For my scottybs meter now what

[JohnnieB]

Originally Posted by bigsal51

So I installed it today.
1. Is it suppose to drop as I'm driving?
2. When do I know when to charge if it showed 36.2 standing still?

1. Yes it will drop while driving. The more amps you are pulling out of the battery pack, the more the pack voltage will drop.
The max amp draw occurs while starting from a stand still and while climbing steep hills and it is best not to allow the voltage to drop below about 32V during these times.

2. The cart needs to be put on charge after each use. The SoC meter will tell you when it is time to turn around and head to where the charger is.
You should never discharge the batteries lower than 50% SoC (State of Charge), which is 36.3V for a 36V battery pack.
Therefore, you should limit your outbound leg to about 75% SoC (37.3V)

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The voltages given on the attached chart are taken about 12 hours after the charger turns off automatically.
Lead-Acid batteries acquire a "Surface charge" while charging, which has to be depleted before the voltage accurately represents the SoC.
The same is true when the batteries are discharged, but the recover far more rapidly, so only about 5 to10 minutes of rest time is need to get an accurate SoC reading.

The age of the batteries and several other factors determine have fast the voltage recovers after a discharge, so just let the batteries rest until the volts stop climbing and you should have a fairly accurate SoC to judge if it is time head back.

Hope this helps.

[bigsal51]

Awesome that's exactly what I needed.

[shrpshtr]

given that info JohnnieB, what happens if you do dip below 50% SoC? it doesn't seem like it would take very long to get down to 50%. are you doing irreparable damage if you drive it for a couple of days camping and it dips below that?

[JohnnieB]

Originally Posted by shrpshtr

given that info JohnnieB, what happens if you do dip below 50% SoC? it doesn't seem like it would take very long to get down to 50%. are you doing irreparable damage if you drive it for a couple of days camping and it dips below that?

Dipping below and staying below are to different animals.

When you have a Digital SoC meter, you will see two different voltages. Static and Dynamic.

Static (aka At-Rest) voltage is used to determine the battery pack's State of Charge (SoC) and is the voltage that should not go below 50% SoC, or at least should not be allowed to stay there very long.
The natural aging process of lead-acid batteries is that a layer of hard sulfate crystals build up on the plates, blocking the normal chemical reactions during discharge, so as batteries get older, they have less storage capacity.
Sulfation of the plates occurs whenever the battery is less than fully charged, but it occurs faster the more the battery is discharged and the longer a battery remains in a partially discharged state, the more sulfating occurs.
Above 70% Soc, the sulfation is modest and that is why it is recommended to initiate a boost charge at least every month when a cart is in long term storage. (Lead-acid batteries self-discharge at about 1% per day, so 30 days takes them down to about 70%)
The sulfation rate increases considerably between 70% and 50%, but does not drastically shorten battery life expectancy as long as the batteries aren't allowed to stay discharged that low for more than a few hours.
Routinely discharging the batteries below 50% and letting them stay that low for days will reduce battery lifespan by years.
In a nutshell, for the longest battery lifespan, recharge after each use.

To determine the battery pack's SoC, the batteries have to be rested (not used).
A. It takes about 12 hours of resting after the charger shuts off to get an accurate voltage reading to determine SoC.
B. It takes about 15 minutes of resting after the cart has been driven to get an accurate voltage reading to determine SoC.

Dynamic (aka under load) voltage is what the digital SoC meter shows while the cart is moving.
A battery's voltage drops while amps are being drawn from it, and the more amps drawn, the greater the voltage drop.
A typical stock series controller will draw about 275A and a typical stock 36V battery back contains six 225AH batteries, so the pack voltage will drop several volts, and golf cart batteries are designed to take that kind of loading, but there are limits to how many amps the can be drawn without damaging the battery.
When the number of amps being drawn cause the voltage to drop below 1.5VPC (Volts per Cell), which is 27.0V for a 36V pack, the surface of the lead plates is physically ripped off by the forces evolved, so during non-destructive load testing, battery manufactures typically limit the amp draw to a level that yields 1.75VPC, or 31.5V for a 36V pack.
Therefore, while driving your 36V cart, you should back off on the throttle if the SoC meter is reading 31.5V or below to avoid battery damage.

Because the voltage drop is determined by both the amps being drawn and the storage capacity of the batteries in the pack, and a battery's storage capacity reduces as it ages, the pack voltage will drop lower on the same hill than it did when the batteries were new.

Hope this helps.

[bigstik40]

Great post by johnnieb !!! A lot ot really good information there.

[scottyb]

Also not that Trojan battery says you can deep discharge their GC batteries to as low as 10% capacity. The batteries will recover with a proper charge. BUT they won't do it too many many times.

Something along the lines of 700 deep discharges opposed to 5000 shallow cycles.

[JohnnieB]

Here is a little something that illustrates that.

Bottom line: The more you routinely discharge your batteries, the sooner they will need replacing.

[shrpshtr]

makes perfect sense. thanks for taking the time to explain. i did not know you should charge the cart up each night. i have been using it a little here and there each week and then just charging it up once a week trying to prevent unnecessary charging cycles.

[JohnnieB]

I use a charger that goes into a float charge mode after the regular charge cycle ends and unless I know I'll be driving my cart again within an hour or so, or working on it, the charger is plugged into it.

Using charge cycles is sort of a Catch-22. Each battery has a limited number of charge cycles, but the more you use, the more you have to use.