pre-charge

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Ray_T
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pre-charge

Hi guys,

My modified ego2 is nearly ready to road test. I have installed an alltrax "axe" controller and have a question about pre-charge. The manual and wiring diagram show a resistor across the high current contactor poles. I understand that this is to keep the capacitors charged so they don't weld the contactor closed when I turn the key. My problem is that if I follow the wiring diagram explicitly, the controller will be connected (through the resistor) directly to the battery pack even with the key in the "off" position, and I don't like the idea of a current draw while the scooter is sitting idle.

I'm wondering if, since I won't be using "go far" mode with the alltrax controller, I could use the lead from the "go far" position on the keyswitch to pre-charge. Would I still need a resistor in the circuit? Could I turn the key to "go far" to pre-charge, then to "go fast" to engage the contactor?

Also, I'm having trouble finding a resistor locally with the values specified by alltrax. how critical is it that I match these values exactly(250ohm, 10watt)? if it's possible to use a different resistor, should I err for higher or lower impedance? higher or lower wattage? what would the effect be?

thanks in advance for any help.

Patrick
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Re: pre-charge

Hi Ray:

You put an Alltrax on an Ego??? Cool! IS this also with your rear suspension? I'd like to hear about it, do tell.

The pre-charge resistor as shown in the diagram will cause a small amount of current to flow at all times. If the caps are at the same voltage level as the batteries, it will be a pretty small amount - you're really just talking about the leakage values inside the controller.. You could measure and see if it's acceptable. If the bike is on the charger it won't make any difference.

If you want to avoid that, you could wire a SPST momentray switch in series with the resistor. Hold the switch down for some seconds before you power on and equalize the voltages. But then you have to do this before every ride.

The value of the resistor isn't critical at all. A smaller resistor with higher wattage, or a larger resistor with less wattage. The larger resistor will also have less current draw than a smaller one.

Patrick

Patrick

Ray_T
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Re: pre-charge

thanks, I think I get it now, I will use the "go far" leads and a resistor to pre-charge then switch to go-fast to get moving.

no suspension yet, my friend that was going to do the welding for me is a little flakey and I haven't been able to nail down a time to build the mounts for the swingarm. I will be posting a journal of my adventures in the "motorcycles and large scooters" section I hope I can remember everything. its too bad that we lost so much when the other site went down.

ILBCNU
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Re: pre-charge

Ray,

Just to let you know the more appropriate location to post a journal is in your Blog.

Thanks,
ILBCNU
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Chas S.
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electromotive
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Re: pre-charge

Hi guys,

My modified ego2 is nearly ready to road test. I have installed an alltrax "axe" controller and have a question about pre-charge. The manual and wiring diagram show a resistor across the high current contactor poles. I understand that this is to keep the capacitors charged so they don't weld the contactor closed when I turn the key. My problem is that if I follow the wiring diagram explicitly, the controller will be connected (through the resistor) directly to the battery pack even with the key in the "off" position, and I don't like the idea of a current draw while the scooter is sitting idle.

I'm wondering if, since I won't be using "go far" mode with the alltrax controller, I could use the lead from the "go far" position on the keyswitch to pre-charge. Would I still need a resistor in the circuit? Could I turn the key to "go far" to pre-charge, then to "go fast" to engage the contactor?

Also, I'm having trouble finding a resistor locally with the values specified by alltrax. how critical is it that I match these values exactly(250ohm, 10watt)? if it's possible to use a different resistor, should I err for higher or lower impedance? higher or lower wattage? what would the effect be?

thanks in advance for any help.
------------

With the controller off, the pre-charge resistor won't be drawing much current, but if the vehicle is going to sit for long periods off (like weeks), then I add a separate switch to disable the pre-charge. You must remember though to turn the pre-charge back on (about a minute) before turning on the key.

colin9876
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Re: pre-charge

I wouldnt worry about the pre charge resistor. does anyone have an estimate of the ohms resistance?, I bet it doesnt draw much current, probably less than the self discharge rate of the battery anyway!

Just out of curiosity can someone explain me the physics? Approx How many Farads capacitor is it, so theoretically how many milliseconds assistance would it give say a 250w motor at start of current draw? Thanks

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