High Current C.A.

[Jay64]

Ok, more newbie questions here. I just got my high current Cycle Analyst and am trying to figure out how to hook it up properly. I went to ebikes.ca and looked at their instructions and this is what they have posted:

The High Current model is like the Stand Alone version but without a molded shunt, so that you can attach it to high amperage sense resistors. The blue wires with a ring terminal go to the (-) side of the sense resistor, while the white/orange striped wire goes to the (+) side of the shunt. The remaining orange wire is connected to the positive leads of the battery pack.

(note: Justin, I'm not trying to steal from your page, just posting up what I am refering to when I am asking these questions.)

First of all, the markings on the shunt that I recieved are: 50MV on the left side; 600 AMP ESR 60 013 MLB on the right side.

I don't see anywhere on the shunt that designates one side as being + and the other as -. Is that just set on how you wire it in with the battery wires? On that note, how exactly do you wire it in with the battery wires? It has a hole drilled through each side of the shunt with a differnt size thread on either side of the hole.


What is the purpose of the different sized threads and how do you attach the battery to them? I am figuring that I probably just put a ring connector on the battery cable, run a bolt through that and attach that to the shunt. Maybe the smaller thread is used to secure the shunt down???? I realize that these are probably really newbie questions, but I have never worked with a shunt before.

 

[silicium]

50mV / 600A = 83 uOhms :? (0.083 mOhm...)

It is not too low for the CA?

Edit:

0.763 to 9.999 mOhm in Low Range Mode
0.0763 to 0.9999 mOhm in High Range Mode

It's ok in High range mode 8)

 

[TylerDurden]

IIRC, The shunt is mounted to a nonconductive support on one side (screws go through support into shunt), the battery cables attach to the other side (shunt in series with battery: batt>shunt>load). The small screws (shown) are to connect your meter.

 

[drewjet]

To wire the shunt think of the shunt like a fuse. Make sure you put it on the negative cable. The power flows through it and the 2 small screws connect to the CA. They read the voltage drop across the shunt and the CA converts that to amps.

 

[Doctorbass]

This is very low mV !!.. or uV i should say!

I would recommand you to twist the sensing wires between the shunt and the CA.. twist that pair of wires as close as you can!.. and keep the lenght as short as possible!


I wonder if someone already measured the current draw by the CA at the sensing input?.. just to ensure that the twisted pair of wire have the right size to avoid introducing error...

Because 100 uOhms at few nano or uA could be a problem.. I just hope the input of the CA is buffered with great quality low noise Op-Amp with offset compensation!

Doc

 

[fechter]

I haven't measured it, but the current in the sensing wires is very low so I don't think you need to worry about the resistance of the wire. Using a twisted pair is a good idea. Shielding would be good too.

 

[Jay64]

So, is there a + and - side of the shunt, or is that just created by the way I hook it up?

 

[TylerDurden]

It is determined by your hookup.

 

[Jay64]

Thanks. That is what it appeared to be, but I just wanted to make sure.

 

[mcstar]

Just FYI,
A shunt is simply a resistor with a very low, but KNOWN resistance. You want the resistance to be low to reduce the amount of power dissipated(especially when the current is high). Conversely, need SOME resistance to get a measurable drop. All you need to know to calculate current is the is the voltage drop and the resistance (V=IR). Knowing this, a shunt must be inline with your load for it to be of use. Having the sensor wires twisted reduces the chance of interference since the voltage drop is low, induced noise can be a big problem especially close to a motor. Keeping the sensor wires short reduces their voltage drop which is not in the path of the load. Since the current going through them is low though (virtually nill) they won't really be a factor.

 

[Jay64]

As far as the shunt size, it was sent with the CA unit from Thunderstruck. The wires with the CA have an outer insulation layer that contains all of them, so I can't really twist them if they are not already twisted in the outer insulation sheath. It looks like the 4th wire (orange) needs to be connected after the on/off switch on the + side of the battery, so I guess I need to get the key switch figured out. For some reason when I switched it to this bike from the TS build it no longer cuts the power out.