Power Supplies for a Remote HSMM Node

Introduction

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

• Relatively small(small as or smaller than a lunchbox)
• Accept 120v input
• Charge and maintain a 12v Sealed-Lead-Acid(SLA) battery
• Drive a variable-load of .5 to 3 amperes while charging the battery
• Not goof up while sitting in the sun in Kansas summer temperatures
• Leak little power from the 12v side when 120v supply is disconnected

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

• Linksys WRT54G wireless router, 8 Watts consumption, 1 Amp max
• EDUP AB-003 8 Watt amplifier output, 2 Amp max
• Ventilation Fan, 4 Watt, .33 Amps

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.

• Pyramid PS12KX-13-8 - $57.83, 12 Amp - more current than needed, but also take up nearly all the space reserved for the power section of the installation.
• MeanWell PSC-100A-C - $38.63, 86% efficient, 7 Amps at -20-50 Centigrade, 3.5 Amps at 70 Centigrade. Link to datasheet.
• MeanWell S-60-12 - $22.30, 73% efficient, 5 Amps at -10-45 Centigrade, 3 Amps at 60 Centigrade. Link to datasheet.

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.

• West Mountain Radio PG40SCR - $156.95, 40 Amps out, charge rates selectable from 1,4,7,10 Amps - Physically a bit on the large side, this device is overkill for my purposes.
• KI0BK Low Loss PWRgate - $49.00, 25 Amps out, charge rate of 3 Amps - Made by KI0BK, all things being equal this is the best amperage/$ of the bunch, but still more than I need. The PWRgate also has a anderson power pole connectors and a nice insulated case - since my enclosure is conductive, the insulated case would be nice.
• Mini-box PicoUPS-100 - $29.95, 10 Amps out, charge rate of 1.2 Amps - This is the cheapest option, although picoUPS makes a 12 Amp version as well.

Special thanks

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

• KI0BK, Jim
• W0NQX, Bob
• K0EQH, Rod
• W0AIB, Larry
• W0JRT, Jerome
• W5GZT, Rod

First design

For my first remote HSMM node, here's the shopping list for the power supply:

• S-60-12 120v->13.8v Power Supply
• PicoUPS-100 controller
• 7Amp-hour SLA

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%