Power Supplies for a Remote HSMM Node

Written 2014-02-03

Tags:Battery HSMM Ham Radio SLA 


Recently, I've been looking for power supply solutions that fit the following needs:

Together, this supply will drive an HSMM node with the following:

I want to set up this power supply in a remote urban location, so it needs to maintain itself as much as possible. I ask what members of the popular Kansas City Amateur Radio Larry's List, and here are some notes from the responses.

Smart Charger

One Larry's List member suggested the Duracomm SC-12. DuraComm is a local Kansas City company. I considered this, but I worry that a battery and variable load in parallel might confuse a charger into not properly floating the battery. On the good side, the SC-12 can run from -20 to 50 Centigrade. It also takes up nearly all of the reserved space.

Small UPSs, or a lighting backup

Another suggestion was to use a small UPS, like an APC BackUPS 500, and run the radio equipment directly from the 12v supply, or maybe less-efficiently use the radio equipment's wall-warts from the 120v output. This was actually my original plan, but the BackUPS 500 I had for the task was too long to fit. However, I will be reusing the battery. Also, the APC BackUPS 500 is only rated for 0 to 40 Centigrade.

AC->DC and DC battery switch

This solution uses two components - an AC to DC converter, followed by a DC driven battery maintainer.

AC->DC converter

For this stage, a switching supply is preferred, since this unit will be outdoor, and switching supplies can offer high efficiencies than linears.

DC battery switch

The DC battery switch serves to charge and maintain the SLA while power is present, and drive the load from the SLA once power has disappeared.

Special thanks

Thanks to the following folks for helping me out with this:

First design

For my first remote HSMM node, here's the shopping list for the power supply: Total load maxes out at 3 amps. Below 45C(115F), the supply can put out 5 amps. Worst case consumption(including spikes) follows:
Status Charger Draw Fan Draw Router Draw Amplifier Draw Total Draw Utilization
Charging and Transmitting 1.2 Amps .33 Amps 1 Amp 2 Amps 4.53 Amps 90%