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Old 07-22-2009, 03:25 PM   #491 (permalink)
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Paul,

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.

Thank you for your help.

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Old 07-22-2009, 10:37 PM   #492 (permalink)
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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...

0.00025 Ohms*1000 Feet/0.0779 Ohms = 3.21 feet of 00 gauge wire.

Or, 3 feet 2.5 inches.

ya!

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.
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Old 07-30-2009, 01:39 PM   #493 (permalink)
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i realy enjoyed reading the tread and im curious at the controller youre planning to build
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Old 07-30-2009, 03:55 PM   #494 (permalink)
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Quote:
Originally Posted by watahyahknow View Post
i realy enjoyed reading the tread and im curious at the controller youre planning to build
Haha... do you still have extra strength remaining to continue reading?

Well, his controller can be found here....
http://ecomodder.com/forum/showthrea...ller-6404.html


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Old 07-31-2009, 12:42 AM   #495 (permalink)
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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
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Old 09-26-2009, 09:03 PM   #496 (permalink)
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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.......
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Old 09-26-2009, 11:15 PM   #497 (permalink)
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I can't wait to hear how it drives!
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Old 11-27-2009, 11:02 PM   #498 (permalink)
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noting the mention of using 00 copper as a shunt. The TC of copper is just over 1/3 % per degree C. I begged some Manganin from a metals supplier and made a couple of shunts to send to Paul. I have plenty of manganin, and if we can settle on a design, I will make up a dozen or so. Brass closet bolts like I used on the last one are really a last resort. I'll keep looking for copper bolts 1x 5/16 - 18.
Actually, the copper shunt may work in your favor. As it heats up, it will give a falsely high reading, at a time when the batteries want you to ease up anyway.
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Old 11-28-2009, 03:50 AM   #499 (permalink)
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i thinki i seen copper bolts used on startmotor relays and on forklifttrucks might want to look in that direction
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Old 11-30-2009, 09:08 PM   #500 (permalink)
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fan / ram-air driven generator and other bits

Paul,

nice thread and good information. thanks a lot. Hopefully it will help with my planned conversion.

As to your request for a fan driven generator to charge the pack while driving...working on it. I have seen a couple designs for this (patents exist) but seem cumbersome and are singular installs.

my planned conversion is:
93 Plymouth Acclaim - front wheel drive
Automatic transmission
your wonderful controller
6 - 24v or 12 - 12v AGM Batteries (144v system)
Motor in the 36/48v range between 100 and 200lbs

currently vehicle is ~2800lbs curb weight. After conversion I would like it to be 2400lbs, but more realistic it will be the same.

Do not know if the automatic transmission is feasible or if I should just yank everything an swap to direct drive on the transaxle- decisions, decisions.

25 or even 50 miles before a recharge is required does not make sense. So a charging system is required. I do not like the gas powered gen idea, it defeats the purpose of the EV, and a hand cranked gen is not good enough. That leaves me with a RAT (Ram Air Turbine) gen. Perhaps we can assist each other.

Basic requirements/ limitations:
1 Charging system does not activate until vehicle is at 25mph
2 Ducting has to be flexible/modifiable for multiple EV installs
3 Charge system output must be greater than motor draw @ selected speeds above 25mph
4 Easily maintainable, easily obtainable parts
5 Supply cooling air to the motor and batts at all speeds above 5mph

That was just off the top of my head, and incomplete to boot. So the questions I have are these: What is the motor drawing at 40mph? Which is more important voltage or current? In your Super Beetle how much room do you have for a ram-air system? Is there still room in the engine compartment or would it have to go into the back seat? Trunk perhaps?

Cost is going to be an issue, but not insurmountable. And I am prototyping already so with more data from you and the others on the list here I think I can get a product from conception to home-shop production fairly quickly. That is, at least, my hope.

keep up the excellent work and thank you.

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