Battery checker


Need info on some type of battery load/checker for ( 12volt 34 type U1 Ah SLA Battery ) These are generally used in electric wheelchairs/scooters. Have been told not to load check these batteries by a couple of local battery stores, but know for a fact the places that sell them do use some sort of load checker for checking on them for warranty puposes. Anyone know for sure & what might be available in a not to expensive checker. Thanks Gimpy.
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Gimpy wrote:

http://www.vard.org/jour/83/20/1/pdf/kauzlarich.pdf
AFAIK the use a standard lead-acid battery but the wheelchairs are driven by a PWM control system rather than as an essentially DC load for starting an automobile, for example. The above link is a paper on some testing procedures/results.
Seems as though would use the chair itself as a test load and check for loaded voltage as the first approximation.
Is there a problem w/ the chair supplier not being able to test or simply wanting something independent?
I don't believe a standard load test is really applicable rather than there being a reason it can't be done, though, in response to initial question.
So, nothing specific, but a few ideas and one reference that might prove educational on the subject.
HTH....
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Thanks HTH, but that article I believe was written for an engineer ? The info I did get from it was stuff I already knew.. I am in a wheelchair & do use an electric scooter outside the house & the scooter does like a wheelchair use 2 U1 batteries in series for 24v. These things are pretty expensive & last year I bought 2 new ones & they petered out in about 4 mo's. My son took them into the store where he bought them & they used some type load tester to determine one OK & one dropped off after a min. or so. Yr's warrt. so they gave me one new battery. What I was looking for was a tester I could use here at the house as I now have a couple of spare batteries & generally trade in 2 for 2 & just could be one of those I'm trading in is still usable ?? This is why I was wondering about a load/tester that would work & not damage anyrthing. Have been told car/truck load testers are a no-no & could damage these batteries?? In anycase thanks for your help. Gimpy

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Gimpy wrote:

One important item about any battery is to limit the depth of discharge. A good voltmeter is a fairly good indication of the condition. I would think that hooking a digital voltmeter to both batteries would provide information on how they are discharging. The problem is that the voltage varies just a small amount from full charge to 75% or 50% state of charge. 100%: 12.65 volts 75%: 12.45 50%: 12.24 25%: 12.06 0%: 11.89
And how you charge is also very important. The goal is to avoid sulfation of the battery. For your purpose a good four stage charger is almost a necessity. Perhaps you already have that.
Section 9:
http://www.batteryfaq.org
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Rich256 wrote:

But a battery can measure correct voltage without supplying useable current. The best way to check would be to solder a pair of leads on a 12v automotive backup bulb, and place the bulb leads & voltmeter leads across the battery terminals at the same time. Or an alternative is to use the bulb by itself - the brightness of the bulb is a good indicator of battery charge under a small load. Bob
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Bob wrote:

Those voltages I give are unloaded and are correct. If you loaded them you will get something completely different. Measuring the unloaded voltage of of a totally discharged battery would produce what you call "correct voltage" but it would be less than 12 volts. Put a load on it and it will drop to near zero.
So if he wants to get a measurement of the state of charge it is possible with the voltmeter. The better alternative is using a hydrometer but that is difficult with with his system.
He needs to know what the state of charge is. Putting a bulb on a 75% discharged battery like his will still produce about the same brightness.
If you have a good calibrated voltmeter such as a Fluke you can get a good idea of what the state of charge is by measuring the unloaded voltage. I neglected to say that those voltages are at a temperature of 80F. They will be slightly higher or lower (perhaps .02v or so) at higher or lower temperatures.
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wrote:

What you want is a meter to read the difference between the batteries WHILE YOU ARE USING THEM. This is easily done with a small cheap voltmeter (preferably center reading) and two equal resisters. Put the resisters in series from +24v to (-) and connect the voltmeter from the center of the pair of resisters to the center joining strap of the batteries (+12 v nominal). The meter should read zero if the batteries have the same voltage under load, and will deflect one way or the other if one battery gets weaker than the other. You could use a cheap digital and read + and - or a center zero analog of about +/- 4 volts or so.
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Nick Hull wrote:

Or what I was thinking of was using two of those cheap meters. One across each battery. Harbor Freight has some that would be good enough. If during use one of the batteries drops more than the other some corrective action might be needed such as a desulfation charge on that battery.
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I suspect a electric wheelchair/mobility chair would use a deep-discharge type of lead acid battery,like a boat trolling motor would use. Auto LA batteries are designed for short,very heavy current draws,then a fast recharge.
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You could rig up an automobile headlight with some test leads. Connect to the battery, if it is good, the bulb should be bright and not dim for many minutes. Probably need to test for only a few minutes to spot a bad battery. You could also connect a voltmeter in parallel if you want to.

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Jim Yanik wrote:

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Gimpy writes:

You want a carbon pile tester:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber636
Walmart and auto parts stores also test batteries, if you can find someone sympathetic enough to thumb in your specs to the automated tester.
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Thanks for all the info guys. A lot of stuff to look over & try
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