superdave
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Federal Signal DCFCTBD Mechanical siren battery charging circuit

Fri Jul 23, 2021 8:06 pm

Hello! First time poster here. I have a question regarding the battery charging circuit. Mechanical siren with T/R, and battery backup (4 12vdc = 48vdc) The sirens in question mainly have the newest single point charger, but I believe the issue would follow to the older style 4 12 volt chargers. Per what is in the field and what is in the manual, the charger wire comes out of the charger to a terminal strip. From the terminal strip it lands on the 48vdc backup battery cable on the T/R contactor. It ALSO lands on the control boards "48volt supply and sense" input. So, after some experimenting I have found that you could have 1 or 4 batteries bad, up to and including 1 or more exploded, and STILL be getting 48-52 charger volts to the control board, which in turn would never trigger the "battery fail" back to the Commander software at the base station. (we are using the commander software on a computer to interact with our sirens.). Federal signal says to program the 3rd T/R relay to force the system to batteries for a monthly test, which will exercise the batteries, HOWEVER it will not allow the "battery fail" sensor to detect the batteries dropping below the trigger voltage because it is ALWAYS seeing the 48-52 volts from the charger. As far as I can tell the only way you could do a test and actually see if the batteries dropped below the trigger voltage would be to turn the AC power off to the actual battery charger itself during the test. Has anyone else seen this, or know something I am missing here.

Thanks

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Re: Federal Signal DCFCTBD Mechanical siren battery charging circuit

Sun Jul 25, 2021 4:21 am

With your set up you should have three large contactors in your DCFCTBD one for the rotator, one for the chopper to run on battery, and one for the chopper to run on the transformer rectifier. The battery contactor and T/R contractor should have a buss bar going between posts on the terminals that connect the contactors together that goes to the siren head fuse. It is kind of backwards the way that charger works. After a run on DC, the charger will trickle charge the batteries at 2 amps until they get to 40V after that it will bulk charge the batteries at 4 amps at 60V, once it gets close to 54V then it switches to float charge. Unfortunately aslong as the AC is on, the charger is going to run as you said, but when the siren runs, the charger is going to cut out to prevent the siren motor from trying to pull power from there. Low battery power is an unsolicited status update that should be transmitted to the Commander base station. Normally when the AC is on your siren is going to run off the T/R as you probably know once the AC fails it will switch to the batteries and run off them. With Commander, you can trigger the system to run a DC only test by sending the AC to disable signal out to the sites. During this test, it should cut the charger off while running off the batteries. If at any point during the test that the batteries drop below 43.5V (+-3%) for 20 seconds during the test it should trigger the low 48v battery USTAT. Seeing that if you did have a battery explode and yet you were still getting 43.5 you may want to take a look at your charger to make sure that there are no issues with it. If a battery was lost you should in theory be below the threshold of 40v of it doing a bulk charge at 60V which could cause the voltage to go back to the FC and trigger an OK battery status. Normally around here most of our low battery USTATS occur during DC testing or in the winter when it gets too cold for the batteries to maintain a decent charge. Also, check to make sure that the 48V coming from the T/R is also not being imputed to the 48V sense on the FC.
Let me know if you have any questions or if I completely missed something.
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