Shunt resistance

[greasypants]

Well I finally got around to doing the controller mods I wanted. Soldered two shunt wires together to increase amperage in my 72v35a controller as well as adding extra copper to the bus bar and upgrading the incoming power lines to 8 gauge stranded copper wire . I also added 10 gauge solid copper wire to all the connections on my nimh battery packs and changed the output wire to 8 gauge. So now running 72v at somewhere between 60 and 80 amps. The problem is I do not have a milliohm meter so I don't know what the new shunt resistance is and can't program my DB2 properly. I set the shunt resistance in th BD at .7 (guessing) and max amps at 50 but I am still blowing my 60 amp fuses. Anyone have an idea what the new shunt resistance may be. I was just going to buy a pile of fuses and slowly change the shunt resistance until the fuse blows at 60 amps as displayed on the BD. Would this give me a close approximation or are the tolerance for fuses not very accurate? I just want to get it as close as possible so the rest of the DB reading are accurate.
Thanks
Greg

 

[Lowell]

You'll need an accurate shunt reading to make the CycleAnalyst readings worthwhile. Find someone with an accurate bench top power supply and push a known current through two phase wires. Adjust the shunt value until the CA amps reading matches the power supply.

If you don't have an adjustable current limit, wiring in external current control would be a good idea to stop you from having too much fun. It makes for a nice cruise control feature as well.

 

[greasypants]

Thanks Lowell, I just tried using my multimeter inline to measure the amperage with the rear wheel spinning in the air.This way I can adjust the shunt resistance to give me the same amp reading on the CA2 but for some reason I cannot set the resistance lower than .728. If I try to set it at say .6 it will default back to .728 . Is this the lowest it can be set ? Do I have to remove some solder from the shunt to increase the resistance above .728 to be able to adjust it ?

 

[greasypants]

Just got an email back from Justin and he said I need to switch the CA to high range in order to go below .728. Did that and now have the resistance dialed in at .43 .

 

[Lowell]

That's a pretty low shunt resistance. Mine is 0.516 ohms, and gives just over 80 amps with the stock current settings. You might want to raise the resistance a little to keep the best measurement accuracy.

 

[greasypants]

Ya I will try and lower it a bit , it peaks at about 98 amps now , a bit to high to measure accurately.

 

[Lowell]

What does the motor go like at 98 amps?

 

[greasypants]

I have the amperage set at 60 in the CA so as not to blow my fuses but the CA still shows max amps at 98 so it must peak for fraction of a second before it comes back down to 60.