Loss of power at 56% battery remaining

mapoopsie

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I've got 4 of the

ML22-12 - 12 Volt 22AH SLA Battery - Mighty Max Battery​

wired in series for 22AH at 48v. These are connected to a 2k BLDC motor/controller setup through a 50amp fuse.

Motor:

Controller:

We have some led lights hooked up, a controller fan and a speedo all probably drawing less than 5amps at 12v.

The problem is that when the battery draws down to ~56%, but go kart starts to sputter/surge. Seems like a capacitor is filling up and discharging every second or so. I assume this is normal behavior for these SLA batteries and there's nothing I can do about it. But I'm hoping this is not normal behavior and I can either introduce a component or adjust a component to allow the battery to drain to closer to 10% before power is lost.
 

EpsilonZero

...still cheaper than a boat!
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SLA batteries are pretty much done at about 50% DOD. Check your voltage under load when it is cutting out; you are almost certainly hitting the low voltage cutoff for your controller.

Also, you're not going to get any battery down to 10% charge without damaging it or severely shortening its lifespan. Even my LiFePO4 isn't supposed to be run below 80% DOD and it just shuts down at 10% to keep it from being destroyed.
 

Functional Artist

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Yup, Ez's diagnosis sounds about right.

Remember most 12V SLA's have a range of ~13.3V down to ~10V
...so, 4 of 'em @48V would be ~53.2V - ~40V

How are you determining "down to ~56%"?

Some kind of a capacity meter
...or monitoring the voltage?
 

mapoopsie

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Yeah, I've got a battery monitor. I'm not sure what the voltage is because I'm getting this information from my son, but the information is present on the monitor (just a matter of recording it). Next time we're out, I'll check voltage when battery is drained. We're getting about 20 minutes before the batteries are toast (aka 56%).
 

Functional Artist

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IMO you should be getting more than ~20 min run time.

What size/weight kart are we talkin' about?

How new are the batteries?

Also, when you say "We have some led lights hooked up, a controller fan and a speedo all probably drawing less than 5amps at 12v."

Do you have all of those components connected to (1) of your 12V batteries
...or are you using a voltage reducer & drawing 12V off of all (4) batteries (the whole 48V pack)?
 

mapoopsie

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It's a Manco Dingo and it's a beast. Batteries are almost a year old (we started the project at the pandemic kick-off). We have all of the 12v accessories running through a voltage reducer. Here's a pic.
20210204_093853.jpg
 

mapoopsie

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7:1 ratio on the 18" stock tires. Yes, FA...you were my inspiration on this build. We've gotten to about 30mph on a slight downhill (almost flat) grade. Can go about 22mph back up that grade. What motor/controller are you running on your manco? I just don't have the low-end torque I was hoping for. Maybe changing to 16" tires would help that. Are there stock 16" tires for the Manco? I will say this thing is so fun in the snow.
 

Functional Artist

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Wow, Kool!
...glad I could help

My ElDingo is long gone 😉
...that 8Kw motor, Kelly 72V 550A controller & a (48V) 2Kwh Chevy Volt module now power my ElMoto :cool:
(2) 2017 - El Moto | DIY Go Karts

Yup, smaller diameter tires or a higher gear ratio (or both) would definitely give you more low end torque
...but, at the expense of some top speed
...plus, your motor, controller & wires should run cooler too :)

Speakin' of wires
Um..."clean up on isle 4" :sneaky:
 

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