I'm trying to design a 12V power system, need a little help.

[KJ4CMA]

Say you want to run 12 volt devices, including electric motors, totaling up to 40 amps. However - you want to interface this system with a battery, AND your power source is 110V AC. Typical duty would be several hours at a time.

The way I see it, there are two options.

1. Use a 50 amp battery charger. Main problem is that it's not designed for this type of use, and apparently most have a pulsed output. You may also run into duty cycle issues.
2. Use a 50 amp power supply. Obviously would handle the duty cycle, but it gets cloudy from here for me.
How would one interface the battery and PS so the following would happen:
1. Run the load (including startup current) continously
2. Charge the battery as long as the 110v was on (without overcharging)
3. Run from either/or without switching.

Essentially, I'm trying to create a 12V UPS, and I'm having some issues. The messed up thing is that every car on the road does exactly this, but the key factor here is the voltage regulation from the alternator. Am I overlooking something?

[KE3WD]

http://www.repeater-builder.com/astr...ron-index.html

[WB2WIK]

Say you want to run 12 volt devices, including electric motors, totaling up to 40 amps. However - you want to interface this system with a battery, AND your power source is 110V AC. Typical duty would be several hours at a time.

The way I see it, there are two options.

1. Use a 50 amp battery charger. Main problem is that it's not designed for this type of use, and apparently most have a pulsed output. You may also run into duty cycle issues.

Nah. Pulsed output is good for batteries. There needn't be any duty cycle issues. Telephone systems have been 100% battery powered since the beginning, but the chargers ("rectifiers") are all powered by AC mains. It works fine, and has been working fine for 100+ years.

2. Use a 50 amp power supply. Obviously would handle the duty cycle, but it gets cloudy from here for me.
How would one interface the battery and PS so the following would happen:
1. Run the load (including startup current) continously
2. Charge the battery as long as the 110v was on (without overcharging)
3. Run from either/or without switching.

That's exactly what UPS's do. Not rocket science, there are hundreds of products on the market like this.

Essentially, I'm trying to create a 12V UPS, and I'm having some issues. The messed up thing is that every car on the road does exactly this, but the key factor here is the voltage regulation from the alternator. Am I overlooking something?

A good UPS is cheaper than one you can build, almost always, since APC and others have economy of scale. I have two 3000W UPS's here which run everything. They're 19" rack mount products that weigh about 70 lbs each, but they're cheap, and made by APC. They do contain multiple lead acid batteries which have a finite life but should be good for 5-6 years or so. Every car on the road doesn't produce 120Vac. They produce DC power from an alternator and battery system. The alternator is a motor-driven generator with usually a 3-phase rectifier and regulator following it. No reason to emulate that at home, unless you always have a motor running.

[WA7PRC]

It's easier than you think. For several years, my rig has been running from three float-charged Group 27 wet cells. They reside next door the shack in my garage. The charger is a homebrew 25A linear regulated power supply, set to 13.8V which yields about 2A of current.

Connected directly to the battery is a 50A Maxi fuse for safety. I use my jumper cables made from 1/0 welding cable to bring power into the shack, where it splits to feed two operating positions via 25A ATC fuses & 10 AWG twisted pair. When I lose commercial power, the rig continues to function. Preparation for FD (Class E) involves this L-O-N-G list:

• Turn float charger off.

[KF5LJW]

It is real easy, and I am a telecom engineer.

You need a good solid 50 to 60 amp 12 volt DC power supply like an Astron RS50A, and a good 12 volt AGM True Deep Cycle battery. No where is how to make it sing. Do not use marine, golf cart, or starting batteries. Stick with a true deep cycle battery.

The Power Supply must have a means of adjusting the output voltage from at least 13 to 14 volts. The reason is because 12 volt batteries float charge voltage varies depending on battery type from 13.2 to 13.8 volts. All the Astron Supplies can be adjusted. Just some of them will require you to open it up and adjust a trim pot.

Due to the large current you are wanting you really need to use an AGM Deep Cycle battery with a minimum 200 AH rating. There are two reasons for this. One is is 50 amps will be available for charge current, and AGM batteries can be charged at a C/4 rate and some as much as a C/1. C/4 on a 200 AH battery = 200 AH / 4 H = 50 amps. Second dis for the same reason except the other direction. AGM batteries have very low internal resistance and can deliver a C/4 discharge rate without significant voltage drop at the terminals. A real good 200 AH AGM battery would be a Concord PVX-2120T.

To make it work is pretty simple. You connect the battery to the output of the PS and let it run. You will be floating the battery. When an dif the power fails you will never notice it except th elights go out but your 12 volt equipment keeps on going. With a 50 amp continuous load you can run about 2 hours to you get to 50% DOD which you never want to go any lower.

[KA1MDA]

Don't forget the blocking diode to keep the battery from backfeeding the power supply during a power failre. Some power supplies don't take kindly to having voltage present at the output terminals with no AC present at thye input!

It is real easy, and I am a telecom engineer.

You need a good solid 50 to 60 amp 12 volt DC power supply like an Astron RS50A, and a good 12 volt AGM True Deep Cycle battery. No where is how to make it sing. Do not use marine, golf cart, or starting batteries. Stick with a true deep cycle battery.

The Power Supply must have a means of adjusting the output voltage from at least 13 to 14 volts. The reason is because 12 volt batteries float charge voltage varies depending on battery type from 13.2 to 13.8 volts. All the Astron Supplies can be adjusted. Just some of them will require you to open it up and adjust a trim pot.

Due to the large current you are wanting you really need to use an AGM Deep Cycle battery with a minimum 200 AH rating. There are two reasons for this. One is is 50 amps will be available for charge current, and AGM batteries can be charged at a C/4 rate and some as much as a C/1. C/4 on a 200 AH battery = 200 AH / 4 H = 50 amps. Second dis for the same reason except the other direction. AGM batteries have very low internal resistance and can deliver a C/4 discharge rate without significant voltage drop at the terminals. A real good 200 AH AGM battery would be a Concord PVX-2120T.

To make it work is pretty simple. You connect the battery to the output of the PS and let it run. You will be floating the battery. When an dif the power fails you will never notice it except th elights go out but your 12 volt equipment keeps on going. With a 50 amp continuous load you can run about 2 hours to you get to 50% DOD which you never want to go any lower.

[KF5LJW]

Don't forget the blocking diode to keep the battery from backfeeding the power supply during a power failure. Some power supplies don't take kindly to having voltage present at the output terminals with no AC present at the input!

That is really not necessary in most cases for a conventional Transformer, Bridge rectifier, series voltage regulator power supply as the output Transistor of the voltage regulator acts as a Blocking Diode. For a 50 to 100 amp diode would require its own heat sink and be kind of expensive. It wouldn't hurt anything except the wallet if it was not needed.

[WX7G]

A 14 volt regulated 50 amp power supply such as an Astron RS-70A might do the job. I have used an RS-20A connected to a battery to run the station. It doesn't care that the battery is connected to it when it is powered off.

The power supply voltage should be set such that a fully charged lead-acid battery draws a float charge equal to 1/500 of its amp-hour rating. If you have a 100 amp hour battery it should draw 0.2 amps when fully charged. This will be close to 14 volts.

[K7JEM]

In the simplest configuration, all you really need is a regulated PS that can also be a charger, and a battery capable of doing what you need it to do. A battery can be left floating on the power supply, pretty much indefinitely, if the voltage is correct. For most applications that voltage will be around 13.6v, +- 3 or 4 tenths of a volt.

The best PS to use for this purpose is an Iota supply, which are designed to be used in RVs as a charger/supply for the 12v battery used to power everything in the RV. They are available new for around $200, or can be picked up from e-bay and other places. They are available from 30 to 75 amps, with 45 and 55 amp units being fairly common.



The legacy Astron supplies can also be used. They require a simple modification to the regulator board, which is basically cut a trace and insert a 10K resistor. That prevents current from the battery from destroying the regulator chip when the AC power is off. We have used both Astron and Iota supplies at remote repeater sites to float charge batteries for many years (around 2 decades). This allows seamless transition to batteries when the power fails, since all that happens is the charger quits working. No relays or diodes or stuff. Just a battery and a power supply.

Joe

[W9GB]

Scott --

Solutions are readily available for the radio amateur, who does not desire DIY build or time/confusion.

West Mountain Radio -- Plug-N-Play for 40 Amps
http://www.westmountainradio.com/con...?page=dc-power

Super PWRgate PG-40S Manual
http://www.westmountainradio.com/pdf/PG40Smanual.pdf