Motor voltage

[orangeman6]

Originally Posted by JohnnieB

When the battery pack has been disconnected for more than a few seconds, you're very likely to get a spark when the last cable is reconnected, whether the last cable is + or -.

The controller has a bank of filter capacitors that are always connected between B- and B+ via the pre-charge resistor or within the controller via a control wire that always has voltage on it. The reason for keeping the filter capacitors charged is to reduce the amount of arcing on the solenoid contacts when they close. There are a great variety of voltage reducers out there and most have filter capacitors that are kept charged.

The net effect is that there is a momentary load if the filter capacitors of either the controller or voltage reducer are less than fully charged when the cable that completes the circuit is landed.

The arc is unavoidable, but one way to reduce it is to connect a resistor (1kΩ or so) between the terminal and last cable landed for a few moments before landing the cable.

Johnnie, didn’t Sergio post something about using a light bulb to do the same thing? Pretty sure he did, but can’t find it or remember how exactly he said to do it.

[JohnnieB]

Originally Posted by orangeman6

Johnnie, didn’t Sergio post something about using a light bulb to do the same thing? Pretty sure he did, but can’t find it or remember how exactly he said to do it.

He probably did. Most anything with a bit of resistance will work, but I suggest a resistor because they are less breakable than glass bulbs.

Something to remember is the lower the resistance, the greater the spark and the cold resistance of an incandescent light bulb is only about 5% to 10% of the hot resistance. (Ohm's law will tell you what the hot resistance is and an Ohmmeter will tell you the cold resistance.)

[420ma]

Originally Posted by JohnnieB

When the battery pack has been disconnected for more than a few seconds, you're very likely to get a spark when the last cable is reconnected, whether the last cable is + or -.

The controller has a bank of filter capacitors that are always connected between B- and B+ via the pre-charge resistor or within the controller via a control wire that always has voltage on it. The reason for keeping the filter capacitors charged is to reduce the amount of arcing on the solenoid contacts when they close. There are a great variety of voltage reducers out there and most have filter capacitors that are kept charged.

The net effect is that there is a momentary load if the filter capacitors of either the controller or voltage reducer are less than fully charged when the cable that completes the circuit is landed.

The arc is unavoidable, but one way to reduce it is to connect a resistor (1kΩ or so) between the terminal and last cable landed for a few moments before landing the cable.

So if th last cable I'm going to land is the one that sparks I should briefly put a resistor in line then remove it and land the cable?

[JohnnieB]

Originally Posted by 420ma

So if th last cable I'm going to land is the one that sparks I should briefly put a resistor in line then remove it and land the cable?

That's how it's done.

The filter capacitors typically have bleed resistors on the for safety reasons (a capacitor can hold a charge for weeks or more), but you'll have several seconds before the voltage on the capacitors is bled down enough to cause much of a spark.

I use clip leads to attach the resistor leads to the terminal and cable end and move the clip lead on the battery terminal out of the way as I'm landing the cable.

[420ma]

I'll give it a try. Thanks.