sizing a dc/dc converter for T100MD1616

[Mark York]

In my earlier post I stated that the incoming battery 12VDC power to our machine was experiencing voltage drop when a large DC motor was started. After more testing we have found the the voltage drops to 8.1 volts. This voltage drop resets the plc. To solve the problem I am trying to source a wide range dc/dc converter with regulated 12VDC output. The only thing I can find in the documentation is to supply a 2 amp power supply. Can anyone advise what the power requirements are if I were to supply regulated power to only the PLC incoming power, the inputs, and the analog supply (for one analog input) on the T100MD16-16+? I have to believe that the PLC power consumption is only a few watts and the inputs woulds be 5-7mA each. The outputs will be fed from the incoming unregulated supply.
Anyone have any idea what size the dc/dc converter should be?
Regards
Mark

[evanh]

I had a big reply but the website decided to erase it.  

Short answer is:  Don't undersize your power supply and, as per the other thread, the DC-DC converter also has to handle the large switching spikes.


Evan

[Mark York]

evanh
Could you send me your reply off the forum? My email address is m-syork@comcast.net. I really don't want to supply a regulated power supply for the entire machine just the plc and analog power supply. Typically dc/dc converters have 1500VDC isolation or more so I don't think that spikes are an issue. I would also filter the front end of the dc/dc for additional protection. The turn on/off voltage range on the inputs are wide enough to not be an issue. We have tested the machine with 2 12 volt batteries. One feeds the plc and analog input the other feeds the rest of the machine. The plc outputs are not directly connected to the loads but are connnected via interposing relays so they only see the relay coils as loads and are connected to the battery that feeds the rest of the system (not the plc/analog battery).  During testing we have had over 1000 operations without a problem. It's just not practical to tell the customer he has to supply 2 batteries, that is why we want to provide a small regulated converter.

[support]

The PLC CPU alone consumes about 0.15A or less.  Each input and output LED consumes about 5mA. The load current is not included since the load is supplied from a separate power supply.

Alternatively, use an external relay (electromechanical or sollid state) to switch your high current load so as not to overload the PLC power and that will eliminate the problem of PLC being reset by voltage spikes.

[evanh]

Mark:  You misunderstand me, I didn't post the whole thing again because I no longer have it.  I typed it online and it got erased when I clicked "Post".