# Deep cycle Question? Bang for buck.



## Ziggythewiz (May 16, 2010)

Bang for buck and lead don't go together well. Just get 100ah lithiums for around $5000. Lead will cost you $2000-$4000 anyway and last .2-.5 times as long, while slowing you down tons.

60 mph is not difficult with almost any battery type.


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## piotrsko (Dec 9, 2007)

figured I'd get that typical lithium answer. Yeah they are better, but sometimes you just gotta go with cheap. then for lithium you gotta get the special $$$ charger, and the whole war about whether or not to do more money for a BMS, all to avoid the fiery battery syndrome.

I have $1725 in my 120v pack of trojan SSC 225's, figure another $1200 to get to 196V which puts me slightly over 1000 lbs and 24 KWH. If you are going to go floodies, then you want ones that DO NOT say CCA ratings because those are not true deep cycle. You also want batteries that are heavier than the typical starter. if two batteries are the same size go with the heavier one. Try trojan, Exide, optima, some have had success with walmart max 29.

BTW couple of people here claim 5 years, couple of thousand cycles on FLA. Jury still out on life of lithium not to mention Chinese battery manufacturers and delivery.

Your conversion, do your own thing. We will now return you to the regularly scheduled debate.


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## Ziggythewiz (May 16, 2010)

piotrsko said:


> figured I'd get that typical lithium answer. Yeah they are better, but sometimes you just gotta go with cheap. then for lithium you gotta get the special $$$ charger, and the whole war about whether or not to do more money for a BMS, all to avoid the fiery battery syndrome.


I'd love to have lithium, but cheaped out and have been quite literally limping by for some time. I even cheaped out on the lead. If you want extreme performance, it's rediculous to even consider lead. The only reason zombie did it was because of the timing. Since then lead has gone up significantly, lithium has come down drastically, and lithium performance has greatly improved. Lead can't really improve, it hasn't changed much in decades.

When I do go lithium, I won't waste money on a BMS, just half bridge it and don't run on the edges.


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## Roy Von Rogers (Mar 21, 2009)

I have a EV that came with lead, even installed an extra battery to get better temporary performance.

When those go down, no way in hell would I even consider lead for a replacement.

If you cant afford to put the most important item in an EV, a lithium battery pack, whats the point of building one.


Roy


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## mechman600 (Oct 16, 2010)

Ziggythewiz said:


> I won't waste money on a BMS, just half bridge it and don't run on the edges.


I hope I'm not hacking this thread too badly, but what does it mean to "half bridge" it? Either a link or brief explanation. I tried a search but didn't get anywhere.

Thanks!


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## skooler (Mar 26, 2011)

mechman600 said:


> I hope I'm not hacking this thread too badly, but what does it mean to "half bridge" it? Either a link or brief explanation. I tried a search but didn't get anywhere.
> 
> Thanks!


Hi mechman,

Its a way of monitoring cells without a BMS.

Simply split the pack in half and measure the voltage accross both halfs (usually with a guage(s) on the dash)

Both halves should read the same, if not then the cells are at different voltages.

Not ideal but a good compromise.

Cheers

Mike


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## Duncan (Dec 8, 2008)

skooler said:


> Hi mechman,
> 
> Its a way of monitoring cells without a BMS.
> 
> ...


Hi Skooler

That description kind of misses the point,

If you monitor your voltage you will see it fluctuating all over the shop as you change loads and charge state.

Splitting into two gauges doesn't really help

The trick is to monitor - *the difference* - between each half of the pack

This removes the main variables and can be a very sensitive measurement -


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## skooler (Mar 26, 2011)

Duncan said:


> Hi Skooler
> 
> That description kind of misses the point,
> 
> ...


Hi Duncan,

I see your point!

I wasn't thinking about the loads!

Thanks for clarifying 

Cheers,

Mike


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## tomofreno (Mar 3, 2009)

CamaroGuy said:


> ok now this may have been answered but i am having trouble finding it.
> 
> I have done some measurements on my potential donor car i have room for somewhere between 14 and 16 batteries depending on the size.
> 
> ...


 You could use 16 Trojan 1275. They are 150Ah 20 hr rate, and about half that at 150A. This graph shows capacity in Ah as a function of discharge current for several different lead acid batteries:
View attachment Peukert graph.pdf

The 6V flooded are the best for capacity, but require the most space and weight. The lifetime you get from them will depend heavily on how you use them. One extreme is Roland on EVDL who has gotten over 8 years. He drives at low speeds for short distances in town, and only does low partial discharges - less than 50%. The other extreme is running high discharge currents and regularly discharging to 20% SOC. People report lifetimes in this case of more like 3 years or less - and that is for deep cycle "golf cart" batteries. Others will fare worse. The AGM do not require watering but are much lower capacity and generally more expensive. US Battery has a similar line of golf cart batteries, 6, 8, and 12V.

I would roughly guess you will use around 30kW +/-20% at 60 mph. If your pack sags to 175V, you would pull about 170A discharge current at 60 mph, giving you around 20 mile range at 80% DoD. (Edit: At 25 F and unheated batteries you would get about half that, or 10 miles. Lead acid capacity drops considerably with temperature) You might want to review the battery section of the wiki on this site for more info.
Disclaimer: I use LiFePO4 myself.


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## Sunking (Aug 10, 2009)

piotrsko said:


> BTW couple of people here claim 5 years, couple of thousand cycles on FLA.


You need to take that with a grain of salt. I have worked with lead acid batteries for 33 years now in the Telecom sector, and th elast 10 years in the solar industry.

In short, cycle life is directly proportional to Depth of Discharge. Additionally number of cycles varies wildly among manufactures due to quality.

5 years is a bit of a stretch of the truth in most cases. The best deep cycle battery made is is the Rolls/Surrette Renewable Energy 5000 Series. If DOD is limited to 20%, then they claim up to 5000 cycles. If you go to 50% only 3000 cycles.

However almost none of the other manufactures can make this claim. Trojan is one of the worse and you will be lucky to get 500 cycles @ 50% DOD. Typical is 300 to 500 cycles @ 50% DOD.

However for an EV, you don't really want a true deep cycle flooded lead acid battery because the internal resistance is fairly high, and they cannot deliver high amounts of current without the voltage collapsing. If you are going to use lead acid technology go with AGM as they have very low internal resistance. For AGM Crown Battery is the best IMHO as you should get about 1000 cycles to 50% DOD


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## piotrsko (Dec 9, 2007)

+1. great answer Tom. Only problem with the 1275's was the huge cost difference which would have made the 120v pack $2250 and more on the 16 pack. They are bigger, heavier and go over 1200 lbs which exceeds the load carrying rate of my truck.

At this rate, lithium then actually becomes competitive with lead if you can score cheap cells for about $1.10 ah delivered. it will still be more expensive, BUT......

And contrary to this stand, at some point after the 500 cycles I may buy lithium, if the promised price comes down. In the mean time I will squeak along with the FLA. BTW FWIW I couldn't get an AGM manufacturer to give me consistent advice on battery selection, and they were hesitant to warranty the install.


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## tomofreno (Mar 3, 2009)

piotrsko said:


> +1. great answer Tom. Only problem with the 1275's was the huge cost difference which would have made the 120v pack $2250 and more on the 16 pack. They are bigger, heavier and go over 1200 lbs which exceeds the load carrying rate of my truck.
> 
> At this rate, lithium then actually becomes competitive with lead if you can score cheap cells for about $1.10 ah delivered. it will still be more expensive, BUT......
> 
> And contrary to this stand, at some point after the 500 cycles I may buy lithium, if the promised price comes down. In the mean time I will squeak along with the FLA. BTW FWIW I couldn't get an AGM manufacturer to give me consistent advice on battery selection, and they were hesitant to warranty the install.


 Yeah, I would go with LiFePO4 myself, but some just want something to experiment around with and change out later, don't want to spring for the higher cost, or are waiting to see how long LiFePO4 last.

To the OP: I wouldn't use solar storage batteries, as another poster suggested. They are not designed for the high discharge currents EV's use. That advice comes from both Mike Brown's book Convert It, and Bob Brant's book Build Your Own Electric Vehicle. They both say to use traction batteries, commonly referred to as golf cart batteries. For example Brown: "Not all deep cycle batteries are appropriate. Marine batteries or standby power batteries are not intended to handle the occasional brief current peaks a car requires. They will not provide as much range or cycle life as a true traction battery." 

You might poke around on EVDL. I think they have a section on batteries there too, and many regulars there with decades of experience with lead acid batteries in EV's such as Roland and Lee Hart. I have heard that the quality of Trojan batteries isn't what it used to be, so maybe US Battery is better now, dunno. Odessey and Optimus are both supposed to be good for high power, but again relatively low capacity (A couple Odessey are in the graph I attached to my earlier post). According to Brant the best bang for your buck is Trojan 6V 125's but that advice was given years ago. Brown prefers US Battery - their 12V is the 1450 I think. 

You won't get more than hundreds of cycles out of any lead acid battery if you pull hundreds of amps and regularly discharge to 20% SOC. Do your homework, read some of these references, and search/post on EVDL.


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