[tomsbradford]

Just bought a 72 Volt 1974 Bug for $1,500. It has a popular EV conversion kit installed. It’s a bit of a project car with a few rust spots here and there and it desperately needs some brake work. The batteries are in a failing or failed condition.
I’ve done some reading through the achieved posts and am now at a level of a little more knowledgeable and dangerous. It appears that 99% of my questions have already been asked and answered. At the risk of asking questions already answered, and since I need to replace the batteries soon, I am requesting a kick start in the right direction.

Let me ask it this way: If you had the following driving conditions and components, what batteries would you buy?

Driving Conditions: Five miles from the house to the commuter train (ten miles round trip). No charger at the train station. Speed limit is 45 MPH. Hilly terrain. One stop sign.
Components:
- 1974 VW Beetle
- Adapter Plate and Shaft Coupler - Motor to transmission(clutch-less)
- Series Motor 40 HP 6.7" dia. X 12.28" long
- 0-5k (pb5)Throttle Box
- Contactor- Kilovac EV200 (2000 amp rupture 200 amp continuous)
- 50-150 VDC Volt Meter
- 0-500 Amp Meter
- 50mv - 500 Amp Shunt
- Fuse - 400 amp slow blow
- Battery Charger - 5-10 amp (adjustable voltage 12-72 VDC)
- 12 vdc Float Charger (for accessory battery)
- Alltrax 7245 Controller
- Six 12-volt Marine 100AH Deep Cycle Lead Acid batteries.

For the purposes of deciding on high or low maintenance solutions, assume that my time is worth $20/hr (debatable) . Did I leave out any important variables?
My calculations and gut feeling led me to this: Six (6) AGM 12V 100AH batteries.
BTW, I am very impressed with how effective this forum is in sharing information on new and converted EVs. I can’t imagine the number of hours a person, unfamiliar with EV technology, would have to expend climbing the initial steep learning curve. Thanks to the pioneers in this field that took time to document their experiences.

 

[major]

Just bought a 72 Volt 1974 Bug for $1,500. It has a popular EV conversion kit installed. It’s a bit of a project car with a few rust spots here and there and it desperately needs some brake work. The batteries are in a failing or failed condition.
I’ve done some reading through the achieved posts and am now at a level of a little more knowledgeable and dangerous. It appears that 99% of my questions have already been asked and answered. At the risk of asking questions already answered, and since I need to replace the batteries soon, I am requesting a kick start in the right direction.

Let me ask it this way: If you had the following driving conditions and components, what batteries would you buy?

Driving Conditions: Five miles from the house to the commuter train (ten miles round trip). No charger at the train station. Speed limit is 45 MPH. Hilly terrain. One stop sign.
Components:
- 1974 VW Beetle
- Adapter Plate and Shaft Coupler - Motor to transmission(clutch-less)
- Series Motor 40 HP 6.7" dia. X 12.28" long
- 0-5k (pb5)Throttle Box
- Contactor- Kilovac EV200 (2000 amp rupture 200 amp continuous)
- 50-150 VDC Volt Meter
- 0-500 Amp Meter
- 50mv - 500 Amp Shunt
- Fuse - 400 amp slow blow
- Battery Charger - 5-10 amp (adjustable voltage 12-72 VDC)
- 12 vdc Float Charger (for accessory battery)
- Alltrax 7245 Controller
- Six 12-volt Marine 100AH Deep Cycle Lead Acid batteries.

For the purposes of deciding on high or low maintenance solutions, assume that my time is worth $20/hr (debatable) . Did I leave out any important variables?
My calculations and gut feeling led me to this: Six (6) AGM 12V 100AH batteries.
BTW, I am very impressed with how effective this forum is in sharing information on new and converted EVs. I can’t imagine the number of hours a person, unfamiliar with EV technology, would have to expend climbing the initial steep learning curve. Thanks to the pioneers in this field that took time to document their experiences.

Hi toms,

Welcome to our forum. From what I read, you don't really know if it runs or how well it will run. Correct? Got any photos?

Regarding new batteries: One school of thought is that newbies will kill their first set, so go for cheap ones. With cheap batteries, that is kind of a self fulfilling prophecy. But using six 12V Pb-Acids will give you marginal range. See this thread and note the actual energy from the battery set. http://www.diyelectriccar.com/forums/showthread.php?t=78826 And those were rated 30% higher than what you propose. You have to hope you could use about 300 Wh/mile to make your 10 mile round trip. That's not too far fetched. But as the batteries age, or in cold weather, you'll likely come up short.

So consider Lithium Batteries. Filling the same space as the Pb batteries consumed, you'd at least double your range and increase battery life by a factor of 3 or more. Of course it will be more expensive. And you'll need to learn how to install and use the Lithium batteries.

Let's see who else chimes in with advice

major

 

[tomsbradford]

The car does run, but I haven't tried to take it farther than the driveway because of bad brakes. One battery will not go above 10.5V. The others seem OK, but I need to check them with a hydrometer. Two of the batteries are smaller than the others. Weird. So, I could go super cheap Pb and let that be the cost of learning. I wouldn't want to kill the expensive Lithiums. Are Lithiums more apt to survive a noob? Tried to upload a photo. Let's see if it works. It's titled Big Orange.

 

[elevatorguy]

It really comes down to budget.
The lead batteries will weigh about 200 pounds more than Lithium of the same amp hour.
The down side of Lithium is you will need a new charger, perhaps a BMS as well.
The difference in the battery cost can be recovered with longer life of the Lithium.

I think for the short distance, cost, and the learning curve, it may be beneficial to go with the lead. There are some unknowns, like how tall are the hills, temperature etc.

 

[zeva]

Despite the higher up-front cost, in the long run lithiums (LiFePO4) are actually more economical than lead acid because their cycle life is so much higher. Buy cheap leads and you might have to replace them after 2 years. Lithiums should last you 10. Also note that due to Peukerts Effect, in EVs lead acids can typically only give half their amp-hour capacity, which levels the scales a lot when doing cost-per-amp-hour calcs.

But lithiums are very prone to damage from over-charging or over-discharging - more so than lead - so you need to run a BMS. They're not difficult to install and shouldn't cost much. A few hundred maybe for a 72V pack.

I'm going to estimate a VW Bug will use about 300wh/ml of energy, so in theory you could do 10 miles with a tiny 3kWh pack (42Ah at 72V). But I'd recommend at least 60Ah cells to avoid regular very deep discharging (which shortens cycle life significantly), and a bit more power. And in practice that'd offer slightly more range than 100Ah lead acids. So 24x 3.2V 60Ah LiFePO4 cells makes a 4.3kWh pack, roughly $2K inc BMS, ~60kg weight.

 

[tomsbradford]

Thank so much. I'll chew on this.

 

[PStechPaul]

You could replace the lead batteries with six of these from Walmart, and they are 12V 100Ah, so you would have 7200 Wh (more like 3600 Wh effectively) for less than $500:
http://www.walmart.com/ip/EverStart-Group-Size-24DC-Marine-Battery/20531540

You should be able to make your 10 mile round trip with these batteries, but within a year they may deteriorate to where it could be marginal. But then you could probably get $50-$100 scrap value or even sell them to someone with less severe demand for $20 each. This would be a quick way to get the vehicle on the road. I agree that lithium would be much preferred, but will cost at least $2000 especially if you add shipping cost and BMS and charger.

You can probably do better than 300 Wh/m if you mostly drive slow and accelerate gingerly. If you average 40 MPH on fairly flat roads, and if your vehicle is 700 kg (1500 lb), my calculator shows only 120 Wh/m, based on a 1% average slope.
http://enginuitysystems.com/EVCalculator.htm

You will be using about 6 kW which is 83A and the batteries have an effective capacity of 53 Ah so you can go for 0.6 hours or 24 miles. This may be optimistic, but not unrealistic. I say better lead than dead!

 

[octagondd]

Thank so much. I'll chew on this.

Yes, up front money is tough to swallow, but when you consider the long run, you would end up buying those LA cells 4-5 more times and I know they ain't cheap either. You would need a new charger, although there are lower priced chargers that will do the job. I am thinking of the Elcon in particular. You also have to decide if you want a BMS or not. You could add a few more cells for more range and run without a BMS, or you could buy small cells and use more of the capacity since it will have a smaller range. Obviously there is a very long debate about that here in the forums, but it is up to you to make that judgement call based on your needs.

I am a non-BMS guy, but if this situation was me, I would think long and hard about using the 60AH cells and a BMS as someone above proposed. If 80 AH cells were available then it would be a no brainer to use those and no BMS, but essentially 100AH is the next level up in LiFePo4.

 

[tomsbradford]

I love it. Nothing like dissension to bring out important key arguements. Sometimes these decisions are based more on art than science. Who knows what the future holds for the cost of Lithium batteries in the next year or two. I've heard that the price is dropping and will continue in that trend as the technology matures. Also, this discussion is bringing to mind that I may not want to drive a VW bug for five more years, when I can possibly "upgrade" to a mass produced EV in two years.

Many many thanks for spurring thought on this subject.

 

[poprock]

Hi Tom, your alltrax 7245 will handle 7x12v . Mine is set at factory 90v max and the extra battery gives a benefit in pickup. The general tone of advice so far seems to be to stick with lead. Probably good advice if you are already considering your next EV

 

[MN Driver]

Wait 90/7=12.86 volts per 12v battery
What voltage are your lead acids right off a charge? Usually its a bit higher than that.

I understand with lithium 90v / 25 cells is 3.6v per cell. 90/26=3.46v per cell. So if you wait just a little bit from being off charge 26 cells is possible.

I'm thinking 13 6 volts batteries might be okay 6.92 volts per battery seems doable.

 

[poprock]

Wait 90/7=12.86 volts per 12v battery
What voltage are your lead acids right off a charge? Usually its a bit higher than that.

I understand with lithium 90v / 25 cells is 3.6v per cell. 90/26=3.46v per cell. So if you wait just a little bit from being off charge 26 cells is possible.

I'm thinking 13 6 volts batteries might be okay 6.92 volts per battery seems doable.

Yes, approx. 92.6 . Controller will not kick in until I leave headlights on for 2-3 min. DC-DC drops voltage . DC-DC is not through ignition at the moment , but will be one day.

 

[BentMike]

Despite the higher up-front cost, in the long run lithiums (LiFePO4)
But lithiums are very prone to damage from over-charging or over-discharging -

Same charger...One extra cell = no over discharge problems, correct? Just never put a too large a voltage across the pack. Then bottom balance and cost of BMS goes away.

I am willing to make a discharge and balance setup. But, I don't have to take it with me so it won't fail on the road. I plan to use a JLD404 for shut down and as a dashboard monitor.


I am leaning this way. Is this wrong headed?

 

[zeva]

To BMS or not to BMS is a contentious issue which has been discussed at length elsewhere so we needn't debate it here, but FWIW I'm in the BMS camp because I've seen too many dead lithium cells over the years, and am reasonably vocal on the subject because I believe it is a safety concern. Under normal operation the BMS shouldn't have to do anything, it's only when something goes wrong that it steps in to protect the batteries - like the last line of defence, or an insurance policy that adds about 10% to the pack cost.

In fact I saw a poignant example just a few weeks ago where someone had a faulty charger putting out too high a voltage. They had no BMS to intervene, and $10K worth of cells went up in flames (literally).

 

[BentMike]

Thank you zeva, I sent a PM if you have the time.

 

[tomsbradford]

Brakes are fixed, except for some minor adjustments. Maiden voyage was fun. Seemed to run ok at 80V on the rolling hills at 35 to 50 MPH. Question: how hot should the motor get? At the opposite end from the transmission, the metal band with vent holes is too hot to keep my hand on for longer than a second - maybe 145F.