The reserve minutes rating for a battery is supposed to be understood as a rating of the complete capacity of a battery. It is not deceptive. The rating should be clearly understood as a measure for how long a battery can last until it is completely discharged when it is discharged at a constant 25 amperes. This measurement tortures a battery so that we get an idea of how good it is. But as users, we need to multiply the reserve minutes rating by whatever percentage is reasonable as a depth of discharge. If the application draws 25 amps, then we can multiply by .5 to get the range for a 50% depth of discharge. Alternatively, we could be even nicer to the batteries and discharge them at 12.5 amps to get the full range of reserve minutes.
Gary
Gary,
My experience seems to agree with your statement that "reserve measurement goes to complete discharge".
Am I the only one that gets annoyed at advertised figures that are 2x of what can be reasonably expected??!
Are the Li battery figures as overstated?
From: Gary Vander Hart <gvanderhart@midco.net>
To: electricboats@yahoogroups.com
Sent: Monday, October 28, 2013 9:14 PM
Subject: Re: [Electric Boats] RE: Hello group
To emphasize the point that different applications have different requirements. I am planning to build a sailboat that will require ballast. Combining the ballast and energy storage feature of lead acid batteries gives it a big advantage over Lithium.
By the way, reserve minutes or reserve capacity ratings are only valid for comparison purposes. This measurement results in a completely discharged battery. The reserve minutes should be divided by 2 to get an approximation for 50% depth of discharge usage rates.
Gary Vander Hart
From: Carter Quillen
Sent: Monday, October 28, 2013 8:58 PM
Subject: Re: Re: [Electric Boats] RE: Hello group
I stand by my contention that there are too many variables with too much error potential to generalize which technology is always the best value right now. Until LiIon prices drop significantly, this will be the reality. LiIon is just still too expensive to say for sure it will be the best value in the end. And while cycle potential is very high for lithium, I think your 10 year life expectancy projection might be a bit optimistic. Everything I've heard is that LiIon dies in about 7 years reguardless of how hard or soft you cycle it. This limitation is inherent in the chemistry.
You can massage the numbers however you like to make your case but every applications is a little different. And, there are always deals out there to make one technology a little more economically better than another each week. Case in point, those used LiIon from Thunderstuck definitely make that the deal of the week and if I had the cash to spend I'd be buying but next week AT&T might be clearing out a bunch of Surrett Telcom batteries at 10 cents on the retail cost that would make them a better deal. Not to mention a deal like the AGMs I got this summer for FREE because they where throwing them away and I was in the right place at the right time. However, when you look at retail to retail right now, I still think the economics are simply just still too close to call when you apply objective error analysis!
Too many application variable, cost variables, and longevity variables to make a definiative call to generalize on which battery system is best for every situation right now in my opinion. If you MUST have optimum performance, LiIon definitely wins hands down but if you want the most energy/$$$ and your performance requirements are not extremely demanding, I think FLA is still the best deal out there. You can agree or disagree but that's just my professional opinion for whatever it's worth.
Capt. Carter Quillen, PE
From: "ewdysar@yahoo.com" <ewdysar@yahoo.com>
To: electricboats@yahoogroups.com
Sent: Monday, October 28, 2013 7:35 PM
Subject: RE: Re: [Electric Boats] RE: Hello group
To: electricboats@yahoogroups.com
Sent: Monday, October 28, 2013 7:35 PM
Subject: RE: Re: [Electric Boats] RE: Hello group
Of course, 8 T-105 batteries are only rated for 10.5kWh (210Ah * 48V) even at $1000 (plus tax and shipping?) that's $0.095/Wh. and that works out to $1357 for a 14.25kWh battery back as listed in the first table, so you're not talking about a significant change in the economic analysis. If one spends $1500 for an 8 pack of T-105's, one is paying much too much ($0.143/Wh)
I used a rate of $0.105/Wh for FLA (a common price including tax andd shipping on the internet for those not near a golf cart shop)
I used a rate of $0.24/Wh for quality AGM (there are some that are cheaper, but not necessarily a better buy)
I used a rate of $0.425/Wh for LiFePO4 (I paid $0.41/Wh for my battery bank including shipping from China, import duties and BMS modules on every cell, I paid no sales tax)
These numbers are for broad comparisons only, weird little deals pop up from time to time and if you can get in on one, you're lucky. Also note that refining your capacities and costs to Watts or Watt Hours allows for realistic comparisons between apples, oranges, and watermelons (or different battery sizes and types)
What my post was alluding to is that there are fewer variables than most people think when considering different battery solutions. There are different goals; initial cost, maintenance, overall cost, lighter weight, smaller volume, greater range, faster charging, longer life, etc. These goals are a personal choice. But if you can prioritize your personal goals, the decision becomes more obvious. And yes, each battery type does have it's strong suit.
What I have found is that Lithium cells are preferred by every person that I know directly that has taken the plunge. Even my boss uses lithium cells for all of his ICE motorcycles, he's never had an electric or hybrid anything and he already talks about the lithium advantages (almost no self discharge and light weight) being worth the money.
---In electricboats@yahoogroups.com, <twowheelinguy@...> wrote:
Val,
I would ad one minor correction to Eric's calcs below. If you shop them hard you can get an eight pack of T-105 for a lot less than $1500. I just bought an eight pack of T-125s for about $1300, (without cores to trade in), and could have gotten T-105s for right at $1000 without cores. The golf cart guys get very competitive with these batteries and often settle for very low margins.
This difference will have a significant effect on the economic analysis. Economics will certainly be affected by the market you are in and you could wind up spending $1500 for an eight pack of T-105s depending where you buy them but you could also spend a lot more for LiIon as well and don't forget that expensive battery management system you better get to go with them to protect your signifcant investment.
I'm not promoting lead acid, even though it's what I have on my boat however, if you have a tight budget, they do work, are a very robust and mature technology, and deserve serious consideration as a battery option even if they are a bit lame when you compare their performance characteristics to Lithium. LiIon is definitely the technology of choice if you want top performance and have the money to spend but lead acid gives you good value with a lot less financial risk. There are sooo many variables when making comparisons between these technologies that I submit it is impossible to definitively say which one is actually the best value.
The biggest downside to FLA is outgassing and maintenance but if you're prepared to deal with these two items properly, I think it can be argued they still deliver a very competative value against any other technology availabe today.
Carter
From: "ewdysar@..." <ewdysar@...>
To: electricboats@yahoogroups.com
Sent: Monday, October 28, 2013 12:37 AM
Subject: [Electric Boats] RE: Hello group
To: electricboats@yahoogroups.com
Sent: Monday, October 28, 2013 12:37 AM
Subject: [Electric Boats] RE: Hello group
Hi Val,
....The prices still seem to be close enough, the lithium prices include passive BMS modules like the ones in my battery pack (less than $300 for 16 independent modules)
Here it is again:
With all the recent talk about FLA vs AGM vs LiFePO4, I think that this post
(#22145 from Sep 6, 2012), provides a fairly good comparison of battery banks
that can deliver the same amount of work. This is as close as I've been able to
get to an "apples to apples" comparison.
You might want to look at the pics in the group folder "Eric's Serenity".
http://groups.yahoo.com/group/electricboats/photos/album/1967401930/pic/list
The last pic is half of my 160Ah 48V traction bank. Lithium is not only
lighter, it is considerably smaller than either FLA or AGM. Weight and size
were high priority when I designed my system.
Fair winds,
Eric
Marina del Rey, CA
Here it is again:
With all the recent talk about FLA vs AGM vs LiFePO4, I think that this post
(#22145 from Sep 6, 2012), provides a fairly good comparison of battery banks
that can deliver the same amount of work. This is as close as I've been able to
get to an "apples to apples" comparison.
You might want to look at the pics in the group folder "Eric's Serenity".
http://groups.yahoo.com/group/electricboats/photos/album/1967401930/pic/list
The last pic is half of my 160Ah 48V traction bank. Lithium is not only
lighter, it is considerably smaller than either FLA or AGM. Weight and size
were high priority when I designed my system.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "Eric" <ewdysar@...> wrote:
>
> ---------------------------------------------
> This is what I posted on April 20 this year in post #21398
>
> Perhaps you mean something like this post that I made back in Jan 2012
(post#20750) and reposted in this month (post #21237). I directly compared the
weight and cost of the same usable capacity of different battery types.
Peukert's has already been factored in. You can read the whole post here
http://groups.yahoo.com/group/electricboats/message/21237
>
> You said "Additional concerns are that the estimated Puekert coefficients
might be 1.0 for Lithium, 1.1 for AGM, and 1.3 for Flooded. Estimated safe
discharge levels might be 80% for Lithium, 60% for AGM, and 50% for Flooded."
>
> In case you want to check my math, for my calcs I used a PE of 1.03 for Li (no
battery is 1.0), 1.1 for AGM and 1.25 for FLA. And you can see that I used
discharge levels of 80%, 70% and 60% respectively.
>
> -- Excerpt from post #21237 -----------------------------------
> Let's do the math for a battery pack that has a usable 2.5 hour range at 2500W
(6.25kWh used).
>
> FLA 14.25kWh to 60% DoD at 2500W = 2.5 hours = 633 lbs, cost about $1500
> AGM 10.5kWh to 70% DoD at 2500W = 2.5 hours = 520 lbs, cost about $2500
> LiFePO4 8.25kWh to 80% DoD at 2500W = 2.5 hours = 200 lbs, cost about $3500
>
> So now the lithiums are 2.3 times the cost of the T-105 FLAs but they are less
than 1/3 the weight for the same range at this load. So for most boaters, I
recommend AGMs as a good balance of price to range.
> ------------------------------------
>
> Another point to consider is that the math is dependent on the load. Because
of Peukert's Effect, higher load/capacity ratios favor Lithium, but lower
load/capacity ratios make AGM and flooded look better. Aiming for the same
amount of energy consumed, here's a similar chart at 4000W for 1.5 hours (6kWh
used)
>
> FLA 15.1kWh to 60% DoD at 4000W = 1.5 hours = 670 lbs, cost about $1600
> AGM 10.5kWh to 70% DoD at 4000W = 1.5 hours = 520 lbs, cost about $2550
> LiFePO4 8kWh to 80% DoD at 4000W = 1.5 hours = 200 lbs, cost about $3400
>
> Here's the another chart at 1500W for 4 hours (6kWh used)
>
> FLA 12.5kWh to 60% DoD at 1500W = 4 hours = 550 lbs, cost about $1350
> AGM 9.6kWh to 70% DoD at 1500W = 4 hours = 475 lbs, cost about $2350
> LiFePO4 7.8kWh to 80% DoD at 1500W = 4 hours = 195 lbs, cost about $3300
>
> Looking at 6kWh usable at both 4000W and 1500W, we can see that FLA cost 40%
of Li at 1500W and 47% of Li at 4000W, entirely because of Peukert's Effect. You
can see where this is trending.
>
> I hope that this helps.
>
> Fair winds,
> Eric
> Marina del Rey, CA
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