John,
That makes sense. I just need to figure out what my voltage floor is and stop motoring when I remove 40-50% or whenever I hit my low limit, whichever comes first. By the way, do you live in Texas? Seems like I remember that from an earlier post. I'm in Corpus Christi.
Chris
Sent from my iPhone
Sent from my iPhone
Chris,Don't be confused here. We're talking about a low voltage cutoff limit, not a "state of charge".There have been threads on this site and others about trying to determine "state of charge" strictly from a voltage reading. That's not what we're talking about here.What we're talking about here is just a lower limit that can be applied on it's own.You're RIGHT - the voltage of the bank will depend on the load. HOWEVER - if the voltage EVER hits the lower limit (whatever you determine that to be), you need to turn off the motor, or at least turn it down (a lot).Depending on the load and the state of the batteries, the battery may recover a bit, and allow you to troll along a little further.The lower voltage limit is debatable, and depends on battery type.My Torqeedo cuts out (pulls the plug itself) if the power ever drops below 36V (9V per "12V" battery). That's really TOO LOW to run down a flooded Lead Acid battery bank.There are some that would say you shouldn't run flooded lead acid batteries below 11V per battery, which would be 44V for your "48V" bank.AGM will probably be similar.Lithium is different, and I don't know what the lower voltage level for a "48V" bank should be.Others might have a better supported opinion of what the lower voltage level should be for your bank.Does this help confuse things? :)JohnFrom: Chris Hudson <clh5_98@yahoo.com>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Tuesday, December 24, 2013 7:39 PM
Subject: Re: [Electric Boats] Battery capacity reduction over time
John,Thanks for the reply. So, how do I know what my low voltage alarm should be set at? The voltage varies with different loading levels, and I thought the only way to determine state of charge using voltage alone is with the bank at rest for 24 hours. My bank is 48V F.L.A.Chris
Sent from my iPhoneChris,If you went STRICTLY on power usage, that would be true.Hopefully (!!), the BMS also has a minimal voltage that would be a separate limit.You are correct, that as the battery ages, it won't hold up as long on a charge. You'll basically get to the lower voltage limit faster. But as long as you have a lower voltage limit alarm / cutoff / warning, you'd be ok.JohnFrom: "clh5_98@yahoo.com" <clh5_98@yahoo.com>
To: electricboats@yahoogroups.com
Sent: Tuesday, December 24, 2013 4:23 PM
Subject: [Electric Boats] Battery capacity reduction over time
Hi Group. I have a battery state of charge monitor for my bank. It looks at discharge rate, applies the Peukert value and the bank size in AH programmed by the user. This works fine for a newer bank, but what about a bank with a few years on it? Should some adjustment in the settings be made over time to the meter to account for decreasing capacity over time? As the battery ages could we unknowingly be killing our banks by discharging them deeper and deeper as they age? Thanks, Chris
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