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Old 10-22-2021, 07:58 PM   #11
Tom47
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Default Re: BigBattery 48v HSKY Discouraging News

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Originally Posted by Ronno6 View Post
Hmmmm, the chart indicates that 53v is about 75%......
BB said that 53v is 99%
That is quite a discrepancy IMO
BB is correct. That is about 3.31 volts per cell which would be 90+ % depending on the decimal amount.

I think all of the charts for lifepo4 are incorrect. Especially the ones I made!!!

Maybe? The charts I made said 100% but this is actually 80% or 53.2 volts. My meter is calibrated to show the resting voltage as 100%. Maybe that is the discrepancy.

Last edited by Tom47; 10-22-2021 at 08:02 PM.. Reason: Maybe?
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Old 10-22-2021, 08:49 PM   #12
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Default Re: BigBattery 48v HSKY Discouraging News

Given the voltage variation with temperature and cycle history, trying to measure SOC by voltage is not very useful with lifepo4 batteries. You need to count electrons.
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Old 10-22-2021, 09:19 PM   #13
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Default Re: BigBattery 48v HSKY Discouraging News

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Given the voltage variation with temperature and cycle history, trying to measure SOC by voltage is not very useful with lifepo4 batteries. You need to count electrons.
Tough to do for sure. Would you say it is more accurate to measure SOC by remaining Ah instead of voltage? It appears to be fairly consistent in my mileage log. Voltage has been all over the place but SOC and Ah are more predictable.

I rode 29.25 miles today and had ending Ah of 28.4. So I used 43.6 Ah which approximates to 1.49 Ah per mile. This has been pretty consistent in 10 logged rides of over 8 miles. 1.42 to 1.60.

Variations may be due to average speed. Faster average speeds seem to have used more Ah per mile. Temperature has been between 65 and 90 however which may throw everything off.
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Old 10-22-2021, 09:45 PM   #14
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Default Re: BigBattery 48v HSKY Discouraging News

Measuring Amp Hours (counting electrons) is the only way I know to get a reasonable measure of SOC with these cells. A good BMS will do that for you but it isn't easy with the wildly fluctuating current in a golf cart while driving. It's easy when charging to measure how much you put in but you really need to know how much is left while driving.
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Old 10-22-2021, 11:46 PM   #15
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Default Re: BigBattery 48v HSKY Discouraging News

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Originally Posted by Tom47 View Post
I've noticed this and have thrown out all my SOC charts. I made a 29.25 mile run today as a test with my 72 Ah battery:

Ending SOC on meter 39.4%

Ending Volts on meter 52.31

Ending Ah on meter 28.4

The voltage according to my charts was around 55%SOC. Could that possibly be correct and my SOC meter incorrect? I think as you said the voltage is not a good indication of SOC.

Then what is correct in these three readings?
Hi Tom,

Forget the voltage. 39.4% of 72Ah is equal to 28.4Ah, so both these numbers (39.4% or 28.4Ah) are what I would be going with.

As Volt_Ampare implied, your SOC meter counts electrons, go with that.

Cheers
Pat.
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Old 10-23-2021, 07:04 AM   #16
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Default Re: BigBattery 48v HSKY Discouraging News

Thanks Pat and V_A!

As usual, you start helping someone else with their problem and end up helping me!

I think it is starting to sink in now.

Tom

And this is my new charging chart:
Attached Files
File Type: pdf LiFePo4 Chart.pdf (22.9 KB, 0 views)

Last edited by Tom47; 10-23-2021 at 07:59 AM.. Reason: Added chart
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Old 10-23-2021, 02:47 PM   #17
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Default Re: BigBattery 48v HSKY Discouraging News

No voltages Tom……I like it.
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Old 10-23-2021, 03:24 PM   #18
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Default Re: BigBattery 48v HSKY Discouraging News

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No voltages Tom……I like it.
Thanks, Pat! Gosh, this makes it so much easier.
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Old 10-24-2021, 02:55 PM   #19
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Default Re: BigBattery 48v HSKY Discouraging News

My cart only needed a 48Ah recharge after the 20 mile run it did last weekend. I only recharged it today too. I think it could probably go 40 miles on a full charge.
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Old 10-24-2021, 03:37 PM   #20
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Default Re: BigBattery 48v HSKY Discouraging News

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My cart only needed a 48Ah recharge after the 20 mile run it did last weekend. I only recharged it today too. I think it could probably go 40 miles on a full charge.
That is 2.4 Ah per mile. With 82.4 usable Ah down to 20% SOC (105Ah minus 20% = 82.4), you should see 34 miles. If you take it down to 5% SOC you would see 41.6 miles, although I don't like running it that low. Close to home, no problem.

I am getting a mile every 1.48Ah. You apparently have more Ah consumption due to the larger tires and higher speed.

I recommend keeping a log of any ride over 5 miles. This will give you a good indication of what to expect in future rides. I charge after any ride of 5 miles or longer. That's about a 10% DOD. Ten of these charges would equal one life cycle.

I'm glad your cart is working great for you. I know you're as glad as I am about going to lithium.
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