Yes please. I would very much like to know what is causing these to go short. I doubt its going on fire, a 10year old battery hardly holds enough energy to sound the sounder, never mind combust.
I guess maybe the battery is leaking something, which somehow causes something to go short which nukes the basically unfused supply going into it. I would love to know how, cause I can't see how it can happen. If they use a series regulator, they would have to short the base up to 12V to turn it full on, but corrosion will eat tracks, not short them.
I would love to find out what is really happening with these. OK, the appropriate fusing seems the best protection, but knowing what the fault is means you can cure it.
Ken
I am also sceptical that a (by that time pretty much dead) Ni-Cd can muster enough heat to start a fire. Apparently it has happened in storage, but I think the majority of Omega fires have involved at least a contribution from the supply to the sounder having shorted (perhaps promoted by a battery failure). The damage around the fusebox area bears witness to this, if nothing else.
The other theories I have:
The batteries are being charged at 15mA on the (admittedly slightly damaged) PCBs I've tested. This exceeds the maximum continuous charge rate for the batteries.
Having said that, one of the live data parameters visible by tech2 suggests that the unit has two charge rates so perhaps after the batteries become fully charged it drops to a lower charge rate.
One PCB that I've post-mortemed had leakage around the MOSFET that switches the signal to the primary of the transformer that drives the piezo siren. It had started to conduct but was caught before it got any worse.
If enough leakage had developed to turn on the MOSFET fully we have the 12v supply across a transformer with a quite low primary DC resistance. Enough to heat it up and catch fire? Maybe. :-/
I have only looked at the later style of sounder without potted PCBs. It seems that the ones that have actually caught fire were on older cars which would suggest they were the earlier design.
Kevin
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Topic: Dreaded powersounder! (Read 2690 times)