Digital voltmeter

[letitbe]

I have purchased a digital voltmeter and put it on the cart. How low of a reading at stop, should I be able to safely operate the cart before recharging? Thanks

JohnnieB:

The question leaves room for interpretation. It could mean something like"How many Days before I need to recharge?", or something like "How far afield can I go before heading home to recharge?”
Some rules of thumb to start with:
You should never, ever, discharge the batteries below a 50% State of Charge. Lead-Acid wet cell batteries have no memory, so they do not need to be discharged before they are recharged. The higher average State of Charge maintained, the greater the battery's life-span.
For the first question, you want to recharge the batteries after each use. Basically, unless you know you'll be using the cart within an hour or so, put it on charge. It doesn't hurt the batteries if you have to terminate the charge before it is complete.
My charger pretty much stays plugged into my cart unless I'm driving it.

The second answer is:
The pack voltage drops pretty low when under load, so you have to let the batteries rest for a few minutes to get a reasonably accurate State of Charge reading. (The reason for this is the electrolyte stratifies during discharge and the terminal voltage will read low. It takes a few minutes to reach an equilibrium. Sort of the opposite of batteries reading high after charging due to the surface charge they acquire during charge.) You don't want to go below 50%, so when the pack voltage after a 5-10 minute rest is 37.5V (75% SoC) it is time to head back to the house, or wherever the charger is located.

That is just a starting point since your batteries might have a little different discharge curve. The way to find out for sure is check the voltage when you get back home. If it is above 36.3V, it is probably safe to let it drop another 0.1V or 0.2V on the outbound leg of your trip. I hope that helps.

Letitbe:
@ 37.5 volts = 75% your system is what, a 48 volt system? I sorry I never stated that I have a 36 volt cart. Going by that 75% would be 27v and @ 31 volts at rest it is @ around 25-24volts when running and bucking. The last 2 times I've been out I've had to stop at least 6 times and let the batteries build back up to get home. I know it is hard on the system and have been watching it and know now when to stop before it gets to that point. What I meant before was, While out with the cart and stopped, how low of a voltage reading should I allow it to have before I should be setting by the charger to charge it and not operating it any further? Also I've read were people have put an extra 12v battery in the 36v systems, for a boost on hills and such. I assume there is an momentary switch in the circuit, but how are they wired into the systems? Is there a diagram on the site somewhere? Thanks

[brian369]

I somewhat go by this . But Usually Charge When Done Riding

[JohnnieB]

Upon reviewing what used to be a PM, I see I fumble-fingered the keyboard.
I made the correction in red below. (I said 37.5V = 75% - Not True -- 37.3V = 75% 37.5V actually = 80% )

Originally Posted by letitbe

i have purchased a digital voltmeter and put it on the cart. How low of a reading at stop, should i be able to safely operate the cart before recharging? Thanks

johnnieb:

The question leaves room for interpretation. It could mean something like"how many days before i need to recharge?", or something like "how far afield can i go before heading home to recharge?”
some rules of thumb to start with:
You should never, ever, discharge the batteries below a 50% state of charge. Lead-acid wet cell batteries have no memory, so they do not need to be discharged before they are recharged. The higher average state of charge maintained, the greater the battery's life-span.
For the first question, you want to recharge the batteries after each use. Basically, unless you know you'll be using the cart within an hour or so, put it on charge. It doesn't hurt the batteries if you have to terminate the charge before it is complete.
My charger pretty much stays plugged into my cart unless i'm driving it.

The second answer is:
The pack voltage drops pretty low when under load, so you have to let the batteries rest for a few minutes to get a reasonably accurate state of charge reading. (the reason for this is the electrolyte stratifies during discharge and the terminal voltage will read low. It takes a few minutes to reach an equilibrium. Sort of the opposite of batteries reading high after charging due to the surface charge they acquire during charge.) you don't want to go below 50%, so when the pack voltage after a 5-10 minute rest is 37.3V (75% soc) it is time to head back to the house, or wherever the charger is located.

That is just a starting point since your batteries might have a little different discharge curve. The way to find out for sure is check the voltage when you get back home. If it is above 36.3v, it is probably safe to let it drop another 0.1v or 0.2v on the outbound leg of your trip. I hope that helps.

[JohnnieB]

Originally Posted by letitbe

Letitbe:
@ 37.5 volts = 75% your system is what, a 48 volt system? I sorry I never stated that I have a 36 volt cart. Going by that 75% would be 27v and @ 31 volts at rest it is @ around 25-24volts when running and bucking. The last 2 times I've been out I've had to stop at least 6 times and let the batteries build back up to get home. I know it is hard on the system and have been watching it and know now when to stop before it gets to that point. What I meant before was, While out with the cart and stopped, how low of a voltage reading should I allow it to have before I should be setting by the charger to charge it and not operating it any further? Also I've read were people have put an extra 12v battery in the 36v systems, for a boost on hills and such. I assume there is an momentary switch in the circuit, but how are they wired into the systems? Is there a diagram on the site somewhere? Thanks

The 75% is SoC (State of Charge).
After a 12 hour rest, 38.2V is considered a full charge on a 36V battery pack.
The open circuit voltage on a deep cycle lead-acid wet cell drops roughly 0.02V for every 10% drop is State of Charge above 50%.
(It is a little more below 50% SoC, but for battery longevity we only use the top 50%)
There are 18 2V cells in a 36V battery pack, so each 0.36V drop in open circuit voltage is about a 10% drop in SoC.

The chart Brian369 posted shown voltage vs State of Charge for various voltage batteries and battery packs.

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You should strive to be sitting next to the charger before the pack (after a 5-10 minute rest) reads 36.3V

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A lot of people add a 12V battery to a 36V cart to run accessories, but it is entirely separate from the 36V battery pack.

There are a lot of technical issues adding a 12V "Boost", but it can be done.
The problem, other than the complexity, is that 12V batteries have far fewer Amp-Hours than 6V batteries of the same physical dimensions, so you are adding a bottle neck in the series chain.

Going to a full time 48V system using six 8V batteries is less complex.
For max performance and run-time, using eight 6V batteries for 48V is better.

ScottyB has a thread on going to a 42V system by adding a 6V battery in the space in front of the driver side wheel wheel that looks interesting.
http://www.buggiesgonewild.com/elect...tml#post796496