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hi! my name is ella. i have recently acquired a 72V karmann ghia conversion. the expected range was 20 miles, but recently the range is much less, like 5 miles. the batteries don't seem to be damaged. they were load tested at o'reillys. the batteries are only a few months old. i checked the water and specific gravity and all seems good. i understand they may be affected by cold, but even after charging (when they should be warm?) we are getting poor range. we are charging with a 5amp 72V schumacher charger. the batteries also often register at over 13V each.
the last drive (of 2 miles) was .5kwh per mile. is that normal?
any ideas? ways to diagnose the problem?
thank you!
 

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Hi
Looks like a nice car
Can you give us more data on the car and battery pack

Did the car EVER have 20 miles range? - most lead acid conversions never ever meet their owners expectations
 

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i have recently acquired a 72V karmann ghia conversion. the expected range was 20 miles...
If those are (for instance) 100 amp-hour (at 20 hours) batteries, the nominal capacity 7.2 kWh. To get 20 miles would imply 0.36 kWh/mile. That consumption would be optimistic, and there's no way the batteries would actually deliver their 20-hour rated capacity under the load of driving a car. So I wonder if it ever had a 20-mile range.

the last drive (of 2 miles) was .5kwh per mile. is that normal?
That seems reasonable to me for the level of technology in this car, but I don't have a good basis for comparison.

How are you measuring the consumption?
 

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I assume you are using six 12-volt batteries to get your 72 volt system. What is the brand/model/type of the batteries? Usually, 6 volt golf cart batteries survive vehicle use better than 12 volt batteries, even if they are called "deep cycle".


Even then, they only have 300-500 cycles in them, or a 1-2 year lifespan under daily usage.



As a point of comparison, I have a Chevy S-10 truck conversion (heavier than yours, but it had more batteries as well) which used 20 golf cart (6v) batteries in a 144v system. I was able to get 20-25 miles of range with new batteries, averaging around 350-500 watt/hours per mile. So the 0.5 kwh of consumption per mile sounds a bit high for a lighter vehicle (check for dragging brakes) but not outside the realm of possibility.


After a year of driving, my range was seriously reduced (10-15 miles), and after 2 to 2.5 years I had to replace the batteries (down to 10 miles of range). I would expect six 12 volt batteries to degrade faster than 20 golf cart batteries, as you are probably hitting them harder.


About 3 years ago I replaced the lead acid batteries with LiIon batteries from a wrecked Nissan leaf (which was an involved procedure, not recommended unless you want to learn a lot.) My battery pack got a lot lighter and has more usable capacity. When I first installed it, I drove 46 miles in one go, although I rarely drive more than 20-25 miles between charges in normal operation and try to be nice to the battery pack.


The LiIon battery pack is much better than the lead acid batteries, and after 3 years it is still going strong (there might be some capacity loss, but not enough for me to notice with my relatively short trips and lack of real instrumentation other than a volt meter and the BMS low cell alarm.) I know that it has at least 12-13 kWh of capacity left, as I regularly re-charge it that much after single drives.
 

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I have 120 volt lead-acid in my '78 VW Bug. I can just barely get 25 miles range, but never do that as it ruins the batteries to drain them so low. I keep a trip to 15 miles max. If you have gone 15 miles with your 72 volt system you may have hurt the batteries. Keep them on a charger at all times and see if the situation improves. I wouldn't go over 10 miles with your system. And watch the voltage; a drop of 10% in the resting voltage means you're in the danger zone. I killed a new set when I had to take a detour on the Interstate and drained them dead. It only takes once.
 

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You haven't said what batteries you have other than they are flooded. I suspect they are just cheap & common auto starting batteries. O'reillys doesn't have the equipment to test EV deep cycle batteries. Their "load" test only confirms a brief starting load. To test a deep cycle EV battery a load of 50 or 75 amps is applied and timed until the voltage drops to 10.5 volts. This is a specification of the battery and is usually around 50 minutes for a new battery.
Your pack is also only as good as the weakest battery.
 

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You haven't said what batteries you have other than they are flooded. I suspect they are just cheap & common auto starting batteries. O'reillys doesn't have the equipment to test EV deep cycle batteries. Their "load" test only confirms a brief starting load. To test a deep cycle EV battery a load of 50 or 75 amps is applied and timed until the voltage drops to 10.5 volts. This is a specification of the battery and is usually around 50 minutes for a new battery.
Your pack is also only as good as the weakest battery.
Good point.
 

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Discussion Starter #9
Hey, thanks everyone for the super helpful responses. sorry for my delay.
so I don't really know much about these batteries except they must be the cheap kind if they don't say how many amp hours are on them and they only cost $100 each, but they are deep cycle or so they say.

my hope is that one of these batteries are bad and I could just replace that one. but how do I find out? the load tester said they are good, and the local auto parts store must also be using a simple tester because it only takes them a minute to do it on their machine. is there a tester that I could buy that could tell me the answer?

I took it for a drive today for 5 miles and the voltage was down to 12.4v per battery. how close to dead is that? my battery charge indicator was flashing red, which I figured means clinically dead, so I don't really get what these indicators measure anyway. does anyone know?
 

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Oh, if that's the case maybe there is nothing really wrong with the batteries? if its just 6 12v batteries getting 70% drained (down to 12.4v) after a 2.5 kwh drive of 5 miles, then my capacity must be 7.5kwh which is to be expected? any thoughts of why the battery charge indicator shows to be so low?
am I doing my math right?
are my brakes dragging?
 

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If its just 6 12v batteries getting 70% drained
30% drained, I think he meant. At 12.4v there is still 70% capacity remaining.

However, when you drive the voltage might be sagging from the motor load, perhaps giving it he false impression that the batteries are nearly empty.

Also, don't just take the total voltage and divide it by the number of batteries. Measure each battery individually when they're discharged (half, full, whatever).

What you might see is: 12.5, 12.5, 11.8, 12.5, 12.5, 12.5

In which case, get rid of the bad battery. Heck, even if you can't replace it, one significantly worse battery might be worse than having only 5 batteries in series (provided you can adjust your new max and min voltages for charging and measuring).
 

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Yep, glass 70% full. I also agree with the poster above - the bank may read voltage X, but distribution among cells may be uneven, especially if some cells are dead or dying.

Seriously, find somebody to help you convert that rig to Nissan Leaf modules.
 

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hah! I thought the batteries would instantly equalize when I'm driving or right after, because I did just what you said and found no difference between the batteries. they were like within hundredth of a voltage apart from each other. well then ok! there is no one bad battery!

I'll have my husband check the brakes, I know they used to be loud and loose, so I'll see if that's part of the problem.

and I didn't think I could get on this forum without being encouraged to switch to Li-ion... any idea how I could find someone to help me with that? I'm still not sure its the right thing considering their absence cost. but it would be so nice to be able to make it to town and back, in the same car... (less than 20 mile round trip)

thanks for the help!
ella.
 

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I'm still not sure its the right thing considering their absence cost.
Salvaged cells will cost roughly the same as a new set of lead-acid batteries (for the same capacity) which you will have to replace soon since LA doesn't have a lot of cycles (300-500). The advantage being the reduction in weight / volume and still greater number of outstanding cycles (1000-2000). Reduction in volume and weight means you can pack more capacity into the vehicle, greatly increasing usable range.
 

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Salvaged cells will cost roughly the same as a new set of lead-acid batteries (for the same capacity) which you will have to replace soon since LA doesn't have a lot of cycles (300-500). The advantage being the reduction in weight / volume and still greater number of outstanding cycles (1000-2000). Reduction in volume and weight means you can pack more capacity into the vehicle, greatly increasing usable range.
It's actually better than that - because of the Peukert effect you only get about half of the actual capacity out of Lead Acids

So while 12 kWh of lithium give you 12 kWh - 12 kWh of Lead only give you 6 kWh of actual capacity
 

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It's actually better than that - because of the Peukert effect you only get about half of the actual capacity out of Lead Acids

So while 12 kWh of lithium give you 12 kWh - 12 kWh of Lead only give you 6 kWh of actual capacity
You only get half if you want to extend the life of the batteries indeed. And if we're being pedantic, you can't get 12kW from 12kW worth of Lithium cells - to extend their life we also need to slightly undercharge them, and we definitely can't discharge them down to 0.
 

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You only get half if you want to extend the life of the batteries indeed. And if we're being pedantic, you can't get 12kW from 12kW worth of Lithium cells - to extend their life we also need to slightly undercharge them, and we definitely can't discharge them down to 0.
I see your pedantic and raise you a pedantic.

Lithium (and I would imagine all batteries) are not capacity measured to zero volts.
 

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Salvaged cells will cost roughly the same as a new set of lead-acid batteries (for the same capacity) which you will have to replace soon since LA doesn't have a lot of cycles (300-500). The advantage being the reduction in weight / volume and still greater number of outstanding cycles (1000-2000). Reduction in volume and weight means you can pack more capacity into the vehicle, greatly increasing usable range.

I made this swap on my S-10. The Salvage Nissan Leaf cells where only about 1/4 of my upgrade cost. I also had to upgrade to a new charger that could be precisely programmed for the LiIon battery voltages and integrate with a BMS, and I had to buy the BMS. In addition, I had to package the Leaf cells to fit into the battery boxes that were designed for Lead Acid batteries previously. It took a LOT more time and effort than swapping out another set of Lead Acid golf cart batteries.


But in the end, it was worth it, as the truck is much more usable (better acceleration, almost double the working range, and the cells are still going strong 3 years later (I'd usually have to swap out Golf Cart batteries every 1.5-2 years).
 
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