adccommunitymod (AutomationDirect) asked a question.
Created Date: July 06,2007
Created By: mossjm
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I need to control a starter relay on a diesel pump (12VDC) from one of AD's relay modules, I am going back and forth between the F2-08TRS and the F2-08TR. I understand that the F2-08TRS costs more because all 8 are isolated, but it appears that the contact rating is 7A/pt whereas the F2-08TR can be up to 10A/pt (although that is the max for that common as well). My question is this: if I am going to only need just one big relay output which one will provide me with the most amperage for that contact. Is it possible/common to parallel relays to get a higher amperage? Thanks Also, I noticed that it is recommended to place a diode across the load for arc suppression to increase the life of the relay. Does anyone have a recommendation for a diode size?
Created Date: July 06,2007
Created by: mossjm
I just noticed on another topic that FACTSTech had a diode recommendation of P6KE47CA for 12/24VDC, sorry for the same question
Created Date: July 06,2007
Created by: Tech Guy
If that starter relay is pulling that much current, I'd definitely use an ice cube type relay to control it. Power the ice cube relay off of a lower amperage PLC card.
If it ever fails it will likely take out the PLC module. $5 ice cube relay or $100 PLC relay card, I'd choose to replace the ice cube even though it will take up slightly more room in the panel.
Created Date: July 06,2007
Created by: FACTSTech
moss, The first thing you need to do is findout what the inrush current is for the starter relay. This can be accomplished by adding a 1 ohm resistor in series with the starter relay. Using a scope observe the waveform across the 1 ohm resistor, then is simple ohms law calculation. If it has a very high inrush, I would suggest to use an interposing relay of proper rating plus. When the life of the relay comes, unplug from socket and continue on. You cannot parallel contacts to get more current, one relay contact is always going to close before the other. The P6KE is sort of a generic part number, folks like to add other letters for various catalogs. is your entire PLC system running from the same power source as the starter relay?
Created Date: July 06,2007
Created by: mossjm
Thanks for all the help guys!
Yes, my PLC system will be running off of the same 12V battery as the starter relay, would it be better if it wasn't?
Created Date: July 06,2007
Created by: Tech Guy
If this is an engine application, what will happen is when the engine starts the starter drag usually will drop the power enought that the PLC will reboot.
You probably need to think about isolating the PLC with a DC-DC convertor if this is the case. This will help to alleviate the voltage drop when the motor starts. Plus it gives an extra layer of filtering to noisy alternator voltage.
Created Date: July 06,2007
Created by: mossjm
I need to control a starter relay on a diesel pump (12VDC) from one of AD's relay modules, I am going back and forth between the F2-08TRS and the F2-08TR. I understand that the F2-08TRS costs more because all 8 are isolated, but it appears that the contact rating is 7A/pt whereas the F2-08TR can be up to 10A/pt (although that is the max for that common as well). My question is this: if I am going to only need just one big relay output which one will provide me with the most amperage for that contact. Is it possible/common to parallel relays to get a higher amperage?
Thanks
Also, I noticed that it is recommended to place a diode across the load for arc suppression to increase the life of the relay. Does anyone have a recommendation for a diode size?