Relays draw too much current from NI 9401 TTL output?

[ngio]

Hi,

I have a NI 9401 DAQ card and wish to control some electromagnetic solenoids through the use of relays.  I would like to simply connect them and go although I'm concerned the current draw from the module would be too high.  I have three 70G-OAC5 relays from GrayHill although the specifications do not tell whether they can be controlled by a TTL output, they simply state the Load Current Range is 0.03A to 3.5A rms.  Is this too high for my DAQ card?   If so, are there any solutions other than purchasing more relays?

Thanks in advance for any guidance,

Nick

[Jake_H]

Hi Nick,

From the 9401 specs (below) it looks like the sourcing output is 2 mA, which is outside of your range.

http://sine.ni.com/ds/app/doc/p/id/ds-86/lang/en

[ngio]

So would this mean I should use an external 5V power source?  perhaps wiring it up with a 5V transistor to link the grounds upon saturation?

If you have any other suggestions I'm willing to exploit them.  I tried finding a suitable relay that can be ran directly from the module but can't seem to locate any yet.  

Thanks,

Nick

[James_D]

Yes you should use an external power source. You will not be able to draw enough current otherwise to drive the relays. I'm afraid I don't know of any specific relays that can run off that small a current.

[jim-henry]

Hi,

I have a PCI-6305

• 24 lines (5 V/TTL) static I/O in 8-bit ports, 2.4 mA
• It used to work OK with Grayhill 70-OAC5 relays on an older Dell computer.

Now I put it in a new Dell Precision T3400 and

the relays don't work.  Sometimes the LED is dim

on the relay board.

The 70-OAC5 says it Max. Logic Supply Current @ Nominal Vcc is 16 mA

It seems that the new computer will not source the same current at the older one.

Any comments?

JIM

[ngio]

From what I know that seems about accurate...  the old computer sourced more current.  Although the relay current draw is way to high for that PCI board, I don't know if I would even use it.  If anything try to use the transistor setup I mentioned in one of the earlier posts to separate the relay from the PCI board while using an external power source.  

Nick