Rechargeable batteries in good condition can, of course, deliver high currents for short periods of time and this may just be enough to start a fire.
Agreed - but they can still give a fair amount of current whist deteriorating, BEFORE they have died completely
(That's an entirely preventable problem as well, of course. A PCB mounted fuse in series with the batteries inside the sounder would have avoided that scenario.)
I see where you are coming from, but a fuse would only have prevented any current draw of the rest of the circuit, if the batteries themselves have failed internally and started to heat up rapidly, then no amount of fuses or protection circuits is going to prevent this. A fuse will only protect anything connected to it.
Those sounders I've post-mortemed have had completely dead batteries but were starting to draw current through the 12v permanent supply due to leakage near the transistor that drives the sounder.
Agreed, but there are two issues here. The first is the dead batteries that you have seen. Once the acid has leaked out and the batteries are indeed completely dead, the risk of combustion has usually passed. This sounder is no longer failing, it has failed. The second issue is indeed the corrosion that is normally found around said transistor. If you measure the current draw and take an average over many failed sounders, you will notice that the draw is usually less than 750mA. The supply to the siren from the car battery is only intended to recharge and keep topped up the internal siren battery voltages, but when it fails, its enough to give enough of a battery drain to flatten the main car battery overnight, but certainly not enough to cause any combustion. This battery drain is a usefull sign that the sounder is faulty - if its only just started to drain the car battery, then change the internal batteries before its corroded to badly to salvage the siren.
In any case, a stand alone sounder fire won't be enough to burn through the bulkhead and trash the interior of the car. That is surely down to inadequately protected wiring in the vehicle?
Siren gets hot when failed - nothing to do with wiring. Hold a lit match to the soundproofing of the car and prove me wrong !! The automotive industry does NOT have any fire regulations when it comes to soundproofing or vehicle interiors - plastic wiring sheaths pass through bulkheads and can often be a good route through for any heat - fire will burn - simple as that.
Hence my recommendation of an inline fuse to prevent a dying / burning power sounder from overloading the wires that supply it.
The inline fuse offers no protection - if it does overload teh car battery, it is only a small amount that will cause battery drain as mentioned earlier
I really think these devices and their installation has been based on the flawed assumption that omitting safety devices provides greater security.
Not sure what you mean by this? The sirens and sounders work fine - BUT !!! Do require some preventative maintenance once in a while in changing the batteries. No battery lasts forever, especially rechargeable ones, and like any other, if neglected, WILL cause problems.
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Topic: Fusing the powersounder (Read 2384 times)