Managing Your Batteries: Page 3 of 3

Intermediate

Inside this Article

Battery Bank
Battery Bank
A Hydrometer
A hydrometer with temperature correction is the most accurate way to determine battery cell state of charge.
Samlex Meter
A simple “gas gauge”-style meter, which converts voltage to reflect a “full-to-empty” reading.
A Shunt
A shunt is a precision resistor that provides accurate voltage drop measurements by which amperage is calculated.
Shunt Wiring Schematic
Always wire your meter’s shunt into the negative side of your battery bank.
OutBack Mate 3
The OutBack Mate 3, a system-integrated monitor, keeps tabs on the whole system, including battery SOC from the FlEXnetDC (next image).
Outback FlEXnetDC Meter
This system-integrated meter feeds the battery SOC data to the network monitor
PentaMetric Meter
A multifeatured stand-alone meter.
Battery Bank
A Hydrometer
Samlex Meter
A Shunt
Shunt Wiring Schematic
OutBack Mate 3
Outback FlEXnetDC Meter
PentaMetric Meter

Display Choices

Stand-alone meters can be mounted some distance from the shunt in a convenient and easily visible place for viewing the display. Integrated and internal meters may have a simple display at the unit, with the rest of the details available through the remote monitor display.

Even the simplest and least expensive of modern amp-hour meters have serial data output, and the more advanced models make it easy for you to connect the system to your PC. You’ll need a PC interface and software from the meter manufacturer. Note that to collect detailed historical data, a computer that’s running all the time is required. Some enthusiasts use an old laptop that’s been retired from daily use just for these logging operations. You can watch your system performance live with a “dashboard” application, analyze your data with a spreadsheet, or even send data to your website or smartphone.

Some system monitors are designed to communicate directly with your home computer network, either through a LAN cable or by wireless. For this data communication, your Internet service and/or routers must be powered on, but your PC doesn’t have to be running. Unless you are a computer programmer, you’ll also need to subscribe to an Internet system monitoring service (which in some cases is free) to establish a secure site to log into your meter, and a way to build monitoring “widgets” to insert into your website or blog.

Your Internet service must include a static IP address to use any of these web-monitoring features, and that may cost extra. With some satellite Internet services, putting a system monitor online may not be allowed—be sure to check with your Internet provider first.

Installation & Setup

Amp-hour meters are easy to install, but be sure to follow the manufacturer's instructions. Before you start, shut down your entire power system using the main DC disconnect. Turn off the PV array breaker and disconnect the battery output cabling in the battery box. You'll need to find a good location for the shunt, keeping in mind that all energy moving into or out of the battery bank must pass through it on the main negative wire. A good location is inside the inverter power panel; many panels have spaces reserved near the main negative buss just for this purpose. You'll need a short cable with lugs on both ends that's the same wire gauge as your battery output cable (since this is part of the negative-side circuit pathway to/from the battery bank).

Next, mount the display panel in a convenient and visible location, and run the cable from the shunt to it. Most displays mount in standard electrical boxes. The cable used is a special multiwire, shielded, twisted-pair bundle that should be purchased directly from the meter manufacturer to make sure it is the right type. If you are installing a system-integrated meter, things are even easier—the special cable from shunt to monitor box will be short, and then you simply plug the monitor into the system network hub with a LAN cable or wireless-to-LAN interface.

After meter installation and powering up your system, your new meter will need to be programmed with your battery bank’s amp-hour capacity, the system voltage, and the voltage level at which your charge controller considers the batteries to be full. Then, you must charge the battery bank to full capacity, usually with a generator, until that “full” voltage level is reached. At that point, your meter takes over, and you are in the monitoring business!

A simple amp-hour meter and shunt costs about $200—a small price to pay considering the total cost of an entire renewable energy system and the relatively fragile nature of its battery bank. If you monitor your battery bank regularly and react accordingly, you can extend its life by many years before replacement is needed.

Access

Author and educator Dan Fink has lived 11 miles off the grid in the northern Colorado mountains since 1991. He teaches classes about off-grid systems and small wind power, and is the executive director of Buckville Energy Consulting, a NABCEP/IREC/ISPQ-accredited continuing education provider. Dan is the coauthor of Homebrew Wind Power.

Battery Monitors: 

Bogart Engineering • www.bogartengineering.com • Amp-hour meters  

Samlex • www.samlex.com • Unitek Batteryguard

Xantrex • www.xantrex.com • Amp-hour meters 

System-Integrated Amp-Hour Meters:

APRS World • www.aprsworld.com 

Magnum Energy • www.magnumenergy.com 

OutBack Power Systems • www.outbackpower.com 

Schneider Electric • www.schneider-electric.com 

SMA America • www.sma-america.com 

Data Acquisition, Networking & Internet monitoring:

APRS World • www.aprsworld.com 

Atkinson Electronics • www.atkinsonelectronics.com 

greenHouse Computers • www.greenhousepc.com 

WattMetrics • www.wattmetrics.com 

Comments (2)

dolph's picture

WHY, is there no mention of Nickel Iron batteries?. You would think that after the over whelming articles posted of the joy of using nickel iron batteries versus lead acid, you would have a multitude of nickel iron articles regarding them. But i don,t see this. I know they are expensive, I say we need a voltage step up system, from the 1.2v of the single ni/fe battery, up to 12v and 24v or 48v so small off grid systems can use just (one) or a couple ni/fe batteries to get the needed voltage, And at a high enough current as well. A modular device, with several step up phases.Then a few 500 or 1000 Amp hour batteries, can be used instead of the 20 to 40 needed for a large system. just step up the voltage to the inverter voltage. Is there any manufacturer, who makes such a devise already?.

Michael Welch's picture

Hi Dolph. While it is true that one of the reasons for multiple batteries is to attain the required voltage, multiple batteries are also needed to increase the total amount of energy available.

For example, your 1.2 V battery at 1,000 AH equals 1.2 kwh. That is not very much energy made available for loads, and not very much storage for solar or wind input.

Also, inverters can use huge amounts of power for surges, like when the fridge comes on or you first turn on a motor. A step-up device like you mention would have to handle hundreds or even thousands of amps at that low of a voltage; and that makes the device cost a lot more.

And don't forget that the lower the voltage, the greater the wiring losses, which means low-voltage systems need to use much more expensive cabling. This is the main reason why PV system designers use higher voltage systems. These days it is even rare to see them design off-grid systems at 12 V -- 24 V and and 48 V systems are much more common.

While I personally still hold out some hope for nickel iron batteries, most people will not use them. The initial cost is high, as you point out, but that is offset by their longevity. Another problem with NiFe batteries is that they have a very high self-discharge rate, which means it takes more energy to keep them topped off. On the good side, they can be discharged a lot more deeply than lead-acid batteries.

Unfortunately, most of the NiFe batteries that have been available in recent years were poorly made, with a lot of failures. With the manufacturers in China, failed batteries are hard to deal with.

I have heard that there are better NiFe batteries coming, and we shall see if the sellers and installers of off-grid systems like them enough to spec them in these systems.

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