where do I get a 500 or 600 amp contactor

[coldair]

I keep getting this error from my Navitas controller and the only thing I can think of is my contactor is not allowing the amperage across it when I accelerate

"Bus Under Voltage Fault
Description: Voltage on controller B+ has dropped below 18V
Check batteries, solenoid and connections"

i saw some pictures of 2 250 amp solenoids with parrel buses but I did not see any 500 amp single pole 48 volt coil solenoids

curranty I have this one WFLNHB 48 Volt 400 Amp Contactor Solenoid Replacement for Golf carts MZJ-400WFLNHB 48 Volt 400 Amp Contactor Solenoid that I had one with my altrax controller after the first one started making poor contact even though it looked like brand new. it would appear to be closed when energized but it would not carry any current. it uses a carbon fiber alignment rod that seemed to have swollen which did not allow the points to contact enough to carry the load

[augiedoggy]

Originally Posted by coldair

I keep getting this error from my Navitas controller and the only thing I can think of is my contactor is not allowing the amperage across it when I accelerate

"Bus Under Voltage Fault
Description: Voltage on controller B+ has dropped below 18V
Check batteries, solenoid and connections"

i saw some pictures of 2 250 amp solenoids with parrel buses but I did not see any 500 amp single pole 48 volt coil solenoids

curranty I have this one WFLNHB 48 Volt 400 Amp Contactor Solenoid Replacement for Golf carts MZJ-400WFLNHB 48 Volt 400 Amp Contactor Solenoid that I had one with my altrax controller after the first one started making poor contact even though it looked like brand new. it would appear to be closed when energized but it would not carry any current. it uses a carbon fiber alignment rod that seemed to have swollen which did not allow the points to contact enough to carry the load

Thats unlikely your issue. most batteries cant consistently supply enough current to overcome the 400amp -1000amp peak contactors.
What battereries are you using? have you double checked all your cables and connections.
Its possible you just have bad contacts on the solenoid. many of the 400amp solenoids have access to the contacts to check and clean them if theres an issue. like mentioned above most 400amp solenoids are designed to handle short bursts of up to 1000amps of power which is more than your navitas can pull by far.

The other possibility is the navitas is damaged. I know many navitas are designed to not need a diode or resistor but did you run one when you ran your alltrax controller? I bet if you were to take measurements after driving the cart hard, at different connection points you will find at least one very hot terminal connection and that may be your issue.

[coldair]

the batteries are 1.5 year old trojan T875 which I charge up every night because the dogs like to take 7 mile long rides every night

[augiedoggy]

Originally Posted by coldair

the batteries are 1.5 year old trojan T875 which I charge up every night because the dogs like to take 7 mile long rides every night

Ok so they dont have the ability to overpower the 400amp continuous rated solenoid let alone 1000a peak. Thanks to the peukert effect.

You likely know this but the amp output of the controller thats fed to the motor is higher than what is actually pulled through that solenoid at all speeds but WOT and even then im not sure how the navitas handles the current but I doubt your consistently pulling 400amps I dont know of any controller that does this.. even my old 575amp alltrax dropped to like 275amps after a couple minutes. You could always look and see what kind of currents your actually pulling through the navitas app. I know the 25" tires are putting a larger load on the motor and system as they rob power but the controller will only output so much for so long to prevent it from having a meltdown.

I really think you have a bad connection or terminal connection on one of your cables. This causes more resistance and things to heat up and fail. after that 7 mile run it should be noticeably hotter than everything else.

If you were actually consistently pulling 400amps thru that 400amp solenoid somehow your batteries would be dead in less than 15 minutes after charging.