# Problems with the Alltrax SPM 72300 Motor controller



## akseminole (Jan 5, 2014)

I have nothing useful to advise you about, however, when you say that you are converting a 6x6 Buffalo truck to electric, images of giant multi ton armored personnel carriers leap to my mind... I presume that my flights of fantasy are just that, because I cannot fathom using a 72 300 controller to move such a beast..


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## major (Apr 4, 2008)

kerf said:


> Hello all,
> 
> I am a high school student in a class working to convert a 6x6 buffalo truck to electric. After many struggles we got everything in place and were excited to turn it on. However when we turn it on the LED status light on the Alltrax SPM 72300 motor controller starts out with the solid green which indicates that it is ready to run. When we pull the throttle it switches to one green six red which indicates a "pre charge failure." I have replaced the pre charge resistor but had no luck and looked on many other forums but have not found anything to fix this.
> 
> PS Do to our retailers not sending us all the parts we needed our Lithium Iron Phosphate batteries were not charged for a few months, we are afraid that they may have depleted low enough to not retain charge and I am wondering if this could be the source of the pre charge failure error.


Hi kerf,

If you don't have a voltmeter, get one. Measure battery and report. Next, post photos and wiring diagram. Who told you to use a precharge resistor and what value? How is it connected and what contactor is it?

Give us more information and we can probably help. 

major


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## kerf (May 5, 2016)

akseminole said:


> I have nothing useful to advise you about, however, when you say that you are converting a 6x6 Buffalo truck to electric, images of giant multi ton armored personnel carriers leap to my mind... I presume that my flights of fantasy are just that, because I cannot fathom using a 72 300 controller to move such a beast..


No we are not converting the military buffalo truck, one of these http://www.muddoxinternational.com/mxi/wp-content/uploads/2014/01/Buff_blk.png


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## kerf (May 5, 2016)

major said:


> Hi kerf,
> 
> If you don't have a voltmeter, get one. Measure battery and report. Next, post photos and wiring diagram. Who told you to use a precharge resistor and what value? How is it connected and what contactor is it?
> 
> ...


We recently measured the voltage of each battery and the pack, each one was steady at 13.2 volts, and the pack was 52. Tomorrow I plan on installing our current sensor, we are using the EMUS BMS system, and use the bluetooth to connect to a tablet with the EMUS app. Im not sure what kind of contractor we have but the resistor is a 420 ohm going from one post to the other on the contractor before going to the motor controller. Here are a few pictures of the build so far. We are extremely close, once we get the pre charge failure error fixed we should be good to go!


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## major (Apr 4, 2008)

kerf said:


> We recently measured the voltage of each battery and the pack, each one was steady at 13.2 volts, and the pack was 52. Tomorrow I plan on installing our current sensor, we are using the EMUS BMS system, and use the bluetooth to connect to a tablet with the EMUS app. Im not sure what kind of contractor we have but the resistor is a 420 ohm going from one post to the other on the contractor before going to the motor controller. Here are a few pictures of the build so far. We are extremely close, once we get the pre charge failure error fixed we should be good to go!


You answered most of my questions. Thanks for photos. Still, why did you use an external precharge resistor?

I have not used that particular model of controller, but many others. Ones that power main contactor coil typically handle precharge internally and do not need external resistance across main contactor. It makes sense that such a resistor would throw an error or fault. 

If the manual does not specify a resistor across MC, don't use one. 

major


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## major (Apr 4, 2008)

Hey kerf,

Looking over your pics, wiring is pretty sloppy. You need to tidy up. Get those cables (and wires) away from the chains and sprockets. Also, I can see the M- cable on the motor is loose and there appears a steel washer between the lug and bottom brass nut. Do not put steel hardware in the high current path. Don't leave connections loose even for a short while. They tend to be forgotten and end up causing damage or fires. Lockwashers on top nut only.

And I don't see a main power fuse.

Just sayin',

major


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## Jayls5 (Apr 1, 2012)

Grab your DMM and set it to OHM's. Actually measure the resistance across the resistor.

The manual recommends a 470 Ohm 10W resistor for a 48v system. It might throw a fault if the resistance is too low, or if the resistor itself is damaged. If you haven't already, make sure you have a diode on the contactor coil as well. I believe it should be a 1N5408.


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## major (Apr 4, 2008)

Jayls5 said:


> Grab your DMM and set it to OHM's. Actually measure the resistance across the resistor.
> 
> The manual recommends a 470 Ohm 10W resistor for a 48v system. It might throw a fault if the resistance is too low, or if the resistor itself is damaged. If you haven't already, make sure you have a diode on the contactor coil as well. I believe it should be a 1N5408.


O.K. I looked at the manual. It does say to use a precharge resistor. It says not to use the diode on the coil when driving both leads from the drive as they have it wired.

Also, check to see if the contactor is welded or otherwise is fully functional. Does it have the proper coil rated voltage?


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## Jayls5 (Apr 1, 2012)

major said:


> It does say to use a precharge resistor. It says not to use the diode on the coil when driving both leads from the drive as they have it wired.


I didn't see that part. I was looking at page 10 on this manual:

http://www.alltraxinc.com/files/DOC113-001-D_OP-SPM-SPB-OPERATORS-MANUAL.pdf


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## ken will (Dec 19, 2009)

kerf said:


> When we pull the throttle it switches to one green six red which indicates a "pre charge failure." I have replaced the pre charge resistor but had no luck and looked on many other forums but have not found anything to fix this.


Are you sure that it is _one_ green six red??
Could it possibly be _two_ green six red?

When the Contactor is closed it shorts out the pre-charge resistor circuit.

The throttle could cause a _two_ green six red error.


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