> For the complete documentation index, see [llms.txt](https://help.security.gallagher.com/smb/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.security.gallagher.com/smb/installing-gallagher-smb/voltage.md).

# Voltage

Gallagher units require **well-regulated power** with good output filtering. 

When selecting the capacity of a power supply it is important to allow for the “**worst case scenario**”. The correct supply will be able to cope with all devices operating simultaneously, charge batteries and allow for possible system design variants. The worst case for supply interruption would be during an emergency when most relays are operational, electric door strikes are operating, lift controllers are used etc. the main AC has been interrupted, back-up batteries have been used, and then main AC supply is restored. 

**The selected power supply must be specified to maintain a regulated voltage of 13.6VDC (±15%).** Calculate that current based on the parameters of the system and allow some for unforeseen conditions. 

Gallagher units require +13.6VDC (±15%) = 11.56VDC to 15.64VDC. 

When daisy-chaining units from the Controller, be careful to check, and stay within, acceptable voltage levels measured at each unit. Voltage start from the Controller at 13.6VDC and as it travels down cable an amount of voltage is lost through each board. There is a slight voltage drop as it passes through each fuse. 

Voltage at each unit should be +13.6VDC (±15%). 

Voltage at each unit should be measured “**under-load**”. Each unit has a different current requirement so measure the voltage at each unit when the unit is operational i.e. a relay board with 20 operational outputs will require extra current and may drop the voltage on the supply cable. 

If the measured voltage at the unit is low, increase the cable size, which will decrease the effective cable resistance, increase the current carrying capacity and effectively maintain a higher voltage at the controller. One way to optimize the voltage to each unit is to run separate power feeds from the same power supply (assuming the power supply has sufficient current capacity). 

Please consider power supply integrity (protection) when installing power. As an example; depending on the lock type used a fire drop relay may be installed in the control cabinet. If two power supplies are used, one for Gallagher units and an independent one for external devices, if the lock fails or pulls down a power supply, the electronics will keep operating and monitoring


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