How many keypads can I have on the DSC PC1616, DSC PC1832, and DSC PC1864?
The DSC PowerSeries line of control panels can have a maximum of 8 keypads. There are many other factors that can limit that number however.
The first is the 700mA current limit for the keypad and auxiliary power. Having too many hardwired keypads, especially PTK5507W touchscreen keypads, can quickly eat up the available amperage. And in fact, no matter what kind of keypad you use, you cannot reach 8 keypads and stay under the 700mA limit. Of course there are ways to add additional power to the system so that you can add more devices to the auxiliary power and keybus. Not just keypads, but things like modules, smoke detectors, motion detectors, and so on. You would want to add additional power supply modules such as the PC5204 to get around this limitation.
Another factor that can come up in rare instances is keybus wire length. There are a couple of things that go into this. The first is total keybus wire length. This is the length of wire added up across all devices. This length can't exceed 3000 feet of wire. The next limitation is the length of wire in a single run to a single device on the keybus. This length can't exceed 1000 feet of wire. For the majority of residential applications this will never come up. Things would need to be wired very inefficiently for this to become a concern usually. However, in some large buildings or if trying to reach a nearby outbuilding or something like that it can become a very important factor to look at. Remember this affects keypads, but also any other modules that are on your keybus.
The final factor that you will need to consider is wireless keypads. To even add any wireless keypads, you will need to have a TR5164 transceiver module. This will allow you to have up to 4 wireless keypads. You are still limited to 8 total keypads, hardwired and wireless combined.