T-Pain Is On A Boat: Re: [Electric Boats] Battery capacity reduction over time

Tuesday, December 24, 2013

Re: [Electric Boats] Battery capacity reduction over time

Chris,

Yup, I'm in Austin, and sail on Lake Travis (that now looks more like a puddle). Lake Travis has come up several quite a bit from it's low this summer, but is STILL DOWN 52 FEET from full - which is more than some lakes are deep! So I guess I'm thankful I can still sail around at all.

I'm looking forward to going to the On the Water Boat show at Kemah, and seeing the big, expensive toys!

When I was first getting started with electric, and somewhat still at this point, my thought was to have two battery banks, so that if I ran one down, I knew I could still get home (though possibly at a slower speed to make SURE I got home).

The reality is that the batteries are much more efficient if you combine them together into a single bank.

The problem is that if you do that, THEN, you have to figure out when your "gas guage is at half a tank".

One might still be tempted to give up the significant efficiency improvement to keep the banks separated, until they have enough experience to manage it. Or - perhaps until they have a genset on board as a backup. :)

Good luck!

John

From: Chris Hudson <clh5_98@yahoo.com>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Tuesday, December 24, 2013 8:27 PM
Subject: Re: [Electric Boats] Battery capacity reduction over time

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

On Dec 24, 2013, at 17:10, oak <oak_box@yahoo.com> wrote:

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? :)

John

From: 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 iPhone

On Dec 24, 2013, at 14:45, oak <oak_box@yahoo.com> wrote:

Chris,
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.

John

From: "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