eHam.net - Amateur Radio (Ham Radio) Community

Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net



[Articles Home]  [Add Article]  

High Capacity Battery Pack for Site Use Portable Operations

from Scott Reaser, K6TAR on October 6, 2017
View comments about this article!

High Capacity Battery Pack for Site Use Portable Operations
Scott Reaser, K6TAR

Handheld battery packs are good for maybe 3 hours use with modest transmit duty cycle. Add a spare pack, and you are good for the first daylight hours of emergency response that might go on for days. So what do you do when you have run down your handheld battery plus a spare you might have?

The supplemental power pack I show here is built around a 7 or 8 amp-hour, 12 volt, sealed lead acid battery. Why this? My tradeoffs were: weight, cost, size and safety. The battery size is a common item used extensively in building emergency lighting and exit signage applications. These batteries are found on many eBay sites. I package the battery with a built-in charger, car accessory socket and PowerPole outputs. A carrying handle completes the package. Two completed units are shown in Figure 1 (Portable Battery Pack).



Portable Battery Pack

How do you make this? Ingredients are shown in Figure 2 (Pack Build Components). This is as originally built before PowerPoles and a carrying handle were added. This is a drill the holes and stick it together project except for maybe the charger.



Pack Build Components

This is a 12 volt wall wart that is repurposed to 13.5 volts. Used and overstock wall warts are stocked by the bin at places like All Electronics and swap meets. Wall wart cases can be popped apart at the part line with judicious pressure and persuasion with slip joint (water pump) pliers. The power inlet prongs part of the case is cutoff, and repurposed as AC in for the power pack box. See Figure 3 (Reclaimed Switching Power Supply). Another to-do is resetting the programmable, 3 terminal, zener reference diode to run the supply at 13.5 volts instead of 12. A control point is held at 2.5 volts. This is taken from a voltage divider from output voltage command to ground. By slightly bridging the ground side of the divider, with about 33K ohms, the output voltage is set upwards to again restore 2.5 volts to the reference point. Figure 4 (Voltage Divider) shows padding the existing surface mount part and the zener (U3). The power input part of a switching power supply floats on AC mains. Be careful what you touch in a running unit.



Reclaimed Switching Power Supply



Voltage Divider

PowerPoles were added as an output. Power output options for everybody! Paired parts mount in a case slot as shown in Figure 5 (PowerPole Mount). In retrospect the center captive pin shown is not needed. Convention for PowerPoles is “Red (plus) on the Right, Tongue on the Top”. Connector insets come in a barrel wire receptacle form (that best requires a pricey crimp tool) and U-shaped receptacles that can be closed with needle nose pliers and soldered.



PowerPole Mount

How the parts are stuffed in is shown in Figure 6 (Box Assembly). Pieces of packing box rigid foam wedge-in the battery. A layer of bubble wrap under the battery wedges it against a closed lid. A bit of Murphy proofing was almost found the hard way in that the barrel of the accessory socket could contact the battery hot terminal on disassembly. Not good. Fixes were to wrap the barrel in friction tape and disconnect both battery “faston” clips before moving parts.



Box Assembly

The handle is a generic drawer pull. Pure serendipity. The part fits nicely and lends a little extra to the finished item. Figure 7 (Completed Unit Power Up) shows first run.



Completed Unit Power Up

Member Comments:
Add A Comment
 
High Capacity Battery Pack for Site Use Portable Operations Reply
by KG4RUL on October 6, 2017 Mail this to a friend!
An unmodified "wall wart" is UL listed. A modified "wall wart" is a potential death trap.

A safer alternative is to package the battery and DC wiring as shown and maintain the battery with a commercial charger such as a BatteryTender Jr. http://products.batterytender.com/Chargers/Battery-Tender-Junior-12V-0-75A.html

It provides a 4-step charging program (Initialization, Bulk Charge, Absorption Mode, Float Mode) which is essential to maximize battery life and performance.

I have no connection with this firm but am a satisfied user of their products.
 
RE: High Capacity Battery Pack for Site Use Portable Operati Reply
by K6AER on October 6, 2017 Mail this to a friend!
I appreciate the authors desire to build a portable battery pack but why a gell cell? The battery has one of the lowest watts per cubic inch of any technology

My choice would to use a Lithium Ion battery pack. The capacity is about 3 times that of a gell cell and a fraction of the weight.
 
RE: High Capacity Battery Pack for Site Use Portable Operati Reply
by KG4RUL on October 6, 2017 Mail this to a friend!
A 12V, 12Ah LFP Battery costs $124.99 with a suitable charger costing $21.99 (total $146.98). A 12V, 12Ah can be bought for $25.95 with the charger coming in at $39.95 (total $65.90). The trade-off is cost vs weight.
 
RE: High Capacity Battery Pack for Site Use Portable Operati Reply
by K6AER on October 6, 2017 Mail this to a friend!
When you run out of electricity in critical communication cost is no longer a factor.
 
RE: High Capacity Battery Pack for Site Use Portable Operati Reply
by N4OI on October 7, 2017 Mail this to a friend!
K6AER replied: "[...] My choice would to use a Lithium Ion battery pack. The capacity is about 3 times that of a gell cell and a fraction of the weight. "

I agree. I used to carry SLAs but have moved to Lion... As an example, I use a Bolt Power D29 18 AH battery pack. In addition to 12V, it also provides for USB, phone and PC power, and will start your car and run a small inverter. It holds a charge for very long time on the shelf. Size and weight are minimal: 3.5 x 7.2 x 1.25 in and 1.3 lb.

Here is a current (no pun) example -- there are different capacities at other price points: https://www.amazon.com/Bolt-Power-D29-18000mAh-Motorcycle/dp/B01N3SEJIJ/ref=sr_1_3?ie=UTF8&qid=1507372370&sr=8-3&keywords=bolt+power+d28+jump+starter

Battery technology is improving at an incredible rate... but SLAs still make good door stops.

73 :>)


 
RE: High Capacity Battery Pack for Site Use Portable Operati Reply
by KG4RUL on October 7, 2017 Mail this to a friend!
I have four 12V, 12AH, SLA batteries that I got for free. They are pull-outs from alarm systems. Most firms arbitrarily replace the batteries after two years. Combine that with a $39.95 charger and I am in business.
 
RE: High Capacity Battery Pack for Site Use Portable Operati Reply
by N9AOP on October 7, 2017 Mail this to a friend!
If you are going to use this setup on a regular basis, lithium makes a lot of sense. If only once every couple of months then SLA is a better and cheaper fit.
I recently bought 6 8AH gels for $8 each from a solar supplier and they were new. Ace is the place had the same battery for $26. Lithium sells for a high price point because that is what folks are willing to pay.
Art
 
RE: High Capacity Battery Pack for Site Use Portable Operati Reply
by AC7CW on October 7, 2017 Mail this to a friend!
The SLA's are so inexpensive you can forget about being careful how you charge them. I used just a series resistor to limit worst case current from a cigarette lighter car outlet on them in the past.
 
High Capacity Battery Pack for Site Use Portable Operations Reply
by K6CRC on October 7, 2017 Mail this to a friend!
Good ideas here! Ham ingenuity in action....

Another option is to look for Belken Power supplies used as backup for old AT&T UVerse routers.
One example is "BELKIN RESIDENTIAL BATTERY BACKUP UPS UNIT REV B Model BU3DC001-12V. " on eBay. Prices from $10 up, most without battery.
May be bigger than the home brew option.
Also, as you said, the gelcells can be found cheap. Check Alarm system companies and for bigger units, companies that service electric wheelchairs.


 
RE: High Capacity Battery Pack for Site Use Portable Operati Reply
by N9AVY on October 8, 2017 Mail this to a friend!
I wouldn't trust the quality of batteries bought on Ebay. You take your chances. I've brought batteries to local club meetings (free pull outs from alarm systems) and some have had less than 7 AH rating .. some were 2 or less. Have a meter that checks batteries and will give voltage and AH readings. If you have a 12 v./ 7 AH battery and it reads 12 volts or less, it's probably bad. A fresh battery should read around 13.6 volts. Buy new.
 
High Capacity Battery Pack for Site Use Portable Operations Reply
by VE3KKQ on October 9, 2017 Mail this to a friend!
This system makes sense for the ham who can balance a lack of finances with ingenuity. In an extended emergency situation, the addition of solar panels for daytime charging would be prudent as well.
 
High Capacity Battery Pack for Site Use Portable Operations Reply
by N6DMR on October 9, 2017 Mail this to a friend!
Old technology solution. I have 16V LiFePo 5 cell battery 10Ah packs which use a DROK control system to limit voltage to 14-15 volts. Major improvement over dry or wet cell 12V old style batteries.


 
Charging concerns Reply
by VE7JMR on October 10, 2017 Mail this to a friend!
I second the concerns about the proposed battery charging solution and would also endorse the Battery Tender solution: http://www.batterytender.com/
 
RE: Charging concerns Reply
by W6EM on October 12, 2017 Mail this to a friend!
I'm certainly no expert on LiO, but most of the packs, including Tesla's auto packs, use the 18650 individual cells, which are series-paralleled to make up packs. If the Bolt Power and other models do things differently, please speak up.

The problem with LiO and LiPO is unequal charging (and discharging) of individual cells, which can manifest itself in overcharging and a great deal of heat dissipation in a single cell......that can lead to a fire. Tesla and some good RC pack chargers use individual cell monitoring technology to prevent overcharging. I don't know how they accomplish equalization of charge, but better than just applying a charger to output terminals of a complex pack of series-parallel cells.

SLA is indeed old technology. And, not as efficient in AH per unit weight. But, it has a long history of predictable charge outcome, and safe means to equalize charge on individual cells if a "smart," multi-mode charger is used. No, not a plug-in modified wall-wart.

Thanks for the article. It showed that ingenuity is still alive in amateur circles. And, a variety of ways to accomplish longer operating times.

As for the comment about SLA terminal voltage. A fully charged 6-cell one, sitting on the shelf that has not just been disconnected from a charger should be about 12.5 to 12.6V. Good hunting.

73,

Lee


 
RE: Charging concerns Reply
by N3NUE on October 13, 2017 Mail this to a friend!
I had used the battery tender for a while for my SLA hunting lights. Then I came across the Battery Minder, which I found to be much more accommodating. These not only charge the SLA batteries and others, but once full charge is realized, it begins to put a pulse (Which you can see on a scope) into the batteries and desulfates the plates, bringing them back to near original condition.This got me a few more years out of my SLA's for my hunting lights before I started using the newer fancy lithium ion LED hunting lights. I still have numerous SLA's that I keep around for emergencies. As a disclaimer, I have no financial interest in the Battery Minder.
 
High Capacity Battery Pack for Site Use Portable Operations Reply
by N0ETR on October 17, 2017 Mail this to a friend!
If you run SLA batteries down to where they won't run a handheld you will ruin them if you do it very many times. It's like leaving your headlights on and running down your car battery. Do it about 3 or four times and you will be buying a new battery.
 
RE: High Capacity Battery Pack for Site Use Portable Operati Reply
by W6EM on October 22, 2017 Mail this to a friend!
Your concern about running down SLAs can be dealt with a simple undervoltage alarm or auto disconnect switch. Or, just a voltmeter.

However, if you undervoltage an LiO cell/battery (like I did) it becomes a doorstop. It won't even accept a charge. So, no forgiveness for even one serious discharge..... SLA forgives. LiO doesn't.

 
Email Subscription
You are not subscribed to discussions on this article.

Subscribe!
My Subscriptions
Subscriptions Help

Other How To Articles
Batteries That Bamboozle
Lost Mobile Mic, Fix
Key Cover
A Radial Plate for Cheapskates