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Unread 02-13-2010, 08:49 AM   #61
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Default Re: Batteries 6-8v or 8-6v

That is some great test info. I don't think anyone has documented the test before.... Thanks for posting that.
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Unread 02-13-2010, 10:48 AM   #62
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Default Re: Batteries 6-8v or 8-6v

Quote:
Originally Posted by ajbrown View Post
FWIW, I have updated with my run with 6-8v. I still have some questions.....:
  1. How much effect is temperature? Most of my tests were under 50 degrees F.
  2. How can I interpret the under load voltages (I have a volt meter hooked up to the pack). Toward the end I was seeing 45-46v on flats at 22MPH, down to 43 to climb steep hill. Should I be keeping this data in detail during test?
  3. Based on the data I have provided can we tell how much further the cart will travel? Trojan mentions NEVER discharge batteries more than 80%, so I guess I could extrapolate....
Here are the results as I remembered to write them down.
Ok as I said before the voltage is pretty much meaningless unless you know the temperature corrected specific gravity reading. The only time you can use the voltage to determine the state of charge is when the battery has been disconnected and rested for 6 hours at 75 degrees F.

The only way you are going to be able to get an accurate assessment is getting a quality bulb type hydrometer, a thermometer, and a very good 4-1/2 digit DMM. Once armed with that you can then build you a spread sheet under two scenerios one under discharge, and one for charging.

Discharge. Make voltage measurement under normal load like going on a flat surface.

1. Measure the temp of the cell under test and record
2. Measure the voltage of the cell under test and record.
3. Measure the specific gravity of the cell under test and record.
4. Calculate the temperature corrected specific gravity with the following formula. Easiest way is to build a MS EXCELL spreadsheet for each cell.
TC SPG = [(.4 x T/F - 23) / 100] + SPG. or .04 points for every 10 degrees above or below 70 degrees F. If below 70 you subtract the correction factor, if above 70 you add. So for example the cell temp is 50 degrees and the SPG measured 1.318 The TC or temp correction = 70 - 50 = 20 degrees so the TC = -.08. So 1.318 - .08 = 1.238 corrected SPG. You then go to the SOC vs SPG chart in the Trojan User Manual and will see 1.238 SPG = 80% SOC. Now correlate that to the voltage measured with a load on it and now you have an accurate voltage SOC...

Charging.

Repeat above procedure except while the batteries are charging.
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Unread 02-13-2010, 01:20 PM   #63
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Default Re: Batteries 6-8v or 8-6v

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Originally Posted by sunking View Post
Ok as I said before the voltage is pretty much meaningless unless you know the temperature corrected specific gravity reading. The only time you can use the voltage to determine the state of charge is when the battery has been disconnected and rested for 6 hours at 75 degrees F.

The only way you are going to be able to get an accurate assessment is getting a quality bulb type hydrometer, a thermometer, and a very good 4-1/2 digit DMM. Once armed with that you can then build you a spread sheet under two scenerios one under discharge, and one for charging.

Discharge. Make voltage measurement under normal load like going on a flat surface.

1. Measure the temp of the cell under test and record
2. Measure the voltage of the cell under test and record.
3. Measure the specific gravity of the cell under test and record.
4. Calculate the temperature corrected specific gravity with the following formula. Easiest way is to build a MS EXCELL spreadsheet for each cell.
TC SPG = [(.4 x T/F - 23) / 100] + SPG. or .04 points for every 10 degrees above or below 70 degrees F. If below 70 you subtract the correction factor, if above 70 you add. So for example the cell temp is 50 degrees and the SPG measured 1.318 The TC or temp correction = 70 - 50 = 20 degrees so the TC = -.08. So 1.318 - .08 = 1.238 corrected SPG. You then go to the SOC vs SPG chart in the Trojan User Manual and will see 1.238 SPG = 80% SOC. Now correlate that to the voltage measured with a load on it and now you have an accurate voltage SOC...

Charging.

Repeat above procedure except while the batteries are charging.
Thanks. This good stuff and I will take some time to absorb it.

So what I am hearing is there is no reliable way to know the state of the pack, i.e., to be sure you only discharge your batteries 50% when all I will have is a voltmeter or more typically an analog VM that comes on most carts.
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Unread 02-13-2010, 01:51 PM   #64
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Default Re: Batteries 6-8v or 8-6v

Great stuff AJ, I'm not a salesman but take a look at the paktrakr. I posted a link earlier in this thread. You can measure the amps being drawn and the the pack voltage at the same time. Maybe ploting that info would be useful? Now we need someone to develope a specific gravity setup that can display it for each cell of each battery on some digital readout.
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Unread 02-13-2010, 05:37 PM   #65
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Default Re: Batteries 6-8v or 8-6v

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Originally Posted by ajbrown View Post
Thanks. This good stuff and I will take some time to absorb it.

So what I am hearing is there is no reliable way to know the state of the pack, i.e., to be sure you only discharge your batteries 50% when all I will have is a voltmeter or more typically an analog VM that comes on most carts.
Well you might want to read it a few more times because I did not mean to imply there is no way to determine the pack SOC with a volt meter. You can but you have to make your own chart using temperature corrected hydrometer readings. After re-reading what I wrote I see I could have done a better job and simplified it a bit.

Righ tnow the wire is reminding me it is about time to get ready to go out for Valentines dinner, so when I get a little more time I will revisit and see if I can simplify it a bit.

One thing you did get correctly is a plain old analog volt meter is not going to cut it.
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Unread 02-17-2010, 09:36 AM   #66
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Default Re: Batteries 6-8v or 8-6v

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Originally Posted by sunking View Post
Well you might want to read it a few more times because I did not mean to imply there is no way to determine the pack SOC with a volt meter. You can but you have to make your own chart using temperature corrected hydrometer readings. After re-reading what I wrote I see I could have done a better job and simplified it a bit.

Righ tnow the wire is reminding me it is about time to get ready to go out for Valentines dinner, so when I get a little more time I will revisit and see if I can simplify it a bit.

One thing you did get correctly is a plain old analog volt meter is not going to cut it.
I truly am interested in more info and I like simple
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Unread 02-17-2010, 09:53 AM   #67
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Default Re: Batteries 6-8v or 8-6v

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Originally Posted by ajbrown View Post
I truly am interested in more info and I like simple
From an engineer .... you are not going to get it simple
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Unread 02-25-2010, 09:45 AM   #68
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Default Re: Batteries 6-8v or 8-6v

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Originally Posted by scottyb View Post
From an engineer .... you are not going to get it simple
Yeah, yeah, yeah, you want easier here you go..

Here is what you are going to need:
  • A note book.
  • Pencil
  • Your battery manufacture Specific Gravity State of Charge. For this example I will use Trojan.
  • A quality bulb type Hydrometer and thermometer
  • Either a 4 digit voltmeter or even better a panel SOC meter installed on the cart.

Pre Conditions and Assumptions:
  • Batteries are fairly new, in good shape, topped off with water, fully charged, and equalized.
  • A flat smooth surface track to drive test.
  • Preferable a nice day in the 70ís so you do not have to make temperature corrections to the specific gravity (SPG) measurements.
  • A couple of hours to perform the test..
Pre-Test Set Up

1. Insure the batteries are fully charged and equalized. To check for equalization use hydrometer and test the SPG of each cell and check that the SPG is within .030 point range. For example a fully charged battery at 75 degrees should read 1.277. The highest reading would be 1.292, and the lowest would be 1.262. If not you will need to equalize the battery and by checking you are sure you have no bad cells or batteries.

2. Next designate a pilot cell for the test. This cell should be in the middle of the SPG range. Using the previous example choose the one closest to 1.277. This cel will be the one you use to measure the SPG during the test.

3. To make life easier do the test when the battery temperature is between 70 and 80 degrees. Doing this will eliminate temperature corrections and make the test much easier.

4. Connect volt meter across the battery pack so you can measure the voltage while driving. If you have one of the SOC meters installed on you dash panel is great, use it.

5. On your note pad make the following chart:
  • 100% = SPG 1.277, Pack Voltage =
  • 90% = SPG 1.258, Pack Voltage =
  • 80% = SPG 1.238, Pack Voltage =
  • 70% = SPG 1.217, Pack Voltage =
  • 60% = SPG 1.195, Pack Voltage =
  • 50% = SPG 1.172, Pack Voltage =

Test Procedure

1. As soon as you are set up with a full charge and conditions met take off on a flat level surface, get up to a cruise speed and read the voltage and record it on the 100% entry line as you now have your 100% SOC voltage in real time under load.

2. Drive for ĺ or a mile or so and take the SPG from your pilot cell. You are looking for it to drop to the 90% level. When you get there, take off driving again, get up to cruise speed and record the voltage on the 90% entry line.

3. Repeat until you get all the way down to 50% and you are done.

4. Donít pull a Bart Simpson and be 2 miles from the house when you get to the 50% SOC.

After you are done you will now have a very accurate SOC record for your battery, or a gas gauge so to speak.
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Unread 02-25-2010, 02:12 PM   #69
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Default Re: Batteries 6-8v or 8-6v

sunking,

This is certainly not common knowledge for me anyway (but not much about carts is yet ). I appreciate you taking the time to 'splain this and will do this test if the weather ever gets to 75 in FL .

Thanks!!
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Unread 02-25-2010, 02:29 PM   #70
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Default Re: Batteries 6-8v or 8-6v

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Originally Posted by ajbrown View Post
sunking,

This is certainly not common knowledge for me anyway (but not much about carts is yet ). I appreciate you taking the time to 'splain this and will do this test if the weather ever gets to 75 in FL .

Thanks!!
AJ you are welcome, I was happy to do it.

Outside air temperature is not all that important, and if your cart has climate controlled shelter is not a factor at all. What is important is the temperature of the battery electrolyte If it is cold outside get the cell temp say above 75 but no higher than 80. There is enough thermal mass in the batteries to keep them above 70 until the test is concluded, Likewise if it is hot start with the battery temp between 70 and 75.

Otherwise if above 80 or below 70 you will have to make a temperature corrected SPG measurement to be accurate. It is not that hard using a laptop and Excel program, it is just an extra step which can complicate the test. Wel Excell takes the complication out of it if you have the formula which I can provide if requested and have access to your battery manufacture spec sheets. Trojan i have already.
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