Station battery power: switch vs direct charging?

[N5BCN]

I'm considering running my station from battery power using one of the two following scenarios:

1)  Connect station directly to battery which is continually being charged by a charger.
2)  Connect station to a switch such as West Mountain Radio's Super PWRgate.  With this option, the station will run from a power supply while house power is on and then switch to a battery when house power cuts out.  The battery is continually charged while house power is on.

My question: what are the pros/cons of each of these setups?

Option 1) seems much simpler to me, but there must be some benefit to Option 2) that I'm not aware of.


73
N5BCN, Brian

[AA4PB]

One downside of the direct charge option is that if power is off long enough that you fully drain the battery then when power comes back on it will take a while before the battery voltage reaches an acceptable operating level. With the switched option operation would return immediatly when power returns even if the battery voltage is low.

As a side issue, if you place a battery directly across a large capacity power supply then you many need to employ some type of charge current limiting to prevent possible battery damage if power comes back on after the battery has been discharged. With small systems the charge current limiter is often just a resistor.

[WX7G]

I operated with a charging battery for years. It works just fine with the battery constantly receiving a float charge of 14.2 volts.

[AA4PB]

Why did you choose 14.2V? I thought 12V lead-acid batteries float charged at 13.8V.

[WX7G]

You can adjust the float voltage to your particular battery by setting the voltage such that the float current is 1/500 the amp-hour rating of the battery.

[NA4IT]

Go to my website http://www.qsl.net/na4it/ and scroll down until you see the battery and charger. Links are above the picture that explain what charger I am using. Several hams in our area have this setup, and all our repeaters use this setup also.

[N5BCN]

NA4IT,

Interesting setup.  A few questions about your setup:

1) Is your station/rig connected directly to the battery or is it connected to the supply/charger?
2) What kind of box houses your battery?
3) Is the battery box vented to outside somehow?


73

N5BCN, Brian

[KB1NXE]

FWIW,

   I use the float via a PG40S Wattgate to a 35Ah AGM battery.  This system works very well and while operating, I am topping off the battery.  I use a Pyramid PS-36KX power supply and have it adjusted to 14.2 volts to meet the needs of the float charge.  If I lose power, there is no transition period as the Schockey Diodes just switch.  If you are in the middle of a transmission,  or copying a message, that can save time.

   However, I built this station to be able to serve the community if the need arises. That battery is only going to work long enough to get the generator online if the dodo hits the rotating mechanism.  Infact, last fall during a QSO party, I had forgotten to turn the power supply on.  The battery lasted over an hour (140 QSOs to be exact).  So, your needs may be different.

   To be 100% honest, I have two of these systems right now.  One feeds the main rig.  The other the backup rig, the VHF/UHF rig and all the accessories I have placed a priority on having available.  I float the main rig across the PS-125 I use for it.  I made up adapter cables to make all connections to the Wattgates.

   Only you can determine how you want it to work.  The above works for me.

Jim

[LA9XSA]

Supply -> Battery -> Radio
Advantages: If there is noise on the DC supply, the battery could "filter" it a bit better than with a diode gate. Less voltage drop from the battery to the radio. If your radio is particular about supply - say, switches off at 11.9 volts or something - it might be better to connect directly to the battery. If your radio accepts a wider range of voltages, this is not as much of an issue.
Disadvantages: If the battery fails, the radio fails. You can't "hot-swap" batteries as easily.

Using a diode gate:
Advantages: If the battery fails, the power supply can run the radio and you can swap the battery without switching off the radio.
Disadvantages: A voltage drop over the diode gate; this can be compensated for by increasing power supply voltage, but you can't compensate for when supplying from the battery.

What I have is a simple diode gate float charger, with a resistor as a current limiter. This only float-charges the battery. If the battery has been worn down, it takes a while to get topped off again. (This design is similar to the PG40 - note the lack of "S" at the end, it's an earlier version with float-only charging.)

I use the float via a PG40S Wattgate to a 35Ah AGM battery.

While the PWRgate PG40 is float-only, the Super PWRgate PG40S contains a staged battery charger; that means KB1NXE is not simply floating the battery. After a power failure, when the battery is low, the PG40S will take the battery through the same bulk and absorption phases as a regular battery charger, before transitioning to the float charge once the battery has been fully charged. That means the PG40S charges the battery up faster than a PG40. That could be useful in a situation with intermittent power, say an emergency where you run your generator for a few minutes at a time, or where gird power comes and goes.

The 14.2 volt setting at the power supply is to compensate for the voltage drop over the float diode in the PG40S, however the manufacturer actually recommends setting the supply to 14.1 volts for gel and 14.5 volts for AGM as well as installing a jumper inside the PG40S. By doing this, the float charge will still be 13.5 volts, but the peak charging voltage will be raised to 14.2 volts since AGM batteries accept a bit more voltage in bulk and absorption than gel cells do.

[NA4IT]

N5BCN,

1) Is your station/rig connected directly to the battery or is it connected to the supply/charger?
The battery and charger are connected to a set of buss bars that all the equipment connects to. Each piece of equipment has it's own fuse.

2) What kind of box houses your battery?
No box needed, the battery is a sealed battery. I do have a wood scrap under it to keep it from scratching the floor. For more info on the battery, see http://www.battery-usa.com/Catalog/12_383.pdf

3) Is the battery box vented to outside somehow?
See above.