Good cheap battery meter

System · September 2007

Where can I get a good meter to check my battery banks? I have two sets of 12V batteries but I can only charge one set at a time so I want to press a button or press a switch to check battery voltage. Another meter to check solar panel voltage and amps would be nice also. I have four 15 watt panels so the max amps are only about 5 amps and volts on open run about 22 volts.

Looking for something cheap (less than about $40) for each.

TIA,
tsp

System2 · September 2007

Re: Good cheap battery meter

I just thought about something else. How about a meter that measures state of charge, i.e., 10%, 20%,...90% and full (100%) charge?

tsp

niel · September 2007

Re: Good cheap battery meter

you can check out these panel meters, but for current you need to know how to match a shunt to it and at what resistance. you could use the old fashioned analog ammeters if the current you wish to measure isn't greater than the meter's rating or it will also need a shunt. for voltage, stay digital if you can as you need some accuate measurements.
http://www.allelectronics.com/cgi-bin/category/385/Meters_(Panel).html
if these won't workout for you then you might just have to save for meters like these: http://store.solar-electric.com/metersmonitors.html

crewzer · September 2007

Re: Good cheap battery meter

How about a meter that measures state of charge, i.e., 10%, 20%,...90% and full (100%) charge?

This can be difficult to accomplish accurately. Battery state-of-charge (SOC) voltage requires no charging sources and/or loads attached to the batteries, and is also affected by battery type (AGM, Gel, flooded-cell), by temperature, and even by manufacturer.

See: http://jgdarden.com/batteryfaq/SoC.xls

There are battery monitors available that can fairly accurately depict battery SOC, but they’re not inexpensive. I use the Xantrex Link-10. See: http://www.xantrex.com/web/id/237/p/1/pt/5/product.asp

Voltage differences may seem small (a fellow once asked me about the "big deal" of 1/10th of a Volt in a 12 V system), but they can actually be rather significant in terms of battery health and performance. For example, one battery manufacturer might specify resting voltages of 12.7 V as 100% SOC, 12.2 V as 50% SOC, and 11.7 V as 0% SOC. This indicates that every 0.1 V represents 10% of capacity. More importantly, perhaps, if we limit discharge to 50% SOC, then each 0.1 V represents 20% of usable capacity.

Trojan Battery’s test chart is a useful guide for flooded-cell batteries. See: http://www.trojanbattery.com/Tech-Support/BatteryMaintenance/Testing.aspx

HTH,
Jim / crewzer

jimskau · September 2007

Re: Good cheap battery meter

Hi guys!
May I humbly suggest a slightly more expensive solution? Check out "Smart gauge UK" on Google. It is a highly reliable voltmeter constantly monitoring in and out of the batteries, recalculating and learning the state of your battery bank as it ages. It provides stored values in percentage and Voltage. Originally designed for the yachting industry it also features the possibility to monitor two separate battery stores. The price however is about 100 Pound Sterling, but I am really glad I made the investment. I feel confident in planning my household consumption by its data, and I often toggle between the two values to try to guess the voltage as percentage. I must admit that the smart gauge often puts me wrong. It is really hard to evaluate anything from the voltage alone on a battery store, as the given voltage is an "in the moment" readout giving no clue of the ageing process in the batteries, meaning how quickly your juice will run out, and the Voltage plunge down to the critical 12,0 V.

Good cheap battery meter

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