Has anybody else purchased one of these. I left it charging overnight and batteries charged to 116%, 115%, 125%, 122% according to the battery beak. The previous RS3 unit we have charged them all to 130%. Trying to figure out if there’s something weird about my batteries or if this charger has a stricter cutoff.
I’m aware that most of the charge beyond a certain point is surface charge, but at what percentage on the beak is that true? I’ll be doing some CBA comparisons to see if they perform any different.
that percentage your talking about is heavily influenced by WHEN you read the batteries. immediately after the charger finishes it will read much higher. the charge absorbs over time and stabilizes after a while and the batteries will read much lower but are still at the same level of charge. it will also completely throw off the internal resistance calculation since the “float” voltage drops dramatically when a load is applied.
the battery beak is a great tool for comparison assuming your testing at the same time since charge completion otherwise it’s not going to be an apples to apples comparison
A lead acid charger has a few phases, bulk, saturation, and perhaps maintenance.
My first thought is if you left them on overnight, they completed bulk and saturation which push the terminal voltage up to and hold it at a higher voltage. Then the charger may have entered maintenance phase where it drops the applied terminal voltage to a lower (but still full), level that results in less outgassing.
Additionally a battery beak measurement taken of a battery just pulled off a charger will not result in an absolute measurement, as you mention the result will be disturbed by surface charge. A better single point measurement would be to wait 24hrs after taking the battery off the charger for that surface charge to better distribute/dissipate then take your measurement.
and when this is not possible like when at competition . do your best to take the reading down at the same time delta since charge completion every time. for us this means as soon as charge is finished the battery gets pulled and tested so we can have comparative data between batteries
Do you mean that when the light turns green you remove the battery from the charger no matter what? Our practice is to take a battery off the charger, beak it to see it is at 130%, and put it directly onto the robot for the next match. All other batteries remain on chargers at all times.
An update. I have found that unplugging and plugging a charged battery back in, waiting for the light to flash red then quickly back to green, and then checking again on the battery beak, quickly bumps the charge percentage up. Doing this once or twice often gets it to 130%.
Then, after waiting, beaking the batteries will result in a lower percentage. I think @Jwal is right about the maintenance phase. I guess the RS4 must just behave differently in maintenance than the RS3 (which would keep them at 130% indefinitely).
Is it possible for someone with elite battery understanding to tell me if this maintenance voltage difference results in a better charged battery for FRC use cases? Has anyone used a battery analyzer to test batteries that were stored with different mainenance voltages
Not claiming elite battery understanding, but float charge isn’t going to matter. The cell voltage is a function of chemistry, with internal resistance being a big factor. The way a battery has been used, and charged, can make a big difference over time. The chemical reactions are reversible, but the reaction rates and other factors can cause the internal resistance to increase. They can also become degraded because of mechanical shock.
Basically, the people who design the good chargers do have elite understanding. It’s much more important to periodically charge batteries over the off season, to track how each battery is doing, to think about formatting cycles on new batteries, and not to run batteries that are degraded in competition matches.
The nice thing about the beak is that it does at least a little load testing, to get internal resistance. This is a much better indicator than any voltage above 100%.
when you take it off is almost irrelevant. I should have clarified. its vs when the charger actually finished and stopped charging. if you did this overnight they were probably finished charging well before midnight unless you started REALLY late.
yes once its in maintenance mode its ding effectively nothing.
