battery packs

Old 08-22-2008, 11:34 AM
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whats a good procedure for checking used matched cell paks?
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Old 08-22-2008, 03:28 PM
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Originally Posted by radsnappy
whats a good procedure for checking used matched cell paks?
Hello Radsnappy,

The easiest way we have found is to use a Competition Electronics Turbo 35. This unit has a cycle mode that you can check batteries with.

If you don't have access to a Turbo 35, another way to do it is with a volt meter, stop watch, some form of discharger (preferably 30 or 35 amp discharger) and graph paper. Set your graph paper up with the voltage readings on the left side of the paper vertically, in increments of .1 volt all the way up to about 7.5 volts. Set your graph paper up with the runtime readings on the bottom of the graph horizontally, in increments of whatever you want (I suggest 10 second increments), all the way up to about 8 minutes.

Follow these steps: 1) fully charge your pack. 2) connect pack to volt meter and record initial voltage reading on your graph paper (use dots on your graph paper). 3) connect battery to discharger at the same time you start the stop watch (easier with another person helping you). 4) This is where it can get tricky, because you have to keep up. Watch your stop watch and volt meter. Every 10 seconds (or whatever increment you set on your graph paper) put a dot on your graph paper according to the readings on your stop watch and volt meter. Continue taking readings every 10 seconds until the voltage reads .9v per cell (5.4v for a 6 cell pack). Once you are finished, you will have a series of dots going across the page. 5) Next, take a pen and connect the dots. This will give you a graph line of your pack. It should start out at about 7.4v on the left side of the page with a downward slope until it reaches 5.4v. You can use different colors for each pack, so that you can overlay more than one pack for comparison. 6) You can compare your graphs to the labels on your cells (if you have matched packs). To compare your graph readings to your cell labels, you will need to divide your graph readings by the number of cells you are checking (not for runtime). For example, if your graph max voltage is 7.4v (for a 6 cell pack), you would divide this by 6, giving you a per cell average of 1.233v. You can then compare this to your cell labels. Since the cells are put together in series, the runtime you record on your graph can be compared to the cell labels. For example, if your graph shows a total runtime of 450 seconds, you can compare this directly to the labels on your cells.

It's actually kind of fun to do this, as it gives you an actual "picture" of how all of your battery packs compare to each other and also how well they are holding up compared to the labels. Don't be alarmed when you see that the graphs you take are not as good as your cell labels, as the runtime and voltage start dropping off only after a dozen runs or so.

Hope that helps.

Jeff
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