# Determining SwitchBlock Relay Drive Limits

Updated Apr 21, 2023

## Issue Details

How do I determine the maximum number of relays I can drive simultaneously on my NI SwitchBlock?

## Solution

The maximum number of relays you can energize at once on a SwitchBlock card or carrier is a function of the power available from the PXI chassis to drive relays, the cooling capabilities of the carrier based on the installed card models and the installed version of NI-DAQmx.  Use the following table to determine the maximum relay drive power per card and per carrier:

 Card Limit Carrier Limit DAQmx 9.2.x Any combination of cards 3.9W 3.9W DAQmx 9.3 and later 2810/2811 cards only 10W 10W DAQmx 9.3 and later At least one 2815/2816 3.9W 3.9W

For example, if you're using DAQmx 9.3 with a carrier that contains five 2810 cards, then neither the carrier nor any card can consume more than 10W to drive relays.  Adding a single 2816 limits the maximum carrier relay drive power to 3.9W, even if no relays are energized on the 2816.

If you attempt to exceed the card/carrier power limit, error -200671 will occur. To continue using your SwitchBlock device after this error occurs, you must reset the device.

Determining Relay Power Consumption
Each energized relay on a 2810 or 2811 card draws 50mW, while each relay on the 2815 and 2816 draws 63mW.

Use the following equation to determine the total power draw for your SwitchBlock Carrier:

`Pcarrier = (#2810/2811 Relays) * 50mW + (#2815/2816 Relays) * 63mW`

Where:
Pcarrier = Total carrier power draw, which must be less than the carrier limit listed above.
#2810/2811 Relays = Number of relays energized on all 2810/2811 cards in carrier
#2815/2816 Relays = Number of relays energized on all 2815/2816 cards in carrier

Use the following equations to determine the total power draw for a single card:
P2810 = (#Energized Relays) * 50mW
P2811 = (#Energized Relays) * 50mW
P2815 = (#Energized Relays) * 63mW
P2816 = (#Energized Relays) * 63mW

Where:
P28xx = Power consumed to energize relays on card.
#Energized Relays = Number of relays energized on card.

SwitchBlock Relay Drive Utility
The attached file SwitchBlock Interactive Power Budget (DAQmx 9.3) provides an interactive user interface to determine the total card and carrier limits based on the modules installed in your carrier.