# Which batteries?



## TheSGC (Nov 15, 2007)

I think you best bet would be the Trojan T1275. They are 12 volt 150 Ah, so twice the capacity of an Optima D31 and nearly the capacity of an 8 volt.

I was going to go with the T1275 for my EV but I decided to get the Walmart MAXX29 because they were cheap and their warranty allows me to abuse them because everyone says you kill your first pack.


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## bblocher (Jul 30, 2008)

I did look at those and I think I have the room but they will put me over my GVWR. 

It seems like I either need to go lithium or go over my weight limits to achieve my range? I guess I need to try to find a way to weigh my car again and see what's the most lead I could cram into it safely and go from there on which road I should take.

I just hate to buy something, whatever it is, and find out I'm a few miles short of what I need 

I also just thought that in order to get those batteries to fit they need to not be orientation sensitive


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## Coley (Jul 26, 2007)

Batteries that have a high cold cranking rating aren't really very good for EVs.

Trojan 8 volts are not bad, but the 6 volts are better for the mileage you are looking for, even with the extra weight.

But that is just my opine....


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## etischer (Jun 16, 2008)

I'm using the D34M (55Ah) for my conversion (312v) and targeting 20 miles range. 

I think the D31 (75Ah) is going to be too small, especially if you are only using half the batteries and expecting 35 miles range.


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## dimitri (May 16, 2008)

There is no way you can make 35 miles on 75Ah batteries. You can't even make it on 150Ah 12V batteries, because of Puekert losses. If I learned anything from my own experience its that 12V batteries are just not good enough to get any decent range. I would consider 8V Golf Cart batts from US or Trojan and lower pack to 120V to fit 15 of them in the car. The biggest issue with 12V batts is amp draw, that's whats killing them. Sure they work great for first 20-25 miles, but then capacity quickly starts to go down.

Look at the numbers, US batt and Trojan 12V is rated 75 amp for 75 minutes. You will probably draw 120-150 amp on average commute, so even not counting Puekert, you will drain the battery in 30-35 minutes. If you add 10-20% of coasting, your pack will last about 45 minutes of driving, lets assume 40 mph on average, you get 30 miles to complete 100% DoD. Obviously I make lots of assumtions, but my 3 months of EV use pretty much support these numbers.

Oh yea, when temperature drops, your range drops with it, so even here in Florida at 45F in the morning my range is shot, I can't even make it back home on single charge.

At this point one of my batteries has failed already, I just replaced it last night.

Sorry for bad news, but I hope someone can learn on my mistakes and not on their own.


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## bblocher (Jul 30, 2008)

The 75 Optimas have an amazing peukert's expontent. I did the math and could get almost 60 Ah out of them over 45 minutes discharge time. I wasn't sure how many amps I'll pull to get to work but others are saying these batteries have gone downhill now anyway compared to what they used to be and as you mentioned I most likely need a lot more Ah for my commute.

With my needed range, limited space and weight I can carry I think I'm going with lithium. I'm thinking of the TS LFP 160 cells (45 cells for 144v nominal). If these things hold up it should make the build perfect. I'll be lighter or close to the original weight and based off what I've heard from some other lithium users I should have at least 100 mile range @ 55mph.
I'm waiting for my quote on this setup and after I get over that shock I'll order them. I guess it's 5+ week wait on these from Elite so even after I order them it's going to suck sitting around waiting for them to arrive


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## RKM (Jun 9, 2008)

bblocher said:


> The 75 Optimas have an amazing peukert's expontent. I did the math and could get almost 60 Ah out of them over 45 minutes discharge time. I wasn't sure how many amps I'll pull to get to work but others are saying these batteries have gone downhill now anyway compared to what they used to be and as you mentioned I most likely need a lot more Ah for my commute.
> 
> With my needed range, limited space and weight I can carry I think I'm going with lithium. I'm thinking of the TS LFP 160 cells (45 cells for 144v nominal). If these things hold up it should make the build perfect. I'll be lighter or close to the original weight and based off what I've heard from some other lithium users I should have at least 100 mile range @ 55mph.
> I'm waiting for my quote on this setup and after I get over that shock I'll order them. I guess it's 5+ week wait on these from Elite so even after I order them it's going to suck sitting around waiting for them to arrive


Brian,

I'm wanting to use 160 Ah LiFePO4 as well. I've noticed that some suppliers want to use 48 cells to create a 144V pack (allowing only 3V per cell versus the nominal 3.2V) rather than 45 cells. 

I've been hoping to avoid TS if possible because of their past unethical deal with memebers of the EV community. I haven't found an alternate supplier, so may go with TS. Has their reputation improved?

TS used to offer a significant discount for volume. Is this still the case? Are you looking for others to join in a purchase?

Thanks.

Rob


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## bblocher (Jul 30, 2008)

RKM said:


> Brian,
> 
> I'm wanting to use 160 Ah LiFePO4 as well. I've noticed that some suppliers want to use 48 cells to create a 144V pack (allowing only 3V per cell versus the nominal 3.2V) rather than 45 cells.
> 
> ...


Yeah I've seen a few other cells with higher and lower nominal voltages. I saw a guys setup that was using the TS cells and he also used 45 cells for the 144v nominal.

I haven't heard anything bad lately about TS. It's hard to find a ton of people using them but I've heard maybe a half a dozen people very satisfied with their builds after going with the TS lithium. I think the most I've heard of so far is 300+ cycles on them but that they were as strong as day one at that point.

You can get the discounts in volume, but I'm pretty sure I'll just be going with Elite Power Solutions for my order. I'm still waiting on my quote for the 160Ah batteries but online they show the 60Ah for $102. Normal price is $156 so that's a 35% discount without worrying about group buys. They are basically ordering once a month or something to get enough orders in for the discount. I've heard a couple that have ordered from them are happy. So hard to feel comfortable with anybody when you're talking about that kind of money


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## bblocher (Jul 30, 2008)

I got the quote from Elite Power Solutions. The percentage is less (17.5%) but I realized that elite is charging (on their website) $1.70/Ah regardless of cell size. Everspring has a non linear pricing curve for cells below 90Ah so it makes comparison hard.

So on to the quote. $1.65/Ah from Elite on the 160Ah cells. List on these cells is $320 from Everspring. If I were to order from them I would only get 12% discount from the 7200Ah order.

The charger and BMS is already listed on their site and can be ordered without directly contacting them. The BMS system doesn't equalize though so you'll still have to build/buy that functionality. I've seen some burn off designs that I'll probably go with first just to get things up and running and then either build or buy a system that will transfer the energy instead for effiiciency. The BMS and charger work together to protect the cells from over charge. Some could probably build a much better setup in a short amount of time but for me it will take learning some new things so I'll do it over time. This setup, however, is the recommended setup from TS so while not optimum for battery performance it's good enough to keep the batteries alive


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## TexasCotton (Sep 18, 2008)

dimitri said:


> There is no way you can make 35 miles on 75Ah batteries. You can't even make it on 150Ah 12V batteries, because of Puekert losses. If I learned anything from my own experience its that 12V batteries are just not good enough to get any decent range. I would consider 8V Golf Cart batts from US or Trojan and lower pack to 120V to fit 15 of them in the car. The biggest issue with 12V batts is amp draw, that's whats killing them. Sure they work great for first 20-25 miles, but then capacity quickly starts to go down.
> 
> Look at the numbers, US batt and Trojan 12V is rated 75 amp for 75 minutes. You will probably draw 120-150 amp on average commute, so even not counting Puekert, you will drain the battery in 30-35 minutes. If you add 10-20% of coasting, your pack will last about 45 minutes of driving, lets assume 40 mph on average, you get 30 miles to complete 100% DoD. Obviously I make lots of assumtions, but my 3 months of EV use pretty much support these numbers.
> 
> ...


Nice post and I love SF


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## bblocher (Jul 30, 2008)

Well I'm commited now. I've made payment for the lithium cells. I'll keep everyone posted on my experience with Elite and the TS cells themselves.

Timelines:
From my understanding they had already placed an order for this month but it was recent and they are going to try to get my order added to that order. If so I think the wait is 5 weeks after they order them before they receive the order. If not then I'm guessing my order goes out the next month which means I'm looking at 2+ months out before actually receiving them...ugh

Wish me luck to return with all good news


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## dimitri (May 16, 2008)

Brian,

good to see that you made up your mind, good luck with your order, seems reasonably priced for US based supplier, IMHO.

I am concerned with their charger/BMS functionality. Are you saying that first battery in the pack to get full charge will shut off the charger and leave the rest of the pack as is? That doesn't sound like a good BMS at all.

So, you are planning to install those voltage clamper modules on each cell to accomplish pack balancing, right? That will still trip BMS and shut off the charger when first cell reports full charge, isn't it?

If you have voltage clampers protecting each cell from overcharge, then what is the point of their BMS? The charger should just stop when it reaches full pack voltage. I guess BMS can be used to monitor discharge, although it does not actively enforce low voltage protection, you will just keep an eye on the screen and not let it go too low.

Let us know if you find a good source for voltage clampers, there was a poster here offering them for $20 from China. Here is a page where Victor from Metricmind was making them himself for his EV, that sounds like a fun project.


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## bblocher (Jul 30, 2008)

dimitri said:


> I am concerned with their charger/BMS functionality. Are you saying that first battery in the pack to get full charge will shut off the charger and leave the rest of the pack as is? That doesn't sound like a good BMS at all.
> 
> So, you are planning to install those voltage clamper modules on each cell to accomplish pack balancing, right? That will still trip BMS and shut off the charger when first cell reports full charge, isn't it?
> 
> If you have voltage clampers protecting each cell from overcharge, then what is the point of their BMS? The charger should just stop when it reaches full pack voltage. I guess BMS can be used to monitor discharge, although it does not actively enforce low voltage protection, you will just keep an eye on the screen and not let it go too low.


You are correct on all your assumptions. The BMS is pretty sub par for the cost but to get the 1 year warranty I'm going with everything recommended at this point.

It's more of a monitoring system than management other than the high voltage cutoff. It will find the first cell to reach the maximum desired voltage and shutoff. I'm not sure if it's configurable or if it just defaults to shutoff at say 4.0v or something. The charger itself will shutoff at full pack voltage unless the BMS steps in and says to do it earlier. So if you had a way to balance the cells quickly then each charge would be gaurenteed to be full.

The simpliest idea I saw that I was going to try first was using zener diodes and a resistor that will start to bypass the current when the cell is at 3.6 volts. This will slow down the charging process on these cells early allowing for lower cells to catch up. It won't rebalance in a single charge as it will be a slow burn off rate but I'm hoping enough to keep up with unbalance rate. I think I have some trial and error coming up and hopefully I can find a zener that can handle however many watts I need to burn.

You are correct on the low voltage detection as well. It will throw up an indicator on the screen warning you but you have to take action. You'd need an inline circuit that could

Eventually I'll end up with a full blown system to make these batteries safe for any driver but to start off with I'll just have to be careful.


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