Batboard

how many amp hours should the batteries be for the Quantar battery revert. Yes I know it's a 24vdc b/u and yes I have a 625w batt revert power supply, units are VHF 125W RFPA

As big as you want them to be. This is a sizing issue, and should be computed for each site (up to some maximum that the charger won't deal with effectively).

What's your duty cycle (measured, not a guess)?
Total station current draw in RX/TX?
How long do you want it to run?

For 10/90...
(.9 * RXcurrent) + (.1 * TXcurrent) * hours.

Adding to foregoing:

The draw power for a Quantar is a bit over 600W when key down and about 60-65W when not (doesn't matter whether squelched or not, as Rx draw is dominated by the exciter, which is always on).

When sizing your batteries as suggested above, remember that you cannot take more than 50% of the nominal capacity (in AH) out without permanently damaging the batteries. Better yet to size so that you are only using 1/4 of the nominal capacity.

For what it is worth, I back up Quantars a bit differently, using 12VDC batteries and a device called the Heart Interface (which handles switching, charging and inverting by itself; makes no use of the Quantar "revert" function and does not cut power back when on batteries). I have two 8G31DT East Penn gel cells, typically, which are worth about a nominal 200 AH. We have tested in a typical duty cycle for "normal" (versus "receiving calls") situation and found the batteries will carry the Quantar for more than six hours and remain within the 25% limitation. (Would have gone longer, but we ran out of time and patience with the test.)

Here are some calcs, though be aware that we can fool ourselves with an excess of precision. (The nominal capacity of a lead-acid battery, for instance, is affected by current draw: less if drawn at more than 5% of nominal capacity and more if drawn at significantly less.)

Based on 625W on Tx and 64W otherwise; and
based on 90-5-5 duty cycle; and
based on 12VDC,

Total amp-hours draw is about 4 per hour.

Should be half that at 24VDC.

Two other cautions:

A) the charger built into the Quantar revert board is not capable of a true float, i.e., zero charge into a fully charged battery. As a result, if the batteries sit for a couple of years without being drawn upon, they will be gassed into a premature death, which you won't realize until the lights go out and the radio powers down prematurely thereafter. If you go this route, the batteries should be load tested at least once per year.

B) the Quantar revert board includes a programmable "equalization" function. This should never be used. In part, the Quantar RSS/CPS allows one to program an "equalization" duration far longer than is safe with lead-acid batteries. Far worse, it allows and envisions unattended equalization. This is an easy way to blow up a battery and start a fire.

As tvsjr pointed out the first thing you need to know is the duty cycle. A simple tool is an electrically driven elapsed time hour meter (the type that doesn’t loose the count if the power goes off) connected to a relay run from the squelch of a receiver listening to the system you're measuring. If you measure say 5 hours use in 2 days then your duty cycle = 5/48 or 10% transmit or 10/90. In a busy city police dispatch channel it's possible to see duty cycles exceeding 50%. You really need to measure this. You can only get away with guessing if the system is very lightly used. Finally the user or customer needs to spec how long they want back up for.

Next you want to think about the battery technology choice. RKG is right than equalizing gel cell technology will kill them real quick but you need to equalize wet 'flooded' lead acid and most absorbed glass mat (AGM) types. Gel units are install and forget (until they need replacing before they die) while AGM need more care and attention but give better service.

I prefer AGM types for remote radio sites where the power really does go off for a day or two until the utility gets around to fixing the line and in case the diesel generator doesn't start. I use gel types for city installs where the power is only ever off for a few hours and it's easier to get in and replace them. YMMV. A typical remote site might have two 100W VHF/UHF Quantars and a 24V 1,150Ah AGM system.

Most people not in public safety will say that’s overkill but remember if the power is out, through say a storm, then this will be the time your system is hammered.

The flooded battery is the most common battery like your standard lead acid car battery. Gel batteries hold the acid in a gel like substance while AGM batteries have the acid suspended in a glass mat separator.

Wet and AGM types are commonly called valve regulated lead acid (VRLA) which means that there is a vent system to allow gas out if necessary. Gel types should never gas so they need no vent, although most have some sort of pressure burst disc for safety.

Gel type like a nice well regulated constant float voltage, usually around 13.8V or so at 20C or 68F. The float voltage needs to be temperature compensated.

Wet and most AGM type need equalizing, that is a higher than normal charge voltage for between 2 and 8 hours, every so often like 6 months to a year. How many volts, how long for, and how often? Well you need to get the data sheet for the actual batteries you intended to use. Everyone in the industry has an opinion, believe none of them and do exactly what the cell manufacturer specifies in the actual data sheet for what you buy.

Correct settings of the battery charger voltage limits are critical and should be recorded and reported by site contractors on each visit and at least once a year.

Hope this helps out your sale.