Battery Voltage Question

[wbhess]

Sorry in advance if this has been gone over before (I'm sure it has). I saw some golf cart voltage charts on here and read that you should never let your cart get below 50% or irreversible damage may occur. If the cart was driven to 50% and left for a small period of time and the volts dropped to 45%, is it going to cause damage to the batteries if the cart is not driven while below 50%?

[JohnnieB]

You're on the right track, but you've got a couple of things mixed up, which is very easy to do with batteries.

We should never let the At-Rest voltage drop below 50% SoC, which is about 36.3V for a 36V pack and about 48.4V for a 48V pack. However, the consequences for doing so is shortening the cradle to grave lifespan of the batteries rather than immediate irreversible damage. In other words, the batteries age a lot faster when they are routinely discharged below 50% SoC, but they don't die suddenly because of it.

True irreversible physical damage starts occurring when the batteries are sucked down to 1.5VPC (Volts per Cell) or lower while driving the cart. That works out to 27V for a 36V pack and 36V for a 48V pack. The plates are distorted and material is sucked off of them, so an instant failure can occur.

It gets complicated because the pack voltage drops when amps are drawn from the pack, the more amps drawn, the more the drop. Making things more complicated, the pack voltage drops almost instantly when amps are drawn, but the voltage recovery is very slow. It takes an hour or more for full recovery after amps being drawn, so you have to wait about 10 or 15 minutes before reading the voltage to make reasonably accurate SoC estimate to determine if you are close to 50% SoC and ought to get the batteries on charge.

[BobBoyce]

Originally Posted by wbhess

Sorry in advance if this has been gone over before (I'm sure it has). I saw some golf cart voltage charts on here and read that you should never let your cart get below 50% or irreversible damage may occur. If the cart was driven to 50% and left for a small period of time and the volts dropped to 45%, is it going to cause damage to the batteries if the cart is not driven while below 50%?

Damage (sulphation) begins whenever the battery pack begins to drop in voltage from full charge. The rate at which the damage occurs increases as the voltage drops more. So the way to decrease this damage is to reduce the amount of time that the batteries spend in a partially dicharged state. So the answer is yes, the damage is occuring while the cart is not being driven. Some sulphation is reversible during recharge, while the sulphation is fresh and still soft. Once the sulphation hardens into crystals, that reversal is much more difficult, and requires desulphation technology. When the batteries drop below 50% SOC, the crystals form larger and more rapidly, and become more permanent. They tend to damage the battery plates when they form, and physical damage to the plates is not reversible.

[Jmzvet]

So even if I drive my cart 100 yards to the mailbox on a full charge, I should plug it back in when I return to the garage, correct?

[BobBoyce]

Originally Posted by Jmzvet

So even if I drive my cart 100 yards to the mailbox on a full charge, I should plug it back in when I return to the garage, correct?

Absolutely. Opportunity charging leads to longest battery life, as long as the charger treats your batteries right.