Big Battery Lithium Conversion Shuddering

[wwkarras]

Hey everyone, first time poster but I have read a ton of threads while working on my 2016 cc precedent project (6" lift, 23's, 4 seater). I recently converted to the Navitas AC 600A kit (installed by a pro) and was getting low voltage warnings down to 35v while under load so Navitas said I must have a bad lead-acid battery or two. I never checked the batteries under load, but voltage is fine sitting out of the cart.

I decided to take the plunge and go straight to a lithium ion pack and landed on the Big Battery 48V/103Ah HSKY pack (max 350A 6sec, 130A continuous) based on reviews, availability, and decent pricing. I have seen videos of carts with this same setup doing wheelies with only the driver and saying it doesn't "cut-out" like Roy Pow packs. I installed the pack and charger and am getting a full charge to 54V when unplugged and with the controller set at anything over 150A max discharge I am getting bad shuddering (what I understand to be the solenoid opening/closing rapidly) when accelerating from a stop or slow speeds to the point where the cart will hardly move. It's worse on blacktop than in grass where the wheels are allowed to spin a bit reducing demand on the battery I'm assuming. What I am seeing on my dash voltmeter and the app is that voltage is dropping down to 47V in this situation when the discharge limit is set to higher values. Running up hills at speed and flat ground it performs well at 35+mph and no issues, but Navitas did have to have me lower my nominal voltage to 44.6V to avoid low voltage warnings causing a reduction in power due to voltage dropping to 47V under load while cruising up a hill. I have sent logs to Navitas and they are supposedly working on something, but I'm sure all that will happen is they'll have me keep my discharge limit low to prevent shuddering and I will not be happy with that level of performance for the $5k+ I have spent on the conversion and battery.

My main question is, is there anything else that could be causing a greater voltage drop under load than bad batteries themselves? It's a little suspect that the large voltage drop occurred with both lead-acid and the new lithium pack. All connections are clean or new and tight and everything else works great on the cart. Any ideas would be greatly appreciated before I return the Big Battery -20% stocking fee and jump to something like an Extreme Team 72V/100Ah pack. My fear is the more money I keep spending on batteries will not solve my voltage drop issue and I am assuming this is the cause of the shuddering and therefore lack of acceleration. Thanks in advance!

[WalterM6]

am getting a full charge to 54V when unplugged

Is that the voltage when the charger shuts off or when the battery sits for a few hours?

[fstop]

Originally Posted by wwkarras

Hey everyone, first time poster but I have read a ton of threads while working on my 2016 cc precedent project (6" lift, 23's, 4 seater). I recently converted to the Navitas AC 600A kit (installed by a pro) and was getting low voltage warnings down to 35v while under load so Navitas said I must have a bad lead-acid battery or two. I never checked the batteries under load, but voltage is fine sitting out of the cart.

I decided to take the plunge and go straight to a lithium ion pack and landed on the Big Battery 48V/103Ah HSKY pack (max 350A 6sec, 130A continuous) based on reviews, availability, and decent pricing. I have seen videos of carts with this same setup doing wheelies with only the driver and saying it doesn't "cut-out" like Roy Pow packs. I installed the pack and charger and am getting a full charge to 54V when unplugged and with the controller set at anything over 150A max discharge I am getting bad shuddering (what I understand to be the solenoid opening/closing rapidly) when accelerating from a stop or slow speeds to the point where the cart will hardly move. It's worse on blacktop than in grass where the wheels are allowed to spin a bit reducing demand on the battery I'm assuming. What I am seeing on my dash voltmeter and the app is that voltage is dropping down to 47V in this situation when the discharge limit is set to higher values. Running up hills at speed and flat ground it performs well at 35+mph and no issues, but Navitas did have to have me lower my nominal voltage to 44.6V to avoid low voltage warnings causing a reduction in power due to voltage dropping to 47V under load while cruising up a hill. I have sent logs to Navitas and they are supposedly working on something, but I'm sure all that will happen is they'll have me keep my discharge limit low to prevent shuddering and I will not be happy with that level of performance for the $5k+ I have spent on the conversion and battery.

My main question is, is there anything else that could be causing a greater voltage drop under load than bad batteries themselves? It's a little suspect that the large voltage drop occurred with both lead-acid and the new lithium pack. All connections are clean or new and tight and everything else works great on the cart. Any ideas would be greatly appreciated before I return the Big Battery -20% stocking fee and jump to something like an Extreme Team 72V/100Ah pack. My fear is the more money I keep spending on batteries will not solve my voltage drop issue and I am assuming this is the cause of the shuddering and therefore lack of acceleration. Thanks in advance!

I'd put a volt meter on the battery terminals - see what you get under load. If it stays above 44v or so, then I'd look at your solenoid. You may have a bad one that is dropping out at voltages where it shouldn't be. A 48v solenoid should stay closed with 42v in most cases I think. You might also look at the cabling for the solenoid coil as well as the controller.

Good luck pinning it down.

[wwkarras]

Originally Posted by WalterM6

Is that the voltage when the charger shuts off or when the battery sits for a few hours?

That is right after I unplug it from the charger, but after cruising around for a few minutes it still stays up around 53V, but drops to 47V or below when peak discharge is set higher, but then the shuddering starts.

My working theory is the large voltage drop is causing the issue. Is this large of a drop typical of other lithium packs?

[wwkarras]

Originally Posted by fstop

I'd put a volt meter on the battery terminals - see what you get under load. If it stays above 44v or so, then I'd look at your solenoid. You may have a bad one that is dropping out at voltages where it shouldn't be. A 48v solenoid should stay closed with 42v in most cases I think. You might also look at the cabling for the solenoid coil as well as the controller.

Good luck pinning it down.

Great, thanks for the reply. It definitely stays above 44v at the solenoid according to the voltmeter on my dash that is hooked directly to the solenoid positive and negative on the controller where the main battery inputs are located.

Is there a way to test the solenoid or just try a new one? A new HD solenoid was installed along with the Navitas kit but maybe it's bad.

[WalterM6]

At 54V you are just charging your batteries to about 75%. With your charger unplugged measure the voltage at the plug on your charger. It should be close to 58V. If it is it might be because one or more of your batteries are out of balance. This would cause your BMS to shut off the charger early. If it is set at 54V look into ways to increase it to near 58V. With your Big Battery BMS do you have access to the parameters in your BMS with either a Bluetooth or computer serial connection?

One last thing. Try to determine what is making you lose power. If it is the Big Battery you will lose all power when it shuts down. (lights, any dash meters). If it is the controller you will just lose power to the motor. All the other 48 and 12v's will still work.

[wwkarras]

Originally Posted by WalterM6

At 54V you are just charging your batteries to about 75%. With your charger unplugged measure the voltage at the plug on your charger. It should be close to 58V. If it is it might be because one or more of your batteries are out of balance. This would cause your BMS to shut off the charger early. If it is set at 54V look into ways to increase it to near 58V. With your Big Battery BMS do you have access to the parameters in your BMS with either a Bluetooth or computer serial connection?

One last thing. Try to determine what is making you lose power. If it is the Big Battery you will lose all power when it shuts down. (lights, any dash meters). If it is the controller you will just lose power to the motor. All the other 48 and 12v's will still work.

Thanks for the reply. It is charging at close to 59V and when I unplug the charger it drops to 54V then. Everything on the dash stays on, lights, etc. so it would appear the battery is not shutting down completely. Unfortunately I can not access the Big Battery BMS, but it would appear then that it is down stream of the battery causing issues, either the controller, solenoid, etc.?

Is a drop down to 47V typical of a lithium pack under hard acceleration, hills, etc.?

[WalterM6]

I've got LiFePo4 batteries and my meter reads around 47V going up steep hills. (E Tn)

[WalterM6]

Additional information. My car will cruise at 50v. When parked it will almost always settle at 52V.

[wwkarras]

Originally Posted by WalterM6

Additional information. My car will cruise at 50v. When parked it will almost always settle at 52V.

That's about where mine is but under full acceleration from a stop or going up a hill it will drop to 47V. My voltmeter also reads amperage and it looks like the battery is providing sufficient amperage based on the max limit set whether it be 300A or 350A even, but the shuddering still occurs. The solenoid is the new Navitas one that comes in the kit so I doubt that is bad. Is there anything else in the cart that could cause the shuddering other than it seems like the battery is providing enough voltage/amperage, but the Navitas controller is not responding well.