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Old 11-18-2021, 10:45 PM   #1
kmoorhead
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Join Date: Mar 2020
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Default Slow drain on battery

I'm guessing the BMS is causing this, but I have a very slow drain on the battery which concerns me if my cart is sitting for more than a couple weeks. What is the best way to install some type of disconnect between the BMS and Battery. I have the 14S Leaf setup. I've disconnected all accessories to rule those out (USB charger, Bluetooth Amplifier, Lights). It must be the BMS.
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Old 11-19-2021, 08:27 AM   #2
Volt_Ampere
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Join Date: May 2012
Location: Rio Verde, Az
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Default Re: Slow drain on battery

Can you unplug the BMS? I used to leave my Leaf cart for 5 months in the summer and I disconnected everything from the pack. I left it charged at about 40% and it stayed that way all summer.
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Old 11-23-2021, 08:43 AM   #3
bronsonj
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Default Re: Slow drain on battery

My Chevy Volt pack was just like VA's leaf pack until I added a voltmeter that's always on. Of course, it takes a long time to move the pack V by 0.1V on the meter, but it added a very slow drain.

Do you have a volt meter on your pack that's on all the time? Could be that meter and the BMS are each adding a small drain.

VA, could a bad cap in the controller add a drain too? I know the resistor across the solenoid keeps the caps charged and am wondering if a bad cap could cause a drain. Guessing if that were true then the resistor across those solenoid leads would be warm.

--- edit ---
What kind of drain are you seeing? 0.1v in a day or two? 0.1v in a week? 1.0v in a day? Depending on what you're seeing may give us a clue. Could be your solenoid is welded shut so it's always full power to the controller even if the controller is off.
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Old 11-23-2021, 08:46 AM   #4
Volt_Ampere
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Default Re: Slow drain on battery

I'm sure that the controller will have a small drain but my guess is that it's a few mA at most. I would always recommend disconnecting the battery lead AND the BMS when leaving the cart for an extended period of time. I would also recommend leaving the pack about 40% charged. Certainly not fully charged.

The Alltrax has the precharge resistor internal - you don't use one on the solenoid. (at least my two are that way)
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Old 11-24-2021, 08:41 PM   #5
jhornbr225
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Default Re: Slow drain on battery

The Alltrax drawing I followed for my build showed an external pre-charge resistor. It calls for a 470 Ohm, but since I'm at almost 57 Volts, I upped my resistor to 510 Ohm 15W. I use the Alltrax SR model for my series cart. I was going to winter the cart, but so far I've been driving it every week, at minimum to take the garbage can to the street.

My BMS is inside a plastic enclosure, and not easy to get to. My batteries however, have balance plugs on them, and to totally disconnect the BMS I plan to disconnect the top battery's plug first, then the middle battery, then the lower battery. On powering up the BMS, I'll start at the bottom battery in the string, then the middle, then the top.

My build is similar to the Leaf battery builds, but I picked up used BMW cells from Battery Hookup, and installed bus plates so that I could parallel up two set of cells. My total configuration is 14S4P, somewhere between 150-180Ah.

Here's my build thread, if interested.

https://buggiesgonewild.com/showthread.php?t=171531
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