Converted to Lithium 48 Volt - Super Slow

E

Elmerfud67

New Member
Good evening,
HELP, PLEASE..
Press the pedal and it will barely drive on trailer. Press pedal and hold it the cart will move as if it has a stall converter. But tops out at 42 mph.
 
It would spin the tires on the concrete with lead acid batteries. Cart set for a year pulled old batteries installed lithium and it runs great @wot.
Almost have to push it to go up any type of incline
 
So this slow down has only occurred after the lithium conversion? That doesn’t sound right, you should have seen an increase in acceleration after the conversion due to less voltage sag and reduced weight. Which lithium battery did you install?
 
I don’t know the power rating of that motor but to spin the tires on a re geared golf cart it’s got to be pulling 400-500 amps. Those batteries are only rated at 60 amps peak so 120A combined for 10 seconds, way short. You would need to get a single lithium battery with a BMS rating high enough for your setup, the peak rating should at least match the amp rating on your controller. Also hills and towing will draw more amps so pay attention to the duration of the peak as well as continuous rating or the battery may cut out under the load.
 
But it’s not sounding like he’s loosing all power as would happen with a bms shut off. It sounds more like insufficient voltage. This is a strange one.

Absolute long shot, and most likely a very silly question, but you weren’t at 72v with the lead acid and have reduced to 48v when going lithium have you?
 
Pat911 said:
But it’s not sounding like he’s loosing all power as would happen with a bms shut off. It sounds more like insufficient voltage. This is a strange one.
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That was my initial thought which is why I didn't suspect a battery problem. Maybe the actual battery cells are the limiting factor, not the BMS, and simply can't supply more current. The rated peak is 2C so if they are using budget cells the batteries may not even be able to supply peak current. You are the lithium expert, does that seem plausible?

The 72v is a good thought but if the OP went from 72v to 48v there would be a reduction in the top speed as well, from the description it sounds like only the low end is affected
 
Golf Cart Wizard said:
That was my initial thought which is why I didn't suspect a battery problem. Maybe the actual battery cells are the limiting factor, not the BMS, and simply can't supply more current. The rated peak is 2C so if they are using budget cells the batteries may not even be able to supply peak current.
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Possible, that’s why I asked him to check the voltage under load, but lithium cells have a very low internal resistance and can supply huge amounts of current if left unchecked. That, and the fact that the BMS should trip to protect the cells in that situation make it unlikely. Allied are quite reputable too so cells SHOULD be of reasonable quality. I don’t suspect a battery problem either.

I guess if the voltage was initially 72v and now 48v that the controller would shut down on low voltage?

Another possibility is bad connections and voltage being lost due to that. @Elmerfud67 , do you have any cables/connections getting hot? As already asked, check the battery voltage under load, but also check the voltage at the controller under load. This will indicate if voltage is being lost in the connections between the battery and the controller.
 
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