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Old 02-09-2014, 03:05 PM   #1
Olman
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Default Question for JohnnieB

Or any other battery guru that wants to answer.

My cart has 8 230ah 6 volt batteries that have been broken in properly. I took it for a 6 mile cruise today (45 degrees). Trip was on the hard roads mostly flat. Total weight riding on the cart was about 370 lbs with me, the boss and the flop eared dawg. My at rest voltage after full charge starting out was 52.7 volts. At rest voltage 1 hour after I got back was 51.2.

Based on these numbers, what do you estimate my range would be given the same conditions at 70 percent and 50 percent SOC? How much difference will it make if the outside temp was 80 degrees?

Thanks in advance for the info.

Dave
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Old 02-09-2014, 08:54 PM   #2
JohnnieB
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Default Re: Question for JohnnieB

At 45°F, your batteries only have about 75% of the AH they have at 80°F, so they are about 175AH batteries rather than 230AH batteries and your range will be about 25% less than it would be in 80° weather.

The battery voltages are off the tops of the charts, but both the starts and stop are off the charts, so I subtracted stop from start and got 1.5V and if I adjust the start voltage to 100% on the charts, the stop comes out at 69%

Adjusting battery AH for 45°, a discharge to 50% SoC would have a range of about 16 miles and about 20 mile in 80° weather.

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I'm not real comfortable with those numbers because the Start and Stop voltages are exceptionally high.

What brand/model batteries?
Can you verify the accuracy of the DVM you measured the voltage with?

If the batteries have rested for about 12 hours, the At-Rest voltage at the start of the trip should be in the 50.9V to 51.2V range depending on battery brand.
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Old 02-09-2014, 09:24 PM   #3
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Thumbs up Re: Question for JohnnieB

JohnnieB, I'm an idiot. The batteries were only off the tender about 10 minutes before I started. Forgot about your 12 hour rule. Also at rest voltage was taken only one hour after cruise. The batteries are Super Start (made by Penn) GC110DT rated at 230 ah. I got them from O'Reilly Auto Parts. Believe it or not, I paid $68.99 each plus tax for the first 6. When I got the other 2 a year later they charged me $89.99 each but waived the $18 each core charge.

If you will indulge me, I will redo the test waiting 12 hours on each end before reading voltages. I am using ScottyB's DVM and it is right on the money compared to my handheld meters.

Thank you for your time sir and as always you da man! I am very envious of your electrical knowledge.
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Old 02-10-2014, 07:20 AM   #4
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Default Re: Question for JohnnieB

What I'm doing equates to calculating an automobile's gas mileage and using it to estimate how far it will go on a half tank of gas. So the more accurate the amount of electrical energy used and the distance traveled are, the more accurate the estimate is likely to be.

Only waiting 8 hours after the charger is disconnected will suffice, but 12 hours will be more accurate.
On the other hand, waiting an hour after the cruise before measuring the Stop voltage is sufficient. In fact, I only wait 30 minutes. I've measured my pack voltage at various intervals after stopping and found that nearly all the voltage recovery occurs in the first 30 minutes and not much more voltage increase is seen during the last half hour.

However, a 51.2V reading an hour after the cart has been on a 6 mile run is higher than expected.
I don't have a Voltage vs SoC chart specifically for East Penn batteries, but from what I can find on-line, it appears that Trojan has the lowest fully charged voltage while US Battery has the highest and I suspect East Penn will fall someplace between the two extremes, like my Exide batteries do.

Attached are charts for Trojan and US Battery. Note that the Volts per 2V cell are within 0.001V other than at 100%, so it seems logical to expect the voltage of a 48V pack an hour after being driven 6 miles to be somewhere on those charts, rather than at the top of the highest one.

I've never been able to get a straight answer from the battery manufacturers, but I believe terminal voltage increases when the batteries are cold. This is because the voltage is directly related to the Specific Gravity of the electrolyte and the SG reads higher when it is cold, so hydrometer readings have to be adjusted for the temperature.

Of course, the temperature should effect both the Start and Stop voltage about the same, so taking the difference between the two and subtracting it from the 100% voltage on the charts, ought to give a fairly reasonable estimate of the energy used.

-------
If possible, define the distance traveled to 1/10 mile and the longer the distance traveled, the better.

Due to rounding, 6 miles could be anywhere between 5.5 and 6.4 or only about an 85% accuracy.
Attached Images
File Type: jpg SoC vs Voltage - Trojan Battery.JPG (56.9 KB, 0 views)
File Type: jpg SoC vs Voltage - US Battery.JPG (58.1 KB, 0 views)
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Old 02-12-2014, 09:56 AM   #5
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Default Re: Question for JohnnieB

Johnnie---

I took the pack off the maintainer and waited 13 hours. The pack voltage on two new DVMs was 52.3 on one and 52.4 on the other. I think I know the reason for the higher voltages. It's this:http://shop.saveabattery.com/48-VOLT...se-2365-48.htm

I bought this about two months ago to use as a float charger/maintainer/desulfator. I mounted it under the seat. If I am not on the cart, it's plugged in. I have noticed that my pack voltage has very slowly risen. I haven't used my big charger since I installed it. On charge voltage is a steady 54.4 volts. An engineer at Granite Digital, the makers of the Save A Battery, and in what I thought was a sales pitch told me that I was going to be surprised at the improvement of my battery pack after extended use. He also said I would be surprised how fast the charger portion would work. I guess he was right on both counts. I simply do not understand how a 50 watt charger can charge 8 230ah batteries as fast as it does. I know it sounds like I am trying to sell these things but that is not the case. I am just trying to understand how it's doing what it's doing.

Anyway the number is 52.3 or 52.4 and the exact GPS mileage is 5.9.

Again, thanks in advance.

Dave
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Old 02-12-2014, 12:21 PM   #6
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Default Re: Question for JohnnieB

You gave me a start voltage and the distance traveled, but no stop voltage.

If I split the difference on the two DVM readings and call 52.35V 100% SoC and use the stop voltage of 51.2V given earlier, there was a voltage decrease of 1.15V. If I use 100% on the Trojan chart and subtract 1.15V, I get a stop SoC of 76% and if I do the same on the US Battery chart, I get 81%.

The 76% yields an estimated range of 12.3 Miles at 45° or about 16.0 Miles at 80°.
The 81% yields an estimated range of 15.5 Miles at 45° or about 20.2 Miles at 80°.

I think the batteries made by East Penn use about the same acid concentration as Trojan does, so my guess is that the lower range estimate is more correct.
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Old 02-12-2014, 12:41 PM   #7
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Default Re: Question for JohnnieB

Thanks Johnnie--

Stop voltage was the same. Any thoughts on the Save A Battery unit?
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Old 02-12-2014, 02:48 PM   #8
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Default Re: Question for JohnnieB

I haven't been able to figure out why the pack voltage is reading higher than the charts after sitting 13 hours, but other than that, the gadgets seem to do what they say they are supposed to do.

The 48V - 50W version only puts out a little over 1A, so it would take about four days to recharge your 230AH pack if you discharged it down to 60% SoC and probably wouldn't be practical for daily use, but it would be good for intermittent use and long term storage.

I'm using a couple of El-cheapo trickle chargers on a riding lawnmower and a car that doesn't get driven much and was planning on getting a couple small DPI float chargers, but I might try a Save-A-Battery instead.

-----------
Does the range estimate seem to be in the ballpark?
It seems low to me, but I don't know what setup you are running.
(Series or Sepex -- Tire height -- Controller ampacity)

Your 8 X 6V-230AH-48V pack stores about 12.0 kWh while my 7 X 6V-245AH-42V pack only stores 10.9 kWh, but my range averages 32.7 Miles when I toss out the two extremes. (One run was flat out all the way and the other run tossed was doing everything I knew to get max range.)
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Old 02-12-2014, 03:03 PM   #9
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Default Re: Question for JohnnieB

Thinking back, the DVM (while charging) read 53.3 volts 4 hours after the test and the normal 54.4 after 24 hours.

All my info is in my Sig. Series cart with Emp 2 speed motor (I leave it on speed setting).
20 inch tires. If you get 30+ range out of your setup, I would have expected the same especially since I have an additional battery. I was just curious. I have completely upgraded
ALL of the electrical hardware on the cart and am trying to get a handle on where I'm at.

Thanks again Johnnie

Dave
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Old 02-12-2014, 03:56 PM   #10
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Default Re: Question for JohnnieB

Quote:
Originally Posted by Olman View Post
That charger brought the pack back within 8 hours after the test!! I know, I know you think I'm full of it but I'm not.

All my info is in my Sig. Series cart with Emp 2 speed motor (I leave it on speed setting).
20 inch tires. If you get 30+ range out of your setup, I would have expected the same especially since I have an additional battery. I was just curious. I have completely upgraded
ALL of the electrical hardware on the cart and am trying to get a handle on where I'm at.

Thanks again Johnnie

Dave
No, I don't think you are full of it. Not in the least. I certainly didn't mean to imply that.

I don't understand how a 50W - 48V charger can replace somewhere in the neighborhood of 3 kWh of energy in 8 hours, but I'll figure it out eventually, I just haven't yet.

--------
I couldn't see you signature block while I was typing on the reply screen, so I missed it.

You've got a series drive, I have a sepex drive.

You had a passenger and a dog with you while my range measurements were with me alone on the cart and I use regen braking, so I put some energy back into the pack when lift my foot off the throttle. I'm not sure how much that increases my range.

I was getting over 35 Miles when I was running a DCX400 and stock motor at 42V. It when down when I replaced the motor and controller.

It takes more torque (amps) to turn your 20" tires than it takes to turn my 18.3" tires, but the cart travels about 8% further for each tire revolution, so that probably cancels out on the range.

I'm curious also. And I think the range estimate for your cart is low.

If possible, when it gets warmer, completely disconnect the Save-A-battery from the battery pack, drive the cart about a mile or so and then let it rest for about half an hour or so. Then measure the pack voltage, that should burn off any surface charge, if that is what we are seeing.

Then drive cart for 6 or more miles like you previously did. (Measure to 1/10 mile with a GPS)
Then let it rest for about the same amount of time you let it rest to get the start voltage.

This should give us about as accurate range estimate as we can get.

Also do two tests, one for each motor speed. The range will most likely be different, but I'm not sure which will be best.

I don't know if it makes any difference or not, but I drive about 10-12 miles when I do range estimates.
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