----- Original Message ----- From: "Lee Hart" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Wednesday, September 04, 2002 12:23 PM Subject: Re: EV Newbie -- 3
> Thomas Shay wrote: > > >>> A 120 volt pack isn't empty when its voltage drops to 105. There's > >>> nothing sacred about 105 volts. A conservative driver wanting to > >>> be kind to his batteries would do well to avoid frequent drops > >>> below 105. A less conservative but still reasonable limit is 90 > >>> volts for short bursts of acceleration or hill climbing. I am not wipping mine hard enough as I keep them 110 and slow up to keep it there > Peter VanDerWal wrote: > > >> We were talking about a constant current draw. By definition, a > >> lead-acid cell is empty (at a given current) when its voltage drops > >> to 1.75V. A 120V (nominal) pack has 60 cells, so when used at a > >> constant current, it is empty when it reaches 105V. > > Both are true. The important point is that batteries don't suddenly go > dead, like an empty gas tank. The rules for lead-acid batteries are: > > 1. The lower the battery's state of charge, the lower the voltage. > - 2.16v/cell = 100%, 1.99v/cell = 0% > > 2. The more current you draw, the lower the voltage. > - a flooded 6v golf cart battery's internal resistance is about > 0.005 ohms at full charge and 77 deg.F > - a sealed AGM 12v Optima battery's internal resistance is about > 0.002 ohms at full charge and 77 deg.F > - voltage under load is about Vload = Vnoload - (Amps x Resistance) > > 3. Internal resistance goes up as the battery runs down > - it can be 2 times higher at 50% state of charge, and > nearing full discharge, the battery is nearly an open circuit > > 4. As the battery gets colder, internal resistance goes up and amphour > capacity goes down, approaching an open circuit and zero amphours > at -40 deg. > > 5. To murder a lead-acid cell, pull it below 1.5v. > - but batteries use many cells in series, and they aren't matched > - so 1.5v x 6 = 9v is not a safe minimum for a 6-cell 12v battery > because one cell might be at 1v when the rest are at 1.6v. > > So, the lower you go in voltage, the luckier you had better be. 9v might > be OK if your 12v battery is new, in good shape, and has been recently > equalized so all cells are as equal as they're going to get. But it will > kill the weakest cell of a battery that is older, not in perfect shape, > and hasn't been equalized. > > Steve Clunn wrote: > > > "There will be no need for war as we have greatly understamated the > > power of the Hood ornamant" > > Steve Clunn (lee are you still with me :-( > > Interesting idea, but wrong topic, Steve. Let's help the EV Newbie with > his questions here. this guy is talking bat abuse in my book but I love me EV batteries and never wip them (work truck, porsch ) can't people slow down . I let my volt meter tell me how fast to drive > I have had to abuse them in emergencys but see the price in lost amp hours . Now let me say this as I do a 20/30 mile run a day .In the old days befor plugs were everywere and I didn't have newbee waiting for my batteries. I drove on old wor out ( pull 50 amphours out and 10.5) after 20k on em I could still go everywere i did as when I had 100 amphours to work with (new ) I just drove a little slower BUT NOT THAT MUCH . I guss i feel somethime with all this talk of how far can I go people will miss some of the EV magic that I love. I talk about it in ot day I tipical day.not Steve Clunn > Lee A. Hart Ring the bells that still can ring > 814 8th Ave. N. Forget your perfect offering > Sartell, MN 56377 USA There is a crack in everything > leeahart_at_earthlink.net That's how the light gets in - Leonard Cohen > >
