How far should battery voltage fall under load

snake91876

93 marathon 48v 300amp controller tryin to run 25" tires cart stalls on hill
And squeals like motor ain't gettin voltage. Batteries are 7 years old but
Charge and settle to 6.3 under load the fall to 4.5 volts is this acceptable.
Do I need more amperage , or let me say what would bigger controller do for me.

BGW

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Sir Nuke

considering your batteries are 7 years old.....that very well could be your problem, considering that the average for well taken care of batteries is about 5 years.

I am guessing you have a pack consisting of 8-6v batteries, is that correct?

and although a full charge, each battery at 6.3 is alright, you are allowing them to pull to much. at 4.5v, its at the point that damage is starting to take place. you shouldn't allow them to go below 5.25v

snake91876

When I put voltage meter on 1 battery while on a hill running
The battery voltage falls to like 4.2 or 4.5 , I am load testing under power.

Sir Nuke

I realize that.....and those voltages I mentioned above are still valid.

snake91876

I do have 8 6v , how do I keep the voltage up or what can I do to keep them from falling back

Sir Nuke

maybe Johnnie will pop in and get another perspective....I know my numbers are right based on 6v batteries.....which should NEVER be drawn down to or below 1.5v per cell or 4.5v.....and to maintain a good healthy battery, never allow then to get below 1.75v per cell or 5.25v

Sir Nuke

seeing as how you are using a single DVM to take your readings....I would highly recommend that you get a dash mounted DVM that reads total pack voltage. to ensure you don't draw more that you should at a heavy load....get off the throttle some, and don't allow the total pack voltage, under load, to go below 42V.

JohnnieB

How far the voltage of a Deep-Cycle, Lead-Acid, Wet-Cell battery drops under load depends on how many amps are being drawn, the storage capacity (AH rating) of the battery and what the battery's SoC (State of Charge) is.

If all 8 batteries start out at 6.3V (50.4V total), their SoC is only 88.5%. Fully charged would be 6.366V per battery or 50.93V for the 48V pack.

At 7 years old, the storage capacity of the batteries will have less than half their original rated capacity, so if they had 225AH 20Hr rating when new, they are most likely about 100AH batteries now.

The 25" tires reduces the stock torque by about 30% where rubber meets the road, but upping the pack voltage from 36V to 48V increases the stock torque by 33%, so the cart's acceleration and hill climbing abilities ought to be more or less stock and shouldn't stall on modest hills. (14° grade or less)

Basically your batteries appear to be beyond their useful lifespan.

To get better acceleration and hill climbing ability (after replacing the batteries), a higher ampacity controller and a high torque motor would help, or go to a smaller diameter tire.

scottyb

Solid advice

yurtle

Never stall a motor if it stops on hills. It will really hurt the batts and may burn up the motor and/or controller.