SOC Meter Testing or Why I Distrust LED Bar Meters

[scottyb]

This is a pic or 2 of a brand new Curtis SOC meter. It sells for $80. Here it is reading full & the DVM is connected to the same terminals it is... and reading below 36v which we all know is less than 50% capacity of the pack aka empty!
Enough said ~ check your SOC meter against a DVM & post your findings here.

[rabbitreborn]

you do realize that according to Trojan as well as E-Z-GO, those batteries are considered usable down to 32.5 volts right? The meter is designed to be bottomed out at that voltage.

[kgsc]

scotty, I know you are the man when it comes to golf carts so I am almost afraid to ask the question... Before you connected the meter, was the pack at full charge ? I was told when I got mine that the SOC meter will "set" itself to a 100% reading when first connected to a power source. I proved it on one of my carts that every time I got in and turned on the key, the meter was at 100%. Until it died on me in the woods. Had to get towed out. Turns out the installer had reversed the + and switched wires so it reset itself every time I turned it on.

Just a thought

[kernal]

Just so happens I did this very thing recently. Subject cart is a 2000 TXT series I've owned since new and is original except for 4 ga. wires installed with new T-105's in July '09. Cart has a 1.87KW(2.5HP) motor and 400amp controller. I used a Garmin GPS. Test was run on paved cart paths with mild hills and many blind corners and oneway tunnels etc. hence the relatively low average speed, but we tried to drive it normally and not for max range. Test goal=determine accuracy of SOC meter. Here is my data.


Oct. 8, 2010. OAT 70 degrees. Tires at 22 PSI. 450lbs of people aboard. 14 Mo. old T-105s.


Battery voltage 12 hours off charger = 38.4
after 9.6 miles = 37.9 15%
after 17.8 miles = 36.9 35% Batt. meter down 4 bars ~1/2
Average Speed 10.7
Percentages are battery capacity used and based on a chart I have seen posted on this forum several times. However, if I read the chart correctly the percentages are based on the batteries starting at 100% and down to 0%. If I assume the batteries are effectively dead at 20% charge remaining then in my case at 17.8 miles I had really used about 50% of the usable capacity of the batteries.
Conclusion: In this case the SOC meter is reasonably accurate and I can tell my daughters/wife/guests that when the meter is half way down, the cart should be home on the charger.

[golfcarfixer]

I prefer the analog SOC meters. Might not be as neat as digital but you can read them in the sunshine.

[scottyb]

Originally Posted by golfcarfixer

I prefer the analog SOC meters. Might not be as neat as digital but you can read them in the sunshine.

You can read digital 'daylight readable' LED meters in the sun.
I will disconnect the meter and recharge the pack. When the pack has settled to 38.2 I will reconnect the meter. I was under the impression that the meter resets itself at 42v which occurs at each recharge.

[golfcarfixer]

Cant say I have seen one of those.

[scottyb]

Originally Posted by rabbitreborn

you do realize that according to Trojan as well as E-Z-GO, those batteries are considered usable down to 32.5 volts right? The meter is designed to be bottomed out at that voltage.

I have contacted Trojan Batteries about this. I will post their reply

[scottyb]

Below is Trojan Battery's response:

We recommend that you recharge your batteries each time they are used for about 30 minutes or the equivalent of one round of golf. During times of storage, it is best to recharge your batteries when they reach a 70% state of charge. You can generally achieve this by manually charging the batteries every 6 weeks when not in use. Thanks.

I am waiting for a more technical response such as a percentage of charge or pack voltage reading. But 30 minutes of use or 70% of charge does not indicate anything below 36v so far... let's see what my request for more specific technical info gets.

[scottyb]

I received more technical info from Trojan Battery Tech Support. It seems we are both right Rabbit, you can safely draw the pack down to 20% of capacity.
Here is their response to my request for more technical info:

I have attached a chart showing the relationship between depth of discharge and life cycles. The less deeply your batteries are discharged, the more cycles you will get from your batteries. You can safely take the batteries to a 20% state of charge (80% depth of discharge) without damaging the batteries. However from the attached chart, you can see that you will not get as many cycles from the batteries if that is done.




Please let me know if you have other questions.



Thanks,



Stacey Delzeit

Technical Support Engineer

Trojan Battery Company


So while you can draw the pack down further it will result in a shortened life span or a reduced # of cycles.
I inquired about the T105 6v battery. Expected life in cycles is as follows when discharged by percentage:

When discharged by 10% to 90% of total capacity expect a lifespan of 5500 cycles
80%= 2910
70%=2044
60%=1569
50%=1287
40%=1087
30%=971
20%=852
10%=760
0% = 100 cycles

You can see in this chart how depth of discharge effects the number of times the batteries can effectively be recharged.
If you used and recharged your cart everyday like a commercial golf course, your discharge rate would greatly effect how long the batteries last. Divide some of these cycle #s by 365 to see for yourselves the difference in 50% and 20% of capacity discharge ....
There was a graph chart attached in pdf. I will convert it and upload shortly.