Battery CAPACITY tester tool?

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Ric

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Does anybody know of a tool to test Ah capacity of domestic batteries?

eBay and Amazon is full of drop-test tools for batteries, but these seem to be oriented towards measuring cold cranking amps of starter batteries. I can't find anything oriented towards deep-discharge batteries that can measure the time to drop to x volts under y discharge current. I know I could mess around with lightbulbs, ammeters and stopwatches - but would prefer a nice robust tool that I can keep on the boat to quickly identify if I have a faulty battery.
 
Ric said:
Does anybody know of a tool to test Ah capacity of domestic batteries?

eBay and Amazon is full of drop-test tools for batteries, but these seem to be oriented towards measuring cold cranking amps of starter batteries. I can't find anything oriented towards deep-discharge batteries that can measure the time to drop to x volts under y discharge current. I know I could mess around with lightbulbs, ammeters and stopwatches - but would prefer a nice robust tool that I can keep on the boat to quickly identify if I have a faulty battery.
Click to expand...

Pretty sure such a thing doesn't exist, unless you paying bucks. And even a close to perfect capacity test can be different one day to the next . http://batteryuniversity.com/learn/article/how_to_measure_capacity

I've an arduino design in the back of my mind for a logger but not get very far with it.

From a play around a while ago...

Discharge3-4-14_zps5ab14cc9-1.jpg
[/image]
 
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GHA,
I have carried out similar tests, by putting a fixed load on a battery (in my case 4 amps), I see a similar decaying voltage, and when it reaches around 11.5 volts, I consider this as the "useful capacity", i.e. hours multiplied by the average discharge current. I notice from your curve that at 14:30, there is a dramatic reduction in voltage with a corresponding reduction in discharge current, did anything happen?
Angus
 
yotter said:
I notice from your curve that at 14:30, there is a dramatic reduction in voltage with a corresponding reduction in discharge current, did anything happen?
Click to expand...
I think that's just how lead acids behave when they're empty. Not sure where the power was coming from the drive the few amps through the load at that point.
 
Seems strange to me that there is not a simple tool already on the market to do this, perhaps combined with one of the more common drop test tools.

I know that standardising the measurement of battery capacity is impossible (I had a long email exchange with Battery Megastore about this because there UK batteries have higher "capacity" than the exact same model sold in France due to different measurement standards). However as long as the tool is used consistently, it would be useful to measure the loss of capacity over time.
 
The ACT 612 battery tester claims offer accurate capacity measurement. Around £250 though. Uses some sort of pulsing and the internal resistance. According to their info it was extensively compared to 20 hour load tests. Wonder if it uses the same sort of methods as the Merlin Smartguage (which you may as well use if you're spending that amount)
 
I have a Midtronics battery conductance tester which provides a readout of CCA. Battery capacity loss can be determined from a comparison between current CCA with historic readings. I find it a good enough guide in my experience.
 
I have a pretty powerful inverter.

I occasionally check my domestic batteries using the inverter and the immersion heater.
It draws about 120 amps so provides a good test of battery capacity.

Tony.
 
Ric said:
The latter is exactly what I envisaged.
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You appeared to want something that gave a result quickly if not instantaneously.

Although this is an obvious advance on lightbulbs ammeters and stopwatches it is still going to take the same time to evaluate the battery.
Since capacities are most usually quoted at the "20 hour" rate adjusting the discharge rate to get close to this would allow comparison with the claimed capacity of the battery.
 
or this one upto 200A..

http://cpc.farnell.com/1/1/209617-act-meters-chrome-ibt-battery-tester-sla.html

The ACT Chrome is an intelligent battery tester, designed for 12V lead acid batteries from 1.2Ah to 200Ah. It allows simulation of a full battery discharge test in seconds. A table on the meter indicates when batteries should be recharged or replaced due to age or operating conditions (65% of rated capacity). A temperature sensitive strip also records ambient temperature.
Click to expand...
 
As said battery capcity in Amp hours is dependent to a great degree on the rate of discharge. The 20 hr rate is usually the spec for design size. This is also the typical rate that you might want to test a battery at. It also means that the test is going to take possibly (hopefully) that amount of time.
So for a typical 100AH battery we need to discharge at 5 amps. A typical in service sort of current in a small boat.
You need a load. preferably for accuracy a constant current load. Relatively simple with transistors etc. Or you cna use a simple resistor or light bulb but with declining current with discharge so the test becomes indicative rather than definitive.
From there you need to monitor the battery voltage and the clock or you can set up a voltage comparator which will switch everything off at a specific cut of voltage. This comparator needs to be connected to a clock or timer so you have a record of when it cut off.
Thus you can have or make a very accurate measure of current taken form the battery or you can have a rough idea.
In practice You also need to be confident that the battery is fully charged. "fully charged" might usefully mean when your in service charging system reckons it is charged. Regardless of whether it is fully charged or not.
I certainly would be doubtful of any tester that claims to be able to predict capcity in a quick test. However most people need their service deep cycle batteries to be able to dopuble as emergency engine start batteries. So a CCA test is useful to ensure it will do that job. But then an engine strt on the doubtful battery is a good CCA test.
The results might not be so meaningful. however. If a battery exhibits something like 50% of claimed capacity it is probably fine and likely as good as you can get. If however it gives only 10% or less then it is probably time to replace it. anything betwen those numbers is up to you. good luck olewill
 
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