Any Batteries That Don't Self Discharge?

[mutant]

36.31 is 50% soc for a 36v pack-48.41 is 50% soc on a 48v pack....below that you will cause significant ,permanent damage shortening the packs life....

[JohnnieB]

Originally Posted by Rickochet

Thanks Johnnie. I always put it in "tow" position. I thought that totally killed any draw.

A PDS controller is in a"Standby" mode when the Run/Tow is in Run and if it senses cart movement (pulses from the speed sensor on motor) it will energize the solenoid, apply max regen braking and sound the beeper. (Walkaway safety feature)

Placing the Run/Tow into Tow turn the controller's electronics Off so the cart can be towed without burning up motor and controller.

However the filter capacitors are still being kept charged via the pre-charge resistor. You can figure out how much current is being drawn by dividing the voltage drop across the per-charge resistor by its Ohmic value.

If the voltage drop is about 5V and the resistor is about 250Ω, the current flow is only about 20 ma, which isn't much, but it adds up over time.

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FWIW: You start out with fully charged batteries, or very near it, when you leave the cart in the parking area, so you only need a solar charger that offsets the self-discharge rate.

All battery pack are different, but in general they self discharge at about 1% of SoC per day. For a standard 225AH 36V pack that is about 2.25AH per day, which is a flow rate of about 100 ma, or about 3.6W.

If you used three relatively inexpensive 12v 7W solar charges connected in series for 36V, your battery pack would stay fairly close to being fully charged as long as the sun came out most every day, unless somebody stole them.

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I wrote this earlier, but my ISP went down, so I'll post it now.

[Rickochet]

Originally Posted by JohnnieB

FWIW: You start out with fully charged batteries, or very near it, when you leave the cart in the parking area, so you only need a solar charger that offsets the self-discharge rate.

If you used three relatively inexpensive 12v 7W solar charges connected in series for 36V, your battery pack would stay fairly close to being fully charged as long as the sun came out most every day, unless somebody stole them.

Bingo. That is what I have been looking for. There are lots small 12v solar chargers and are somewhat inexpensive but I have not found any in 36v and not sure any could be run in series to 36v. We have discussed this in other threads. I had thought about getting three and and hooking them up to three two batteries pairs and see but I never pursued it. I will be bringing it home soon for the winter so lots of time for more research.

Thanks for the info Johnnie. Will at least install a disconnect switch.

[Rickochet]

Originally Posted by mutant

36.31 is 50% soc for a 36v pack-48.41 is 50% soc on a 48v pack....below that you will cause significant ,permanent damage shortening the packs life....

So, I am guessing a 48v will self discharge to 50% SOC at the same rate as a 36v? If that is so, a higher voltage cart will not help my situation.

Thanks for the info.

[JohnnieB]

Originally Posted by Rickochet

Johnnie, I noticed on the Trojan website that they advertise batteries with "T-2" technology. I thought that I saw somewhere that these discharge less than the old tech batteries. So, I wonder if I upgraded to a new set or red Trojan's if this would help my situation?

A new set of batteries and a higher AH batteries will most definitely help, but I don't know one way or the other if the T-2 technology lessens the self discharge rate.

Originally Posted by Rickochet

Just curious, is 32v cut off applicable to both 36v and 48v carts? If so would a 48v cart improve my situation?

The 32V cutoff is probably based on the battery industry practice of not discharging batteries below 1.75 VPC (Volts per Cell) when doing non-destructive testing and automatic load testers for cart batteries consider 1.75VPC as completely discharged. That works out to 31.5V for a 36V pack (18 X 2V cells) and 42.0V for a 48V pack (24 x 2V cells).

However, for short and long term cart storage, you don't want to let the batteries to drop below 70% SoC. That is where the rapid aging process kicks in and drastically shortens the battery's usable lifespan. For Trojan batteries, 70% SoC is about 2.06VPC, or 37.1V for a 36V pack.

[bird6246]

i use the 32 volt as my own guide, you start to notice power loss at that point. you dont want your pack voltage to drop into the 25 volt range, then the charger might not kick on. 48 volt carts, the charger might not kick on around 36 volts, And yes the newer RED trojans are awesome

[JohnnieB]

Originally Posted by Rickochet

So, I am guessing a 48v will self discharge to 50% SOC at the same rate as a 36v? If that is so, a higher voltage cart will not help my situation.

Thanks for the info.

Actually a higher voltage pack would help. Granted a 48V pack it will discharge to 50% SoC in about the same time as a 36V pack, but at 50% SoC, a 36V pack is 36.3V while a 48V pack is 48.4V. (See attached SoC vs Voltage chart)

The performance between the parking area and the houseboat would still be dismal, but the odds of getting there without having to push the cart would be better.


Actually, a 42V pack would probably serve your purposes better. Seven 6V batteries, even the black box Trojan type, will have more storage capacity than most 6 X 8V battery packs. (See attached list of various batteries in various voltage packs.)

[Rickochet]

Originally Posted by JohnnieB

All battery pack are different, but in general they self discharge at about 1% of SoC per day.

So, if my discharge rate is 1%/day it will be 30 days tomorrow that would be 70% SOC which would be 37.14 v. It will be interesting so see what my DVM reads. If too low I can get it towed to where I can plug the charger in.

Also, you mentioned maybe adding a 7th 6v battery. Would I need to upgrade the controller?

[JohnnieB]

Originally Posted by Rickochet

So, if my discharge rate is 1%/day it will be 30 days tomorrow that would be 70% SOC which would be 37.14 v. It will be interesting so see what my DVM reads. If too low I can get it towed to where I can plug the charger in.

Also, you mentioned maybe adding a 7th 6v battery. Would I need to upgrade the controller?

Be sure to check the battery pack voltage before you move the cart and you ought to have a pretty good idea of what your specific battery pack's self discharge rate is.

The stock PDS controller and solenoid are only rated for 36V, so you need to replace controller and the solenoid to go to 42V. With an Alltrax XCT48400PDS and matching solenoid, your cart will do up to about 28 MPH on stock height (18") tires, but the XCT is user programmable and you can limit the motor RPM down to any speed you feel comfortable with.

FWIW: Most solenoids are voltage specific, but the one I use (Super-duty unit that Carts Unlimited sells) works at 36V, 423V and 48V, so you don't have to change it if you decide to go to 48V in the future, or back to 36V.

[Rickochet]

Originally Posted by JohnnieB

Be sure to check the battery pack voltage before you move the cart and you ought to have a pretty good idea of what your specific battery pack's self discharge rate is.

Will do. BTW I just checked the new T-105 data sheet and it says, "Self discharge rate 5 – 15% per month depending on storage
temperature conditions."

If that is the case, a set of new 105's and a cut-off switch should take care of my situation. Not cheap but less than trying to upgrade to a gas cart.