| Author |
Message |
David Ljung Madison (Daveola)
Registered Member
Username: Daveola
Post Number: 62
Registered: 11-2005
Posted From: 62.20.76.142
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, July 14, 2006 - 12:00 pm: | |
I've heard that it's generally a good idea to limit DoD (Depth of Discharge) of batteries to prolong battery life. This seemed reasonable, but looking at specs from battery manufacturers makes me wonder. I couldn't find consistent specs for Trojan cycles based on DoD in one place, but the Exide Energystore batteries are rated as:
1500 cycles to 80%, 2500 cycles to 50%, 3300 cycles to 30%, 4000 cycles to 10% DoD.
If we presume that we need to use our batteries to store a specific amount of kWh, then it isn't necessarily a question of how many cycles, but how many kWh our battery bank will live. So, 2500 cycles at 50% is actually longer life than 3300 cycles at 30% (since it's supplying 5/3 the kWh before we cycle).
I am NOT suggesting that we go to 100% DoD, I understand that is a bad idea. But it seems to me that 50% and 80% DoD isn't so bad for most batteries, and 50% may be even better than 10 or 30% DoD.
I've also been told that the last 10% of *charge* takes more time and energy. If this is true, then it also makes sense from an efficiency perspective to discharge more than 20 or 30%.
Any factors I'm missing or mistakes or thoughts from anyone on this?
Also, a question:
I'm trying to figure out my maximum charge rates. I've read that C/5 is generally a safe charging rate, but I can't find much more info on charging rates - anyone have any info on that? |
niles steckbauer (Niles500)
Registered Member
Username: Niles500
Post Number: 656
Registered: 11-2004
Posted From: 24.129.157.85
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, July 14, 2006 - 12:59 pm: | |
I believe you are reading it wrong i.e. -
Discharging 80% will allow for max 1500 charge cycles
Discharging 10% will allow for max 4000 charge cycles
or 2500 less charge cycles - remembering that this is under ideal situations and actual MMV
KWh is the available capacity when new - charging cycles has no bearing on KWh except the number of deep discharges may reduce KWh capacity over time - HTH |
Jon W.
Unregistered guest
Posted From: 69.254.107.71
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, July 14, 2006 - 1:54 pm: | |
If we assume one discharge cycle per day, then the life of the batteries in time appears to be lengthened, but I think there are enough variables to throw that concept out the window.
I am approaching the battery life issue from another perspective. I presume that if I want to limit the voltage to a higher limit when I charge them that there is no downside to that. The batteries will last longer. Whether correct or not that is how I approach charging. But as compelling a reason for charging that that is, I am just running my generator because I bought it, I might as well use it because I bought the coach to be comfortable and to use all of its creature comforts, and with an expected life of about 25,000 or more hours I won't wear it out anytime soon.
So I look solely at my batteries as something that will keep my coach powered up only when I want to sleep or don't want to kick on the generator, such as when only going to be gone for a little while. |
David Ljung Madison (Daveola)
Registered Member
Username: Daveola
Post Number: 63
Registered: 11-2005
Posted From: 62.20.76.142
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, July 14, 2006 - 2:09 pm: | |
I was reading it exactly as you suggested..
My assumption is that when we discharge to 50% then we are pulling out about 5 times as many kWh then if we discharge to 10% - a reasonable assumption I think, regardless of what the battery capacity is at new.
If that assumption is correct, then unless a 10% DoD gives us more than 5 times the cycles as a 50% discharge, then it makes sense to discharge to 50%.
If you assume one discharge cycle per day, then the calculations don't necessarily matter, your DoD is whatever kWh you use in a given day.
Does that clarify what I was talking about? |
David Ljung Madison (Daveola)
Registered Member
Username: Daveola
Post Number: 64
Registered: 11-2005
Posted From: 62.20.76.142
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, July 14, 2006 - 2:39 pm: | |
So, maybe I'm confused, but I was under the impression that a charge cycle means to charge it from it's DoD. In other words, 2000 cycles for a 25% DoD means that you can charge it back up from the 75% capacity. But now I'm wondering if a 'charge cycle' represents charging 100% of the battery capacity - in other words, 2000 'charge cycles' from 75% capacity would be 8000 recharges.
Anyone have a definition of 'cycles' with regards to sealed lead acid batteries? |
Tom Caffrey (Pvcces)
Registered Member
Username: Pvcces
Post Number: 957
Registered: 5-2001
Posted From: 65.74.70.16
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, July 14, 2006 - 10:31 pm: | |
David, I think you got it right the first time. Enjoy your batteries; they'll tolerate quite a lot if they get a decent recharge occaisionally.
Now, you could spend a little time studying desulfators. I think that they're worth it.
For what it's worth.
Tom Caffrey PD4106-2576
Suncatcher
Ketchikan, Alaska |
David Ljung Madison (Daveola)
Registered Member
Username: Daveola
Post Number: 65
Registered: 11-2005
Posted From: 62.20.76.142
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 15, 2006 - 8:11 am: | |
Thanks for the note, Tom - that raises another good question - has anyone tried desulfators and seen an actual increase in battery life in a controlled experiment? These seem like they might be a scam. |
David Ljung Madison (Daveola)
Registered Member
Username: Daveola
Post Number: 66
Registered: 11-2005
Posted From: 62.20.76.142
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 15, 2006 - 8:35 am: | |
Ooops...
Before starting a new topic on top of an old topic, I should have searched the board..
Interesting discussion:
http://www.busnut.com/bbs/messages/233/12080.html
If anyone has any followup, I'd love to hear it. |
Tom Caffrey (Pvcces)
Registered Member
Username: Pvcces
Post Number: 959
Registered: 5-2001
Posted From: 65.74.70.16
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 15, 2006 - 10:13 pm: | |
David, you probably saw my post in there. As for further information, we have around 50 batteries, many of which are in storage.
We quit buying batteries around 5 years ago because we don't need to anymore. We do pick up some from NAPA's junk pile occaisionally.
We recondition the ones we have with desufators and a few small chargers. The only failures we've seen in any recent times have been ones from NAPA that really were bad. If we recover them, we keep them.
We just set up a small scale alternative power system using ALL recovered batteries, around 900 amp-hours of 12 volts. They work fine.
As fas as we can see, the ringing of the crystals is what makes it work. The small desulfators pulse around 3,000 times a second, and that starts a ringing in the cells up around 3 mhz.
The recoverable batteries usually show improvement in the first week and a big improvement within 3 weeks or so.
Good luck.
Tom Caffrey PD4106-2576
Suncatcher
Ketchikan, Alaska |