).

Or maybe use a very large computer type un-interruptible power supply, apparently there are variations of ways to do the job, although this may fall into the realm of the professional systems as described previously.

Thanks
Joel

 

[mmckenna]

FWIW, chargers are available that are specifically designed to allow continuous connection of equipment to the served battery without degradation. Telephone companies and professional radio systems have done exactly that for years. But you will not find them at the local auto parts/RV store, and they are priced accordingly.

Quite expensive. There's more to it than what most hobbyists are willing to tolerate. Batteries can be float charged, but it has to be precise, it has to compensate for temperature variations, and it needs to be set to the specific battery specifications.

The charging system has to be very tightly controlled. As you said, not an RV store sort of product. If you like your batteries, low voltage disconnects are a good idea.

This is from one of my remote sites. It's -48vdc and only running about 36 amps of load.