SOC Meter Testing or Why I Distrust LED Bar Meters

[scottyb]

I looks clear from the information given by Trojan Battery support technicians that the further you discharge the battery the fewer times it will recover fully.
This is why I am interested in seeing a voltmeter in the dash as opposed to a 'fuel gauge'.

[BLakeside]

Thanks for doing the digging scottyb. Leave the "fuel gauges" for the fork lifts. I too will be using a volt meter in my dash board.

[kernal]

Very good info especially the cycles part. Thanks for taking the time to do the research. I too was interested in the accuracy of the Curtis digital SOC meter on my cart and was considering installing a digital gage for pack voltage on the dash. This is why I did the test as per my previous post on this thread. My conclusion was that on my cart the SOC meter is accurate enough to be used like a fuel gage on a car and thus understandable for the women in my life.

Also, correct me if I am wrong on this. On the graph you posted from Trojan it shows 36.1 volts as 50% of battery capacity. But if 20% of battery capacity remaining is considered dead or not safely usable then wouldn't a pack voltage of about 36.9 be closer to 50% of USABLE battery capacity?

[rabbitreborn]

Scotty, why then does trojan (and every other battery manufacturer) insist that to definatively discover a "bad" battery you have to perform a discharge test which results in the battery pack being drawn down to 31.5 volts? A "perfect" test according to Trojan is 6 batteries all reading 5.25 volts each after 100+ minutes of discharge. If the depth of discharge according to their own testing methods is 31.5 volts, how then is 35.44 considered 70% discharged?

For that matter, what are they considering a fully charged pack voltage to be?

[scottyb]

This is the SOC chart which I originally got from their website a couple of years ago. That is where I get my volts to SOC % numbers. Here's the chart.

[dougmcp]

With respect to Scotty, I have used these Curtis meters for years and find them very useful as an indication of charge level, not voltage.
I think the whole concept of a state of charge meter is a little misunderstood.
It is not a voltmeter, it is a gauge that measures a percentage of charge remaining based on the initial input. They essentially take a pre-established level of charge and determine the percentage remaining. If the initial input was 36v it would start from that set point, if it was 38v it would start there.
Each bar represents 8% of the charge so when it drops to the second bar from full the amount remaining is between 86% and 92% of a full charge.
The Curtis meters are suitable for + or - 25% of the their voltage rating.
These meters reset themselves each time the charger goes through its charge cycle and the starting voltage could be different each time, depending on when your charger stopped charging and the voltage level at that time.
There are some Chinese knockoffs of these out there which I have also tried and they do not have the same accuracy as the Curtis units. I would avoid those.

[scottyb]

That's good info too, Doug. I will do a little more testing on my Curtis.... Right now I am recharging that cart and the pack is at 42.6 and charging

[kernal]

Originally Posted by dougmcp

With respect to Scotty, I have used these Curtis meters for years and find them very useful as an indication of charge level, not voltage.
I think the whole concept of a state of charge meter is a little misunderstood.
It is not a voltmeter, it is a gauge that measures a percentage of charge remaining based on the initial input. They essentially take a pre-established level of charge and determine the percentage remaining. If the initial input was 36v it would start from that set point, if it was 38v it would start there.
Each bar represents 8% of the charge so when it drops to the second bar from full the amount remaining is between 86% and 92% of a full charge.
The Curtis meters are suitable for + or - 25% of the their voltage rating.
These meters reset themselves each time the charger goes through its charge cycle and the starting voltage could be different each time, depending on when your charger stopped charging and the voltage level at that time.
There are some Chinese knockoffs of these out there which I have also tried and they do not have the same accuracy as the Curtis units. I would avoid those.

dougmcp, This sort of implies that my "36volt" SOC meter would work if I converted to 48 volts. Yes/no ?

[scottyb]

Rabbit I don't know why, but the information from Ezgo and Trojan does seem to contradict.

[dougmcp]

Originally Posted by kernal

dougmcp, This sort of implies that my "36volt" SOC meter would work if I converted to 48 volts. Yes/no ?

Well, yes and no, a 36v meter will only go 9v either way and you also have to include the actual voltage of a fully charged pack. You can not use it for the 48v pack.
I currently use a 36v Curtis meter on my 48v conversion but it is only wired to 5x8v batteries (40v, 42.5v charged) and it works well.