Fatal Flaws!

Another nasty realisation looks like it might be the death of the first version of the PRC344 battery warning module!

Yesterday it came to light that a further 100k resistor was required. Not a difficult thing to add in itself. But while shopping for the 4M7 resistors needed for the timing, and realising that they are rather expensive, a consideration of the alternative, that is going to a 10uF capacitor and dropping the resistor down to 470k, led to the discovery that the 1uF ceramic capacitors im using are only rated at 16V!

I really dont know how far I could safely push that rating! A quick test shows that the voltage on the capacitor peaks at about 16V for a 24V supply. But, a freshly charged battery could easily be up to near 28V! And there are also single use 33V Lithium batteries out there! A check at 28V showed the capacitor to have over 19V on it!

There are 10uF 35V SMD tantalum capacitors available at good prices, but these are considerably bigger than the 1uF 0603 ceramic! No chance of a retro-fit mod here!

So, although I have a fair bit of cash tied up in the parts stock for these v.1 modules, it is looking risky to sell them as capable of being reliable in a 24V Clansman system. One option might be to add a potential divider on the supply line to keep the voltages safe of course! I will test that out. The whole module takes only a couple of mA so it should be a safe method, if a little untidy.


But another issue is that a non 50/50 duty cycle is preferred, and to do that requires extra parts anyway. I will test this out on breadboard, but whether I then invest in a v.2 module for sale will have to depend on if there is likely to be enough demand. I am also however going to test out whether or not I can do away with the switching transistor.

So the v.1 warning module looks like it might be a bit of a hybrid SMT/through hole unit, with fixed 3sec on/3sec off warning. This would at least save the project!