HVAC Controller

[CBisson]

I am working on a RFQ for a customer. They have a HVAC control panel that needs to be replaced. They want to use a PLC to do the job. There are a couple of twists. Battery voltage is 37.5 VDC. All of the digital inputs and some of the digital outputs will also be 37.5 VDC. Does anyone know of a PLC that will work at this voltage? In addition they want a Portable Test Unit. (Laptop with HMI) This will be a service device. When the plug it in they want to be able to see the current version of PLC software. Controll all of the temprature setpoints. Controll all of the timers. See current status of I/O devices. Change status of I/O. Not be able to edit the core code in the PLC. And, when unplugged have the PLC revert back to Normal operation. Thanx Chip

[rlp122]

Good luck with that. IIRC 36 volts was a short lived standard back in the 60's. We had a hot backup for a lift system that used it at the zinc refinery I worked at back in the early 90's. Getting parts was a nightmare. You might want to look at a DC-DC converter and use some resistors on the inputs to drop the voltage to an acceptable level such as 24V.