another question. I was following your mathematical computation on how to make your own shunt and amp meter. Now here is the problem. I have made a 2/0 wire cut to exactly 1'-4" or 16". And Im also using the same cheap HF digital tester. But my reading is half of what it should. So instead of 200 amps, it was reading 400 amps. In order to correct the reading, do i need to shorten the wire half? or lengthen it twice?
Im assuming I need to lengthen the wire twice the length of what it is now.
Hello! You are using the HF volt meter, so you have to put it on the 200mV setting. Now, it will show numbers from 0 to 200, where 200 means 200mV. What I did was choose the length of copper so that 400 amps corresponds to 100 on the volt meter, so that it was like a %. So, for example, 50 means 200 amps.
Let's say you want to measure 0 to 400 amps. And you want a reading of 100 on the volt meter to mean 400 amps. You would do this:
V = I*R
0.1 = 400*R
0.00025 = R
So, you need 0.00025 Ohms of resistance. 00 gauge wire has 0.0779 Ohms of resistance per 1000 feet, so the length you need is...
If you want it to measure 500 amps instead, change the 400 above to 500. If you want the volt meter to read from 0 to 200, then change the 0.1 above to 0.2.
__________________ As I watch the old man walk on the sidewalk below my window, I think "Some day old man, I will be like you. So why not give me your coat?" Then I go downstairs to get his coat, but he's gone. Hey, maybe he was Zorro.
thanks for the link i found it as well while reading about the E-vette it seems to be one circuit repeated a couple of times seems to work whell as long as it stays cool enough
I'm doing a '72 VW Ghia with Ford Th!nk guts. 72V, about 6 HP continuous. Tough in a way as it needs not only the controller but the cluster gauge as they "talk" to one another. And, the motor is SEPEX controlled (not series wound). Lastly you're stuck using their original contactor as the gauge switches on/off the contactor, but at a very low amperage which can't be easily duplicated using, say, an Albright contactor. Also the throttle is a special one-off that is hard to duplicate....but the motor is good for about 35 MPH continuous, if you live in a cool place and don't go more than a few miles...I have a Shumacher 72V charger/Northern Tool. Same plate/motor mount setup as yours, more or less....requires a 400 amp fuse inline with the 6 min batts. (1 12V separately runs all auxilliary things including a 400 watt heater-defroster). About to test! The Th!nk Neighbor is speed limited to 25MPH but the controller can be reprogrammed to do 35 continuous for about $170. HOWEVER I spent about $2.5K on this project!! I'd go your route if I had it to do over again.......
__________________ As I watch the old man walk on the sidewalk below my window, I think "Some day old man, I will be like you. So why not give me your coat?" Then I go downstairs to get his coat, but he's gone. Hey, maybe he was Zorro.
(09-07-2009)
