Calculate exact state of charge

[EzGoRN]

What is the formula to calculate the exact state of charge for a 36v cart?

[scottyb]

Get a refractometer > https://www.google.com/search?q=refr...hrome&ie=UTF-8
And test each cell ?

[EzGoRN]

Sorry I knew what I meant but didn't express it correctly. I want to be able to calculate the SOC based on my pack voltage after a trip. Say its 37.4v at the end of the trip; how can I calculate SOC based on 38.2v full charge.

[handtools]

How about a chart like this?

CartsUnlimitedStateofChargeChart.png

[JohnnieB]

Originally Posted by EzGoRN

Sorry I knew what I meant but didn't express it correctly. I want to be able to calculate the SOC based on my pack voltage after a trip. Say its 37.4v at the end of the trip; how can I calculate SOC based on 38.2v full charge.

Even with a refractometer it's a SoC estimate rather than exact SoC value. The only way to find out how much energy is stored in a lead-acid battery is to measure how much can be drained from it, than you'll know how much was in it.

Different brand batteries have different SoC charts, what brand batteries do you have?

To get a reasonably accurate SoC estimate using a SoC chart, the batteries have to be at rest. That means about 12 hours after being charged or about an hour after being used.

Battery voltage drops when amps are drawn, so a SoC estimate made immediately after cart stops will be artificially low. However, the voltage recovery rate is exponential in nature and about 98% of the recovery occurs in the first 15 minutes.

[LukeL]

I’ve been using the app from Revolution golf cars for a while. I think it’s called GolfCarCaddy. Works great on iOS, anyway.