zapped,
Thanks for the tip. So could go battery, rpp diode, tvs diode, fuse, load --- all in series on the +12V supply line?
This diode should do the trick yes? Enough forward current capacity to handle device requirements while minimizing foward voltage drop...
I don't know how the word Zener got in there....just a normal diode on the GND lines to prevent any sort of current flow in that direction. That alone should provide reverse polarity protection or any sort of induced current.
So definitely going to go 12V system, but want to provide all the extra protection I can. So would a TVS diode on the incoming PWR lines after the fuse make sense as well as a Zener diode on the GND lines? Is this a comprehensive way to protect my devices...
The input range of the NI DAQ is 11-30 VDC. The DAQ pulses the load cells at 10VDC, therefore I wanted to ensure proper operation throughout the range of charge hence the 24V system selection.
Warp,
Could you, in layman's terms, briefly explain what you are asserting when power is switched...
The system is extremely simple, only RF Modem, NI DAQ, 2 batteries. No item in the system has ever failed except the RF modem.
The OEM recommended that I connect ground of battery connection to the frame as their theory is somehow potential is being built up in the frame and finding its way...
Furthermore, wouldn't the easy answer here be diode protection on both wires? That would protect me from reverse polarity and back current yes? If there was enough current to blow zero ohm resistors wouldn't a diode get smoked too?
Okay, I followed up with the OEM to get more detail on their failure analysis. Apparently there is a pair of zero Ohm resistors that are part of the power circuitry that failed. OEM says the only way that could have happened is reverse polarity connection (possible but unlikely, but I would...
I guess my mechanicalness in me just won't let this go --- so when someone designs a PCB...they specify the trace for a given portion of a circuit, presumably the thickness and width of the trace, to be able to carry the design voltage and current. Someone like me comes along oversupplies...
Mike:
Each device is connected in parallel to a pair of 12V batteries in series, thus 24VDC nominal. The procedure is to switch off the power, now the devices see nothing, change the batteries and reswitch the power on. At no time is there ever just one battery connected to the system and each...
So the Zener would provide some protection, gauranteeing only a safe voltage is reaching the device --- sounds like a good idea.
I'd really like to uncover the true underlying cause to the overvoltage in the first place.
Yes, the batteries are removed from the system to charge. The charger I use is a Samlex SEC-1230A. It has DIP switches to change the charge profile for various types of batteries. In the case of of the Gel Cell its a 3 stage charge with 13.5V Float and 14.0V Boost. So I guess it would be...
Thanks for the reply. The batteries are deep cycle, so they are charged seperately, connected and discharged over a period of about 2.5 weeks then replaced with freshly charged batteries. So this is purely battery power which as I understand it should be quite stable under all conditions.
So...
Hey everyone, first of all --- great website, long time lurker, first time poster. Thanks to all who contribute.
I have a National Instruments data acquisition device and a 900Mhz serial modem being powered by two 12V gel batteries in series. The DAQ and RF modem are in a NEMA rated enclosure...
