Re: Battery sag vs. SOC (Buddy Mills)

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Re: Battery sag vs. SOC (Buddy Mills)

fred ungewitter
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Begin Original Message: 5
Date: Wed, 25 Nov 2009 18:54:13 -0500
From: "Buddy Mills" <[hidden email]>
Subject: [EVDL] Battery sag vs. SOC

I have been running my EV for a couple of weeks now and have about 200
miles.  Mostly short trips to break in the batteries and a few up to 20
miles and keeping an eye on the SOC.  Was wondering about voltage sag.  I
know that my DEKA 831Gs have a lot of sag but I would like to know how the
80% DOD comes into play.  Today I decided to push it a little bit more.  The
sag was quite noticeable, voltage less then desirable by the SOC meter while
in use,  but once I stopped, waited about 5 minutes the SOC was at about 25%
(75% DOD).  After another 30 minutes of sitting it was at 50% SOC.  



The question I have is do I monitor for the sag voltage or can I take them
down to 80% DOD of  the resting voltage.  I want to insure that don't
destroy these Deka in the 1st few months.



TIA

Buddy Mills

End Original Message: 5


     
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Re: Battery sag vs. SOC (Buddy Mills)

fred ungewitter
I'll try this again, but not press the wrong key this time...

Buddy, we've got fourteen Deka 8G31s in two different EVs and I would suggest that running the pack down to 80 percent DoD might mean a one year pack.  Dekas are not known for giving up too much in the amperage department and really object to much more than 1C discharge.  Our first EV, a Xebra is running near the end of the third year for half the pack and only six months short on the other half. I made the mistake of taking it too deep into a drive and probably damaged three of the batteries. Replacing them and installing equalizers (PowerCheqs) and keeping a close eye on the DoD is why it's still alive, in my opinion.

We use a CycleAnalyst and the Peukert numbers for lead-acid to keep the depth to fifty percent.  The 8G31s are 98ah batteries, but at 1C discharge level, you can expect half that, to about 49ah capacity, but that's to one hundred percent discharge. I'd venture a guess that 25 ah is as far as you'd want to go with these expensive blocks of lead.

What are you using to determine SOC?  We also have a PakTrakr installed in our EV fleet, but the SOC figure on that is not as useful as the direct ah reading of the CycleAnalyst.

I've put a label on the CA panel reading "pedal up: 66v, pedal down: 63v" so my wife knows not to reach those numbers.  If she sees 66 volts while underway, she better be pulling into the garage and that's still far deeper than I'd like to see.  Because everyone's foot is calibrated at a different pressure level, voltage is such an uncertain method of determining SOC or DOD.

fred ungewitter
daytona beach, fl
rav4ev, xebra sd, gizmo ev, Focus Designs SBU
------------------------------


Begin Original Message: 5
Date: Wed, 25 Nov 2009 18:54:13 -0500
From: "Buddy Mills" <[hidden email]>
Subject: [EVDL] Battery sag vs. SOC
To: <[hidden email]>
Message-ID: <000b01ca6e2a$97540c30$c5fc2490$@net>
Content-Type: text/plain; charset="us-ascii"

I have been running my EV for a couple of weeks now and have about 200
miles.  Mostly short trips to break in the batteries and a few up to 20
miles and keeping an eye on the SOC.  Was wondering about voltage sag.  I
know that my DEKA 831Gs have a lot of sag but I would like to know how the
80% DOD comes into play.  Today I decided to push it a little bit more.  The
sag was quite noticeable, voltage less then desirable by the SOC meter while
in use,  but once I stopped, waited about 5 minutes the SOC was at about 25%
(75% DOD).  After another 30 minutes of sitting it was at 50% SOC.  



The question I have is do I monitor for the sag voltage or can I take them
down to 80% DOD of  the resting voltage.  I want to insure that don't
destroy these Deka in the 1st few months.



TIA

Buddy Mills

End Original Message: 5

------------------------------



     
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