| Author | Message | ||
     Erik G. Burrows (Erik) Senior Member Username: Erik Post Number: 279 Registered: 04-2002 |
Some interesting data about my exide orbital batteries, some of you might find interesting: Due to low voltage readings from my batteries, I decided to run a test on my batteries, which are wired in parallel. I fully charged the batteries, then turned on every electrical device I could think of, and graphed the voltage drop over an hour. Here's the result:  The red line are actual readings. Once I saw the beginning of the exponential drop (all lead-acid batteries have a discharge graph of this shape), I stopped the test, and estimated the rest of the graph for scale. (In green) As you can see, my fully-charged batteries register only 12 volta (12.33 exactly), when every document generally covering lead-acid batteries says that the fully-charged voltage should be 12.6 volts, and that such a battery is 50% discharged at 12.4 volts. Since my batteries never even got up to 12.4, I was worried they were dead. What this test shows me is that my battery's discharge pattern is simply shifted down, and a bit steeper. Full charge is 12.3 volts, while a 50% depth-of-discharge registers about 11.5 volts. Since the outside temperature is about 65 degrees Fahrenheit, this could partially account, but I believe the design of the Exide spiral-cell batteries exhibit slightly different behavior from simple plate or glass-matte lead-acid batteries, resulting in lower voltages and a steeper discharge graph. | ||
| Peter Matusov (Pmatusov) Senior Member Username: Pmatusov Post Number: 1187 Registered: 09-2002 |
Erik, I have two Optimas and one Exide, and they all are under 12.6! I worried about one (that I've had for four years), but stopped after seeing the other two to behave the same way. | ||
| Erik G. Burrows (Erik) Senior Member Username: Erik Post Number: 280 Registered: 04-2002 |
Now we know. I'm perfectly happy to have a battery system running at a couple of tenths of a volt lower than normal, just so long as I have an idea of when the depth of discharge is getting too low. Now, I know not to panic when I see the volts drop below 12.0. | ||
| Bazzle (Bazzle) Member Username: Bazzle Post Number: 56 Registered: 09-2003 |
Hope your voltmeter has been calibrated? bazzle  | ||
| Erik G. Burrows (Erik) Senior Member Username: Erik Post Number: 281 Registered: 04-2002 |
My voltmeter always shows 0.1 volts higher than the voltage readout of my ham radio (which is on the end of a long cable run). | ||
| Erik G. Burrows (Erik) Senior Member Username: Erik Post Number: 283 Registered: 04-2002 |
Hmmm... You know what though? Since these readings were taken during the test, while the batteries were under load, the readings would be low due to the internal resistance of the batteries. To get a no-load reading, I'd have to use this graph to discharge my batteries to a known state (say 50% DOD), let them settle, then take a reading. That would give the offset. I think I'll do that today, now that my batteries have been sitting on a trickle charger over night. | ||
| Erik G. Burrows (Erik) Senior Member Username: Erik Post Number: 284 Registered: 04-2002 |
That difference for my test load (for my 2 year old, parallel wired) batteries is 0.55 volts. You can check out my full analysis, graph, and state of charge table at battery analysis |
