Thanks Lee, I am charging sparingly anyway, because I need to keep my household electric consumption close to 300 kWh per month or pay a hefty higher rate for the overage, I managed to get the home itself near 100 kWh/mo by switching to LED lights and using a gas dryer, heater and cooktop and the 3 adults in the household use a laptop each, so the times that I charge (typically 4 weekdays as I like to commute by bike once a week) and at least once a weekend, I can get about 10kWh per charge and stay around the 200 kWh/mo budget for charging; luckily I can charge at work as well, so typically I leave work with an (almost) full pack after 6-8 hours of level 1 charging. (I tend to start my work from home, then go to the office after traffic has cleared). Since I also charge level 1 at home, my charging current is never more than 12A, ramping down to below 10A when charging is under way or when the grid is weak at the outlet, only if I plug in at a 240V J1772 can I get 20A of charge current into the pack (120V nomonal, rising to ~147V under full charge, with current falling to about 4-5A at that voltage from the resonant transformer. The only thing I can select on my Bycan charger is whether I want the shutoff after 2 hours or 8 hours after detecting the 147V max charge voltage. (The latter is the "equalizing" mode) The charger is not often allowed to complete this anyway, on average 1 or 2 times a month.
I am a little concerned if I may have reversed a few cells at the moments that I needed to go a little further than the pack wanted, due to unexpected hills or when driving more freeway (fast) than anticipated, causing the pack to sag (under load) below 90V which I then tend to counter by reducing power and trying to keep voltage above 90V under load, nursing the car along until I can plug in an recharge immediately... Anyway, time will tell if these cells are weak and deteriorating or simply getting older. Cor van de Water Chief Scientist Proxim Wireless Corporation http://www.proxim.com Email: cwa...@proxim.com Private: http://www.cvandewater.info Skype: cor_van_de_water XoIP: +31877841130 Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203 -----Original Message----- From: Lee Hart [mailto:leeah...@earthlink.net] Sent: Sun 8/23/2015 1:49 PM To: Cor van de Water; Electric Vehicle Discussion List Subject: Re: [EVDL] Difference in water use per cell for GC batteries Cor van de Water via EV wrote: > My pack of 20 Golfcart batteries is now almost 4 years old and > it has brought my truck over 14k miles so far, but tonight when > I inspected a couple of the batteries I noticed something strange - > while some cells had minimal water loss (level about 1/2" under the > top of the cell) there were several other cells that barely had their > plates covered, the level had gone down more than a full inch in those! > How can this difference be explained? 4-5 years is about right for Sam's Club (Eveready a.k.a. Interstate) golf cart batteries. That's what I've been getting, too. Trojans and US Battery brands are a little better. As others have noted, water usage increases as a flooded lead-acid battery ages. This happens for several reasons; some due to the battery, and some due to the charger. Flooded batteries use a lead-antimony alloy for the plates. The antimony hardens the plates (makes them stronger), which extends life. But it also increases water usage, the self-discharge rate, and lowers the fully-charged voltage. As the battery ages, the antimony migrates to the surface of the plates. This worsens all these effects. The battery gasses more, uses more water, and its fully charged voltage will be less. (It doesn't otherwise affect the amphour capacity, though. Loss of capacity comes from other effects.) Most chargers do not compensate for new/old batteries. They blindly charge all batteries as if they are new. This means that old batteries get charged to too high a voltage. That significantly worsens gassing and water usage. The resulting chronic overcharging also shortens life. (This is why the batteries in an old batteries tend to "suddenly" all die together). Big industrial EV chargers use the dv/dt or di/dt algorithms to compensate for battery age, and thus extend their life. Rather than charge to a specific ending voltage (or current), they charge until the *rate of change* in voltage or current goes below some limit. If your charger has this option, use it. If not, your best bet is to reduce your charger's end-of-charge voltage (for example, from 2.5v/cell to 2.45v/cell). Also increase your final charging current (from 4 amps to 8 amps). In other words, rather than shutting off at 7.5v at 4 amps, change it to shut off at 7.35v at 8 amps. Old batteries also need more frequent equalization. While you might only need to do this every 2 months when new, it could need to be done ever 2 weeks when old. "Equalization" is a long slow low-current charge to an "unlimited" voltage. Basically, you charge at something like 2-4 amps until the voltage stops rising. If you take care of them in their "declining years", the batteries can easily provide double the life and number of miles before the pack needs to be replaced. :-) -- Do the thing that needs to be done, even if no one else yet notices that it needs doing. -- anonymous -- Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
