PLC Supply Power Quality

[mark73165]

I have a customer who is insisting on using the battery charging system of a diesel engine (24vdc)to power his AB CompactLogix plc. There is a 6" PanelView Plus HMI also installed. The charger is a pulse type which cycles +-3volt or possibly higher at a high frequency. We are encouraging the customer to use a quality AC to DC supply or even a DC to DC converter.

Does anyone know if Allen Bradley has any technical bulletin to cover the required power quality.In their specifications they only list the range of operation voltages. I cannot find what the maximum a/c ripple is or voltage fluctuations in their literature.

Any info would help. Thanks Mark

 

[BryanG]

I use DC/DC converters on a lot of diesel engine battery supplied jobs, here is a typical 200 watt universal input (10.6V-32V input). If I know that they will be using 24V supply then I go with one of these that automatically drops out below 21.6 volts to avoid deep discharge of the battery. If you have any analogue inputs or outputs don't even think about using the battery voltage directly.

Bryan

 

[mark73165]

Bryan
This is our feelings also. We even had the charger manufacturer give a statement that the supplied power is not instrumentation quality. I seems that if the statement does not come from Allen Bradley the customer will insist on using the charging system to power the plc.

Thanks Mark

 

[BobB]

I use DC/DC switch modes on all PLCs with generators anyway. Protects the power supplies in the PLCs from lots of rubbish and high voltages. I use Meanwell from Taiwan without any problems at all. They are available all over the world as far as I know. I generally do not even use the charging system on the generator and disconnect and use a proper charger such as a Xantrex. US manufacture - owned by Schneider. Not cheap but good.
By the way, I never groiund the negative from the switchmode - lose isolation that way - let it float. Many will say NO NO!! Never had a problem.